Photoreception and sensory transduction will be investigated for two blue- light responses of the unicellular sporangiophore of the fungus Phycomyces. Both phototropism and the light-growth response occur over an absolute operating range of 10 decades in light intensity from 10-9 to 10 W m-2. This range and the associated adaptation phenomena are similar to those that occur in visual receptor cells. The long term objective of the proposed research is to understand the processes by which a light stimulus is transduced into a cellular response, particularly in organisms with specific blue-light sensitivity associated with flavin chromophores. In Phycomyces, a model organism, genetic and physiological approaches can be effectively combined. Action spectra for phototropism and the light-growth response will be measured in different intensity ranges to characterize the low and high intensity photosystems of the sporangiophore. Phototropism action spectra will be obtained with continuous and pulsed light protocols. Experiments on kinetics of phototropism will be recorded with time-lapse video equipment and analyzed with the aid of an tracking machine using a novel method. The results will be compared with phototropic balance spectra to determine how each of the blue-light responses uses the components of the photoreceptor system. The recently discovered dependence of dark adaptation on dim, subliminal light will be pursued to help establish which photoreceptor mediates this effect, which is sensitive to green and red as well as blue light. System-identification experiments on the light-growth response will be continued on the tracking machine with Gaussian white noise and sum-of-sinusoids test stimuli to measure the dynamic and nonlinear aspects of this response. These experiments will involve both wild-type and mutant strains, and will be interpreted with analytical models for the kinetics of the photosensory transduction chain. A new theory, developed elsewhere, concerning light distribution around a sporangiophore will be tested experimentally by recording the azimuthal light pattern around a sporangiophore illuminated with a horizontal laser beam. This theory is important for interpretation of phototropism action spectra and is fundamental for theories of phototropism. Finally, cellular physiology methods will be applied to sporangiophores and protoplasts. Effector substances and indicator dyes will be introduced by direct uptake, injection, and electroporation; modified blue-light responses and effects will be monitored in preparations from wild type and mutant strains. These approaches are directed towards identifying molecular components and pathways associated with the blue light responses of Phycomyces.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Visual Sciences B Study Section (VISB)
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Syracuse University
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Chen, X Y; Xiong, Y Q; Lipson, E D (1993) Action spectrum for subliminal light control of adaptation in Phycomyces phototropism. Photochem Photobiol 58:425-31
Sineshchekov, A V; Lipson, E D (1992) Effect of calcium on dark adaptation in Phycomyces phototropism. Photochem Photobiol 56:667-75
Ensminger, P A; Lipson, E D (1991) Action spectra of the light-growth response in three behavioral mutants of Phycomyces. Planta 184:506-9
Ensminger, P A; Chen, X Y; Lipson, E D (1990) Action spectra for photogravitropism of Phycomyces wild type and three behavioral mutants (L150, L152, and L154). Photochem Photobiol 51:681-7
Palit, A; Pratap, P R; Lipson, E D (1989) System analysis of Phycomyces light-growth response: madC, madG, and madH mutants. Biophys J 55:519-26
Palit, A; Lipson, E D (1989) System analysis of Phycomyces light-growth response in single and double night-blind mutants. Biol Cybern 60:385-93
Galland, P; Corrochano, L M; Lipson, E D (1989) Subliminal light control of dark adaptation kinetics in Phycomyces phototropism. Photochem Photobiol 49:485-91
Galland, P; Orejas, M; Lipson, E D (1989) Light-controlled adaptation kinetics in Phycomyces: evidence for a novel yellow-light absorbing pigment. Photochem Photobiol 49:493-9
Lipson, E; Pratap, P (1988) System analysis of Phycomyces light-growth response with Gaussian white noise and sum-of-sinusoids test stimuli. Ann Biomed Eng 16:95-109
Galland, P; Lipson, E D (1987) Blue-light reception in Phycomyces phototropism: evidence for two photosystems operating in low- and high-intensity ranges. Proc Natl Acad Sci U S A 84:104-8

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