Acquisition of desiccation tolerance during seed development is associated with oxidative processes in rice

Desiccation tolerance is an important characteristic of rice seed quality during seed drying. In this study, two varieties of Oryza sativa L. subsp. japonica (Jiucaiqing and Wuyunjing 7) were used to investigate the dynamic changes in rice seeds that are associated with desiccation tolerance (germination traits produced by dried seeds), grain mass (GW), moisture content (MC), and electrical conductivity (EC) during seed development (18 to 42 days after heading (DAH)). Changes in the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in fresh, dry, and imbibed states, and antioxidant enzyme activity (superoxide dismutase (SOD); catalase (CAT); and glutathione reductase (GR)) in fresh and imbibed seeds were also evaluated during seed development. The results showed that seeds started to acquire desiccation tolerance at 26 DAH and reached the highest levels at 38 DAH. The increase in GW and decline in MC coincided with the acquisition of desiccation tolerance. MDA and H2O2 levels, and SOD, CAT, and GR activities in fresh and imbibed seeds rapidly decreased during the early developmental stages (18-30 DAH), and then their levels gradually stabilized (30-42 DAH). Regression analyses indicated that H2O2 levels in fresh seeds was negatively correlated with seed germination, whereas SOD activity in imbibed seeds was positively correlated with seed germination. H2O2 and SOD are, therefore, good parameters for assessing desiccation tolerance during rice seed development.