表油菜素内酯对盐胁迫下湖南稷子幼苗的缓解作用

【目的】湖南稷子（Echinochloa frumentacea）是一种高产、优质草料兼用牧草，种植区土壤盐碱化严重影响其正常生长发育和产量。表油油菜内酯（EBR）是油菜甾醇类(BRs)植物激素的活性类似物。探讨表油菜素内酯对湖南稷子耐盐性的调控作用及其缓解盐胁迫伤害的作用机制，为其应用于盐渍化土壤上湖南稷子生产提供理论依据。【方法】以湖南稷子品种‘宁稷1号’幼苗为试验材料，在筛选适宜盐胁迫浓度的基础上，设置对照、盐（150 mmol/L NaCl）和不同浓度的表油菜素内酯（1，10，100 μg/L）单独及复合处理，采用水培试验考察各处理幼苗生长指标、抗逆生理指标、光合作用指标、离子稳态、编码盐过敏（SOS）信号转导途径及抗氧化酶相关基因表达量的变化。【结果】（1）与对照相比，单独盐胁迫处理湖南稷子幼苗生长（株高、根长、生物量等）受到显著抑制，叶片光合作用指标[叶绿素含量及叶绿素荧光参数Y(Ⅱ)、Fv’/Fm’、ETR、qP等]、渗透调节物质（脯氨酸、可溶性蛋白）含量、抗氧化酶（SOD、POD、CAT、APX)活性显著降低；根系K+、Ca2+和Mg2+含量显著减少，而根系Na+含量显著增加；而叶片活性氧（超氧阴离子、过氧化氢）含量、细胞膜透性（丙二醛含量、相对电导率）却显著提高；同时叶片相关基因表达量显著下调。但单独喷施表油菜素内酯处理对以上指标大多无显著影响。（2）喷施不同浓度表油菜素内酯处理均能有效缓解盐胁迫后湖南稷子上述指标的不利变化，并以10 μg/L表油菜素内酯处理（SS+E10）效果最佳。（3）与单独盐胁迫处理相比，SS+E10处理湖南稷子幼苗生长指标以及叶片渗透调节物质含量、抗氧化酶活性、光合作用指标显著提高，叶片的细胞膜透性和活性氧含量显著降低；根系细胞内Na+积累显著减少，根系K+、Ca2+和Mg2+含量显著增加，Na+/K+稳态平衡得到调节；SOS信号转导途径和抗氧化酶相关基因的表达量显著上调。【结论】叶面喷施表油菜素内酯能显著上调盐胁迫下湖南稷子幼苗叶片SOS信号转导途径和抗氧化酶相关基因的表达量，增强其抗氧化和渗透调节能力，减轻膜脂过氧化和细胞膜损伤程度,，维持根系离子稳态平衡，有效保护幼苗叶片的光合作用和正常生长，对促进湖南稷子耐盐性具有显著调控作用，并以10 μg/L EBR处理效果最佳。

Mitigation effect of epibrassinolide on Echinochloa frumentacea seedlings under salt stress

【Objective】 Echinochloa frumentacea is a high-yielding and high-quality forage grass that can be used as both forage and feed. The soil salinization in the planting area seriously affects its normal growth, development, and yield. Epioilcanola (EBR) is an active analogue of brassinosteroid (BRs) plant hormones. To offer a theoretical foundation for the application of EBR to the production of E. frumentacea on salinized soils, it is necessary to investigate the regulatory effects of this lactone on the salt tolerance of E. frumentacea as well as its mode of action to mitigate the salt stress damage. 【Methods】E. frumentacea variety ''Ningji No.1'' seedlings were employed as test subjects. After determining the appropriate concentrations of salt stress, separate treatments were set up using salt (150 mmol/L NaCl) and various concentrations of EBR (1, 10, and 100 μg/L). The hydroponic test was used to examine changes in growth indexes, physiological stress resistance indexes, photosynthesis indexes, ionic homeostasis, encoding the signaling pathway of salt allergy (SOS), and the expression of genes related to antioxidant enzymes in the seedling under each treatment. 【Results】 (1) E. frumentacea seedlings treated with salt stress alone showed significantly slower growth (plant height, root length, biomass, etc.) when compared to the control; leaf photosynthesis indexes (chlorophyll content and chlorophyll fluorescence parameter Y(Ⅱ), Fv''/Fm'', ETR, qP, etc.); osmotic regulating substance content (proline content, soluble Proline content, soluble protein content); and antioxidant enzyme (SOD, POD, CAT, APX) activities were significantly reduced; root K+, Ca2+, and Mg2+ contents were significantly decreased, but root Na+ content was significantly increased; leaf reactive oxygen species (superoxide anion, hydrogen peroxide) content and cell membrane permeability (malondialdehyde content, relative conductivity) were significantly increased; in the meantime Nevertheless, the use of EBR therapy alone did not significantly impact the majority of the aforementioned indices.(2) After salt stress, E. frumentacea adverse alterations in the aforementioned indices were effectively reduced by spraying various doses of EBR treatments; the greatest results were obtained with 10μg/L EBR treatment (SS+E10).(3) Compared with the salt stress treatment alone, the growth indexes as well as the content of osmoregulatory substances, antioxidant enzymes and photosynthesis indexes of E. frumentacea seedlings treated with SS+E10 were significantly improved, the cell membrane permeability and reactive oxygen species content of leaves were significantly reduced; the intracellular Na+ accumulation in the root cells was significantly reduced, and the content of K+, Ca2+ and Mg2+ in the root system was significantly increased, and the homeostatic balance of Na+/K+ ions was regulated; and the expression of the genes related to the SOS signaling pathway and antioxidant enzymes was significantly up-regulated. 【Conclusion】 Foliar spraying of EBR significantly up-regulated the expression of SOS signaling pathway and antioxidant enzyme-related genes in the leaves of E. frumentacea seedlings under salt stress, enhanced their antioxidant and osmoregulatory abilities, reduced the degree of membrane lipid peroxidation and cell membrane damage, maintained the balance of ionic homeostasis in the root system, and effectively protected the photosynthesis and normal growth of seedling leaves, which had a significant regulatory effect on the promotion of salt tolerance in E. frumentacea and had the best effect with the treatment of 10μg/L EBR.