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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.

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    Genetic modification of shade-avoidance: overexpression of homologous phytochrome genes in tomato
    Husaineid, S.H. - \ 2007
    Wageningen University. Promotor(en): Linus van der Plas, co-promotor(en): Sander van der Krol. - [S.l.] : S.n. - ISBN 9789085045120 - 152
    solanum lycopersicum - tomaten - schaduw - fytochroom - genen - transgene planten - licht - groei - gewasdichtheid - solanum lycopersicum - tomatoes - shade - phytochrome - genes - transgenic plants - light - growth - crop density
    Photomorphogenesis
    Kendrick, R.E. ; Weller, J.L. - \ 2003
    In: Encyclopedia of Applied Plant Sciences / Thomas, B., Murphy, D.J., Murray, B.G., Elsevier/Academic Press - ISBN 9780122270505 - p. 1069 - 1076.
    fotoperiodiciteit - fototropie - fotoreceptoren - lichtregiem - fytochroom - zaadkieming - photoperiodism - phototropism - photoreceptors - light regime - phytochrome - seed germination
    Leaf senescence in alstroemeria : regulation by phytochrome gibberellins and cytokinins
    Kappers, I.F. - \ 1998
    Agricultural University. Promotor(en): L.H.W. van der Plas; W.J.R.M. Jordi; F.M. Maas. - S.l. : S.n. - ISBN 9789054859192 - 143
    bladeren - veroudering - alstroemeria - alstroemeriaceae - fytochroom - plantenpigmenten - gibberellinen - cytokininen - verouderen - gebruiksduur - leaves - senescence - alstroemeria - alstroemeriaceae - phytochrome - plant pigments - gibberellins - cytokinins - aging - longevity

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

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

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

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

    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.
    Mutants as an aid to the study of higher plant photomorphogenesis
    Adamse, P. - \ 1988
    Agricultural University. Promotor(en): W.J. Vredenberg; R.E. Kendrick. - S.l. : Adamse - 140
    licht - fotoperiodiciteit - fytochroom - plantenpigmenten - genetische variatie - mutaties - light - photoperiodism - phytochrome - plant pigments - genetic variation - mutations

    Study of photomorphogenesis is often complicated by the interaction of different photoreceptors regulating a given process or by the induction of multiple effects by a single photoreceptor. Mutants in which particular components of the morphogenetic pathways are eliminated provide the possibility of studying a more simplified form of photomorphogenesis. Three classes of photomorphogenetic mutants are proposed: photoreceptor, transduction chain and response mutants. In this study three mutants have been used: two have an elongated hypocotyl when grown in white light (the aurea ( au ) tomato mutant and the long hypocotyl ( lh ) cucumber mutant) and one with an enhanced pigment synthesis (the high pigment ( hp ) tomato mutant). The au mutant appears to be a photoreceptor mutant, lacking spectrophotometrically and immunochemically detectable labile phytochrome (lP). The lh mutant is proposed to lack stable phytochrome ( s P) or its function. These mutants enabled the role of s P, l P. and blue light (BL)/UV- photoreceptor(s) in several photophysiological processes to be studied. The results of these experiments indicate that l P plays a role in both hypocotyl elongation and anthocyanin synthesis in etiolated seedlings. This provides direct evidence that the 'bulk' l P is functional. In etiolated seedlings the au tomato mutant with its deficiency in l P is 'red-blind' and has a shift of fluence rate response curves for hypocotyl inhibition by BL and UV-A approximately l order of magnitude to higher fluence rates. In light-grown plants it is proposed that s P regulates the end-of-day far-red light (FR) response and the inhibition of hypocotyl elongation due to light perception by the cotyledons. Furthermore, these mutants with reduced phytochrome (P) content provide direct experimental evidence that the FR absorbing form of P (Pfr) is the active form indeed. If removal of the red light (RL) absorbing form of P (Pr) is the active photomorphogenetic process, instead of an increase of Pfr, seedlings with a reduced P content would be expected to be short. However, dark-grown seedlings of lh mutant and au mutant are both elongated. The hp mutant with its enhanced anthocyanin synthesis has enabled induction of anthocyanin synthesis in tomato seedlings in response to a single RL pulse to be observed, whereas in wild type this synthesis it too low to be measured. Study of anthocyanin synthesis with the aid of the hp mutant, the au mutant and the au/hp double mutant supports the conclusion that P is the terminal photoreceptor involved in tomato and that BL (operating through the BL/UV-photoreceptor or P) sensitizes the seedling to P action at a later stage. Using a computer-controlled apparatus for continuous growth measurement, designed and constructed for this study, it has been possible to show the differences in kinetics of hypocotyl inhibition by BL or RL in both the lh mutant and its wild type. In BL inhibition started almost immediately after the onset of irradiation, whereas in RL a lag period of several hours was observed.

