Uptake and distribution of nickel and other metals in the hyperaccumulator Berkheya coddii

Berkheya coddii is a fast-growing, high biomass nickel (Ni) hyperaccumulator plant that has recently attracted attention for its possible use in the phytoextraction of Ni. The mechanisms of Ni accumulation, however, are not well understood in this plant. Plants were grown hydroponically in varying Ni concentrations to assess the uptake and distribution of Ni, and other metals, at the whole plant level. X-ray microanalyses (EDXA) of frozen hydrated tissues were conducted to determine the distribution of Ni at the cellular level in the leaves. Most Ni was found in the shoots, especially in the leaves. Leaf Ni concentration increased with age, whereas older stem sections had lower Ni concentrations than new growth. EDXA analyses revealed that the cuticle of the upper epidermis had a significantly higher Ni concentration than the rest of the leaf. The Ni concentrations in the other leaf tissues were not significantly different. This pattern of distribution contrasts sharply with some other hyperaccumulator species that commonly show a preferential accumulation of Ni and other metals in the vacuoles of the epidermal cells.