Interaction between Chloroplasts and Mitochondria in Microalgae: Role of Glycolysis.

In a mutant strain of Chlamydomonas reinhardtii devoid of active ribulose 1,5-bisphosphate carboxylase oxygenase, the addition of mitochondrial inhibitors in the dark resulted in a pronounced decrease in cellular ATP, a fall of the glucose 6-phosphate content, and a rise of the NADPH concentration. These biochemical changes were accompanied by an increase of the fluorescence level, showing changes in the redox state of the chloroplastic electron transport chain. Similar results were obtained in presence of an uncoupler. These data indicated that alterations in the mitochondrial electron transport chain in dark could affect the chloroplastic chain, probably through variations of the glycolysis activity. When mitochondrial oxidases were blocked, illumination of the algae reversed the effect of the inhibitors on the ATP and glucose 6-phosphate concentrations. This last result suggested that the chloroplastic photophosphorylations in these algae played a major role in the control of the glycolytic flux.