Selenium promotes soybean sprout growth via enhanced antioxidant capacity and nutrient mobilisation

Selenium (Se) biofortification of soybean sprouts presents a promising approach for enhancing dietary Se intake. However, the physiological mechanisms of Se promoting growth remain poorly understood. Here, we investigated the effects of selenite (Na2SeO3) at concentrations of 0, 2.5, 5.0, 7.5, and 10 μmol/L on soybean sprout development over 72 h. The results indicated that 5.0 and 7.5 μmol/L Na2SeO3 significantly promoted hypocotyl elongation and biomass accumulation. Se predominantly accumulated in the radicle, followed by the hypocotyl and cotyledon. Moderate selenite levels enhanced the activities of superoxide dismutase, peroxidase, and ascorbate peroxidase; increased the concentrations of reduced glutathione, ascorbic acid, and free proline; and effectively suppressed the accumulation of superoxide anion and hydrogen peroxide, thereby reducing malondialdehyde (MDA) concentration and alleviating oxidative stress. Concurrently, amylase and protease activities in cotyledons were stimulated, accelerating the hydrolysis of storage reserves. The resulting increases in soluble sugars, proteins, and free amino acids in the hypocotyl supported its elongation and biomass increase. In contrast, 10 μmol/L Na2SeO3 suppressed antioxidant enzyme activities, elevated reactive oxygen species and MDA levels, and inhibited growth. Collectively, these findings demonstrate that moderate Se enhances soybean sprout growth primarily by increasing antioxidant capacity, reducing oxidative stress, and facilitating the mobilisation of storage reserves toward the elongating hypocotyl, thereby revealing key physiological mechanisms for cultivating high-quality, Se-enriched sprouts.