This research is designed to test the effects of extended darkness on the photosynthetic competence of benthic and planktonic diatoms. Lagrangian models of estuarine light fields surrounding phytoplankton and benthic algae indicate that exposure to darkness for from 2 5 days is a common occurrence. Preliminary evidence indicates that there is considerable species variation in the physiological competence after several days of darkness but the factors accounting for these differences are unknown. Metabolic and physiological changes during extended darkness are hypothesized to alter the photosynthetic apparatus and the subsequently ability of the cell to respond to light. The research focuses on two time scales of photosynthetic regulation. The extended time scale of hours days will be studied using measurements of the change in photosynthetic components including photosynthetic and quenching pigments, ribulose1,5 bisphosphate carboxylaseloxygenase (Rubisco), carbohydrate and protein. Short time-scale (minutes) responses will be evaluated using measurements of the kinetics of photosynthetic induction and of Rubisco activation and deactivation. Short time scale experiments will be interpreted in the context of the ability of cells to withstand brief exposures to bright light subsequent to prolonged darkness. It is anticipated that this research will lead to a more relevant framework for interpreting fluctuating light effects in estuarine habitats than can be had without considering the physiological 'costs' of periodic confinement to darkness.
