Changes in metal-binding peptides due to acclimation to cadmium transferred between ramets of Salvinia minima.

Different ramets of a clonal plant exploiting a patchily metal-contaminated habitat may be exposed to different levels of toxic metals. This study investigated whether the exposure of older ("parent") ramets to Cd affected the levels of metal-binding peptides and essential elements in younger ("daughter") ramets which were not exposed to ambient Cd. Pre-treatment of parent ramets of Salvinia minima with 50 μg Cd·l-1 increased the levels of thiols and phytochelatins (PCs), decreased Mg and increased Cu, Zn and S in daughter ramets growing in a Cd-free medium. Acclimation of parents to lower Cd levels (10 and 25 μg Cd·l-1) increased thiols and decreased cysteine and glutathione in daughters, but did not increase PCs. Parental acclimation to all Cd concentrations tested reduced PC production in daughter ramets during subsequent Cd exposure. Daughter ramets from parents pre-treated with 25 μg Cd·l-1 were more Cd tolerant than controls. Although the tolerant daughters contained 35% more thiols than controls, fractionation of tissue Cd showed no difference between the control and tolerant ramets in the fraction of Cd bound by thiol compounds. Thus, while the acclimation of parent plants to Cd increased levels of metal-binding peptides and thiols in daughter ramets, the relationship between these compounds and the Cd tolerance of daughters is unclear.