Role of Charge and Size in the Translocation and Distribution of Zinc Oxide Particles in Wheat Cells

Nanoscale fertilizers offer the potential to sustainably enhance crop yield and quality. Foliar application of nano-fertilizers may improve utilization efficiency and significantly mitigate environmental risks compared to conventional chemical fertilizers applied through either soil or foliar routes. However, limited understanding of how the mechanisms controlling nanoparticle delivery and distribution are affected by nanoparticle properties impedes the efficacy and application of nano-fertilizers. Here, 2 mmol L–1 zinc oxide particles with different characterizations (sizes, shapes, and charges) were used to investigate delivery and distribution processes in wheat leaves and cells. Results suggested that the adsorption of ZnO particles onto the leaf surface and cell wall was enhanced by both smaller sizes (main factor) and positive charges. Three-dimensional confocal laser scanning microscopy images indicated that positively charged nanoparticles distributed more uniformly inside the leaf than negatively charged ones. At the cellular level, only nanoscale particles could cross the cell wall and be transported into the cytoplasm. However, the translocation of both nanoscale and bulk particles was observed in unwalled cells, with uptake of the smaller particles being enhanced by positive charges. These findings provide valuable information for the optimized design of nano-fertilizers to improve their use and efficacy in agriculture.