EFFECTS OF HOST-TISSUE HOMOGENATE OF THE SCLERACTINIAN CORAL PLESIASTREA-VERSIPORA ON GLYCEROL METABOLISM IN ISOLATED SYMBIOTIC DINOFLAGELLATES

Symbiotic dinoflagellate algae (Symbiodinium sp.) isolated from the sc leractinian coral Plesiastrea versipora and incubated in homogenized h ost tissue released 4 to 7 times as much glycerol (14 to 46 nmol glyce rol/10(6) algae) as those incubated in seawater (3 to 6 nmol glycerol/ 10(6) algae) after 4 h incubation in the light. During this period, no release of triglycerides was detected. Intracellular glycerol increas ed 2- to 3-fold in algae incubated in host homogenate, but remained un changed in algae incubated in seawater at a concentration of 0.82 +/- 0.47 nmol glycerol/10(6) algae. In each incubation condition, intracel lular triglyceride levels increased. However, in algae incubated in ho st homogenate, the intracellular levels of triglycerides reached only about 75% of the amount reached in algae incubated in seawater (max. 1 8.55 +/- 2.40 nmol glycerol/10(6) cells). Host homogenate did not stim ulate the release of glycerol from algae during dark incubation. These data show that the glycerol released by algae incubated in host-tissu e homogenate was derived from increased synthesis of glycerol or from diversion of some glycerol or other photosynthetic intermediates from incorporation into algal triglyceride stores, and did not come from ex isting stores.