Green-synthesized lanthanum nanostructures modulate redox balance and phytochemical responses in lead-stressed Zataria multiflora.

Lead (Pb) toxicity disrupts redox homeostasis and impairs phytochemical stability in medicinal plants; however, nanomaterial-based approaches to alleviate oxidative stress under Pb stress have not been extensively studied. In the present study, lanthanum-based nanostructures (La-based NCs) were prepared using an eco-friendly method employing Arabic gum and spermine, and their efficacy in alleviating Pb-stress-induced oxidative damage in Zataria multiflora was investigated. The plants were subjected to different levels of Pb contamination (0, 250, 500, and 750 mg/kg) and then treated with La-based NCs at doses ranging from 0 to 200 ppm. The effect of Pb toxicity (750 mg/kg) led to an increase in indicators of oxidative stress, including H₂O₂ and MDA, along with a significant decrease in the activity of phytochemicals and antioxidant response. Treatment with La-based NCs significantly improved these effects dose-dependently, showing the optimal dose at 100 ppm. At 100 ppm of La-based NCs treatment, oxidative damage was decreased by 40-60%, whereas antioxidant responses were stimulated by 35-70%. Simultaneously, metabolic stability was enhanced through the recovery of essential oils and related phytochemical characteristics. Particularly, La-based NCs stabilized with Arabic gum consistently showed greater activity than those stabilized with spermine, suggesting a stabilization-mediated influence on redox reactions and plant-NCs interactions. This study demonstrates that green-synthesized La-based NCs have potential applications as modulators of oxidative stress and antioxidants within the plant system under Pb stress.