COPPER-SENSITIVE MUTANT OF ARABIDOPSIS-THALIANA

A Cu-sensitive mutant, cup1-1, of Arabidopsis thaliana has a pattern o f heavy-metal sensitivity different from that of the cad1 and cad2 mut ants, which are deficient in phytochelatin biosynthesis. The latter ar e significantly sensitive to Cd and Hg and only slightly sensitive to Cu, whereas the cup1-1 mutant is significantly sensitive to Cu, slight ly sensitive to Cd, and not more sensitive to Hg, compared to the wild type. Genetic analysis has shown that the sensitive phenotype is rece ssive to the wild type and segregates as a single Mendelian locus, whi ch has been mapped to chromosome 1. Genetic and biochemical studies de monstrate that the cup1-1 mutant is not affected in phytochelatin bios ynthesis or function. The sensitive phenotype of the cup1-1 mutant is associated with, and probably due to, increased accumulation of higher levels of Cd and Cu compared with the wild type. Consistent with this , a Cu-inducible, root-specific metallothionein gene, MT2a, is express ed in cup1-1 roots under conditions in which it is not expressed in th e wild type. Undifferentiated cup1-1 callus tissue did not show the Cu -sensitive phenotype, suggesting that the mutant phenotype, in contras t to cad1 and cad2, is not expressed at the cellular level.