EFFECTS OF FREE AMINO-ACIDS ON THE ISOLATED SYMBIOTIC ALGAE OF THE CORAL PLESIASTREA-VERSIPORA (LAMARCK) - ABSENCE OF A HOST RELEASE FACTORRESPONSE

Symbiotic algae incubated in host tissue homogenate of the coral Plesi astrea versipora for 2 h in the light released at least four and a hal f times as much photosynthetically fixed carbon (range 13.8 +/- 3.1 to 158 +/- 9.5 nmol C/10(6) algae) as algae incubated in seawater (range 1.4 +/- 0.3 to 10.8 +/- 0.6 nmol C/10(6) algae) indicating the presen ce of 'host release factor'. When algae were incubated in a low molecu lar weight fraction of homogenate containing partially purified 'host release factor' they also released more carbon (range 62.2 +/- 3.7 to 279 +/- 11.4 nmol C/10(6) algae) than algae incubated in seawater. Thi s low molecular weight fraction contained free amino acids. We tested the hypothesis that the free amino acids in this fraction were respons ible for 'host release factor' activity. Algae incubated in a mixture of free amino acids equivalent to those found in this fraction, releas ed more fixed carbon (range 2.4 +/- 0.3 to 25.2 +/- 0.2 nmol C/10(6) a lgae) than algae incubated in seawater but in each experiment, release was much lower than when algae were incubated in host tissue homogena te. These data indicate that the stimulation of release of photosynthe tically fixed carbon from the symbiotic algae of Plesiastrea versipora incubated in partially purified host release factor is not primarily due to the presence of free amino acids. We are continuing further stu dies to determine the exact nature of the active compound. (C) 1998 El sevier Science Inc. All rights reserved.