The unusual property of the sand violet, Viola rupestris, to cope with heavy metal toxicity

Abstract

For investigating the capacity for accumulation of heavy metals and their avoidance, a number of parameters were compared in plants of the sand violet (Viola rupestris) growing on a heavy metal heap and on a non-contaminated reference site, both rich in limestone. The plants collected from both sites showed large differences in the numbers and sizes of reproductive structures and the content of heavy metals both in roots and leaves. The accumulation capability for Zn, Cd and Pb in roots and leaves of the violets from the heavy metal site was high although not comparable to some heavy metal plants. High numbers of oxalate crystals were observed in plants from the polluted site which may serve to detoxify not only Ca, but also Zn, Cd and Pb. Almost all reproductive structures examined were lower in numbers and sizes in the plants from the contaminated site compared to the situation in the reference violets. The heavy metal content in the capsules of the plants from the heavy metal site, was, however, not as high as in roots and leaves which is seemingly a general phenomenon of plants occurring on heavy metal soils and being exposed to the toxicity of these elements. The present findings could serve as a basis for molecular studies on the adaptions of non-metallophytic plants to stress caused by heavy metal toxicity in contaminated soils.