Effects of zinc oxide nanoparticles on antioxidants, chlorophyll contents, and proline in Persicaria hydropiper L. and its potential for Pb phytoremediation

Abstract

Applications of nanoparticles and plants for efficient restoration of heavy metal-polluted water and soil are an emerging approach and need to be explored. Hydroponic study was performed to find the role of zinc oxide nanoparticles (ZnO NPs) in plant growth, antioxidative response, and lead (Pb) accumulation in Persicaria hydropiper. Seedlings were grown in Pb-polluted media amended with 5, 10, 15, and 20 mg L-1 ZnO NPs. Inductively coupled plasma spectroscopy (ICP) was used for Pb analysis in plant tissues. Pb significantly inhibited seedling growth, and ZnO NPs alleviated Pb-induced stress by promoting plant growth, and improved chlorophyll and carotenoid contents. Oxidative stress ameliorated in ZnO NPs exposed seedlings through enhanced production of free proline, phenolics, flavonoids, and activation of antioxidative enzymes. Pb accumulation boosted in ZnO NP treatments, and highly significant increase in Pb accumulation in roots (255.60 +/- 4.80 mg kg(-1)), stem (124.07 +/- 2.84 mg kg(-1)), and leaves (92.00 +/- 3.22 mg kg(-1)) was observed in T3 (15 mg L-1 ZnO NPs) for P. hydropiper. Contrarily, ZnO NPs at 20 mg L-1 dose suppressed plant growth, Pb accumulation, secondary metabolites, and antioxidative enzyme activities. Moreover, positive correlation was found in Pb accumulation with free proline and secondary metabolite contents in plant tissues. These results suggest that ZnO NPs at optimum concentration may augment efficacy of plants to remove heavy metal from polluted water through nanophytoremediation.