The influence of elevated CO2 on the activities of antioxidative enzymes in two soybean genotypes

The effects of ele vated compared to current atmospheric CO2 concentration (720 and 365 µL L -1 , respec­ tively) on antioxidative enzymatic activities of two soybean (Glycine max (L.) Merr.) genotypes (R and S) grown in open-top field chambers were investigated. Enzymatic activities of leaves collected 40, 47, 54 and 61 d after plant­ ing were measured. Elevated CO2 significantly decreased activities of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APOD, EC 1.11.1.7), gluta­ thione peroxidase (GPOD, EC 1.11.1.9) and glutathione reductase (GR, EC 1.6.4.2) in both genotypes. The activi­ ties of dehydroascorbate reductase (DAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDAR, EC 1.1.5.4.) increased in genotype S, but decreased in genotype R under elevated CO2. Elevated CO2 decreased rubisco activity and rubisco, chlorophyll, carotenoids and total soluble protein contents in both genotypes. Results indicate that con­ stitutive antioxidative enzymatic activities may decrease in a high-CO2 world. Significant CO2 × genotype interac­ tions, however, suggest that there may be key genotypic differences in response patterns, potentially conferring differential resistance to biotic and abiotic stress.