Arsenic stress responses in sensitive and tolerant rice of North-East, India

Arsenic (As) significantly affects production and quality of rice (Oryza sativa L), the global staple food. Therefore, there is a need for As tolerant rice and so, present work is designed to identify the highest As tolerant and sensitive rice cultivars of North-East (NE), India, and the key mechanisms for the sensitivity and tolerance. Hydroponically grown twenty rice cultivars of NE were analyzed for the changes in growth, As content and Arsenic tolerant index % (ATI%) after 7th day of As treatments (0, 100 and 300 µM), where Phougak rice was found to be the highest tolerant having highest ATI% while cultivar with IC no. 200507 with least ATI%, the highly sensitive to As. The sensitivity and tolerance of the rice against As were further analyzed through the evaluation of morphological and histochemical changes, relative water content, chlorophyll content, hydrogen peroxide (H₂O₂) and lipid peroxidation level, and antioxidant metabolites and enzymes activities. Arsenic significantly increased H₂O₂ level, resulted into lipid peroxidation and cell death in sensitive rice, moreover, scanning electron microscopy also revealed damaging effect of As in the plant. However, no damaging effect was observed in the tolerant rice, but considerable increase of ascorbate and glutathione content and activity of antioxidant enzymes were recorded. Hence, high accumulation of As induced ROS in sensitive rice, while constant detoxification of the ROS in tolerant rice by efficient antioxidant defence system could be the reasons for the sensitivity of 200507 and tolerance of Phougak rice to As stress.