Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 66

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    On the role of vaccine dose and antigenic distance in the transmission dynamics of Highly Pathogenic Avian Influenza (HPAI) H5N1 virus and its selected mutants in vaccinated animals
    Sitaras, Ioannis - \ 2017
    Wageningen University. Promotor(en): M.C.M. Jong, co-promotor(en): B. Peeters. - Wageningen : Wageningen University - ISBN 9789463438063 - 209
    avian influenza viruses - avian influenza - disease transmission - vaccines - vaccination - dosage - antigenic variation - mutants - mutations - immunity - vaccine development - virology - epidemiology - aviaire influenzavirussen - aviaire influenza - ziekteoverdracht - vaccins - vaccinatie - dosering - antigene variatie - mutanten - mutaties - immuniteit - vaccinontwikkeling - virologie - epidemiologie

    Influenza virus infections can cause high morbidity and mortality rates among animals and humans, and result in staggering direct and indirect financial losses amounting to billions of US dollars. Ever since it emerged in 1996 in Guangdong province, People’s Republic of China, one particular highly pathogenic avian influenza (HPAI) H5N1 virus has spread globally, and is responsible for massive losses of poultry, as well as human infections. For these reasons, HPAI H5N1 is considered as one of the viruses possible to cause a future influenza pandemic.

    One of the main reasons why influenza is a recurring problem is its ability to constantly evolve through the selection of mutants that are able to avoid immunity (be it natural or acquired). Due to the accumulation of mutations during genome replication, diverse/variant influenza genome sequences co-exist in a virus pool (quasispecies). These sequences can contain mutations that are able to confer selective advantages to the influenza virus given the opportunity. As a consequence, whenever a situation arises that places the virus under any type of pressure that the dominant virus sequence cannot cope with (i.e. immune pressure, selective receptor binding, etc.), the virus with the genome sequence that allows it to better adapt to that particular pressure becomes selected and takes over.

    Because of the influenza virus’s high rate of mutations, a global surveillance network is in place to monitor changes in circulating strains among humans that would warrant an update of the vaccines used. For human influenza strains, vaccines are updated frequently (every one or two years) and a similar situation holds true for racehorse vaccination. For avian influenza vaccination, however, the situation is different. In most countries, vaccination against avian influenza is not used, and in the countries where vaccines are used (either as routine or emergency measures), they are not updated as frequently as human vaccines are. In addition, in many instances vaccination against avian influenza viruses has met with some spectacular failures, since it failed to produce a level of immunity that would protect against circulating field strains. These vaccination failures have often been attributed to the fact that without constant vaccine updating (as is done for human influenza), the vaccines used are not able to keep up with continuously evolving antigenic variants selected in the field, and thus to protect poultry against them. In addition, since it is known that immune pressure resulting from vaccination can be a driving force in the evolution of influenza viruses and the selection of immune-escape mutants, there is a school of thought that posits that vaccination against avian influenza is not only a very expensive affair (especially if vaccines need to be frequently updated), but can also lead to selection of mutants that are able to avoid vaccination-induced immunity.

    The research reported in this thesis started with addressing the gaps in the knowledge regarding the role of vaccination-induced immunity in the selection of immune-escape mutants of HPAI H5N1, and if there is a way for vaccines to still be able to protect against antigenically-distant variants of the vaccine seed strain, without the need for frequent vaccine updates.

    Our first step in studying influenza virus evolution and selection of immune-escape mutants was to investigate how antigenic pressure may drive the selection of such mutants, and what the effect of the selected mutations on the pathogenicity and transmissibility of the mutants may be. Although there exist a variety of methods to select for influenza virus mutations (i.e. monoclonal antibodies, site-directed mutagenesis, reverse genetics, etc.), none of them is representative of selection as it happens in a vaccinated animal. In Chapter 2, we discuss in detail a laboratory-based system we have developed, in which immune-escape mutants are selected using homologous polyclonal chicken sera, similar to how they are selected in the field due to vaccination- induced immune pressure. We find that selection takes place early on, and additional mutations are selected when immune pressure is increased. Antigenic distances between the selected mutants and their parent strains are also increased throughout the selection process, but not in a linear fashion. Our selection system proved to be robust and replicable, and to be representative of selection in the field, since the mutations we selected for are also found in naturally-selected field isolates, and the antigenic distances between our selected mutants and their parent strains are similar to antigenic distances between vaccine strains and field isolates.

    We continued our research by addressing the roles played by vaccine dose (and resulting immunity) and antigenic distance between vaccine and challenge strains, in the transmission of HPAI H5N1 viruses, by employing transmission experiments using vaccinated chickens (Chapter 3). To our surprise, we found that the effect of antigenic distances between vaccine and challenge strains on transmission is very small compared to the effect of vaccine dose. We then quantified, for the first time, the minimum level of immunity and minimum percentage of the vaccinated population exhibiting said immunity, in order for vaccines to be able to protect against transmission even of strains that are antigenically distant to the vaccine seed strain. Transmission of such strains in well-vaccinated populations would allow for a scenario where vaccination- induced immunity may drive the selection of immune-escape mutants. Our results show that in order for vaccines to prevent transmission of antigenically distant strains (such as the ones resulting from selection due to immune pressure), the threshold level of immunity against these strains should be ≥23 haemagglutination inhibition units (HIU), in at least 86.5% of the vaccinated population. This level of immunity can be estimated by knowing the antigenic distance between the vaccine and challenge (field) strain, and the HI titre against the vaccine strain, which would then allow the approximate level of immunity against the field strain to be deduced. For example, assuming the HI titre against a vaccine strain is 210 HIU, and the distance with the challenge (field) strain is 24 HIU, according to our results the vaccine should be able to protect against the challenge strain, because the difference in HI titres should be around 26 HIU (i.e. above 23 HIU). These results, taken together with our previous work on selection of mutants, where we showed that the antigenic distances between our mutants and their parent strains are representative of distances found in the field, point to the fact that it is unlikely that vaccination-induced immunity can lead to selection of mutants able to escape it, given that a threshold level of immunity in a minimum percentage of the vaccinated population is achieved. As a consequence, we believe that constant vaccine updating may not be necessary for avian influenza viruses, as long as a threshold level of immunity is maintained. This makes vaccination a more attractive control measure, both from a health perspective and a financial one, than just applying biosecurity measures.

    To examine the effect the mutations in the haemagglutinin protein of our selected mutants may have in their transmission among chickens vaccinated with the parent strain, we used reverse genetics techniques to insert the HA gene of our most antigenically distant mutant into the parent strain backbone (Chapter 4). We vaccinated animals with a sub-optimal dose of vaccine, and we concluded that the mutations we selected for did not allow the mutant to avoid even low levels of immunity, such as the ones resulting from a sub-optimal vaccine dose (which resembles a poor field vaccination scenario). At the same time, the HA mutations we selected for did not appear to have a negative effect either on the pathogenicity of the mutant, or its ability to transmit to unvaccinated animals, since both parameters were comparable to the parent strain.

