PHYTOCHROME-A REGULATES RED-LIGHT INDUCTION OF PHOTOTROPIC ENHANCEMENT IN ARABIDOPSIS

Phytochrome A (phyA) and phytochrome 8 photoreceptors have distinct ro les in the regulation of plant growth and development. Studies using s pecific photomorphogenic mutants and transgenic plants overexpressing phytochrome have supported an evolving picture in which phyA and phyto chrome B are responsive to continuous far-red and red light, respectiv ely. Photomorphogenic mutants of Arabidopsis thaliana that had been se lected for their inability to respond to continuous irradiance conditi ons were tested for their ability to carry out red-light-induced enhan cement of phototropism, which is an inductive phytochrome response. We conclude that phyA is the primary photoreceptor regulating this respo nse and provide evidence suggesting that a common regulatory domain in the phyA polypeptide functions for both high-irradiance and inductive phytochrome responses.