Enzymes of the glycolate pathway in plants without CO₂-photorespiration

Abstract

Extracts, mainly from mesophyll cells, were obtained by grinding cells in a Waring Blendor; then extracts of parenchyma sheath cells were obtained by exhaustive grinding of the blender residue in a roller mill or mortar with sand. The specific activities of P-glycolate phosphatase, glycolate oxidase, catalase and reduced nicotinamide adenine dinucleotide- (NADH-) hydroxypyruvate reductase were fourfold higher in extracts of the parenchyma sheath cells than in the mesophyll cells from corn, sugarcane, and Atriplex rosea. P-Glycerate phosphatase was mainly located in the mesophyll cells. The total activity of glycolate oxidase in plants without CO 2 -photorespiration averaged about one-third that found in other plants on a wet-weight basis. Glycolate oxidase activity in Atriplex rosea, without CO 2 -photorespiration, was about the same as in Atriplex patula, with CO 2 -photorespiration. It is concluded that enzymes for glycolate metabolism are present in all leaves in substantial amounts and are located in both cell types, although a higher specific activity is in the parenchyma sheath cells. Thus it is proposed that photorespiration occurs in all plants, but that CO 2 evolution from glycolate metabolism is not manifested in plants which have high levels of activity for the C 4 -dicarboxylic acid cycle of CO 2 fixation.