Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Unifying Insights into the Desiccation Tolerance Mechanisms of Resurrection Plants and Seeds
    Farrant, Jill M. ; Moore, John P. ; Hilhorst, Henk W.M. - \ 2020
    Frontiers in Plant Science 11 (2020). - ISSN 1664-462X
    desiccation tolerance - homoiochlorophyllous - longevity - priming - senescence - subcellular glasses - sugars
    Predicting survival in dairy cattle by combining genomic breeding values and phenotypic information
    Heide, E.M.M. van der; Veerkamp, R.F. ; Pelt, M.L. van; Kamphuis, C. ; Ducro, B.J. - \ 2020
    Journal of Dairy Science 103 (2020)1. - ISSN 0022-0302 - p. 556 - 571.
    dairy cow - individual prediction - longevity - survival

    Advances in technology and improved data collection have increased the availability of genomic estimated breeding values (gEBV) and phenotypic information on dairy farms. This information could be used for the prediction of complex traits such as survival, which can in turn be used in replacement heifer management. In this study, we investigated which gEBV and phenotypic variables are of use in the prediction of survival. Survival was defined as survival to second lactation, plus 2 wk, a binary trait. A data set was obtained of 6,847 heifers that were all genotyped at birth. Each heifer had 50 gEBV and up to 62 phenotypic variables that became gradually available over time. Stepwise variable selection on 70% of the data was used to create multiple regression models to predict survival with data available at 5 decision moments: distinct points in the life of a heifer at which new phenotypic information becomes available. The remaining 30% of the data were kept apart to investigate predictive performance of the models on independent data. A combination of gEBV and phenotypic variables always resulted in the model with the highest Akaike information criterion value. The gEBV selected were longevity, feet and leg score, exterior score, udder score, and udder health score. Phenotypic variables on fertility, age at first calving, and milk quantity were important once available. It was impossible to predict individual survival accurately, but the mean predicted probability of survival of the surviving heifers was always higher than the mean predicted probability of the nonsurviving group (difference ranged from 0.014 to 0.028). The model obtained 2.0 to 3.0% more surviving heifers when the highest scoring 50% of heifers were selected compared with randomly selected heifers. Combining phenotypic information and gEBV always resulted in the highest scoring models for the prediction of survival, and especially improved early predictive performance. By selecting the heifers with the highest predicted probability of survival, increased survival could be realized at the population level in practice.

    Data from: No gains for bigger brains: functional and neuroanatomical consequences of relative brain size in a parasitic wasp
    Woude, E. van der; Groothuis, J. ; Smid, H.M. - \ 2019
    artificial selection - trade-offs - constraints - insects - host-parasite interaction - bidirectional artificial selection - brain-size - appetitive olfactory conditioning - brain scaling - parasitic wasp - parasitoid - longevity - Nasonia vitripennis
    Heritable genetic variation in relative brain size can underlie the relationship between brain performance and the relative size of the brain. We used bidirectional artificial selection to study the consequences of genetic variation in relative brain size on brain morphology, cognition and longevity in Nasonia vitripennis parasitoid wasps. Our results show a robust change in relative brain size after 26 generations of selection and 6 generations of relaxation. Total average neuropil volume of the brain was 16% larger in wasps selected for relatively large brains than in wasps selected for relatively small brains, whereas the body length of the large-brained wasps was smaller. Furthermore, the relative volume of the antennal lobes was larger in wasps with relatively large brains. Relative brain size did not influence olfactory memory retention, whereas wasps that were selected for larger relative brain size had a shorter longevity, which was even further reduced after a learning experience. These effects of genetic variation on neuropil composition and memory retention are different from previously described effects of phenotypic plasticity in absolute brain size. In conclusion, having relatively large brains may be costly for N. vitripennis, whereas no cognitive benefits were recorded.
    Exploiting whole genome sequence variants in cattle breeding : Unraveling the distribution of genetic variants and role of rare variants in genomic evaluation
    Zhang, Qianqian - \ 2017
    Wageningen University. Promotor(en): H. Bovenhuis; M.S. Lund, co-promotor(en): G. Sahana; M. Calus; B. Guldbrandtsen. - Wageningen : Wageningen University - ISBN 9788793643147 - 249
    cattle - genomes - genetic variation - inbreeding - homozygosity - longevity - quantitative traits - animal breeding - animal genetics - rundvee - genomen - genetische variatie - inteelt - homozygotie - gebruiksduur - kwantitatieve kenmerken - dierveredeling - diergenetica

    The availability of whole genome sequence data enables to better explore the genetic mechanisms underlying different quantitative traits that are targeted in animal breeding. This thesis presents different strategies and perspectives on utilization of whole genome sequence variants in cattle breeding. Using whole genome sequence variants, I show the genetic variation, recent and ancient inbreeding, and genome-wide pattern of introgression across the demographic and breeding history in different cattle populations. Using the latest genomic tools, I demonstrate that recent inbreeding can accurately be estimated by runs of homozygosity (ROH). This can further be utilized in breeding programs to control inbreeding in breeding programs. In chapter 2 and 4, by in-depth genomic analysis on whole genome sequence data, I demonstrate that the distribution of functional genetic variants in ROH regions and introgressed haplotypes was shaped by recent selective breeding in cattle populations. The contribution of whole genome sequence variants to the phenotypic variation partly depends on their allele frequencies. Common variants associated with different traits have been identified and explain a considerable proportion of the genetic variance. For example, common variants from whole genome sequence associated with longevity have been identified in chapter 5. However, the identified common variants cannot explain the full genetic variance, and rare variants might play an important role here. Rare variants may account for a large proportion of the whole genome sequence variants, but are often ignored in genomic evaluation, partly because of difficulty to identify associations between rare variants and phenotypes. I compared the powers of different gene-based association mapping methods that combine the rare variants within a gene using a simulation study. Those gene- based methods had a higher power for mapping rare variants compared with mixed linear models applying single marker tests that are commonly used for common variants. Moreover, I explored the role of rare and low-frequency variants in the variation of different complex traits and their impact on genomic prediction reliability. Rare and low-frequency variants contributed relatively more to variation for health-related traits than production traits, reflecting the potential of improving prediction reliability using rare and low-frequency variants for health-related traits. However, in practice, only marginal improvement was observed using selected rare and low-frequency variants when combined with 50k SNP genotype data on the reliability of genomic prediction for fertility, longevity and health traits. A simulation study did show that reliability of genomic prediction could be improved provided that causal rare and low-frequency variants affecting a trait are known.

    Genetic improvement of longevity in dairy cows
    Pelt, Mathijs van - \ 2017
    Wageningen University. Promotor(en): Roel Veerkamp, co-promotor(en): T.H.E. Meuwissen. - Wageningen : Wageningen University - ISBN 9789463430821 - 188
    dairy cows - longevity - genetic improvement - breeding value - genetic analysis - survival - animal models - animal genetics - melkkoeien - gebruiksduur - genetische verbetering - fokwaarde - genetische analyse - overleving - diermodellen - diergenetica

    Improving longevity helps to increase the profit of the farmer, and it is seen as an important measure of improved animal welfare and sustainability of the sector. Breeding values for longevity have been published since in 1999 in the Netherlands. For AI-companies and farmers it is necessary that breeding values are accurately estimated and will remain stable for the rest of life. However, current breeding values for longevity of bulls seem to fluctuate more than expected. The main aim of this thesis was to revisit the genetics of longevity and develop a genetic evaluation model for longevity, where breeding values reflect the true breeding value quicker during early life and therefore breeding values become more stable. Genetic parameters were estimated for survival up to 72 months after first calving with a random regression model (RRM). Survival rates were higher in early life than later in life (99 vs. 95%). Survival was genetically not the same trait across the entire lifespan, because genetic correlations differ from unity between different time intervals, especially when intervals were further apart. Survival in the first year after first calving was investigated more in depth. Survival of heifers has improved considerably in the past 25 years, initially due to the focus on a high milk production. More recently, the importance of a high milk production for survival has been reduced. Therefore functional survival was defined as survival adjusted for within-herd production level. For survival the optimum age at first calving was around 24 months, whereas for functional survival calving before 24 months resulted in a higher survival. Over years, genetic correlations between survival in different 5-yr intervals were below unity, whereas for functional survival genetic correlations did not indicate that survival changed over years. This suggested that a genetic evaluation using historical data should analyze functional survival rather than survival. A new genetic evaluation system for longevity was developed based on a RRM analyzing functional survival. Based on the correlation between the first breeding value of a bull and his later breeding values, the ranking of bulls was shown to be more stable for RRM than the current genetic evaluation. Bias in breeding value was observed, mainly for bulls with a large proportion of living daughters. Adjusting for within-herd production level reduced this bias in the breeding values greatly. Before implementing this new model for genetic evaluation, the cause of this bias needs to be further investigated.

    Genetic changes of survival traits over the past 25 yr in Dutch dairy cattle
    Pelt, M.L. van; Ducrocq, V. ; Jong, G. de; Calus, M.P.L. ; Veerkamp, R.F. - \ 2016
    Journal of Dairy Science 99 (2016)12. - ISSN 0022-0302 - p. 9810 - 9819.
    genetic correlation - longevity - survival

    Genetic correlations and heritabilities for survival were investigated over a period of 25 yr to evaluate if survival in first lactation has become a different trait and if this is affected by adjusting for production level. Survival after first calving until 12 mo after calving (surv_12mo) and survival of first lactation (surv_1st_lac) were analyzed in Dutch black-and-white cows. The data set contained 1,108,745 animals for surv_12mo and 1,062,276 animals for surv_1st_lac, with first calving between 1989 and 2013. The trait survival as recorded over 25 yr was split in five 5-yr intervals to enable a multitrait analysis. Bivariate models using subsets of the full data set and multitrait and autoregressive models using the full data set were used. Survival and functional survival were analyzed. Functional survival was defined as survival adjusted for within-herd production level for 305-d yield of combined kilograms of fat and protein. Mean survival increased over time, whereas genetic variances and heritability decreased. Bivariate models yielded large standard errors on genetic correlations due to poor connectedness between the extreme 5-yr intervals. The more parsimonious models using the full data set gave nonunity genetic correlations. Genetic correlations for survival were below 0.90 between intervals separated by 1 or more 5-yr intervals. Genetic correlations for functional survival did not indicate that definition of survival changed (≥0.90). The difference in genetic correlations between survival and functional survival is likely explained by lower emphasis of dairy farmers on culling in first lactation for low yield in more recent years. This suggests that genetic evaluation for longevity using historical data should analyze functional survival rather than survival.

    Changes in the genetic level and the effects of age at first calving and milk production on survival during the first lactation over the last 25 years
    Pelt, M.L. van; Jong, G. de; Veerkamp, R.F. - \ 2016
    Animal 10 (2016)12. - ISSN 1751-7311 - p. 2043 - 2050.
    age at first calving - dairy cattle - longevity - survival - within-herd production level

    Survival during the first year after first calving was investigated over the last 25 years, 1989–2013, as well as how the association of survival with season of calving, age at first calving (AFC) and within-herd production level has changed over that period. The data set contained 1 108 745 Dutch black-and-white cows in 2185 herds. Linear models were used to estimate (1) effect of year and season and their interaction and (2) effect of AFC, within-herd production level, and 5-year intervals and their two-way interactions, and the genetic trend. All models contained AFC and percentage of Holstein Friesian as a fixed effect, and herd-year-season, sire and maternal grandsire as random effects. Survival and functional survival were analysed. Functional survival was defined as survival adjusted for within-herd production level. Survival rate increased by 8% up to 92% in the last 25 years. When accounting for pedigree, survival showed no improvement up to 1999, but improved since then. Genetically, survival increased 3% to 4% but functional survival did not increase over the 25 years. We found an interesting difference between the genetic trends for survival and functional survival for bulls born between 1985 and 1999, where the trend for survival was still increasing, but was negative for functional survival. Since 1999, genetic trend picked up again for both survival and functional survival. AFC, season of calving and within-herd production level affected survival. Survival rate decreased 0.6%/month for survival and 1.5% for functional survival between AFC of 24 and 32 months. Calving in summer resulted in 2.0% higher survival than calving in winter. Within herd, low-producing cows had a lower survival rate than high-producing cows. However, these effects became less important during the recent years. Based on survival optimum AFC is around 24 months, but based on functional survival it is better to have an AFC

    Antibodies and longevity of dairy cattle : genetic analysis
    Klerk, B. de - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Jan van der Poel; Bart Ducro. - Wageningen : Wageningen University - ISBN 9789462577589 - 134
    dairy cattle - dairy cows - antibodies - longevity - genetic analysis - breeding value - genomes - genetic improvement - animal genetics - melkvee - melkkoeien - antilichamen - gebruiksduur - genetische analyse - fokwaarde - genomen - genetische verbetering - diergenetica

    The dairy sector has a big impact on food production for the growing world population and contributes substantially to the world economy. In order to produce food in a sustainable way, dairy cows need to be able to produce milk without problems and as long as possible. Therefore, breeding programs focuses on improvement of important traits for dairy cows. In order to improve desirable traits and obtain genetic gain there is a constant need for optimization of breeding programs and search for useful parameters to include within breeding programs. Over the last several decades, breeding in dairy cattle mainly focused on production and fertility traits, with less emphasis on health traits. Health problems, however, can cause substantial economic losses to the dairy industry. The economic losses, together with the rising awareness of animal welfare, increased herd size, and less attention for individual animals, have led to an increased need to focus more on health traits. Longevity is strongly related to disease resistance, since a more healthy cow will live a longer productive life (longevity). The identification of biomarkers and the detection of genes controlling health and longevity, would not only greatly enhance the understanding of such traits but also offer the opportunity to improve breeding schemes. The objectives of this thesis therefore were 1) to find an easy measurable disease resistance related biomarker in dairy cows, 2) identify the relation between antibodies and longevity, 3) identify genomic regions that are involved with antibody production/expression. In this thesis antibodies are investigated as parameter for longevity. Antibodies might be a novel parameter that enables selection of cows with an improved ability to stay healthy and to remain productive over a longer period of time. In this thesis antibodies bindiging the naive antigen keyhole limpet hemocyanin (KLH) were assumed to be natural antibodies. Antibodies binding bacteria-derived antigens lipoteichoic acid (LTA), lipopolysaccharide (LPS) and peptidoglycan (PGN) were assumed to be specific antibodies. In chapter 2 it was shown that levels of antibodies are heritable (up to h2 = 0.23). Additionally, antibody levels measured in milk and blood are genetically highly correlated (± 0.80) for the two studied isotypes (IgG and IgM). On the other hand, phenotypically, natural antibodies (from both IgG and IgM isotype) measured in milk cannot be interpreted as the same trait (phenotypic correlation = ± 0.40). In chapter 3 and 4 it was shown that levels of antibodies (both natural-and specific antibodies) showed a negative relation with longevity: first lactation cows with low IgM or IgG levels were found to have a longer productive life. When using estimated breeding values for longevity, only a significant relation was found between natural antibody level (IgM binding KLH) and longevity. Lastly chapter 5 reports on a genome-wide-association study (GWAS), to detect genes contributing to genetic variation in natural antibody level. For natural antibody isotype IgG, genomic regions with a significant association were found on chromosome 21 (BTA). These regions included genes have impact on in isotype class switching (from IgM to IgG). The gained knowledge on relations between antibodies and longevity and the gained insight on genes responsible for natural antibodies level make antibodies potential interesting biomarkers for longevity.

