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Plant Physiology 60:693-696 (1977)
© 1977 American Society of Plant Biologists

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Articles

pH Dependence of Photosynthesis and Photorespiration in Soybean Leaf Cells

Jerome C. Servaitesa,1

William L. Ogrenb

a Department of Agronomy, University of Illinois, Urbana, Illinois 61801, b United States Department of Agriculture, Agriculture Research Service, Urbana, Illinois 61801

The effect of pH on the kinetics of photosynthesis, O2 inhibition of photosynthesis, and photorespiration was examined with mesophyll cells isolated from soybean (Glycine max [L.] Merr.) leaves. At constant, subsaturating bicarbonate concentration (0.5 mM), O2 inhibition of photosynthesis increased with increasing pH because high pH shifts the CO2-bicarbonate equilibrium toward bicarbonate, thereby reducing the CO2 concentration. At constant, substrating CO2 concentrations, cell photorespiration decreased with increasing pH. This was indicated by decreases in the CO2 compensation concentration, O2 inhibition of photosynthesis, and glycine synthesis. Km(CO2) values for isolated cell photosynthesis and in vitro ribulose-1, 5-diphosphate carboxylase activity decreased with increasing pH, while the Ki(O2) for both systems was similar at all pH values. The responses to pH of the corresponding kinetic constants of cell photosynthesis and in vitro RuDP carboxylase with respect to CO2 and O2 were identical. This provides additional evidence that the relative rates of photosynthesis and photorespiration in C3 plants are determined by the kinetic properties of RuDP carboxylase.

1 Present address: Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706.






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ASPB Publications PLANT PHYSIOLOGY® THE PLANT CELL
Copyright © 1977 by the American Society of Plant Biologists