    Flower colours and pigments in tulip cultivars
    Eijk, J.P. van; Keulen, H.A. van; Dijk, A.J. van - \ 1987
    Wageningen : IVT (Rapport / Instituut voor de Veredeling van Tuinbouwgewassen 236) - 15
    kleur - tuinbouwgewassen - sierplanten - fytochroom - plantenpigmenten - Tulipa - bloemen - colour - horticultural crops - ornamental plants - phytochrome - plant pigments - Tulipa - flowers
    Aanvullend op eerder onderzoek, waarbij bijna 500 oude en nieuwe tulpencultivars op bloempigmenten werden geanalyseerd, worden in tabelvorm van diezelfde cultivars nu de bloemkleur en de relatieve hoeveelheden carotenoiden, delfinidine, cyanidine, pelargonidine en flavonolen aangegeven
    Phytochrome and greening in etioplasts
    Kraak, H.L. - \ 1986
    Landbouwhogeschool Wageningen. Promotor(en): W.J. Vredenberg; R.E. Kendrick. - Wageningen : Kraak - 111
    chloroplasten - fytochroom - plantenpigmenten - chloroplasts - phytochrome - plant pigments

    This thesis is concerned with the role played by phytochrome (P) in the development of etioplasts into chloroplasts.

    Previously dark-grown maize seedlings are not as sensitive as pea seedlings to very low fluences of red light (R) with regard to induction of rapid chlorophyll (Chl) accumulation in white light (WL), but a very low fluence response (VLFR) has been established in this plant species as well. Much higher fluences of a second R pre-irradiation are required to give an additional effect (low fluence response or LFR). When the effect of far-red light (FR) as such is accounted for, the effects of both a first and a second R pre- irradiation are 60-80% reversible by FR in maize seedlings. In high irradiance WL, the lag phase of Chl accumulation is of considerably longer duration. This indicates that photodestruction of Chl plays a role in the occurrence of a lag phase in Chl accumulation. R has a relatively large effect in high irradiance WL (Chapter 3).

    Phytochrome (P) was measured spectrophotometrically for the first time in purified etioplast preparations obtained in complete darkness from dark-grown seedlings (D etioplasts) (Chapter 4). The P content of etioplast preparations from R pre-irradiated seedlings marginally exceeded that of D etioplasts. While the total P content of maize leaves, as measured in homogenates, decreased after R irradiation as a result of Pfr dark destruction, the P content of etioplasts from similar seedlings remained constant.

    Attempts to demonstrate a physiological effect of etioplast- associated P were not successful. Preliminary studies on ultrastructural development of etioplasts (Chapter 5) showed that the invitro development during 1 h WL did not completely parallel development insitu . An effect of invivo R pre-irradiation on prolamellar body transformation, which was evident insitu , was not observed invitro . Insitu , formation of incipient grana in WL was stimulated by R pre-irradiation, however, isolated etioplasts proved incapable of forming incipient grana.

    In the dark, following a short irradiation, regeneration of phototransformable protochlorophyll(ide) (PChl(ide)) was observed in isolated etioplasts (Chapters 6 and 7). However, regeneration kinetics differed from those invivo and no effect of invivo R pre-irradiation could be demonstrated. Invivo , the rate of PChl(ide) regeneration was increased by Pfr (Chapter 6).

