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Genetically-engineered populus hybrids and metalliferous soil remediation Schmidt, Monica A.


With global heavy metal pollution increasing, there is a need for innovative metal decontamination processes. Plants that have the ability to sequester metal contaminants within their tissues promise to be a cost-effective soil remediation practice. A poplar hybrid clone, Populus alba x P.tremula (INRA clone 717-1B4), was selected for this soil metal remediation research due to its large biomass and extensive deep tap root system that enables it to encounter many contaminants within its surroundings. The response of poplar to heavy metal stress, primarily cadmium and copper, was studied at the molecular level as a means to assess its metal stress-induced defense mechanisms. Metal toxicity tests and chemical inhibition studies to limit the formation of phytochelatins indicate that this metal-chelating compound plays a role in conferring tolerance to both Cd and Cu stress. Metallothioneins were seen to be constitutively expressed in all tissue regardless of metal stress conditions. Conversely, the production of phytochelatins, as monitored by the expression of the glutathione synthetase gene, was seen to be strongly induced by both Cd and Cu-stress in leaf and stem tissue and weakly induced in root tissue. Genetically-engineered poplar hybrids, that express the fission yeast Schizosaccharomyces pombe vacuole transporter gene, HMT, were produced. After exposure to cadmium stress, it was found that the transformants analyzed did not exhibit an enhanced level of metal tolerance nor did they accumulate elevated levels of metal ions within their tissues. It was hypothesized that in order for this particular poplar hybrid to be engineered to have the metalaccumulating phenotype that both the HMT vacuole membrane transporter and the up-regulation of phytochelatins in roots would be needed.

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