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 50µmol of metal ion concentration and at 25µmol 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.

Response of the pea roots defense systems to the two-element combinations of metals (Cu, Zn, Cd, Pb).

The presence of the single metals (Cd, Pb, Cu, Zn) induces ROS (reactive oxygen species) production and causes oxidative stress in plants. While applied in two-element combinations, trace metals impact organisms in a more complex way. To assess the resultant effect we treated the pea grown hydroponically with the trace metals in variants: CuPb, CuCd, CuZn, PbCd, ZnPb, ZnCd in concentrations of 25 µM for each metal ion. Abiotic stress inhibited root elongation growth, decreased biomass production, induced changes in root colour and morphology. It changed rate of ROS production, malondialdehyde content, increased activity and altered gene expression of defence enzymes (superoxide dysmutase, catalase, ascorbate peroxidase, glutathione reductase, γ-glutamylcysteine synthetase).