Interactions between cd and zn in relation to their hyperaccumulation in thlaspi caerulescens

Ganges, an ecotype of Thlaspi caerulescens from southern France accumulates both Zn and Cd to extraordinary levels in the shoots. The interactions between Zn and Cd in this ecotype were investigated using solution culture and pot experiments with soil. Results from both relatively long-term (4 weeks) and short-term (1 week) solution culture experiments indicated that Cd accumulation in the shoots was not affected by the supply of a 4 to 10fold excess of Zn, whereas the Cd concentration of the roots decreased with increasing Zn concentration in the solution. By contrast, the supply of an equimolar concentration of Cd significantly reduced the Zn concentration in both roots and shoots. However, when 4-fold more Zn than Cd was supplied, Cd-induced decrease in Zn accumulation was not observed. In soil treated with Cd or Zn, addition of one metal increased the metal concentration of the other in the soil solution. However, Zn accumulation by T. caerulescens decreased by Cd addition, whereas Cd accumulation was not affected by Zn addition. These results suggested that the Ganges ecotype of T. caerulescens displayed different uptake systems for Cd and Zn, and that Cd competed with Zn uptake while Zn did not compete with Cd uptake.