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

Abstract

Hydroponically grown Picea abies (L.) Karst, seedlings were exposed to lead (5 μM Pb) and zeatin-riboside (ZR) treatments (1 μM, periodically) in a factorial experiment. Exposure of the roots to cytokinin reduced the total Pb content in the spruce seedlings by ca. 50%. X-ray microanalysis revealed that this was mainly due to decreased Pb concentrations in stelar tissues of the root, a major part of which was located in granules of parenchymatic cells containing high amounts of sulphur and phosphorus. As a result of reduced uptake, negative effects of Pb on root elongation were largely ameliorated by ZR. In addition, ZR alleviated the Pb-induced decrease in photosynthetic pigments, although it stimulated Pb translocation to the shoot. The results demonstrate that Pb translocation to the shoot is not a simple uncontrolled process in which a fixed proportion of Pb taken up by the roots is delivered to the shoots.