Influence of Temperature on the Ratio of Ribulose Bisphosphate Carboxylase to Oxygenase Activities and on the Ratio of Photosynthesis to Photorespiration of Leaves

Lehnherr, B., Mächler, F. and Nösberger, J. 1985. Influence of temperature on the ratio of ribulose bisphosphate carboxylase to oxygenase activities and on the ratio of photosynthesis to photorespiration of leaves.—J. exp. Bot. 36: 1117–1125. Rates of net and gross photosynthesis of intact white clover leaves were measured by infrared gas analysis and by short term uptake of 14CO2 respectively. Ribulose bisphosphate carboxylase oxygenase (RuBPCO) was purified from young leaves and kinetic properties investigated in combined and separate assays. The ratio of carboxylase to oxygenase activities was compared with the ratio of photosynthesis to photorespiration at various temperatures and CO2 concentrations. The ratio of photosynthesis to photorespiration at 30 Pa p(CO2) was consistent with the ratio of carboxylase activity to oxygenase activity when each was measured above 20 °C. However, the ratio of photosynthesis to photorespiration increased with decreasing temperature, whereas the ratio of carboxylase to oxygenase activity was independent of temperature. This resulted in a disagreement between the measurements on the purified enzyme and intact leaf at low temperature. No disagreement between enzyme and leaf at low temperature occurred, when the ratio of photosynthesis to photorespiration was determined at increased CO2 concentrations. The results suggest an effect of low temperature and low CO2 concentration on the ratio of photosynthesis to photorespiration independent of the enzyme.