Hematite nanoparticles influence ultrastructure, antioxidant defenses, gene expression, and alleviate cadmium toxicity in Zea mays

The present study describes the response of Zea mays to hematite nanoparticles (NPs) using five concentrations ranged from 500 to 8000 mg kg(-1), and Cd2+ concentrations (110 or 130 mg kg(-1) Cd2+) only or combined with 500 mg kg(-1) NPs, using soil culture. The endpoints measured were root/shoot growth, elements uptake, ultra-structural alterations, lipid peroxidation, some antioxidant enzyme activities, and their relative gene expressions. The results indicated that hematite NPs exhibited a dual behavior, in which 500 mg kg(-1) NPs significantly enhanced maize growth, while 4000 and 8000 mg kg(-1) NPs significantly increased lipid peroxidation and superoxide dismutase (SOD) activity displaying positive correlation with SOD expression in shoots (r = +0.472, p < .05). Ultrastructure micrographs revealed the appearance of aggregated NPs inside the vacuoles. The stunted growth, perturbed ultra-structure, and high lipid peroxidation were used as toxicity biomarkers for Cd2+. However, combined treatments of 500 mg kg(-1) NPs and Cd2+ significantly stimulated growth and glutathione reductase activity, while significantly reduced catalase (CAT) activity displaying positive correlation with CAT expression in roots (r = +0.694, p < .01). In conclusion, hematite NPs could alleviate Cd2+ toxicity not at the level of antioxidant defense, but by affecting mechanisms of Cd2+ detoxification.