Functional insights into antioxidant pathways and phenyl propanoid pathway gene expression modulated by nanoparticles in chili (Capsicum annuum)

Enhancing plant health to improve crop quality remains a significant challenge in modern agriculture. In the present study, pepper ( Capsicum annuum ) plants were treated with different nanoparticles (Ag, Cu, CuAg, CS, CSCu, CSAg, R-Ag, R-STS, and AgN) through foliar application and subsequently exposed to thrips infestation. The results showed that nanoparticle treatments influenced plant physiological and biochemical responses in a concentration-dependent manner. Higher nanoparticle concentrations (60–100 mg L −1 ) were associated with reduced thrips infestation and improved physiological parameters, including increased soluble sugar and chlorophyll content. Nanoparticle treatments were also associated with enhanced expression of genes involved in capsaicinoid biosynthesis and phenylpropanoid metabolism, including AT3 , as well as increased levels of total phenols, flavonoids, and capsaicinoids. In addition, the expression of antioxidant-related genes such as SOD , POD , and GST increased following nanoparticle application, suggesting activation of antioxidant defense mechanisms. Changes in the expression of capsaicinoid biosynthetic genes may be linked to physiological responses such as improved photosynthetic performance and soluble sugar accumulation observed in our earlier work. Overall, these findings indicate that nanoparticle treatments can influence metabolic and defense-related pathways in pepper plants, potentially contributing to enhanced accumulation of secondary metabolites and antioxidant compounds.