    Premature culling of production animals; ethical questions related to killing animals in food production
    Bruijnis, M.R.N. ; Meijboom, F.L.B. ; Stassen, E.N. - \ 2016
    In: The end of animal life: a start for ethical debate / E.N., Stassen, F.L.B., Meijboom, Wageningen, the Netherlands : Wageningen Academic Publishers - ISBN 9789086862603 - p. 149 - 166.
    animal welfare - longevity - production animals
    The aim of this chapter is to analyse the importance of longevity in relation to the welfare of production animals. I hypothesize that the concept of longevity helps to support the moral intuition that premature culling of animals is a moral wrong. The analysis shows that the interpretation of the concept of animal welfare is important for decisions on whether or not to cull animals, but also for the measures that should be taken to prevent premature culling. This is illustrated by two examples in animal production, one example relating to dairy cattle and the other to breeding sows. These two types of farming have in common that in these practices animals are necessary to produce products, yet this production does not require– the animal itself to be killed. My proposal is to accept the view on animal welfare according to which longevity is accepted as an independent moral argument. Acceptance of this view substantiates the intuition that premature culling of animals is a moral wrong, because it shows that we have additional reasons to give the interests of animals more weight. In order to respect this view, some common practices in animal farming will become the subject of debate, as illustrated in the two cases.
    Data from: Sex-specific effects of natural and sexual selection on the evolution of life span and ageing in Drosophila simulans
    Archer, C.R. ; Duffy, E. ; Hosken, D.J. ; Mokkonen, M. ; Okada, K. ; Oku, K. ; Sharma, M.D. ; Hunt, J. - \ 2015
    University of Exeter
    senescence - drosophila simulans - Experimental evolution - sexual conflict - evolutionary response - ageing rates - longevity
    1. Variation in the strength of age-dependent natural selection shapes differences in ageing rates across species and populations. Likewise, sexual selection can promote divergent patterns of senescence across the sexes. However, the effects of these processes on the evolution of ageing have largely been considered independently, and interactions between them are poorly understood. 2. We use experimental evolution to investigate how natural and sexual selection affect life span and ageing in Drosophila simulans. 3. Replicate populations were evolved under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and at one of two temperatures, 25 °C (relaxed natural selection) or 27 °C (enhanced natural selection), in a fully factorial design. We measured longevity in 150 individually housed flies taken from each of three replicate populations per selection regime. 4. We found that natural and sexual selection affected the evolution of life span via sex-specific effects on different ageing parameters (ageing rate vs. baseline mortality): natural selection reduced the rate of ageing in both sexes but increased male baseline mortality, while sexual selection elevated baseline mortality in both sexes but particularly in males. 5. This means that sexual and natural selection interacted to reduce male life span but acted on female life span by independently affecting particular ageing parameters. Sex-specific effects of sexual and natural selection may help explain the diverse patterns of ageing seen in nature but complicate predictions about how ageing and life span evolve across the sexes.
    A gene co-expression network predicts functional genes controlling the re-establishment of desiccation tolerance in germinated Arabidopsis thaliana seeds
    Dias Costa, M.C. ; Righetti, K. ; Nijveen, H. ; Yazdanpanah, F. ; Ligterink, W. ; Buitink, J. ; Hilhorst, H.W.M. - \ 2015
    Planta 242 (2015)2. - ISSN 0032-0935 - p. 435 - 449.
    medicago-truncatula seeds - transcription factors - expression data - abiotic stress - dormancy - drought - identification - maturation - longevity - software
    Main conclusion During re-establishment of desiccation tolerance (DT), early events promote initial protection and growth arrest, while late events promote stress adaptation and contribute to survival in the dry state. Mature seeds of Arabidopsis thaliana are desiccation tolerant, but they lose desiccation tolerance (DT) while progressing to germination. Yet, there is a small developmental window during which DT can be rescued by treatment with abscisic acid (ABA). To gain temporal resolution and identify relevant genes in this process, data from a time series of microarrays were used to build a gene co-expression network. The network has two regions, namely early response (ER) and late response (LR). Genes in the ER region are related to biological processes, such as dormancy, acquisition of DT and drought, amplification of signals, growth arrest and induction of protection mechanisms (such as LEA proteins). Genes in the LR region lead to inhibition of photosynthesis and primary metabolism, promote adaptation to stress conditions and contribute to seed longevity. Phenotyping of 12 hubs in relation to re-establishment of DT with T-DNA insertion lines indicated a significant increase in the ability to re-establish DT compared with the wild-type in the lines cbsx4, at3g53040 and at4g25580, suggesting the operation of redundant and compensatory mechanisms. Moreover, we show that re-establishment of DT by polyethylene glycol and ABA occurs through partially overlapping mechanisms. Our data confirm that co-expression network analysis is a valid approach to examine data from time series of transcriptome analysis, as it provides promising insights into biologically relevant relations that help to generate new information about the roles of certain genes for DT.
    Effect of antimicrobial compounds on cut Gerbera flowers: Poor relation between stem bending and numbers of bacteria in the vase water
    Witte, Y. van de; Harkema, H. ; Doorn, W.G. van - \ 2014
    Postharvest Biology and Technology 91 (2014). - ISSN 0925-5214 - p. 78 - 83.
    jamesonii flowers - essential oils - rose flowers - membranes - longevity - stress - sugars - plants - life - acid
    Gerbera flowers (Gerbera jamesonii) often show stem bending. In four cultivars (Tamara, Liesbeth, Cora, and Mickey), we tested the effects on bending of antimicrobial compounds (chlorine bleach, a slow release chlorine compound, 8-hydroxyquinoline citrate [HQC], silver nitrate, carvacrol and thymol), some combined with sugars. At concentrations used for other cut flowers, inclusion in the vase solution of several of the antimicrobial compounds delayed bending, had no effect, or hastened bending. Hastening of bending was found at higher concentrations. It was accompanied with visible damage on the stem ends. Results with HQC indicated high toxicity as it did not delay bending at any of the concentration tested (100-400 mg L-1). At 200 mg L-1 HQC induced growth of bacteria that were not found in the controls. The number of bacteria in the vase water showed a low correlation with bending. Visible toxicity on the stem surface was often associated with a high bacteria count. However, at relatively high concentrations of the antimicrobial compounds stem bending was associated with a low count. This indicated an effect other than bacteria. Water uptake was low in stems that bent early. It is hypothesized that material from dead stem cells resulted in a xylem blockage which led to early bending. Sucrose at 15 g L-1 in combination with an antimicrobial compound (slow release chlorine, HQC) resulted in the absence of stem damage and produced much less bending than the same concentration of the antimicrobial compounds alone. Sucrose apparently counteracted the toxic effects of the antimicrobial chemicals. (C) 2014 Published by Elsevier B.V.
    Combating inflammaging through a Mediterranean whole diet approach: The NU-AGE project's conceptual framework and design
    Santoro, A. ; Pini, E. ; Scurti, M. ; Palmas, G. ; Berendsen, A.M. ; Brzozowska, A.M. ; Groot, C.P.G.M. de; Feskens, E.J.M. ; Vos, W.M. de - \ 2014
    Mechanisms of Ageing and Development 136-137 (2014). - ISSN 0047-6374 - p. 3 - 13.
    cd8(+) t-cells - style diet - cellular senescence - older-adults - longevity - immunosenescence - phenotype - frailty - system - muscle
    The development of a chronic, low grade, inflammatory status named “inflammaging” is a major characteristic of ageing, which plays a critical role in the pathogenesis of age-related diseases. Inflammaging is both local and systemic, and a variety of organs and systems contribute inflammatory stimuli that accumulate lifelong. The NU-AGE rationale is that a one year Mediterranean whole diet (considered by UNESCO a heritage of humanity), newly designed to meet the nutritional needs of the elderly, will reduce inflammaging in fully characterized subjects aged 65–79 years of age, and will have systemic beneficial effects on health status (physical and cognitive). Before and after the dietary intervention a comprehensive set of analyses, including omics (transcriptomics, epigenetics, metabolomics and metagenomics) will be performed to identify the underpinning molecular mechanisms. NU-AGE will set up a comprehensive database as a tool for a systems biology approach to inflammaging and nutrition. NU-AGE is highly interdisciplinary, includes leading research centres in Europe on nutrition and ageing, and is complemented by EU multinational food industries and SMEs, interested in the production of functional and enriched/advanced traditional food tailored for the elderly market, and European Federations targeting policy makers and major stakeholders, from consumers to EU Food & Drink Industries.
    Preservation of seed viability during 25 years of storage under standard genebank conditions
    Treuren, R. van; Groot, E.C. de; Hintum, T.J.L. van - \ 2013
    Genetic Resources and Crop Evolution 60 (2013)4. - ISSN 0925-9864 - p. 1407 - 1421.
    desiccation-tolerance - longevity - brassicaceae - germination - maturity
    Maintaining sufficient viability is critical to the sustainability of ex situ conserved seed collections. For this reason, accessions are regenerated when viability falls below a predefined threshold. Viability is monitored by determining the germination ability of accessions at predefined time intervals. Optimizing the frequency of these germination tests, in order to avoid waste of resources, is hampered by the scarce availability of data about seed longevity, particularly for material maintained under genebank conditions. Here we report on the analysis of nearly 40,000 germination test results collected for a wide range of crop species over a 25-years period by the centre for genetic resources, the Netherlands (CGN), where seeds of genebank accessions are dried to 3–7 % moisture content and stored for the long term under near-vacuum in aluminium foil bags at -20 °C. The results indicate that seed viability is well maintained for the large majority of seed lots during the first 25 years after regeneration as only 3.3 % of the monitoring tests revealed below-threshold germination values. It is argued that the majority of these sub-standard seed lots are due to other causes than seed ageing, including dormancy problems and estimation error in germination testing. For material, maintained under the seed management procedures and storage conditions practiced by CGN, it is therefore recommended to delay the first germination monitoring tests to 25 years after regeneration.
    Foot disorders in dairy cattle : a socio-economic approach to improve dairy cow welfare
    Bruijnis, M.R.N. - \ 2012
    Wageningen University. Promotor(en): Elsbeth Stassen, co-promotor(en): Henk Hogeveen. - S.l. : s.n. - ISBN 9789461733924 - 174
    melkvee - melkkoeien - voetziekten - dierenwelzijn - diergezondheid - sociale economie - simulatiemodellen - verliezen - gebruiksduur - melkveehouderij - dairy cattle - dairy cows - foot diseases - animal welfare - animal health - socioeconomics - simulation models - losses - longevity - dairy farming
    Klauwaandoeningen en de kreupelheid die daardoor ontstaat zijn een belangrijk probleem in de huidige melkveehouderij. Op basis van de incidentie, duur en ernst van klauwaandoeningen, worden ze aangemerkt als het belangrijkste welzijnsprobleem. Ondanks dat er veel kennis is over de klauwaandoeningen en de risicofactoren, is het probleem nog niet afgenomen. Bovendien onderschatten melkveehouders de grootte van het probleem van klauwaandoeningen, evenals de relatie met kreupelheid.
    Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions
    Groot, S.P.C. ; Surki, A.A. ; Vos, R.C.H. de; Kodde, J. - \ 2012
    Annals of Botany 110 (2012)6. - ISSN 0305-7364 - p. 1149 - 1159.
    controlled deterioration - moisture-content - vitamin-e - gaseous environment - digitalis-purpurea - lipid-peroxidation - water-content - barley seeds - longevity - germination
    Background and Aims Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen. Methods Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed. Key Results The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH. Conclusions Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice
    Genetic variation for stress-response hormesis in C. elegans lifespan
    Rodriguez Sanchez, M. ; Snoek, L.B. ; Riksen, J.A.G. ; Bevers, R.P.J. ; Kammenga, J.E. - \ 2012
    Experimental Gerontology 47 (2012)8. - ISSN 0531-5565 - p. 581 - 587.
    quantitative trait loci - genotype-environment interactions - nematode caenorhabditis-elegans - long-lived mutant - drosophila-melanogaster - heat-shock - history traits - natural variation - longevity - resistance
    Increased lifespan can be associated with greater resistance to many different stressors, most notably thermal stress. Such hormetic effects have also been found in C. elegans where short-term exposure to heat lengthens the lifespan. Genetic investigations have been carried out using mutation perturbations in a single genotype, the wild type Bristol N2. Yet, induced mutations do not yield insight regarding the natural genetic variation of thermal tolerance and lifespan. We investigated the genetic variation of heat-shock recovery, i.e. hormetic effects on lifespan and associated quantitative trait loci (QTL) in C. elegans. Heat-shock resulted in an 18% lifespan increase in wild type CB4856 whereas N2 did not show a lifespan elongation. Using recombinant inbred lines (RILs) derived from a cross between wild types N2 and CB4856 we found natural variation in stress-response hormesis in lifespan. Approx. 28% of the RILs displayed a hormesis effect in lifespan. We did not find any hormesis effects for total offspring. Across the RILs there was no relation between lifespan and offspring. The ability to recover from heat-shock mapped to a significant QTL on chromosome II which overlapped with a QTL for offspring under heat-shock conditions. The QTL was confirmed by introgressing relatively small CB4856 regions into chromosome II of N2. Our observations show that there is natural variation in hormetic effects on C. elegans lifespan for heat-shock and that this variation is genetically determined.
    Winter Survival of Individual Honey Bees and Honey Bee Colonies Depends on Level of Varroa destructor Infestation
    Dooremalen, C. van; Gerritsen, L.J.M. ; Cornelissen, B. ; Steen, J.J.M. van der; Langevelde, F. van; Blacquiere, T. - \ 2012
    PLoS ONE 7 (2012)4. - ISSN 1932-6203
    apis-mellifera colonies - jacobsoni oud - oxalic-acid - life-span - population - acari - hymenoptera - longevity - physiology - declines
    Background: Recent elevated winter loss of honey bee colonies is a major concern. The presence of the mite Varroa destructor in colonies places an important pressure on bee health. V. destructor shortens the lifespan of individual bees, while long lifespan during winter is a primary requirement to survive until the next spring. We investigated in two subsequent years the effects of different levels of V. destructor infestation during the transition from short-lived summer bees to long-lived winter bees on the lifespan of individual bees and the survival of bee colonies during winter. Colonies treated earlier in the season to reduce V. destructor infestation during the development of winter bees were expected to have longer bee lifespan and higher colony survival after winter. Methodology/Principal Findings: Mite infestation was reduced using acaricide treatments during different months (July, August, September, or not treated). We found that the number of capped brood cells decreased drastically between August and November, while at the same time, the lifespan of the bees (marked cohorts) increased indicating the transition to winter bees. Low V. destructor infestation levels before and during the transition to winter bees resulted in an increase in lifespan of bees and higher colony survival compared to colonies that were not treated and that had higher infestation levels. A variety of stress-related factors could have contributed to the variation in longevity and winter survival that we found between years. Conclusions/Significance: This study contributes to theory about the multiple causes for the recent elevated colony losses in honey bees. Our study shows the correlation between long lifespan of winter bees and colony loss in spring. Moreover, we show that colonies treated earlier in the season had reduced V. destructor infestation during the development of winter bees resulting in longer bee lifespan and higher colony survival after winter.
    How honey bees of successive age classes are distributed over a one storey, ten frames hive
    Steen, J.J.M. van der; Cornelissen, B. ; Donders, J.N.L.C. ; Blacquière, T. ; Dooremalen, C. van - \ 2012
    Journal of Apicultural Research 51 (2012)2. - ISSN 0021-8839 - p. 174 - 178.
    worker honeybees - apis-mellifera - longevity - products - length - life
    In honey bee studies focusing on physiology, disease diagnosis or bio indication, bees are sampled from the colony. This raises the question of where in the colony samples must be taken from for specific study objectives. In this study we recorded where bees of known age are found in the hive. We recorded in a single brood box with ten frames in August that the mean proportion of bees of one (41%), two (23%), three (17%), four (11%) and five (8%) week old bees did not differ between frames. Additionally we found that there was a significant mortality of young bees in the first week after emergence. This may be partly due to the study set up but is also a natural phenomenon
    Changed gene expression for candidate ageing genes in long-lived Bicyclus anynana butterflies
    Pijpe, J. ; Pul, N. ; Duijn, S. van; Brakefield, P.M. ; Zwaan, B.J. - \ 2011
    Experimental Gerontology 46 (2011)6. - ISSN 0531-5565 - p. 426 - 434.
    quantitative trait loci - extend life-span - drosophila-melanogaster - oxidative damage - caenorhabditis-elegans - starvation resistance - adaptive evolution - stress resistance - natural variation - longevity
    Candidate genes for the regulation of lifespan have emerged from studies that use mutants and genetically manipulated model organisms. However, it is rarely addressed whether these genes contribute to lifespan variation in populations of these species that capture natural standing genetic variation. Here, we explore expression variation in three candidate ageing genes, Indy, sod2, and catalase, in Bicyclus anynana, a butterfly with well understood ecology. We used lines established from natural populations and artificially selected for increased adult starvation resistance. They show a considerable increase in adult lifespan under both starvation and optimal food conditions. We measured adult butterflies of various ages, under a range of optimal and starvation diets, from two selected populations and one unselected control population. In all lines, Indy and catalase are up-regulated in response to starvation while this is not evident for sod2. Under starvation, Indy and catalase are up-regulated in, while this is not evident for sod2. Under optimal food conditions, Indy is down-regulated at a later age, with Indy expression showing relatively high inter-individual variation. We find differences between the selected lines and the unselected line. Under starvation conditions, expression is higher for catalase in one, and for sod2 in both selected lines. Importantly, sod2 expression is also higher in the selected populations under optimal food conditions. We conclude that sod2, but not Indy, is involved in the response to artificial selection for increased starvation resistance. The role of catalase is less clear because of the differences between the two selected lines. Moreover, sod2 appears to be a candidate gene that underpins the genetic correlation between starvation resistance and longevity. Our study indicates that some, but not all, genes identified through mutant screens in other organisms may underpin standing genetic variation for ageing-related traits in stocks of Bicyclus butterflies established from natural populations. Clearly, this needs to be investigated in other organisms as well, especially in the organisms to which mutants screens were applied. This information will narrow down the list of genes that underpin variation in lifespan and ageing in extant populations of organisms, and which may serve as candidate genes in humans
    Purple witchweed (Striga hermonthica) germination and seedbank depletion under different crops, fallow, and bare soil
    Mourik, T.A. van; Stomph, T.J. ; Murdoch, A.J. - \ 2011
    Weed Biology and Management 11 (2011)2. - ISSN 1444-6162 - p. 100 - 110.
    long-term management - strategy evaluation - population-model - longevity - sorghum - banks - seeds
    Seedbank density is an important aspect that determines the amount of damage that the parasitic weed, purple witchweed (Striga hermonthica; hereafter, called “Striga”), causes on its crop hosts. The seedbank depletion of Striga was measured in Mali and Niger during the 2004 rainy season under the host crops, pearl millet and sorghum, the non-host crops, cowpea and sesame, the intercrops of pearl millet or sorghum with cowpea or sesame, and fallow with or without weeding. Two methods were used and compared; namely, a seed bag method and a soil-sampling method. The fate of the seeds was assessed by a seed press test. Seed germination, as determined by the presence of empty seed coats, contributed most to the seedbank depletion of Striga under a variety of crop covers and fallow. The highest seedbank depletion was found under the monocultures of the host crops. The intercrops of the host and non-host crops caused less seedbank depletion, followed by the monocultures of the non-host crops, fallow, and bare soil. The seed bag method and the soil-sampling method yielded similar percentages of seedbank depletion, while the former allowed for distinguishing between the germinated and diseased seeds. The results suggest that, although all the tested crop species can cause the seed germination and seedbank depletion of Striga, management by using host cereal crops causes the highest amount of germination and has the highest potential to deplete the soil seed bank, provided that seed production is prevented
    Organic matter and seed survival of Striga hermonthica - Mechanisms for seed depletion in the soil
    Ayongwa, G.C. ; Stomph, T.J. ; Belder, P. ; Leffelaar, P.A. ; Kuyper, T.W. - \ 2011
    Crop Protection 30 (2011)12. - ISSN 0261-2194 - p. 1594 - 1600.
    long-term management - strategy evaluation - ethylene production - fusarium-oxysporum - population-model - del. benth. - germination - decomposition - stimulation - longevity
    Seed survival of Striga hermonthica is influenced by amendments of organic matter; however, the role of organic matter quality (C:N ratio) and mechanisms for enhanced seed decay are inadequately understood. In a field experiment, plots received a single dose of 6 t organic matter per hectare but with large differences in quality in terms of C:N ratio. Soil moisture, soil temperature and soil ethylene concentrations were measured, while buried nylon seed bags were periodically withdrawn from the soil and assayed for seed viability and germination. Organic matter amendments incorporated in the soil significantly depressed S. hermonthica seed survival. The effect was strongest with organic matter of high quality. Organic matter of low-quality enhanced soil water content during the first five days after a rainfall event and resulted in a 0.5 °C lower soil temperature. The highest observed ethylene concentrations in the soil were between 2 and 3 ppm, high enough to stimulate S. hermonthica seed germination. Maximal seed germination in vitro was obtained after 48 h of exposure to 1 ppm ethylene. However, observed changes in seed germination and viability of retrieved seed batches (seed survival) did not correlate with soil ethylene concentrations. The latter in turn did not differ between qualities of the applied organic matter. Seed survival decreased with increasing time of burial, especially after 4–8 weeks. As S. hermonthica attachment mainly occurs during the first four weeks of the cropping season the observed effect of seed decay may hardly be beneficial for the on-going cropping season. Nutrient release through decomposition of organic matter, enhancing decay of S. hermonthica seeds, is proposed as the probable cause of seed depletion in the soil.
