硫化氢通过抑制镉离子内流降低拟南芥体内的镉毒性

硫化氢（H₂S）作为一种新兴的气体信号分子，在植物体内主要由半胱氨酸脱巯基酶（CDes）降解半胱氨酸产生。已有报道表明，H₂S信号与植物激素共同作用增强植物的镉（Cd）耐受。然而，H₂S信号响应重金属Cd胁迫的作用机制尚缺乏系统研究。本文以拟南芥为实验材料，从不同水平探究H₂S分子对Cd胁迫诱导氧化应激的保护作用。结果表明，CDes基因表达量和H₂S的产率随CdCl₂浓度升高而逐渐增加。重金属Cd胁迫导致幼苗干重降低约33%、体内过氧化氢显著增加、丙二醛含量升高约110%、超氧化物歧化酶活性增加约100%、谷胱甘肽还原酶活性和过氧化氢酶活性分别下降27%和21%，还原性谷胱甘肽含量随之显著降低。生理浓度NaHS（H₂S供体）预处理显著缓解以上Cd胁迫产生的影响，使恢复到对照水平。同时，H₂S处理可显著下调质膜中Cd转运蛋白（HMA4和IRT1）的表达，同时上调液泡膜中MRP3和CAX2的表达。利用非损伤微测技术测定植物根系Cd²⁺的流动速度和流动方向。结果显示，生理浓度的H2S显著抑制Cd^{2 +}内流，最终表现为植物叶片和根中的Cd含量显著降低，分别下降了15%和38.4%。总之，在Cd胁迫条件下，H₂S信号可激活植物体内的抗氧化酶促和非酶促系统，以清除细胞内H₂O₂。H₂S对Cd²⁺转运和液泡区式化的调节，降低了体内Cd²⁺的浓度，减小Cd毒性对植物生长的影响。为理解农作物应对重金属胁迫的机制提供了新的思路。

Hydrogen Sulfide Alleviates Cadmium Toxicity by Restricting Cd2+ Influx in Arabidopsis

As an emerging gasotransmitter, hydrogen sulfide (H₂S) is mainly produced by cysteine desulfhydrases (CDes) responsible for the degradation of cysteine in plants. It has been reported that H₂S signal interacted with plant hormones in response to heavy metal cadmium (Cd) stress. However, the mechanism based on systematic study is still limited. In the present study, we evaluated the protective effect of H₂S against Cd-induced oxidative stress from different levels in Arabidopsis seedlings. The expression levels of CDes and H2S production were gradually increased dependent on the concentration of CdCl₂. Cd stress caused a decrease of the dry weight of seedlings by about 33%, and an increase of hydrogen peroxide markedly and malondialdehyde content by about 110%. The activity of superoxide dismutase (SOD) increased by two fold, and catalase and glutathione reductase activities decreased by 27% and 21%, respectively, which caused the reduced glutathione content significantly. Prior to metal exposure, seedlings pretreated with NaHS as a H₂S donor significantly recovered all the above changes to control levels. H₂S treatment downregulated the expression of Cd transporter in plasma membrane (HMA4 and IRT1), while upregulated those in vacuolar membrane (MRP3 and CAX2). Non-invasive micro-test technique (NMT) data showed that NaHS inhibited Cd²⁺ influx, therefore the Cd content in leaves and roots was significantly decreased by 15% and 38.4%, respectively. Together, these results suggested that H₂S upregulated antioxidant enzymatic and no-enzymatic systems under Cd²⁺ stress and then scavenged the Cd^2+-elicited H₂O₂ within cells. The regulation in Cd²⁺ transport and vacuolar sequestration by H₂S reduced the concentration of Cd²⁺, subsequently. In final, Cd²⁺ toxicity was restricted in Arabidopsis. It provides a new method for understanding the mechanism of crop response to heavy metal stress.