Cadmium loading into potato tubers: the roles of the periderm, xylem and phloem

The mobility of Cd in potato plants (Solanum tuberosum ) was examined using both short-term radioisotopic labelling with Cd-109 and long-term growth experiments in soil supplemented with Cd, with an emphasis on the pathways through which Cd is taken up by tubers. Split-pot experiments showed that tubers and their associated stolons and stolon roots contribute only a minor fraction to the overall Cd absorption by the plant. Most of the Cd was absorbed by the basal roots. Cd-109 absorbed from the soil was rapidly exported to other parts of the plant, especially the stem, with significant amounts appearing in the tubers within 30 h. Application of Cd-109 to leaves showed that Cd can be rapidly distributed via the phloem to all tissues. The results suggest that unlike Ca, Cd has high mobility in plants in both xylem and phloem, and that stems may have an important role in transfer between these two pathways.