Previously, we developed a transgenic tobacco BY2 cell line (GT6) in which glycosylation was modified by expressing human beta(1,4)galactosyltransferase (beta GalT). In this study, we produced a mouse monoclonal antibody in GT6 cells, and determined the sugar chain structures of plant-produced antibodies. Galactose-extended N-linked glycans comprised 16.7%, and high-mannose-type and complex-type glycans comprised 38.5% and 35.0% of the total number of glycans, respectively. N-linked glycans with the plant-specific sugars beta(1,2)-xylose and alpha(1,3)-fucose comprised 9.8%. The introduction of human beta GalT into suspension cultured tobacco cells resulted in the production of recombinant proteins with galactose-extended glycans and decreased contents of beta(1,2)-xylose and alpha(1,3)-fucose. (c) 2007 Elsevier Inc. All rights reserved.