Genes thought to allow plants to accumulate large amounts of metal in their tissues have been identified and cloned by a Purdue University scientist.
The finding may lead to new crop plants that can clean up industrial contamination, new foods that fight disease, and reduced work for some farmers.
David E. Salt, associate professor of plant molecular physiology and principal investigator on the project, said that the discovery opens up new avenues for plant breeders.
"This is really one of the first tools that we've got to manipulate this process of metal hyperaccumulation," he said. "So what we're going to do now is to start expressing these genes in non-accumulating plants to see if we can turn them into metal-accumulating plants."
The genes were identified from the tiny wild mustard Thlaspi goesingense, a plant that lives in the Austrian Alps, where it hyper-accumulates nickel. The plant is similar to the nonmetal-accumulating plant Arabidopsis thaliana, which is commonly used in scientific research.
The research is published in the August 14 issue of the Proceedings of the National Academy of Science.
Salt said more than 350 species of plants are known to accumulate metal such as nickel, zinc, copper, cadmium, selenium, or manganese in high levels.
"The plant species that we're interested in can accumulate one percent of their dry biomass as nickel. In a normal plant you might expect to find 10 to 100 parts per million of nickel in their tissue, and these plants can accumulate 10,000 parts per million," he said. "So they obviously have this extraordinary capacity to accumulate metals, and they do this in the wild without any interference from man. They just do this for a living."
Hyper-accumulating plants store the metal in microscopic structures in their cells called vacuoles. The vacuoles are membrane-lined structures that protect the rest of the cell from the toxic effects of the metal. Interestingly, the protective membranes that surround the vacuoles closely resemble cell membranes in the human liver that serve a similar function.
Scientists aren't completely sure why some rare plants try to grab as much metal as they can, but studies indicate that they do this to stop insects and other creatures from eating them.
Just as people hate to bite down on a piece of aluminum foil, insects tend to avoid eating plants that taste like metal.
"You can imagine if you're a bug and you bite down on a plant and it's got 10,000 parts per million of nickel in its leaf, it's not going to taste too good," Salt said.
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