Selective transport of zinc, manganese, nickel, cobalt and cadmium in the root system and transfer to the leaves in young wheat plants

Background and Aims The uptake, translocation and redistribution of the heavy metals zinc, manganese, nickel, cobalt and cadmium are relevant for plant nutrition as well as for the quality of harvested plant products. The long-distance transport of these heavy metals within the root system and the release to the shoot in young wheat (Triticum aestivum 'Arina') plants were investigated. Methods After the application of Zn-65, Mn-54, Ni-63, Co-57 and Cd-109 for 24 h to one seminal root (the other seminal roots being excised) of 54-h-old wheat seedlings, the labelled plants were incubated for several days in hydroponic culture on a medium without radionuclides. Key Results The content of Zn-65 decreased quickly in the labelled part of the root. After the transfer of Zn-65 from the roots to the shoot, a further redistribution in the phloem from older to younger leaves was observed. In contrast to Zn-65, Cd-109 was released more slowly from the roots to the leaves and was subsequently redistributed in the phloem to the youngest leaves only at trace levels. The content of Ni-63 decreased quickly in the labelled part of the root, moving to the newly formed parts of the root system and also accumulating transiently in the expanding leaves. The Mn-54 content decreased quickly in the labelled part of the root and increased simultaneously in leaf 1. A strong retention in the labelled part of the root was observed after supplying Co-57. Conclusions The dynamics of redistribution of Zn-65, Mn-54, Ni-63, Co-57 and Cd-109 differed considerably. The rapid redistribution of Ni-63 from older to younger leaves throughout the experiment indicated a high mobility in the phloem, while Mn-54 was mobile only in the xylem and Co-57 was retained in the labelled root without being loaded into the xylem.