Nano-chitosan boosts sesame plant anti-herbivore defenses and seed nutritional metabolites

Abstract

Activating the natural immunity of plants against insect herbivores scores within the global targets of improving food security, while simultaneously reducing pesticide load in the environment. Chitosan nanoparticles (CNPs) are non-toxic and biodegradable stimulants of plant growth that might also activate plant defenses against biotic stresses. We here explored if and how CNPs can stimulate sesame plant resistance against insect herbivores, and jointly improve seed nutritional quality. For this, we compared the effects of CNPs with the addition of bulk chitosan (CS) on sesame plant defenses against the highly voracious caterpillars of Spodoptera litura. We found that foliar application of 100 mg L⁻¹ CNPs resulted in the highest resistance of sesame plants against S. litura and alleviated plant oxidative stress by increasing the activities of antioxidant enzymes. Mechanistically, CNP application increased plant resistance against S. litura by activating endogenous signaling cascades (Ca²⁺ influx and phytohormone accumulation) and enhancing defense metabolite (e.g., sesamolin, shanzhiside methyl ester) production via the up-regulation of defense metabolite biosynthesis genes. Finally, we found that CNP application improved the nutritional quality of sesame seeds under field conditions. Altogether, these results indicated that CNPs could act as an alternative and ecofriendly nanostimulant for inducing plant insect resistance and improving food nutritional quality in agroecosystems.