Functional Analysis Of Tomato LeENH1Gene Under Salt Stress

High salinity is one of the major adverse environmental factors that affect plant growthand lead to yield loss in crops. The toxicity of ions, particularly Na⁺, is the main reason forplant growth inhibition in saline soils. Salt stress causes excess accumulation of toxic Na⁺inthe cytosol and a deficiency of essential ions, such as K⁺. K⁺participates in numerousphysiological processes, such as enzyme activity regulation, protein synthesis, andosmoregulation. Excess Na⁺in the cytosol inhibits photosynthesis and cause PSIIphotoinhibition and lipid peroxidation.The salt overly sensitive pathway has an important function in plant salinity tolerance.The enhancer of SOS3-1（ENH1） participates in a new salinity stress pathway with SOS2butwithout SOS3. However, the mechanism by which ENH1affects the reestablishment of ionhomeostasis, photosynthesis, and ROS levels remains unclear. In this research, to investigatethe physiological effects and functional mechanism of ENH1under salt stress, ENH1wasisolated from tomato and overexpressed in tobacco. The main results are as follow:（1） The subcellular localization of LeENH1was investigated in tobacco protoplasts. Theresults indicated that LeENH1localized in the chloroplasts. Total RNA was used forquantitative RT-PCR （qRT-PCR）. The expression level of LeENH1was the lowest in the rootsand the highest in the leaves. In the stems, flowers, and fruits, the expression level of LeENH1was very low.（2） The sense transgenic tobacco plants were obtained. Under salt stress, the sproutingpercentage, fresh weight, and dry weight of transgenic plants were higher than those ofwild-type （WT） plants. The chlorophyll content, net photosynthetic rate, and maximalphotochemical efficiency of PSII in transgenic plants decreased more slowly than those inWT plants. The results indicated that the damage of photosynthetic apparatus was alleviatedin transgenic plants under salt stress. （3） The overexpression of LeENH1in tobacco excluded Na⁺from the cytosol andretained high K⁺levels in the cytosol to reestablish ion homeostasis.（4） Histochemical detection of H₂O₂and O₂and quantitative analysis of H₂O₂showedthat the overexpression of LeENH1decreased ROS production in the chloroplasts. APXreduces H₂O₂to H₂O ascorbate （AsA） as an electron donor. More than50%of APX in thechloroplasts are tAPX. Under salt stress, the tAPX activity in WT plants was significantlyinhibited than that in transgenic plants. Higher tAPX activity in transgenic plants canscavenge more ROS under salt stress.