Responses of Antioxidant Enzymes to Chronic Free-Air Ozone Stress in Rice (Oryza sativa L.) Cultivars with Different Ozone-Sensitivities

Free-air O3 enrichment was used to investigate the responses of different antioxidant mechanisms in different rice (Oryza sativa L.) cultivars – O3-sensitive hybrid indica (O3-S) cultivars and O3-tolerant conventional japonica (O3-T) cultivars across all growth stages. Elevated [O3] induced increases in reactive oxygen species (ROS) production in O3-S cultivars, which were more pronounced in the later growing stages. In O3-S cultivars, continuous O3 stress decreased catalase (CAT), peroxidase (POD) and glutathione peroxidase (GPX) activities, while in O3-T cultivars, short-term O3 stress decreased superoxide dismutase (SOD), CAT, POD and GPX activities. The same POD isozyme patterns were observed in both O3-S and O3-T cultivars, while SOD and APX isozymes varied by cultivar. The results suggest that O3 tolerance might be improved at different rice development stages through regulating the responses of antioxidant mechanisms to O3 stress.