Iron oxide nanoparticles (FeO-NPs) mitigate salt stress in peanut seedlings by enhancing photosynthesis, osmoregulation, and antioxidant activity

Soil salinization constitutes a major constraint to agricultural sustainability worldwide, with elevated sodium chloride levels inducing complex physiological disruptions that compromise crop productivity. As an innovative approach to abiotic stress mitigation, iron oxide nanoparticles (FeO-NPs) demonstrate unique advantages in enhancing iron bioavailability and modulating plant stress responses. This investigation systematically evaluated the efficacy of FeO-NPs in ameliorating NaCl-induced stress (150 mM) in peanut (Arachis hypogaea L.) through foliar application of nanoparticle gradients (0, 25, 50, 100 mg/kg), with particular emphasis on photosynthetic apparatus protection and redox homeostasis regulation. Results demonstrated that salt stress significantly reduced growth parameters, photosynthetic pigments, gas exchange, and chlorophyll fluorescence, while elevating oxidative stress markers and antioxidant enzyme activities. Notably, FeO-NP application at 50 mg L⁻¹ demonstrated optimal efficacy in counteracting salinity effects. Treated plants exhibited remarkable recovery in morphological parameters, achieving 20.13–68.67 % greater shoot/root elongation and 36.18–53.20 % higher biomass accumulation compared to salt-stressed controls. The nanoparticles significantly enhanced photosynthetic performance through multiple mechanisms: including elevated chlorophyll, restored carotenoids, higher net photosynthesis (P_n), alongside improved stomatal conductance (G_s) and PSII efficiency (F_v/F_m). The protective mechanism of FeO-NPs involved to cellular homeostasis regulation, augmented accumulation of osmolytes (proline, soluble proteins, sugars) and significant enhancement of antioxidant system components, including elevated activities of SOD, POD, and CAT. These coordinated responses effectively mitigated oxidative damage, reducing reactive oxygen species accumulation and lipid peroxidation (MDA) content relative to NaCl-treated plants. These findings highlight the application of FeO-NPs could be a promising strategy to enhance salt tolerance in peanuts through multi-faceted physiological and biochemical mechanisms.