CADMIUM UPTAKE BY LUPINUS-ALBUS (L) - CADMIUM EXCRETION, A POSSIBLE MECHANISM OF CADMIUM TOLERANCE

Cadmium (Cd) uptake by white lupin (Lupinus albus) was studied at low Cd concentrations (0.05nM to 5 muM) in hydroponic solution. Ten 12-day old seedlings were pretreated in 0.5 mM CaCl2 solution in presence and absence of metabolic inhibitors (DCCD, DNP or NaN3). Cadmium solutions were labelled with carrier free (CdCl2)-Cd-109. Cadmium uptake was measured after a 2 h desorption in unlabelled CdCl2 solution. In the absence of any metabolic inhibitor and at 5 muM Cd, roots absorbed 235.23 mug Cd/g root dry weight. Over the range of 1nM to 5 muM Cd, exchangeable Cd represented approximately 5% of the absorbed fraction, and about 25% of the total absorbed Cd was adsorbed to the root. Cadmium was passively absorbed to about 30% as observed in the presence of the inhibitor (DCCD). Ative absorption which represented 70% of Cd uptake involved H+-ATPase carriers. Cadmium absorption was reduced to 30 and 20% in presence of lanthanum (La3+) and zinc (Zn2+), respectively which suggested that calcium (Ca), Cd, and Zn use the same carriers. Cadmium uptake in presence of DNP or NaN3 was approximately 4- fold that in control. Data showed presomption for an excretion of Cd out of root cells which could be the expression of a detoxification process limiting cell contamination.