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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    Biologische bestrijdingsmiddelen kunnen imago ernstig schaden
    Sukkel, W. - \ 1999
    Ekoland 19 (1999)6. - ISSN 0926-9142 - p. 8 - 9.
    pesticiden - gewasbescherming - bacillus thuringiensis - pyrethrinen - piperonylbutoxide - koperoxychloride - pesticidenwerking - ongediertedodende eigenschappen - nadelige gevolgen - selectiviteit - toxiciteit - onbedoelde effecten - niet-doelorganismen - biologische landbouw - alternatieve landbouw - regelingen - wetgeving - beleid - Nederland - pesticides - plant protection - bacillus thuringiensis - pyrethrins - piperonyl butoxide - copper oxychloride - pesticidal action - pesticidal properties - adverse effects - selectivity - toxicity - nontarget effects - nontarget organisms - organic farming - alternative farming - regulations - legislation - policy - Netherlands
    In Nederland zijn zijn voor de akkerbouw en de vollegrondsgroententeelt slechts vier biologische (niet-synthetische) middelen toegestaan: Bacillus thuringiensis, pyretrine + piperonylbutoxide, koperoxychloride en zwavel. Een opsomming van de tot nu toe bekende eigenschappen (doelorganismen; toegelaten gewassen; effectiviteit; giftigheid voor niet-doelorganismen; milieueffecten)
    Biologisch effect van luchtondersteuning
    IJzendoorn, M.T. van; Zande, J.C. van de; Meier, R. - \ 1995
    Landbouwmechanisatie 46 (1995)1. - ISSN 0023-7795 - p. 38 - 39.
    dosering - motoren - fungiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - plantenziekteverwekkende schimmels - gewasbescherming - pneumatische kracht - aardappelen - solanum tuberosum - spuitapparaten - phytophthora infestans - machines - dosage - engines - fungicides - pesticidal action - pesticidal properties - pesticides - plant pathogenic fungi - plant protection - pneumatic power - potatoes - sprayers
    Ingeaan wordt op een proef in aardappelen (Bintje), waarbij gekeken wordt naar het effect van luchtondersteuning, dosering en spuitinterval op het voorkomen van Phytophthora infestans
    Biological activity of triazole fungicides towards Botrytis cinerea
    Stehmann, C. - \ 1995
    Agricultural University. Promotor(en): P.J.G.M. de Wit; M.A. de Waard. - S.l. : Stehmann - ISBN 9789054853671 - 159
    plantenziekteverwekkende schimmels - deuteromycotina - gewasbescherming - fungiciden - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - moniliaceae - plant pathogenic fungi - deuteromycotina - plant protection - fungicides - pesticides - pesticidal action - pesticidal properties - moniliaceae

    Botrytis cinerea Pers. ex Fr., the causal agent of grey mould, is one of the most ubiquitous plant pathogens. The fungus is of high economic importance in various major crops and during transport and storage of agricultural products. Protectant fungicides such as chlorothalonil, dichlofluanid, folpet or thiram are widely used for disease control. Since their introduction in the 1960S/1970s, systemic fungicides such as the benzimidazoles or dicarboximides have been used extensively. However, their effectivity is severely hampered by a rapid development of resistance to these fungicides.

    Antifungal activity of N1-substituted azoles was discovered in the late 1960s. Since then, a large number of azole derivatives have been developed as agricultural fungicides and antimycotics. The mode of action of these azoles is based on inhibition of the cytochrome P450-dependent sterol 14α-demethylase (P450 14DM ), an enzyme of the sterol pathway. By now, sterol demethylation inhibitors (DMIs) comprise about 35 commercial products and represent the most important group of systemic fungicides. DMI fungicides are commonly applied in control of rusts, powdery mildews and scabs. Only few of them are registered for control of B. cinerea . This is ascribed to a limited field performance for which the reasons are not evident. A replacement of dicarboximides or benzimidazoles by DMI fungicides would be attractive, since DMIs have a number of advantages over other fungicides including a relatively low resistance risk.