    Authenticity of old cultivars in genebank collections: a case study on lettuce
    Wouw, M.J. van de; Treuren, R. van; Hintum, T.J.L. van - \ 2011
    Crop Science 51 (2011)2. - ISSN 0011-183X - p. 736 - 746.
    genenbanken - slasoorten - aflp - oude plantenrassen - ex-situ conservering - cultivarauthenticiteit - lactuca sativa - rassen (planten) - cultivars - gene banks - lettuces - amplified fragment length polymorphism - old varieties - ex situ conservation - cultivar authenticity - lactuca sativa - varieties - cultivars - genetic diversity - maintenance - accessions - longevity - level - l.
    Ex situ collections in genebanks conserve many old cultivars that had disappeared from mainstream agriculture before modern genebanks were established. The collections incorporated cultivars from many sources, such as botanical gardens and working collections, sometimes with little further information on their origin. Many old cultivars with identical or synonymous names are maintained in multiple collections and often more than once within collections. This research investigates the authenticity of old cultivars in genebanks using a large lettuce (Lactuca sativa L.) collection as a case study. Accessions presumed to be identical, based on the cultivar names accompanying the accessions, were compared for their DNA marker profiles, based on amplified fragment length polymorphisms (AFLPs). Using the genetic similarity of these accessions, the probability of authenticity of the old cultivars maintained in the collection was estimated. Separate analyses were done for different classes of cultivars, on the basis of the year of release or the donor history of the cultivar. The two largest cultivar groups within the collection, Sans Rivale à Graine Blanche and Maikönig, were analyzed in detail. Nonauthenticity of the investigated cultivars appeared to be high. This was especially true for the oldest cultivars, but even for the cultivars released from the 1960s to 1990 it was estimated that approximately 10% was not authentic. Recommendations to improve authenticity of cultivars in ex situ collections were presented
    Heritability of foot conformation and its relationship to sports performance in a Dutch warmblood horse population.
    Ducro, B.J. ; Bovenhuis, H. ; Back, W. - \ 2009
    Equine Veterinary Journal 41 (2009)2. - ISSN 0425-1644 - p. 139 - 143.
    swedish warmblood - racehorses - parameters - longevity - dressage - balance - traits - health
    Reasons for performing study: Warmblood horse studbooks aim to breed horses with a conformation that will enable elite future performance, but reduce the risk of injuries and lameness. Negative conformational traits, such as asymmetrical or 'uneven' forefeet would possibly diminish performance. Objectives: To assess the prevalence and heritability of uneven feet and its genetic relationship to other conformation traits as well as to sporting performance later in life in Warmblood riding horses. Methods: The databases of the Royal Dutch Warmblood Studbook (KWPN, n = 44,840 horses) and Royal Dutch Equestrian Sports Federation (KNHS, n = 33,459 horses in dressage and n = 30,474 horses in showjumping) were linked through the unique number of each registered horse. Therefore, heritabilities and genetic and phenotypic correlations could be estimated from the scores of the jury at studbook admission and the sports performance of that population in dressage and jumping over the period 1990-2002. Results: The prevalence of uneven feet was 5.3% on average, and increased from under 4.5% during the first 3 years of recording to over 8% in the years from 2000 onwards. Heritability estimates of foot conformation traits were moderate and ranged from 0.16 for heel height to 0.27 for hoof shape. The genetic correlation between the trait of uneven feet and performance in competition was negative but weak: -0.09 with dressage and -0.12 with showjumping. Conclusions: Predisposition to uneven feet can be reduced by selection. Because of weak genetic correlations, the increased prevalence is not directly associated with selection for better sports performance or higher conformation grade. If the trait 'uneven feet' arises from a disproportionate relationship between height at the withers and neck length, then selection on conformation grade might result in development of uneven feet. In general, limb conformation has a moderate genetic relationship to conformation grade and foot conformation traits have a genetic relationship to sporting performance. Reducing occurrence of uneven feet by selection is possible, without limiting progress in sport performance.
    Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity
    Winkler, K. ; Wäckers, F.L. ; Kaufman, L.V. ; Larraz, V. ; Lenteren, J.C. van - \ 2009
    Biological Control 50 (2009)3. - ISSN 1049-9644 - p. 299 - 306.
    diadegma-insulare hymenoptera - diamondback moth lepidoptera - biological-control - nutritional state - floral resources - field conditions - honeydew sugars - aphid honeydew - longevity - ichneumonidae
    In conservation biological control, diversification of the agro ecosystem with flowering vegetation is seen as an important tool to support the broad range of predators and parasitoids that require nectar and pollen sources to survive and reproduce. In order to identify flowering plants that provide suitable food sources for natural enemies without supporting the pest species, we analyzed the exploitation of 19 flowering plants by two important lepidopteran cabbage pests, Pieris rapae and Plutella xylostella, and their hymenopteran parasitoids, Cotesia glomerata and Diadegma semiclausum. The experiments were conducted at 90% r.h., while Pieris rapae was tested both at 45% r.h. and at 90% r.h. At 45 ± 5% r.h., corresponding with field conditions at which P. rapae is predominantly active, the butterfly was unable to feed on a number of exposed floral nectar sources whose nectar was successfully exploited at 90% r.h. The broader nectar exploitation by P. rapae at the high humidity is presumably explained by the resulting decrease in nectar viscosity. When comparing D. semiclausum and its herbivorous host P. xylostella, the herbivore exploited a broader range of plants. However, those plants that benefited both the parasitoid and the herbivore had a much stronger effect on the longevity of the parasitoid. The results from the accessibility bioassay suggest that flowers where nectar is not accessible can have a negative impact on insect survival presumably by stimulating foraging without providing accessible nectar. Our results underline the importance of considering species-specific environmental conditions when fine-tuning the choice of nectar sources to be used in conservation biological control programs.
    Influence of foot conformation on length of competitive life in a Dutch warmblood horse population.
    Ducro, B.J. ; Gorissen, B.M.C. ; Eldik, P. van; Back, W. - \ 2009
    Equine Veterinary Journal 41 (2009)2. - ISSN 0425-1644 - p. 144 - 148.
    swedish warmblood - longevity - traits
    Reasons for performing study: Warmblood horse studbooks aim to breed horses with a conformation that will enable elite future sports performance, but reduce the risk of early retirement due to lameness. Negative conformational traits, such as asymmetrical or 'uneven' forefeet may possibly shorten the career of sporthorses. Objectives: To investigate the significance of foot conformation at young age to duration of the career of sporthorses. Methods: Databases of the Royal Dutch Warmblood Studbook (KWPN) and of the Royal Dutch Equestrian Sports Federation (KNHS) were matched and resulted in a dataset comprising 23,116 records of horses for which their conformation scores and duration of their sports career were available. Survival analysis was used to determine which of the conformation traits had a significant effect on duration of sports career in dressage and jumping at basic and elite level.Results: Duration of competitive life was shorter for jumping than for dressage. A different set of risk factors was found for each level and discipline. The trait 'uneven feet' tended to shorten the competitive life in dressage, but was a significant risk factor at the elite level of jumping. Conclusions: Limb conformation and, in particular, the conformation of the distal limb, are important for duration of competitive life. From the prevalence of uneven feet in sports disciplines, it may be concluded that this is an undesirable trait, particularly at the elite level of jumping, since uneven feet have a detrimental effect on the duration of competitive life in a sporthorse population. Potential relevance: This study provided evidence that the conformation trait uneven feet has a negative effect on Warmblood jumping performance and, therefore, breeders should be encouraged to avoid this phenomenon at foal age.
    Breeding for robustness in cattle
    Klopcic, M. ; Reents, R. ; Philipsson, J. ; Kuipers, A. - \ 2009
    Wageningen : Wageningen Academic Publishers (EAAP publication no. 126) - ISBN 9789086860845 - 281
    rundvee - bos - dierveredeling - fokkerijmethoden - gebruiksduur - ziekteresistentie - melkvee - rundveerassen - vruchtbaarheid - genetische variatie - prestatiekenmerken - cattle - bos - animal breeding - animal breeding methods - longevity - disease resistance - dairy cattle - cattle breeds - fertility - genetic variation - performance traits
    Effects of flower attractiveness and nectar availability in field margins on biological control by parasitoids
    Bianchi, F.J.J.A. ; Wackers, F.L. - \ 2008
    Biological Control 46 (2008)3. - ISSN 1049-9644 - p. 400 - 408.
    habitat management - natural enemies - arthropod pests - sugar analysis - weed strips - food - longevity - hosts - wasps - hymenoptera
    Flowering plants have been shown to differ with regard to their attractiveness to parasitoids and nectar accessibility. These floral traits are likely to affect the foraging performance of parasitoids in agricultural landscapes. Using a spatially explicit simulation model we explore how the attractiveness and nectar availability of flowering field margins affects their impact on parasitoids and ultimately on pest populations in crops. The model simulates the movement, nectar feeding and parasitism of parasitoids in an agroecosystem composed of a crop and adjacent flower margin. The perception of olfactory cues emitted by flowers and host-infestcd plants drives the movement of the parasitoid. Its preference for floral nectar or hosts is described as a function of its internal energy status. Model validation reveals that simulations and measurements of the spatial distribution and energy status of parasitoids are generally in good agreement. Model simulations suggest that aggregation of parasitoids at flower strips are caused by a prolonged longevity of parasitoids feeding on floral nectar as well as by attraction of parasitoids from the surrounding area. We found no indication for depletion of parasitoids in the field interior as a result of migration towards flower strips. Simulations further suggest that the attractiveness of flowers is an important characteristic that should be taken into account for the selection of flowering plants. This study implies that tailoring nectar supply to the requirements of parasitoids holds potential to increase their effectiveness as biological control agents.
    A mitochondrial mutator plasmid that causes senescence under dietary restricted conditions
    Maas, M.F.P.M. ; Hoekstra, R.F. ; Debets, A.J.M. - \ 2007
    BMC Genetics 8 (2007)9. - ISSN 1471-2156 - p. 1 - 12.
    podospora-anserina - linear plasmids - neurospora-intermedia - calorie restriction - dna-sequences - genomic dna - longevity - mutant - pal2-1 - amplification
    Background Calorie or dietary restriction extends life span in a wide range of organisms including the filamentous fungus Podospora anserina. Under dietary restricted conditions, P. anserina isolates are several-fold longer lived. This is however not the case in isolates that carry one of the pAL2-1 homologous mitochondrial plasmids. Results We show that the pAL2-1 homologues act as 'insertional mutators' of the mitochondrial genome, which may explain their negative effect on life span extension. Sequencing revealed at least fourteen unique plasmid integration sites, of which twelve were located within the mitochondrial genome and two within copies of the plasmid itself. The plasmids were able to integrate in their entirety, via a non-homologous mode of recombination. Some of the integrated plasmid copies were truncated, which probably resulted from secondary, post-integrative, recombination processes. Integration sites were predominantly located within and surrounding the region containing the mitochondrial rDNA loci. Conclusion We propose a model for the mechanism of integration, based on innate modes of mtDNA recombination, and discuss its possible link with the plasmid's negative effect on dietary restriction mediated life span extension.
    Afvoerleeftijd geen betrouwbare maat voor duurzaamheid
    Ouweltjes, W. - \ 2006
    V-focus 3 (2006)1. - ISSN 1574-1575 - p. 18 - 19.
    melkveehouderij - melkkoeien - melkproductie - productieve levensduur - gebruiksduur - duurzaamheid (sustainability) - kuddes (flocks) - selectie - agrarische bedrijfsvoering - meting - dairy farming - dairy cows - milk production - productive life - longevity - sustainability - flocks - selection - farm management - measurement
    Niet een hoge afvoerleeftijd maar een laag celgetal (in relatie tot de leeftijd) duidt op een bovengemiddelde duurzaamheid. Dit betekent dat bij het beoordelen van het tankmelkcelgetal rekening moet worden gehouden met de leeftijd van de veestapel.Het rekenmodel voor het vervangingsbeleid gaat ervan uit dat er steeds vervangende vaarzen voorhanden zijn. In de praktijk is dat lang niet altijd het geval. Veel boeren fokken zelf hun vaarzen op en daarmee is de jongveeopfok sterk bepalend voor het vervangingsbeleid. Door minder jongvee op te fokken wordt de afvoerleeftijd wel hoger, maar daarmee wordt de veestapel nog niet duurzamer. Op het LageKostenbedrijf (LKB) bleek uit de ziekteregistratie en de vruchtbaarheidsgegevens dat de duurzaamheid van de oude veestapel te wensen overliet. Omdat er weinig jongvee instroomde, is steeds getracht zoveel mogelijk dieren opnieuw drachtig te krijgen. Ook het gemiddelde geometrische celgetal van de afgevoerde dieren was hoog, namelijk 333.000 cellen/ml. Daarnaast zijn jaarlijks enkele dieren vanwege acute gezondheidsproblemen afgevoerd. De lage vervanging kon alleen worden behaald door extra kosten te maken voor diergezondheid. Zou er wel ruimte zijn geweest voor vrijwillige vervanging, dan zouden bij een gelijkblijvende duurzaamheid, dieren sneller zijn afgevoerd waardoor de afvoerleeftijd zou zijn gedaald. De afvoerleeftijd is dan ook geen betrouwbare maat voor duurzaamheid. Een betere indicatie van de duurzaamheid van een veestapel wordt waarschijnlijk verkregen als naast de afvoerleeftijd, ook de kosten voor diergezondheid en vruchtbaarheid worden meegenomen. Of dat zo is, wordt het komende jaar nader onderzocht.
    Infection of the malaria mosquito Anopheles gambiae with the entomopathogenic fungus Metarhizium anisopliae reduces blood feeding and fecundity
    Scholte, E.J. ; Knols, B.G.J. ; Takken, W. - \ 2006
    Journal of Invertebrate Pathology 91 (2006)1. - ISSN 0022-2011 - p. 43 - 49.
    schistocerca-gregaria - desert locust - destruxins - reduction - flavoviride - consumption - longevity - culicidae - pathogen - survival
    The entomopathogenic fungus Metarhizium anisopliae is being considered as a biocontrol agent against adult African malaria vectors. In addition to causing significant mortality, this pathogen is known to cause reductions in feeding and fecundity in a range of insects. In the present study we investigated whether infection with M. anisopliae affected blood feeding and fecundity of adult female malaria vectors Anopheles gambiae Giles sensu stricto. Mosquitoes were contaminated with either a low or a moderately high dose of oil-formulated conidia of M. anisopliae, and offered a single human blood meal 48, 72, or 96 h later to assess feeding propensity and individual blood meal size. In a second experiment, individual fungus-infected females were offered a blood meal every third day (to a total of 8 gonotrophic cycles), and allowed to oviposit after each cycle in order to quantify feeding propensity and fecundity. Infected females took smaller blood meals and displayed reduced feeding propensity. It was found that mosquitoes, inoculated with a moderately high dose of fungal conidia, exhibited reduced appetite related to increasing fungal growth. Of the fungus-infected females, the proportion of mosquitoes taking the second blood meal was reduced with 51%. This was further reduced to 35.3% by the 4th blood meal. During 8 feeding opportunities, the average number of blood meals taken by uninfected females was 4.39, against 3.40 (low dose), and 2.07 (high dose) blood meals for the fungus-infected females. Moreover, infected females produced fewer eggs per gonotrophic cycle and had a lower life-time fecundity. Epidemiological models show that both blood feeding and fecundity are among the most important factors affecting the likelihood of a mosquito transmitting malaria, which suggests that this fungus may have potential as biocontrol agent for vector-borne disease control
    Cloning of DOG1, a quantitative trait locus controlling seed dormancy in Arabidopsis
    Bentsink, L. ; Jowett, J. ; Hanhart, C.J. ; Koornneef, M. - \ 2006
    Proceedings of the National Academy of Sciences of the United States of America 103 (2006)45. - ISSN 0027-8424 - p. 17042 - 17047.
    natural allelic variation - thaliana l heynh - abscisic-acid - gibberellin biosynthesis - embryo development - germination - mutants - gene - longevity - maintenance
    Genetic variation for seed dormancy in nature is a typical quantitative trait controlled by multiple loci on which environmental factors have a strong effect. Finding the genes underlying dormancy quantitative trait loci is a major scientific challenge, which also has relevance for agriculture and ecology. In this study we describe the identification of the DELAY OF GERMINATION 1 (DOG1) gene previously identified as a quantitative trait locus involved in the control of seed dormancy. This gene was isolated by a combination of positional cloning and mutant analysis and is absolutely required for the induction of seed dormancy. DOG1 is a member of a small gene family of unknown molecular function, with five members in Arabidopsis. The functional natural allelic variation present in Arabidopsis is caused by polymorphisms in the cis-regulatory region of the DOG1 gene and results in considerable expression differences between the DOG1 alleles of the accessions analyzed
    Effect of seed maturity on sensitiviy of seed towards physical sanitation treatments
    Groot, S.P.C. ; Birnbaum, Y.E. ; Rop, N. ; Jalink, H. ; Forsberg, G. ; Kromphardt, C. ; Werner, S. ; Koch, E. - \ 2006
    Seed Science and Technology 34 (2006)2. - ISSN 0251-0952 - p. 403 - 413.
    zaadproductie - plantenziekten - brassica oleracea - daucus carota - heetwaterbehandeling - rijpheid - seed production - plant diseases - brassica oleracea - daucus carota - hot water treatment - maturity - chlorophyll fluorescence - brassica-oleracea - borne pathogens - aerated steam - humid air - hot - longevity
    Physical sanitation methods are used by the seed industry to prevent transmission of seed-borne diseases, but sensitivity varies between seed lots. The effect of seed maturity on the sensitivity to hot water, aerated steam and electron treatments was studied. Two Brassica oleracea L. and two Daucus carota L. seed lots from commercial production were selected for containing relatively large amounts of less mature seeds. Each seed lot was sorted into three maturity fractions based on the levels of chlorophyll fluorescence of individual seeds. Less mature B. oleracea and D. carota seeds were more susceptible to hot water treatments and less mature B. oleracea seeds to the aerated steam treatment. Seed maturity did not influence the sensitivity to the applied electron seed treatments. Seed lots were not selected for infections with seed-borne pathogens, however the less mature seeds were observed to be more frequently infected. It would be advisable to harvest seeds as mature as possible and to remove less mature seeds during seed processing. Sorting seeds by their level of chlorophyll fluorescence provides a useful method of sorting B. oleracea and D. carota seed lots. This would result in more efficient physical sanitation of seed lots
    Life expectancy in a follow-up study of a birth cohort of boxer dogs from post weaning to 10-years of age
    Hagen, M.A.E. van; Ducro, B.J. ; Knol, B.W. - \ 2005
    American Journal of Veterinary Research 66 (2005)9. - ISSN 0002-9645 - p. 1646 - 1650.
    survival analysis - insured dogs - mortality - longevity - breeds - death - heritability - puppies - sweden
    Objective-To determine mortality rate over time, risk factors for death, and heritability of life expectancy in Boxers. Animals-1,733 purebred Boxers born in The Netherlands between January 1994 and March 1995. Procedure-Dogs were followed up from weaning (ie, 49 days of age) to 10 years of age through use of a written questionnaire sent to owners every 6 months. Mortality rate over time, risk factors potentially associated with death, and heritability of life expectancy were examined by use of a proportional hazards model based on the Weibull distribution. Results Estimated mortality rate during the 10-year study period for this birth cohort of Boxers was 45%. The probability of surviving to 5 years of age was 88%; the probability of surviving to 10 years of age was 55%. Estimated effective heritability of life expectancy was 0.076, meaning that in this population, an estimated 76% of the observed variation in life expectancy could be attributed to genetic differences among dogs that were passed from parents to their offspring. Conclusions and Clinical Relevance-Results suggest that cumulative incidence of death from weaning to 10 years of age among this birth cohort of Boxers was 45%. The estimated heritability of life expectancy suggested that life expectancy can be improved by use of selective breeding.
    Root infection of sugar beet by Cercospora beticola in a climate chamber and in the field
    Vereijssen, J. ; Schneider, J.H.M. ; Termorshuizen, A.J. - \ 2005
    European Journal of Plant Pathology 112 (2005)3. - ISSN 0929-1873 - p. 201 - 210.
    gray leaf-spot - north-carolina - zeae-maydis - dispersal - tillage - conidia - soil - longevity - survival - release
    Sugar beet root infection by Cercospora beticola, the causal agent of Cercospora leaf spot (CLS), was studied in a climate chamber and in the field. In the climate chamber, root incubation of susceptible seedlings with a conidial suspension resulted in disease incidences that were significantly different for two sugar beet cultivars (Auris: 0.8 ± 0.14 and A00170: 0.5 ± 0.18; P <0.05) with regard to the control treatment 35 days after root incubation in a standard potting soil-fine river sand mixture. In a field trial with susceptible cv. Savannah with soil-incorporated CLS-infested leaf material, disease developed four weeks earlier in the infested plots than in the control plots. The probability that disease develops in the field was significantly higher for the infested than for the control plots (P <0.05). Symptomless plants from infested field plots transferred to the glasshouse to induce leaf spot symptoms showed a significantly higher probability to induce symptom development (0.4 ± 0.08), than plants from control plots (0.02 ± 0.02) (P 20°C) and high relative humidity (> 95) in our climate chamber or after canopy closure in the field. Quantification of root infection and long term survival in soil is necessary to assess its contribution to the epidemiology and life cycle of Cercospora beticola. Cultural methods such as a wider crop rotation, management of crop debris and ploughing systems may provide control strategies alternative to or reducing fungicide input.
    Breeding for longevity in Italian Chianina cattle
    Forabosco, F. - \ 2005
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Piter Bijma; R. Bozzi. - Wageningen : - ISBN 9789085042662 - 153
    chianina - vleesvee - gebruiksduur - productieve levensduur - fenotypen - rundvleesproductie - genetische analyse - lineaire modellen - overleving - rentabiliteit - kenmerken - selectief fokken - genetische verbetering - chianina - beef cattle - longevity - productive life - phenotypes - beef production - genetic analysis - linear models - survival - profitability - traits - selective breeding - genetic improvement

