Stress Responses and Accumulation Characteristics of Duckweed (Landoltia punctata) to Lead Oxide Nanoparticles
Lead oxide nanoparticles (PbO NPs) are increasingly released into aquatic environments from industrial processes, posing ecological risks. Duckweed (Landoltia punctata) is a known lead hyperaccumulator, but its physiological and biochemical responses to PbO NPs remain unexplored. This study synthesized PbO NPs via a plant-mediated biosynthesis method and exposed L. punctata to concentrations of 0 (control), 10, 20, 30, and 40 mg·L−1 in hydroponic culture for 7 days. Results showed concentration-dependent effects: low concentrations (10–20 mg·L−1) stimulated growth, while high concentrations (≥30 mg·L−1) inhibited fresh weight, growth rate, and root length. Chlorophyll b content decreased significantly at ≥20 mg·L−1 (by 14.09%, 10.79%, and 18.48% at 20, 30, and 40 mg·L−1, respectively), while carotenoid content increased. Malondialdehyde content and activities of superoxide dismutase, peroxidase, and catalase increased with PbO NPs concentration, indicating oxidative stress. Lead accumulation reached 1265.65 mg·kg−1 at 30 mg·L−1 and 2030.01 mg·kg−1 at 40 mg·L−1, with bioconcentration factors >1 and lead removal rates above 68.94%. Subcellular distribution showed lead predominantly in the cell wall fraction, followed by soluble components and organelles. These findings demonstrate that L. punctata exhibits strong PbO NPs accumulation and stress tolerance, supporting its use in phytoremediation of metal nanoparticle-contaminated waters.