GAINESVILLE, Fla. — Arsenic is notorious for its toxic effects on people, but it can be just as dangerous to plants – most of them, anyway.
One exception is the Chinese brake fern, a nondescript-looking bracken that can soak up huge quantities of the toxic metal without apparent harm.
Years after discovering the fern’s remarkable ability, known as hyperaccumulation, University of Florida researchers have pinpointed the first gene that makes it possible. The findings were reported last month in the online edition of The Journal of Biological Chemistry.
The gene controls production of a protein known as a glutaredoxin that helps the fern tolerate arsenic, said Bala Rathinasabapathi, an associate professor with UF’s horticultural sciences department, part of the Institute of Food and Agricultural Sciences. The gene could provide a first step toward engineering transgenic plants for cleanup of contaminated water and soil.
“This particular gene seems to be making the cells resist arsenic, at the same time reducing the amount of arsenic inside the tissue,” Rathinasabapathi said. Glutaredoxins help plants resist stress; the one used in the UF study is the first shown to be associated with arsenic processing in plants.
The Chinese brake fern itself may have some application for remediating arsenic-soaked soil, he said, but it’s not ideally suited to the task because it grows only in warm climates and has a shallow root system.
Fast-growing, deep-rooted trees that tolerate a wide range of climates would be ideal for soil cleanup, and aquatic plants could be used to draw arsenic from contaminated bodies of water, Rathinasabapathi said.
But more research is needed to pinpoint additional genes that enable the brake fern to tolerate arsenic, and others that control hyperaccumulation. Previous UF studies have shown that brake ferns can take up so much arsenic that it comprises 2.3 percent of their dry weight.
Both traits are needed for transgenic plants useful in phytoremediation, the practice of using plants to eliminate environmental hazards.
“They go hand in hand,” Rathinasabapathi said. “We are going one at a time because it allows us to dissect the more complex phenomena much more readily by taking one gene at a time.”
The research team – which includes Rathinasabapathi and postdoctoral associate Sabarinath Sundaram of UF’s horticultural sciences department; Lena Ma, a professor with UF’s soil and water science department; and Barry Rosen, chairman of the biochemistry and molecular biology department of the Wayne State University School of Medicine – transferred the gene to E. coli bacteria, which then showed enhanced arsenic tolerance and enabled researchers to dissect the gene’s functional role.
The study was funded by a grant from the U.S. Department of Agriculture.
Another UF project, in progress, focuses on transferring the gene to a model plant to determine whether the trait will carry over to other types of plants.
Fern genes could also be used to improve crops for drought and salinity tolerance, Rathinasabapathi said.
Nationwide, arsenic is the Environmental Protection Agency’s top priority for Superfund hazardous materials cleanup. The carcinogenic metal has been used in pesticides, herbicides and wood preservatives, and also occurs naturally, where it’s sometimes present in large enough quantities to pose a health hazard.
In parts of Asia, notably India, Bangladesh and China, naturally occurring arsenic contaminates drinking and irrigation water used by millions, Rathinasabapathi said.
The UF research represents an important step toward understanding arsenic metabolism in plants, said Andrew Meharg, chair of Biogeochemistry with the University of Aberdeen’s School of Biological Sciences in Aberdeen, Scotland.
Meharg is the author of Venomous Earth – How Arsenic Caused the World’s Worst Mass Poisoning, which states that in India and Bangladesh, 40 million to 80 million people are at risk from drinking arsenic-contaminated well water. For some sites, he said, phytoremediation can be an important – and green – alternative to nonsustainable remediation technologies.