    The aim of the study described in this thesis is to identify factors involved in the limited field performance of DMI fungicides towards B. cinerea . The study is restricted to the largest group of DMIs, the triazoles. Before presenting results obtained in this study a literature review on the biology and control of B. cinerea , the mode of action and mechanisms involved in selective fungitoxicity of DMI fungicides, and factors responsible for discrepancies in laboratory and field pesticide performance is given ( chapter 1 ). Biological activity of triazoles towards B. cinerea was investigated in vitro with cell-free assays ( chapters 3 - 4 ) and toxicity assays ( chapters 3 - 7) and in vivo on different hosts ( chapter 5 ).

    The first step in the research presented in this thesis was the development of a cell-free assay for sterol synthesis from the model fungus Penicillium italicum ( Moniliaceae ) according to a method described for Aspergillus fumigatus ( chapter 2 ). Subsequently, the method developed was adopted for Botrytis cinerea ( chapter 3). This assay was used to study the relationship between chemical structure and biological activity of commercial and experimental triazoles and stereoisomers of cyproconazole,SSF-109 and tebuconazole towards B. cinerea ( chapter 4 ). On basis of these experiments intrinsic inhibitory activity of triazoles towards P450 14DM of the target pathogen was determined. in following experiments, factors which influence In vivo activity or field performance were Investigated. In vivo activity of triazole fungicides towards B. cinerea was tested on foliar-sprayed tomato plants and diptreated grape berries, and compared with that of selected benzimidazoles and dicarboximides ( chapter 5 ). in this context was also studied whether biological compounds could specifically antagonize activity of triazoles ( chapter 5 ). Variation in triazole sensitivity of the pathogen population was studied for field isolates (121) of B. cinerea collected during 1970 - 1992 in Europe and israel ( chapter 6 ). in this survey less sensitive populations were detected. A putative mechanism of resistance to DMI fungicides in field isolates with a relatively low sensitivity to DMIs was studied and compared with that operating in laboratory-generated DMI-resistant mutants ( chapter 7 ). Effects of inhibitors of mitochondrial respiration and multisite-inhibiting fungicides on accumulation of tebuconazole were tested to evaluate their potency as candidate compounds in synergistic mixtures with DMIs ( chapter 7 ). The development of synergistic mixtures may improve biological activity of DMI fungicides in control of B. cinerea.

    Mode of action of the phenylpyrrole fungicide fenpiclonil in Fusarium sulphureum
    Jespers, A.B.K. - \ 1994
    Agricultural University. Promotor(en): P.J.G.M. de Wit; M.A. de Waard. - S.l. : Jespers - ISBN 9789054852087 - 129
    gewasbescherming - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - fungiciden - derivaten - deuteromycotina - pyrrool - tuberculariaceae - plant protection - pesticides - pesticidal action - pesticidal properties - fungicides - derivatives - deuteromycotina - pyrrole - tuberculariaceae

    In the last few decades, plant disease control has become heavily dependent on fungicides. Most modem fungicides were discovered by random synthesis and empirical optimization of lead structures. In general, these fungicides have specific modes of action and meet modem enviromnental criteria. A disadvantage of modem fungicides is the potency of plant pathogens to acquire fungicide resistance. This phenomenon urges the agrochemical industry to search for chemicals with new modes of action. Natural products often have unique modes of action and can be used as lead structures in chemical synthesis programmes. One natural lead structure is the antifungal antibiotic pyrrolnitrin, produced by several Pseudomonas species. Its use in an optimization programme of CIBA-GEIGY A.G., Basel, Switzerland, led to the development of the highly active phenylpyrrole fungicides fenpiclonil (CGA 142705) and fludioxonil (CGA 173506). The elucidation of the mode of action of fenpiclonil is the topic of this thesis.

    Fenpiclonil is toxic to representatives of Ascomycetes, Basidiomycetes and Deuteromycetes. Its effect on several physiological processes was studied using the fungus Fusarium sulphureum as a sensitive target organism. The EC 50 of fenpiclonil to radial growth on PDA and mycelial growth in Czapek Dox liquid medium is 0.5 and 4 μM, respectively.

    Fenpiclonil accumulates to a high level in mycelium of F. sulphureum and in artificial liposomes. The accumulation appears to be the result of a physico-chemical partitioning of the fungicide over lipids in mycelium and the medium. Accumulation is reversible as the fungicide is readily released from mycelium by washing with water. The fungus does not metabolize fenpiclonil upon incubation for 24 hours.

