Physiological Role And Molecular Mechanism Of Brassinolide-Mediated Polyamines-Dependent Enhanced Salt Tolerance Of Tomato

The salt stress caused by soil salinization to plants has become one of the most important environmental stresses in the world.Tomato is an important vegetable crop and is widely planted in my country.Its cultivation area and output rank first in the world.Tomatoes are moderately sensitive to soil salt,so salt stress will have a negative effect on their growth,yield and fruit quality.24-Epibrassinolide(EBL)is a brassinosteroid compound,and its application is beneficial to improve the tolerance of plants to abiotic stress.In this study,tomato "Hezuo 903" was used as the test material.Under salt stress,the plant growth regulator EBL and polyamine biosynthesis inhibitor D-arginine(D-Arg)were soaked or sprayed to explore its effects on tomato germination and growth.,Photosynthesis,ion homeostasis,redox homeostasis,and osmotic adjustment substance accumulation.Through exclusive analysis,we study the response mechanism of PAs metabolism in tomato leaves under salt stress to plant salt tolerance under the action of exogenous EBL,and finally adopt transcription Group sequencing was used to analyze and verify the EBL regulation of gene expression in tomato seedlings under short-term salt stress and the role of endogenous polyamines.The main results are as follows:1.Under salt stress,EBL seed soaking can significantly increase the germination rate,seed vigor index and seedling biomass of tomato seeds.At the same time,exogenous spraying of EBL can significantly promote the growth of various organs of tomato plants,and maintain the ion homeostasis within the plant under salt stress by promoting the absorption and transport of K+ by the plant and reducing the accumulation of Na+ in the plant.In addition,EBL can increase the photosynthetic pigment content of plants and increase the photosynthesis of plant leaves under salt stress.The salt-stressed tomato seed germination,seedling growth,ion homeostasis,photosynthetic pigment level,and photosynthetic capacity under the combined treatment with EBL alone and D-Arg+EBL combined treatment all decreased to varying degrees.Compared with the D-Arg treatment,the D-Arg+EBL combination treatment improved tomato seedling growth and seed vigor to varying degrees,and the plant’s biomass,water content,ion homeostasis,photosynthetic pigment,and photosynthetic capacity were also different.The degree of rise.It shows that the endogenous PAs synthesis of tomato seeds or plants has an important contribution to EBL to enhance the salt tolerance of plants,especially in seed germination.EBL enhances the salt tolerance of tomato seeds or plants.In addition to polyamine endogenous regulatory pathways,there are other regulatory pathways,especially in the seedling stage.2.Under salt stress,EBL spraying significantly enhanced the antioxidant enzyme activity of tomato leaves,increased proline,betaine,soluble protein,typical soluble sugar and reduced glutathione content,reduced plant leaf ROS,and reduced MDA content,Relieve cell damage.However,under salt stress,compared with EBL spraying alone,the above-mentioned antioxidant enzymes and solutes of tomato plants under combined D-Arg+EBL spraying were reduced to varying degrees,resulting in increased ROS and MDA content in plant leaves and increased cell damage.Compared with D-Arg spraying,under the combined spraying of D-Arg+EBL,the ROS and MDA levels of salt-stressed tomato plants decreased to varying degrees,the antioxidant enzyme activity increased to varying degrees,proline,betaine,and soluble protein,Sucrose content increased to varying degrees,the overall improvement of the plant’s antioxidant capacity and the alleviation of cell damage were enhanced,but the glucose content further decreased.It shows that the endogenous PAs synthesis of tomato plants has a significant effect in enhancing the solute accumulation of the plant and the enhancement of the antioxidant capacity of the plant.In addition to regulating the synthesis of PAs,EBL also regulates other regulatory pathways related to the enhancement of plant antioxidants.3.Under salt stress,spraying EBL increased the activities of arginine decarboxylase(ADC)and ornithine decarboxylase(ODC)to varying degrees,while reducing the enzymes of diamine oxidase(DAO)and polyamine oxidase(PAO)Live,and significantly increase the content of free,bound and bound PAs.Under salt stress,compared with EBL spraying alone,the enzyme activities of ADC and ODC in tomato leaves under the combined spraying of D-Arg+EBL decreased,while the enzyme activities of DAO and PAO increased,resulting in free state,bound state and bound state.The content of state PAs generally showed a downward trend,which proves the inhibitory effect of D-Arg on PAs accumulation.Under salt stress,compared with D-Arg spraying,the combined spraying of D-Arg+EBL increased the enzyme activities of ADC and ODC of tomato plants to different degrees,but decreased the enzyme activities of DAO and PAO,thereby increasing the free state and binding to different degrees.The content of PAs in state and bound state.It shows that spraying EBL can adjust the metabolism of tomato plants and increase the content of endogenous PAs.4.Salt stress inhibits the growth of tomato seedlings and accelerates the senescence of tomato leaves,while exogenous application of EBL can improve the negative effects of salt stress on plants and improve their salt tolerance.The short-term salt treatment also confirmed the above conclusions at the molecular level.We used the selected DEGs to perform GO enrichment analysis and found that EBL regulates the expression of genes related to salt stress and defense responses in tomato seedling leaves.EBL improves the activity of these three antioxidant enzymes by regulating the expression of genes related to POD,SOD and CAT,thereby eliminating excess ROS in leaves.In addition,the metabolic pathways affected by EBL are mainly related to photosynthesis and substance synthesis and metabolism.Therefore,promoting photosynthesis and regulating the synthesis and metabolism of substances is one of the main strategies of EBL to improve salt stress tolerance.In addition,we noticed that EBL also affects the plant’s MAPK signal transduction pathway,which improves plant resistance to stress by increasing the activity of antioxidant enzymes and accumulating active substances.Similarly,spraying EBL on the basis of spraying D-Arg enriched DEGs in terms of organic nitrogen synthesis and metabolism,oxidative stress,photosynthesis,and up-regulated the Arg biosynthetic pathway.Finally,we found that EBL can regulate the expression level of a variety of TFs,and WRKY,NAC,ERF,and MYB all play a positive regulatory role in plant salt tolerance.These transcription factors are involved in encoding plant endogenous growth substances and improving plant resistance.Sex,and participate in the process of plants coping with abiotic stress.