LOW-MOLECULAR-WEIGHT FACTOR FROM PLESIASTREA-VERSIPORA (SCLERACTINIA)THAT MODIFIES RELEASE AND GLYCEROL METABOLISM OF ISOLATED SYMBIOTIC ALGAE

When symbiotic dinoflagellate algae (Symbiodinium sp., isolated from t he coral Plesiastrea versipora) were incubated with (NaHCO3)-C-14 in t he light in seawater, they released 22.69 +/- 9.16 nmol carbon/10(6) a lgae. Release of photosynthetically fixed carbon was stimulated more t han six-fold for algae incubated in host-tissue homogenate (148.54 +/- 97.03 nmol C/10(6) algae) and more than four-fold (102.00 +/- 49.16 n mol C/10(6) algae) for algae incubated in a low molecular weight fract ion (less than or equal to 1 000 M-r) prepared from host homogenate. S oluble released C-14-labelled products, as determined by chromatograph y and autoradiography, were the same when algae were incubated in eith er host homogenate or the low molecular weight fraction. After 4 h inc ubation in the light (300 mu mol photons m(-2) s(-1)), intracellular g lycerol increased in algae incubated with the low molecular weight fra ction (an increase of 0.39 to 0.67 nmol glycerol/10(6) algae) compared with little or no increase in algae incubated in seawater (0 to 0.12 nmol glycerol/10(6) algae). Partial inhibition of triglyceride synthes is (up to 51%) was also observed when algae were incubated in the low molecular weight fraction. All these effects are the same as those obs erved when algae were incubated in host homogenate. These data indicat e that the ''host release-factor'' activity of P. versipora is a compo und of low molecular weight.