    At its EC 50 (4 μM), feripiclonil does not immediately affect oxygen consumption, nuclear division, and DNA-, RNA-, protein-, chitin-, ergosterol- and (phospho)lipid biosynthesis. However, accumulation of amino acids and sugars is instantaneously inhibited at concentrations ranging from 4.2- 42 μM), The reduction in accumulation is accompanied by an increased accumulation of the membrane potential probe tetraphenylphosphonium(TPP +) bromide (TPP +) and a marginal change of the proton gradient probe propionic acid. This suggests that the biochemical mechanism of action of fenpiclonil may be related to membrane dependent transport processes. The increased accumulation of TPP +is probably the result of changes of potentials over membranes of various cell compartments rather than from plasma membrane hyperpolarization. The fungicide neither influences membrane fluidity in artificial liposomes nor amino acid accumulation in bacterial vesicles. Thus, accumulation of the fungicide does not aspecifically effect functioning of various types of membranes.

    At its EC 15 (0.4 μM), fenpiclonil selectively inhibits accumulation and incorporation of various monosaccharides into macromolecules of F. sulphureum . This effect was not observed with a fenpiclonil-resistant laboratory isolate of the fungus. Various less active structural analogues of fenpiclonil also inhibit accumulation and incorporation ot monosaccharides into macromolecules, but to a lesser extent. Strongest inhibition (58%) was observed for the incorporation of [U- 14C]glucose in hyphal wall glycan fractions. Biosynthesis of these glycans is catalysed by glycan synthases in the plasma membrane. However, fenpiclonil does not directly interfere with these enzymes, since their activity is not inhibited in a cell-free assay. Furthermore, the precursor of glycans, uridinediphosphoglucose, does not accumulate upon fenpiclonil treatment. All effects described were observed within 15 min of incubation with the fungicide, and indicate that the mechanism of action of fenpiclonil may be related to glucose metabolism.

    Fenpiclonil (0.4 μM) inhibits the production of [ 14C]carbon dioxide in mycelium incubated in a medium with glucose as the carbon source. However, no differential effect on [ 14 C]carbon dioxide production with glucose labelled at different carbon positions was observed. The fungicide does not inhibit [ 14C]carbon dioxide production using acetate as the carbon source. These results indicate that metabolisation of glucose is neither affected by inhibition of pyruvate dehydrogenase activity nor of enzymes in the TCA-cycle. Therefore, the site of action of fenpiclonil is most likely located in early steps of glycolysis.

    Fenpiclonil inhibits the accumulation of 2-deoxy[U- 14C]glucose in starved mycelium loaded with 2-deoxyglucose. Fungicide treatment results within one min of incubation in an increased content of 2- deoxy[U- 14C]glucose and a decreased content of 2-deoxy [U- 14C]glucose-6-phosphate. The fungicide does not effect cell-free phosphorylation of glucose and the mycelial ATP concentration. These results indicate that the mode of action of fenpiclonil is due to inhibition of transport-associated phosphorylation of glucose. Inhibition of glucose phosphorylation will cause a cascade of metabolic events leading to the toxic action of the fungicide. A major event may be the accumulation of polyols which was not observed in an osmotically-sensitive and fenpiclonil resistant laboratory isolate of the fungus.

    Physical conditions affecting pyrethroid toxicity in arthropods
    Jagers op Akkerhuis, G. - \ 1993
    Agricultural University. Promotor(en): J.H. Koeman. - S.l. : Jagers op Akkerhuis - ISBN 9789054851592 - 197
    geleedpotigen - gewasbescherming - insecticiden - acariciden - mollusciciden - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - arthropods - plant protection - insecticides - acaricides - molluscicides - pesticides - pesticidal action - pesticidal properties

    The aim of this thesis was to obtain mechanistic information about how the toxicity of pesticides in the field is affected by physical factors, pesticide bioavailability and arthropod behaviour. The pyrethroid insecticide deltamethrin and linyphiid spiders were selected as pesticide-effect model. In Part I of this thesis the relationships between the toxic action of deltamethrin, physical factors and spider behaviour were studied in field experiments, and attention was focused on the contribution of walking behaviour to pesticide exposure. in Part 11 laboratory experiments were carried out where special attention was payed to residual bioavailability of deltamethrin and the effects of this compound on the behaviour and hygrothermal physiology of female O. apicatus .

