Fluorescent protein content and stress tolerance of two color morphs of the coral Galaxea fascicularis

Fluorescent proteins in corals have been re­ ported to have photoprotective function for algal sym­ bionts, though it remains controversial whether the coral fluorescent proteins are actually photoprotective. Green (Gs) and brown (B) morphs of the coral Galaxea fascicularis have different contents of green fluorescent protein (GFP). To understand the function of GFP in the stress responses of the coral, we exposed polyps isolated from B and Gs morph colonies to medium or strong light (200 and 1000 μmol quanta ms) at 26 or 32°C for 6 h. Polyps were then allowed to recover for 6 h under dim light. Although the GFP content was markedly different between Gs and B morphs, in hospite zooxanthellae in polyps of both morphs showed similar decreases in photochemical efficiency (Fv /Fm) after strong light treat­ ment at normal or high temperature. Isolated zooxanthellae of both morphs showed similar decrease in the photo­ chemical efficiency under light stress, indicating that they had similar tolerance to light stress. The present results suggest that fluorescent protein does not increase the tolerance of polyps to strong light and high temperature stress in G. fascicularis and that further studies are nec­ essary to elucidate the function of GFP in this coral.