    Finally, we studied the role inter-animal variation in immunity – as measured by HI titres – has in the accuracy of antigenic cartography calculations (Chapter 5). We found that using sera from more than one animal significantly increased the accuracy of antigenic distance calculations, since it takes into account individual differences in immune responses to vaccination, an inevitable phenomenon documented in both humans and animals. In addition, we increased the accuracy of antigenic maps by avoiding the use of dimension-reducing algorithms as is currently done. By not reducing the dimensionality of virus positioning in space, our maps retain the original geometry between strains or sera, leading to more accurate positioning (Chapters 2 and 5). We hope that improving the accuracy of antigenic cartography can lead to a more precise surveillance of influenza evolution and better informed decisions regarding the need to update vaccines.

    Taken collectively, our results can improve field vaccination outcomes, since they provide guidelines on how to increase vaccination efficiency in stopping transmission of even antigenically-distant strains. In addition, our method for selecting for immune- escape mutants can be a valuable addition to research on influenza virus evolution. Moreover, policy making decisions regarding vaccination against any type of influenza can also benefit from our improvement on antigenic cartography accuracy, saving unnecessary costs in vaccine updating, and reducing morbidity and mortality of both animals and humans.

    Isolation, characterization and engineering of Bacillus smithii : a novel thermophilic platform organism for green chemical production
    Bosma, E.F. - \ 2015
    Wageningen University. Promotor(en): Willem de Vos; John van der Oost, co-promotor(en): Richard van Kranenburg. - Wageningen : Wageningen University - ISBN 9789462575073 - 220
    bacillus smithii - bacillus (bacteria) - biobrandstoffen - chemicaliën uit biologische grondstoffen - thermofielen - metabolische profilering - genoomanalyse - mutaties - isolatie - bioengineering - karakterisering - bacillus smithii - bacillus (bacteria) - biofuels - biobased chemicals - thermophiles - metabolic profiling - genome analysis - mutations - isolation - bioengineering - characterization

    Due to the globally increasing demand for chemicals and fuels and the high environmental impact and limited amount of fossil resources, there is a growing interest in green chemicals and fuels derived from renewable resources. As described in Chapter 1, one of the most feasible alternatives on the short term is microbial conversion of the sugars in biomass to fuels and chemicals in a biorefinery. To be economically and ethically feasible, non-food biomass should be used as a resource, which is often difficult with currently used production organisms. Also, to be economically feasible, the costs of green chemicals and fuels need to be further reduced to be below the costs of products based on fossil resources. To do so, other organisms than the currently most-used platform organisms such as Escherichia coli and Saccharomyces cerevisiae should be used. Ideally, this alternative organism is genetically accessible, has high productivity, titre and yield, is flexible in carbon source, robust, moderately thermophilic, acidophilic, facultatively anaerobic and has little nutritional requirements. The organisms that come closest to these criteria are thermophilic bacilli, which form a diverse class of organisms in the family of Bacillaceae. This thesis describes the isolation, characterization and metabolic engineering of Bacillus smithii, a novel potential thermophilic platform organism.

    Chapter 2 provides more detail on the use of thermophilic microorganisms as platform organisms for green chemical production in a biorefinery concept. As commercially available enzyme mixtures used in the simultaneous saccharification and fermentation (SSF) of biomass have their optimum temperature around 50-60°C, using a moderately thermophilic organism would reduce the costs of the SSF process compared to when using mesophiles by reducing the amount of required enzyme. Also, thermophilic processes are less prone to contaminations, and substrate and product solubility are increased. Several successful examples of the application of facultatively anaerobic thermophiles for green chemical production from lignocellulose in an SSF setting are for example Bacillus coagulans for lactic acid production and Bacillus licheniformis for 2,3-butanediol production. However, whereas strongly developed genetic toolboxes are available for current mesophilic production organisms, these tools are still in their infancy for thermophilic organisms. Such tools are required to optimize production and to study metabolism. Thermophilic organisms show a wide variety in metabolism and in many cases the metabolism of these organisms is still poorly understood, hampering full optimization. Chapter 2 furthermore provides an overview of transformation, integration and counter-selection methods currently used for thermophiles. Although several deletion mutants have been constructed using these methods, not all of them are entirely markerless and most are not suited as high-throughput engineering tools, stressing the need for further research in this area.

    Despite several facultatively anaerobic thermophiles being described as genetically accessible, this feature is still one the major bottlenecks in developing these organisms into platform organisms. Therefore, in Chapter 3, we set out to isolate a facultatively anaerobic, moderately thermophilic bacterium that was genetically accessible and produced high titers of organic acids. A total of 267 strains of different thermophilic bacilli species were isolated from compost and screened for C5 and C6 sugar utilization and acid production. The 44 best strains were screened for genetic accessibility via electroporation. Only 3 strains tested positive for this, namely Geobacillus thermodenitrificans strains ET 144-2 and ET 251 and B. smithii strain ET 138. In subsequent evaluations in lab-scale bioreactors at 55°C and pH 6.5 on glucose, the two G. thermodenitrificans strains performed poorly whereas B. smithii performed well with high titers, yields and productivity of mainly lactate. In similar lab-scale reactors, this strain also performed well on xylose and at pH 5.5 and was still able to perform for 48 at pH 4.5. The electroporation protocol for this strain was optimized, resulting in a maximum efficiency of 5x103 colonies per µg plasmid pNW33n. Two other B. smithii strains, among which the type strain DSM 4216T, were also shown to be transformable with pNW33n. This is the first time that genetic accessibility is described for B. smithii and it is the first step towards developing it into a platform organism, for which it appears to be suitable based on its efficient C5 and C6 sugar utilization and acid production profile.

    In order to become a platform organism and to study its atypical metabolism, a genetic toolbox needs to be established for B. smithii. Chapter 5 describes the development of a markerless gene deletion method for B. smithii. For strains ET 138 and DSM 4216T, the ldhL gene was markerlessly removed via double homologous recombination using plasmid pNW33n. Despite the replicative nature of this plasmid at 55°C, mixtures of single and double crossovers were readily obtained. A pure double crossover deletion mutant was obtained after several transfers on a more defined medium containing acetate or lactate and PCR-based screenings. To eliminate the possibility of mixed genotypes, we subsequently developed a lacZ-counter-selection system, which is based on the toxicity of high X-gal concentrations in the presence of the plasmid-encoded lacZ gene. Using this method, the sporulation-specific sigma factor sigF and pyruvate dehydrogenase complex E1-α pdhA were consecutively removed from the B. smithii ET 138 genome in a markerless way. An initial evaluation of the growth and production profiles of the mutant strains in tubes showed that removal of the ldhL gene eliminates l-lactate production and causes a severe decrease in anaerobic growth and production capacities. B. smithii mutants lacking the sigF gene were unable to sporulate and removal of the pdhA gene eliminated acetate production and rendered the strains auxotrophic for acetate.

