Differential responses of maize (Zea mays) at the physiological, biomolecular, and nutrient levels when cultivated in the presence of nano or bulk ZnO or CuO or Zn2+ or Cu2+ ions

Abstract

Expanding applications of metal-based nanoparticles (NPs) in industry and agriculture have influenced agro-ecosystems. However, relatively little is known about the bioaccumulation, distribution, and phytotoxicity of ZnO-NPs, CuO-NPs, ZnO-bulk, CuO-bulk, Zn2+, or Cu2+ in maize. Plants were exposed to 0.05–2 mg ml−1 or g−1 of six tested materials in agar (7 days) in hydroponic medium (20 days), or sandy-clay-loam soil (20 or 40 days). Seed germination, emergence and lengths of plumules, principal and seminal roots were significantly inhibited by ZnO-NPs, CuO-NPs, Zn2+, and Cu2+. Toxicity was more pronounced in hydroponic culture than in soil, and perceptible alterations in biomolecules were evident. ICP-MS analysis exhibited progressive uptake of metals while morphological, elemental, and surface/deeper scanning showed translocation and distribution of NPs in tissues. Tested materials induced enhanced superoxide radical production, lipid peroxidation, and antioxidant enzymes and proline levels. Exposure significantly reduced P-accumulation, photosynthesis, and protein production. Zn2+ and Cu2+ were found to be more toxic than NPs. Compared to 20 days exposure in soil, toxicity slightly increased after 40 days. ZnO-NPs and CuO-NPs increased apoptotic sub-G1 population by 22.4% and 38%, respectively. These results provide a better understanding of the mechanistic aspects responsible for the nanotoxicities of ZnO- and CuO-NPs in maize.