Machado, Altair Toledo, et al. “N-Partitioning, Nitrate Reductase and Glutamine Synthetase Activities in Two Contrasting Varieties of Maize”. Pesquisa Agropecuaria Brasileira, vol. 36, no. 2, Feb. 2001, pp. 249-56, doi:10.1590/S1678-3921.pab2001.v36.6136.