Antioxidant Enzymes and Aldehyde Releasing Capacity of Rice Cultivars (oryza Sativa L.) as Determinants of Anaerobic Seedling Establishment Capacity

The activities of antioxidant enzymes and levels of antioxidants involved in oxygen detoxification were studied in seedlings of three indica rice (Oryza sativa L.) cultivars, namely Panikekoa and T 1471 that show good capacity for anaerobic seedling establishment (tolerant reaction) and IR 42 which has a poor anaerobic seedling establishment capacity (susceptible reaction). The activities of the antioxidant enzymes tested decreased under submergence. The activity of glutathione reductase (GR, EC 1.6.4.2) was found to be more sensitive compared to the other enzymes. On the other hand, the activity of superoxide dismutase (SOD, EC 1.15.1.9) was comparatively stable. After 5 days of submergence tolerant cultivars maintained almost 3-fold higher glutathione reductase activity than the susceptible cultivar. During submergence the tolerant cultivars showed comparatively less ascorbic acid oxidase (AAO, EC 1.10.3.3) activity and had greater ascorbic acid content. The activities of superoxide dismutase, catalase (CAT, EC 1.11.1.6), peroxidase (POX, EC 1.11.1.7), ascorbic acid peroxidase (APX, EC 1.11.1.11) and polyphenol oxidase (PPO, EC 1.14.18.1) were also higher in tolerant cultivars during submergence compared to the susceptible cultivar. Submergence was found to induce aldehyde releasing capacity in rice seedlings which was more apparent in the susceptible cultivar.