Study Of The Concentration Effect And Physiological Mechanism Of Brassinolide On Salt Tolerant Regulation In Tomato

Due to natural factors or unreasonable irrigation by people or rapid development of facility agriculture,soil salinization has gradually increased and seriously affecting crop growth,yield and quality.Tomato(Solanum lycopersicum)is one of the most widely cultivated crops,the soil salinization inhibits its growth and causes huge economic losses.24-epibrassinolide(EBL)is one of the brassinosteroids(BRs),which is beneficial for improving the stress resistance of plants,crop yield and quality.However,there are few studies on the regulation of salt tolerance of tomato by exogenous EBL.Therefore,the study was carried out from two aspects,one is the study of seed soaking of EBL and then germination,the other is spraying of exogenous EBL on tomato plants to investigate the concentration effect and physiological and biochemical mechanism of EBL on salt tolerance regulation of tomato under salt stress,and to provide theoretical basis for improving salt tolerance of tomato plants in production.The main results and conclusions of this study were showed as follows:1.In terms of germination rate,length of root and hypocotyl,fresh weight of seedlings and seed vigor,soaking seeds with 10-9 mol L-1 EBL showed significantly promoted the effect of tomato seed germination under high salt stress,mainly because EBL actively promoted the transformation of substancein in tomato seed germination,such as the content of soluble sugar(SS),soluble protein(SP)and proline(Pro)were increased.At the same time,the activities of superoxide dismutase(SOD)and peroxidase(POD)were enhanced,which improved the oxidative stress induced by salt stress in tomato seed germination.However,EBL showed a slightly the effect of promoting seed germination under low salt stress,and the concentrations of EBL soaked seeds were too high,which showed inhibition effect on seeds germination under all treatments.2.Exogenous spraying of EBL with different concentration on tomato leaf surface was consistent with the results of soaking seeds germination,that is,10-9 mol L-1 EBL promoted the best,which can significantly promote the growth of different organs of tomato plants,significantly increase the selective absorption of K+in roots and shoots,reduce the accumulation of Na+in tomato plants,and increase the ratio of K+/Na+,maintains ion homeostasis,and significantly increases chlorophyll content,net photo synthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)and maximum fluorescence(Fm),PSⅡ actual photochemical efficiency(ΦPSⅡ)and PSⅡmaximum photochemical efficiency(Fv/Fm),thereby significantly improving leaf photosynthesis and promoting accumulation of biomass in different organs under salt stress.3.Exogenous EBL increased the activities of antioxidant enzymes(ie SOD,POD,CAT,APX)and pro content in different organs of tomato plants under NaCl stress.It could resulte in a significant increase in anthocyanin content in stems and leaves of tomato plants,but exogenous EBL significantly reduced anthocyanin content in stems and leaves under salt stress.Exogenous EBL reduced the contents of malondialdehyde(MDA)and Na+in different organs of tomato plants,and promoted the absorption of K+,Ca2+,Mg2+,especially the K+/Na+,Ca2+/Na+and Mg2+/Na+in the U-stem and U-leaves,maintained the transport and absorption of mineral nutrients ions in order to improved salt tolerance of tomato plants.4.Under salt stress,the content of free and conjugated putrescine(Put)in different organs of tomato plants increased significantly,while exogenous EBL could reduce the accumulation of Put in different organs,especially conjugated Put or bound Put,and promote the accumulation of Spermidine(Spd)and spermine(Spm)in different forms.The activities of diamine oxidase(DAO)and polyamine oxidase(PAO)increased in different organs of tomatoes under salt stress,and the activity of these two enzymes decreased after treatment with exogenous EBL.On the contrary,the activities of Arginine decarboxylase(ADC)and Ornithine decarboxylase(ODC)in different organs of tomato were significantly decreased under salt stress,but exogenous EBL significantly increased ADC and ODC activity.Therefore,exogenous EBL can regulate the level of polyamines,increase the accumulation of Spd and Spm,increase the tolerance to salt stress and promote the growth of tomato by regulating the activity of key enzymes in polyamines metabolism.In conclusion,the above results indicated that EBL had obvious concentration effect.among which 10-9 mol L-1 EBL had the best treatment effect.It can significantly promote tomato germination,growth and development,effectively regulate physiological and biochemical changes in tomato and improve its salt tolerance.It provides theoretical and practical reference for tomato breeding,salt-tolerant cultivation and EBL to alleviate plant salt damage.