High-and low-intensity photosystems inPhycomycesphototropism: Effects of mutations in genesmadA, madB, andmadC

✍ Scribed by A. Palit; P. Galland; E. D. Lipson

• Book ID: 104753158
• Publisher: Springer-Verlag
• Year: 1989
• Tongue: English
• Weight: 675 KB
• Volume: 177
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00392623

✦ Synopsis

Sporangiophores of Phycomyces blakesleeanus Burgeff that have been grown in darkness and are then suddenly exposed to unilateral light show a two-step bending response rather than a smooth, monotonic response found in light-adapted specimens (Galland and Lipson, 1987, Proc. Natl. Acad. Sci. USA 84, 104-108). The stepwise bending is controlled by two photosystems optimized for the low-and high-intensity ranges. These two photosystems have now been studied in phototropism mutants with defects in genes madA, madB, and madC. All three mutations raise the threshold of the low-intensity (low-fluence) photosystem by about 10(6)-fold and that of the high-intensity (high-fluence) system by about 10(3)-fold. Estimates for the light-adaptation time constants of the low-and high-intensity photosystems show that the mutants are affected in adaptation. In the mutants, the light-adaptation kinetics are only slightly affected in the low-intensity photosystem but, for the high-intensity photosystem, the kinetics are considerably slower than in the wild type.