| Salinity is one of the major abiotic stresses affecting crop productivity and quality drastically. Salinity affects plant growth and development, destroys physio-biochemical function and results in death of plant cells and plant itself through osmotic stress, ionic stress and nutrition imbalance caused by excess of Na+ and Cl-. Thus it makes significant academic and practical sense to explore the effects of salinity on crop and the mechanism of salt stress, to improve the salt resistance and the output and quality of crop. Wheat(Triticum aestivum L.) is one of the major cultivated crops in our country now. In order to understand the mechanism of salt tolerance from the aspect of physio-biochemistry and epigenetics, the physio-biochemical traits and the change of DNA methylation of salt-tolerant wheat Dekang-961 and salt-sensitive wheat Lumai-15 under salt stress were examined.Dry weight declined in both cultivars under salt stress, with salinity stress being more prominent in sensitive Lumai-15. Upon exposure to salinity, an increase in lipid peroxidation level was found in the root of both Dekang-961 and Lumai-15, and it was higher in the latter. Salt stress induced the rate of K+/Na+ to decline in the root of the two cultivars, and the rate of decline was higher in Lumai-15. The activities of SOD, POD and CAT increased due to the increase in salt concentration in the root of Dekang-961 and Lumai-15, but the rate of increase was significantly higher in the former at both NaCl concentrations. So it can be seen that the growth of plants declined for salinity restrained the growth of glycophyte. The salt resistant cultivar showed higher level of constitutive and induced activities of antioxidant enzyme and lower lipid peroxidation, accordingly cell membrane injuring less; it kept the ratio of K+/Na+ higher, suffering lighter ionic toxicity.While plenty of physiological studies have described the negative effect of salt stress and the mechanism of salt tolerance, considerably less information exists on the epigenetic impacts of salt stress. Two complementary approaches were used to evaluate methylation changes in the root DNA of the two cultivars under salt stress: high pressure liquid chromatography (HPLC) and methylation-sensitive amplified polymorphism (MSAP). HPLC analysis showed global decrease of 5-methylcytosine (5mC) content in both cultivars, and MSAP analysis showed extensive methylation changes in CCGG sequences, with the net result being hypomethylation. However, the level of demethylation was higher in Dekang-961 than that in Lumai-15. Thereby, the present work suggested that most of the cytosine DNA methylation changes induced by salt stress could be related to hypomethylation events and most of them were directed to specific sequences, not random ones. Furthermore this response was the same in Dekang-961 and Lumai-15, and there was a larger demethylation in the former, suggesting salt stress induced changes of the degree and patterns of DNA methylation.5-azacytidine is a demethylating agent. Compared to only salt-treated treatment, plants treated with 5-azaC under salt stress had higher dry weight, lower MDA content, higher rate of K+/Na+, higher SOD, POD and CAT activities, lower DNA methylation in the root of the two cultivars. Consequerntly,5-azacytidine alleviated the restraint of growth and ionic toxicity of wheat under salt stress. With 5-azacytidine wheat obviously ameliorated the salt stress through increasing the activities of SOD, POD and CAT and reducing lipid peroxidation, suggesting 5-azaC was in favor of improving slat resistance of wheat.
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