The application of selenium enhances salt stress tolerance of sesame plants through regulation of key metabolic responses

Salinity stress severely limits sesame productivity. Although selenium (Se) can alleviate the effects of salinity in many crops, its role in sesame remains unclear. This study is the first to systematically evaluate the physiological, biochemical, and molecular responses of sesame to Se under salt stress, highlighting its potential to enhance tolerance and crop performance. Sesame plants (Sesamum indicum L.) were exposed to varying NaCl concentrations (0, 75, and 150 mM) with or without Se supplementation (50 mg L⁻¹). Selenium application significantly mitigated the adverse effects of salt stress by increasing whole-plant length, dry and fresh biomass, and enhancing photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), thereby promoting growth and biomass accumulation. Salt stress induced oxidative damage, evidenced by elevated hydrogen peroxide content; however, Se treatment reduced oxidative stress by increasing enzymatic antioxidant activities (SOD by 36% and CAT by 46%) and non-enzymatic antioxidants (flavonoids by 27%). Under saline conditions, Se also stimulated the biosynthesis of auxin, abscisic acid, and gibberellin. Exogenous Se application significantly decreased levels of palmitoleic, linoleic, oleic, linolenic, arachidic, behenic, and lignoceric acids under salt stress. Moreover, Se upregulated the salt stress-responsive gene Na⁺/H⁺ exchanger 1 (NHX1), improving ionic homeostasis. Multivariate analyses, including principal component analysis (PCA) and Pearson correlation, confirmed distinct treatment separations and revealed strong positive and negative correlations among physiological and stress-related traits. These findings underscore the comprehensive protective role of Se in enhancing salt stress tolerance in sesame by modulating growth, photosynthesis, antioxidant defense, hormone regulation, fatty acid composition, and ionic balance.