    Part I: Field studies

    Field studies have shown that high walking activity in spiders after deltamethrin application leads to a strong reduction of the trapping success (Chapter 6). This supports the hypothesis that walking activity is an important means of exposure to residues of deltamethrin for spiders on the soil surface. The testing of the above hypothesis was made possible by the spraying of the pesticide under conditions of low and high spider walking activity, the use of small plots that still allowed for independent replication, and the use of a low level of toxicant application rate. The low application rate was chosen so that trapping success would then depend both on physical factors and the effect of the toxicant. The prediction of daily spider walking activity in relation to physical factors was based on observations of the effects of physical factors and internal activity rhythms on trapping success. Factors showing a very high positive or negative relationship with trapping success were identified in an experiment in which the number of spiders trapped daily in 30 pitfall traps for a period of 72 days was correlated with a number of easily measurable physical factors using multivariate analysis (Chapter 2). Another experiment demonstrated that spiders posess highly predictable, species dependent nicthemeral activity rhythms which are little affected by varying physical conditions, the latter implying an internal mechanism, i.e. some physiological factor (Chapter 3). It was shown that the independence of treatments for at least one week could be assured when traps in a certain field are surrounded by a similarly treated boundery of 7 meters, as spider migration into a sprayed plot was found to be relatively slow; however, the spatial distribution of spider activity showed rapid changes in relation to microclimatic conditions in the crop (Chapter 4). An appropriate low dose rate for deltamethrin was determined to be between 0.2 and 0.5 g ai ha -1deltamethrin (Chapter 5).

    Part II: Laboratory studies

    Laboratory experiments were used to study the bioavailability of deltamethrin in substrate, and the effect of deltamethrin on the hygrothermal physiology and behaviour of 0. apicatus.

    Using [ 14C]deltamethrin, it was shown that residual bioavailability was more than 100 times higher for moss or fungi covering the soil, than for the clay soil used in the experiments. Bioavailability showed an exponential decline over time with a halflife of 157 min and was raised by increasing water content of the soil only at 63% (dwt), at which humidity the soil was water- logged. The rate of pesticide uptake by 0. apicatusdecreased with distance walked (Chapter 7).

    Experiments on the hygrothermal physiology of female 0. apicatus,indicated that water loss is probably the main cause of mortality following deltamethrin poisoning. Water loss in 0. apicatusisthe sum of evaporation and deltamethrin induced water excretion. Evaporation was related linearly to the vapour pressure deficit of the air, and showed an exponential increase with temperature in relation to water conductivity of the cuticle. Deltamethrin induced water excretion was independent of the vapour pressure deficit, and showed an increase with dose and temperature (Chapter 8).

    As long as spiders are able to walk, they can compensate for water loss by drinking. Immobile spiders loose the capacity to drink free water and are therefore vulnerable to lethal water loss. In this respect it should be noted that the results in chapter 8 indicated that the immobilisation rate of spiders poisoned by deltamethrin depends on the humidity of the air. A simulation model combining quantitative measurements of the independent effects of deltamethrin on immobilisation and water excretion is presented in Chapter 9. The model simulates mortality in a laboratory population of female 0. apicatusat different air humidities and temperatures.

    Biochemical mechanisms involved in selective fungitoxicity of fungicides which inhibit sterol 14[alpha]-demethylation
    Kapteyn, J.C. - \ 1993
    Agricultural University. Promotor(en): J. Dekker; M.A. de Waard. - S.l. : Kapteyn - ISBN 9789054851035 - 129
    gewasbescherming - fungiciden - schimmels - mycologie - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - toxicologie - biochemie - plant protection - fungicides - fungi - mycology - pesticides - pesticidal action - pesticidal properties - toxicology - biochemistry

    Sterol demethylation inhibitors (DMIs) are antifungal agents which inhibit the biosynthesis of ergosterol by binding to cytochrome-P450-dependent sterol 14ce-demethylase (P450 14DM ). These compounds significantly differ in both toxicity and selectivity. This thesis presents results of studies on several potential mechanisms of selective fungitoxicity of DMIs.

