Ni-induced oxidative stress in roots of the Ni hyperaccumulator, Alyssum bertolonii

The aim of this study was to determine whether superior antioxidative defences contribute to Ni tolerance in roots of the hyperaccumulator species, Alyssum bertolonii. Antioxidative responses were compared in hairy roots of A. bertolonii and the nonhyperaccumulator, Nicotiana tabacum. Growth, Ni uptake, antioxidative enzyme activities, lipid peroxidation and concentrations of H2O2 and surface-SH groups were measured in hairy root cultures exposed to 25 ppm (426 mum) Ni. Growth of A. bertolonii roots was not affected by Ni, whereas Ni prevented N. tabacum root growth. Endogenous activities of superoxide dismutase and catalase were 2.4 and >500 times greater, respectively, in A. bertolonii roots than in N. tabacum. H2O2 levels rose significantly with Ni treatment in both species, by factors of 3.6 and 8.6, respectively. Compared with N. tabacum, oxidative damage may be minimised in A. bertolonii roots by high endogenous activities of catalase and, to a lesser extent, superoxide dismutase. As accumulation of H2O2 was not detrimental to A. bertolonii, enhanced mechanisms for tolerating active oxygen species may also be present.