Regions of lead uptake in Lemna minor plants and localization of this metal within selected parts of the root

Abstract

Investigations were carried out to determine the sites of lead uptake within the frond and the root of Lemna minor. With the sodium rhodizonate four regions favoured in lead uptake were distinguished: the frond region between the base and the node, the basal part of the root, and the regions at the proximal and distal ends of the root cap. For analysis in electron microscope only the root regions were chosen. The highest rate of lead uptake was found in the basal part of the root. Lead was present in the apoplast of this region after 5 min of exposure and was observed in the stelar cells after 30 min of incubation. Lead deposits were detected mostly in the cell walls adjacent to the plasma membrane and in the lumen of several endomembrane compartments - the endoplasmic reticulum (ER), dictyosomal vesicles, nuclear envelope and the vacuoles. Lead induced changes of cell ultrastructure; an increase in the number of membraneous structures, swelling of ER cisternae and distortion of the dictyosomal cistemae were observed after 2 to 6 h of exposure.