Selenite alleviates PEG-induced drought stress during rice seed germination through antioxidant regulation and osmotic adjustment

Drought stress severely impairs seed germination. Selenium (Se) is a potential mitigator of abiotic stress, but its physiological mechanisms in alleviating osmotic stress during seed germination remain poorly understood. This study investigated how Se alleviates the inhibition of rice seed germination induced by polyethylene glycol (PEG)-simulated drought. The results indicated that co-application of Se and PEG effectively alleviated the PEG-induced suppression of germination. Se significantly increased the activities of superoxide dismutase by 31.0%, peroxidase by 39.0%, catalase by 42.9%, and ascorbate peroxidase by 41.8%, along with elevating the concentrations of glutathione by 19.0% and ascorbate by 38.3%. Consequently, Se attenuated the PEG-induced burst of reactive oxygen species, reducing H2O2 by 21.0% and O2- by 19.1%, and alleviated lipid peroxidation, as reflected by a 20.0% decrease in malondialdehyde concentration. Furthermore, Se partially restored osmotic homeostasis by increasing the accumulation of soluble sugars by 15.9%, soluble proteins by 11.4%, free amino acids by 18.4%, and free proline by 26.3%. It also counteracted PEG-imposed inhibition of hydrolytic enzymes, enhancing α-amylase and protease activities by 26.6% and 11.2%, respectively. Notably, Se accumulation in seeds was reduced under PEG stress, suggesting impaired the penetration of exogenous Se under PEG-simulated drought. Collectively, these results demonstrate that Se alleviates PEG-induced osmotic stress in germinating rice seeds by enhancing antioxidant capacity, maintaining osmotic balance, and sustaining reserve mobilisation.