Application of FeO nanoparticles improves the growth, antioxidant power, flavonoid content, and essential oil yield and composition of Boiss.

Boiss., an endemic and endangered medicinal and aromatic plant in Iran, showcases distinct botanical characteristics and therapeutic promise. According to the IUCN grouping criteria, this plant is facing challenges due to overcollection from its natural habitats. To address this issue, there is an increasing inclination towards cultivating this species within agricultural systems. This study aimed to evaluate the impact of applying FeO nanoparticles (NPs) at varying concentrations (50, 100, and 200 mg L), as well as bulk FeO at the same concentrations, on the growth, essential oil production, antioxidant capacity, total phenol, and flavonoid content of . The foliar application of 100 and/or 200 mg L of FeO NPs resulted in the greatest leaf length and dry weight, while FeO NPs at the level of 100 mg L led to the highest leaf/stem ratio. Additionally, spraying 200 mg L of FeO NPs and all concentrations of bulk FeO positively impacted chlorophyll and carotenoid levels. Both nano and bulk FeO supplements stimulated HO production and subsequently enhanced enzymatic antioxidant activity. The use of 50 mg L of FeO NPs resulted in the highest flavonoid content and non-enzymatic antioxidant activity. Meanwhile, the highest essential oil content and yield was achieved by the application of 50 and/or 100 mg L FeO NPs. The addition of low concentration of FeO NPs (50 mg L) resulted in a significant increase in the concentration of geranial, while a higher supply of FeO NPs (200 mg L) significantly decreased the percentage of neral in the essential oil. Overall, the application of FeO NPs demonstrated significant potential for increased biomass, enhanced yield, essential oil production, and phytochemical attributes. The findings highlight the versatility of FeO NPs at optimal concentrations, acting as both a nano-fertilizer and a nano-inducer, promoting the production and accumulation of valuable secondary metabolites in plants.