Some aspects of the kinetics of cadmium and thallium uptake by fronds of Lemna minor L.

Abstract

SUMMARYA Study of influx and accumulation of Tl and Cd by Lemna minor has revealed a number of contrasting features which arise from the basic physico-chemical properties of the two elements. Short-term influx of Cd over a range of concentration (0-1-10 //.M) followed a linear trend while that of Tl over the same range produced a profile with a plateau at the higher concentrations, indicating saturation of the absorption mechanisms. Application of Ca and K antagonists aiming to indicate the nature of the absorption mechanisms did not reveal any consistent trends. Long-term exposure of the plant to Cd and Tl produced steady-state concentrations after 250 and 140 h respectively, by which stage Lemna had accumulated nearly twice as much Cd than Tl. It appears that a significant amount of Cd is probably in the Donnan free-space and strongly bound to cell constituents from which the element is depurated slowly and continuously in Cd-free medium. It is concluded that Tl is tenaciously held in the plant tissues, perhaps in the cell vacuole, as 80 % of the steady-state concentration is retained by the plant even after 140 h in Tl-free medium. The influence of several external physical and chemical factors further emphasizes the contrasting nature of the two elements; Tl uptake is almost entirely an active process and ion activity of Tl is relatively unaffected by changes in pH and ligand concentration. Cd uptake involves both active and passive components, ion activity is markedly reduced at low H"^ ion concentrations and in the presence of ligands, such as EDTA. Inhibition of uptake was found for both elements in the presence of competing ions.

Cadmium uptake and subcellular compartmentation in the ectomycorrhizal fungus Paxillus involutus

“…An increase of pH in the incubation medium led to an inhibition of Cd uptake. At high pH values, Cd# + ions may be hydrolysed and possibly precipitate as sparingly soluble hydroxides (Kwan & Smith, 1991). These lower Cd concentrations also induced a reduced uptake by fungal cells.…”

Growth and photosynthetic responses of Lemna minor L. exposed to cadmium in combination with zinc or copper / Rast i fotosinteza u vodene leće (Lemna minor L.) izložene kadmiju u kombinaciji s cinkom ili bakrom

“…, and an even lower concentration of Cd, have already been confirmed to affect plant metabolism (20, 23,43,44). It is also wellknown that Zn and Cu added in amounts above optimal level have adverse effects on plant growth (20,45).…”

Accumulated forms of thallium and cadmium inLemna minor. II. Relationship between duration of exposure and metal-protein binding

“…Il has been suggested previously that the contrasting behaviour in the uptake and accumulation of Tl and Cd by Lemna minor can be explained in terms of the differences in physicochemical properties between the two elements and by their similarity with those of the essential elements, such as potassium, calcium and zinc (Kwan, 1988;Kwan and Smith, 1990 in press). This study, which has concentrated on the forms or species of the elements in the aqueous phase extracted from Lemna fronds, further endorses these basic differences and the similarity between Tl and K, and Cd and Zn.…”