Regulation Of Methyl Jasmonate To Spikelet-opening And Seed-setting Of Photo-Thermo-Sensitive Genic Male Sterile Rice Lines Subjected To High Temperature Stress During Anthesis

Two-line hybrid rice using photo-thermo-sensitive genic male sterility as the core technology is the main way to utilize rice heterosis in China.In recent years,extreme high temperature weather occurs frequently,which seriously decreases the spikelet-opening rate and seed-setting rate of photo-thermo-sensitive genic male sterile(PTSGMS)rice lines,leading to a decline in seed production of two-line hybrid rice.It would be very important to understand the effect of high temperature on PTSGMS rice lines and how to alleviate the damage of high temperature to the seed production of two-line hybrid rice.As a chemical regulator and signal transduction substance that is closely related to stress resistance,methyl jasmonate(MeJA)participates in responses to various stresses and promotes the floret-opening in cereal crops.However,little information is available whether MeJA could alleviate the damage of high temperature to PTSGMS rice lines.Therefore,two PTSGMS rice lines,Peiai 64S and Shen 08S,and an inbred Yangdao 6 as a restorer line,which are currently planted in production,were used and grown in pots.Three treatments were conducted during anthesis,that is,normal temperature+spraying water,high temperature+spraying water,and high temperature+spraying MeJA.The effect of high temperature on spikelet-opening and seed-setting and the role and physiological mechanism in which spraying MeJA regulates spikelet-opening and seed-setting of PTSGMS rice lines were investigated.The main results are as follows:1.Compared with the treatment of normal temperature+spraying water,the treatment of high temperature+spraying water significantly reduced the seed-setting rate and seed yield of PTSGMS rice lines.However,the treatment of high temperature+spraying MeJA significantly increased the seed-setting rate and seed yield of PTSGMS rice lines in relative to the treatment of high temperature+spraying water.2.In comparison with those under the treatment of normal temperature+spraying water,the glume opening angle,fresh weight of the lodicules,and the contents of soluble sugar,jasmonic acid and MeJA in the lodicules were increased significantly under the treatment of high temperature+spraying water on the first day of the treatments,but they were decreased on the second day during the treatments and on the first day after the treatments were finished.Compared with the treatment of high temperature+spraying water,the treatment of high temperature+spraying MeJA significantly increased the glume opening angle,fresh weight of the lodicules,and the contents of soluble sugar,jasmonic acid and MeJA in the lodicules on the first day of spraying MeJA,resulting in increases in spikelet-opening rate and the stigma exsertion rate.3.The contents of malondialdehyde,hydrogen peroxide,and oxygen free radical in leaves were significantly increased,and the contents of glutathione and ascorbic acid and the activities of superoxide dismutase,catalase,peroxidase,glutathione reductase,and ascorbate peroxidase in leaves were significantly decreased under the treatment of high temperature+spraying water when compared with under the treatment of normal temperature+spraying water.The treatment of high temperature+spraying MeJA significantly decreased the contents of malondialdehyde,hydrogen peroxide,and oxygen free radical and significantly increased the contents of glutathione and ascorbic acid and the activities of superoxide dismutase,catalase,peroxidase,glutathione reductase,and ascorbate peroxidase in leaves in comparison with the treatment of high temperature+spraying water.4.The treatment of high temperature+spraying water increased leaf temperature and panicle temperature and decreased net photosynthetic rate,transpiration rate and stomatal conductance of leaves in comparison with the treatment of normal temperature+spraying water.The treatment of high temperature+spraying MeJA significantly decreased the leaf temperature and panicle temperature and significantly increased the net photosynthetic rate,transpiration rate and stomatal conductance of leaves when compared with the treatment of high temperature+spraying water.5.When compared with the treatment of normal temperature+spraying water,the treatment of high temperature+spraying water decreased the contents of indole acetic acid,zeatin+zeatin riboside and gibberellins,while increased the content of abscisie acid in the flag leaf.The treatment of high temperature+spraying MeJA significantly increased the contents of indole acetic acid,zeatin and zeatin riboside,gibberellins and abscisic acid in the flag leaf relative to the treatment of high temperature+spraying water.The results indicate that spraying MeJA under high temperature stress could significantly alleviate the adverse effects of high temperature on spikelet-opening and seed-setting of PTSGMS rice lines.Spraying MeJA promotes water absorption for the lodicules and increases both spikelet-opening rate and stigma exsertion rate through elevating the contents of jasmonic ascid,MeJA and soluble sugar in lodicules and the increase in fresh weight of lodicules.The roles of spraying MeJA in the alleviating adverse effects of high temperature on the spikelet-opening and seed-setting are also attributed to the increases in other hormones,photosynthesis and antioxidant capacity of leaves in PTSGMS rice lines.