Hydrogen Sulfide Relieves The Damage Of Tomato Plants Caused By Salt Stress Through Ethylene Signaling Pathway

Salt stress has now become a serious global environmental problem.Nearly one third of the world's arable land has become or will become saline-alkali land,which affects the development of crops and results in the reduction of crop yield.Tomato?Solanum lycopersicum L?is an important cash crop in China,with high nutritional value and delicious flavor.As the whole genome of tomato has been sequenced,and it is also a moderately salt-sensitive crop,tomato can be used as experimental material to study the mechanism and mitigation measures in response to salt stress.As the third gasotransmitter,the physiological function of endogenous H₂S has been gradually revealed.In animals,endogenous H₂S plays an important role in cardiovascular system,nervous system,immune system,respiratory system and reproductive system.In plants,endogenous H₂S improves seed germination rate,promotes the formation and development of roots,improves plant photosynthesis,and delays plant senescence.Moreover,studies have also shown that endogenous H₂S plays an important role in the resistance of plant to drought stress,heavy metal stress,cold stress,high temperature stress and salt stress.In this experiment,the tomato cv.Alisa Craig was used as the experimental material to explore the mechanism about how H₂S alleviate the salt stress.The main results are as follows:1.Salt stress caused a decrease in fresh weight,affected photosynthesis,reduced chlorophyll content in leaves,and caused the accumulation of harmful substance MDA in tomatoes.Salt stress induced the production of endogenous H₂S,and the exogenous H₂S fumigation increased the fresh weight,plant height,chlorophyll content and decreased the accumulation of MDA,alleviated the effects of salt stress on tomato seedlings.2.The expression level changes of SlOAS2,SlOAS4,SlOAS5 and SlOAS6 from the OASTL family were detected,and the expression of SlOAS2,SlOAS5 and SlOAS6 were induced under salt stress,while exogenous H₂S inhibited their expression.SlOAS2 might be the major gene responsible for the endogenous production of H₂S in tomato plant under salt stress,while SlOAS4 was not involved in the endogenous production of H₂S under salt stress.The SlOAS2 knockout plants have now constructed to further investigate the role of SlOAS2 in tomato salt tolerance at the genetic level.3.Salt stress caused oxidative stress and osmotic stress in tomato plants.Under salt stress,H₂S could activate the antioxidant enzymes SOD,POD,CAT and APX to cope with oxidative stress,among which SOD and POD played a major role in this process.Moreover H₂S could further increase proline content under salt stress to combat the influence of osmotic stress.Therefore,H₂S was involved in the antioxidant system and osmotic regulation system of plants in response to salt stress.4.The key genes in ethylene biosynthesis and signal transduction,such as ACS6,ACO1,ERF3,ETR4 and ETR10,were detected under salt stress and exogenous H₂S treatment.These genes were significantly induced to express under H₂S treatment.Combined with pharmacological experiments,H₂S might act in the upstream of ethylene to respond to salt stress.