A PRELIMINARY-STUDY OF THE FACTORS AFFECTING THE KINETICS OF CADMIUM UPTAKE BY THE LIVERWORT DUMORTIERA-HIRSUTA

Intra- and extracellular Cd uptakes by the liverwort Dumortiera hirsut a (SW) Nees. were investigated. While intracellular Cd uptake was line ar with time and displayed Michaelis-Menten kinetics, extracellular Cd uptake displayed saturation kinetics. K-m and V-max were 149 +/- 19 m u M and 11.0 +/- 0.8 mu mol g(-1) h(-1) respectively. Intra-, and to a lesser extent, extracellular uptakes were temperature dependent. Ligh t stimulated intracellular Cd uptake by c. 15%. The rate of intracellu lar Cd uptake in the dark was probably not directly linked to the supp ly of respirable reserves, because storage for 20 days in the dark did not affect it. incubating the liverwort concurrently with Cd and equi molar concentrations of Ca, Mg or Zn all reduced intra- and extracellu lar Cd uptake, which suggests that the Cd uptake systems had low speci ficity. Pretreatment of plants with 80 mM KNO3 stimulated Cd uptake, a pparently because the K removed potentially competing ions from the ce ll waif. Results are compared with similar investigations on other cry ptogams.