Poison suckers
the first transgenic system for removing arsenic from the soil by using genetically modified plants is on the anvil. It could have major impact on arsenic pollution, which is a growing threat to the environment and human health worldwide. In most cases, arsenic-polluted sites have not been cleaned up because the cost of digging up the soils and removing them to storage sites is prohibitive and environmentally destructive.
The plants have been developed by researchers from Athens-based University of Georgia (uga), Detroit-based Wayne State University and Indiana-based Purdue University. During their experiments, the researchers discovered that by inserting two genes of the bacterium Escherichia coli into arabidopsis, the weedy plant did precisely what they wished. Usually, most arsenic in surface soil and water exists primarily in its oxidised form called arsenate. Plants actively take up arsenate, mistaking it for phosphate and transfer it to their leaves. But this proves fatal for them. Therefore, to save the plants, the team engineered the first gene called ars c to be turned on strongly by light. The activated gene reduced arsenate to a more toxic compound called arsenite. Thereafter, the second gene, ecs, created more sulphur sinks to bind tightly to arsenate, making it less biologically available. Consequently, instead of dying from exposure, the modified plants absolutely thrived on the arsenic. In tests, 96 per cent to 100 per cent of arsenic in leaves was reduced to arsenite and bound by sulphur. Harvesting of these plants meant removing arsenic pollution from the contaminated site.
The problems facing the research team were daunting. First of all, arsenic is highly toxic to most plants, so the idea of using a plant to withdraw arsenic from the soil seemed counter intuitive. Still, the researchers knew from other experiments that certain genes can make plants tolerate substances that normally sicken or kill them. "Our working hypothesis was that controlling the electrochemical state of arsenic in the above-ground tissues and increasing organic sulphur