Photorespiration and Glycolate Metabolism in Tobacco Leaves1

Abstract

The stimulating effect of light on the evolution of CO2 from tobacco leaves into CO2‐free air was suppressed by inhibition of glycolate oxidase with α‐hydroxy‐2‐pyridinemethanesulfonic acid. The inhibitor strongly inhibited photosynthesis at both 25 and 35 C. The CO2 compensation concentration increased indefinitely for leaves treated with inhibitor. Glycolate accumulation in leaves treated with inhibitor was strongly dependent on inhibitor concentration and light intensity and was linear with time up to one hour. Temperature for growth or during the experiments had little effect on accumulation.The possible internal CO2 from the oxidation of glycolate calculated on the basis of glycolate accumulation under optimal conditions indicates that photorespiration from glycolate as a substrate may be at least 2‐fold dark respiration. Although the possible rate of respiration from glycolate metabolism was large, it was not sufficient to account for the differences in photosynthesis between maize and tobacco on the assumption that this difference was due to internal recycling of CO2 in tobacco.