Dissimilarity of ascorbate–glutathione (AsA–GSH) cycle mechanism in two rice (Oryza sativa L.) cultivars under experimental free-air ozone exposure

Abstract

Rising tropospheric ozone concentrations ([O3]) can lead to considerable damage to agricultural crops. Experimental data have shown that the relationship between O3 injury and yield loss differs with crop species and that O3 sensitivity differs among cultivars of the same species. To explore a breeding strategy to adapt crops to high [O3], it is necessary to investigate the different mechanisms for cultivar resistance to O3 stress. Although several chamber-based studies have examined antioxidant defence differences in rice (Oryza sativa L.) cultivars in response to elevated [O3], such as the utilisation of the ascorbate–glutathione (AsA–GSH) cycle to eliminate reactive oxygen species (ROS), little research has been conducted under free-air O3 enrichment (O3-FACE) to address the different AsA–GSH cycle responses of rice cultivars. In this experiment, O3-FACE was used to investigate the AsA–GSH cycle in two rice cultivars, SY63 (O3-sensitive) and WXJ14 (O3-resistant). The results indicated that, compared with the ambient [O3], elevated [O3] (1.5×ambient [O3]) induced increases in the superoxide anion (O2−) production rate, hydrogen peroxide (H2O2) content, malondialdehyde (MDA) content and relative electrical conductivity; increases that were greater in SY63 than in WXJ14. Continuous O3 stress also resulted in a less efficient metabolism of the AsA–GSH cycle in SY63 compared to WXJ14. The results indicated that in SY63, elevated [O3] accelerated ROS metabolism rates, and the antioxidant system could not prevent oxidative damage, thus increasing membrane lipid peroxidation. In contrast, in WXJ14, there was transient damage in response to elevated [O3] early in the sampling period, which triggered the ROS to stimulate the antioxidant system to avoid O3 stress. Our results suggested that ROS detoxification by the AsA–GSH cycle under long-term exposure to an O3-enriched atmosphere plays a more important role in an O3-resistant rice cultivar than in an O3-sensitive rice cultivar and that a better understanding of antioxidant system mechanisms is essential to the assessment of different rice cultivars’ responses to future tropospheric [O3].