Nickel hyperaccumulation in shoot cultures of Alyssum markgrafii
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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+.