Objective This mechanism of exogenous sodium nitroprusside (SNP) improving the reactive oxygen species (ROS) metabolism at germination stage of rice was studied.

Methods A seed soaking experiment was conducted using a alkali-sensitive rice cultivar 'Zhonghua 11' (ZH11) and a alkali-tolerant cultivar 'Ning jing 52' (NJ52) as test materials. Four soaking treatments were applied: distilled water (CK), SNP 30 μmol/L solution (CK+SNP), 20 mmol/L NaHCO₃∶Na₂CO₃ solution (AS), and 20 mmol/L AS + 30 μmol/L SNP (AS+SNP). Seeds were soaked and allowed to germinate under these treatments for 7 days. Then The buds were sampled for investigation of germination, analysis of hormone content, enzyme activities and expression levels of genes related to ROS metabolism.

Results Alkali stress significantly inhibited germination and bud growth of both cultivars, compared to the control, with particularly pronounced inhibition observed in the bud and root lengths of ZH11. However, AS+SNP treatment was observed to significantly increase germination rate, bud and root lengths of both cultivars, relative to AS treatment, and the ameliorative effect was more pronounced in NJ52 than in ZH11 AS treatment significantly reduced gibberellin (GA) content and increased abscisic acid (ABA) content in both cultivars, Up regulated the expression levels of GA synthesis genes (OsGA3ox2, OsGA20ox1) and decreased that of ABA metabolism genes (OsNCED2, OsABA8ox2) significantly, compared to the control. AS+SNP treatment observed significantly increased GA content and decreased ABA content by up-regulating GA synthesis genes and down-regulating ABA metabolism genes, relative to that of AS treatment. These hormonal changes helped to break dormancy and promote seed germination. AS treatment significantly induced excessive accumulation of ROS (H₂O₂ and \rmO_\small 2^\overline \,\cdot\, ), activated the antioxidant system as evidenced by increased activities of peroxidase (POD), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and glutathione peroxidase (GPX), along with up-regulated expression of related genes. The content of oxidized glutathione (GSSG) and the expression levels of its related genes were also significantly increased. AS+SNP treatment significantly reduced ROS levels, synergistically enhanced the antioxidant defense system, further increased the activity of antioxidant enzymes and the expression of their corresponding genes, and significantly improved the efficiency of the ascorbic acid-glutathione (AsA-GSH) cycle. Notably, NJ52 exhibited a stronger antioxidant capacity than ZH11.

Conclusion Exogenous SNP effectively maintains cellular redox homeostasis by synergistically regulating ROS metabolism, enhancing the antioxidant defense system, and modulating hormonal balance, thereby promoting seed germination under alkali stress. Alkali-tolerant cultivar response is more pronounced to the regulation effect of SNP.