Modulation of salt tolerance in Echinochloa frumentacea by foliar spraying of epibrassinolide

Abstract [Objective] Soil salinization seriously affects the growth, development, and yield of the forage grass E. frumentacea. We aim to investigate the regulatory effects of epibrassinolide (EBR) on salt tolerance of E. frumentacea and its mechanism, in order to provide a theoretical basis for its application in forage production. [Methods] Seedlings of ‘Ningji 1’ variety were used as materials. Based on the screening of suitable salt concentrations, control, salt (150 mmol/L NaCl), and EBR (1, 10, 100 μg/L), either alone or in combination, were set up. A hydroponic test was used to investigate the changes in seedling growth, stress tolerant physiology, photosynthesis, ionic homeostasis, and the expression of genes related to the signaling pathway (SOS) and antioxidant enzymes. [Results] Compared with control, seedling growth, including plant height, root length, biomass, etc., was inhibited under salt stress. Photosynthesis indexes, including chlorophyll content and actual photochemical efficiency of PSⅡ [Y(Ⅱ)], maximum photochemical efficiency of PSⅡ (Fv'/Fm'), electron transport rate (ETR), photochemical quenching coefficient (qP), etc., as well as osmoregulatory substance (proline, soluble proteins) content and antioxidant enzyme (SOD, POD, CAT, and APX) activities were reduced under salt stress. Root K+ , Ca2+ , and Mg2+ contents were decreased, while root Na+ content was increased under salt stress. Leaf reactive oxygen species (superoxide anion, hydrogen peroxide) content, and cell membrane permeability (malondialdehyde content, relative conductivity) were increased under salt stress; gene expression was significantly down-regulated. Most of the above indexes were not significantly affected by EBR treatment alone. Spraying different concentrations of EBR could effectively alleviate the unfavorable changes of the above indexes under salt stress, and the best effect was achieved by 10 μg/L EBR. [Conclusion] Foliar spraying of EBR up-regulated the expression of SOS signaling pathway and antioxidant enzyme-related genes in the leaves of E. frumentacea seedlings under salt stress, enhanced the antioxidant and osmoregulatory abilities, maintained ion homeostasis in the root, protected photosynthesis and growth, and improved salt tolerance.