Photorespiration and Glycolate Metabolism: A Re-examination and Correlation of Some Previous Studies

Abstract

Some previous studies of photorespiration and glycolate oxidation were re-examined and correlated by infra-red CO(2) analysis. Data about rate of photosynthesis and oxygen sensitivity indicated that complete inhibition of photosynthesis with 3-(3,4-dichlorophenyl)-1,1 dimethyl urea (DCMU) allowed dark respiration to continue in the light. Photorespiration was also inhibited. The oxygen sensitivity of glycolate-stimulated CO(2) production was found to be compatible with the proposal that glycolate is a substrate of photorespiration. Both ;in vivo' and ;in vitro' studies of the alga Nitella flexilis have revealed a pathway of glycolate oxidation similar to that of higher plants. DCMU inhibition of photosynthesis by Nitella gave results similar to those for the monocotyledons tested. Under very low light intensity, carbon dioxide compensation in corn was measurable but was not sensitive to high oxygen concentration. It appears that the lack of photorespiration in this plant is not the end result of efficient internal recycling of CO(2) to photosynthesis.