Hyperaccumulation of nickel by hairy roots of Alyssum species: Comparison with whole regenerated plants

Hairy roots were used to investigate nickel uptake by the hyperaccumulator species, Alyssum bertolonii, A. tenium, and A. troodii. The Ni biosorption capacity of A. tenium hairy roots was lower than for other types of biomass such as bacteria and algae; in short-term (9-h) equilibrium studies, the h ighest Ni content measured in the roots was 17 500 mug g(-1) dry weight at a liquid concentration of about 4000 ppm. Using longterm hairy root culture s, it was demonstrated that Ni tolerance and hyperaccumulation do not neces sarily depend on the presence of shoots or root-shoot translocation. A. ber tolonii hairy roots remained healthy in appearance and continued to grow in the presence of 20-100 ppm Ni, accumulating up to 7200 mug g(-1) dry weigh t Ni. In contrast, hairy roots of Nicotiana tabacum turned dark brown at 20 ppm Ni and growth was negligible. The ability to grow at high external Ni concentrations allowed hyperaccumulator hairy roots to remove much greater amounts of heavy metals from the culture liquid than nonhyperaccumulator ha iry roots, even though biomass Ni concentrations were similar. Although hai ry roots proved to be a useful tool for investigating Ni hyperaccumulation, there were significant differences in the Ni uptake capacity of hairy root s and whole plants. Regenerated plants of A. tenium were much more tolerant of Ni and capable of accumulating higher Ni concentrations than hairy root s of this species.