    Wavelength shifts of the 77K fluorescence emission maxima of newly formed chlorophyll(ide) (Chl(ide)) after a short irradiation were studied in leaves and isolated etioplasts. Derivative spectroscopy and curve fitting were applied to study kinetics of these shifts (Chapter 7). The first shift, a red shift, was slower in isolated etioplasts than in leaves. No effect of R pre-irradiation was observed on the rate of this shift. The subsequent blue shift, the so-called Shibata shift, was more rapid, but less complete in isolated etioplasts than in leaves. Whereas in leaves the rate of the Shibata shift was increased by Pfr, this was hardly, if at all, detectable in isolated etioplasts. The amount of phototransformable PChl(ide) decreased and the rate of the Shibata shift increased during storage of isolated etioplasts at 4 °C in darkness. Newly formed Chl(ide) proved unstable in isolated etioplasts.

    The above results point to a decisive influence of the cytoplasm on the development of etioplasts in WL. In this respect, polypeptides of Chl-protein complexes synthesized in the cytoplasm may play an important role. However, a direct influence of etioplast-associated P in the development of etioplasts into chloroplasts, e.g. on permeability of the etioplast envelope, can not be excluded. Evidence for such an effect is found in the observation that the potentiating effect of a R pre-irradiation with regard to rapid Chl accumulation in WL is still partially reversible by FR after a dark period of 24 h. While Pfr in bulk P had already disappeared due to dark destruction after 4 h of darkness, the amount of P associated with etioplasts appeared not to decrease (see above). It is attractive to attribute at least that part of R potentiation which shows a long-term reversibility by FR, to apparently relatively stable etioplast-associated Pfr.

    The results are discussed in relation to the phytochrome transport model of Raven and Spruit (Chapter 8). It is concluded that, though they do not provide a direct support for the model, they are not in disagreement with it. The transport model still appears to give an attractive explanation for a number of P responses, such as the VLFR and the Zea P paradox.

    Enige literatuur over RF (= Ratio Front) : waarden van plantenkleurstoffen bij papier- of dunnelaag-chromatografie = Some literature on RF (= Ratio Front) : values of plant pigments in paper or thin-layer chromatography
    Anonymous, - \ 1982
    Wageningen : Pudoc (Literatuurlijst / Centrum voor Landbouwpublikaties en Landbouwdocumentatie no. 4597)
    dunnelaagchromatografie - papierchromatografie - fytochroom - plantenpigmenten - bibliografieën - literatuuroverzichten - thin layer chromatography - paper chromatography - phytochrome - plant pigments - bibliographies - literature reviews
    The genetics of some planthormones and photoreceptors in Arabidopsis thaliana (L.) Heynh.
    Koornneef, M. - \ 1982
    Landbouwhogeschool Wageningen. Promotor(en): J.H. van der Veen. - Wageningen : Koornneef - 157
    brassicaceae - genetische variatie - genetica - heritability - overerving - mutagenese - mutagenen - mutaties - fytochroom - plantengroeiregulatoren - plantenpigmenten - brassicaceae - genetic variation - genetics - heritability - inheritance - mutagenesis - mutagens - mutations - phytochrome - plant growth regulators - plant pigments - cum laude
    This thesis describes the isolation and characterization in Arabidopsis thaliana (L.) Heynh. of induced mutants, deficient for gibberellins (GA's), abscisic acid (ABA) and photoreceptors.

    These compounds are known to regulate various facets of plant growth and differentiation, so mutants lacking one of these substances are expected to be affected in several aspects of their physiology. It is shown in this thesis that the earliest expression of these mutants occurs during seed development and seed germination. Therefore these processes form an excellent phase to screen for these mutants.

    Planthormone and photoreceptor mutants in relation to seed physiology.

    In general three major periods may be distinguished in the history of a seed: 1) Seed development and maturation, 2) developmental arrest of the mature seed, characterized either by a dormant state in which seeds even do not germinate under favourable environmental conditions, or by a quiescent state in which seeds only require rehydration, and 3) germination, starting with water uptake and often requiring breaking of dormancy, which is triggered by specific environmental factors such as light and temperature. Planthormones may play a regulatory role in all three phases.

    Non-germinating GA-responsive mutants as described in Chapter 1 have a strongly reduced gibberellin biosynthesis (Barendse, pers.comm.) which may lead to an increased level of dormancy and/or to the inability of the seeds to
    break dormancy after imbibition of mature seeds. Clearly the presence of GA's, either by de novo GA synthesis, or by hydrolysis of bound forms, is not always a prerequisite for seed germination: genotypes that combine GA- and ABA deficiency like the revertants of non-germinating ga-1 mutants described in Chapter 2 do readily germinate.

