VALINE UPTAKE BY THE SCLERACTINIAN CORAL GALAXEA-FASCICULARIS - CHARACTERIZATION AND EFFECT OF LIGHT AND NUTRITIONAL-STATUS

The characteristics of valine uptake by isolated microcolonies of Gala xea fascicularis (Linnaeus 1758) were studied under various conditions including light, dark and feeding. The results demonstrated the prese nce of: (1) a linear component which might represent either a diffusio nal transport or a low-affinity carrier-mediated transport (apparent c arrier affinity > 250 mumol . l-1), and (2) a high-affinity active car rier-mediated transport (apparent carrier affinity about 5 mumol . l-1 ). The latter is mediated by two different systems: (i) a Na+-dependen t carrier, stimulated by light and operative in both fed and unfed pol yps, and (ii) a Na+-independent carrier, light insensitive and present only in unfed polyps. Competition experiments with other amino acids show that the Na+-dependent carrier is highly specific for neutral ami no acids, as indicated by the high inhibition constants of basic and a cidic amino acids. Our results suggest that the energy supplied by zoo xanthellae photosynthates is necessary for the process of amino acid u ptake, and that the Na+-dependent carrier responsible for valine uptak e by G. fascicularis is similar to the B0,+ system.