Physiological role of exogenously applied glycinebetaine to improve drought tolerance in fine grain aromatic rice (Oryza sativa L.)

Rice performance under drought stress is mainly impeded by oxidative damage and hampered plant water status, which may be improved by exogenous use of osmoprotectants. In this study, the role of glycinebetaine (GB) to improve drought tolerance in rice (Oryza sativa L.) cultivar Super-basmati was evaluated. GB was used both as seed and foliar application. For priming, seeds were soaked in 50, 100 and 150 mg l^-1 aerated solution of GB for 48 h. At four-leaf stage, one set of plants was subjected to drought stress, while the other set kept at full field capacity. Drought was maintained at 50 % of field capacity by watering when needed. For exogenous application, 50, 100 and 150 mg l^-1 GB levels were applied at five-leaf stage. Drought stress greatly reduced the rice growth while GB application improved it both under well-watered and drought conditions. Drought tolerance in rice was strongly related to the maintenance of tissue water potential and antioxidant system, which improved the integrity of cellular membranes and enabled the plant to maintain high photosynthesis. Foliar treatments were more effective than the seed treatments, while among the GB treatment, foliar application with 100 mg l^-1 was the most effective.