    Chapter 2 gives a literature review on the mode of action of DMIs, their specific interaction with P450 14DM and selective fungitoxicity.

    Chapter 3 describes the selective fungitoxic actions of two DMIs, prochloraz and an experimental triazole fungicide, to selected plant pathogenic fungi showing significant differences in sensitivity to these compounds. Results indicate that the relatively high toxicity of prochloraz to the fungi tested could not be explained by the slightly higher acccumulation of prochloraz. As for prochloraz, there was no general correlation between sensitivity of the fungi tested and fungicide accumulation. The same situation held true for the triazole compound. However, the low-DMI-resistant isolate of P. italicum , E 300-3 , did exhibit decreased accumulation of both DMIs, which may be responsible for the low level of acquired DMI-resistance in this isolate. Since the high-resistant isolate H 17 did not show a further decrease in accumulation of both DMIs, additional mechanisms for resistance in this particular isolate may be involved. Results also show that under the experimental conditions used most fungi tested did not metabolise both DMIs. This implicates that fungal metabolism also does not play a major role in selective fungitoxicity of DMIs. Metabolism also does not generally explain the differences in toxicities of prochloraz and the triazole compound to each individual species. In this respect, Rhizoctonia solani behaved exceptionally, since this fungus metabolised prochloraz to a non- fungitoxic compound. This correlates with its low prochloraz sensitivity.

    In Chapter 4 the role of plasma membrane potential in mediating the observed reduced accumulation of two other DMIs, fenarimol and imazalil, by resistant isolates of P. italicum was studied. As found for prochloraz and the experimental triazole compound (Chapter 3), the results confirm that decreased accumulation of these DMIs is responsible for a low level of resistance only and that additional mechanisms may operate in isolates with a medium and high degree of resistance. With all isolates of P.italicum fenarimol accumulation was mediated by an energy- dependent efflux. This was not obviously the case for imazalil. Since no correlation between the accumulation of DMIs and tetraphenyl phosphonium bromide, a probe for measuring plasma membrane potential, could be found, it was concluded that the plasma membrane potential is not involved in accumulation of fenarimol and imazalil by P. italicum . Hence, the mechanism involved in the reduced fungicide accumulation remains unsolved.

    Chapter 5 describes a procedure to isolate microsomal cytochrome P450 isozymes from Ustilago maydis . As demonstrated by difference spectroscopy (type II binding spectra) the the DMIs investigated bind with their heterocyclic nitrogen atom to the oxidized haem iron atom in the protoporphyrinic moiety of the isozymes. However, the DMI concentrations which cause half saturation of type II binding spectra (IC 50 -type II) did not correlate with the fungicidal activities of the azoles. In the carbon monoxide(CO)-displacement tests binding of CO to ferrous cytochrome-P450 was only slightly inhibited to different degrees by the DMIs tested. The inhibition of CO binding did not correlate with fungitoxicity of these DMIs. It was, therefore, concluded that the spectrophotometric studies are not useful for evaluating toxicity of DMIs to U. maydis .

    In Chapter 6 the interaction of various DMIs and experimental compounds with P450 14DM from P. italicum was studied by difference spectroscopy using microsomal P450 isozymes, and assays with cell-free extracts capable of synthesizing ergosterol from [ 14C] mevalonate. Similar to the results obtained with microsomal preparations of U. maydis (Chapter 5), neither type II binding spectra nor CO-displacement tests were useful to assess fungitoxicity of the test compounds. In contrast, the cell-free sterol 14α-demethylase assay gave valuable information. I 50 values (concentrations of compounds which inhibit cell-free sterol synthesis by 50%) varied from 4.3x10 -9to 4.4x10 -5M. The assay ranked the compounds tested in order of fungitoxicity. Results presented in Chapter 6 support the general view that the inhibitory potency of azole fungicides against P450 14DM activity is influenced by the N, substituent of the azole moiety, since structural changes in the N 1 substituent of prochloraz clearly affected the inhibition of cell- free P450 14DM activity. However, the intrinsic inhibitory potency of azoles is not exclusively affected by their N 1 substituent. It was demonstrated that the nature of the azole moiety is also important.

