Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: IV. The Effect of Light Intensity on the Carbon Dioxide Compensation Point

The carbon dioxide compensation point () was found to vary whenmeasured at increasing light intensities, in plants grown ata constant illumination. This response varied with the physiologicalage of the leaf. The also varied when measured at a constantillumination, with plants grown at different light intensities.The activity of the enzymes RuDP carboxylase, nitrate reductase,glycollate oxidase, and catalase was found to be influencedby the light intensity at which the plants were grown. A goodcorrelation was obtained between the measured and the ratioof nitrate reductase: RuDP carboxylase activities, suggestingthat nitrate reductase may be used as an indirect measure ofphotorespiration in plants receiving nitrate as the sole nitrogensource.