EXPRESSION OF MOUSE METALLOTHIONEIN-I GENE CONFERS CADMIUM RESISTANCEIN TRANSGENIC TOBACCO PLANTS

Transgenic tobacco plants containing a mouse metallothionein-I (MT-I) gene fused to the cauliflower mosaic virus 35S (CaMV 35S) promoter and nopaline synthase (nos) polyadenylation site were obtained by transfo rming tobacco leaf discs with an Agrobacterium tumefaciens strain carr ying the chimaeric gene. Transformants were directly selected and root ed on medium containing cadmium and kanamycin. A total of 49 individua l transgenic tobacco plants were regenerated. Among them 20% showed a very high expression level and their growth was unaffected by up to 20 0 mu M cadmium, whereas the growth of control plants was severely affe cted leaf chlorosis occurred on medium containing only 10 mu M cadmium . The concentration of MT-I in leaves of control and transgenic tobacc o was determined with Cd/ haemoglobin saturation assay, a polarographi c method and western blotting. In addition, seeds from self-fertilized transgenic plants were germinated on medium containing toxic levels o f cadmium and scored for tolerance/susceptibility to this heavy metal. The ratio of tolerant to susceptible plants was 3:1 indicating that t he metallothionein gene is inherited as a single locus.