    The objective of this thesis was to evaluate genetic aspects of longevity (LPL) in the Chianina beef cattle population in order to define how to include this trait in selection criteria. The Chianina breed has been raised for over twenty-two centuries inItalyand today this breed is present in different countries across Europe, South and Central America,Australia,Canada and the USA. Its characteristics of somatic gigantism and rapid growth are combined with enormous resistance to harsh environmental conditions, great ease of calving and an excellent meat quality. In this breed longevity was recorded as the length of productive life (LPL), defined as years from the age at the insemination that resulted in the birth of the first calf to the date of culling or censoring. Six mo were added after the last date of calving to account for the time that the calf remains with the cow. The LPL was equal to 5.97 years on average. Heritability was equal to 0.11 when both censored and uncensored data were included to estimate longevity with the survival analysis. Type traits were used as an early predictor of profitability and muscularity traits were the most important parameters for longevity among the factors studied. Cows with approximately one calf per year remained in the herd longer than cows with fewer calves.Cows with a long LPL were more profitable than cows with short LPL. The final score could be used as an early predictor of profitability. An increase of one day unit in LPL was associated with an increase of +0.19 /cow per year and +1.65 /cow on a lifetime basis. Including longevity in both the Chianina breeding index and breeding goal either using empirical or economical weights has the positive effect of increasing the response (+2.97 and +4.92 days/year respectively). Beef breeding organizations should consider the opportunity to include longevity in a future breeding scheme to increase profit and to promote the well-being and welfare of the cows.

