Nickel hyperaccumulation in shoot cultures of Alyssum markgrafii

Shoot cultures of Alyssum markgrafii O.E. Shulz, endemic nickel hyperaccumulating species of central Balkan, were established and maintained on Murashige and Skoog medium supplemented with 0.2 mg dm(-3) benzyladenine (BA). Nickel in form of NiCl2 . 6 H2O was supplemented at 22 different concentrations ranging from 0.0001 to 15 mM but none of them was lethal to cultures. High Ni2+ concentrations (10 mM or more) arrested shoot growth which, upon transfer to Ni-free medium, commenced via axillary bud proliferation. Shoots that developed from axillary buds through the subculture manifested increased tolerance to Ni2+ expressed as shoot elongation. Shoot multiplication and dry biomass production decreased with increase of N2+ in medium. Only the accumulation of Ni2+ in tissues increased with Ni2+ content of the medium. Apart from shoot cultures, high Ni2+ accumulation was registered in undifferentiated callus cultured on medium with 0.5 mg dm(-3) BA and 0.5 mg dm(-3) naphthylacetic acid. Highest content of accumulated Ni was 2.37 mu g g(-1) (d.m.) in shoots and 2.65 mu g g(-1) (d.m.) in callus, both measured on medium with 15 mM Ni2+.nul