Introduction: Silver nanoparticles (AgNPs) have attracted considerable attention because of their unique physicochemical properties and extensive applications in various fields. Their release into agricultural environments may expose plants to nanoparticle-induced stress. AgNPs can disturb cellular redox homeostasis and induce oxidative stress, thereby affecting physiological processes, plant growth and yield. Soybean (Glycine max L.) is one of the most important leguminous crops and a major source of plant-based protein and oil, making the assessment of its responses to AgNPs particularly important. Nitric oxide (NO) is an important signaling molecule involved in plant responses to environmental stresses, while sodium nitroprusside (SNP) is widely used as an exogenous NO donor. The application of SNP may therefore contribute to the regulation of plant responses under stressful conditions. Accordingly, the present study was conducted to investigate the potential of SNP to alleviate the adverse effects of AgNP-induced stress in soybean cv. Williams.

Materials and Methods: The experiment was conducted as a factorial experiment based on a randomized complete block design with three replications at Shahrood University of Technology. The experimental treatments consisted of three concentrations of foliar-applied AgNPs (0, 1.5 and 3 g L⁻¹) and two concentrations of foliar-applied SNP (0 and 120 μM). Following treatment application, several growth, photosynthetic pigment and yield-related traits were evaluated. In addition, silver accumulation in the leaves and seeds was determined to assess the relationship between Ag accumulation and plant responses to AgNP exposure. Correlation analysis and principal component analysis (PCA) were also performed to investigate the relationships among silver accumulation and the measured growth, pigment and yield-related traits and to identify the major patterns of variation among the experimental treatments.

Results: The results showed that AgNP application generally reduced the measured traits in soybean, with greater reductions observed at the higher nanoparticle concentration. In the absence of SNP, foliar application of AgNPs at concentrations of 1.5 and 3 g L⁻¹ reduced protein yield by 14% and 77%, respectively, compared with the control. These findings indicate that increasing AgNP concentration can adversely affect soybean productivity and protein accumulation. In contrast, the application of SNP partially alleviated the negative effects associated with AgNP exposure. For example, under application of 3 g L⁻¹ AgNPs, the use of SNP increased seed oil yield by 54% compared with the corresponding treatment without SNP. This finding suggests that exogenous SNP can improve the response of soybean to AgNP-induced stress and partially compensate for the reduction in yield-related traits. Correlation analysis further revealed that silver accumulation in the leaves and seeds was negatively associated with most growth, photosynthetic pigment and yield-related traits. Principal component analysis also revealed distinct patterns of variation among the experimental treatments and illustrated the associations between silver accumulation and the measured plant traits.

Conclusion: Overall, the findings demonstrated that AgNP exposure, particularly at higher concentrations, adversely affected soybean growth, photosynthetic pigments and yield-related traits. In contrast, exogenous SNP application was able to partially mitigate the adverse effects of AgNPs and improve some of the evaluated traits. The negative associations between silver accumulation in the leaves and seeds and most growth, pigment and yield-related traits highlight the importance of silver accumulation in the response of soybean to AgNP-induced stress. Therefore, SNP may be considered a potential treatment for reducing the adverse effects of AgNP stress in soybean. However, further studies are required to elucidate the underlying mechanisms, particularly the direct role of nitric oxide in regulating silver accumulation and antioxidant defense responses under AgNP-induced stress.