Transport interactions between cadmium and zinc in roots of bread and durum wheat seedlings

Field studies have shown that the addition of Zn to Cd-containing soils can help reduce accumulation of Cd in crop plants. To understand the mechanisms involved, this study used ¹⁰⁹Cd and ⁶⁵Zn to examine the transport interactions of Zn and Cd at the root cell plasma membrane of bread wheat ( Triticum aestivum L.) and durum wheat ( Triticum turgidum L. var. durum ). Results showed that Cd²⁺ uptake was inhibited by Zn²⁺ and Zn²⁺ uptake was inhibited by Cd²⁺. Concentration-dependent uptake of both Cd²⁺ and Zn²⁺ consisted of a combination of linear binding by cell walls and saturable, Michaelis-Menten influx across the plasma membrane. Saturable influx data from experiments with and without 10 µm concentrations of the corresponding inhibiting ion were converted to double reciprocal plots. The results revealed a competitive interaction between Cd²⁺ and Zn²⁺, confirming that Cd²⁺ and Zn²⁺ share a common transport system at the root cell plasma membrane in both bread and durum wheat. The study suggests that breeding or agronomic strategies that aim to decrease Cd uptake or increase Zn uptake must take into account the potential accompanying change in transport of the competing ion.