A variant cell line of Medicago saliva L. resistant to methionine (100 mmol/L) was selected .from calli treated with 1.5 mmol/L sodium azide. Plants were regenerated from this selected cell line. After growing for 6 months on the medium devoid of selection pressure, the variant cell line still showed high level of resistance, which was 7.2-fold higher than that of the wild type. This indicated the stability of the resistance expression. The variant cell line also expressed a 3.3-fold higher cross-resistance to ethionine, than that of the wild type. The contents of methionine, lysine, threonine and isoleucine in the variant calli were respectively 2.0, 1.43, 1.71 and 1.57 times higher than those in the wild type. However, in the variant regenerated plantlets they respectively were 2.0, 1.33, 1.22 and 1.22 times higher than those in the wild type regenerants. Four new protein bands, viz. 65 kD, 23 kD, 20 kD and 18 kD, appeared in the SDS-PAGE pattern of soluble proteins in the variant calli. In the peroxidase isoenzyme electrophoresis pattern, two new bands were also observed in the variant calli.
