Sulfolipid Metabolism in Chlorella

When S-deficient cells of Chlorella cllipsoidea were incubated in radio-sulfate in light or in aerobic darkness for 1 hour, equal amounts of radioactivity were found in sulfolipid and glutathione but none was detected in sulfoquinovosyl glycerol which is one of the major S-compounds in this alga. No assimilation of radiosulfate was observed under anaerobic darkness.To elucidate the function of sulfolipid in algal cells uniformly (35)S-labeled Chlorella cells were transferred to S-deficient culture medium or unlabeled normal culture medium and the changes of radioactivity in sulfolipid and the related compounds were followed. A) On incubating (35)S-labeled algal cells in S-deficient medium under photosynthetic conditions, the amounts of radioactivity in sulfate, sulfoquinovosyl glycerol and sulfolipid decreased rapidly. B) When (35)S-labeled cells were cultured photoautotrophically in unlabeled medium, no decrease of radioactivity was observed in sulfoquinovosyl glycerol and sulfolipid. C) A decrease of (35)S-sulfolipid and an increase of (35)S-sulfoquinovosyl glycerol were observed when the uniformly (35)S-labeled algal cells were illuminated in CO(2)-free air.When S-deficient Chlorella cells were incubated in (35)S-sulfolipid under photosynthetic conditions, significant radioactivity was found in the insoluble fraction of the cells. A similar result was observed when normal Chlorella cells were incubated in (14)C-sulfolipid and CO(2)-free air.It is inferred from these observations that sulfolipid is a reservoir of sulfur and carbon compounds.In order to ascertain if the sulfolipid is involved in the mechanism of photosynthetic oxygen evolution, the rate of photosynthesis was measured during the incubation of (35)S-labeled cells in a S-deficient medium. Parallelism was not observed between the rate of photosynthetic activity and the decrease of sulfolipid.