Photoperiodism and Effects of Indoleamines in a Unicellular Alga, Gonyaulax polyedra

Abstract

Mediation of photoperiodic effects by indoleamines, especially melatonin, is known in higher vertebrates. A similar mechanism may occur in a unicellular alga, the dinoflagellate Gonyaulax polyedra. This organism entered the dormant stage of a cyst upon short-day treatment at lowered temperatures. Interruption of darkness by 2 hours of light prevented cyst formation, even when the overall duration of light was the same as in cyst-inducing short days. When given in a noninducing photoperiod, melatonin and an analog, 5-methoxytryptamine, substances that had previously been shown to occur in Gonyaulax, provoked cyst formation. Methoxylated indoleamines may play a role as mediators of darkness in this unicellular, in a similar way as in vertebrates, suggesting a common biochemical basis of photoperiodism.

Temperature and daylength regulate encystment in calcareous cyst-forming dinoflagellates

“…Short-day photoperiodic responses are inhibited by a light-break during the dark phase (Dring 1984), and our results with S. rotunda confirm that cyst formation may be regulated by a photoperiodic-sensitive mechanism. Daylength has been shown to govern shifts from the motile flagellate stage to a temporary cyst in the dinoflagellate Lingulodinium polyedrum (= Gonyaulax polyedra) (Balzer & Hardeland 1991), and development and life history phase of macroalgae change depending on daylength (Dring 1984(Dring , 1988. Daylength has been shown to influence sexual reproduction of the diatom Pseudo-nitzschia multiseries, for which a positive correlation was found between gamete production and hours of light exposure per 24 h (Hiltz et al 2000).…”

“…This reflects the existence of species-specific temperature windows under which encystment can occur, which are more restricted than the temperature ranges for vegetative reproduction (Anderson et al 1984(Anderson et al , 1985. In Lingulodinium polyedrum, the shift from motile cells to temporary cysts is under strict photoperiodic control at 15°C, while no cysts are formed at 20°C (Balzer & Hardeland 1991). Temperature may thus block or modify the response to daylength, and examples of restricted temperature windows for photoperiodic responses can be found in macroalgae (Dring 1984) and higher plants.…”

Melatonin Metabolism in the Central Nervous System

“…It may be noted that this is not generally the case in the living world. In dinoflagellates, 5-MT is a much more powerful agent than melatonin [7,45]. Beyond the specific melatonin deacetylases found in retinas and pineals, the role of other AAAs has remained unclear.…”

Melatonin and 5-methoxytryptamine in non-metazoans

“…Since 5MT is much more efficient as a regulator of various functions, for example as an inducer of asexual cysts, as a stimulator of bioluminescence and cytoplasmic acidification [2,3,13,14,17], the question remains as to whether all the other actions are not also due to 5MT. Recent findings in Crypthecodinium cohnii [38,39], showing increases in calcium influx and in the formation of inositol phosphates, are affected by the problem that, apart from the extremely high concentrations required, the dose-responses to melatonin and 5MT are relatively similar, despite the strong difference in cyst-inducing efficiency.…”

“…[38,39]). Moreover, the effects can be conditional, as in Gonyaulax polyedra, in which the encystment response occurs only at a lower temperature [2,13,14]; such a treatment leads to enormous accumulations of melatonin anyway (transiently more than 1 mM) and finally to high concentrations of 5-methoxytryptamine (= 5MT) [ 12,15].…”