Accumulation mechanisms and heavy metal tolerance of a nickel hyperaccumulator

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Abstract
Alyssum bertoionii Desv., a crucifer which grows only in Tuscany on serpentine soil, is characterized by high Ni concentration in its leaves and a high tolerance to this element. In this research, the Co and Zn tolerance of A. bertolonii has been tested and compared with that of Ni. Although the Zn concentration in the serpentine soil on which the plant grows is lower than that of Co, root growth showed no significant difference for these two elements. In excised roots, on the other hand, Co and Zn compete with Ni uptake and accumulation. Seedlings do not show any inhibition in the translocation of these three elements. They are all rapidly carried to and accumulate in the shoots, but the uptake and traslocation of Zn does not show the saturation trend found for Ni and Co. The same gel filtration fractions contain the three elements in association with malic acid, involved in Ni tolerance.