    Apart from the absence of endogenous factors such as gibberellins, also the lack of receptors for environmental factors that normally break dormancy might prevent germination. An example are the hy-1 and hy-2 mutants (Chapter 4), which are characterized by an increased hypocotyl length in white light and the absence of detectable phytochrome in dark grown hypocotyls. It was shown by Spruit et al. (1980), that these mutants hardly show any germination and correspondingly, have strongly reduced levels of phytochrome in their seeds. Their reduced germination capacity is restored by (relatively high) concentrations of exogeneously applied GA 4+7 (Koornneef et al., 1981). Consequently one might expect such phytochrome deficient mutants to occur among the GA responsive non-germination mutants in Arabidopsis, like van der Veen and Bosma actually found for a tomato mutant (see Koornneef et al., 1981). Remarkably this was not the case in Arabidopsis. The reason for this seems to be the absence of a light requirement in the hy mutants from the M 2 populations screened for non-germinating mutants of Arabidopsis. It happened that these M 2 seeds in all cases were harvested from M 1 plants grown in winter, in contrast to the seeds studied by Spruit et al. (1980) which were harvested in summer. We have observed during a number of years that seeds (including wild-type seeds), which developed in winter (natural daylight with additional continuous light by Philips TL 57) were less dormant than seeds from summer grown mother plants (long days, high light intensity, no additional light). Relevant environmental factors in this respect may be light intensity, light quality (McCullough and Shropshire, 1970) and daylength (Karssen, 1970; Luiten, 1982). The effect of light quality (McCullough and Shropshire, 1970) indicates that phytochrome may be involved in the determination of the level of dormancy.

    To select mutants with a reduced or absent seed dormancy, one may choose those conditions, where the wild-type is clearly dormant. However, the high and probably complex environmental variability of this character and the relatively rapid change in the level of dormancy during dry storage of the seeds makes this selection system less attractive.

    Selection for revertants in the progeny of mutagen treated non-germinating ga-1 mutants proved to be an effective procedure to isolate mutants with a reduced dormancy (Chapter 2). As the reverting effect (restored germination) was caused by a mutation at a different locus, the ga-1 allele could be replaced by its wild-type allele by crossing the revertant with the wild-type parent followed by selection in F 2 . These newly selected monogenic recessive mutants had a reduced level of ABA in the leaves and in both the developing and ripe seeds. Correspondingly the mutant allele was called aba (ABA-types are aba/aba plants).

    The germination of seeds collected at different stages of their development on both ABA- and wild-type plants showed that dormancy developed during the last part of seed maturation in wild-type, but not in the aba -mutant. This shows that the function of ABA is dormancy induction. ABA determinations in unripe siliquae showed a peak level of ABA at about 10-12 days after anthesis, followed subsequently by a decrease, a short period at a constant level and a further decrease (Chapter 3). In addition to ABA-type mothers with ABA-type embryo's and wild-type mothers with wild-type embryo's, one can also obtain by means of the appropriate reciprocal crosses ABA-type mothers with wild-type embryo's and wild-type mothers with (50%) ABA type embryo's. So the effects of maternal and embryonic genotype can be separated. It was found (Chapter 3) that the genotype of the mother plant regulated the sharp rise in ABA content halfway seed development (maternal ABA). The genotype of the embryo and endosperm was responsible for a second ABA fraction (embryonic ABA), which reached lower levels; but persisted for some time after the maximum in maternal ABA. The onset of dormancy showed a good correlation with the presence of the embryonic ABA fraction and not with the maternal ABA.

    Another category of mutants which also may give some understanding of the role of ABA in seed germination are the ABA tolerant mutants recently isolated by us in Arabidopsis. Compared to wild-type these mutants require an upto 20 fold higher concentration of exogeneously applied ABA to inhibit seed germination. These mutants too are characterized by a reduced seed dormancy.

    Other genetically determined factors than those mentioned above are certainly also involved in seed development and seed germination. Thus in Arabidopsis mutations leading to the absence of seed coat pigments (transparent testa) and simultaneously to the absence of a mucilage layer around the seed have a reduced dormancy (Koornneef, 1981). The latter seedcoat characters are determined purely by the maternal genotype.

