Cadmium tolerance and toxicity, oxygen radical processes and molecular damage in cadmium-tolerant and cadmium-sensitive clones of Holcus lanatus L.

Two clones of the grass Holcus lanatus from a metal-contaminated (Hallen Wood, Avonmouth, UK) and an uncontaminated site (Totley, Sheffield, UK) accumulated cadmium from Cd-amended hydroponic cultures, the Totley material to two-fold higher concentrations than the Hallen Wood. The Totley clone showed impaired growth at relatively low Cd concentrations; the reduction in parallel tolerance indices (TIs) to 50% occurred at an external Cd concentration of 53 pM compared with 94 pM in the Cd-tolerant Hallen Wood material. In both clones Cd was transported to the shoots; in the non-tolerant (Cd-sensitive) Totley tissues the two-fold greater Cd accumulation was accompanied by a two-fold rise in lipid peroxidation, indicative of membrane damage by reactive oxygen species in the shoot, though not in the roots. Evidence for the involvement of activated forms of oxygen was also seen in the highly significant correlations between Cd uptake into the shoot and the activities of superoxide dismutase (r = 0-95) and guaiacol peroxidase (r = 0-96), but confined to the sensitive Totley material. It was concluded that one potentially highly-damaging effect of Cd was to promote the generation of partly-reduced and highly-reactive forms of oxygen in the Cd-sensitive clone and that the site of activated oxygen formation was the shoot rather than the root.