Trichloroethylene is a heavily used industrial degreaser that's made its way into groundwater because of improper disposal. Both unaltered poplars and the transgenic poplar plants produce the enzymes to break down trichloroethylene, C2HCl3, into chloride ions harmless salt that the plant sheds and recombines the carbon and hydrogen with oxygen to produce water and carbon dioxide.
The transgenic poplar plants just do it a lot faster. The enzymes used to metabolize the contaminants are from a group called cytochrome P450 found in both plants and animals. Poplars have a lot of P450s and Doty said scientists hope to eventually sort them to find ways to manipulate the plant's own genes to ramp up pollution degradation. In the meantime they are conducting experiments inserting a gene that produces cytochrome P450 in mammalian livers, in this case the livers of rabbits. Poplar genes producing cytochrome P450 is expressed in all their cells, but not at the rates achieved by the transgenics.
"We overcame the rate-limiting step by causing the poplar plants to overexpress the first enzyme in the degradative pathway," Doty said. "Using the mammalian gene is just a step toward the day when we understand the poplar P450 genes well enough to use promoters to enhance production of their own enzymes that degrade contaminants. With the plant's own genes, the results should be even better."
Mammalian cytochrome P450 has already been used in transgenic plants that can detoxify herbicides applied to fields to kill weeds. Japanese researchers, for example, published findings in 2005 about using a human gene to make rice plants degrade a suite of herbicides, something they said could help reduce the load of herbicides in paddy fields and streams.
Along with the trichloroethylene tests, the new results also found improved
|Contact: Sandra Hines|
University of Washington