[Relations between carbonic anhydrase activity and uptake of HCO3 (-) and Cl (-) in photosynthesis by Scenedesmus obliquus].

Synchronized, young cells of Scenedesmus obliquus when adapted to air plus 1.5% CO2 have only about 1/20 of the carbonic anhydrase activity of air-adapted cells. At pH 9.2 (where HCO3 (-) is the prevailing form of inorganic carbon) such cultures do not evolve much O2 at 50·10(3) lux, in contrast to air-adapted cells. In contrast, at pH 5.8 (where CO2 prevails) there is not much difference in O2 evolution rate between cultures adapted to different CO2-levels. It is concluded that carbonic anhydrase activity is necessary for the utilisation of HCO3 (-) but not of CO2 in photosynthesis by Scenedesmus.Air-adapted cells take up about 0.3 μmoles Cl(-)/g FW from 0.1 mM KCl solution (pH 5.8) within the first minute of illumination. The same amount is released when the light is switched off. The light induced Cl(-)-uptake is inhibited by addition of HCO3 (-) or high pH, and may be interpreted as an alternative uptake of Cl(-) instead of HCO3 (-).As cells adapted to air plus 1.5% CO2 do not show this light induced Cl(-)-uptake and as the inhibitor of carbonic anhydrase, diamox, affects Cl(-)-uptake of air-adapted cells, it is suggested that carbonic anhydrase may be involved in the uptake of Cl(-) and HCO3 (-).