    DNA : the recipe book for all the processes in the plant : all cells have the same generic information
    Heuvelink, E. ; Kierkels, T. - \ 2015
    In Greenhouses : the international magazine for greenhouse growers 4 (2015)4. - ISSN 2215-0633 - p. 12 - 13.
    dna - plantenveredeling - genetische modificatie - transfer rna - messenger rna - ribosomen - eiwitten - aminozuren - enzymen - mutaties - dna - plant breeding - genetic engineering - transfer rna - messenger rna - ribosomes - proteins - amino acids - enzymes - mutations
    It’s sometimes called a blueprint: DNA, the carrier of genetic information. But the term recipe book covers it better. It explains how the plant can respond to changing conditions. Plant breeders take advantage of natural variations in DNA. Genetic modification can make their job easier.
    Wat is erfelijkheid?
    Maurice - Van Eijndhoven, M.H.T. ; Oldenbroek, Kor - \ 2015
    Zeldzaam huisdier 40 (2015)3. - ISSN 0929-905X - p. 10 - 12.
    heritability - rassen (dieren) - dierveredeling - dna - eigenschappen - spermatozoön - eicellen - bevruchting - genen - allelen - homozygoten - heterozygoten - mutaties - genetische merkers - heritability - breeds - animal breeding - dna - properties - spermatozoa - ova - fertilization - genes - alleles - homozygotes - heterozygotes - mutations - genetic markers
    Eigenschappen van dieren zijn in meer of mindere mate erfelijk. Ze gaan over van ouders op nakomelingen. Maar ervaren fokkers weten dat in de fokkerij 1+1 geen 2 is. Welke wetmatigheden en welke toevalligheden spelen een rol in de erfelijkheid? Wat heeft het DNA-onderzoek ons daar recentelijk over geleerd en wat kunnen we daarmee?
    A mutation breeding program to improve the quality of the oil crop Crambe abyssinica
    Cheng, J. - \ 2014
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Elma Salentijn; Robert van Loo. - Wageningen : Wageningen University - ISBN 9789461739629 - 180
    crambe abyssinica - plantenveredeling - moleculaire veredeling - veredelingsprogramma's - mutaties - olieleverende planten - brandstofgewassen - biobased economy - crambe abyssinica - plant breeding - molecular breeding - breeding programmes - mutations - oil plants - fuel crops - biobased economy
    Since C. abyssinica is considered to be an ideal crop for industrial oil, further improving the value of crambe oil is of importance. The value of crambe oil can be improved by increasing the C22:1 content or reducing polyunsaturated fatty acids (PUFA). To improve crambe oil by a non-GM approach, a mutant population (12,480 lines) was established from the EMS-treated seeds of C. abyssinica cv. ‘Galactica’. Furthermore, the mutants in CaFAD2 were detected by 454-amplicon sequencing and Illumina sequencing.
    Onderzoek naar de resistentie van de bruine rat in Nederland - 2012
    Lee, T.A.J. van der; Gent-Pelzer, M.P.E. van; Schilder, H. ; Huis in 'T Veld, J.W.H. ; Meerburg, B.G. - \ 2013
    Lelystad : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 690) - 21
    rattus norvegicus - resistentie tegen rodenticiden - feces - genetische verandering - mutaties - rattus norvegicus - rodenticide resistance - faeces - genetic change - mutations
    Development and application of a quick test for resistance of brown rats against rodenticides.
    TILLING & EcoTILLING in tomato : harvesting artificial and natural genetic diversity
    Gady, A.L.F. - \ 2011
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Christian Bachem. - [S.l.] : S.n. - ISBN 9789085859352 - 141
    solanum lycopersicum - tomaten - mutatieanalyse - mutaties - rijp worden - vruchten - metabolisme - genetische diversiteit - plantenveredeling - solanum lycopersicum - tomatoes - mutational analysis - mutations - ripening - fruits - metabolism - genetic diversity - plant breeding

    Mutations in genes controlling specific traits of interest are widely used in plant breeding to introduce particular characteristics in commercial varieties. The establishment of a large mutant collections and the identification of mutations in candidate genes controling traits of interest represents an important resource for plant breeding. Chemical mutagenesis with EMS produces G/C to A/T transitions and is a well-characterized method to generate a saturated mutant population. The TILLING (Targeting Induced Local Lesions IN Genomes) process enables the identification of mutations in specific genes of interest and produces heteromorphic as well as knock-out alleles.

    In order to apply the TILLING strategy to tomato, we have created two new populations of 8025 M2 and 6600 M3 lines respectively derived from seed treatment with 1% EMS of Solanum esculentum (var. TPAADASU). To screen the collection for mutations in selected genes, two novel high-throughput SNP detection technologies were adapted. Firstly, Conformation Sensitive Capillary Electrophoresis (CSCE) and secondly, high resolution DNA-melting analysis (HRM). Our results indicate a mutation frequency of 1,1 mutation per 1kb per 1000 plants.

    Mutations in genes involved in carotenoid biosynthesis and tolerance to salinity stress, Psy1 and ProDh, were identified. Characterisation of the mutant lines, carrying knock-out or amino acid substitution alleles, using plant growth assays, metabolic profiling and gene expression studies allowed the demonstration of the TILLING strategy as an efficient method for plant breeding purposes and plant biology research.

    EcoTILLING was set up using the HRM based SNP screening method to screen the EU-SOL and CBSG tomato core collections for candidates genes involved in sugar metabolism. 13 haplotypes over 6 target genes were identified and related to the studied trait, total soluble sugars. We show that HRM is a fast and cost effective method to unravel natural genetic diversity in candidate genes.

