The Effect of Exogenous Nitroprusside on Sugar Metabolism in Rice Seedlings Under Alkaline Stress

Sodium nitroprusside (SNP), as an exogenous nitric oxide (NO) donor, plays a critical regulatory role in plant stress responses. This study aimed to investigate the effects of exogenous SNP on sugar metabolism in rice seedlings under alkaline stress, for providing a theoretical basis for elucidating the mechanism of SNP enhancing rice alkali tolerance.

Seedlings of rice cultivars Zhonghua 11 and Ningjing 52 were used as test materials. Four treatments were applied: control (CK), CK+SNP (50 µmol·L^-1), alkaline stress (AS, a mixed alkaline solution containing NaHCO₃ and Na₂CO₃ at a 1:1 ratio, pH 9.55, 20 mmol·L^-1), and AS+SNP (20 mmol·L^-1 AS+50 µmol·L^-1 SNP). The effects of these treatments on sugar metabolism in the seedlings of the two rice cultivars were analyzed.

Compared with AS treatment, AS+SNP treatment significantly increased rice seedling height, root length, fresh weight, and dry weight of rice seedlings. AS+SNP treatment upregulated the expression of chlorophyll synthase-related genes (OsChlH, OsCAO1, and OsCAO2), thereby increasing chlorophyll content and promoting photosynthesis. Concurrently, it upregulated the expression of the sucrose invertase gene OsNIN1, leading to decreased fructose and sucrose content but increased glucose content, which facilitated glycolysis and the tricarboxylic acid cycle, promoting the accumulation of malate and citrate to maintain energy balance. Additionally, SNP induced the expression of sucrose phosphate synthase OsSPS1, gibberellin synthase-related genes (OsGA3ox2, and OsGA20ox1), and proline synthesis gene (OsP5CS), increasing the levels of gibberellin (GA), abscisic acid (ABA), proline (Pro), and soluble sugar. This regulation helped maintain osmotic and hormonal balance and promoted sucrose transport from source to sink tissues.

Exogenous SNP application enhanced rice seedling tolerance to alkaline stress by upregulating chlorophyll biosynthesis genes, promoting chlorophyll accumulation, and sustaining photosynthetic efficiency, thereby facilitating glucose synthesis. Moreover, SNP activated glycolysis and the tricarboxylic acid cycle, directing sugar metabolites toward malate and citrate production, thus promoting organic acid accumulation. Additionally, exogenous SNP modulated osmotic regulation and GA/ABA hormonal balance, facilitating sucrose transport and sugar metabolic pathway activation, and ensuring efficient energy metabolism. These mechanisms collectively improved rice seedling resilience under alkaline stress.