Nanoparticles in Plant Abiotic Stress Resilience

Climate change, along with the increasing incidence of drought, salinity, nutrient depletion, and extreme temperatures, is severely constraining global agricultural productivity. In recent years, nanoparticles (NPs) have emerged as effective modulators of plant physiology; however, a comprehensive understanding of their comparative performance across different stress conditions remains limited. This review synthesizes recent advances on silicon dioxide (SiO2), zinc oxide (ZnO), copper oxide (CuO), iron oxide (FeO), silver (Ag), and titanium dioxide/titania (TiO2) NPs, emphasizing their mechanistic roles and quantifying their effectiveness in enhancing plant resilience. Evidence indicates that SiO2 NPs primarily enhance antioxidant defense, regulate ion homeostasis, improve water-use efficiency, and promote root development under drought and salinity stress. For example, SiO2 NPs at 250 mg L-1 increased chlorophyll content and boosted antioxidant enzyme activity. ZnO NPs contribute to stress tolerance by strengthening antioxidant systems, maintaining membrane stability, improving osmotic adjustment, and enhancing nutrient uptake under drought, salinity, and nutrient-deficient conditions. Their effects on antioxidant defenses are consistently strong: plants treated with 100 mg L-1 ZnO NPs exhibited marked increases in pigment concentrations (+58-73% for chlorophyll a, +142-149% for chlorophyll b, and +176-193% for carotenoids). Cu NPs also demonstrated protective effects: doses of 20 mg L-1 can reduce cadmium (Cd) accumulation in leaves (-12.6%) and roots (-38.6%). Iron(II) oxide NPs (FeO NPs), applied at 20-100 mg L-1, promote better growth and photosynthesis in barley by regulating gene expression. Additionally, TiO2 NPs at 200 ppm have been shown to enhance salt tolerance in eggplant by improving antioxidant defense, protecting photosynthetic function, and reducing oxidative damage. By integrating these quantitative results with mechanistic insights, this review clarifies how NPs modulate plant performance under stress. It also identifies key knowledge gaps related to dose optimization, long-term environmental fate, and safety assessment. Overall, the findings highlight both the potential and the challenges of incorporating nanotechnology into future strategies aimed at strengthening crop resilience under accelerating climate stress.