Abstract Exogenous salicylic acid (SA) can alleviate salt stress in plants. Previous researches have been focused on SA’s role in leaf morphological and physiological characteristics, however, little information is available on its role in both leaf photosynthesis and root system architecture (RSA). A hydroponic study was conducted to analyze biomass, leaf photosynthesis, RSA parameters and expression of RSA genes in cucumber seedlings grown under four treatments, including control (CK), 50 mM NaCl (NaCl), 0.3 mM SA (SA) and 50 mM NaCl plus 0.3 mM SA (NaCl + SA). The results showed that compared with CK, both NaCl and SA treatments severely reduced relative growth rate (RGR) and leaf photosynthetic parameters (Fv/Fm, ΦII and Pn). However, compared with NaCl treatment, NaCl + SA treatment significantly increased RGR, leaf photosynthetic (Fv/Fm, ΦII and Pn) and RSA (total root length, root surface area, number and total length of primary and secondary LR) parameters. In addition, compared with CK, although both NaCl and SA treatments down-regulated expression of GL2 gene and up-regulated expression of RHD2 gene, NaCl + SA treatment notably up-regulated expression of NAC1, NAC2, GL2, EXP and down-regulated expression of RHD2. It is concluded that exogenous SA alleviated salt stress via effectively promoting leaf photosynthesis and RSA in cucumber seedlings. SA-mediated increment in expression of RSA genes, total length and number of primary and secondary LR could contribute to the improved RSA.

中文翻译：

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外源水杨酸通过改善黄瓜幼苗的叶片光合作用和根系结构减轻盐胁迫

摘要 外源水杨酸（SA）可以缓解植物的盐胁迫。以前的研究一直集中在 SA 在叶片形态和生理特征中的作用，然而，关于其在叶片光合作用和根系结构 (RSA) 中的作用的信息很少。进行水培研究以分析在四种处理下生长的黄瓜幼苗中的生物量、叶片光合作用、RSA 参数和 RSA 基因的表达，包括对照 (CK)、50 mM NaCl (NaCl)、0.3 mM SA (SA) 和 50 mM NaCl加 0.3 mM SA（NaCl + SA）。结果表明，与CK相比，NaCl和SA处理均严重降低了相对生长速率（RGR）和叶片光合参数（Fv/Fm、ΦII和Pn）。然而，与NaCl处理相比，NaCl+SA处理显着提高了RGR、叶片光合（Fv/Fm、ΦII 和 Pn) 和 RSA（总根长、根表面积、初级和次级 LR 的数量和总长度）参数。此外，与CK相比，虽然NaCl和SA处理均下调GL2基因的表达，上调RHD2基因的表达，但NaCl+SA处理显着上调NAC1、NAC2、GL2、EXP的表达并下调RHD2 的表达。结论外源SA通过有效促进黄瓜幼苗叶片光合作用和RSA减轻盐胁迫。SA 介导的 RSA 基因表达、总长度和初级和次级 LR 数量的增加可能有助于改善 RSA。尽管NaCl和SA处理均下调GL2基因的表达并上调RHD2基因的表达，但NaCl+SA处理显着上调NAC1、NAC2、GL2、EXP的表达并下调RHD2的表达。结论外源SA通过有效促进黄瓜幼苗叶片光合作用和RSA减轻盐胁迫。SA 介导的 RSA 基因表达、总长度和初级和次级 LR 数量的增加可能有助于改善 RSA。尽管NaCl和SA处理均下调GL2基因的表达并上调RHD2基因的表达，但NaCl+SA处理显着上调NAC1、NAC2、GL2、EXP的表达并下调RHD2的表达。结论外源SA通过有效促进黄瓜幼苗叶片光合作用和RSA减轻盐胁迫。SA 介导的 RSA 基因表达、总长度和初级和次级 LR 数量的增加可能有助于改善 RSA。