A POSSIBLE CONTROL BY A PHYTOCHROME-LIKE PHOTORECEPTOR OF CHLOROPHYLL SYNTHESIS IN THE GREEN ALGA Ulva rigida

Chlorophyll synthesis is stimulated by red light pulses in the green alga Ulva rigida C. Aghard. Chlorophyll synthesis in darkness is greater after longer red light pulses (30 min) than after shorter red light pulses (5 min). Chlorophyll synthesis was higher after red light pulses of 14 Wm_-2 fluence rate than after those of 7 Wm_-2. The effect of red light showed some far-red reversibility. The reversion by far-red light was higher after red light pulses of 4 min than after those of 30 min. These results indicate the existence of a rapid induction of chlorophyll synthesis during the red light pulses and a fast escape from photoreversibility. The percentage of reversion is also affected by the fluence rate of the light pulses. The reversion was reduced by about 15% when the photon fluence rate was increased from 7 to 14 Wm_-2. Reversion was also observed when red and far-red light pulses were applied successively. Thus, phytochrome or a phytochrome-like photoreceptor could be involved in the induction of chlorophyll synthesis in Ulva rigida.