Long Term Salinity Stress Reveals Variety Specific Differences in Root Oxidative Stress Response

Salinity stress induces oxidative stress caused by reactive oxygen species (ROS): superoxide radicals, hydrogen peroxide (H2O2) and hydroxyl radicals. Activities of both enzymatic and non-enzymatic components of the antioxidant system and related growth parameters were studied in the roots of the salt tolerant rice variety FL478 and the sensitive variety IR29 in response to long term stress (12 d) induced by 50 mmol/L NaCl. The comparative study showed that FL478 maintained higher relative growth rate and lower Na+/K+ in the roots than IR29 due to a higher membrane stability index that effectively exclude Na+. Lower TBARS (thiobarbituric acid reactive substance) content in FL478 roots indicated that its membrane was relatively unaffected by ROS despite high H2O2 content recorded under the salinity stress. Relatively higher superoxide dismutase activity along with a parallel increase in transcript level of superoxide dismutase (Os07g46990) in FL478 indicated that this protein might make a vital contribution to salt stress tolerance. Although the content of ascorbic acid remained unchanged in FL478, the activity of ascorbic peroxidases (APOXs) was reduced comparably in the both varieties. Transcriptomic data showed that a larger number of peroxidase genes were upregulated in FL478 compared to IR29 and several of which might provide engineering targets to improve rice salt tolerance.