Binding of Cd to non-specific metal-binding peptides (phytochelatins) in birch roots has been suggested as an explanation for tolerance to Cd toxicity in birch (Betula pendula). In the present study, the tolerance of birch roots to Cd was further investigated by using buthionine sulphoximine (BSO) as an inhibitor of phytochelatin synthesis. Birch seedlings, grown in nutrient solution at pH 4.2, were exposed to 0 or 2 μM CdCl2 combined with 0 or 0.1 mM BSO for 6 d. Plant growth (fresh weight increase and shoot to root dry weight ratio) and the nutrient composition in fine roots, whole roots and shoots were determined. The effects of Cd on growth confirms the results of earlier studies on birch, suggesting a reduced shoot growth, but preserved or stimulated root growth. When Cd and BSO were combined, overall plant growth was severely reduced. BSO was also shown to aggravate Cd-induced reductions of root and shoot concentrations of K, Ca and Mg but to impede the accumulation of Cd.

The results suggest that phytochelatins participate in protecting the root against Cd interferences with growth, possibly by restricting Cd-induced changes in the nutrient composition of the plant.