    Planthormone and photoreceptor mutants in relation to other physiological effects.

    Non-germinating mutants at the loci ga-1, ga-2 and ga-3, when made to germinate by adding gibberellin, initially develop into normal looking seedlings. Later on they become dark green bushy dwarfs with reduced petals and stamens. Regular GA-spraying from the seedling stage onwards maintains the wild-type phenotype completely or nearly so (Chapter 1). The strong and quick response of the dwarfs to GA sprays (the elongation of the petals of older dwarfs becomes visible within two days) clearly demonstrates the essential role of gibberellin in elongation growth.

    Recently the non-germinating ga alleles were shown to have a strongly re duced kaurene synthetase activity in young siliquae compared to wild type. These analyses were performed by Dr. G.W.M. Barendse (pers.comm.). This indicates that these genes control some early step(s) in GA biosynthesis.

    Apart from mutants that do not germinate without GA, also more or less normally germinating GA responsive dwarfs were isolated. Half of these were found to be allelic to the non-germinating ga-1 , ga-2 and ga-3 mutants. These mutant alleles behave like so called "leaky alleles", i.e. the alleles are only partly defective and produce sufficient GA for seed germination, but not enough to give normal elongation growth.

    GA sensitive dwarfs were also found at two other loci ( ga-4 , ga-5 )of which no non-germinating alleles have been isolated so far (Chapter 1). These mutants have normal or slightly reduced kaurene synthetase activity (Barendse, pers.comm.), which indicates that these genes regulate steps beyond kaurene, or affect GA metabolism in another way. It is also possible that in the mutants cell elonga tion factors are blocked for which the relatively high concentration of exogeneously applied GA may substitute. Locus ga-4 seems to control interconversions between GA's, which is suggested by the insensitivity of ga-4 dwarfs to GA 9 . which gibberellin is effective with mutants at the other 4 loci.

    Abscisic acid (ABA) deficient mutants are characterized not only by reduced seed dormancy but also by disturbed water relations (wiltiness, withering), probably as a result of failure to close the stomata upon conditions of water stress (Chapter 2). This is characteristic for ABA deficient mutants in tomato (Tal and Nevo, 1973) and potato (Quarrie, 1982). ABA deficient mutants in maize are in addition to a reduced seed dormancy (viviparous mutants, gene symbol op) characterized by the failure to synthesize carotenoids and they accumulate precursors of these pigments (Robichaud et al., 1980). As ABA deficient mutants in Arabidopsis, tomato and potato have normal pigments, it is suggested that in the latter species the ABA biosynthesis may be blocked in the last part of the pathway, whilst in the maize mutants it is blocked at an earlier stage, i.e. where ABA and carotenoids still have a common pathway.

    Some of the photoreceptor mutants are affected in their germination behaviour as discussed above. However, the most conspicuous effect observed is the partial lack of light induced inhibition of hypocotyl elongation (Chapter 4). Mutants in Arabidopsis, and also in tomato and cucumber (Koornneef et al., 1981; Koornneef et al., unpublished), that have an elongated hypocotyl when grown in white light, were shown to have locus-specific alterations in the spectra of light inhibition when grown in light of restricted spectra] regions. In these "colour blind" mutants at two loci (hy-1 and hy-2) little or no spectrophotometrically detectable phytochrome was present in dark grown hypocotyls, nor was it in the seeds. In these mutants the inhibitory effect of red and farred was almost absent. Mutants of other genes were characterized by the absence only of red inhibition (hy-3) or by a decreased sensitivity to the shorter wavelengths of the spectrum (hy-4, hy-5). Hy-5 also showed a reduced inhibitory effect of far-red light. The differential sensitivity of the genotypes to specific spectral regions strongly suggests the involvement of more than one pigment in the inhibition by light of hypocotyl elongation and probably also in other photomorphogenetic processes. Some authors ascribed this role solely to phytochrome (Schäfer, 1976).

    Since under specific conditions phytochrome could nevertheless be detected in so called phytochrome deficient mutants (Koornneef and Spruit, unpublished) the genes hy-1 and hy-2 probably do not represent the structural genes of the phytochrome protein or the phytochrome chromophore, but instead may play a role in the regulation of phytochrome metabolism.

