NEUTRAL LIPIDS AS MAJOR STORAGE PRODUCTS IN ZOOSPORES OF THE GIANT-KELP MACROCYSTIS-PYRIFERA (PHAEOPHYCEAE)

Neutral lipids, consisting primarily of triacylglycerols, were found to be a major form of carbon reserve in zoospores of the giant kelp Macrocystis pyrifera (L.) C. Ag. The fluorescent stain Nile Red revealed large lipid droplets in the posterior end of the cell, which comprised 20-41% of cellular carbon in newly released spores. Flow cytometric analyses of newly released spores stained with Nile Red revealed considerable variation in the neutral lipid content among spores that was independent of spore size. Lipid droplets were consumed during germination in spores maintained either under constant light or in continual darkness. The availability of light appeared to delay, but did not preclude, lipid use. The rate of lipid use during germination varied considerably among germlings with some cells consuming all of their lipid reserves within 5 h after release. In addition to zoospores, lipid droplets were observed in both male and female gametes. Numerous droplets were observed in eggs, while single lipid droplets were observed in sperm. Neutral lipid droplets were not observed in gametophytes or sporophytes except in developing gametes and spores. Large lipid reserves thus seem to be confined to the microscopic life history stages that presumably have relatively high energy demands. By serving as a supplemental fuel reserve, neutral lipids may be important in extending the effective range of zoospore dispersal.