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 H ₂ O₂ and surface -SH groups were measured in hairy root cultures exposed to 25 ppm (426 µm) 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 . H ₂ O₂ 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 H ₂ O₂ was not detrimental to A. bertolonii, enhanced mechanisms for tolerating active oxygen species may also be present.