    Responses to stress of Caenorhabditis elegans populations with different reproductive strategies
    Alda Alvarez, O. ; Jager, T. ; Kooijman, S.A.L.M. ; Kammenga, J.E. - \ 2005
    Functional Ecology 19 (2005)4. - ISSN 0269-8463 - p. 656 - 664.
    sperm competition - toxicity tests - life-cycle - sex - fertilization - recombination - longevity - genetics - cadmium - growth
    Hermaphroditic and gonochoric reproduction are essentially different reproductive strategies that may lead to diverging population responses to adverse environmental conditions. Each strategy implies different physiological mechanisms, which affect life-history traits and represent different ways of dealing with stress. We studied the performance of hermaphroditic vs gonochoric strains in the nematode Caenorhabditis elegans exposed to cadmium stress at the individual and population level. Under control conditions, the gonochoric strain started reproduction earlier than the hermaphroditic strain at a smaller size. This was due to an earlier switch from sperm to oocyte production triggered by male sperm availability. Under cadmium stress hermaphrodites showed a decrease in the size at onset of reproduction, presumably as a strategy to maintain a high population growth rate. In contrast the body size of gonochoric nematodes was not affected. A process-based model (DEBtox) was used as a tool for analysing life-history data and calculating population growth rates. The model fitted the data well using physiologically relevant parameters such as ageing, survival or reproduction related parameters. The simultaneous fit of all life-history traits was used to obtain populations growth rate estimates. The differences between the two C. elegans strains were reflected at the population level. Lower population growth rates, as calculated by DEBtox, were found in the gonochoric strain, largely determined by the proportion of males in the offspring. From the overall results we suggest that the differences found between both populations are due to the reproductive strategy. Under control conditions, CB strain (with gonochoric reproduction) does not favour population growth rates in the short term due to faster ageing and copulation costs on survival. Furthermore, in response to stress this strain also showed lower performance than the N2 hermaphroditic strain, mainly due to a higher sensitivity of survival to the stressor
    Relationship between profitability and type traits and derivation of economic values for reproduction and survival traits in Chianina beef cows
    Forabosco, F. ; Bozzi, R. ; Boettcher, P. ; Filippini, F. ; Bijma, P. ; Arendonk, J.A.M. van - \ 2005
    Journal of Animal Science 83 (2005). - ISSN 0021-8812 - p. 2043 - 2051.
    restricted maximum-likelihood - spanish holstein cows - dairy-cattle - animal-model - herd life - variance-components - genetic evaluation - profit equations - longevity - selection
    The objectives of this study were 1) to propose a profit function for Italian Chianina beef cattle; 2) to derive economic values for some biological variables in beef cows, specifically, production expressed as the number of calves born alive per year (NACY), age at the insemination that resulted in the birth of the first calf (FI), and length of productive life (LPL); and 3) to investigate the relationship between the phenotypic profit function and type traits as early predictors of profitability in the Chianina beef cattle population. The average profit was 196/(cow·yr) for the length of productive life (LPL) and was obtained as the difference between the average income of 1,375/(cow·yr) for LPL and costs of 1,178/(cow·yr) of LPL. The mean LPL was equal to 5.97 yr, so the average total phenotypic profit per cow on a lifetime basis was 1,175. A normative approach was used to derive the economic weights for the biological variables. The most important trait was the number of calves born alive (+4.03·cow¿1·yr¿1 and +24.06/cow). An increase of 1 d in LPL was associated with an increase of +0.19/(cow·yr) and +1.65/cow on a lifetime basis. Increasing FI by 1 d decreased profit by 0.42/(cow·yr) and 2.51/cow. Phenotypic profit per cow had a heritability of 0.29. Heritabilities for eight muscularity traits ranged from 0.16 to 0.23, and for the seven body size traits between 0.21 and 0.30. The conformation trait final score can be used as an early predictor of profitability. The sale price of the animal and differences in the revenue and costs of offspring due to muscularity should be included in a future profit function
    Survival and vigour of ultra-dry seeds after ten years of hermetic storage
    Hong, T.D. ; Ellis, R.H. ; Astley, D. ; Pinnegar, A.E. ; Groot, S.P.C. ; Kraak, H.L. - \ 2005
    Seed Science and Technology 33 (2005)2. - ISSN 0251-0952 - p. 449 - 460.
    zaadkieming - groeikracht - uitdrogingstolerantie - daucus carota - aardnoten - koolzaad - allium cepa - opslag van zaden - seed germination - vigour - desiccation tolerance - daucus carota - groundnuts - rape - allium cepa - seed storage - moisture-content limit - logarithmic relation - theoretical basis - longevity - temperatures - groundnut - protocols - lettuce
    Seeds of carrot, groundnut, lettuce, oilseed rape and onion were stored hermetically in laminated aluminium foil packets in four environments (dry or ultra-dry moisture contents combined factorially with temperatures of 20 degrees C or -20 degrees C), replicated at several sites. After ten years' hermetic storage, seed moisture content, equilibrium relative humidity, viability (assessed by ability to germinate normally in standard germination tests) and vigour were determined. After a decade, the change in seed moisture content of samples stored at -20 degrees C was small or nil. Except for groundnut and lettuce (where loss in viability was about 8 and 3%, respectively), no loss in viability was detected after 10 years' hermetic storage at -20 degrees C. In all cases, there was no difference in seed survival between moisture contents at this temperature (P > 0.25). Comparison of seed vigour (root length and rate of germination) also confirmed that drying to moisture contents in equilibrium with 10-12% r.h. had no detrimental effect to longevity when stored at -20 degrees C: the only significant (P <0.05) differences detected were slightly greater root lengths for ultra-dry storage of four of the six seed lots. Seed moisture content had increased after a decade at 20 degrees C (generally to the level in equilibrium with ambient relative humidity). Hence, sub-zero temperature storage helped maintain the long-term integrity of the laminated aluminium foil packets, as well as that of the seeds within.
    Why high seed densities within buried mesh bags may overestimate depletion rates of soil seed banks
    Mourik, T.A. van; Stomph, T.J. ; Murdoch, A.J. - \ 2005
    Journal of Applied Ecology 42 (2005)2. - ISSN 0021-8901 - p. 299 - 305.
    striga-hermonthica - weed seeds - longevity - emergence - viability - dynamics - rotation - dormancy - losses - fields
    1. Estimates of seed bank depletion rates are essential for modelling and management of plant populations. The seed bag burial method is often used to measure seed mortality in the soil. However, the density of seeds within seed bags is higher than densities in natural seed banks, which may elevate levels of pathogens and influence seed mortality. The aim of this study was to quantify the effects of fungi and seed density within buried mesh bags on the mortality of seeds. Striga hermonthica was chosen as the study species because it has been widely studied but different methods for measuring seed mortality in the soil have yielded contradictory estimates. 2. Seed bags were buried in soil and exhumed at regular time intervals to monitor mortality of the seeds in three field experiments during two rainy seasons. The effect of fungal activity on seed mortality was evaluated in a fungi exclusion experiment. Differences in seed-to-seed interaction were obtained by using two and four densities within the seed bags in consecutive years. Densities were created by mixing 1000 seeds with 0, 10, 100 or 1000 g of coarse sand. 3. The mortality rate was significantly lower when fungi were excluded, indicating the possible role of pathogenic fungi. 4. Decreasing the density of seeds in bags significantly reduced seed mortality, most probably because of decreased seed-to-seed contamination by pathogenic fungi. 5. Synthesis and applications. Models of plant populations in general and annual weeds in particular often use values from the literature for seed bank depletion rates. These depletion rates have often been estimated by the seed bag burial method, yet seed density within seed bags may be unrealistically high. Consequently, estimates of seed mortality rates may be too high because of an overestimation of the effects of soil or seed-borne pathogens. Species that have been classified from such studies as having short-lived seed banks may need to be re-assessed using realistic densities either within seed bags or otherwise. Similarly, models of seed bank dynamics based on such overestimated depletion rates may lead to incorrect conclusions regarding the seed banks and, perhaps, the management of weeds and rare species
    The mitochondrial plasmid pAL2-1 reduces calorie restriction mediated life span extension in the filamentous fungus Podospora anserina.
    Maas, M.F.P.M. ; Boer, H.J. de; Debets, A.J.M. ; Hoekstra, R.F. - \ 2004
    Fungal Genetics and Biology 41 (2004)9. - ISSN 1087-1845 - p. 865 - 871.
    senescence - organisms - longevity - dynamics - mutant - dna
    Calorie restriction is the only life span extending regimen known that applies to all aging organisms. Although most fungi do not appear to senesce, all natural isolates of the modular filamentous fungus Podospora anserina have a limited life span. In this paper, we show that calorie restriction extends life span also in Podospora anserina. The response to glucose limitation varies significantly among 23 natural isolates from a local population in The Netherlands, ranging from no effect up to a 5-fold life span extension. The isolate dependent effect is largely due to the presence or absence of pAL2-1 homologous plasmids. These mitochondrial plasmids are associated with reduced life span under calorie restricted conditions, Suggesting a causal link. This has been substantiated using three combinations of isogenic isolates with and Without plasmids. A model is proposed to explain how pAL2-1 homologues influence the response to calorie restriction. (C) 2004 Elsevier Inc. All rights reserved.
    Productivity and longevity of weaned sows
    Prunier, A. ; Soede, N.M. ; Quesnel, H. ; Kemp, B. - \ 2003
    In: Weaning the pig - concepts and consequences / Pluske, J.R., Le Dividich, J., Verstegen, M.W.A., Wageningen : Wageningen Academic Publishers - ISBN 9789076998176 - p. 385 - 419.
    varkens - zeugen - levensduur - gebruiksduur - zeugvoortplanting - vervangingspercentage - pigs - sows - lifespan - longevity - sow reproduction - replacement rate
    Oude koe niet hetzelfde als duurzame koe
    Ouweltjes, W. - \ 2002
    Praktijkkompas. Rundvee 16 (2002)6. - ISSN 1570-8586 - p. 20 - 21.
    melkveehouderij - melkvee - melkkoeien - duurzaamheid (sustainability) - gebruiksduur - productieve levensduur - vervanging - veestapelstructuur - leeftijd - leeftijdsstructuur - dairy farming - dairy cattle - dairy cows - sustainability - longevity - productive life - replacement - herd structure - age - age structure
    De gedachte is dat minder duurzaamheid tot meer vervanging leidt.
    Biological glasses : nature's way to preserve life
    Buitink, J. - \ 2000
    Agricultural University. Promotor(en): L.H.W. van der Plas; F.A. Hoekstra; M.A. Hemminga. - S.l. : s.n. - ISBN 9789058082398 - 202
    zaden - stuifmeel - germplasm - anhydrobiose - glazig worden - verouderen - gebruiksduur - paramagnetische elektronenresonantiespectroscopie - seeds - pollen - germplasm - anhydrobiosis - vitrification - aging - longevity - electron paramagnetic resonance spectroscopy - cum laude

