ENDOGENOUS SUBSTRATE FOR ENERGY-METABOLISM AND ULTRASTRUCTURAL CORRELATES IN SPERMATOZOA OF THE SEA-URCHIN DIADEMA-SETOSUM

Energy metabolism in spermatozoa of the sea urchin Diadema setosum of the order Diadematoida was examined. The spermatozoa contained not onl y several kinds of phospholipids and cholesterol, but also triglycerid e (TG). Glycogen and glucose were present at extremely low levels. Fol lowing dilution of dry sperm and incubation in seawater, the TG conten t decreased rapidly. Other lipids, however, remained at constant level s, except for a slight increase in the level of free fatty acid. High lipase activity was demonstrated in the spermatozoa. C-14-labeled fatt y acid was oxidized to (CO2)-C-14. Ultrastructural study also showed t hat lipid globules were present at the bottom of the midpiece. After i ncubation in seawater, morphological changes in the lipid globules wer e observed and some vacuoles appeared. Thus, the results obtained stro ngly suggest that D. setosum spermatozoa obtain energy through oxidati on of fatty acid from TG stored in the lipid globules at the midpieces . (C) 1995 Wiley-Liss, Inc.