Role of Nanoparticles in Enhancing Plant Secondary Metabolite Production

Secondary metabolites are a diverse array of compounds produced by plants. Although not directly involved in growth and development of plants, secondary metabolites are crucial in overall survival of the plants. Primarily complex organic compounds like phenolics, flavonoids, alkaloids, and terpenoids, these metabolites have essential roles in plant defense, communication, and stress resistance. Furthermore, secondary metabolites of plants have been exploited for its wider applications in pharmaceuticals, nutraceuticals, cosmetics, and agriculture. As naturally these functional compounds are found in lower quantities in plants unsuitable for commercial extraction, elicitors are employed to enhance the production. Nanoparticles (NPs) have emerged as one of the effective elicitors to enhance secondary metabolite production, due to their nanoscale size (1–100 nm), large surface area, reactivity, and capacity to mimic stress conditions in plants. As secondary metabolites are produced by plants in stressed condition, NPs are effective elicitors as the mechanism involves generation of reactive oxygen species (ROS) that stresses the plant cell and activates various defense related pathways. Activation of signaling molecules such as jasmonic acid, salicylic acid, and ethylene stimulate defense-related enzymes and transcriptional activation of genes involved in secondary metabolism. Studies has shown ZnO, Ag, CuO, TiO2 enhancing flavonoid and phenolic accumulation in crop plants like tomato, wheat, maize, and other commercial plants. To mitigate the toxicity of metal oxides as nanoparticle elicitors, nontoxic biopolymeric nanoparticles using chitosan and methyl jasmonate are being utilized in plant cell suspension. Thus, a wide range of metallic and nonmetallic nanoparticles represent a promising biotechnological approach to increase secondary metabolite yield to expand pharmaceutical, nutraceutical, and agricultural applications.