Ecotypic Variation and Copper-Sensitive Mutants

A new vertical mesh transfer (VMT) technique has been developed to facilitate the rapid isolation of plant metal-tolerance mutants. l h e technique i s quantitative, allowing comparisons of the growth responses of different strains or ecotypes. Using the VMT technique, we have characterized the dose responses of 1 O ecotypes of Arabidopsis fhaliana to Cuz+, Znz+, NiZ+, Cr3+, Cd2+, and AI3+. Ecotypic variations in the highest concentration causing no inhibition and the lowest concentration causing complete inhibition for the six metals were observed. Two ecotypes, Ws and Enkheim, exhibited an inducible tolerance mechanism in response to copper. Pretreatment of Ws with the highest concentration causing no inhibition for copper resulted in a shifting of the lowest concentration causing complete inhibition to a higher value. Partia1 cross-induction and cross-tolerance between Cuz+ and ZnZ+ were demonstrated. In addition, ethyl methanesulfonate-mutagenized Columbia seeds were screened for copper-sensitive (cus) mutants using the VMT procedure. Thus far, 59 putative cus mutants have survived retesting to the M, or M, generation. When grown on gellan gum supplemented with 30 p~ CuCI,, cus mutants develop marked toxicity symptoms. A copper dose-response curve of the cusl mutant showed that the metal-sensitive phenotype i s specific for the lower concentration range.