Salicylic Acid Alleviates Cold Stress in Rice via Regulating Nutrient Absorption, Osmotic Material Content, Antioxidation System, and Expression of Cold Tolerance Genes

Rice (Oryza sativa L.) is one of the most important crops in the world, but cold stress during its seedling stage often results in stunted growth and yield loss. This study aimed to explore the regulatory effect of the plant hormone salicylic acid (SA) on the cold tolerance of rice seedlings and its underlying physiological and molecular mechanisms. In the present study, the application of SA to the seedling substrate significantly increased the germination rate and germination index of rice seeds, promoted the nutrient uptake of rice seedlings, increased the content of osmotic regulators proline and soluble protein, and increased the cell water potential under cold stress conditions. The application of SA also reduced the reactive oxygen species content and alleviated peroxidation damage to the plasma membrane in rice plants by enhancing peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) activities, and ascorbic acid content. Furthermore, under cold stress conditions, the application of SA led to an increase in the relative expression levels of cold signal transduction genes (OsCOLD1, OsCDPK7, OsMYB), osmotic regulation genes (OsCOIN, OsLti6a, OsLti6b, OsICE1), and oxidative stress genes (OsTrx23, OsFER1, OsSODB, OsTERF2). In summary, the application of SA improves the cold tolerance of rice seedlings through multiple mechanisms, including nutrient absorption, osmotic regulation, enzymatic and non-enzymatic oxidation regulation and activation of cold tolerance genes expression.