METABOLITE INACTIVATION OF PHOTOSYSTEM-II IN CHLORELLA - COMPARISON OF STARCH-ACCUMULATING AND LIPID-ACCUMULATING STRAINS

Photosystem II was inactivated in Chlorella under conditions of nitro ren deficiency during either heterotrophic growth of algae on glucose or dark incubation at supraoptimal temperatures (40-42 degrees C). Ina ctivation manifested itself as a decrease in the relative yield of var iable chlorophyll fluorescence (F-v/F-m), The decline in variable fluo rescence was examined in two strains of Chlorella pyrenoidosa differin g in the composition and location of their assimilates stored upon nit rogen starvation. In strain CALU-175, which accumulates starch in the chloroplasts as the major product, the F-v/F-m ratio was reduced from 0.7 to 0.15 under conditions of nitrogen starvation and to 0.3-0.35 in cells grown in darkness on glucose or incubated at 43 degrees C for 2 4 h. In strain IPPAS-S2, which accumulates lipids in the cytoplasm, va riable fluorescence was insignificantly reduced by nitrogen starvation . When grown heterotrophically on glucose or incubated in darkness at 43 degrees C, this strain exhibited only a slight decrease in the F-v/ F-m ratio. These results confirm the suggestion that, in all three tre atments, PS II inactivation is triggered by the accumulation of interm ediates of carbon metabolism in the chloroplasts.