Effect Of Exogenous Nitrogen On Sources Of NO And Salt Tolerance Of Wheat Under NaCl Stress

Salinity is one of the major abiotic stresses in the world, which affects the plant growth and crop production. Nitric oxide (NO) is a freely diffusible, gaseous compound and with important signal role in living organisms. In plants, NO has a role in controlling plant growth and development, and can affect the response of plants to stress. NO has two different effects on plants: protection and toxicity depending on its concentration. Therefore, the relationship between the concentration of nitric oxide donor sodium nitroprusside (SNP) and the physiological responses of plants to salt stress needs to be further investigated. In the present study, effect of exogenous nitrogen and SNP on produce of NO and salt tolerance of wheat (LM 15) were investigated under NaCl stress. The results are as follows.1. The effect of NO donor SNP on seed germination,concentrations of Na⁺ and K⁺ and water content in embryos of seeds of wheat (LM 15) under salt stress was investigated. The results showed that 150 mmol/L NaCl decreased seed germination, while addition of 0.08 mmol/L SNP markedly alleviated the reduction of seed germination induced by NaCl stress. However, SNP supply had no effect on total seed germination after ungerminated seeds in different treatments were transferred to distilled water. Under salinity, water content in seeds, especially in embryos increased with the SNP supply, but SNP supply had no effect on the contents of Na⁺ and K⁺ in embryos. The present results suggested that the positive effect of NO on seed germination under salinity may be due to its role in alleviating the osmotic stress, but not ion toxicity of salinity for seeds of wheat during seed germination stage.2. In this study, effect of NO donor SNP on proton secretion and ion content of radicle of wheat (LM 15) under NaCl stress were examined. The results indicated that 75 mmol/L NaCl inhibited the growth of the radicle, while addition of 0.08 mmol/L SNP into 75 mmol/L NaCl solution markedly mitigated the inhibitionin redical growth, increased the velocity of proton extrusion, decreased Na⁺/K⁺ ration,and the content of MDA of radicle.3. Effect of exogenous nitrogen on NO produce and salt tolerance of wheat under NaCl stress was investigated. The results showed that higher concentration of NO₃^--N increased K⁺ content, and fresh and dry weights, decreased Na⁺ content. Furthermore, higher NO₃^--N supply increased the leaf NO content, which may be resulted from higher activity of nitrate reductase, while the elevated leaf NO under salinity may be mainly resulted from higher activity of NOS.