CIRCADIAN REGULATION OF BIOLUMINESCENCE IN THE DINOFLAGELLATE PYROCYSTIS-LUNULA

In the unicellular algae Pyrocystis lunula Schutt and Gonyaulax polyed ra Stein, bioluminescence and its circadian regulation are similar in several respects, but there are also several important differences. As in G. polyedra, P. lunula emits light both as bright flashes and as a low intensity glow. At 20-degrees-C, the individual flashes are consi derably brighter than in G. polyedra, and their durations are typicall y less than 500 ms. Both species show a circadian rhythm in the freque ncy of spontaneous flashes, which peaks in the night-phase under light -dark cycles and continues in both continuous light and dark. However, compared to G. polyedra, the circadian system in P. lunula is more se nsitive to light. 10 min exposures (500 mumol.m-2.s-1 white light) can shift the phase of the rhythm by more than 8 h, and rhythmicity is co mpletely suppressed at an irradiance above 20 mumol.M-2.S-1, where the G. polyedra rhythym persists for weeks. Like G. polyedra, period leng th increases with increasing irradiance of continuous red light but de creases with increasing intensity Of continuous blue light. The glow i n P. lunula differs markedly from that in G. polyedra in that it occur s at about the same intensity at all times during the circadian cycle; thus, it is not under circadian control but may fluctuate 5-10-fold i n intensity within a time frame of seconds. This suggests that the glo w may differ in its physiological basis in the two organisms. The resu lts also indicate that the circadian regulation of luciferase activity differs in the two species. In G. polyedra, the organelle responsible for bioluminescence and luciferase is lost and then reformed on a dai ly basis; in P. lunula, the luciferase is conserved and localized else where during the nonbioluminescent phase of the cycle.