Cultivation in the Dark of the Blue-green Alga Fremyella diplosiphon. A Photoreversible Effect of Green and Red Light on Growth Rate

The blue-green alga Fremyella diplosiphon Drouet can be grown in the dark on a medium consisting of mineral salts, glucose, and casein hydrolysate. A variety of organic substances was tested for effectiveness as a carbon or nitrogen source. The most effective individual compounds were glucose and citrulline, respectively. A daily irradiation of 5 min green light depresses the dark growth rate. The effect of green is reversible by brief irradiation with red light, and multiple photoreversibility was demonstrated. This green, red-reversible effect on dark growth rate may be related to other photomorphogenic responses to brief irradiation with green and red in the Cyanophyta. A master photoreversible pigment similar to phytochrome is a possible photoreceptor for these effects.