Key Techniques And Mechanisms Of Improving The Salt Tolerance Of Cucumber Seedlings By Exogenous Spermidine

Salt stress is an important abiotic stress factor that restricts the growth and development of plants.The application of growth regulators can alleviate the stress on plants and increase the biomass of crops.The results showed that exogenous spermidine(Spd)could improve the tolerance of plants under salt stress.In this study,the salt-sensitive cucumber variety’Jinchun No.2’(Cucumis sativus L.cv.’Jinchun No.2’)was used as a test material to study the alleviation effect of exogenous Spd on salt stress injury of cucumber seedlings In addition,the key application techniques of Spd were summarized,and the mechanism of Spd to improve the salt tolerance of cucumber seedlings was discussed.The main results were as follows:1.Under salt stress,exogenous spraying of Spd could alleviate the inhibition of salt stress on cucumber seedling growth,significantly increase the seedling index and G value,and significantly reduce the MDA content of leaves and significantly improve the osmotic adjustment ability.Combined with previous studies,the key technique for relieving salt stress damage of cucumber seedlings by using exogenous spermidine is as follows:when the third leaves of the cucumber seedlings are fully expanded,the spraying of 1 mM Spd on the leaves for 7 d continuously can significantly improve the tolerance of the seedling to salt stress,which is an effective measure to cultivate strong cucumber seedlings in saline soil.2.The content of endogenous GA3 in cucumber leaves treated with Spd for 7 days under salt stress was detected by HPLC.It was found that Spd enhanced the accumulation of endogenous GA3.The results of qRT-PCR and gibberellin oxidase activity assay showed that Spd induced the expression of GA-related genes and enhanced the activity of gibberellin oxidase under salt stress.The results indicated that exogenous Spd promoted the accumulation of GA3 in cucumber leaves under salt stress by increasing the activity of key enzyme for GA synthesis and its gene expression level,so as to improve plant salt tolerance.3.The results of qRT-PCR and Western blot showed that the CsGT-3b gene was induced by salt stress and Spd could upregulate the expression of CsGT-3b under salt stress.The CsGT-3b promoter sequence was obtained from the NCBI database and the 1278 bp upstream from the start codon(ATG)of CsGT-3b was isolated for further analysis.The GUS staining and GUS fluorescence quantification results indicated that GA3 can activate the CsGT-3b gene promoter and promote the involvement of CsGT-3b in stress response.Further studies demonstrated GA3 could regulate the expression of the CsGT-3b gene.The above results indicate that Spd regulates CsGT-3b expression and that this regulation is mediated by GA3.These results have deepened the understanding of the molecular mechanism by which spermidine enhances plant salt tolerance.