title: Circadian photosynthetic reductant flow in the dinoflagellate Lingulodinium is limited by carbon availability.
abstract: Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide a selective advantage to cells adapted to daily light/dark cycles. However, the biochemical links between the clock and the overt rhythms in cell physiology are generally not known. Here, we examine the circadian rhythm in O₂ evolution by cultures of the dinoflagellate Lingulodinium, a rhythm previously ascribed to rhythmic electron flow through photosystem II. We find that O₂ evolution rates increase when CO₂ concentrations are increased, either following addition of DIC or a rapid decrease in culture pH. In medium containing only nitrate as an electron acceptor, O₂ evolution rates mirror the circadian rhythm of nitrate reductase activity in the cells. Furthermore, competition between photosynthetic electron flow to carbon and to nitrate varies in its relative efficiency through the day-night cycle. We also find, using simultaneous and continuous monitoring of pH and O₂ evolution rates over several days, that while culture pH is normally rhythmic, circadian changes in rates of O₂ evolution depend not on the external pH but on levels of internal electron acceptors. We propose that the photosynthetic electron transport rhythm in Lingulodinium is driven by the availability of a reductant sink.
authors.affiliation: Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, 4101 Sherbrooke est, Montréal, Québec H1X2B2, Canada.
authors.forename: Tyler D B
authors.initials: TD
authors.lastname: Mackenzie
authors.forename: David
authors.initials: D
authors.lastname: Morse
mesh_terms: D001683:Biological Clocks / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D004141:Dinoflagellida / Q000502:physiology*; D004579:Electron Transport / Q000502:physiology; D009566:Nitrates / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D017440:Photoperiod; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D019163:Reducing Agents / Q000378:metabolism*
chemical_list: D009566:Nitrates; D045332:Photosystem II Protein Complex; D019163:Reducing Agents; D002245:Carbon Dioxide; D010100:Oxygen