HISTOCHEMICAL INVESTIGATION OF CADMIUM AND LEAD DISTRIBUTION IN PLANTS

A new histochemical method was developed based on dithizone and 4-(2-p yridylazo)resorcinol application for investigating cadmium and lead di stribution in plants. The roots of maize (Zea mays L.) seedlings were incubated in cadmium nitrate or lead nitrate solutions for various per iods of time. During the first day, the heavy metals applied at both l ethal and nonlethal concentrations penetrated into the rhizodermis and outer layers of the root cortex. During the second day, Pb and Cd wer e essentially distributed throughout all tissues of the dying roots. H owever, in the solutions causing 50% root growth inhibition, they pene trated only the root cap, rhizodermis, and cortex. Heavy metals were f ound only in conductive tissues and adjacent parenchyma cells in the r oots incubated in more diluted solutions. The heavy-metal occurrence i n the shoot tissues was poor. In all treatments, the cell walls were s tained more brightly than cytoplasm, but nuclei remained unstained. Th us, a nonuniform distribution of absorbed heavy metals throughout root tissues was demonstrated.