Somatic hybridization studies with a nitrate reductase deficient mutant line of nicotiana tabacum cultivar gatersleben Cooper Bland, S.; Kumar, A.; Cocking, F.C. Journal of Embryology and Experimental Morphology 82(Suppl): 14 1984 0022-0752 https://eurekamag.com/research/029/181/029181555.php