Light is a crucial signal for zoosporogenesis and gametogenesis in some green microalgae

Patterns of reproduction were investigated in some microalgal species of Chlorophyceae (Botryosphaerella sudetica, Neochloris aquatica, Neochloris vigensis, Bracteacoccus minor). Under continuous light, the microalgae reproduced asexually producing autospores. However, appropriate manipulation of external conditions led to a change in the reproduction pattern towards production of zoospores or gametes. Production of zoospores and gametes was inhibited by light; motile cells emerged when microalgae were cultivated in darkness. The period of dark treatment necessary for zoosporogenesis or gametogenesis differed substantially among species that were tested. Sexual reproduction was observed in Neochloris vigensis and Bracteacoccus minor, whose generative life cycle had not been previously reported. The morphology of motile cells, the mode of sexual reproduction, and the efficiency of both the production of motile stages and mating events, were investigated. In order to gain detailed insights into patterns of reproduction, Botryosphaerella sudetica was selected for investigation under different light treatments. Non-actinic red light applied in the early phase of dark cultivation (up to 2 h) suppressed both zoosporogenesis and gametogenesis. However, after a 3-h dark pre-treatment, red light treatment had no effect on zoosporogenesis or gametogenesis. In contrast, non-actinic blue light did not block zoosporogenesis or gametogenesis, regardless of the time of treatment. The possible role of a red-light photoreceptor in zoosporogenesis and gametogenesis is discussed.