Effects of binary metal combinations on zinc, copper, cadmium and lead uptake and distribution in Brassica juncea

The interaction between lead, copper, cadmium and zinc in their binary combinations was investigated in Indian mustard seedlings (Brassica juncea L. var. Malopolska). Fourteen-days-old seedlings were treated with Pb(NO3)2, CuSO4, CdCl2, ZnSO4 at 50 μmol of metal ion concentration and at 25 μmol of each metal ion in combinations. Metal combinations were generally more inhibiting in terms of biomass production. This inhibiting effect followed an order: Cu + Cd > Cu + Zn, Cd + Pb > Cu + Pb > Zn + Pb, Cu > Cd > Zn > Zn + Cd > Pb. We observed synergistic and antagonistic effects of metal uptake in binary metal treatments, suggesting metal crosstalk at the plant uptake site. Metal content in plant tissues varied among different combinations. The metal concentrations followed an order of Pb > Cu > Zn > Cd in roots, Zn > Cu > Pb > Cd in the stem and Zn > Cu > Cd > Pb in leaves. Presence of metals altered the distribution of micronutrients (Cu, Zn) in plants: Cu concentration was lowered in roots and leaves and increased in stems; Zn content was increased in plants, with stems having up to 4 or 5 times more Zn than in control plants.