Hydrogen-rich water mitigates zinc oxide nanoparticle toxicity in arugula: a focus on growth and antioxidant defense

The escalating use of zinc oxide nanoparticles (ZnO-NPs) necessitates a deeper understanding of their phytotoxicity in edible plants. Although hydrogen-rich water (HRW) mitigates abiotic stress, its capacity to counteract ZnO-NP damage in arugula (Eruca sativa L.) remains unexplored. The capacity of exogenous HRW at 50% and 100% saturation to mitigate ZnO-NP (150 mg L^- 1) toxicity in arugula was investigated. Four treatment groups were established: control, ZnO-NPs alone, and ZnO-NPs combined with 50% or 100% HRW. Physiological and biochemical responses were evaluated in both seedlings and mature leaves. HRW effectively counteracted ZnO-NP stress and enhanced growth, increasing the tolerance index (TI) by 12.37% (50% HRW) and 17.74% (100% HRW) in early stages. HRW treatments at 50% and 100% increased shoot growth by 67.73% and 83.95% and root growth by 165.49% and 130.97%, respectively. Photosynthetic pigments were recovered by an average of 30.96% (50% HRW) and 43.78% (100% HRW). Furthermore, 100% HRW boosted superoxide dismutase (SOD) activity by 34.01%-89.85% and catalase (CAT) activity by 55.10%-29.78% in leaves and seedlings, respectively. Conversely, ZnO-NP exposure elevated zinc (Zn) concentrations and translocation factor (TF) and stimulated oxidative stress markers, including malondialdehyde (MDA), anthocyanins, ascorbic acid (AsA), proline, and peroxidase (POD); HRW application reversed these damaging effects. A stage-specific stress response was observed: seedlings accumulated higher concentrations of hydrogen peroxide (H₂O₂) scavengers, including cysteine (Cyst), glutathione (GSH), phenolics, and soluble proteins, whereas mature leaves showed decreases in these levels. HRW mitigated the accumulation of these protective compounds in seedlings while boosting them in leaves. These results suggest that HRW treatments have practical implications for enhancing arugula's capacity to tolerate ZnO-NP exposure. This study offers crucial mechanistic insights and robust data for environmental toxicologists. Furthermore, it provides a valuable reference for the potential environmental applications of HRW in contaminated agricultural systems.