Nickel stimulates copper uptake by nickel-hyperaccumulator plants in the genus Alyssum

Abstract

The greatest number of nickel (Ni)-hyperaccumulator plants belonging to the genus Alyssum originate from serpentine soils. They possess physiological mechanisms that enable them tolerate very high internal concentrations of Ni. The specificity of these traits has still not been fully clarified; however, by studying the interactions of different metals, some clues may be given. In the present study, the tolerance, uptake, accumulation and interactions of Ni and copper (Cu) were assessed in a range of Alyssum species. A. bracteatum (Harsin and Paveh populations) and A. inflatum were selected as Ni hyperaccumulators from western Iran. A. montanum and A. saxatile were selected as non-accumulators originating from the Mediterranean region, now being used as ornamental plants. Different concentrations of Ni (0, 100 and 250 µM for hyperaccumulators and 0, 10 and 25 µM for the non-accumulator plants), and Cu (0.5, 1 and 2.5 µM) were employed as treatments in a hydroponic growth experiment with a fully randomised factorial design. No tolerance to high concentrations of Cu was observed in any of the species tested. In the presence of Ni, an increased Cu concentration was observed in both roots and shoots of the Ni-hyperaccumulator plants, but not in the non-accumulators. Furthermore, no negative interaction was detected between Ni and Cu in metal uptake by roots, suggesting that different uptake mechanisms are involved. Stimulation of Cu uptake by Ni in the Ni hyperaccumulators hints that this particular feature may be among the characteristics that enable them to hyperaccumulate Ni, unlike their congeneric non-accumulators.