Preliminary research on lead absorption and translocation in root tip cells of Populus nigra 'Italica' Moench

Observations were carried out to define the place of lead absorption within three regions of the poplar adventitious root tip (Populus nigra "Italica" Moench.) after 24-hour exposure to a solution of Pb(N03)2 (25 mg dm-3 Pb). Deposits of lead were not observed in certain cells of the apical part of the meristem. In other cells, lead deposits were first observed in the lumen of several endomembrane compartments - the endoplasmic reticulum, dictyosomal stacks and nuclear envelope. Certain differences were noted in the amount of deposits in protoplasts with varied electron density. In the cells with greater deposits, lead was also observed in the cytoplasm, the mitochondria and the paramural bodies. Practically no lead precipitated in the cell wall. The presence of lead in the form of small deposit granules in the plasmodesmata may suggest transfer from cell to cell.