Phytoremediation of cadmium-contaminated soils by young Douglas fir trees: effects of cadmium exposure on cell wall composition.

Douglas fir trees grown on an artificially Cd-contaminated soil, can tolerate this trace element (up to 68 mg/kg in soil) during several months. Most of the absorbed Cd is retained in roots (25 mg/kg DM), but transfer to aerial part is also effective. Showing the highest content, up to 6 mg/kg DM, among all the aboveground parts, barks seem to be a preferred storage compartment. However, the transfer factor is quite low, about 0.3. Another objective of this study was to compare the cell wall components of trees exposed to increasing Cd amounts in soil. A decrease in lignin and an increase in pectin contents were observed in response to increasing soil cadmium concentration. A concurrent reduction in methyl-esterification of pectin suggests than the structure of this major binding site could therefore be modified as a reaction to cadmium contamination. Future prospects will focus on the modulation of pectin composition in response to Cd exposure.