Effect of low temperatures on the activity of oxygen‐scavenging enzymes in two populations of the C4 grass Echinochloa crus‐galli

Abstract

To discriminate among possible mechanisms responsible for the differential response to cold temperatures among ecotypes of the C4 grass weed species Echinochloa crus‐galli (L.) Beauv., the specific activities of five oxygen‐scavenging enzymes responsible for the elimination or reduction of free radicals and hydrogen peroxide during cold‐induced photoinhibition were determined in 5‐week‐old plants of two populations of the species collected from sites of contrasting climates, Québec (QUE) and Mississippi (MISS). Enzyme activities were measured at temperatures ranging from 5 to 30°C. The specific activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase were significantly higher in cold‐adapted QUE plants at low assay temperatures than in warm‐adapted MISS plants at the same temperature. The specific activities of superoxide dismutase assayed at 5 and 25°C were similar among plants of the two E. crus‐galli populations. Ascorbate concentrations were not different among plants of the two populations, suggesting that the observed differences in the specific activities of ascorbate peroxidase assayed at 5°C, truly reflect a better capacity of the QUE enzyme to reduce H2O2 to water at temperature conditions associated with the photoinhibitory process. The enhanced specific activity of four of the five oxygen‐scavenging enzymes measured in the cold‐adapted QUE population at low assay temperatures correlates with the syndrome of cold‐adapted features reported for plants of this population in earlier studies.