Proline, hydrogen peroxide, membrane stability and antioxidant enzyme activity as potential indicators for salt tolerance in rice (Oryza sativa L.)

Abstract

In order to compare differential growth, physiological and biochemical responses of rice cultivars differing in salt tolerance, four rice cultivars; tolerant Pokkali (PK), moderately tolerant Luang Anan (LA) and two sensitive cultivars Khao Dawk Mali 105 (KDML 105) and Pathumthani 60 (PT 60) were grown in hydroponic culture for 2 weeks and then subjected to NaCl stress at 6 or 12 dS m-1 for thirteen days. The tolerant cultivar (PK) exhibited clearly different pattern of responses from the other cultivars in most of the examined aspects including lower growth inhibition, lower inhibition of net photosynthetic rate, lower Na+/K+ ratio in the shoots, less proline accumulation in the shoots, less membrane damage, lower hydrogen peroxide production, higher catalase and lower guaiacol peroxidase activities. Other parameters including Na+/K+ ratio in roots, proline accumulation in roots and osmotic potential in both roots and shoots did not show appropriate association with the level of salt tolerance. The reduction in growth resulted from drastic reduction in net photosynthetic rate which was observed as early as 24 h after exposure to stress and continued to decrease dramatically. Growth retardation was also related to salt-induced accumulation of hydrogen peroxide which caused lipid peroxidation and membrane leakage. Higher catalase activity in the tolerant cultivar played an important role in combating the hydrogen peroxide, leading to less damage and higher tolerance. The activity of peroxidase was lower in the tolerant cultivar than in the sensitive ones. The observed negative relationship between the amount of proline accumulation and the level of salt tolerance did not support the widely advocated role of proline as an osmoprotectant under salt stress. Further investigation needs to be done to determine the role of this compatible osmolyte in salinity stress response in rice. For practical purpose, those parameters which showed differential pattern of responses including lower Na+/K+ ratio in the shoots, less proline accumulation in the shoots, lower reduction in net photosynthesis rate, lower electrolyte leakage, lower hydrogen peroxide accumulation, higher catalase and lower guaiacol peroxidase activities may be regarded as potential biochemical indicators for selection of salt tolerant rice and targets for improvement through transgenic approaches. © 2012 Asian Network for Scientific Information.