Mechanism Of Brassinolide Alleviating Salt Stress In Peanut

Peanut is one of the important oil crops.Most of peanut varieties are salt-sensitive,the growth and productivity of which are severely affected by salt stress.24-epibrassinolide(EBL)plays an important role in regulating plant growth,development and stress resistance.However,the effect and mechanism of exogenous EBL on the salt tolerance of peanut remain unclear.In this study,peanut cultivar Kainong 1715 was used as material to explore the response of EBL to peanut salt stress through the analysis of physiological indexes and gene expression profile under salt stress.The main results are as follows:1.Peanut seedlings of 12 d were treated with five NaCl concentrations.Compared with CK,150 m M NaCl treatment showed significant decline in plant height and biomass were decreased while MDA content were increased.The results showd that 150 m M NaCl stress seriously inhibited the growth of peanut seedlings.Therefore,150 m M NaCl was selected as the stress concentration.2.Peanut seedlings of 12 d were treated with 150 m M NaCl stress and five different EBL concentrations,respectively.Compared with treated 150 m M NaCl alone,the plant height and biomass of peanut seedlings,the height of main stemand the fresh weight of seedlings were increased significantly while the content of MDA(22.98%)were significantly reduced when treated with 150 m M NaCl together with foliar spraying of 0.1 μM EBL.0.1 μM EBL effectively alleviated the salt stress of peanut seedlings.3.To illuminate the mechanism of EBL in alleviating peanut salt stress,peanut seedlings of12 d were treated with CK(control),N(150 m M NaCl),NE(150 m M NaCl + 0.1 μM EBL)and E(0.1 μM EBL).Compared with CK,150 m M NaCl treatment significantly decreased the growth indexes of peanut seedlings and elevated contents of ROS and MDA,indicating that NaCl stress caused peanut seedlings to suffer oxidative stress and damage cell membrane.Treatment with both 150 m M NaCl and foliar spraying of 0.1 μM EBL significantly induced CAT activity,reduced ROS content and MDA content,thereby protecting cell membrane.Compared with CK,150 m M NaCl treatment significantly increased the contents of proline and soluble sugar,while the relative water content of leaves decreased significantly,indicating that150 m M NaCl stress caused peanut seedlings to suffer osmotic stress,and the seedlings alleviated osmotic stress by accumulating osmotic regulators;Compared with NaCl stress alone,simultaneous treatment with 150 m M NaCl and foliar spraying of 0.1 μM EBL significantly increased the content of proline and soluble sugar,and the relative water content of leaves,indicating that EBL effectively alleviated the osmotic stress of peanut seedlings.In addition,under NaCl stress,the photochemical reaction efficiency of peanut seedlings lowered significantly.Howerver,treatment with NE enhanced the chlorophyll content and photochemical reaction efficiency of peanut seedlings,reduced heat dissipation,which promoted the growth of peanut seedlings and improved the salt tolerance of seedlings.4.The gene expression profiles of peanut seedlings under four treatments showed that under NaCl stress,EBL treatment up-regulated peroxisome related genes PMP34,and genes related to accumulation of soluble sugar such as SPS2 and BFRUCT1,and down-regulated genes related to degradation proline PRODH.Furthermore,EBL treatment up-regulated genes regulating ion balance including NHX7 and NHX8,and also regulated phytohormone such as BR,ABA and auxin related genes to promote seedling growth and stress adaptation under salt stress.Taken together,our results revealed that EBL may enhance the antioxidant defense system by up-regulating peroxisome-related genes PMP34,accumulate soluble sugar and proline by up-regulating SPS2 and BFRUCT1 and down-regulating PRODH,and maintain ion homeostasis by up-regulating NHX7 and NHX8.The plant hormones were also involved in the process to alleviate salt stress of peanut.This study provides valuable information for salt resistance study in peanut and lay the foundation for using BR to enhance salt tolerance during peanut production.