    Chapter 7 presents the development of a sterol 14α-demethylase assay with cell-free extracts of the filamentous plant pathogen Botrytis cinerea . Extracts were obtained by mechanical disruption of young germlings in a Bead-Beater apparatus. The C4-desmethyl sterol fraction accounted for 39% of the non-saponifiable lipids formed and consisted of three distinct compounds. Ergosterol was the major one. The cell-free system had a pH optimum for synthesis of C 4 -desmethyl sterols at pH 7.3-7.4. Cell-free synthesis of C 4 -desmethyl sterols was inhibited by the imidazole fungicide imazalil (IC 50 9.lx10 -9M).

    The Botrytis assay was used to screen prochloraz and several prochloraz analogues for their intrinsic inhibitory potency (Chapter 8). Their IC 50 values ranged from 2.6x10 -9to 4.4x10 -7M. The compounds were also tested in cell-free assays of Saccharomyces cerevisiae . The test compounds were less potent in the yeast assay than in the one of Botrytis . Therefore, it was concluded that the Botrytis assay is more suitable for screening compounds biochemically for their potency to inhibit P450 14DM activity than the yeast assay. Results confirm that the inhibitory activity of prochloraz analogues on P450 14DM activity depends on the nature of their N 1 substituent and their azole moiety.

    Unexpectedly, addition of an amino group at C 2 in the imidazole moiety of prochloraz caused a change in its mode of action in sterol synthesis of P. italicum and B.cinerea (Chapter 8). This was supported by the fact that laboratory-generated triadimenol-resistant strains of B. cinerea exhibited cross resistance to triadimenol and prochloraz, but not to its amino-substituted analogue. Like most compounds, this analogue was less potent in the assays from P. italicum and S. cerevisiae than in the one from B. cinerea. In yeast, this compound did not inhibit sterol biosynthesis at another step in the pathway, but only P450 14DM activity. These findings indicate that biochemical screening tests should preferentially be carried out with cell-free assays from the target pathogen of interest.

    It is concluded that the selective fungitoxicity of DMIs is in part determined by their potency to inhibit P450 14DM activity. Further studies should elucidate which other mechanisms are involved in selective fungitoxicity.

    Effects of imazalil on sterol composition of sensitive and DMI-resistant isolates of Penicillium italicum.
    Guan, J. ; Kerkenaar, A. ; Waard, M.A. de - \ 1989
    Netherlands Journal of Plant Pathology 95 (1989)Suppl. 1. - ISSN 0028-2944 - p. 73 - 86.
    fungiciden - penicillium - pesticidenwerking - ongediertedodende eigenschappen - resistentie tegen pesticiden - pesticiden - gewasbescherming - fungicides - penicillium - pesticidal action - pesticidal properties - pesticide resistance - pesticides - plant protection
    Molecular aspects of herbicide binding in chloroplasts = [Molekulaire aspekten van herbicide binding in chloroplasten]
    Naber, D. - \ 1989
    Agricultural University. Promotor(en): W.J. Vredenberg; J.J.S. van Rensen. - S.l. : Naber - 116
    gewasbescherming - herbiciden - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - plant protection - herbicides - pesticides - pesticidal action - pesticidal properties

    Many weed-controlling agents act by inhibiting the process of photosynthesis. Their mode of action is a displacement of the secondary quinone electron acceptor of photosystem II from its proteinaceous binding environment. This results in a blocking of the electron transport. Consequently plants are no longer able to produce ATP and to reduce NADP +, which eventually leads to starvation and death.

    In this thesis an attempt is made to characterize the interactions of herbicides with their binding environment. Several herbicides were used to measure binding kinetics in a wildtype and a triazine -resistant biotype of Common Lambsquarters, Chenopodium album L.

    In Chapter 1 a general introduction is given on photosynthesis, chloroplast structure and function, the chloroplast genome, and herbicide action and resistances.