    On the evolution of pesticide resistance in Phytophthora infestans : an experimental evolution approach
    Bosmans, S. - \ 2009
    Wageningen University. Promotor(en): Rolf Hoekstra, co-promotor(en): Fons Debets; Arjan de Visser. - [S.l.] : S.n. - ISBN 9789085853091 - 141
    phytophthora infestans - metaxalyl - resistentie tegen pesticiden - fungicidentolerantie - moleculaire genetica - mutaties - evolutie - phytophthora infestans - metalaxyl - pesticide resistance - fungicide tolerance - molecular genetics - mutations - evolution
    Resistance to antimicrobial agents is a serious problem for both medicine and agriculture. The initial success of such toxins is due to absence of resistant genotypes in pathogen populations before treatment. The initial low frequency of resistance may be explained by negative pleiotropic effects of the resistance mutations on fitness in the absence of the toxin. However, when resistant and sensitive natural isolates are compared, no cost of resistance may often be seen. This high fitness of resistant genotypes is explained by the existence of compensatory mutations, i.e. mutations that ameliorate the negative effect of the initial resistance mutation. The accumulation of these compensatory mutations can only occur at a sufficient rate if the population of resistant genotypes is large, which in part depends on the pesticide use. As a result, resistance may be stably maintained in a population after pesticide treatment, whereas it was absent before pesticide treatment.
    Resistance to the phenylamide pesticide metalaxyl is common in populations of Phytophthora infestans, the oomycete that causes the late blight disease in potato. This resistance evolved within a few years after metalaxyl became commercially available in 1977. Such fast evolution of pesticide resistance may present a serious threat for potato production. However, fast evolution of resistance to other pesticides has not been described in P. infestans, whereas resistance to metalaxyl and other pesticides are common in other oomycetes.
    In the absence of metalaxyl, resistant isolates of P. infestans have a higher fitness during epidemics compared to sensitive isolates. This observation has led to the assumption that metalaxyl resistance has a direct positive effect on epidemic fitness. A reduction of the survival during the winter has been put forward as an explanation for the absence of resistance before the commercial release of metalaxyl. However, given a high mutation rate towards metalaxyl resistance, a direct positive effect of metalaxyl resistance would always lead to a high frequency of resistance, even in the absence of metalaxyl.
    In this thesis, we report on an experimental evolution approach to investigate the fast evolution and apparent stability of metalaxyl resistance in P. infestans. We used an experimental evolution procedure because it has several advantages. First, it enables a detailed inspection of the trajectory of evolutionary changes (e.g. in resistance phenotype). Second, it enables comparisons of fitness components between near-isogenic genotypes that only differ in their sensitivity to metalaxyl, whereas conclusions based on comparisons of field isolates and offspring from sexual crosses are hampered by differences in the genetic background.
    Two experiments were performed to investigate the rate of evolution of resistance to a number of pesticides. First, we used a fluctuation test to estimate the mutation rate towards resistance against metalaxyl, fluazinam and cyazofamid. This fluctuation test, however, was not suitable to estimate the mutation rate in P. infestans, due to background growth of sensitive genotypes for metalaxyl and due to the low amount of zoospores that can be obtained from a single colony for the other two pesticides. Second, we analyzed the response of selection on low pesticide concentrations. Serial transfer of zoospores on a constant low concentration of metalaxyl resulted in full resistance. The same procedure on a low concentration of cyazofamid with a similar effect on growth rate, however, did not result in full resistance.
    The genotypes that emerged after the selection procedure were compared with the sensitive ancestor with respect to a number of fitness components in the absence of metalaxyl. This approach did not reveal a cost of resistance. On the contrary, resistant genotypes showed a higher in vitro fitness compared to their sensitive ancestor. However, the results from a population survey during a nation-wide ban of metalaxyl containing pesticides in the Netherlands were suggestive of a negative effect of resistance on winter survival and on epidemic fitness. These results suggest that the relative high frequency of metalaxyl resistant isolates on untreated fields can only be explained by assuming that metalaxyl resistance has an initial cost that is followed by compensatory mutations that only restores epidemic fitness. A new selection procedure that included serial transfer of zoospores, revealed a small initial cost on in vitro performance by increasing the lag phase before the start of growth. Subsequent compensatory evolution under the selection conditions could then explain the absence of a cost of resistance in previous experiments. However, no such compensatory evolution was directly observed in this latter selection procedure.
    The results presented in this thesis suggest that metalaxyl resistance is selected on a wide range of concentrations, whereas this is not the case for (some) other pesticides. This may explain the relative fast evolution of resistance to metalaxyl relative to that for other pesticides. Additionally, the absence of resistance before the commercial release of metalaxyl can be explained by a negative effect due to delaying growth. Finally, the methodology of experimental evolution may be a valuable addition to the multitude of methods used to study the population dynamics of this important pathogen.
    On the ecology and evolution of fungal senescence
    Maas, M.F.P.M. - \ 2005
    Wageningen University. Promotor(en): Rolf Hoekstra, co-promotor(en): Fons Debets. - [S.l.] : S.n. - ISBN 9789085042846 - 118
    pezizomycotina - neurospora - veroudering - verouderen - ecologie - evolutie - mitochondria - plasmiden - celbiologie - mutaties - genetica - pezizomycotina - neurospora - senescence - aging - ecology - evolution - mitochondria - plasmids - cellular biology - mutations - genetics
    Aging evolves in the shadow of natural selection: Since the efficiency of natural selection declines with age, organisms will over the course of generations accumulate intrinsic, genetic factors that have a negative effect only late in life. This is generally known as the 'mutation accumulation' theory of aging. Should these factors additionally have apleiotropic, positive effect early on in life, for example on fertility, they could even befavoredby natural selection. This is known as the 'antagonisticpleiotropy' theory of aging. Aging is thus expected to be a multi-causal process resulting from intrinsic factors with negative effects late in life and possibly additional, positive effects early in life. It can be seen as the result of a lack of investment in somatic maintenance, a legacy of an organism's evolutionary past.

    In contrast to unitary organisms like most animals, modular organisms like plants, fungi and colonial invertebrates should not be subject to aging: In these organisms, there is no clear distinction between germ line and soma. Because the germ line should be immortal, in modular organisms aging or senescence is generally not expected, though parts or modules may be subject to aging or senescence. Though this is rare, there are striking examples oforganismalsenescence in fungi and plants, in which all parts of an individual die at the same time.

    This thesis deals with aging in two genera of filamentous fungi:NeurosporaandPodospora. It deals with the question whether there are similarities, both at the proximate or mechanistic level and at the ultimate or evolutionary level, between aging processes in fungi and aging processes as we know them from animals. It is shown that, at least in the pseudo-homothallic filamentousascomycetePodosporaanserina, aging is an intrinsic andmulticausalprocess as may be expected. An analysis of natural variation in life span shows that the main source of variation in life span corresponds to the presence or absence of mitochondrial plasmids, molecular parasites that interfere with respiration. Variation that arises spontaneously in the laboratory often corresponds to mitochondrial mutations in the electron transport chain. The latter mutations are all associated with the induction of alternative; nuclear encoded respiratory pathways and this leads via a yet unknown route to a stabilization of the otherwise unstable mitochondrial genome, a reduced level of reactive oxygen species as well as a reduced energy level. These mutations hence confer longevity at the cost of fertility. In addition to spontaneous mutations and chemical modifications of the electron transport chain, a dietary  reduction in the amount of glucose can extend life span in fungi. The latter effect is strongly reduced by the presence of a type of mitochondrial plasmid that interferes with respiration, which indicates that it is strongly dependent on properly functioning mitochondria. The latter underlines the critical role of mitochondria in the fungal senescence
    Physiology and genetics of leptin in periparturient dairy cows
    Liefers, S.C. - \ 2004
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Tette van der Lende; Roel Veerkamp. - [S.l.] : S.n. - ISBN 9789058089984 - 135
    melkkoeien - melkvee - hormonen - partus - dierfysiologie - genetica - vruchtbaarheid - melkresultaten - genetische polymorfie - genen - mutaties - selectief fokken - dairy cows - dairy cattle - hormones - parturition - animal physiology - genetics - fertility - dairy performance - genetic polymorphism - genes - mutations - selective breeding
    In dairy cattle, the increase in milk yield has been accompanied by a decrease in fertility and a more negative energy balance. As the hormone leptin is involved in regulation of nutritional status and reproductive function (Chapter 2) this is an interesting protein to investigate during the periparturient period in dairy cattle when many changes take place both in energy metabolism and reproductive physiology. The objectives of this study weretoget insight into the function of leptin during the periparturient period and to perform an association study between polymorphisms in the bovine leptin and leptin receptor gene and fertility and production traits.The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms,and related to differences in fertility and production traits.Leptin levels were described during the periparturient period in dairy cows and also associations with the genotyped polymorphisms and fertility and production traits were calculated.In Chapter 2 a literature overview regarding leptin and its receptor and their role in metabolic processes and fertility was given. This Chapter also includes recent literature, which was published during the investigations that were described in other Chapters of this thesis.

