ULTRASTRUCTURAL-STUDY OF ENDOGENOUS ENERGY SUBSTRATES IN SPERMATOZOA OF THE SEA-URCHINS ARBACIA-LIXULA AND PARACENTROTUS-LIVIDUS

Spermatozoa of the sea urchins, Arbacia lixula and Paracentrotus livid us, use endogenous triglyceride (TG) and phosphatidylcholine (PC), res pectively, to produce energy for swimming. The present study examined ultrastructurally the location of TG and PC available for utilization in energy metabolism in spermatozoa of these species. The A. lixula sp ermatozoon contained several lipid globules in the midpiece proximally from the head. After incubation with seawater, TG levels decreased an d morphological changes in the lipid globules were observed. Some lipi d globules lost their smooth spherical shape, and their surface became irregular and uneven. Vacuoles of various sizes and forms also appear ed near the lipid globules. In contrast, P. lividus spermatozoa posses sed lipid bodies, instead of lipid globules, in the space between the mitochondrial outer and inner membranes. After incubation with seawate r, the lipid bodies became small and finally disappeared, coincident w ith a decrease in the level of PC. These results strongly suggest that TG and PC, as endogenous substrates providing energy for motility, ar e stored in the lipid globules of A. lixula spermatozoa and the lipid bodies of P. lividus spermatozoa, respectively.