Effect of Oxygen on the Rate of Photorespiration in Detached Tobacco Leaves

Abstract

Abstract The rate of carbon dioxide exchange in both light and darkness by detached tobacco leaves placed at various oxygen concentrations was measured by an Infra‐Red CO 2 Analyzer and a Clark oxygen electrode. It was observed that during illumination oxygen had two different effects. One was to stimulate carbon dioxide evolution and the other to inhibit carbon dioxide absorption. Concentration of carbon dioxide at compensation point was found to be a linear function of oxygen concentration and this has been explained as due mainly to an increased evolution of carbon dioxide. Such an evolution during illumination has been called photorespiration. Increased concentrations of oxygen also had a stimulating effect on the magnitude of the initial post‐illumination burst of carbon dioxide in darkness, but no effect on the subsequent steady rates. These data have been explained as due to the suspension of regular respiration in darkness and its replacement by a different process, tentatively called photorespiration. A second effect of oxygen was to reduce the efficiency (called “carboxylation efficiency”) with which a leaf was able to remove carbon dioxide from the atmosphere.