PHOTOTROPISM OF THE Phycomyces SPORANGIOPHORE: A COMPARISON WITH HIGHER PLANTS

Galland, Paul

doi:10.1111/j.1751-1097.1990.tb01780.x

Cited by 38 publications

(18 citation statements)

References 95 publications

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“…To achieve this goal we combined the technical advantages of the novel RSS with the genetic and physiological advantages that are provided by the unicellular zygomycete, Phycomyces blakesleeanus, whose blue-light receptor system has been investigated in great detail (Galland 1990;Fukshansky 1993). In our search for cryptochrome-associated LIACs we were guided by general considerations of¯avin chemistry as well as by speci®c predictions about the LIACs made in the context of Phycomyces photophysiology.…”

Section: Introductionmentioning

confidence: 99%

Light-induced absorbance changes in Phycomyces : evidence for cryptochrome-associated flavosemiquinones

Schmidt

Galland

1999

Planta

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Light-induced absorbance changes (LIACs), which are associated with early photochemical events of blue-light transduction, were detected in growing zones of Phycomyces sporangiophores. The novel LIACs meet all the essential requirements for a spectrophotometric photoreceptor assay which was previously unavailable for blue-light receptors (cryptochromes). In-vivo absorption spectra of growing zones were derived from reflection spectra which were measured with a novel rapid-scan spectrophotometer. To detect photoreceptor-associated absorbance changes white mutants were employed which lack the interfering bulk pigment beta-carotene. Blue and white light, not however red light, induced in these strains absorbance changes near 460-490 and 600-620 nm. The LIACs were absent in light-insensitive mutants with defects in the genes madA, madB and madC. Because these genes affect photosensory adaptation and the blue-light receptor itself, the novel in-vivo LIACs must be associated with photochemical events which occur early in the transduction chain. The spectral characteristics of the LIACs are in accordance with a blue- and red-light absorbing flavosemiquinone which is generated upon light absorption by an oxidized flavin receptor. It is proposed that the flavosemiquinone functions itself as photoreceptor which mediates several red-light responses of Phycomyces.

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Section: Introductionmentioning

confidence: 99%

Light-induced absorbance changes in Phycomyces : evidence for cryptochrome-associated flavosemiquinones

Schmidt

Galland

1999

Planta

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“…After the refractory period, full sensitivity is slowly regenerated (7). Adaptation also occurs in phototropism (1,3,4,5,7). This poses particular problems for the study of second positive phototropism, because relatively long exposures to light are required, and the sensitivity of the plant may vary during the course of an exposure.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Adaptation in Phototropism of Arabidopsis thaliana

Janoudi

Poff

1991

Plant Physiol.

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Phototropic curvature has been measured for etiolated Arabidopsis thaliana seedlings with and without a preirradiation. A bilateral preirradiation with 450-nm light at a fluence greater than about 0.1 micromole per square meter causes a rapid desensitization to a subsequent 450-nanometer unilateral irradiation at 0.5 micromole per square meter. Following a refractory period, the capacity to respond phototropically recovers to the predesensitization level, and the response is then enhanced. The length of the refractory period is between 10 and 20 minutes. Both the time needed for recovery and the extent of enhancement increase with increasing fluence of the bilateral preirradiation. Based on the relative spectral sensitivities of desensitization and enhancement, these responses can be separated. Desensitization is induced by blue light but not by red light. Enhancement, however, is induced by both blue and red light. Thus, enhancement can be induced without desensitization but not vice versa. Both desensitization and enhancement affect only the magnitude of the response and do not affect the fluence threshold.It has long been known that receptor systems in plants have a built-in process for producing a change in sensitivity to a stimulus. In this process, known as adaptation, an exposure to a stimulus may be followed by a refractory period, during which the plant is insensitive to the stimulus. After the refractory period, full sensitivity is slowly regenerated (7). Adaptation also occurs in phototropism (1,3,4,5,7). This poses particular problems for the study of second positive phototropism, because relatively long exposures to light are required, and the sensitivity of the plant may vary during the course of an exposure.The objective of this work was to characterize adaptation in phototropism by Arabidopsis thaliana as a first step toward evaluating adaptation's role in second positive phototropism. We show that adaptation consists of desensitization, a refractory period, recovery, and enhancement. The first three occur following an exposure to blue light while enhancement occurs following an exposure to either blue or red light. MATERIALS AND METHODSSeedlings of Arabidopsis thaliana (L.) Heynh. strain 'Estland' were grown as previously described (6) microassay wells containing 0.7% (w/v) agar. Seed germination was potentiated by chilling at 5 ± 1°C in darkness for 3 d, and then exposing to white light for 20 h at 25 ± 1°C. Following the white light irradiation, the strips were transferred into darkness at 25 ± 1°C for 42 h, at the end of which the seedlings were exposed to the appropriate photostimulus. The seedlings were maintained throughout at a RH greater than 90%. Because green light is known not to be phototropically 'safe' (9), all manipulations were performed in complete darkness. Light SourcesThe white light (50 ,umol m-2 s'), which was used to potentiate seed germination, was provided by two General Electric (Cleveland, OH) Delux Cool-White fluorescent tubes. A slide projector equipped with...

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“…We decided to apply the same experimental rationale to P. blakesleeanus, a lower eukaryote long known mainly for the complex behavior of its sporangiophores (fruiting bodies) in response to blue light (reviewed in Galland, 1990). Two easily assayable photoresponses of this organism were chosen as markers in our experiments: morphogenesis and carotenogenesis.…”

Section: Resultsmentioning

confidence: 99%