EFFECTS OF CADMIUM-ZINC INTERACTIONS ON HYDROPONICALLY GROWN BEAN (PHASEOLUS-VULGARIS L)

Bean (Phaseolus vulgaris L. cv. Morgan) plants were grown 14 days in n utrient solution at two concentrations of cadmium (2 and 5 mu M) and t wo of zinc (10 and 25 mu M) singly and in factorial combination. The d ecrease of growth was more pronounced in shoots for Cd treatments and in roots for Zn. The combination of Cd and Zn resulted in synergistic and additive, but not protective, effects on the growth. Plant concent rations of Mn, Cu and Mg were slightly involved in the interaction, wh ile Fe, Ca and K were unaltered with all treatments. However, some com binations of Cd + Zn increased the contents of Cd and Zn, respectively , in shoots and in roots. This was confirmed by the time course of met al accumulations in short-term and no-mineral competition experiment. Fourteen-day-old seedlings growing in full nutrient solution were tran sferred to distilled water supplemented with 10 mu M Cd, 50 mu M Zn an d 10 mu M Cd + 50 mu M Zn for 24 h. When the two metals were simultane ously applied: the roots retained less cadmium and the Cd percent in s hoots increased. Inversely, zinc was higher in the roots to the detrim ent of its allocation to shoots. These results, together, suggest that synergism and additivity of Cd-Zn interactions might be, essentially, related to an inadequate compartmentation of cadmium and zinc burdens . The metal levels increased in the sensitive sites, where they would be relatively 'excluded' in the case of individual stress regime. (C) 1997 Elsevier Science Ireland Ltd.