ON THE PLEIOTROPY OF INDOLEAMINE ACTIONS IN A DINOFLAGELLATE, GONYAULAX-POLYEDRA - COMPARISON OF 5-METHOXYTRYPTAMINE WITH 5-FLUOROTRYPTAMINES AND 6-FLUOROTRYPTAMINES

In Gonyaulax polyedra, 5-methoxytryptamine (5-MT), 5-fluorotryptamine (5-FT) and 6-fluoro-tryptamine (6-FT) are similarly potent stimulators of bioluminescence. When given in long-days (light/dark cycle of 16:8 hr), 5-methoxytryptamine is a strong inducer of cyst formation, leading to complete encystment of the entire cell population down to concentrations of 5 x 10(-6) M, whereas 5- and 6-fluorotryptamines only elicit incomplete encystment, especially with regard to the capability of the individual cells to form cyst walls (5-FT: about one half of cells; 6-FT: maximally 1/5); the fluorotryptamines lead, however, to an immobilization of cells and retractions of the protoplast from the theca (6-FT greater-than-or-equal-to 5 x 10(-6) M; 5-FT greater-than-or-equal-to 10(-5) M). Gonyaulax extracts catalyse photo-oxidation of the three indoleamines: 5-MT leads to an accumulation of the homologous 5-methoylated kynuramine, whereas only minor amounts of fluorinated kynuramines were obtained. In a superoxide anion-generating system, 5-MT and 5-FT are predominantly oxidized to substituted kynuramines; 6-FT undergoes the homologous reaction, but is further converted into a non-fluorescent product.