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Blue‐Light Receptor Requirement for Gravitropism, Autochemotropism and Ethylene Response in Phycomyces *
Author(s) -
Campuzano Victoria,
Galland Paul,
Alvarez Maria I.,
Eslava Arturo P.
Publication year - 1996
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1996.tb05674.x
Subject(s) - phototropism , phycomyces , mutant , gravitropism , phycomyces blakesleeanus , biology , biophysics , action spectrum , light sensitivity , genetics , gene , chemistry , blue light , arabidopsis , physics , optics
Light, gravity and ethylene represent for plants and fungi important environmental cues for spatial orientation and growth regulation. Coordination of the frequently conflicting stimuli requires signal‐integration sites, which, however, remain largely unidentified. The genetic and physiological basis for signal integration was investigated with a set of phototropism mutants (genotype mad ) of the UV‐ and blue‐light‐sensitive fungus Phycomyces blakes‐leeanus , which responds also to gravity, ethylene and nearby obstacles (autochemotropism or avoidance response). Both, class 1 and class 2 mutants display a reduced sensitivity to visible light. Class 1 mutants with defects in genes mad A, B, C, Z have preserved their sensitivity to gravity and ethylene, whereas class 2 mutants with defects in genes mad D, E, F, G, J have lost it. We found that the phototropic sensitivity of class 1 mutants is affected roughly to the same extent in far UV and blue light. In contrast, the sensitivity loss of class 2 mutants is restricted mainly to the near‐UV and the blue‐light region, whereas the sensitivity to far UV is only mildly affected. This behavior of the class 2 mutants indicates that different photoreceptors mediate phototropism in far‐UV and in near‐UVhlue light. The photogravitropic action spectra for two class 2 mutants with defects in genes mad F and mad J display distortions between 342 and 530 nm and a bathochromic shift relative to the action spectrum of the wild type. These features indicate that the mad F and mad J mutants are affected at the level of the blue‐light photoreceptor system. As an implication we infer that an intact near‐UVhlue‐light photoreceptor system is required even in darkness for negative gravitropism, the ethylene response and autochemotropism. In Phycomyces , signal integration occurs, at least in part, at the level of the near‐U Vhlue‐light photoreceptor system.