Uptake of hematite nanoparticles in maize and their role in cell cycle dynamics, PCNA expression and mitigation of cadmium stress.

Cadmium toxicity is considered a major threat to several crops worldwide. Hematite nanoparticles (NPs), due to their small size and large specific surface area, could be applied as an adsorbent for toxic heavy metals in soil. Also, they serve as an efficient nano-fertilizer, promoting Fe availability and biomass production in plants, thus enabling Cd2+ -induced stress tolerance. The phytotoxicity of five different concentrations of hematite NPs, ranging from 500 to 8,000 mg·kg-1 , and Cd2+ concentrations (110 or 130 mg·kg-1 Cd2+ ) alone or combined with 500 mg·kg-1 NPs was evaluated in maize. The changes in fresh weight, element analysis, cell cycle regulation, DNA banding patterns and proliferating cell nuclear antigen (PCNA) expression were used as biomarkers. The results revealed that increased fresh weight and fewest polymorphic DNA bands were detectable after treatment with 500 mg·kg-1 NPs. However, at 8,000 mg·kg-1 NPs, PCNA expression increased significantly, which resulted in cell cycle arrest at the G1/S checkpoint in roots. Significant reductions in fresh weight, altered nutrient profiles and cell cycle perturbations are considered symptoms of Cd2+ toxicity in maize. Conversely, amending 500 mg·kg-1 NPs with 130 mg·kg-1 Cd2+ increased fresh weight, Fe concentration and genomic template stability, while reducing Cd2+ uptake and PCNA1 expression. Overall, 8,000 mg·kg-1 hematite NPs interfered with the cellular homeostatic balance of maize, resulting in a cascade of genotoxic events, leading to growth inhibition. Although 500 mg·kg-1 hematite NPs alleviated Cd2+ -induced DNA damage to a certain extent, their impact on cell cycle progression requires further verification.