Does copper tolerance give cadmium tolerance in Mimulus guttatus

Abstract

Copper tolerance in Mimulus guttatus Fischer ex DC, is controlled by a single major gene, plus a number of minor genes (or modifiers) which elevate copper tolerance. Homozygous copper tolerant and nontolerant lines derived from Marin County, California, were screened in dose-response experiments against both copper and cadmium. Significant differences were found between these lines for copper, but not for cadmium, suggesting that cadmium tolerance is not conferred by the major copper tolerance gene. Ten selection lines, derived from three different copper mines, which all carry the major tolerance gene but vary in the degree of tolerance to copper were also screened against copper and cadmium. No significant correlation between copper and cadmium tolerances was found. Screening of modifier lines, in which modifiers for differing degrees of copper tolerance were inserted into a nontolerant background, showed that genotypes possessing fewer copper modifiers yield higher cadmium tolerance than those genotypes which have a greater number of modifiers. These results suggest that copper and cadmium tolerance are governed by independent genes in this species.