Time course of oxygen evolution during photosynthesis in synchronized cultures of algae

Abstract

Oxygen evolution in synchronized cultures of Chlorella 7-11-05 was studied at several light intensities in Warburg s carbonate-bicarbonate buffer No. 9 as a suspending fluid. The initial rate and the time course of the gas exchange during photosynthetic experiments were found to vary with the developmental status of cells and, for cells in a given developmental stage, with light intensity. Generally, in younger cells the rate increased and in older cells it decreased with time. Both the upward and the downward trends for cells of a given age were enhanced by increasing light intensities. At a given light intensity the downward trend was intensified by progress in cell development. As a consequence, the increase in the rate in younger cells diminished with time and the decrease in the rate in older cells was intensified with time. The conclusion was drawn that the observed rate of gas exchange and its changes with time are the net results of a competition between the upward reaction and the downward reaction. The dependence of these reactions on the processes of building up and pulling down photosynthetic machinery and the connection of the rates of these processes with the anabolic and catabolic activity in the course of cell development are discussed.