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 CO2-photorespiration averaged about one-third that found in other plants on a wet-weight basis. Glycolate oxidase activity in Atriplex rosea, without CO2-photorespiration, was about the same as in Atriplex patula, with CO2-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 CO2 evolution from glycolate metabolism is not manifested in plants which have high levels of activity for the C4-dicarboxylic acid cycle of CO2 fixation.