Application Of Exogenous Melatonin In Maintaining Seed Germination And Seedling Growth Of Cotton Under Salt Stress

In the present paper,two salt-tolerant and two salt-sensitive cotton varieties were used as materials to research the effects of seed priming with melatonin on seed germination and seedling emergence.The effects of melatonin on chlorophyll content,osmotic protective substances,antioxidant enzyme activity and Na+ and K+ content of cotton seedlings under salt stress were analyzed to explore the function of melatonin on alleviating the damage of salt stress in cotton,and to propose appropriate using concentration,providing methods and measures for its application in production practice.The main results were as follows:1.Effects of melatonin on germination and emergence of cotton seeds under salt stress(1)Salt stress significantly reduced the relative germination potential,relative germination rate and relative germination index of 4 varieties.The seed germination under salt stress condition was improved by melatonin priming.The improving effect of 50,100,150 and 200 ?mol/L melatonin were different in different varieties,but under 100 and 150 ?mol/L treatment,the germination indexes of the four cultivars were significantly higher than that of the salt stress control,suggesting that 100 and 150 ?mol/L melatonin priming may be suitable for more varieties.(2)Salt stress prevented the elongation of root and hypocotyls,inhibited the occurrence of lateral root and reduced the growth of cotton seedling.The restraint of salt stress on all observed indexes was reduced by 50-200 ?mol/L melatonin to different degrees,and the difference between observed indexes under 100 ?mol/L melatonin treatment and those of salt-stress control was significant in the tested varieties.2.Effects of melatonin root-irrigation on the physiological and biochemical indexes in cotton seedling under salt stress(1)The content of chlorophyll,proline and soluble sugar were decreased under salt stress.The melatonin root-irrigation can alleviated the decrease of chlorophyll content in leaves of different varieties under salt stress,and further increased the content of proline and soluble sugar.(2)Under salt stress,MDA content and POD activity increased,SOD activity decreased in the all tested varieties.The melatonin root-irrigation decreased the content of MDA,and increased the activity of POD and SOD in leaves of different varieties under salt stress.(3)Salt stress caused the significant increase of Na+,and the decline of K+ content and K+/Na+ ratio in the tested varieties.The melatonin root-irrigation reduced Na+ content in leaves of different varieties under salt stress,also decreased the K+ content in two salt-tolerant varieties,but increased that of two salt-sensitive varieties.Further,the melatonin root-irrigation increased the K+/Na+ ratio in all tested varieties.(4)The effects of different concentrations of melatonin on different varieties were different.For most varieties and many indicators,100 ?mol/L melatonin was a suitable concentration for use.