Cerium Oxide Nanoparticle Protects Maize from Cobalt Stress: Insights from Transcriptomics and Oxidative Stress Response Analysis

Nanozymes are a class of functional nanomaterials and potential next-generation artificial enzymes that exhibit catalytic properties. However, their role against cobalt (Co) stress and the underlying mechanisms remain largely unexplored. This study aimed to investigate the potential of cerium oxide nanoparticles (CeO₂ NPs as nanozymes) against Co-induced stress in maize and to uncover the underlying physiological and molecular mechanisms. Maize seeds were primed with CeO₂ NPs at 500 mg L^–1 and exposed to 300 μM Co stress under hydroponic conditions. Results showed that Co accumulated in the roots and is subsequently translocated to aboveground tissues, affecting several key growth parameters in maize plants. In contrast, CeO₂ NPs alleviated these adverse effects by enhancing growth and nutrient contents while reducing Co uptake. Photosynthesis and antioxidant enzyme activities were increased, while reactive oxygen species and malondialdehyde were reduced. Additionally, RNA-Seq analysis revealed significant alterations in the expression of key genes related to ion binding, metal transporters, and metabolite biosynthesis, offering molecular evidence of their role under Co stress. Notably, KEGG and GO analyses highlighted significant differences in hormonal signaling, phenylpropanoid biosynthesis, and glutathione metabolism in primed maize under Co stress. Taken together, this study demonstrates that CeO₂ NPs ameliorate Co toxicity in maize by preserving leaf ultrastructure, enhancing antioxidant defense and nutrient uptake, decreasing Co accumulation in roots and shoots, and providing a promising nanozyme-based approach for maize protection against Co-induced toxicity.