Root-applied cytokinin reduces lead uptake and affects its distribution inNorway spruce seedlings

Hydroponically grown Picea abies (L.) Karst. seedlings were exposed to lead (5 mu M Pb) and zeatin-riboside (ZR) treatments (1 mu M, periodically) in a factorial experiment. Exposure of the roots to cytokinin reduced the tota l ph content in the spruce seedlings by ca, 50%. X-ray microanalysis reveal ed that this was mainly due to decreased Pb concentrations in stelar tissue s of the root, a major part of which was located in granules of parenchymat ic cells containing high amounts of sulphur and phosphorus. As a result of reduced uptake, negative effects of Ph on root elongation were largely amel iorated by ZR, In addition, ZR alleviated the Ph-induced decrease in photos ynthetic pigments, although it stimulated Ph translocation to the shoot. Th e results demonstrate that ph translocation to the shoot is not a simple un controlled process in which a fixed proportion of Ph taken up by the roots is delivered to the shoots.