Exogenous Application of Selenium Nanoparticles (Se-NPs) to Mitigate Salt Stress in Soybean-Evaluation of Physiological, Molecular and Biochemical Processes

Salt stress is identified as a significant abiotic stress that hampers agricultural sustainability globally. The study was carried out to investigate the potential mitigating effects of selenium nanoparticles (Se-NPs) on salt stress in soybean. Two weeks old grown soybean seedlings were subjected to salt stress conditions (4000 mg L^− 1 of sea salts). The plants were foliar sprayed with Se-NPs at concentrations of 0.0, 0.5, 1.0 and 1.5 mg L^− 1 twice. The first application was applied at four weeks from sowing and the second application was added after two weeks from the first application. Compared to control, Se-NPs application mitigates the negative effect of salinity on plant growth to a variable extent. This improvement may be attributed to several factors such as increased the concentrations of photosynthetic pigments, total soluble sugars and total protein. In addition, Se-NPs alleviated the adversely effect of oxidative stress by increasing the antioxidant activities and potassium contents without markedly increase in the sodium content of the soybean leaf tissues. Also, Se-NPs enhanced the biosynthesis of secondary metabolites such as total phenolic content under salinity. Moreover, Se-NPs spray significantly reinforced the development of conducting secondary tissues in the leaves and roots of the treated plants. GmHKT1 gene transcription was markedly up-regulated in salinized soybean and foliar sprayed with Se-NPs as a molecular strategy to cope with the salinity. Based on the obtained results, among the different doses of Se-NPs, soybean plants sprayed with 1.0 mg L^− 1 Se-NPs showed better salt tolerance. The foliar spray of Se-NPs may be considered as a promising approach to enhance salt tolerance in soybean plants, which could have significant implications for improving agricultural sustainability in salt-affected regions.