Effects Of Exogenous Methyl Jasmonate On The Metabolism Of Organic Osmolytes And Ascorbate-glutathione Cycle In Maize Seedlings Under Osmotic Stress

Osmotic stress is one of the major abiotic stresses which affect plant growth and development.Maize?Zea mays L.?is an important cereal crop in China.Osmotic stress is a serious limiting factor for distribution and production of maize.Some studies showed that jasmonic acid?JA?and methyl jasmonate?MeJA?could enhance osmotic stress tolerance in many plant species.However,information available on the mechanism of osmotic stress tolerance in plants induced by JA and MeJA are unconfirmed.In this dissertation,maize?Deyu 4?seedlings were used as experimental materials to study the effects of MeJA on the metabolism of major organic osmolytes and ascorbate-glutathione?AsA-GSH?cycle under osmotic stress.The main results are detailed as follows:1?Effect of exogenous MeJA on the metabolism of major organic osmolytes in maize seedlings under osmotic stress.?1?Effect of exogenous MeJA on some physiological parameters of maize seedlings under osmotic stress.Maize seedlings under osmotic stress were treated with MeJA(0?50?75?100?125?150?300 mmol·L^-1)for 96 h,and tissue vitality,electrolyte leakage,and MDA content in maize seedlings were assayed.The results showed that treatment with 75?mol·L^-11 MeJA significantly increased tissue vitality and decreased electrolyte leakage and MDA content compared to the seedlings subjected to osmotic stress treatment alone,indicating that exogenous MeJA can enhance osmotic stress tolerance of maize seedlings.?2?Effect of exogenous MeJA on proline metabolism in maize seedlings under osmotic stressTreatment with 75?mol·L^-11 MeJA significantly enhanced osmotic stress-induced proline accumulation.MeJA also induced an almost immediate and rapid increase of?¹-pyrroline-5-carboxylate synthetase?P5CS?and ornithine aminotransferase activities,the key enzymes of proline biosynthesis,and up-regulated JcP5CS and ZmOAT expression,but it decreased the activity of proline dehydrogenase?ProDH?,a key enzyme of proline degradation,and inhibited ZmProDH expression.These results indicated that MeJA might be involved in signal transduction events,leading to proline accumulation in maize seedlings under osmotic stress,and that MeJA-induced proline accumulation is a combined result of the activation of proline biosynthesis and the simultaneous inhibition of the proline degradation pathway.?3?Effect of exogenous MeJA on the metabolism of glycinebetaine and trehalose in maize seedlings under osmotic stressIn the present work,we studied the effect of of MeJA on the metabolism of glycinebetaine and trehalose in maize seedlings under osmotic stress.The results showed that MeJA treatment significantly enhanced the accumulation of glycine betaine in maize seedlings under osmotic stress.It also increased the activity of betaine aldehyde dehydrogenase?BADH?,a key enzyme for the glycinebataine biosynhthesis,and improved the expression level of the ZmBADH and ZmCMO.In addition,Treatment with 75?mol·L^-1MeJA also increased the content of trehalose,and improved the activity of trehalose-6-phosphate synthase?TPS?,and up-regulated the expression of ZmTPS.The results suggested that MeJA might play a key role in the biosynthesis of glycinebetaine and trehalose.2?Effect of exogenous MeJA on the AsA-GSH cycle in maize seedlings under osmotic stress.Treatment with 75?mol·L^-1MeJA significantly enhanced the content of ascorbate?AsA?and glutathione?GSH?,and elevated the ratio of ascorbate/dehydro-ascorbate?AsA/DHA?and reduced glutathione/oxidized glutathione?GSH/GSSG?in maize seedlings under osmotic stress.MeJA treatment also increased the activities of dehydroascorbate reductase?DHAR?,monodehydroascorbate reductase?MDHAR?,ascorbate peroxidase?APX?,superoxide dismutase?SOD?,catalase?CAT?and glutathione reductase?GR?,the key enzymes the glutathione-ascorbate cycle,and up-regulated ZmAPX?ZmGR?ZmCAT?ZmSOD?ZmDHAR and ZmMDHAR genes expression in maize seedlings under osmotic stress.In addition,exogenous MeJA treatment decreased the concentrations of malondialdehyde?MDA?,hydrogen peroxide and superoxide anion radical in maize seedlings under osmotic stress,indicating that exogenous MeJA can enhance antioxidant capacity of maize seedlings under osmotic stress.These results indicate that exogenous MeJA can increase osmotic stress tolerance of the maize seedlings,and this increase is likely associated with up-regulation of osmoregulation and antioxidant capacity by MeJA.