Comparative physiological and metabolomic analyses revealed that foliar spraying with zinc oxide and silica nanoparticles modulates metabolite profiles in cucumber (Cucumis sativus L.)

Previous studies have reported crop toxicity of zinc oxide nanoparticles (ZnO-NPs) by root exposure and that silica nanoparticles (SiO2-NPs) modulate crop growth and soil physicochemical properties. In this study, we determined the effects of foliar exposure to ZnO-NPs and SiO2-NPs on the growth and metabolomic profile of cucumber seedlings. Foliar spraying with ZnO-NPs and SiO2-NPs improved cucumber plant performance, as indicated by increases in chlorophyll contents, chlorophyll fluorescence parameters, and the fresh/dry weights of leaves and roots. According to metabolomic analysis results, foliar exposure to ZnO-NPs and SiO2-NPs induced pronounced changes in the metabolome, especially in the leaves. Besides, ZnO-NP or SiO2-NP treatments either upregulated or downregulated the contents of amino acids, organic acids, sugars and glycosides, and secondary metabolites, indicating that the two NPs affected both primary metabolism and secondary metabolism. The elevated levels of several secondary metabolites involved in antioxidative defense imply that the two NPs potentially regulate stress resistance in plants. Overall, these results indicate that different from root exposure, foliar exposure to ZnO-NPs or SiO2-NPs is beneficial to plant growth. The present study provides a theoretical basis for the environmental assessment and application of these two NPs in agricultural production.

Automated summary

The study found that foliar exposure to ZnO-NPs and SiO2-NPs improved cucumber plant growth and metabolism, including increased chlorophyll content and fresh/dry weight. Metabolomic analysis showed that both nanoparticles significantly altered the metabolome, especially in leaves.