Heavy metals in white lupin: uptake, root-to-shoot transfer and redistribution within the plant

The translocation of manganese (Mn), nickel (Ni) cobalt (Co), zinc (Zn) and cadmium (Cd) in white lupin (Lupinus albus cv. Amiga) was compared considering root-to-shoot transport, and redistribution in the root system and in the shoot, as well as the content at different stages of cluster roots and in other roots. To investigate the redistribution of these heavy metals, lupin plants were labelled via the root for 24 h with radionuclides and subsequently grown hydroponically for several weeks. Mn-54, Ni-61 and Zn-65 were transported via the xylem to the shoot, Ni-63 and Zn-65 were redistributed afterwards via the phloem from older to younger leaves, while Mn-54 remained in the oldest leaves. A strong retention in the root was observed for Co-57 and Cd-109. Cluster roots contained higher concentrations of all heavy metals than noncluster roots. Concentrations were generally higher at the beginning of cluster root development (juvenile and immature stages). Mature cluster roots also contained high levels of Mn-54 and Co-57, but only reduced concentrations of Ni-63, Zn-65 and Cd-109.