Foliar Selenium Nanoparticles Application Promotes the Growth of Maize (Zea mays L.) Seedlings by Regulating Carbon, Nitrogen and Oxidative Stress Metabolism

Current understanding of selenium (Se) nanoparticles (SeNPs) effects on growth of C4 cereals is deeply scarce, and thus a hydroponic experiment was conducted to explore the physiological, biochemical, and metabolites variations in maize following foliar application of SeO32- and SeNPs each at 2 and 20 mg/L. The results demonstrated that fresh weight of Se foliar-applied leaves (Se-leaves) significantly increased by 27% after foliar application of SeNPs at 20 mg/L, which was mainly attributed to the improved photosynthetic efficiency (50%–78%) and stomatal conductance (46%–60%) of Se-leaves. Foliar-applied SeNPs and SeO32- both increased the Se concentration of each part of maize, while SeNPs was more efficient in improving the Se concentration, and Se was mainly accumulated in the cell wall. Significant increase was observed in GSH (14%–64%), POD (6%–24%), SOD (2%–11%), CAT (55%–73%), APX (50%–90%) at SeNPs application in comparison with control. Metabolomic results indicated that foliar application of 20 mg/L SeNPs significantly up-regulated 42 metabolites, which were mainly carbohydrates, amino acids, ketone and phenol, vitamin, and ten metabolic pathways (2 metabolic pathways related with carbon metabolism, 5 related with nitrogen metabolism, and 1 related with oxidative stress metabolism) was improved. Therefore, SeNPs mainly enhanced the antioxidant capacity by improving metabolic pathways of glutathione metabolism, carbon metabolism, and nitrogen metabolism and finally improved various physiological indexes of maize to boost the growth of maize.