Light-induced absorbance changes in Phycomyces: evidence for cryptochrome-associated flavosemiquinones |
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Authors: | Werner Schmidt Paul Galland |
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Institution: | Fachbereich Biologie/Botanik, Philipps-Universit?t, Lahnberge, D-35032 Marburg, Germany, DE
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Abstract: | 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 unavailaible 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 β-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.
Received: 28 September 1998 / Accepted: 25 November 1998 |
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Keywords: | : Blue-light receptor Flavin Light-induced absorbance changes Phototropism mutants Phycomyces Red-light receptor Semiquinone |
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