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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    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.

    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.

    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.
    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
    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.
    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.

    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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