Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.

Abstract

The carbon dioxide compensation point (Γ) was found to vary under constant environmental conditions, as the duration of light treatment increased, and also with leaf age. The activities of RuDP carboxylase, catalase, glycollate oxidase, and nitrate reductase were found to vary with duration of the light treatment during the course of a single day. RuDP carboxylase activity was found to exhibit a rhythmic fluctuation of activity with age, which had a frequency common to all the leaves examined. The activities of RuDP carboxylase, glycollate oxidase, and nitrate reductase in the leaves was found to increase with ascending leaf position; the activities generally decreased with leaf age. The ratio of nitrate reductase activity to RuDP carboxylase activity was found to give an excellent correlation with measured T, and the value of nitrate reductase as an indirect measure of photorespiration and the relationship between nitrogen metabolism and photorespiration is discussed.