Characterization of Photosynthetic Rhythms in Marine Dinoflagellates

Abstract

Using data from light-dark cultures of Gonyaulaxpolyedra entrained to a 24-hour cyde, whole ceUi absorption curves and photosynthesishrradiance curves were constructed for various circadian times. While whole celi absorbance and half-satuntion constants of photosynthesis showed no statisticd difference that could be directly related to the photosynthetic rhythm, the initid slope of the photosynthesis-irradiance curve was a time-dependent parameter which altered in direct proportion to the change in photosynthetic capadty. The results indicated a temporal change in the relative quantum yield of photosynthesis, and the circadian rhythmicity of light-limited photosynthesis was establisbed under constant conditions. Circadian rhythmidty was detected in room temperature chlorophyil fluorescence yield. Low temperature fluorescence kinetics also showed fluctuations. The results suggest that regulation of photosynthesis by the biological dock of Gonyaulax may be mediated through the membrane-bound light reactions and a partial explanation of the underlying mechanism is proposed.Once one accepts the idea that photosynthesis can be regulated by a biological clock, the question is how is the overt rhythm in photosynthetic capacity mediated. Photosynthesis could be regulated either through the membrane-bound light reactions and/or through the more loosely membrane-associated dark reactions involved in CO2 fixation. Observations of conformational changes in chloroplast shape or thylakoid orientation (9, 23), periodicity in shapes of photosynthesis-irradiance curves (16)(17)(18)22), lack of periodicity in dark reaction enzyme activity (3,8), and periodicity in the activity of the photosystems (16,17), have led some workers to suggest that the circadian oscillator regulates photosynthesis through some modifying interaction with the photosystems imbedded in the thylakoid membrane. In contrast, the reported periodicity in glyceraldehyde 3-P-dehydrogenase in Euglena and the lack of periodicity in the relative quantum yield of photosynthesis observed in photosynthesisirradiance curves have been cited by workers who favor mediation by the circadian oscillator through the dark reactions of photosynthesis (25).The difficulty in trying to make an independent interpretation of the results from several of these studies lies in their experimental design. Often only synchronized cultures entrained to light-dark cycles have been used to look for rhythmicity in photosynthetic parameters other than photosynthetic capacity 1 This investigation was supported by National Science Foundation Grant BMS 72-02221A03. (3,(16)(17)(18)25). In these cases, it is difficult to discern whether the observed rhythmicity is derived from a circadian oscillation or the cell division cycle. Similarly, the observation of a diurnal periodicity in a light-dark cycle is not sufficient to demonstrate control by a biological clock. Rather, the rhythmicity of a cell parameter must also free run under constant conditions, be independent of cell division, and hav...

Temporal and spatial variability of photosynthetic parameters and community respiration in Long Island Sound

“…High measurements of α B have also been observed in other studies , Malone & Neale 1981, Kelly & Doering 1997 contrasts with that reported in diel (MacCaull & Platt 1977, Prézelin & Sweeney 1977, daily (Cote & Platt 1983) and seasonal ) P-I studies, where range factors of α B were similar to or less than P B m . In those studies, however, P-I parameters did not necessarily correlate temporally, as was observed in the present study.…”

Environmental forcing versus endogenous control of photosynthesis in intertidal epilithic microalgae

“…The perpetuation of the weak circadian cycle observed in situ under constant conditions was proof of an endogenous control of the photosynthetic response of the microalgae (Prezelin & Sweeney 1977). Thus, during neap tide, when the stress of semidiurnal exposure is absent, the circadian variations in the photosynthetic response of epilithic microalgae are, at least in part, regulated by endogenous phasing.…”

"What watch? ... such much!"* Complexity and evolution of circadian clocks

“…The other light input pathway responds both to red and blue light, possibly sharing pigments with the photosynthesis machinery. Pharmacological inhibition of photosynthesis affects the Gonyaulax circadian system (Johnson and Hastings 1989;Roenneberg 1994), and photosynthesis is itself an output of the clock (Prezelin and Sweeney 1977;Sweeney 1986). Thus, it represents a metabolic feedback loop.…”