The other two transgenic lines were engineered to produce more of the enzymes gamma-glutamyl cysteine synthetase (ECS) and glutathione synthetase (GS), both of which play key roles in the production of glutathione. Glutathione, part of the plant's antioxidant system, may be buffering the impact of the contaminants, said the researchers.
The ECS and GS lines absorbed 2.8 times and 2.3 times more selenium respectively than the wild plants. Moreover, the GS plants seemed particularly tolerant of the contaminated soil, growing 80 percent as well as the GS plants planted in clean soil.
Because USDA regulators are scrupulous about experiments involving genetically modified plants in the field, the researchers took great care to minimize the transfer of genes through pollen.
"Before we started the study, we took aerial surveys to ensure that no other mustard-related plant species were being grown in the vicinity," said Banuelos.
He noted that every morning trained workers swept through the fields to literally nip any flowers in the bud, and that netting and buried chicken wire were used to keep wildlife away from the plants.
"One of the challenges in developing transgenic plants for remediation is engineering them in such a way that the risk of gene transfer is reduced or eliminated," said Banuelos.
Terry said that techniques now being developed by plant geneticists -- such as modifying chloroplast DNA rather than nuclear DNA -- will eventually reduce the need for such constant monitoring. Since chloroplast DNA is maternally inherited, there is little risk of pollen transfer, said Terry.
Terry said it's worth pursuing methods of improving phytoremediation because there are benefits unique to plants.
"A particularly promising aspect about mustard plants is that they can metabolize selenium int
Source:University of California - Berkeley