CHRONOBIOLOGY OF INDOLEAMINES IN THE DINOFLAGELLATE GONYAULAX-POLYEDRA - METABOLISM AND EFFECTS RELATED TO CIRCADIAN RHYTHMICITY AND PHOTOPERIODISM

The marine bioluminescent dinoflagellate Gonyaulax polyedra is capable of producing various indoleamines. The first enzyme in their formatio n, tryptophan hydroxylase, exhibits a high-amplitude circadian rhythm with a maximum during photophase. Hydroxyindole-O-methyltransferase sh ows a biphasic pattern with a major maximum during scotophase. 5-Metho xylated indoleamines, such as melatonin and 5-methoxytryptamine, peak at the beginning and in the second half of scotophase, respectively. A drop in temperature from 20 to 15 degrees C leads to dramatic increas es of melatonin, up to more than 50 ng/mg protein. This effect may exp lain why a lower temperature sensitizes this organism to photoperiodic , indoleamine-mediated induction of asexual cysts. Melatonin can be ca tabolized either enzymatically or non-enzymatically. The non-enzymatic pathway involves free radicals, e.g.,photooxidant cation radicals, an d leads to the formation of N-1- acetyl-N-2-formyl-5-methoxykynuramine . Enzymatic catabolism comprises deacetylation to 5-methoxytryptamine and formation of 5-methoxytryptophol. 5-Methoxytryptamine represents a key substance acting as a stimulator of bioluminescence and a mediato r of the encystment response. It opens proton channels in the membrane of an intracellular acidic vacuole system which is loaded by the acti on of a V-type ATPase, as shown by experiments using bafilomycin A(1).