Selenium and seaweed extracts exhibit synergistic actions in regulating antioxidant defense in rice under salt stress

Salinity creates a serious constraint on production by profoundly diminishing plant development, physiological performance, and yield potential, thereby threatening global food security. Given the reported stress-mitigating roles of selenium (Se) and seaweed extracts (SWEs) (Ascophyllum nodosum) in plants, a controlled investigation was performed using rice (Oryza sativa L., cv. BRRI dhan100) to evaluate their effectiveness in enhancing tolerance to saline conditions. Rice seedlings were exposed to salinity stress induced by 75 mM NaCl, while parallel treatments received foliar application of sodium selenate (Na2SeO4; 25 µM L−1) along with soil drenching of 0.1% SWE. Exposure to salt stress distinctly suppressed plant growth attributes, and led to substantial reductions in biomass accumulation, leaf relative water content, chlorophyll concentration, and chlorophyll fluorescence parameters. Salinity also disrupted ionic homeostasis, as reflected by an elevated Na+/K+ ratio and a decline in calcium content. Furthermore, salt stress intensified oxidative damage, evidenced by increased hydrogen peroxide, lipid peroxidation accumulation, proline content, methylglyoxal levels, and electrolyte leakage. In addition, salinity diminished the concentrations of key non-enzymatic antioxidants, and suppressed the activities of major antioxidant enzymes, including monodehydroascorbate reductase, glutathione S-transferases, glutathione peroxidase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and components of the glyoxalase system. In contrast, combined application of Se and SWEs significantly strengthened the effectiveness ofthe AsA–GSH cycle, restored antioxidant enzyme activities, and improved ionic regulation under saline conditions. These protective effects collectively alleviated salinity-induced oxidative stress and physiological impairment. Overall, the combined supplementation of Se and SWEs substantially strengthened the antioxidant defense capacity of rice plants, thereby improving their resilience to salt-induced damage and contributing to enhanced salinity tolerance.