RECIPROCAL EFFECTS OF PLATINUM AND LEAD ON THE WATER HOUSEHOLD OF POPLAR CUTTINGS

In order to study the accumulation rates and effects of platinum as in fluenced by lead, experiments were performed with poplar cuttings in a growth chamber. The heavy metals were added at a final concentration of 34.8 ppb each to nutrient solutions as PtCl4 and Pb(NO3)(2). The va riants were 1) control; 2) permanent Pt treatment for 6 weeks; 3) pret reatment with Pt plus subsequent treatment with Pb (three weeks each), and 4) heavy metal application in inverse order to variant 3. The exp eriments revealed that platinum accumulates in the roots of poplar cut tings to a higher degree than lead. It is translocated from the roots to other plant parts to an extremely low degree. Lead is displaced fro m the roots by subsequent Pc treatment. Insoluble platinum was found t o be associated especially on the cell walls of the rhizodermis and ex odermis of the root tips. Accumulation of platinum in the roots leads to a gradual depletion of the plants' water supply. The disturbance of the water household causes a reduction of the transpirational surface , lowered transpiration rates and enhanced root growth. All these alte rations are induced as a means oi coping water stress. From the result s of this experiment, the conclusion can be drawn that, under the chos en experimental conditions, platinum manifests a higher toxicity than lead in plant roots because of its higher accumulation rates.