Nickel and copper tolerance and toxicity in three Tuscan populations of Silene paradoxa

Three Tuscan ecotypes of Silene paradoxa L. were studied to evaluate the occurrence of multiple tolerance or co-tolerance mechanisms and to underline some tolerance strategies in plants naturally adapted to toxic concentrations of heavy metals. Seeds were collected from non-toxic calcareous soil, a serpentine outcrop with high nickel content and a copper mine dump. The evaluation of the toxic effects of the metals on root growth showed the copper-tolerant population as nickel co-tolerant, whereas the opposite was not the case. This suggests the occurrence of a non-reciprocal co-tolerance mechanism. The nickel-tolerant population seemed able to tolerate nickel by limiting its inhibiting effect on the peroxisomal H2O2 scavenging enzymes since, in the sensitive population, this inhibition revealed itself as one of the causes of nickel-induced oxidative stress. A very low copper root and shoot concentration seemed to be characteristic of the copper-tolerant population, combined with a low susceptibility to metal-induced oxidative stress.