Nanoselenium Foliar Applications Enhance the Nutrient Quality of Pepper by Activating the Capsaicinoid Synthetic Pathway

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.