Low molecular-weight factor from Plesiastrea versipora (Scleractinia) that modifies release and glycerol metabolism of isolated symbiotic algae

Abstract

When symbiotic dinoflagellate algae (Symbiodinium sp., isolated from the coral Plesiastrea versipora) were incubated with NaH14CO3 in the light in seawater, they released 22.69±9.16 nmol carbon/106 algae. Release of photosynthetically fixed carbon was stimulated more than six-fold for algae incubated in host-tissue homogenate (148.54±97.03 nmol C/106 algae) and more than four-fold (102.00±49.16 nmol C/106 algae) for algae incubated in a low molecular weight fraction (≤1 000 M r ) prepared from host homogenate. Soluble released 14C-labelled products, as determined by chromatography and autoradiography, were the same when algae were incubated in either host homogenate or the low molecular weight fraction. After 4 h incubation in the light (300 mol photons m−2 s−1),␣intracellular␣glycerol increased in algae incubated with the low molecular weight fraction (an increase of 0.39 to␣0.67 nmol glycerol/106 algae) compared with little or no increase in algae incubated in seawater (0 to 0.12 nmol glycerol/106 algae). Partial inhibition of triglyceride synthesis (up to 51%) was also observed when algae were incubated in the low molecular weight fraction. All these effects are the same as those observed when algae were incubated in host homogenate. These data indicate that the “host release-factor” activity of P.␣versipora is a compound of low molecular weight.