PIGMENT GRANULES AND HYPERICIN-LIKE FLUORESCENCE IN THE MARINE CILIATE FABREA-SALINA

Fabrea salina is a light-sensitive marine ciliate, which shows positiv e phototaxis and photophobic step-down response. It belongs to the ord er Heterosrichida, like Blepharisma japonicum and Stentor coeruleus, b ut, differently from those, it appears colorless when observed under t he optical microscope. Living F. salina cells do not significantly flu oresce, but a fluorescence, similar to that observed in the fresh-wate r ciliate B. japonicum, becomes easily detectable when the cells are d ead or severely damaged by chemical or physical treatments. This evide nce suggests that F. salina might contain an endogenous pigment, proba bly belonging to the class of hypericins. In the case of B. japonicum, this pigment is localized in pigment granules preferentially located close to the cell membrane. The ultrastructural studies reported here reveal that also F. salina contains membranated pigment granules very similar with respect to localization, size and appearance to the pigme nt granules described in B. japonicum. An approximate evaluation shows that the relative density of these granules in F. salina is much lowe r than in B. japonicum, which may account for the apparent colorless o f F. salina. Absorption and emission fluorometric measurements of soni cated samples of cells show that the florescence of the endogenous pig ment of F. sabina is very similar to that of a hypericin-like pigment, From these results we can draw the preliminary conclusion that F. sal ina contains a small amount of a hypericin-like pigment, organized in membranated granules. The role of such pigment in the photoreceptive p rocesses is still an open problem.