FREE HISTIDINE AS A METAL CHELATOR IN PLANTS THAT ACCUMULATE NICKEL

A NUMBER of terrestrial plants accumulate large quantities of metals s uch as zinc, manganese, nickel, cobalt and copper in their shoots(1). The largest group of these so-called 'metal hyperaccumulators' is foun d in the genus Alyssum, in which nickel concentrations can reach 3% of leaf dry biomass(2,3), Apart from their intrinsic interest, plants ex hibiting this trait could be of value in the decontamination of metal- polluted soils(4-6). However, the biochemical basis of the capacity fo r metal accumulation has not been elucidated. Here we report that expo sing hyperaccumulator species of Alyssum to nickel elicits a large and proportional increase in the levels of free histidine, which is shown to be coordinated with nickel in vivo. Moreover, supplying histidine to a non-accumulating species greatly increases both its nickel tolera nce and capacity for nickel transport to the shoot, indicating that en hanced production of histidine is responsible for the nickel hyperaccu mulation phenotype in Alyssum.