Zinc-resistant Cell Lines of Haplopappus gracilis

Abstract

Ionic zinc (Zn2+) was completely toxic to wild type (Wt) cellsof Haplopappus gracilis (Nun.) Gray at a concentration of 7 mM in Gamborg B5 medium. On this medium stable, zinc-resistant calli developed from Wt suspension cells at a frequency of 10-7. Although most zinc-resistant cell lines were tetraploid, the resistance was not causally related with increased ploidy level. Zinc resistance was maintained after culturing the selected cell lines for two years in the absence of selection pressure. The zinc resistance was not expressed constitutively but was inducible. Zinc uptake was equal for the zinc-resistant and the Wt cell lines. An intracellularly located zinc resistance mechanismis most likely. However, a mechanism based on increased production of cellular carboxylate can be excluded. The utility of the zinc-resistant cell lines for somatic cell genetics is discussed.