CAROTENOIDS IN MOLLUSCA - APPROACHING THE FUNCTIONS

Carotenoids in eight species of freshwater and sea mollusks were inves tigated. In the nonreproductive organs of all species, only all-trans C-40-xanthophylls were found. Carotenes are limited to hepatopancreas. No carotenoid derivatives or carotenoids with <10 conjugated double b onds were detected. Carotenoids in molluskan cells are present in ail subcellular fractions; the major part of them is located in plasma mem brane. There are no special carotenoid-containing pigmented granules ( ''cytosomes,'' ''carotenoxysomes'') in molluskan cells. Comparison of both Raman and absorption spectra of carotenoids in situ with those in CHCl3 suggests that pigments are dissolved in lipid matrix of membran es and not bound to proteins. No changes of carotenoid content or caro tenoid pattern in Dreissena polymorpha, Unio pictorum and Viviparus co ntectus were observed during 10 days of starvation. There were no chan ges in isolated gills within 2 days as well. In the freshwater species with the exception of D. polymorpha, carotenoid content changes after the fast water temperature changes: with elevation of temperature, th e carotenoid content in organs increases and vice versa, without any c hange in carotenoid composition. This phenomenon is shown to be due to rearrangement of pigments between the hepatopancreas and other organs . The results suggest that the role of carotenoids in molluskan tissue s is not connected with their chemical transformations. The most proba ble function of carotenoids in mollusks is the stabilisation of cell m embranes' fluidity.