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 formation, tryptophan hydroxylase, exhibits a high-amplitude circadian rhythm with a maximum during photophase. Hydroxyindole-O-methyltransferase shows a biphasic pattern with a major maximum during scotophase. 5-Methoxylated 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 increases of melatonin, up to more than 50 ng/mg protein. This effect may explain why a lower temperature sensitizes this organism to photoperiodic, indoleamine-mediated induction of asexual cysts. Melatonin can be catabolized either enzymatically or non-enzymatically. The non-enzymatic pathway involves free radicals, e.g., photooxidant cation radicals, and leads to the formation of N1-acetyl-N2- 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 mediator of the encystment response. It opens proton channels in the membrane of an intracellular acidic vacuole system which is loaded by the action of a V-type ATPase, as shown by experiments using bafilomycin A1.
Hardeland
R
R
Zoologisches Institut, Universitaet Goettingen, Germany.
Fuhrberg
B
B
Uría
H
H
Behrmann
G
G
Meyer
T J
TJ
Burkhardt
S
S
Poeggeler
B
B
D008735:5-Methoxytryptamine / Q000378:metabolism; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D004141:Dinoflagellida / Q000378:metabolism / Q000502:physiology*; D008163:Luminescent Measurements; D008550:Melatonin / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D013696:Temperature; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
D008735:5-Methoxytryptamine; D014365:Tryptophan Hydroxylase; D008550:Melatonin