    Physiology of Leptin

    In Chapter 4 leptin levels during the periparturient period in dairy cows were described and these levels were related to differences in production and reproduction traits. Leptin concentrations in the periparturient cow undergo remarkable changes; leptinconcentrations were high during late pregnancy and declined to a nadir at parturition.

    The reason of elevated plasma leptin during pregnancy in ruminants seems to be the increase in adipose tissue leptin mRNA due to the lack of a negative feedback (leptin resistance state) and the increase in adiposity. We observed an association of live weight during lactation and prepartum leptin concentrations (Chapter 4) but did not investigate the association between prepartum live weight and leptin concentrations.

    The reason of the decline in leptin levels towards parturition and during lactation is the mobilization of adipose tissue. Leptin concentrations seem to reflect the state of energy balance during lactation; plasma leptin concentrations were lower in cows with a mean negative energy balance during lactation (Chapter 4).

    Further analysis indicated that a combination of three polymorphisms located at the leptin promoter region explained 14.3% of the variance in prepartum leptin concentrations. The two extreme combinations with the highest and lowest prepartum leptin concentrations could be used to investigate the function of leptin concentrations in pregnant cows.

    Genetics of Leptin

    Leptin influences feed intake, energy balance and fertility and therefore the leptin gene and the leptin receptor gene are possible candidate genes to investigate effects on energy balance and fertility in lactating cows. The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms, but also to detect putative transcription factor binding sites on the leptin promoter region. An association study was performed with the found polymorphisms. Associations of allgenotyped polymorphisms with fertility and production traits measured in dairy cows during the periparturient period (Chapters 3 and 7) and alsodifferences in leptin levels between genotypes of all genotyped polymorphisms were analyzed (Chapters 5, 6, and 7).

    An intronic polymorphism (RFLP1) located on intron 2 of the leptin gene explained a significant part of the variation in milk yield, with differences of 0.5 genetic standard deviation between the two extreme genotypes (Chapter 3). However, because this polymorphism is located at an intronic region and because the polymorphisms found in the exons of the leptin gene were not associated with milk yield, we can not exclude that the causative gene is in linkage disequilibrium with this polymorphism. On the promoter region of the leptin gene SNP -1457 was associated with first postpartum luteal activity ( p =0.017) and with weight loss between week 1 and its minimum weight ( p =0.027), where more weight loss occurred together with a later first postpartum luteal activity.Fertility traits are considered to be important to select for and this SNP could be a potential candidate marker to be informative for fertility in dairy cows. SNP -963 was associated with energy balance ( p =0.015) and dry matterintake (p = 0.030), where a higher dry matter intake occurred together with a higher energy balance (Chapter 7).

    In order to find an optimal genotype combination with a high milk yield, a good energy balance and fertility some new analysis were performed in Chapter 8. Two genotype combinations of three SNPs were defined in this Chapter and a next experiment and calculations of economical values per trait have to validate if one of these genotype combinations would be a possible candidate to be used in selection.

    The R4C polymorphism, located at exon 2 of the leptin gene, received a lot of attention by several research groups because of its putative effect on the leptin structure, but several studies, including our study, did not provide convincing evidence that the R4C polymorphism influences the structure and function of leptin. Other studies showed an effect on milk yield in dairy cattle and carcass fat content in beef cattle. On the basis of these results a commercially available R4C-test was developed to improve breeding values in both dairy and beef cattle.

    Polymorphisms in the leptin and leptin receptor gene have shown to be associated with differences in leptin concentration during late pregnancy (Chapters 5 and 6) but, surprisingly, not during lactation. As the promoter of leptin regulates the expression of leptin, polymorphisms at this region could play an important role in the found differences in plasma leptin levels during late pregnancy. Therefore in Chapter 7 we sequenced the leptin promoter and analyzed the sequence for transcription factor binding sites and polymorphisms. All genotyped polymorphisms were associated with prepartum leptin concentrations but in Chapter 8 we showed that three polymorphisms located on a 135 bp promoter region (282 to 147 bp before the transcription start site) seemed to be important for differences in leptin concentrations during late pregnancy. Also significant differences during the lactation period were found between the two genotype combinations with the highest en lowest leptin concentrations. We proposed a putative pregnancy-dependent enhancer to be located at this site on the leptin promoter.

    In conclusion, polymorphisms in the leptin gene and its promoter region are associated with traits in dairy cattle like milk yield (RFLP1), energy balance (SNP -963) and fertility (SNP -1457). Further experiments and calculations are needed to investigate if a combination of these three polymorphisms would be useful in future selection. On the promoter region a pregnancy-dependent enhancer might be located. A combination of polymorphisms located at this region might be useful to investigate the function of high leptin levels during pregnancy.

