MAINTENANCE OF MESOPHILIC STRAINS OF CHLOROCOCCALES ALGAE BY THE METHOD OF PERIODICAL SUBCULTURING AT LOWERED TEMPERATURE IN THE LIGHT OR IN DARKNESS

It was hypothesized earlier that the mesophilic strains of the Chloroc occales maintained in collections by periodical subculturing require a lowered temperature and darkness, as light is unfavorable for their v iability. To verify this hypothesis, 16 strains of algae, including th e genera Ankistrodesmus, Chlorella, and Scenedesmus from the order Chl orococcales, were analyzed. To estimate cell viability, the ratio of l iving to dead cells was counted after cells were stained with methylen e blue or erythrosine. In addition, the efficiency of photosystem II w as judged from the measurements of chlorophyll fluorescence (F-v/F-m). The value of F-v/F-m after 3-month maintenance in darkness was higher than after maintenance in the light for 15 of 16 studied strains. Reg ardless of light conditions during maintenance, the values of the para meters studied did not reflect species specificity. The decrease in ce ll viability after maintenance in the light apparently results from li ght inhibition of the photosynthetic apparatus when the pregrowing alg al cells are transferred to conditions of lowered temperature. An unfa vorable combination of light and temperature could affect the restorat ion of photosystem II during subsequent maintenance as well. Besides, drying cells under light on agarized media could also contribute to mo re drastic damage. We suggest that mesophilic strains of Chlorococcale s algae should be maintained at lowered temperature in darkness.