Effects Of Methyl Jasmonate On Resistance To High Temperature In Rice

Methyl jasmonate(MeJA)is a typical representative of jasmonates,the new type of plant hormone.Its’ effects on plant stress resistances and rice floret opening have been well elucidated.This study explored the physiological effects of MeJA on high temperature resistance in rice seedlings and the effects of MeJA on escaping high temperature harm during floret opening in rice.The main results are as follows:1.Seedlings of rice varieties Wuyunjing No.7 or Tianyou 998 at 3-leaf stage were sprayed with 0-3 mmol/L MeJA solutions at 27℃.After 24 h,seedlings were shifted to phytotrons with temperature set at 40℃,and leaf samples were taken for physiological and biochemical analyses at 6h,12 h and 24 h,respectively.The results showed: MeJA increased water content,enzyme activities of catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD),but decreased contents of free proline and malondialdehyde(MDA)of seedling leaves under high temperature of 40℃.2.Seedlings of rice varieties Wuyunjing No.7 were cultured in 28℃ phytotrons.At 3-leaf stage,seedlings were sprayed with 0-5 mmol/L Me JA and then shifted to phytotrons with higher temperatures after 24 h.Photosynthetic characters and plant hormones contents were measured at 0h,6h,12 h and 24 h after high temperature treatments,respectively.The results showed:(1)Stomatal conductance,transpiration and photosynthetic rates of control leaves were increased by temperature of 38℃ and decreased by temperature of 45℃.MeJA increased stomatal conductance,transpiration and photosynthetic rates at 28℃;when seedlings were shifed to higher temperature,stomatal conductance,transpiration and photosynthetic rates had no significant changes at 38℃,but decreased sharply at 45℃.(2)Both 38℃ and 45℃ increased contents of IAA,MeJA and ABA after 6h treatment.At 28℃,while 1-5 mmol/L MeJA increased MeJA content they showed no effects on IAA and ABA contents;when seedlings were shifed to higher temperature,MeJA inhibited the increasing of IAA contents caused by 6h high temperature treatments,1mmol/L MeJA inhibited the increasing of ABA contents caused by temperature of 38℃,1-5 mmol/L MeJA enhanced the increasing of ABA contents caused by temperature of 45℃.3.Using rice varieties Jinyougui 99 and ⅡYou 838 as experiment material,and imitating high temperature environment by artificial supplementary heating,panicles were sprayed with 1 mmol MeJA at 7:00 in heading stage and the effects of MeJA on escaping high temperature by enhancing floret opening were investigated.The results showed: In Jinyougui 99,period of floret opening to closing was shifted from 10:00-13:30 to 8:00-11:30 and temperature of opening to closing was decreased from 31-40℃ to 28-34℃ by MeJA treatment.MeJA significantly increased seed seting rate and panicle yield in both rice varieties.