    Chapter 2 describes the methods used to isolate chloroplasts and to measure oxygen production. Also the fluorescence induction measurements are described, which can be used as a rapid method to discriminate between herbicide-sensitive and -resistant plants. Procedures for the simultaneous isolation of total plant nucleic acids, for the separation of DNA and RNA and for the respective sequence analyses are outlined.

    In Chapter 3 a model is described which can be used to simulate flash- induced oxygen production by isolated thylakoids. In the literature a model was described before, which explains the observed 4-step oscillation in flash-induced oxygen evolution by assuming the existence of 4 different S-states of the oxygen evolving complex. This model is refined here by assuming the values of the miss parameters αto be dependent on both the redox state of the quinone acceptor complex (Q A .Fe.Q B ) of photosystem II and on the S-state transition involved. The best fit between theoretical and experimental oxygen evolution patterns is obtained when 4 different miss parameters are distinguished, corresponding with the 4 S-state transitions of the oxygen evolving complex. The values of two of these αparameters, notably those for the 2 ndand 4 thflash, are found to approach 0, while the other two have values of about 0.2 and 0.4. The value for the double hit parameter βis found to be about 0.06. The oxygen evolving complexes of thoroughly dark adapted chloroplasts are found to be for almost 100 % in the most stable single oxidized state S 1 . A fraction of 30 % of the reaction centers is assumed to be connected to a oneelectron donor D, which is able to reduce the S 2 - or S 3 -state of the oxygen evolving complex with a half time of 2-3 seconds.

    In Chapter 4 the derived model is used to determine the exchange ,parameters of herbicides with the secondary acceptor Q B . These exchanges, which influence the oxygen evolution patterns, can be determined by comparing experimental and theoretical patterns for various herbicide concentrations and flash frequencies. The I 50 -values derived from the measurements are in agreement with values measured with other methods. The resistance to triazine compounds proved to be caused by an increase in the herbicide release rather than by a lower binding rate. Configuration around a chiral carbon atom, present in two pairs of isomers of cyanoacrylate inhibitors, has a strong influence on inhibition properties. The differences are largely due to alterations in the release kinetics. This observation suggests that herbicide binding is determined mainly by physical properties, like e.g. hydrophobicity. A stationary binding, resulting in a significant electron transport inhibition, requires a strict molecular shape.

    In Chapter 5 partial sequence analyses from DNA and mRNA isolated from a Chenopodium album wildtype and a triazine -resistant biotype are presented. The only difference found was an adenine to guanine point mutation resulting in a serine to glycine alteration at position 264 in the D1 (herbicide binding) protein.

    The thesis is concluded with Chapter 6, the general discussion, in which an alternative explanation for redox reactions at the photosystem II acceptor side is presented. In this model the non-heme iron, located between the primary and the secondary acceptor of photosystem II, is proposed to play an active role in in vivo electron transport.

