Effects Of Salt Stress On Nitrogen Metabolism In Rice And The Regulating Pathway Of Nitric Oxide

Salt stress seriously inhibited the growth and development of rice.Nitric oxide(NO)was involved in the regulation of many physiological metabolism processes in plants,especially in plants under stress conditions.Nitrogen metabolism promoted by some substances and choice of metabolism process with less energy consumption may play an important role in enhancing salt tolerance,nutrient absorption and utilization of rice.At present,the research on NO regulation of nitrogen metabolism under salt stress is mostly reported in other plants.The related NO regulation researches in rice mainly concentreated on antioxidant enzyme activity.However,the specific pathway and intervention mechanism of NO regulation on nitrogen metabolism in rice have not been reported.In this study,hydroponics and soil culture were used.Two rice varieties,Jinyuan 85(salt tolerant)and Liaojing 763(salt sensitive),with four treatments,Control,Sodium nitroprusside(SNP,NO donor),Salt and Salt+SNP,were applied in the hydroponic experiment.The effects of NO on the stress-resistant substances,the activities of nitrogen metabolizing enzymes and the expression of nitrogen metabolizing related genes in rice was studied to clarify the regulatory effect of NO on rice physiology and biochemistry,and to elucidate the mechanism of exogenous NO in improving rice salt tolerance and regulating nitrogen metabolism.Soil culture experiment focused on the regulation of no on rice yield potential under salt stress.The results show that:1.According to the response characteristics of rice seedlings to different salt stress concentrations,the varieties with higher salt tolerance and salt sensitivity were preliminarily selected.Furthermore,the characteristics of seedling growth,accumulation of sodium and potassium,osmotic adjustment substances and other changes with the increase of salt stress intensity of the primary rice varieties were further clarified.Based on the growth cycle and growth characteristics of each rice variety,two rice varieties with great differences in salt tolerance were selected,namely,Jinyuan 85(salt tolerant)and Liaojing 763(salt sensitive).According to the response characteristics of Jinyuan 85 and Liaojing 763to SNP,the suitable SNP concentrations of Jinyuan 85 and Liaojing 763 were determined to be 10?mol·L-~1 and 25?mol·L-~1,respectively.2.Exogenous NO has a positive regulatory effect on improving salt tolerance in rice and reducing Na~+entry into rice leaves.Compared with the simple salt treatment,the peroxidase activity was significantly increased in Jinyuan 85 and Liaojing 763,as well as the proline content of the leaves in Salt+SNP treatment.After one day of salt stress,the endogenous NO produced in rice increased,which indicated that NO was responsive to salt stress.It was speculated that NO might be involved in the regulation of rice plant response in the early stage of salt stress.3.NO application mainly increased nitrogen content,glutamate dehydrogenase activity and sucrose accumulation in rice leaves under salt stress.The expression level of NO regulated genes varied with different salt tolerance rice varieties.For Liaojing 763,under salt stress,NO mainly increased nitrogen metabolism by regulating the expression of genes related to nitrogen metabolism.Gene expression related to nitrogen metabolism was significantly up-regulated in Jinyuan 85 under salt stress,however exogenous NO significantly reduced the gene expression level induced by salt,promoting more energy transfer to defense against adversity.4.The results of pot experiment showed that NO alleviated the inhibition of salt stress on rice growth and promoted dry matter accumulation.Under salt stress,NO application increased the rice seed setting rate,and reduced the yield loss.Different rice varieties under salt stress have different response mechanisms to NO regulation,which may be related to the characteristics of rice varieties tested.Under salt stress,the energy and substance used to maintain the normal physiological metabolism process in rice plants have to be divided into two parts,of which one part is used to provide the energy to resist salt stress and enhance salt tolerance,the other part is used to maintain the basic growth and metabolism activities.Sucrose,proline and other substances not only can provide reducing power for rice nitrogen metabolism,but also can be used as osmoregulation substances.Therefore,NO may be used as a signal to regulate the balance between salt tolerance and nitrogen metabolism to make rice plants better adapt to salt stress.