Salicylic acid (SA) and hydrogen sulfide (H2S) have been proved to be multifunctional signal molecules to participate in the response of plants to abiotic stresses. However, it is still unclear whether there is interaction between SA and H2S in response to chilling intensity of cucumber seedlings. Here, we found SA was sensitive to chilling intensity. Under normal condition, NaHS (H2S donor) or removing endogenous H2S with hypotaurine (HT, a specific scavenger of H2S) and DL-propargylglycine (PAG, a specific inhibitor of H2S) has no effect on endogenous SA level; however, SA induced endogenous H2S content and activated the activities and mRNA level of l-/d-cysteine desulfhydrase (l-/d-CD), and inhibiting endogenous SA with paclobutrazol (PAC) or 2-aminoindan-2-phosphonic acid (AIP) blocked this effect, implying H2S may play a role after SA signal. Further studies showed that both SA and NaHS notably alleviated chilling injury, which was evidenced by lower electrolyte leakage (EL), MDA content, and ROS accumulation, compared with H2O treatment. Of note, SA and H2S improved the activities and mRNA level of antioxidant enzymes (SOD, POD, CAT, APX, and GR) as well as the contents of AsA and GSH. Additionally, the chilling-response genes (ICE, CBF1, and COR) were obviously upregulated by exogenous SA and NaHS. However, the positive effect of SA on chilling tolerance was inhibited by HT, whereas PAC or AIP did not affect NaHS-induced chilling tolerance. Taken together, the data reveals that H2S acts as a downstream signal of SA-induced chilling tolerance of cucumber via modulating antioxidant system and chilling-response genes.

中文翻译：

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水杨酸诱导的黄瓜幼苗耐冷性需要硫化氢

水杨酸（SA）和硫化氢（H2S）已被证明是参与植物对非生物胁迫响应的多功能信号分子。然而，尚不清楚SA和H2S之间是否存在响应黄瓜幼苗低温强度的相互作用。在这里，我们发现 SA 对寒冷强度敏感。正常情况下，NaHS（H2S供体）或用亚牛磺酸（HT，H2S的特异性清除剂）和DL-炔丙基甘氨酸（PAG，H2S的特异性抑制剂）去除内源性H2S对内源性SA水平没有影响；然而，SA 诱导内源性 H2S 含量并激活 l-/d-半胱氨酸脱硫酶 (l-/d-CD) 的活性和 mRNA 水平，并用多效唑 (PAC) 或 2-氨基茚满-2-膦酸抑制内源性 SA。 AIP) 阻止了这种效应，暗示 H2S 可能在 SA 信号之后起作用。进一步的研究表明，与 H2O 处理相比，SA 和 NaHS 均显着减轻了冷害，这可以通过更低的电解质泄漏 (EL)、MDA 含量和 ROS 积累来证明。值得注意的是，SA 和 H2S 提高了抗氧化酶（SOD、POD、CAT、APX 和 GR）的活性和 mRNA 水平以及 AsA 和 GSH 的含量。此外，外源性 SA 和 NaHS 明显上调了寒冷反应基因（ICE、CBF1 和 COR）。然而，SA 对耐寒性的积极影响被 HT 抑制，而 PAC 或 AIP 不影响 NaHS 诱导的耐寒性。综上所述，数据表明 H2S 通过调节抗氧化系统和抗寒反应基因，作为 SA 诱导黄瓜抗寒性的下游信号。