Increasing the crop quality through enhancement of plant health is a challenging task. In this study, nanoselenium (nano-Se) was sprayed on pepper leaves, and the pepper components were compared to those of selenite. It was found that nano-Se (20 mg/L) resulted in a greater performance of plant health. It increased the chlorophyll and soluble sugar levels, which could activate phenylpropane and branched-chain fatty acid pathways, as well as AT3-related enzymes and gene expressions. These led to an enhancement for the synthesis of capsaicinoids, flavonoids, and total phenols. The nano-Se treatment also significantly promoted the expression of phyto-hormones synthesis genes, and consequently increased jasmonic, abscisic, and salicylic acid levels. Proline pathway-related compounds were increased, which could decrease the malondialdehyde and hydroxyl radical levels in crops. This study shows that nano-Se activated capsaicinoid pathways by enhancing photosynthesis and raising soluble sugar levels. The capsaicinoid contents in peppers were then increased, which consequently promoted the accumulation of secondary metabolites and antioxidants.

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Aphids are one of the most destructive insects in many cultivated plants including wheat, which can cause significant yield loss and damage the quality of agricultural products. Therefore, it is essential to control the occurrence of aphids during wheat growth. Previous studies reported the alterations in the resistance of wheat to pests induced by several external factors such as nutrients in soils and nano-carbonaceous materials. In this study, nanoselenium (nano-Se) was sprayed on wheat leaves at several concentration levels (1.0, 5.0, and 20 mg/L). Nano-Se (5.0 mg/L) could significantly reduce Sitobion avenae number (36%) compared with the control. The foliar application of nano-Se was found to enhance the antioxidation capacity by reducing MDA concentration and increasing GSH-Px, CAT, GSH, Pro and VE concentrations. Phenylpropane pathway was activated after the application of nano-Se, with significantly increasing apigenin and caffeic acid concentrations. The highlevel expression of the related genes (TaBx1A, TaBx3A, TaBx4A, TaASMT2, and TaCOMT) induced the increasing melatonin concentration by 88.6% and DIMBOA concentration by 64.3%. Different ratios of the secondary metabolites to nano-Se were conducted to examine the effects on wheat resistance to the Sitobion avenae.The results revealed the combination of nano-Se and melatonin can achieve the best overall performance by reducing the Sitobion avenae infection by 52.2%. The results from this study suggest that the coordinative applications nano-Se and melatonin combination could be more effectively improve the wheat resistance to aphids via promotion of volatile organic compound synthesis and modulation in phenylpropane and indole metabolism pathways.

Selenium (Se) can promote the growth and resistance of agricultural crops as fertilizers, while the role of nano-selenium (nano-Se) against Cd remains unclear in pepper plants (Capsicum annuum L.). Biofortification with nano-Se observably restored Cd stress by decreasing the level of Cd in plant tissues and boosting the accumulation in biomass. The Se compounds transformed by nano-Se were primarily in the form of SeMet and MeSeCys in pepper tissues. Differential metabolites and the genes of plant signal transduction and lignin biosynthesis were measured by employing transcriptomics and determining target metabolites. The number of lignin-related genes (PAL, CAD, 4CL, and COMT) and contents of metabolites (sinapyl alcohol, phenylalanine, p-coumaryl alcohol, caffeyl alcohol, and coniferaldehyde) were remarkably enhanced by treatment with Cd1Se0.2, thus, maintaining the integrity of cell walls in the roots. It also enhanced signal transduction by plant hormones and responsive resistance by inducing the biosynthesis of genes (BZR1, LOX3, and NCDE1) and metabolites (brassinolide, abscisic acid, and jasmonic acid) in the roots and leaves. In general, this study can enable a better understanding of the protective mechanism of nano-Se in improving the capacity of plants to resist environmental stress.