Maize seedlings have higher nitrate and nitrite reductase levels in leaves than roots, with nitrate reductase being more active in leaves. Glutamate dehydrogenase activity is higher in roots, indicating they are more involved in ammonium assimilation. Seminal roots are more active in nitrate assimilation, while nodal adventitious roots are more active in ammonium assimilation during the first 20 days of seedling growth.