Melatonin and iron play important roles in the growth processes and production of secondary metabolites in medicinal plants. To evaluate the effects of melatonin and Chitosan-Coated Iron Oxide Nanoparticles (Fe-CTs NPs) on peppermint growth, essential oil content and constituents, total carbohydrates and antioxidant enzyme activities, a factorial experiment was conducted based on randomized complete block design (CRBD) with three replications (n = 3). Treatments consisted of different concentrations of melatonin (0, 100, and 200 mg L1 ) and Fe-CTs NPs (0, 7.5, and 15 mg L1 ). During the experiment, foliar applications of melatonin and Fe-CTs NPs were performed three times with 20 days’ interval. Treatments with melatonin, and Fe-CTs NPs had significant effects on the studied traits. The results showed that with increasing melatonin and FeCTs NPs concentrations, fresh and dry weights, total carbohydrates, and leaf area index were significantly (P < 0.05) increased in treated plants. The highest CAT and APX activities were observed in plants treated with melatonin at 100 mg L1 and Fe-CTs NPs at 15 mg L1 . Eucalyptol, Menthyl acetate, Thiophene, 2-ethyl-5-(2- methylpropyl), Mint furanone, and Viridiflorol were found as the major essential oil constituents in peppermint plants under experimental treatments. Moreover, analytical results showed that the highest amount of Menthol (38.48 %) was obtained in plants exposed to Fe-CTs NPs at 7.5 mg L1 , however, the highest L-Menthone (30.53 %) was observed in plants treated with melatonin at 200 mg L1 and Fe-CTs NPs at 15 mg L1 . The findings provide insights into the regulatory mechanisms of melatonin and Fe-CTs NPs on peppermint growth, physiology and biosynthesis of volatile compounds.
