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.