Mechanism Of MeJa Enhancing Salt Tolerance Of Glycyrrhiza Uralensis In Seed Germination And Seedling Growth Stages

Salt stress is one of the main abiotic stress factors affecting plants.Enhancing plant salt tolerance through exogenous substances is a hot spot in studying plant salt resistance mechanisms.Methyl jasmonate?MeJA?is involved in the regulation of various physiological functions in plants and plays an important role in regulating plant resistance to abiotic stress.Glycyrrhiza uralensis Fisch.was used as the research material to design exogenous MeJA under salt stress.Seed germination and indoor sand culture seedling growth experiment were used to study the seed germination,seedling growth and antioxidant metabolism of MeJA under salt stress.The effects of MeJA on the salt tolerance in germination seeds and seedlings of G.uralensis were studied,which provided a scientific basis for further improving the salt tolerance of cultivated G.uralensis.The main results and conclusions are as follows:1.Effects of MeJA on seeds germination characteristics of G.uralensis and physiological and biochemical characteristics of early seedlings under salt stress?1?Under salt stress,germination rate,germination potential,germination index,vigor index and early root length,radicle root length,embryo length and germ size of G.uralensis seeds were all inhibited.MeJA significantly increased G.uralensis seeds germination potential,germination index,vigor index,radicle length,radicle rough,germ length and germ size of G.uralensis,and the dry matter was significantly improved.Indicating that MeJA could significantly alleviate the adverse effects of salt stress on G.uralensis seeds germination.?2?MeJA can effectively increase the activities of SOD,POD and GPX and the contents of AsA and GSH in G.uralensis seeds germination stage under salt stress,thus reducing reactive oxygen species.MeJA decreased the levels of H₂O₂ and O₂^-and the content of MDA,indicating that MeJA reduced the antioxidant oxygen level in G.uralensis seeds germination stage by reducing the antioxidant capacity and alleviated the cell membrane lipid peroxidation damage caused by salt stress,thus alleviating the damage of salt stress on early seedlings of G.uralensis seeds germination stage.?3?MeJA reduced Na⁺and Cl^-contents,increased Ca²⁺content and K⁺/Na⁺ratio in G.uralensis seeds germination stage under salt stress,and further increased the contents of proline and soluble protein.Indicating that MeJA induced Ca²⁺signaling way to participate in the regulation of the synthesis of osmotic substances in the early salt-tolerant process of G.uralensis,thereby maintaining the osmotic potential of plant cells and alleviating the osmotic stress and ionic toxicity caused by salt stress.?4?MeJA could increase the sucrose content and SS activity in G.uralensis seeds germination stage under salt stress,but the activity of INV decreased,indicating that MeJA enhanced the carbon metabolism of in G.uralensis seeds germination stage by increasing the sucrose content and SS activity.However,MeJA reduced the NR activity in G.uralensis seeds germination stage,reduced the reduction of nitrate nitrogen,decreased the activities of GOGAT and GS,and weakened the GS/GOGAT cycle,which weakened the assimilation ability of NH₄⁺in GS/GOGAT cycle.Indicating that MeJA increases the osmotic adjustment ability of plants by increasing the contents of nitrogen metabolites,and different metabolites can also prevent membrane peroxidation,thereby increasing the adaptability of G.uralensis seeds germination stage to salt stress.?5?MeJA treatment significantly reduced ABA content in G.uralensis seeds germination stage,increased IAA content,but had no effect on GA₃ content;MeJA further increased the ratio of IAA/ABA,GA₃/ABA,GA₃/IAA,indicating that MeJA can increase the content and balance of hormones in plants,thus alleviating the inhibition of salt stress on plant growth and the premature aging caused by salt stress.2.Effects of MeJA on the growth,physiological and biochemical characteristics of G.uralensis seedlings under salt stress?1?Salt stress decreased the main root length,plant height,main root thickness,number of leaves and lateral roots of G.uralensis seedlings,and decreased the biomass of G.uralensis seedlings.MeJA significantly increased the main root length and lateral root number of G.uralensis seedlings under salt stress,and the biomass has also increased significantly.It indicated that MeJA could significantly promote the root growth of G.uralensis seedlings under salt stress.?2?MeJA treatment can reduce the activities of POD,CAT,APX and GR in G.uralensis seedlings under salt stress,and reduce the contents of H₂O₂ and MDA,thereby alleviating the membrane lipid peroxidation damage caused by salt stress on G.uralensis seedlings,but MeJA has not changed SOD activity and O₂^-production under salt stress.The results were inconsistent with the results of G.uralensis seeds germination stage,indicating that the effect of MeJA on the antioxidant system of G.uralensis under salt stress varies with plant growth stages.?3?MeJA treatment increased the activities of SPS and SS and the sucrose content in G.uralensis seedlings under salt stress,which was consistent with the results of carbon metabolism in G.uralensis seeds germination stage,indicating that MeJA may not affect the carbon metabolism of G.uralensis seedlings under salt stress.MeJA significantly increased the activities of NR,GS and GOGAT in G.uralensis seedlings under salt stress,and the contents of NO₂^-and NO₃^-also increased significantly.The results of nitrogen metabolism substrate were consistent with those in G.uralensis seeds germination stage,indicating that MeJA can also increase the osmotic adjustment ability of plants by increasing the contents of nitrogen metabolites,thereby increasing the salt tolerance of G.uralensis seedlings.?4?MeJA increased the content and accumulation of total flavonoids,total polysaccharide,total saponin in G.uralensis seedlings,and glycyrrhizic acid content and accumulation,glycyrrhizin accumulation,and licochalcone A accumulation also showed an upward trend.These results indicated that MeJA can alleviate salt stressby alleviating oxidative damage and enhancing carbon and nitrogen metabolism in G.uralensis seedlings,thus promoting the growth of G.uralensis seedlings,it is different from effects on the G.uralensis seeds germination,indicating that MeJA can alleviate salt stress by mitigating oxidative damage,thereby improving the adaptability of G.uralensis seedlings to salt stress.MeJA can also effectively induce the accumulation of primary metabolites and secondary metabolites,thereby promoting biomass in G.uralensis seedlings.