The Protective Role of Sodium Nitroprusside in Alleviating Salt Stress During Germination and Seedling Establishment of Thai Eggplant

Thai eggplant (Solanum melongena L. cv. Chao Phraya), a widely cultivated vegetable with increasing global demand, is highly susceptible to salinity stress, which can severely impair seed germination and early seedling development. This study investigated the effects of sodium nitroprusside (SNP), a nitric oxide (NO) donor, on seed germination and seedling growth under salt stress conditions. Seeds were pre-treated with SNP at concentrations of 0, 0.05, 0.1, and 0.2 mM for 24 h and subsequently germinated under saline conditions with NaCl solutions (0, 100, and 200 mM). SNP pre-treatment, particularly at 0.05 and 0.1 mM, significantly improved germination percentage and germination rate in seeds exposed to 200 mM NaCl compared to untreated controls. Increased NaCl concentrations induced oxidative stress in seedlings, as evidenced by elevated hydrogen peroxide (H2O2) accumulation, which in turn caused lipid peroxidation, reflected by higher malondialdehyde (MDA) levels. Salt stress significantly increased ascorbate peroxidase (APX) activity, whereas catalase (CAT) activity showed no significant change across treatments. Correlation analysis revealed that APX activity was positively correlated with oxidative stress markers (H2O2) and delayed germination (T50/MGT), whereas CAT activity showed no significant correlation with these parameters. In contrast, elevated APX activity was strongly and negatively correlated with overall seedling growth and vigor (SVI/GI), indicating that the underlying stress condition had a detrimental effect on plant performance. Overall, SNP pre-treatment, particularly at 0.05 and 0.1 mM, significantly enhanced salt tolerance by promoting germination (increasing GP and reducing T50/MGT) and improving seedling growth (SL and RL). This protective effect is associated with improved redox regulation and partial mitigation of oxidative damage, as reflected by changes in H2O2, MDA, and APX; however, excessive SNP concentrations may exert phytotoxic effects, highlighting the importance of optimal dosing.