Green-Synthesized Zinc Oxide Nanoparticles Mitigate Salt Stress in Soybean

Soybean [Glycine max (L.) Merrill] is a high value leguminous crop characterized by its excellent protein and oil qualities. The legume is also excellent as human food, animal feed, industrial raw material and for its ability to improve soil quality through nitrogen fixation. However, while this crop has all these attractive attributes and benefits, its agricultural production is seriously affected by salt stress. Thus, any research effort aimed at understanding the physiological response of this crop to salt stress is worthwhile. In this study, we report the green synthesis of zinc oxide nanoparticles (ZnO-NPs) and use of such NPs as a priming agent, to mitigate salt stress in a PAN 1644R soybean variety that is commonly grown in the tropics. Findings showed that while salt stress (100 mM NaCl) significantly affected key plant attributes such as seed germination (e.g., delay), early seedling development (e.g., stunted radicles), morphological features (e.g., pale leaves), physiological traits (e.g., low chlorophyll content) and physiological processes (e.g., reduced photosynthesis), the ZnO-NPs (at 200 mg·L−1 dosage) used counteracted all these effects, allowing plants to grow optimally with enhanced statuses. We then concluded that the ZnO-NPs mitigate salt stress in soybean, underscoring the importance of this study to food security and sustainable agricultural practices.