    Adaptive recovery after fitness reduction: the role of population size.
    Hoekstra, R.F. - \ 2003
    In: Quality Control and production of Biological Control Agents : theory and testing procedures / van Lenteren, J.C., [S.l.] : CAB International - ISBN 9780851996882 - p. 89 - 92.
    natuurlijke vijanden - massakweek - fitheid - populatiegenetica - mutaties - genetic drift - natural enemies - mass rearing - fitness - population genetics - mutations - genetic drift
    Mutation breeding: theory and practical applications.
    Harten, A.M. van - \ 1998
    Cambridge : Cambridge University Press - ISBN 9780521470742 - 353
    mutaties - plantenveredeling - mutations - plant breeding
    Marker assisted elucidation of the origin of 2n-gametes in diploid potato
    Bastiaanssen, H.J.M. - \ 1997
    Agricultural University. Promotor(en): E. Jacobsen; M.S. Ramanna. - S.l. : Bastiaanssen - ISBN 9789054857594 - 150
    haploïdie - polyploïdie - mutaties - plantenveredeling - genomen - solanum tuberosum - aardappelen - haploidy - polyploidy - mutations - plant breeding - genomes - solanum tuberosum - potatoes
    This thesis describes the selection and evaluation of diploid potato clones (2n=2x=24) that produce unreduced or 2n-gametes with 24 chromosomes instead of the normal reduced n-gametes with 12 chromosomes. To elucidate the modes of origin of the 2n-gametes, the progenies derived from such gametes were analysed for different marker loci of one chromosome. Besides the already known mechanisms of First and Second Division Restitution (FDR and SDR) in potato, the multilocus analysis showed the additional mechanism of Post-Meiotic Restitution (PMR) resulting in completely homozygous 2n-gametes. The FDR and SDR 2n-gametes were used for gene-centromere mapping. Multilocus analysis of SDR 2n-gametes showed the map position of the centromere of chromosome 8 in relation to the RFLP-loci. These genetic analyses also demonstrated the occurrence of a single crossover per chromosome arm (high level of chiasma interference). In the light of these findings, it is possible to construct more critical genetic maps of potato.
    Genetic analysis of seed development in Arabidopsis thaliana = [Genetische analyse van de zaadontwikkeling in Arabidopsis thaliana]
    Leon - Kloosterziel, K. - \ 1997
    Agricultural University. Promotor(en): M. Koornneef. - S.l. : Leon-Kloosterziel - ISBN 9789054857709 - 119
    genen - genomen - mutaties - mutagenese - mutagenen - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - brassicaceae - zaadzetting - zaden - formatie - kieming - zaadkieming - kiemrust - genes - genomes - mutations - mutagenesis - mutagens - plant physiology - plant development - fruits - ripening - brassicaceae - seed set - seeds - formation - germination - seed germination - seed dormancy

    This thesis deals with the genetic aspects of seed development in Arabidopsisthaliana. Mutants affected in several aspects of seed development and, more specifically, in seed maturation have been isolated by various selection procedures. The mutants have been analyzed genetically, physiologically, and morphologically. Some of the mutants are impaired in the biosynthesis or sensitivity to the plant hormone, abscisic acid (ABA). All ABA-related mutants show reduced seed dormancy, indicating the important role of this hormone in the establishment of dormancy. In a direct screen for reduced dormancy, two mutants (rdo) with reduced dormancy were found. These were not ABA-deficient and showed the same sensitivity to ABA, ethylene, auxin, and cytokinin as the wild-type. In contrast to this embryo-determined reduced dormancy, reduced dormancy can also originate in an altered seed coat (testa), like in the altered testa shape ( ats ) mutant. Here, the altered testa shape is caused by a defect in the development of the integuments. Extreme ABA-insensitive mutants ( abi3 ) have green seeds that fail to complete many other aspects of seed maturation, including the induction of dormancy and desiccation tolerance, and the accumulation of seed storage proteins and lipids. In addition to abi3 mutants, lec and fus mutants exhibit such a severely disturbed seed maturation as well, with dark purple seeds due to anthocyanin accumulation. The fus3 mutant shows normal ABA-sensitivity. These various seed maturation mutants indicate that specific genes, some acting dependently and some acting independently from ABA, are responsible for seed maturation programs. The seed maturation mutants were subjected to a physiological and biochemical analysis. A GA-deficient mutant was combined with these mutants. Analysis of these double mutants indicated that seeds of the abi3 and lec mutants did not require GA for germination, in contrast to fus3 seeds. This correlates with ABA-sensitivity for germination. The composition of storage proteins and carbohydrates in abi3 , lec, and fus3 mutant seeds has been compared. The abi3 , lec, and fus3 mutants all showed severely reduced storage proteins. The desiccation intolerance of these seed maturation mutants was not correlated with the lack of specific carbohydrates. Furthermore, the mutants had a higher total content of carbohydrates. This is probably a consequence of the lower levels of storage lipids and proteins.
    Statistical identification of major genes in pigs
    Janss, L.L.G. - \ 1997
    Agricultural University. Promotor(en): E.W. Brascamp; J.A.M. van Arendonk. - S.l. : Janss - ISBN 9789054855972 - 158
    genetica - heritability - genetische variatie - varkens - kwantitatieve genetica - populatiedynamica - selectie - mutaties - isolatie - genetics - heritability - genetic variation - pigs - quantitative genetics - population dynamics - selection - mutations - isolation

    Litter size is an important characteristic in pig breeding. Apart from selection within available lines, also the development of a synthetic line with the Chinese Meishan breed could be an interesting approach to obtain a line with an increased level of litter size. To investigate genetic aspects of traits of interest in such a synthetic line, Dutch pig breeding companies have produced F 1 and F 2 Meishan x Western crossbreds. This thesis focusses on one important genetic aspect, the presence of major genes. In Chapters 2 to 4, statistical methodology to model a major gene inheritance is investigated and developed Chapters 5 and 6 consider analysis of data collected on the produced Meishan crossbreds for presence of major genes. To develop a synthetic line with Meishan, presence of major genes affecting litter size, growth and fatness is of interest. Additionally, the presence of major genes is investigated for meat quality traits.

    Statistical methodology

    In Chapter 2, the possibility to detect major genes by use of F 1 and F 2 is investigated. Here, special attention is paid to the situation where alleles at the major locus are fixed in the founder populations. Using 1000 F 2 observations, the power to detect major genes reaches more than 95% for additive and completely dominant effects (difference between homozygotes) of 4 and 2 residual standard deviations, respectively. When F, data is included, any increase in variance from F 1 to F 2 biases parameter estimates and leads to putative detection of a major gene. Also when in reality alleles at the major locus segregate in the founder populations, parameter estimates become biased, unless the average allele frequency in the founder populations is exactly 0.5. Use of data and use of a model in which alleles segregate in parents, e.g. F 3 data, is concluded to give better robustness and larger power. The latter is confirmed in a separate study, as referenced in Chapter 7, which shows that effects up to 4 times as small can be detected when alleles at the major locus segregate in the founder lines. Based on the findings in Chapter 2, Chapters 3 and 4 focus on the development of general models for a mixed inheritance. Use of such models is referred to as 'segregation analysis'.

