LIGHT‐INDUCED ABSORBANCE CHANGES IN <i>PHYCOMYCES</i> PHOTOMUTANTS

Abstract

Abstract— Blue‐light‐induced absorbance changes indicating the reduction of a b ‐type cytochrome by a flavin photoreceptor have been reported elsewhere for Dictyostelium, Neurospora , and Phycomyces . On the basis of action spectra alone these absorbance changes were associated with the blue‐light physiological photoresponses in the latter two organisms. We have investigated phototropically abnormal mutants of Phycomyces in order to determine if there were common defects in blue‐light‐induced absorbance changes and photophysiology. However, mutants representing four genes, madA, madB, madC , and madE , the first two of which are associated with early steps in the sensory pathway, showed blue‐light‐induced absorbance changes identical to those in a phototropically normal strain. A pigment kinetics model, which was used to interpret dose‐response data, indicated a rather low quantum yield of 0.015 for the light‐induced absorbance changes. Similar blue‐light induced absorbance changes were observed in HeLa cells. These cells are derived from a human cervical carcinoma and are thus very unlikely to possess any natural photophysiology. Our results question the relevance of these blue‐light‐induced absorbance changes regarding the blue‐light receptor for physiological responses in various organisms.