    As a result of drying, the cytoplasm of desiccation-tolerant organisms, such as seed and pollen, enters into a highly viscous, solid-like, semi-equilibrium state: the glassy state. The work in this dissertation is focussed on the function and characteristics of intracellular glasses in these organisms.

    It was established that intracellular glasses are formed in both desiccation-tolerant and -intolerant pollen (chapter 1). However, desiccation-intolerant pollen loses its viability during drying before intracellular glasses are formed. This indicates that desiccation tolerance is not related with the formation of glasses during drying. Storage of cattail ( Typha latifolia ) pollen under different water contents and temperatures revealed the existence of an optimum water content for survival at a constant relative humidity (11-15%) (chapter 2). The water content corresponding to this relative humidity shifted to higher values with lower storage temperatures, and was found to be associated with the Brunauer, Emmet, and Teller monolayer value. Drying of the pollen below these water contents had detrimental effects on longevity. The water content-temperature combinations of optimal storage were found to be below the glass transition curve, indicating that optimum storage conditions are achieved when intracellular glasses are present. There was a change in ageing kinetics of cattail pollen associated with the melting of the intracellular glass. Above the glass transition temperature (T g ) the activation energy of the ageing rates increased two to three times. This suggests that the presence of glasses in the dry state improves storage stability by decreasing viscosity and, thus, ageing rate. It was concluded that T g curves might be useful for predictions of storage longevity above optimum water contents. However, they cannot be used solely to predict the precise conditions of optimum storage. Subsequently, we sought for a more direct measurement to assess the viscosity of the cytoplasm of tissues.

    For this purpose, we used electron paramagnetic resonance (EPR) spectroscopy to study the molecular mobility of the hydrophilic nitroxide spin probe 3-carboxy-proxyl (CP) that was incorporated into embryonic axes of pea seeds and cattail pollen. Using the distance between the outer extrema of the EPR spectrum (2 A zz ) as a measure of molecular mobility, a sharp increase in mobility was observed at a definite temperature during heating (chapter 3). This temperature increased with decreasing water content of the samples, and was found to be associated with the melting of the glassy state as measured by differential scanning calorimetry (DSC). Molecular mobility was found to be inversely correlated with storage stability: the higher the molecular mobility, the shorter the longevity: with decreasing water content, the molecular mobility reached a minimum, in concert with ageing rates. At very low water contents, both molecular mobility and ageing rates increased again. Minimum mobility and maximum storage stability occurred at similar water contents, suggesting that storage stability might be partially controlled by molecular mobility. To understand the nature of the changes in 2 A zz in spectra of CP in the tissues, echo detected (ED) EPR spectroscopy was employed (chapter 4). The shape of the ED EPR spectrum revealed the presence of librational motion of the spin probe, a motion typically present in glassy materials. The change in 2 A zz appeared to be the result of librational motion of the spin probe.

    With the use of saturation transfer (ST) EPR spectroscopy, a more quantitative measure of molecular mobility was acquired: the rotational correlation time (τ R ), which corresponds to the time it takes for the spin probe to rotate a radian around its axis (chapter 5). At room temperature,τ R of CP in pea embryonic axes increased during drying from 10 -11 s in de hydrated state to 10 -4 s in the dry state. At T gR was constant ataproximately10 -4 s for all water contents studied. The temperature dependence ofτ R at all water contents studied followed Arrhenius behaviour with a break at T g . The temperature effect onτ R above T g was much smaller in pea axes as found previously for sugar and polymer glasses. Thus, the melting of the intracellular glass by raising the temperature caused only a moderate increase in molecular mobility in the cytoplasm as compared to a huge increase in amorphous sugars.

    The application of saturation transfer EPR spectroscopy to biological tissues enabled a quantitative comparison between storage stability and molecular mobility in different tissues (section III). The temperature and moisture dependence of ageing rates of seeds and pollen was found to correlate with the rotational motion of CP in the cytoplasm (chapter 6-8). An increase in the temperature resulted in a faster rotational motion in the cytoplasm of cattail pollen, analogous to faster ageing rates (chapter 6). Decreasing the water content of the pollen resulted in a decrease in rotational motion until a minimum was reached, after which rotational motion slightly increased again. The water content at which this minimal rotational motion was observed increased with decreasing temperature, comparable to the pattern of ageing rate. A significant linear relationship was found between ageing rates and rotational motion in the cytoplasm of the pollen.

    We also investigated the relationship between the longevity of lettuce seeds and the molecular mobility in the cytoplasm of their radicles (chapter 7). Longevity of lettuce seeds was predicted using the viability equation of Ellis and Roberts. Increasing the temperature resulted in faster rotational motion and shorter longevity. There was a linear relationship between the logarithms of rotational motion and estimated longevity for temperatures above 5°C, which is the same temperature range for which experimental data were used to obtain the viability constants of the viability equation. Below 5°C, there was a deviation from linearity, which might stem from inaccurate predictions by the viability equation at low temperatures.

    Chapter 8 further demonstrates that there is a linear relationship between the logarithms of rotational motion in the cytoplasm of seed and pollen of several plant species and their ageing rates or longevities. This linearity suggests that cytoplasmic mobility might be an important controlling factor of ageing rates. The linear relationship between the two parameters could be used to predict lifespan of germplasm at low temperatures (at which experimental determination of longevity is practically impossible) by simply measuring theτ R values at these low temperatures (chapter 7 and 8). Based on the predictions using the linear regression between ageing rate and rotational motion of CP in pea embryonic axes, an optimum water content of storage was found. This optimum water content shifted to higher values with lowering the storage temperature, as was found previously for cattail pollen based on experimental data (chapter 2). It was predicted that the longevity of seeds at high (0.12 to 0.16 g/g) water content is much higher than previously suggested on the basis of the viability equation. The predictions show that drying germplasm too far leads to decreased longevity compared to storage of germplasm at higher water contents, suggesting that current storage protocols might have to be re-examined.

    Desiccation-tolerant organisms contain large amounts of soluble sugars. This, and the fact that sugars are excellent glass-formers has led to the suggestion that sugars play an important role in intracellular glass formation. The presence and amounts of oligosaccharides have been found to correlate with longevity. Furthermore, oligosaccharide glasses are known to increase the T g and viscosity of model sucrose glasses. This suggests that oligosaccharides might enhance the stability of intracellular glasses (chapter 9 and 10). Osmo-priming, i.e. pre-imbibition of seeds in an osmotic solution, can result in a decrease in oligosaccharide content and longevity. Priming pea seeds decreased the total oligosaccharide content in the embryonic axes (chapter 9). Despite the change in oligosaccharide:sucrose ratio, no differences in T g values were detected in the dry axes before and after priming as determined by DSC. Also no difference was found between the rotational mobility of CP in dry untreated axes and that of dry primed axes. Chapter 10 demonstrates that osmo-priming of impatiens and bell pepper seeds resulted in considerable decreases in longevity and oligosaccharide contents, while sucrose contents increased. Again, no differences in the T g curves were found between control and primed impatiens seeds. Similarly, there was no difference in rotational motion of CP in the cytoplasm between control and primed impatiens seeds and between control and primed bell pepper embryonic axes. It was concluded that oligosaccharides in seeds do not appear to affect the stability of the intracellular glassy state, and that the reduced longevity after priming is not the result of increased molecular mobility in the cytoplasm.

    To understand the nature and composition of biological glasses we investigated the molecular mobility around T g in sugars, poly-L-lysine and dry desiccation-tolerant biological systems, using ST-EPR, 1 H-NMR and FTIR spectroscopy. Two distinct changes in the temperature dependence of molecular mobility were detected in sugars and poly-L-lysine. With heating, the first change was associated with the melting of the glassy state (T g ). The second change, at which the molecular mobility abruptly increased over several orders of magnitude, was found to correspond with a critical temperature (T c ) where the dynamics of the system changed from solid-like to liquid-like. The temperature interval between T g and T c increased with increasing molecular weight of the sugars. The interval between T g and T c in biological tissues was over 50°C, implying that the stability remained high even at temperatures far above T g . A comparably high T c -T g interval was found for the molecular mobility of poly-L-lysine, suggesting that proteins rather than sugars play an important role in the intracellular glass formation. The exceptionally high T c of intracellular glasses is expected to provide excellent long-term stability to dry organisms, maintaining a slow molecular motion in the cytoplasm even at temperatures far above T g .

    Leaf senescence in alstroemeria : regulation by phytochrome gibberellins and cytokinins
    Kappers, I.F. - \ 1998
    Agricultural University. Promotor(en): L.H.W. van der Plas; W.J.R.M. Jordi; F.M. Maas. - S.l. : S.n. - ISBN 9789054859192 - 143
    bladeren - veroudering - alstroemeria - alstroemeriaceae - fytochroom - plantenpigmenten - gibberellinen - cytokininen - verouderen - gebruiksduur - leaves - senescence - alstroemeria - alstroemeriaceae - phytochrome - plant pigments - gibberellins - cytokinins - aging - longevity

    Leaf senescence in plants is a regulated process influenced by light as well as phytohormones. In the present study the putative role of the phytohormones cytokinins and gibberellins as mediators for the light signal on leaf senescence in alstroemeria was studied. It was found that low photon fluences of red light ensured maximal delay of chlorophyll and protein breakdown. This effect of red light could be completely counteracted by a subsequent far red irradiation, indicating phytochrome involvement.

    Application studies with gibberellins showed that GA 4 was most effective in delaying leaf senescence and it was proven that GA 4 is not converted into GA 1 but is biologically active by itself. A total of 11 gibberellins was detected to be endogenous in alstroemeria leaves. During senescence the relative concentration of precursors and active gibberellins decreased whereas that of inactivated gibberellins increased strongly. Although irradiation of the leaves with red light resulted in delayed senescence and a higher GA 4 concentration compared to dark-incubated leaves, based on the obtained results, GAs are not considered to act as mediators for the transduction of the light signal.

    Alstroemeria leaves were found to contain isoprenoid-derived cytokinins and aromatic cytokinins. Irradiation of leaves with red light resulted in a transient increase in meta -topolin and meta -topolin riboside approximately one hour after the start of illumination. No light related changes in concentration were found for other cytokinins in these leaves.

    Although the visual effect of red light, cytokinins and gibberellins is similar, the mode of action of the regulators may be different. It was found that both red light and meta -topolin had a positive effect on chlorophyll biosynthetic reactions as well as on the rate of photosynthesis and expression of genes encoding for chlorophyll binding proteins ( cab ). GA 4 did not positively affect these parameters. The chlorophyll catabolic reaction, determined as Mg-dechelatase activity was not differentially affected by either meta -topolin, GA 4 or red light. From the results, it is suggested that aromatic cytokinins are primarily involved in regulation of leaf senescence and can function as a mediator for the transduction of the phytochrome signal.