    In Chapter 3, an advancement is made for use of analytical approaches to segregation analysis. It is noted that animal breeding pedigrees, as opposed to human pedigrees, generally contain many loops, such that exact computation of likelihoods is
    infeasible. Loops in animal breeding pedigrees arise due to multiple matings, i.e. sires are generally mated to several dams, and due to inbreeding. Multiple matings generally already create many loops when considering 3-generation pedigrees. In Chapter 3, 'iterative peeling' is introduced, a method equivalent to the traditional recursive peeling method to compute exact likelihoods in non-looped pedigrees, but which also can be used to obtain approximate likelihoods in looped pedigrees. In simulations, hypothesis testing and parameter estimation are compared based on approximated likelihoods in looped pedigrees and exact likelihoods in non-looped pedigrees. This shows that no biases are introduced by the approximation in looped pedigrees. Iterative peeling is developed and investigated using a monogenic model, but could be extended to compute likelihoods for a mixed inheritance model. Such extension, however, was not made because an alternative non-analytical approach became available and was developed in Chapter 4. 0

    In Chapter 4, the application of Gibbs sampling is considered for inference in a mixed inheritance model. Gibbs sampling is a Markov chain Monte Carlo procedure which does not require analytical approximation. The approximation in such an approach is of a different nature: a marginal posterior distribution, or a feature thereof, is estimated based on a finite sample from the true posterior distribution. To generate such a sample, a Markov chain is constructed with an equilibrium distribution equal to the posterior distribution to be approximated. For application of Gibbs sampling to a mixed inheritance model, an implementation on scalar components, as used for human populations, appears not efficient because mixing of parameters in the Markov chain is slow. Therefore, an approach with blockwise sampling of genotypes is proposed for use in animal populations. The blockwise sampling, by which genotypes of a sire and its final progeny were sampled jointly, is effective to improve mixing. In Chapter 4 it is concluded that further measures to improve mixing could be looked for. In later Chapters such a further improvement is found in the additional use of a relaxation technique. In Chapter 4, inferences are made from a single Gibbs chain. In later Chapters, this approach is improved by use of multiple chains from which convergence of the Gibbs sampler is assessed by comparison of between- and within chain variances in an analysis- of-variance. The use of Bayesian estimators, which is feasible when using Gibbs sampling, is found preferable over the use of classical maximum likelihood estimators. In Chapter 7, it is discussed that the use of Bayeslian procedures fits in a general trend to better account for uncertainty in statistical estimation procedures.

    Analysis of data

    In Chapters 5 and 6, analysis of data obtained on the Meishan crossbreds is presented. In Chapter 5, presence of major genes affecting meat quality traits is investigated using data from F 2 individuals. Cooking loss, drip loss, two pH measurements, intramuscular fat, shearforce and back-fat thickness (by HGP measurement) are found to be likely influenced by a major gene. In all cases, a recessive allele is found, which originates from one of the founder lines, likely the Meishan breed. By studying associations between genotypes for major genes affecting the various traits, it is concluded that cooking loss, two pH measurements and possibly backfat thickness are influenced by one gene, and that a second gene influences intramuscular fat and possibly shearforce and drip loss. The statistical findings are supported by demonstrating marked differences in vanances of families of fathers inferred as carriers and families of fathers inferred as non-carriers.

    In Chapter 6, presence of major genes is investigated for two growth traits, backfat thickness (by" ultrasonic measurement) and litter size at first and second parity, using data from F 1 and F 2 crossbreds. Here, two analyses are performed for each trait. In a first analysis, joint analysis of F, and F 2 crossbred data is performed, in which different error variances are fitted for F 1 and F 2 observations. In this first analysis, significant contributions of major-gene variance are found for the two growth traits, for backfat, and for litter size at first parity. In a second analysis, analysis of F 2 data only is performed to check whether no biases are introduced in the joint analysis of F 1 and F 2 data. In the second analysis, no major genes are found for growth traits. Major genes affecting backfat and litter size at first parity are confirmed. Effects of the gene affecting backfat are similar to the effects of the gene affecting backfat identified in Chapter 5, and this likely is the same gene. The major genes affecting backfat and litter size are dominant genes, of which the recessive alleles can be considered unfavourable.. the recessive alleles of these genes cause an increase of backfat and a decrease of litter size.

    General results from the statistical analyses indicate that further molecular genetic research effort to map these genes will have a high probability of success. III Chapter 7 benefits are discussed from selection against the recessive alleles of the genes influencing backfat and litter size, as well as use of the gene affecting intramuscular fat to produce extra-tasty quality meat.


    In this thesis, segregation analysis (SA) is made applicable for use in animal populations. SA will be a valuable addition to linkage analysis, where SA will be more typically applied to large amounts of data which are routinely collected. In the search for genes affecting quantitative traits, SA can directly identify functional genes, and can estimate genotypes of animals for such a functional gene. In combination with linkage analyses, this could supply important aids for molecular geneticists to locate functional genes. In this thesis, a number of major genes was identified to affect traits in the Meishan crosses. Further genetic analyses could generate more knowledge on the regulation of the quantitative traits involved and will aid in assessing the value of these genes for practical breeding. Chapter 8 additionally describes expected variance changes in a synthetic line, which could aid to optimise selection in such a line.

    Marktintroductie van genetisch gemodificeerde voedingsmiddelen. Doelstellingen demonstratieproject
    Kok, E.J. ; Noordam, M.Y. ; Noteborn, H.P.J.M. - \ 1996
    Voeding 57 (1996)7/8. - ISSN 0042-7926 - p. 20 - 23.
    voedsel - voedselindustrie - voedselinspectie - voedselvoorziening - voedseltechnologie - voedingsmiddelen - genetische modificatie - genomen - overheidsbeleid - haploïdie - gezondheidszorg - bedrijfsvoering - marketing - maaltijden - mutaties - voeding - plantenveredeling - polyploïdie - volksgezondheid - recombinant dna - food - food industry - food inspection - food supply - food technology - foods - genetic engineering - genomes - government policy - haploidy - health care - management - meals - mutations - nutrition - plant breeding - polyploidy - public health
    Aandacht voor het demonstratieproject "Risicoanalyse van genetisch gemodificeerde voedingsmiddelen als basis voor marktintroductie". Verslag van een workshop
    Mycosphaerella graminicola on wheat : genetic variation and histopathology
    Kema, G.H.J. - \ 1996
    Agricultural University. Promotor(en): J.C. Zadoks; C.H. van Silfhout. - S.l. : KEMA - ISBN 9789090094861 - 141
    plantenziekteverwekkende schimmels - triticum aestivum - tarwe - hexaploïdie - dothideales - planten - parasitisme - fysiologie - gastheer parasiet relaties - genetische variatie - mutaties - mycosphaerellaceae - plant pathogenic fungi - triticum aestivum - wheat - hexaploidy - dothideales - plants - parasitism - physiology - host parasite relationships - genetic variation - mutations - mycosphaerellaceae