    Further genetic aspects of plant hormone and light receptor mutants.

    Mutation frequencies for the different groups of loci were estimated for ethylmethanesulphonate (EMS), fast neutrons and X-rays (Chapter 5). Average mutation frequencies calculated per diploid cell, per locus and per MM EMS during 1 hr at 24 °C, were for ga-1, ga-2, ga-3 8.0 ± 1.8 x 10 -6, for hy-1, hy-2, hy-3 4.2 ± 1.4 x 10 -6and for the aba locus about 27 x 10 -6. These mutation frequencies are relatively high compared to other loci studied by us and others. It is not excluded that in these categories loci escaped detection simply because of a low mutation frequency.

    It is a good custum to locate newly induced mutations on the organisms gene map, especially when they are the basis of extensive research like our ga, aba and hy mutants. Unfortunately, the gene map of Arabidopsis was rather fragmentary, and contradictory or wrong conclusions about linkage relations could be found in literature. Since we had gradually built up the complete set of 5 primary trisomics supplemented with a number of telotrisomics (one chromosome arm extra) and also made a collection of mutations at many loci, induced in the course of various experiments at our department and supplemented with mutants described in literature, we had a good starting point to construct a more representative gene map for Arabidopsis. The required scale of operations was only feasable thanks to the accurate assistance of many students who performed trisomic analysis and gene mapping as part of their university training program. Important further additional data were obtained from the department of Genetics of Groningen University and from literature.

    The trisomic analysis aimed at assigning linkage groups (via representative markers) to the different chromosomes is described in Chapter 6. The gene maps in centimorgans for the five Arabidopsis chromosomes is presented in Chapter 7. On the basis of 76 loci mapped the genetic length of the Arabidopsis chromosomes now compares well with that of individual chromosomes in e.g. tomato and maize. This notwithstanding the small size of the Arabidopsis chromosomes.

    Genes with a similar mutant phenotype (and probably comparable functions) seem to be distributed at random over the Arabidopsis genome.

    Our set of mutants at the ga-1 locus of Arabidopsis provides an excellent opportunity for fine structure analysis of the gene. The system has a very high resolving power, for the intragenic recombinants are found as the rare wild-type seedlings among thousands of non-germinating seeds per petri dish. The results show (Chapter 8) that 8 different alleles could be arranged into an internally consistent map on the basis of the frequencies of intragenic recombinants. One fast neutron induced allele behaved as an intragenic deletion. The order of the sites with respect to other genes on chromosome 4 could be established.

    Membranes and phytochrome action
    Wassink, E.C. - \ 1974
    Wageningen : Veenman (Mededelingen / Landbouwhogeschool Wageningen 74-22) - 5
    fytochroom - plantenpigmenten - celmembranen - phytochrome - plant pigments - cell membranes
    Chlorophyll formation and phytochrome
    Raven, C.W. - \ 1973
    Landbouwhogeschool Wageningen. Promotor(en): E.C. Wassink. - Wageningen : Veenman - 100
    fytochroom - plantenpigmenten - chlorofyl - licht - fotoperiode - fotoperiodiciteit - schaduw - phytochrome - plant pigments - chlorophyll - light - photoperiod - photoperiodism - shade

    The rôle of phytochrome in the regeneration of protochlorophyll (Pchl) in darkness following short exposures to light, as well as in the accumulation of chlorophyll- a (Chl- a ) in continuous light in previously dark-grown seedlings of pea, bean, and maize has been the subject of the present investigation.

    The in vitro red absorption peak of Chl- a was situated at shorter wavelengths, if a dark period was inserted between the moment of Pchl phototransformation and that of pigment extraction (Chapter 5, fig. 8). There was a considerable pigment photobleaching during Pchl photoconversion in high quantum flux densities (2.2 x 10 4ergs/cm 2sec) of red light (fig. 10). The effectivity of red (651 nm) light in Pchl phototransformation surpassed that of blue (442 nm) light about two times (fig. 11.).