    Selection for longevity in dairy cattle
    Vollema, A.R. - \ 1998
    Agricultural University. Promotor(en): E.W. Brascamp; A.F. Groen. - S.l. : Vollema - ISBN 9789054858782 - 155
    melkvee - selectief fokken - kunstmatige selectie - fokwaarde - gebruiksduur - productieve levensduur - kenmerken - heritability - dairy cattle - selective breeding - artificial selection - breeding value - longevity - productive life - traits - heritability

    This thesis deals with several aspects of longevity of dairy cattle. When breeding organizations want to implement longevity in their breeding programs they have to make several decisions. This thesis aims to give tools to make those decisions.

    Chapter 2 gives an overview of the literature containing estimates of heritabilities of longevity traits and correlations between longevity and conformation traits. The results of Chapters 3 and 4 of this thesis are included as well. There are many different definitions of longevity. In this thesis, two distinctions are made: 1. between lifetime and stayability traits, and 2. between uncorrected and functional longevity traits. Lifetime traits measure the period a cow is alive or producing, and are usually expressed in days. Stayability traits measure whether or not a cow is alive at a certain point in time. Functional longevity traits are corrected for milk production, thus aiming to be a better measure for involuntary culling. In Chapters 1 and 7 of this thesis, residual longevity is introduced, which is longevity corrected not only for milk production but also for all other traits that are already in the breeding goal. So far, this trait has not been used in practice. From the literature it is concluded that, in general, heritability of longevity traits is below 0.10. The heritability of stayability traits is lower (around 0.04) than that of lifetime traits (around 0.09), and the heritability of functional longevity traits is lower (around 0.07 for lifetime traits and around 0.03 for stayability traits) than that of uncorrected longevity traits. Genetic correlations among different longevity traits are generally strong. Genetic correlations between longevity and conformation traits are strongest for conformation traits describing the mammary system and, to a lesser extent, feet and legs. The reliability of a breeding value prediction of a sire based solely on the conformation information of his daughters is approximately 55% at maximum.

    In Chapter 3, the longevity realized of cows born in different years (1978 through 1985) has been calculated. Longevity of cows born in 1978 through 1984 decreases, and longevity of cows born in 1985 is at the same level as the longevity of cows born in 1978. In 1984, the quota system was implemented in the Netherlands and farmers culled 20% more cows than their normal annual culling percentage. These cows, of course, were born before 1984. Besides this process, during the eighties large-scale crossing with Holstein-Friesian bulls took place. The original Dutch-Friesian cow population was replaced by Holstein-Friesians, and this process was accelerated by imlementation of the quota system. Both processes not only affected longevity of dairy cows realized in the Netherlands, but also the estimates of heritabilities. Data on cows born in 1978, 1982, or 1985 were used to estimate heritabilities, and the estimates were highest for the 1978 dataset, lower for the 1982 dataset, and lowest for the 1985 dataset. Possible explanations are that the population was under strong selection during the period considered, that the genetic background of the population changed, and that under the quota system, farmers base their culling decisions on a shorter planning horizon, thus increasing the environmental variation of longevity traits.

    In Chapter 4, data on cows born in different years (1978, 1982, and 1989/1990) were used to estimate genetic correlations between longevity and conformation traits. These parameters were also affected by the changing population structure during the eighties. In the 1978 data file, the correlation between functional herdlife and type was rather weak (0.16) while in the 1982 data file, this correlation was very strong (0.46). For the 1989/1990 data file, only stayability traits could be analysed because cows had not had enough time to be culled. The correlation between functional stayability until 48 months of age and type was 0.21. The strongest correlation was between functional stayability and the subjective score for udder (0.93), followed by the subjective score for feet and legs (0.43). The estimate of 0.93 is probably too high but also from other studies it was concluded that, apart from production, the udder is the most important factor determining longevity of a dairy cow. From Chapters 3 and 4 it was concluded that especially in an upgrading population estimates of genetic parameters should be based on the most recent data possible, and that estimation of these parameters should be repeated regularly.

    In Chapter 5 the value of a relatively new method in animal breeding was investigated: survival analysis. Survival analysis differs in two aspects from traditional methods of analysis: 1. it correctly utilizes information from censored records, i.e., records of cows that are still alive at the moment of data collection; and 2. effects can be modelled in a time-dependent way, yielding a more realistic model. Breeding values of sires for longevity were estimated in three different ways: as the average realized longevity of the sire's daughters, with a best linear unbiased prediction, and with survival analysis. This was done using data from small and from large farms to identify a possible genotype by environment interaction. The phenotypic average of the sire's daughters had weak rank correlations with the other two methods of breeding value prediction (ranging from -0.32 to 0.46). The correlation between the best linear unbiased prediction and the survival analysis prediction was strong (-0.91 and -0.94 on small and large farms, respectively) if only uncensored records were used in the survival analysis, and weaker (-0.71 on both small and large farms) if censored records were included as well. Correlations were negative due to the definition of the traits: in the best linear unbiased prediction the length of productive life was analysed, and in the survival analysis the risk of being culled. A long length of productive life is associated with a small risk of being culled. Thus it was concluded that best linear unbiased prediction and survival analysis mainly differ by the data that can be included in the analysis. No different rankings of sires on small or large farms were found with any of the three methods. From the survival analysis, it appeared that cows with a high percentage of Holstein-Friesian genes had a lower chance of being culled than cows with a low percentage, confirming the hypothesis in Chapters 3 and 4.

    Even though censored records can be analysed as well in survival analysis, a certain number of uncensored data is needed for a reliable breeding value prediction. Young bulls will probably not have a sufficient large number of daughters that have already been culled. Thus, conformation traits might be used for an early breeding value prediction, because they have reasonably strong correlations with longevity and can be measured early in a cow's life. In practice, a breeding value prediction will contain parental information on longevity, direct information on longevity of a sire's daughters, and indirect information on conformation of a sire's daughters. In Chapter 6 survival analysis was used to investigate the importance of conformation traits for the risk of a cow to be culled. This risk was corrected for milk production. Both the phenotypes of the cows themselves and their sires' breeding values for conformation were included in a model. The cows' phenotypes explained more variation in the risk of being culled than their sires' breeding values. In general, smaller cows with a steep rump angle, shallow udder, high score for udder and for feet and legs had the lowest chance of being culled. Survival analysis was also used to predict breeding values of sires for longevity based solely on the longevity of their daughters. These breeding values were correlated with the sires' national proofs for conformation traits, to obtain approximations of genetic correlations. The correlations were strong for nearly all conformation traits except height, rear legs set, and size. In the national proofs the conformation traits were not corrected for each other, while in the survival analysis they were.

    In Chapter 7 it was argued that survival analysis should be used whenever possible to predict breeding values for longevity, even though with current computer capacities only a sire model can be used. Choosing this method implies that a lifetime trait has to be analysed. If length of productive life is analysed, a Weibull model can be assumed, which simplifies the calculations. In practice, this breeding value prediction will have to be combined with information on conformation to obtain a reliable breeding value for longevity early in a bull's life. Because most breeding programs of dairy cows pay already much attention to milk production, functional longevity will be more informative for breeding decisions than uncorrected longevity.

    Vooronderzoek meidoornsterfte duingebied Oost-Ameland
    Slim, P.A. - \ 1997
    Wageningen : DLO-Instituut voor Bos- en Natuuronderzoek (IBN-rapport 307) - 25
    duinen - duinplanten - vegetatie - plantengemeenschappen - dood - gebruiksduur - planten - bedreigde soorten - uitsterven - rosaceae - crataegus monogyna - nederland - friesland - nederlandse waddeneilanden - dunes - duneland plants - vegetation - plant communities - death - longevity - plants - endangered species - extinction - rosaceae - crataegus monogyna - netherlands - friesland - dutch wadden islands
    Vooronderzoek duindoornsterfte duingebied Oost-Ameland
    Slim, P.A. - \ 1997
    Wageningen : DLO-Instituut voor Bos- en Natuuronderzoek (IBN-rapport 295) - 61
    duinen - duinplanten - vegetatie - plantengemeenschappen - dood - gebruiksduur - planten - bedreigde soorten - uitsterven - elaeagnaceae - hippophae rhamnoides - nederland - friesland - nederlandse waddeneilanden - dunes - duneland plants - vegetation - plant communities - death - longevity - plants - endangered species - extinction - elaeagnaceae - hippophae rhamnoides - netherlands - friesland - dutch wadden islands
    Het beheer van het bomenbestand van Park Randenbroek in Amersfoort
    Bervaes, J.C.A.M. ; Oosterbaan, A. ; Kopinga, J. ; Berg, C.A. van den; Wegman, R. - \ 1996
    Wageningen : IBN-DLO - 41
    bosbouw - parken - gebruiksduur - bomen - zeer oude of karakteristieke bomen - verzorgen van jonge opstanden - groene zones - publieke tuinen - bedrijfsvoering - nederland - bosopstanden - veluwe - gelderland - forestry - parks - longevity - trees - veteran or remarkable trees - tending - green belts - public gardens - management - netherlands - forest stands - veluwe - gelderland
    Voorspelbaarheid van de steelknik bij Gerbera jamesonii
    Vries, T. de - \ 1994
    Wageningen : CPRO-DLO - 11
    dood - gebruiksduur - sierplanten - asteraceae - death - longevity - ornamental plants - asteraceae
    Nematodes and decomposition in intertidal ecosystems
    Alkemade, J.R.M. - \ 1993
    Agricultural University. Promotor(en): A.F. van der Wal; M.A. Hemminga. - S.l. : Alkemade - ISBN 9789054851462 - 145
    stranden - vegetatie - pratylenchus - heteroderidae - tylenchidae - dood - gebruiksduur - herbivoren - halofyten - beaches - vegetation - pratylenchus - heteroderidae - tylenchidae - death - longevity - herbivores - halophytes
    Introduction

    Salt marshes in temperate regions are very productive natural vegetations. These vegetations frequently reach an above-ground production of more than 1 kg of dry weight per m 2per year. Herbivores consume only a small proportion of the annual plant production. Almost the entire amount of above ground plants dies after senescence. A small proportion may be washed away by the tides, but the major part remains at the salt marsh where it decomposes in the canopy or at the sediment surface.

    Dead plant material is primarily decomposed by micro-organisms, such as fungi and bacteria. The chemical composition of the detritus to a large extent determines the rate of decomposition. A number of abiotic factors, such as temperature and humidity, also influence the decomposition process. In addition the process may be affected by fauna, present on the decomposing plant material.

    In this thesis the role of nematodes in decomposition of Spartina anglica was studied. This plant species commonly occurs in salt marshes of Western Europe. In addition, one chapter is dedicated to the association between nematodes and decomposing seaweed in a completely different habitat: an Antarctic beach. In the first part of this thesis the relation between decomposition and naturally occurring nematode populations is studied. This part consists mainly of field studies. Nematodes, which are associated with the decomposition process are identified, and the population dynamics of one of these species is studied in detail. The second part of this thesis is dedicated to laboratory and model studies which were carried out to investigate the effects of nematodes on decomposition of S.anglica detritus and the possible mechanism underlying these effects.

    Nematode populations on decomposing plant material

    Nematodes are abundant on both S.anglica litter and on stranded Antarctic seaweed. We found that on standing dead Spartina anglica plant parts the nematode population frequently reached densities of 3000 individuals per g DW. When leaf material on the sediment surface was investigated even much higher nematode densities were found, up to 47,000 individuals per g DW. At Antarctic beaches nematode densities up to 26,000 individuals per g DW were found on seaweed wrack.

    Although numerous, not all of these nematodes present on plant detritus are expected to influence the decomposition process. In chapter I an attempt was made to distinguish the nematode species which play a role in decomposition of S. anglica detritus from nematodes which do not have such a role. As decomposition is largely a microbial process, higher decomposition rates presumably coincide with a higher microbial production and, consequently, a higher availability of food for microbivorous nematodes. Amongst the microbivorous nematodes, those species were considered of possible importance to the decomposition process when their numbers increased with increasing decomposition rate. In the experiments, mesh containers, filled with Spartina anglica leaves, were placed on the sediment surface. Different decomposition rates were induced by using decaying leaf material of different ages and by repeating the experiments during four subsequent seasons. Mesh containers with inert material (plastic drinking straws) served as controls. Sixty nematode species were found in the mesh containers. Using a multivariate analysis (redundancy analysis) different nematode communities were found on plant material with different decomposition rates. These differences were caused by the changing abundance of only a few species. The majority of the species were found in equal numbers in treatments with decomposing Spartina leaves and in the control treatment. The numbers of individuals of those species which appeared closely correlated with the decomposition rate of Spartina anglica leaf-detritus were all bacterivorous nematodes. Numerically the most dominant were species of the family Monhysteridae ( Diplolaimelloides bruciei, Diplolaimella dievengatensis, Monhystera parva ). The highest numbers of these nematodes were found in treatments with the highest decomposition rates i.e. on decaying fresh leaves, during the warmer seasons. In the winter, when decomposition is slower, their numbers were lower.

    The species diversity on standing dead plant parts of Spartina anglica is much lower than the species diversity on the sediment surface in mesh containers filled with S.anglica leaves. The dominant species on standing dead plants are the bacterivorous nematodes Diplolaimelloides bruciei, Monhystera disjuncta and Pellioditis marina. In chapter 11 a study is presented on the population dynamics of D. bruciei. This species was commonly found on above ground plant parts of Spartina. In a field study, population densities of this species were estimated on four classes of S.anglica plant material, representing the whole range of decomposition stages found in the canopy. D. bruciei was found throughout the year on all types of plant material, including living green plant parts. The population densities were highest on the older plant material, where densities of 1000-2000 individuals per g DW were reached. The highest densities were recorded in late summer and autumn.

