盐胁迫是制约植物生长发育的重要的非生物胁迫因素，而施用生长调节物质可以缓解植物遭受的压力，提高作物的生物量。研究证明，外源亚精胺（Spd）可以提高植物在盐胁迫下的耐受力。本研究以盐敏感的黄瓜品种‘津春 2 号’（Cucumis sativus L. cv. ‘Jinchun No. 2’ ）为试材，研究外源Spd对黄瓜幼苗盐胁迫伤害的缓解作用，总结出Spd使用的关键技术，并对Spd提高黄瓜幼苗耐盐性的机制进行探讨。主要研究结果如下： 1. 盐胁迫下，外源喷施Spd可明显缓解盐胁迫对黄瓜幼苗生长的抑制作用，显著提高壮苗指数和G值，使叶片MDA含量明显降低，渗透调节能力显著提高。结合前期研究，总结出利用外源Spd缓解黄瓜幼苗盐胁迫伤害的关键技术为：在黄瓜幼苗三叶一心时，叶面喷施1 mM的Spd，连续喷施7 d，并提出了相应的技术方案。 2. 采用HPLC法检测盐胁迫下Spd处理7 d的黄瓜叶片内源GA3含量，发现Spd增强了内源GA3含量的积累。qRT-PCR和赤霉素氧化酶活性检测结果表明，盐胁迫下Spd诱导与GA合成相关基因的表达，增强赤霉素氧化酶的活性，表明盐胁迫下外源Spd通过提高GA合成关键酶活性及其基因表达水平，促进黄瓜叶片中GA3积累，从而提高植株耐盐性。 3. qRT-PCR及免疫印迹结果表明，CsGT-3b受盐胁迫诱导，并且盐胁迫下Spd可调控CsGT-3b表达。据NCBI数据库获得黄瓜GT-3b基因5´上游序列，克隆获得CsGT-3b启动子1278 bp序列，并预测该启动子中可能存在响应GA的顺式作用元件，进一步通过烟草叶片瞬时转化体系证实GA3能激活CsGT-3b基因启动子，促进 CsGT-3b参与胁迫防御反应。进一步研究结果表明，GA3可上调CsGT-3b表达。上述结果表明，Spd调控CsGT-3b表达是由GA3介导的。本研究结果深化了对Spd提高植物抗盐性分子机制的理解。

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.