    The initial rates and ultimate level of Pchl regeneration were strongly depressed in older leaves (Chapter 6). In young seedlings Pchl regeneration in darkness after an illumination, generally, stopped after having reached its initial level (e.g. figs. 16, 18, and 19), which level (either expressed as pigment content per g fr. w. or per constant number of leaves) was not affected by simultaneous leaf growth over a prolonged period (fig. 54). Thus, we concluded that the number of Pchl regeneration sites per cell is constant during the first hours of greening. Red-far red control of the initial rates of Pchl regeneration could not be demonstrated (figs. 16, 17, 18, and table 1). In older maize leaves, an effect attributable to phytochrome was observed upon the final level of Pchl, reached in prolonged darkness (fig. 18). In intact bean seedlings, however, even five repetitive exposures to red and red followed by far red, at 2-hour intervals, did not significantly alter the final level of Pchl (fig. 19).

    The duration of the lag phase in Chl- a formation was increased, and the ultimate rate of Chl- a accumulation depressed in pea seedlings continuously exposed to white fluorescent light of high intensity (60,000 ergs/cm 2sec) (figs. 23 and 25) which we ascribe to photodestruction of freshly formed chlorophyllous pigments (Chapter 7). The duration of the lag phase in Chl- b formation was even more sensitive than that of Chl- a formation to the intensity of the light (fig. 24).

    In detached leaves and leaves of seedlings with the cotyledons removed, Chl- a formation was very poor as compared with leaves on intact plants (section 7.2.1.2.). Chl- a synthesis of detached leaves was only partly restored by sucrose supply. Application of δ-aminolevulinic acid had no stimulating effect on the rate of Chl- a formation in the light (fig. 26 and section 8.2. 1.) nor on the accumulation of Pchl in darkness (section 7.3.). This renders unlikely that synthesis of this compound is a bottleneck in Chl- a formation.

    Continuous red light (646-651 nm) was the most effective wavelength range for Chl- a formation and accumulation of carotenoids; they were much weaker in the blue (442 nm) (section 7.2.2.). The nature of the photoreceptor pigment(s) involved could not be established with certainty (sections 7.2.2. and 7.3). The increase in fresh weight of pea plumules during continuous illumination is most likely mediated by phytochrome (fig. 36). Electron micrographs demonstrated that internal structural development of etioplasts was especially rapid in continuous blue light (section 7.2.3). During the first hours of greening in white light, three photoreceptor systems may be simultaneously active.

    In intact seedlings the stimulatory effect of brief pre-exposures to red light on rapid Chl- a accumulation in continuous light was retained during a dark period of at least 48 hours (Chapter 8, figs. 38 and 40). This may be related to the irreversible concomitant light induced rise in fresh and dry weight of leaves (figs. 48 and 41, respectively), which may be paralleled by equally irreversible growth and development of etioplasts (section 9.3). Excised leaves were completely insensitive to irradiations of the type, inductive in intact plants (fig. 39).

    Considerable differences in sensitivity to red light (fig. 42) were not accompanied by similar differences in spectrophotometrically demonstrable phytochrome (fig. 43).

    Pea leaves were found extremely light sensitive (fig. 44): even relatively short exposures to weak green 'safelight' induced rapid Chl- a accumulation in subsequent continuous white light (fig. 45). The action spectrum pointed to phytochrome as the photoreceptor pigment (fig. 46).

    Induction by red light was hardly reversible by subsequent far red in various cultivars of pea and bean, and in young maize seedlings (table 4), owing to considerable inductive capacity of far red (Chapter 9). Far red reversibility of the effect induced by red increased considerably with increasing duration of dark incubation between pre-irradiation and continuous white light (fig. 48). Fairly complete red-far red reversal occurred in plants de-etiolated by pre-irradiation some hours prior to the inductive treatment (fig. 50). Even relatively short exposures to green safelight caused de-etiolation with concomitant increase in subsequent red- far red antagonism (fig. 52). We define as de-etiolated the state of a completely dark-grown seedling treated with a photobiologically inductive amount of light (see p. 1, and p. 77).

    In order to explain the difference between completely dark-grown and deetiolated seedlings in their sensitivity to far red induction and red-far red photoreversibility, a model is presented, involving transport of phytochrome during de-etiolation to receptor sites of restricted capacity which then become activated to initiate the physiological response (figs. 57 and 58, section 9.1).