    Eindverslag van de werkgroep DD, 1971 - 1976
    Lebbink, G. - \ 1978
    Haren : I.B. (Rapport / Instituut voor bodemvruchtbaarheid no. 7-78) - 42
    desinfecteren - nematiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - bodem - bodemfumigatie - mestinjectie - grondsterilisatie - disinfestation - nematicides - pesticidal action - pesticidal properties - pesticides - plant protection - soil - soil fumigation - soil injection - soil sterilization
    Response of pasture grass to thionazin and other pesticides
    Ennik, G.C. ; Baan Hofman, T. - \ 1977
    Wageningen : Pudoc, Centre for Agricultural Publishing and Documentation (Agricultural research reports 867) - 41
    graslanden - nematiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - plantenziekten - afwijkingen, planten - plantenziektekunde - plantenplagen - gewasbescherming - grasslands - nematicides - pesticidal action - pesticidal properties - pesticides - plant diseases - plant disorders - plant pathology - plant pests - plant protection
    Metam - Natrium (Vapam) in de grond
    Anonymous, - \ 1976
    Wageningen : Pudoc (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 3961)
    bibliografieën - desinfecteren - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - metam - bodemfumigatie - grondsterilisatie - bibliographies - disinfestation - pesticidal action - pesticidal properties - pesticides - plant protection - soil fumigation - soil sterilization
    Herbiciden(Di - , Fen - , Mon - , en Neburon) in de grond
    Anonymous, - \ 1972
    Wageningen : [s.n.] (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 3396)
    luchtverontreiniging - bibliografieën - oogstschade - herbiciden - persistentie - pesticidenwerking - ongediertedodende eigenschappen - pesticidenresiduen - pesticiden - fysicochemische eigenschappen - gewasbescherming - bodemchemie - bodemverontreiniging - bodemeigenschappen - air pollution - bibliographies - crop damage - herbicides - persistence - pesticidal action - pesticidal properties - pesticide residues - pesticides - physicochemical properties - plant protection - soil chemistry - soil pollution - soil properties
    A comparison of the in vitro antifungal spectra of thiophanates and benomyl
    Bollen, G.J. - \ 1972
    Wageningen : [s.n.] (Mededeling / Laboratorium voor phytopathologie no. 279) - 10
    fungiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - fungicides - pesticidal action - pesticidal properties - pesticides - plant protection
    On the mode of action of the organophosphorus fungicide Hinosan
    Waard, M.A. de - \ 1972
    Wageningen : [s.n.] (Mededeling / Laboratorium voor phytopathologie no. 280) - 3
    fungiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - fungicides - pesticidal action - pesticidal properties - pesticides - plant protection
    Werkingswijze en toxicologie van bestrijdingsmiddelen
    Anonymous, - \ 1971
    Wageningen : [s.n.] (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 3302)
    gewasbescherming - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - nadelige gevolgen - gewervelde dieren - mens - toxicologie - bibliografieën - plant protection - pesticides - pesticidal action - pesticidal properties - adverse effects - vertebrates - man - toxicology - bibliographies
    Consequences of modern weed control for crop growing techniques
    Zweep, W. van der - \ 1971
    Wageningen : [s.n.] (Mededeling / Instituut voor biologisch en scheikundig onderzoek van landbouwgewassen no. 439) - 6
    herbiciden - parasitaire planten - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - onkruiden - herbicides - parasitic plants - pesticidal action - pesticidal properties - pesticides - plant protection - weeds
    On the specificity of the in vitro and in vivo antifungal activity of benomyl
    Bollen, G.J. ; Fuchs, A. - \ 1970
    Wageningen : [s.n.] (Mededeling / Laboratorium voor Phytopathologie no. 268) - 14
    fungiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - systemische werking - fungicides - pesticidal action - pesticidal properties - pesticides - plant protection - systemic action
    L-methionine induced inhibition of powdery mildew and its reversal by folic acid
    Dekker, J. - \ 1969
    Wageningen : [s.n.] (Mededeling / Laboratorium voor phytopathologie no. 251) - 4
    fungiciden - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - plantenziekteverwekkende schimmels - gewasbescherming - foliumzuur - fungicides - pesticidal action - pesticidal properties - pesticides - plant pathogenic fungi - plant protection - folic acid
    Rearing of the fruit tree leafroller Adoxophyes reticulana HB. on an artificial diet for the evaluation of pesticides; Observations on the dispersal of Adoxophyes reticulana HB. in the orchard with light and sex traps
    Jong, D.J. ; Minks, A.K. - \ 1968
    Wageningen : [s.n.] (Mededeling / Instituut voor plantenziektenkundig onderzoek no. 502-503) - 17
    insectenplagen - tortricidae - insecten - plantenplagen - vruchtbomen - boomgaarden - gewasbescherming - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - kweken - microlepidoptera - insect pests - insects - plant pests - fruit trees - orchards - plant protection - pesticides - pesticidal action - pesticidal properties - rearing
    The effect of derivates of 1,4 - oxathiin on Puccinia horiana in Chrysanthemum morifolium
    Zadoks, J.C. ; Kodde, A. ; Hoogkamer, W. - \ 1968
    Wageningen : [s.n.] (Mededeling / Laboratorium voor phytopathologie no. 253) - 4
    fungiciden - sierplanten - pesticidenwerking - ongediertedodende eigenschappen - pesticiden - gewasbescherming - chrysanthemum - fungicides - ornamental plants - pesticidal action - pesticidal properties - pesticides - plant protection
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