Exogenous ?-Aminobutyric Acid Regulates Reactive Oxygen Species And Chlorophyll Metabolism To Enchance Salinity-Alkalinity Stress Tolerance In Muskmelon Seedlings

Melon is an improtant economic crop in the northwest of China,which is suitable for cultivation in weakly acidic soil.However soil salinity-alkilinity is currently a serious phenomenon which has been become a major abiotic stress to affect plant growth and development.?-aminobutyric acid?GABA?is widely founded in animal and plant with having a certain improvement effect on the growth and development of melon seedlings under salinity-alkalinity stress.However,the interactions between cellular redox signaling and chlorophyll?Chl?metabolism involved in GABA-induced salinity-alkalinity stress tolerance in plants is still largely unknown.In this study,hydroponic experiments were performed using the salt-sensitive muskmelon?Cucumis melo L.cv.Yipintianxia No.208?as experimental material.The study focused on:The effects of GABA on Reactive Oxygen Species metabolism of muskmelon seedlings under salinity-alkalinity stress;The effects of GABA on chlorophyll metabolism of muskmelon seedlings under salinity-alkalinity stress;The effects of H₂O₂,GSH,and AsA in GABA-induced tolerance response to oxidative stress under salinity-alkalinity stress.The main results are as follows:1.The effects of exogenous GABA and GABA synthesis inhibitors?3-MP?on growth inhibition and oxidative damage of muskmelon seedlings were studied under salinity-alkalinity stress.The results showed that the salinity-alkalinity stress caused excessive accumulation of ROS,which in turn poisoned the cells,resulting in a large amount of malondialdehyde?MDA?,electrolyte leakage and increased relative electrical conductivity?REC?,the growth of plants was inhibited,but the dry weight of plants decreased,the leaf area decreased,the roots growth was inhibited by different degrees.Exogenous spraying of GABA significantly alleviated the above-mentioned damage caused by salinity-alkalinity stress,and the ability of exogenous GABA to scavenge ROS in leaves was superior to roots.Under salinity-alkalinity stress,inhibition of endogenous GABA synthesis caused more serious damage,while exogenous application of GABA on plants could alleviate oxidative damage to a certain extent,but could not significantly alleviate the inhibition of plant growth caused by inhibition of the endogenous GABA.In summary,GABA plays an important role in the elimination of ROS,protecting membrane stability and inhibition of plant growth in muskmelon seedlings under salinity-alkalinity stress.The normal metabolism of GABA plays an important part in plant growth and development.2.The effects of exogenous GABA on the antioxidant system of muskmelon seedlings under salinity-alkalinity stress were studied.The results indicated that GABA show inconsistent regulation of antioxidant systems in leaf and root under salinity-alkalinity stress.Exogenous GABA in leaves mainly attenuated oxidative damage by increasing SOD activity and promoting the circulation of AsA-GSH,while the regulating effect on roots was weaker than that on leaves.Therefore,spraying GABA on leaves could alleviate the salinity-alkalinity stress of muskmelon seedlings,and the leaf mitigation effect was preferable to the root.3.The effects of H₂O₂,AsA and GSH on GABA-induced salinity tolerance were investigated using H₂O₂,AsA and GSH synthesis inhibitors?DMTU,DPI,BSO and AF?.The results showed that H₂O₂,AsA or GSH can alleviate the salinity-alkalinity stress of muskmelon.Inhibition of endogenous H₂O₂ synthesis,the effect of GABA on alleviating salinity-alkalinity stress is limited,but inhibition of endogenous GSH or AsA had no significant effect on the function of GABA.In addition,exogenous GABA induced H₂O₂accumulated rapidly in a short time under non-stress conditions,while reduced the H₂O₂accumulated under salinity-alkalinity stress.Therefore,H₂O₂,AsA and GSH played an important role in improving the tolerance of muskmelon seedlings to salinity-alkalinity stress.Among them,H₂O₂ may act as a signaling substance to mediate GABA regulation of ROS metabolism under salinity-alkalinity stress,while AsA and GSH are more likely to act as antioxidants to balance the metabolism of ROS.4.The effects of exogenous application of GABA on chlorophyll biosynthesis of muskmelon seedlings under salinity-alkalinity stress were studied.The results showed that the salinity-alkalinity stress promote the accumulation of chlorophyll and its precursors at various stages of chlorophyll synthesis.However,the salinity-alkalinity stress only increased the expression level of the ALAD gene,decreased the expression levels of PBGD,POR,CHLM,CHLG,and CAO.Furthermore,with the increase of stress time,the accumulation of endogenous glutamate?Glu?was increased,the accumulation of endogenous GABA was decreased,but the ALA content was increased,which indicated that salinity-alkalinity stress may promote the conversion of Glu to ALA,but inhibit the conversion to GABA.GABA application could reduce the accumulation of chlorophyll and its intermediates induced by salinity-alkalinity stress,and make its level closer to normal value,alleviating the photodamage caused by the accumulation of chlorophyll-synthesized intermediates on muskmelon seedlings,thus alleviating the salinity-alkalinity stress.