THE ROLE OF METAL TRANSPORT AND TOLERANCE IN NICKEL HYPERACCUMULATIONBY THLASPI GOESINGENSE HALACSY

Metal hyperaccumulators are plants that are capable of extracting meta ls from the soil and accumulating them to extraordinary concentrations in aboveground tissues (greater than 0.1% dry biomass Ni or Co or gre ater than 1% dry biomass Zn or Mn). Approximately 400 hyperaccumulator species have been identified, according to the analysis of field-coll ected specimens. Metal hyperaccumulators are interesting model organis ms to study for the development of a phytoremediation technology, the use of plants to remove pollutant metals from soils. However, little i s known about the molecular, biochemical, and physiological processes that result in the hyperaccumulator phenotype. We investigated the rol e of Ni tolerance and transport in Ni hyperaccumulation by Thlaspi goe singense, using plant biomass production, evapotranspiration, and prot oplast viability assays, and by following short-and long-term uptake o f Ni into roots and shoots. As long as both species (T. goesingense an d Thlaspi arvense) were unaffected by Ni toxicity, the rates of Ni tra nslocation from roots to shoots were the same in both the hyper-and no naccumulator species. Our data suggest that Ni tolerance is sufficient to explain the Ni hyperaccumulator phenotype observed in hydroponical ly cultured T. goesingense when compared with the Ni-sensitive nonhype raccumulator T. arvense.