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Photorespiration and Glycolate Metabolism in Tobacco Leaves¹

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 -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.

Key Words: photosynthesis • respiration in tobacco

² Crop Physiologist. Present address: Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55101.

Received for publication June 26, 1967.