Effect of vanadate on photosynthesis and the ATP/ADP ratio in low-CO-adapted Chlamydomonas reinhardtii cells.

We have assessed the effect of vanadate as an inhibitor of plasma-membrane ATPase on photosynthesis and the ATP/ADP ratio in Chlamydomonas reinhardtii CW-92 (a mutant strain lacking a cell wall). This effect was compared in low-CO-adapted cells grown in media bubbled with air containing 400 or 70 μL · L CO. Evidence is presented indicating that cells grown at 70 μL · L CO have a higher rate of photosynthetic O evolution than cells grown at 400 μL · L CO, at limiting carbon concentrations. Extracellular and intracellular carbonic-anhydrase activities were, however, similar in cells grown in both of the low-carbon conditions. Vanadate inhibited, to a different extent, the HCO-dependent O evolution in cells grown at 400 and 70 μL · L CO. At 400 μM vanadate, inhibition reached 70-75% in cells grown at 400 μL · L but only 50% in those grown at 70 μL · L CO. The ATP/ADP ratios determined with and without vanadate at limiting concentrations of dissolved inorganic carbon indicated that more ATP was hydrolysed in algae grown at 70 μL · L than in those grown at 400 μL · L CO. We conclude that the maximal capacity to accumulate dissolved inorganic carbon is inversely related to the CO concentration in the medium. Activation and - or synthesis of vanadate-sensitive ATPase may be the major explanation for the higher capacity for HCO-dependent O evolution in cells grown under limited CO concentrations. [ABSTRACT FROM AUTHOR]