Somatic hybridization of nitrate reductase deficient mutants of nicotiana tabacum by protoplast fusion Glimelius, K.; Eriksson, T.; Grafe, R.; Muller, A.J. Physiologia Plantarum 44(3): 273-277 1978 0031-9317 10.1111/j.1399-3054.1978.tb08631.x https://eurekamag.com/research/006/437/006437518.php