A field experiment was carried out in the College of Agricultural Engineering Sciences - University of Baghdad, during the fall season of 2021 to find out which cultivated cultivars of maize are efficient under nitrogen fertilization. The experiment was applied according to an RCBD (split-plot design with three replications). The cultivars of the experiment (Baghdad, 5018, Sarah) supply three levels of nitrogen fertilizer, which are N1 (100 kg.N/ha), N2 (200 kg.N/ha) and N3 (300 kg.N/ha). The statistical analysis results showed the superiority of the Sarah genotype, which gave the highest value of SOD and CAT enzymes, reaching 11.59 units mg-1 and 10.76 units mg-1 . Protein sequentially, while cultivar5018 outperformed as it gave the highest value of POD enzyme, which was 5.43 units mg-1.protein, and there were no significant differences between genotypes in NR enzyme. The increase in nitrogen fertilizer caused an increase in the values of oxidation and reduction enzymes, as the nitrogen level N3 gave the highest value for SOD, POD, CAT and nitrate reduction enzymes NR, reaching 11.59 mg-1 and 6.94 mg-1 units. Protein and 16.40 mg-1 units. Protein and 6.30 mg-1 units. Protein sequentially. The results of the molecular analysis using the Real-Time PCR technique showed the expression of the ZmNR1 gene. The analysis showed that the cultivated genotypes contained the gene in varying proportions as the gene expression increased in the compositions to which the nitrogen fertilizer was added. The value ranged from (0.16) to (49.46) times (a copy of the gene), where the highest expression of the gene was (49.46) for the Sarah cultivar when The nitrogen level N2 also gave the same gene expression ZmNR1 (15.01) folds. The cultivars of maize varied among them in their tolerance to excess or deficiency of nitrogen and in their ability to express the ZmNR1 gene, one of the most important nitrogen-carrying genes for maize crops. Keywords: maize, gene expression, nitrate reductase, antioxidant enzymes