    S. anglica vegetations are regularly flooded at high tide, which potentially reduces the nematode population density on the plant material, as nematodes may be flushed from the plants. Since in situ measurements of the flooding effect are not possible, the population dynamics of D. bruciei was studied in the laboratory under a controlled flooding regime. The population densities of D.bruciei indeed seemed to be highly influenced by flooding. A considerable part of the population disappeared during flooding, but on younger, yellow, decomposing leaves the rate of removal by flushing was much lower than on older, brown, leaves. This is probably caused by the change of the leaf structure during decomposition. Nematodes may become less well attached to the leaf surface when the groove structure of the leaves disappears with progressive decay; consequently, a higher proportion is flushed away. The growth rate of the population, however, was equal on both leaf types. The growth rate of the nematode population, as estimated in the laboratory, was used to calculate the total production of nematodes in the field. It was shown that the total biomass production of D. bruciei equalled 114 mg C per m 2per year. If 30% of the detritus was decomposed by bacteria and a trophic efficiency of 10 % is assumed, the total amount of bacteria] carbon ingested by D.bruciei accounted for 7.5 % of the total bacterial biomass produced. It was estimated that the dominant bacterivorous nematodes together may consume over 20% of the total bacterial biomass production.

    In chapter III a study of nematodes found in stranded seaweed at an Antarctic beach is presented. Large amounts of seaweed are deposited along the coast of Admiralty Bay, King George Island, Antarctica. The stranded seaweed partly decomposes on the beach and supports populations of various meiofauna species, mostly nematodes. The factors determining the number of nematodes found in the seaweed packages were studied. The densities of nematodes appeared to be correlated primarily with salinity, height and C:N ratio of the detritus. Salinity and height were most likely related to the flooding regime in conjunction with the off-stream of melt water. Decomposition rate appeared mainly determined by the water content and the sediment composition. Melt water run-off or the impact of the surf probably increased seaweed weight losses in these situations.

    The effect of nematodes on decomposition of S.anglica

    Experiments with D. bruciei, a species numerously present on standing dead S.anglica plants (see chapter II), were set up to study the effect of this nematode on decomposition (chapter IV). Green and yellow leaves were placed on agar in petri dishes and inoculated with D. bruciei. CO 2 production was determined regularly after inoculation. Weight, carbon and nitrogen losses were determined at the end of the experiment, 30 days after inoculation. In the presence of nematodes, CO 2 -production on green, decaying leaves increased by 20 - 25 %. Losses of dry weight, carbon and nitrogen during decomposition increased with at least 30 %. On yellow, more senescent leaves no effect on CO 2 -production was found, but losses of dry weight, carbon and nitrogen tended to be higher in the presence of nematodes. The results of this study show that D.bruciei may enhance the decomposition rate of S.anglica -leaves; the extent of the stimulatory effect, however, depends on leaf condition and the population density of the nematode. The minimal nematode population density for a measurable stimulatory effect was estimated to be 4000 individuals per g DW of S.anglica leaves. As described in chapter II, field population densities are often of the same order of magnitude.

    A part of the senescent S.anglica leaves and stems decompose at the sediment surface, where the material is covered with sediment. In chapter I a clear correlation was found between the number of the bacterivorous nematode Diplolaimella dievengatensis and the decomposition rate of S.anglica detritus present on the sediment surface. The effect of the D.dievengatensis on the carbon mineralization of S.anglica detritus was examined in a laboratory experiment (chapter V). Detritus mixed with sediment appeared to decompose at higher rates in the presence of the nematodes. CO 2 production per hour was 74 % higher in the presence of the nematode than in its absence; O 2 consumption per hour increased to a similar extent. Diffusion coefficients were calculated from measurements of both O 2 consumption, using gas chromatography, and O 2 micro-gradients, using micro-electrodes. The apparent diffusion coefficient of O 2 in the sediment in the presence of nematodes was 40% to 70 % higher than the bulk sediment diffusion coefficient. Since the increase of the CO 2 production and of the diffusion of oxygen in the presence of nematodes was of the same magnitude, we concluded that the enhanced turnover time of Spartina detritus presumably was largely caused by the bioturbation activity of the nematodes.

    A simulation model was constructed to quantify the relations between decomposing S.anglica detritus, bacteria and their grazers (chapter VI). The model takes the various stages of above ground litter decomposition into account. The heterogeneity of the decomposing litter was described by a number of successive quality classes. Decomposition was considered to be primarily a microbial process. The microbial population was assumed to consist of a number of successional species each possessing a unique preference for the different quality classes. Grazers were all considered as a single species grazing upon all microbial species. Three mechanisms by which grazers may stimulate decomposition were evaluated using the data from the laboratory study presented in chapter IV. In the first place: if the microbial population grows to a certain maximal density than removing microbial biomass by grazers may stimulate decomposition since space is created for growth of new microbes at the expense of organic substrate. In the second place: the excretion of highly nutritive mucus by grazers may stimulate bacterial growth. In the third place: reworking of the sediment-detritus-microbial mixture in the grooves of the leaves (see also chapter II), or in the upper layer of the sediment may increase the oxygen availability and may, by mechanical force, enlarge the surface of the substrate on which the microbes attack. The model calculations suggested that removing of microbial biomass by grazers has some stimulatory effect on the decomposition rate of detritus, but not enough to account for the total effect. Recycling of organic matter by excretion of mucus seemed to have no effect at all.

    According to the model, bioturbation or reworking contributed most to the stimulation of the decomposition rate.

    The model was validated with field data. The model could describe field data obtained from a variety of locations. The biomass of bacteria and grazers estimated by the model were in the same order of magnitude as those found in the field. The model is useful to evaluate decomposition data from different studies and calculate an approximate amount of microbes and primary grazers available for higher trophic levels.

    When the model calculations were performed over a period of about a year the stimulating effect of grazers gradually seemed to vanish. This is in agreement with the experiments described in chapter IV, which show that the effect of nematodes on decomposing yellow leaves were less pronounced than on green leaves. Thus, any stimulatory effect of nematodes on decomposition of Spartina anglica in the salt marsh may be restricted to the first stages of the decomposition process.

    Het belang van oude bomen voor vleermuizen
    Limpens, H.J.G.A. ; Bongers, W. ; Kopinga, J. - \ 1991
    De Levende Natuur 92 (1991)4. - ISSN 0024-1520 - p. 139 - 144.
    chiroptera - bosbouw - gebruiksduur - bomen - zeer oude of karakteristieke bomen - chiroptera - forestry - longevity - trees - veteran or remarkable trees
    Initial events and inter-organ relations during senescence of orchid (Cymbidium) flowers
    Woltering, E.J. - \ 1990
    Agricultural University. Promotor(en): J. Bruinsma; F.A. Hoekstra. - S.l. : Woltering - 158
    sierplanten - orchidaceae - plantenfysiologie - plantenontwikkeling - bloemen - bloei - dood - gebruiksduur - houdbaarheid (kwaliteit) - cymbidium - ornamental plants - orchidaceae - plant physiology - plant development - flowers - flowering - death - longevity - keeping quality - cymbidium

    During storage and transportation, harvested crops are continuously exposed to all kinds of stress, such as desiccation and mechanical damage. These conditions are known to shorten shelf life and this is often associated with an earlier appearance of the sudden upsurge in ethylene production. It is doubtful whether this so-called autocatalytic ethylene production, although presumably necessary for the coordination and integration of the senescence process, is the trigger of senescence. Rather, changes in membrane properties or in ethylene sensitivity at an early stage of senescence may be responsible. An increase in the sensitivity to ethylene may, in turn, be an effect of the synthesis of so-called ethylene-sensitivity factors or the disappearance of inhibiting substances (chapter 1).

    In Cymbidium flowers, as in other orchids, the stigma, style and stamens are united in an organ called the central column. Two pollinia, covered by an antherious tissue called the anther cap, are positioned on top of the central column. Removal of the pollinia and/or the anther cap (emasculation) is known to dramatically advance the senescence process. In nature, emasculation is carried out by insects, while searching for nectar in the flower, or by mice that feed on these apparently tasteful flower parts. As a result of suboptimal conditions during cultivation the anther caps may be abscised spontaneously, while during postharvest life the flowers may lose their anther cap due to handling.

    Emasculation generally leads in about one day to red coloration of the labellum (lip), a modified petal differing in shape and color from the others. As the early effect of emasculation is very reproducible and easy to assess visibly, the Cymbidium flower was taken as a model system to study the biochemical changes that appear during stress(emasculation)-induced senescence. The purpose of the work described in this thesis, was to determine the factor(s) responsible for the advanced senescence and to analyse the interorgan relations during the senescence process.

    From the literature it was derived that the negative effects of emasculation may be due to wounding. The disruption of a presumed cytokinin flow from the pollinia and the anther cap to the central column may also be involved. Concerning the communication between the floral parts, the biological precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) as well as so-called ethylene-sensitivity factors ( e.g. short-chain, saturated fatty acids) were suggested to be involved.

    By using a very sensitive laser-driven photoacoustic detection system for ethylene we were able to show the existence of a small peak in ethylene production almost immediately after emasculation (chapters 2 and 3). This small and short-lasting increase in ethylene production appeared well before the visible symptoms ( e.g. coloration of the lip), indicating a causal relationship.

    Red coloration of the lip as a result of anthocyanin accumulation becomes visible within approximately one day after emasculation. This process is preceded by a pronounced increase in the activity of the key enzyme in phenylpropanoid metabolism, phenylalanine ammonia-lyase (PAL). A similar effect is apparent after treatment of the flower or the isolated lip with ethylene and inhibitors of ethylene synthesis and ethylene action greatly inhibit coloration. It is therefore concluded that lip coloration is regulated by ethylene (chapters 4 and 5).

    Desiccation of the rostellum, an anther-derived tissue that is uncovered by emasculation, was found to be the primary factor in emasculation-induced ethylene production (chapter 6). Desiccation leads, possibly through the release of "endogenous elicitors", to an increase in the levels of ACC and malonyl-ACC in the top of the central column, which means that the endogenous elicitor locally stimulated the ACC-synthase activity (chapter 7). Determination of the ethylene production in different flower parts isolated at different times after emasculation, revealed that only the production of the central column shows a significant increase. The other flower parts, including the lip, have only very low productions (chapter 8).

    Following emasculation, the lip does not show an increase in ethylene production but does show an ethylene effect (coloration). It may therefore be concluded that the sensitivity to ethylene has increased. Similar arguments were used by other authors to introduce a role for unknown sensitivity factors in senescence of Petunia and carnation flowers.

    However, in vivo measurement of the ethylene production in the central column and the remaining portion of the flower showed that the major part of the ethylene (ca. 80%) is produced by the remaining portion and only a small amount by the central column i.e. at the site of ACC synthesis. In this way it was shown that ACC is rapidly translocated within the flower and that measurements in isolated flower parts do not yield valuable information concerning the in vivo ethylene production (chapter 8). The same is true for the translocation of ACC. Although ACC is rapidly translocated from the central column to the perianth, it is largely immobile in isolated columns (chapter 9). With ACC as a transported intermediate, localized stress affects the senescence processes in all the flower parts. Ethylene Itself was also found to be translocated within the flower and an additional role in the coordination of the senescence process is suggested (chapter 8). No indications for the existence of (mobile) ethylene-sensitivity factors were found and also no biological activity of the wilting and ethylene-sensitivity factors mentioned in the literature was apparent in this system (chapter 9).

    The emasculation-induced ethylene production has a significant effect on the internal ethylene concentration in all the floral parts. As a result, an increase in the activity of different senescence-related enzymes, e.g. PAL and the ethylene forming enzyme (EFE), was observed (chapter 7). In addition, emasculation leads to an increase in membrane permeability (chapter 3). Although the ethylene production and the internal concentration both decrease to the initial level within one day, the EFE-activity is maintained at a high level for a longer period of time. This higher EFE-activity may stimulate, through negative feedback control rather than by its ethylene production, the ACC-synthase activity, leading to an earlier appearance of the more pronounced upsurge in ethylene production that accompanies senescence (chapter 10).

    Patterns in tree and branch-fall in a West-African rain forest
    Vooren, A.P. van - \ 1985
    Wageningen : LH - 34
    vertakking - dode bomen - dood - ecologie - bosbouw - gebruiksduur - natuurlijke takafstoting - tropische regenbossen - tropen - vegetatie - west-afrika - branching - dead trees - death - ecology - forestry - longevity - natural pruning - tropical rain forests - tropics - vegetation - west africa
    Het uitstalleven van bewaarde Golden Delicious appelen
    Schouten, S.P. ; Schaik, A.C.R. van; Schaap, G. - \ 1982
    NL : Sprenger Instituut (Rapport / Sprenger Instituut no. 2222) - 7
    appels - dood - gebruiksduur - malus - nederland - opslag - apples - death - longevity - malus - netherlands - storage
    Verslag van een onderzoek naar de houdbaarheid van Golden Delicious appels bij kamertemperatuur in relatie tot de lengte van de bewaarperiode bij lage temperatuur
    Het vaasleven van in twee verschillende koelsystemen bewaarde rozen
    Harkema, H. - \ 1982
    Wageningen : Sprenger Instituut (Rapport / Sprenger Instituut no. 2221) - 13
    snijbloemen - dood - gebruiksduur - nederland - rosaceae - cut flowers - death - longevity - netherlands - rosaceae
    Onderzocht worden "natte koeling" en de gebruikelijke koeling, evenals de invloed van de voedingsoplossing in de vaas op de houdbaarheid van rozen
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