Effects Of Ethylene On Medicago Sativa L. Seed Germination And Seedling Growth Under Salt Stress And Investigations On The Mechanism

Soil salinity is one of the most common stresses that affects plant growth and yield.In order to adapt to saline conditions,plant evolved a series of morphological,physiological and biochemical strategies.Medicago sativa L.is a kind of herbaceous legume plant with well-developed perennial rhizomes,and it has good palatability and rich protein,so it is widely planted in Eurasia and all over the world.However,soil salinity is a major factor reducing the yield of Alfalfa.In this study,Alfalfa was treatedwithexogenousadditionofethephon?ETH?,1-aminocyclopropane-1-carboxylic acid?ACC?and silver thiosulfate?STS?in sodium chloride?NaCl?solution.The content of related physiological indicators and the expression of ethylene related genes of Alfalfa seeds at germination stage were determined.The regulatory mechanism of ethylene during germination of Alfalfa seeds under salt stress was analyzed,which would provide theoretical basis for improving saline-alkali soil and increasing Alfalfa yield in saline-alkali soil.The main results of this project are as follows:1.In the initial stage of NaCl stress,plants mainly undergo rapid osmotic stress and slow ion stress,osmotic stress affects the growth of Alfalfa,and ion stress affects the germination of Alfalfa seeds.2.Addition of ETH in salt solution would reduce the accumulation of malondialdehyde?MDA?and hydrogen peroxide?H₂O₂?and increase peroxidase?POD?activity,which improved the antioxidant ability of Alfalfa,reduced the accumulation of harmful substances and alleviated the degree of oxidative damage of cell membrane system.Addition of ETH,ACC and STS can improve the salt tolerance of Alfalfa by increasing the content of proline?PRO?under salt stress.In contrast,addition of STS in salt solution would decrease POD activity and inhibit Alfalfa seed germination.Therefore,Alfalfa seed survival rates can be improved by adding ETH and ACC in saline environment.3.NaCl treatment can degrade chlorophyll in Alfalfa leaves,thus,the growth of Alfalfa leaves and plants will be affected,but ETH and ACC can increase the chlorophyll content in leaves and promote the growth of Alfalfa leaves.4.Under salt stress,exogenous addition of ETH and ACC can increase the germination rate of Alfalfa seeds to the control level?distilled water treatment?,and ACC can alleviate the inhibition of salt stress on the growth of Alfalfa root and seedling.However,addition of STS in salt solution inhibites Alfalfa seed germination,but promotes the growth of Alfalfa root and seedling.By analyzing the expression level of ethylene synthesis and signal pathway related genes,we concluded that the mechanisms of ethylene in salt stress were as follows:ETH promotes the growth of Alfalfa leaves in saline-alkali soil by reducing the expression of MsACO and MsERF8 genes,and increases Alfalfa germination rate in saline-alkali soil by upregulating MsERF11 gene;ACC increases Alfalfa germination rate in saline-alkali soil by increasing MsERF11 gene expression and participating in melatonin?MT?metabolism pathway;STS promotes the growth of Alfalfa root and seedling in saline-alkali soil by reducing the expression of MsACO and MsERF8 genes,and reducing the expression of MsERF11 gene to inhibite the Alfalfa seed germination.