Engineered Nickel Oxide Nanoparticle Causes Substantial Physicochemical Perturbation in Plants

Area of Science:

• Environmental Science
• Plant Biology
• Toxicology

Background:

• Engineered nickel oxide nanoparticle (NiO-NP) concentrations are increasing in the environment due to industrial use, leading to greater plant exposure.
• While nickel is an essential micronutrient, NiO-NP is a human carcinogen and its interaction with plants, particularly its cellular and genotoxic effects, is not well understood.
• Previous studies suggest NiO-NP can cause plant stress, cytotoxicity, and growth retardation, but detailed investigations into cellular responses and genotoxicity are lacking.

Purpose of the Study:

• To investigate the cytotoxicity, internalization, and effects on the antioxidant enzyme system of NiO-NP in the model plant *Allium cepa* L.
• To assess the genotoxic potential of NiO-NP in *A. cepa* L. and four related economically important species (*Allium sativum* L., *Allium schoenoprasum* L., *Allium porrum* L., and *Allium fistulosum* L.).
• To evaluate the impact of varying NiO-NP concentrations on biochemical profiles and genotoxicity in *Allium* species.

Main Methods:

• Root tips of *Allium* species were exposed to seven different concentrations of NiO-NP (10–500 mg L⁻¹).
• Deionized distilled water served as the negative control, and 0.4 mM EMS solution as the positive control.
• Genotoxic endpoints including mitotic indices (MI), chromosomal aberrations (CAs), and chromosome breaks were analyzed. Biochemical markers such as malonaldehyde (MDA) and antioxidant enzymes (catalase, superoxide dismutase, guaiacol peroxidase) were assessed.

Main Results:

• NiO-NP induced genotoxicity in all tested *Allium* species, evidenced by decreased MI and increased CAs and chromosome breaks, even at a low dose of 10 mg L⁻¹.
• Exposure to NiO-NP significantly increased lipid peroxidation (MDA) and altered the activity of antioxidant enzymes (CAT, SOD, POD), indicating oxidative stress and disruption of cellular homeostasis.
• A dose-dependent decrease in MI was observed with increasing NiO-NP concentration, accompanied by a rise in antioxidant enzyme activity and MDA formation.

Conclusions:

• Engineered nickel oxide nanoparticles exhibit significant genotoxic effects on plants, impacting cellular processes and physiological balance.
• NiO-NP exposure leads to oxidative stress and disrupts the antioxidant defense system in *Allium* species.
• Based on the observed cytotoxicity and genotoxicity, NiO-NP should be recognized as a significant environmental hazard.