For bioremediation to be practical, heavy metals would need to be transported from roots to shoots. Initially, the UCSD biologists thought it unlikely that phytochelatins could perform this function. "We thought maybe the phytochelatins would be trapped in roots," says Ji-Ming Gong, a postdoctoral fellow in Schroeder's lab and the first author on the paper.
To find out, Schroeder's group used mutant plants that do not make their own phytochelatins. Although phytochelatins are found in most plants, they used Arabidopsis, a relative of the mustard plant, commonly used by plant biologists because of its well characterized genetics and readily available mutant varieties. The researchers took a mutant variety of Arabidopsis, which lacks the genes to synthesize phytochelatins, and genetically modified the mutant plants, targeting the gene for the enzyme that synthesizes phytochelatins to the roots of the plant.
To their surprise, the phytochelatins, while only synthesized in the roots, were found in the leaves and stems as well. In addition, when the researchers exposed the roots of the genetically modified plants to cadmium, arsenate and mercury, the plants had restored resistance to these heavy metals. Furthermore, expression of the gene only in roots increased the accumulation of cadmium in leaves. This suggests that engineering plants with the gene to synthesize phytochelatins in roots could make plants contribute to bioremediation.
"We demonstrated that phytochelatins can be transported from roots to shoots and that phytochelatins have a key role in preventing cadmium over-accumulation in
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Contact: Sherry Seethaler
sseethaler@ucsd.edu
858-534-4656
University of California - San Diego
8-Aug-2003