| Summary: | Selenium stress can adversely affect plants by inhibiting growth, impairing oxidative stress resistance, and inducing toxicity. In this experiment, we investigated the effect of exogenous 24-epibrassinolide (24-EBL; 2.0 mg/L), a brassinosteroid (BR), on alleviating selenium stress in peach trees by analyzing its impact on biomass, selenium accumulation, and the expression of selenium metabolism-related genes in peach seedlings. The results demonstrated that 24-EBL could effectively mitigate biomass loss in peach seedlings exposed to selenium stress. Compared to the Se treatment alone, the 24-EBL+Se treatment resulted in a significant 16.55% increase in root selenium content and a more pronounced 30.39% increase in selenium content in the aboveground parts. Regarding the subcellular distribution, the cell wall was the primary site of Se deposition, accounting for 42.3% and 49.8% in the root and aboveground parts, respectively, in the Se treatment. 24-EBL further enhanced Se distribution at this site, reaching 42.9% and 63.2% in root and aboveground parts, respectively, in the 24-EBL+Se treatment. The 24-EBL+Se treatment significantly increased the contents of different chemical forms of Se, including ethanol-soluble, water-soluble, and salt-soluble Se. The quantitative real-time PCR (qRT-PCR) results indicated that the Se treatment promoted the expression of organic Se assimilation genes (<i>SATs</i>, <i>OAS-TL B</i>, and <i>OAS-TL C</i>), and 24-EBL application further increased their expression. Meanwhile, the Se-only treatment up-regulated the organic Se metabolism gene <i>CGS1</i>. Consequently, we propose that 24-EBL alleviates Se stress in peach seedlings by enhancing Se uptake and assimilation, and by adjusting subcellular distribution and chemical forms.
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