Differential allocation of cadmium and zinc in durum wheat during grain filling as revealed by stable isotope labeling

Background and aims Cereals can be made safer and more nutritious by reducing cadmium (Cd) and enhancing zinc (Zn) levels. To respectively regulate the accumulation of these chemically similar elements in grains, it is essential to understand the differences between Cd and Zn allocation to grains. Methods In durum wheat ( Triticum durum ), dual-isotope ( 111 Cd and 67 Zn) labeling was used to trace the post-anthesis uptake fluxes separately from the remobilization of pre-anthesis vegetative pools. Laser ablation inductively coupled mass spectrometry was used to investigate the spatial distribution of Cd and Zn in the uppermost node. Results Among the shoot organs, both pre- and post-anthesis derived Cd was more allocated to the high-transpiring organs (i.e., bracts and flag leaves) whereas Zn was more to the grain. Cadmium was likely less efficiently transferred from the xylem to the phloem as suggested by the elemental maps which showed that Cd was more abundant than Zn in the xylem of the uppermost node. Furthermore, unlike Zn, Cd was not significantly remobilized from the high-transpiring organs, which further limited the allocation of Cd to the grain. Conclusion High-transpiring organs are sources of grain Zn but irreversible sinks of Cd. Agronomic strategies that enhance Cd sequestration and Zn remobilization in high-transpiring organs could contribute to producing grains with low Cd and high Zn concentrations.