Silicon improves seed germination and seedling growth and alleviates salt stress in Medicago sativa L. by regulating seed reserve mobilization and antioxidant system defense

Exogenous application of silicon (Si) provides benefits to various plant species, including alfalfa. However, knowledge about the effects of Si on seed germination in alfalfa under salt stress is still scarce. Therefore, this study aimed at exploring the effect of Si on Medicago sativa L. seed germination and seedling growth under salinity. Seeds of two Moroccan alfalfa varieties, Ouad Lmaleh (OL) and Demnate 201 (Dm), and the European variety NS Mediana ZMS V (NS Med) were germinated with 200 mM NaCl solution with or without 3 mM Si. The obtained results showed that salt stress significantly reduced germination traits, reserve mobilization and embryo viability. However, exogenous Si counteracted the negative impact of salinity on seed germination by enhancing reserve mobilization and embryo viability. Si alleviated salt-mediated oxidative stress in alfalfa by reducing hydrogen peroxide (H2O2), electrolyte leakage and malondialdehyde contents and by increasing proline accumulation. Besides, H2O2 staining revealed that Si reduced H2O2 accumulation induced by salt stress. Enzyme activity analyses revealed that Si triggered the activity of some critical enzymes related to oxidative stress alleviation, including superoxide dismutase (SOD) and catalase, together with an accumulation of SOD isoforms, as visualized by native gel PAGE. Furthermore, as compared to Si-untreated salt-stressed control, data showed a key role of Si in alleviating the devastating impact of salt by reducing Na+ content and increasing K+ content, leading to higher K+/Na+ ratio. Our findings suggest that 3 mM Si application can constitute a promising way to improve alfalfa seed germination and seedlings growth under salt stress.