    As for the rôle of phytochrome in the greening process, it is concluded that the biosynthetic pathway leading to Pchl and Chl- a is not directly under phytochrome control. However, P fr is postulated to increase the capacity of the biosynthetic system forming Pchl by stimulating synthesis of structural proteins, enabling rapid build-up of the photosynthetic apparatus as soon as Chl molecules are being continuously supplied by phototransformation of Pchl. During this process, Chl is supposed to be detached from the Pchl regeneration sites, and the availability of empty regeneration sites is supposed to activate Pchl
    biosynthesis.

    Phytochrome-mediated enhancement of the rate of phytolization might well be another factor favouring Chl- a accumulation in continuous illumination by facilitating the protection of the freshly formed chlorophylls from photodestruction. A similar function may be ascribed to certain red light induced carotenoid pigments, at least for greening in light with an appreciable content of shorter wavelengths.

    Spectrophotometers for the study of phytochrome in vivo
    Spruit, C.J.P. - \ 1970
    Wageningen : Veenman (Mededelingen Landbouwhogeschool Wageningen 70-14) - 18
    fytochroom - plantenpigmenten - analyse - spectrofotometrie - meting - schatting - registreren - gegevens verzamelen - onderzoek - optica - wetenschappelijk onderzoek - wetenschap - natuurwetenschappen - phytochrome - plant pigments - analysis - spectrophotometry - measurement - estimation - recording - data collection - research - optics - scientific research - science - natural sciences
    Phytochrome in seeds of some curcurbitaceae: in vivo spectrophotometry
    Malcoste, R. ; Boisard, J. ; Spruit, C.J.P. ; Rollin, P. - \ 1970
    Wageningen : Veenman (Mededelingen Landbouwhogeschool Wageningen 70-16) - 16
    cucurbita - pompoenen - fytochroom - plantenpigmenten - analyse - spectrofotometrie - wetenschap - natuurwetenschappen - cucurbita - pumpkins - phytochrome - plant pigments - analysis - spectrophotometry - science - natural sciences
    Photoreactions in phytochrome - containing extracts from etiolated pea seedlings
    Spruit, C.J.P. - \ 1967
    Wageningen : [s.n.] (Mededelingen / Landbouwhogeschool Wageningen no. 67-15) - 9
    plantkunde - pisum sativum - erwten - fytochroom - plantenpigmenten - plantensamenstelling - cultuurmethoden - botany - pisum sativum - peas - phytochrome - plant pigments - plant composition - cultural methods
    Phytochrome decay and reversal in leaves and stem sections of etiolated pea seedlings
    Spruit, C.J.P. - \ 1967
    Wageningen : Veenman (Mededelingen / Landbouwhogeschool Wageningen 67-14) - 6
    plantkunde - pisum sativum - erwten - fytochroom - plantenpigmenten - plantensamenstelling - cultuurmethoden - botany - pisum sativum - peas - phytochrome - plant pigments - plant composition - cultural methods
    Thermal reactions following illumination of phytochrome
    Spruit, C.J.P. - \ 1966
    Wageningen : Veenman (Mededelingen / Landbouwhogeschool Wageningen 66-15) - 7
    fytochroom - plantenpigmenten - stress - fysische factoren - phytochrome - plant pigments - stress - physical factors
    The influence of the phytochrome reaction on the growth of Lemna Minor L
    Rombach, J. - \ 1965
    Wageningen : Veenman (Mededelingen van de Landbouwhogeschool Wageningen 65-14) - 11
    lemnaceae - lemna - fytochroom - plantenpigmenten - vacuolen - licht - fotoperiode - fotoperiodiciteit - schaduw - lemnaceae - lemna - phytochrome - plant pigments - vacuoles - light - photoperiod - photoperiodism - shade
    Absorption spectrum changes during dark decay of phytochrome-730 in plants
    Spruit, C.J.P. - \ 1965
    Wageningen : Veenman (Mededelingen van de Landbouwhogeschool 65-12) - 6
    pisum sativum - erwten - fytochroom - plantenpigmenten - plantkunde - licht - fotoperiode - fotoperiodiciteit - schaduw - pisum sativum - peas - phytochrome - plant pigments - botany - light - photoperiod - photoperiodism - shade
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