    The research described in this thesis was focused on a comprehensive understanding of the generation and extent of genetic variation, and its effects on host cultivars in the wheat- Mycosphaerella graminicola pathosystem. Inoculation experiments were conducted in the seedling stage and adult plant stages under field conditions over several years. These experiments encompassed nearly 100 isolates of the pathogen tested on some 50 wheat cultivars. Parametric and non-parametric statistical analyses were employed on large data and very small data sets, and indicated that in all experiments cultivar x isolate interactions were significant. Pathogen isolates originating from bread wheat and durum wheat appeared to be adapted to their hosts, respectively. Molecular analysis of the interternally transcribed spacer regions of isolates from both forms, indicated that these were taxonomically closely related. The inoculation experiments indicated that specificity is an important characteristic of the pathosystem. After having determined the wide genetic variation in the pathosystem, experiments were conducted to elucidate the mating system of the pathogen. The results indicated a bipolar heterothallic mating system and RAPD analyses of progenies showed regular Mendelian inheritance. Furthermore it was shown that the pathogen is able to complete several generative cycles within a season. Hence, genetic recombination appears to be the driving force behind the determined vast genetic variation. Biochemical and histological experiments were conducted involving compatible and incompatible interactions with the host plant in order to elucidate the resistance mechanism of wheat to the pathogen.
    Physiological functions of phytochromes in tomato : a study using photomorphogenic mutants = [Fysiologische functies van fytochromen in tomaat : een studie gebruikmakend van fotomorfogenetische mutanten]
    Kerckhoffs, L.H.J. - \ 1996
    Agricultural University. Promotor(en): W.J. Vredenberg; R.E. Kendrick. - S.l. : Kerkchoffs - ISBN 9789054856276 - 195
    fytochroom - plantenpigmenten - fotosynthese - solanum lycopersicum - tomaten - genetische variatie - mutaties - phytochrome - plant pigments - photosynthesis - solanum lycopersicum - tomatoes - genetic variation - mutations

    Plant morphogenesis is influenced greatly by the irradiance, quality, direction and periodicity of the ambient light. At least three different photomorphogenic photoreceptors have been distinguished: (i) the red light (R)- and far-red light (FR)- absorbing phytochromes; (ii) the UV-A and blue light (B)-absorbing cryptochromes; and (iii) the UV-B photoreceptor. The phytochromes, which are the best characterized photosensory photoreceptors, are encoded by a small multigene family. In tomato (Lycopersicon esculentum Mill.) five phytochrome genes have been cloned: PHYA, PHYB1, PHYB2, PHYE and PHYF. In this thesis a genetic approach is used to assign functions to the different phytochrome types in tomato. Two classes of phytochrome mutants in tomato were analyzed both molecularly and physiologically: (i) phytochrome photoreceptor mutants: f ar- r ed light- i nsensitive (fri) mutants, deficient in phytochrome A (phyA); t emporarily r ed light- i nsensitive (tri) mutants, deficient in phytochrome B1 (phyB1) and a phytochrome chromophore biosynthesis mutant aurea (au); (ii) signal transduction chain mutants: h igh- p igment- 1(hp-1),h igh- p igment- 2(hp-2), a tro v iolacea (atv) and I ntensive p igmentation ( Ip ). In adult plant stages fri mutants are hardly phenotypically distinguishable from wild type (WT) in white light (WL). The phyB1 -deficient tri mutants are only insensitive during the first two days upon transition from darkness to R. The tri mutants are slightly taller than the WT when grown in WL. The kinetics of stem elongation rate of these mutants were determined very precisely using a custom-built plant growth-measuring apparatus as well as their response to vegetational shade light. The immature fruits of hp-1 and hp-2 mutants have higher chlorophyll levels and are darker-green in colour than WT. The signal transduction chain mutants all exhibit exaggerated phytochrome responses, i.e. high anthocyanin synthesis and short hypocotyl length compared to WT. Anthocyanin biosynthesis that accumulated during a 24-h period of different monochromatic irradiations was determined. At 660 nm the fluence rate-response relationships for induction of anthocyanin in WT are complex, showing a low fluence rate response (LFRR) and a fluence rate dependent high irradiance response (HIR), which have been attributed to phyA and phyB 1, respectively. The hp-1 mutant exhibits a strong amplification of both the LFRR and HIR. The atv mutant shows strongest amplification of the HIR component. The Ip mutant exhibits an exaggerated anthocyanin response in B. The results are discussed in relationship to the published work on photomorphogenesis.
    Zelfklonering in melkzuurbacteriën: voedselveilige genetische veranderingen.
    Vos, W.M. de - \ 1995
    Voedingsmiddelentechnologie 28 (1995)23. - ISSN 0042-7934 - p. 11 - 14.
    dierlijke producten - bacteriën - kiemgetal - bacteriologie - consumenteninformatie - bescherming van de consument - consumenten - vraag - voedsel - voedseladditieven - voedselinspectie - voedingsmiddelenwetgeving - voedingsmiddelen - genetische modificatie - regering - overheidsbeleid - melkzuurbacteriën - lactobacillus - wetgeving - mutaties - voedingseducatie - voedingsinformatie - recombinant dna - recombinatie - onderzoek - animal products - bacteria - bacterial count - bacteriology - consumer information - consumer protection - consumers - demand - food - food additives - food inspection - food legislation - foods - genetic engineering - government - government policy - lactic acid bacteria - legislation - mutations - nutrition education - nutrition information - recombination - research
    Bij deze techniek wordt alleen genetisch materiaal gebruikt dat van nature in de soort aanwezig is. De natuurlijke genetische barrieres worden dus niet doorbroken
    Basic aspects of potato breeding via the diploid level
    Hutten, R.C.B. - \ 1994
    Agricultural University. Promotor(en): J.G.T. Hermsen. - S.l. : Hutten - ISBN 9789054852926 - 93
    haploïdie - polyploïdie - mutaties - plantenveredeling - genomen - solanum tuberosum - aardappelen - haploidy - polyploidy - mutations - plant breeding - genomes - solanum tuberosum - potatoes

    In this thesis research is presented on all steps in a potato breeding program via the diploid level: dihaploid induction, selection at the diploid level and sexual polyploidization. In spite of the significant seed parent x pollinator interaction estimated, IVP 101 was found to have a significant higher dihaploid induction ability than the widely used pollinators IVP 35 and IVP 48. Significant differences in dihaploid production ability between seed parents were also found. Dihaploid populations from 31 varieties or breeding lines were evaluated for occurrence and frequency of mutant phenotypes, for tuberization, flowering, pollen stainability, 2n-pollen production and resistance to Ro-1. The expression of yield, yield components, vine maturity, under water weight and chip colour at the diploid and tetraploid level and the parental effects on these characters of 4x . 2x progenies were investigated to find an answer to the question whether at the diploid level other selection criteria should be employed than at the tetraploid level when selecting tetraploid breeding lines. For yield direct selection at the diploid level had no effect on the performance of tetraploid progeny. For under water weight more stringent and for vine maturity less stringent selection criteria were required at the diploid level than at the tetraploid level. The frequently reported superiority of FDR 2n-gametes versus SDR 2n-gametes could be confirmed for yield only. For vine maturity, under water weight and chip colour no considerable differences were found between means of FDR and SDR progenies from reciprocal 4x-2x crosses.

    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.