Effects Of Exogenous Melatonin On Salt Tolerance In Radish(Raphaus Sativus L.)

Radish(Raphanus sativus L.)is an important root and vegetable crop originating in China,occupying an important position in vegetable production and supply.Radish edible roots are susceptible to varying degrees of salt damage,and different genotypes have significant differences in salt tolerance.Therefore,how to create a new salt-resistant new germplasm,cultivate new varieties of salt-resistant radish,becoming an important issue in the field of vegetable genetics and breeding.Melatonin(MT)is a tryptophan derivative,which has the ability to protect plant chlorophyll,promote plant root growth,delay senescence and enhance plant resistance to stress,but its resistance to radish and its regulation Mechanism has not yet been clarified.In view of this,the salt tolerance of different genotypes of radish was selected,and the effect of exogenous melatonin on the antioxidant system of radish seedling under salt stress was studied by using the salt-resistant variety"NAU-XBC’ as the material,and the RNA-seq technique was used to identify the genes that responded to the salt stress response of melon to the theoretical basis of genetic improvement and germplasm innovation of radish salt tolerance.The main achievements obtained were as follows:1.Through the analysis of salt tolerance index and morphological index of radish varieties,the root length,true leaf number,plant height,root fresh weight and leaf fresh weight of the five characters were selected as the salt tolerance index,and the salt tolerant genotypes of radish were screened.Through the cluster analysis of comprehensive salt tolerance evaluation(D value),Thirty-six varieties of radish were divided into five categories:Nau-XGXBY,Nau-HX1 and Nau-LLYH belong to the high salt sensitive material;Nau-NRH3,Nau-NS40,Nau-LLXHT and Nau-BYC belong to the type of salt sensitive materials;Nau-QTYH,Nau-NSP,Nau-XLM and other 15 radish varieties belonging to moderate salt tolerant types.Nau-CNZBT,Nau-LLZQH,Nau-LLDHP and other five radish varieties belong to the type of salt tolerant materials;Nau-127,Nau-XLB and Nau-LLCXH belong to the high salt resistance type material.2.The effects of melatonin of soluble protein,superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),malondialdehyde(MDA),superoxide anion(O2·-),ascorbate peroxidase(APX)and glutathione reductase(GR)activities in medium salt-resistant radish variety "NAU-XBC’ for the material to analyze the antioxidant system components.The results showed that the activity of SOD,POD,CAT,APX and GR increased first and then decreased under salt stress,and the contents of MDA and O2·-were increased rapidly,and after spraying melatonin,The activity of MDA was significantly increased,and the contents of MDA and O2·-were significantly decreased.The results indicated that exogenous melatonin could raise the activities of antioxidant enzymes and decrease the membrane lipid peroxidation for radish seedlings,which could alleviate the damage of salt stress and improve the salt stress adaptability of plant.3.The RNA-Seq technique was used to analyze the differential expression of melatonin in radish stress response of radish.In the untreated(CK)and Na-treated 1(150 mMNa),a total of 3278 significantly differentially-expressed genes(DEGs)were detected consisted of 2,154 up-and 2,460 down-regulated genes between the two libraries.In the untreated(CK)and Na-treated 2(150 mMNa+100 μmol/LMT),a total of 2244 significantly differentially-expressed genes were detected consisted of 1047 up-and 1197 down-regulated genes between the two libraries.Na-treated 1(150 mM Na)and Na-treated 2(150 mMNa+100 μmol/LMT),Totally,8709 differentially expressed genes including 3931 up-regulated and 4778 down-regulated genes were identified.RT-qPCR analysis revealed that the expression profiles of DEGs were in line with results from the RNA-Seq analysis.Functional annotation analysis revealed that DEGs under Salt stress were predominately involved in transcription factors,auxin regulation,Ca2+ signal transduction and so on.The results will help to understand the regulation of melatonin related genes in salt stress response and improve the salt tolerance of radish seedlings.