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Plant Studied for Soaking Skills

Posted on: Wednesday, 3 August 2005, 21:00 CDT

Aug. 3--In an effort to speed up the process of absorbing selenium from the soil, researchers at the University of California at Berkeley have genetically modified an Indian mustard plant so that it soaks up the element about four times more rapidly than its wild counterpart.

Selenium poisoning in the San Joaquin Valley came into focus in the 1980s when biologists began spotting deformities in birds, which were blamed on the contaminated irrigation drain water held in the Kesterson Reservoir.

While the new transgenic plants may absorb selenium more efficiently, scientists also face the challenge of containing the spread of the modified genes to other unaltered plants.

Research is forging ahead, but actual introduction of these transgenic plants for widespread use isn't likely to happen anytime soon because of that concern.

A series of field trials with the genetically modified mustard plants have been conducted at the U.S. Department of Agriculture's research services facility in Parlier. Results of the first trial in April 2003 were published in a report in February this year.

Three other lines of transgenic plants were tested last year, the results of which are likely to be made public by end of this year.

"This is the first trial of its kind for proof of concept and to get people more interested in the option," said Danika L. LeDuc, co-author of the report. LeDuc is a postdoctoral researcher with Norman Terry, co-lead author of the paper and professor of plant and microbiology at UC Berkeley's College of Natural Resources.

Selenium is a naturally occurring element that both humans and animals need. While it is good when consumed in the right proportions -- 70-100 parts per billion a day for humans and 50-300 ppb a day for animals like cattle -- either a deficit or overdose can cause toxicity or deformities, said Gary S. Banuelos, a soil scientist with the Parlier center who conducted the field trials.

Animals deficient in selenium could suffer from white muscle disease and reproductive problems. An overdose can cause blind staggers, a disease that makes animals' movements unsteady, or can cause the deformities in birds.

In humans, selenium is an important building block for antioxidants in the body. An overdose can lead to nail and hair loss.

Indian mustard is particularly popular with researchers as a decontaminant because it can absorb and break down the selenium -- which exists in the soil in the form of a salt or selenate -- to a gas called dimethyl selenide, which then dissipates into the air.

This process takes time in a wild plant. The genetically modified plants can do this much faster, LeDuc said.

Ever since the Kesterson Reservoir controversy erupted, selenium contamination has been a serious concern. High selenium concentrations also have been found in Wyoming, Utah, Texas, North Carolina and Pennsylvania.

"It's a broad scale geologic kind of problem," said Mike Saiki, a biologist at the Western Fisheries Research Center's field service facility in Dixon, a Solano County city between Sacramento and San Francisco.

While the problem is aggravated due to irrigated agriculture on the West Coast, coal-fired power plants contribute to high selenium levels on the East Coast, Saiki said.

Colorado is also on the selenium watchlist for deposits found in the Arkansas River. Concerns are growing that runoff water from overirrigation that flows into the river may be increasing selenium concentrations in Colorado and neighboring Kansas.

Banuelos, who is co-lead author of the mustard plant report, has been working on selenium contamination for 17 years. The idea that plants might help absorb contaminants first struck Banuelos while traveling abroad.

During his stay in Germany as a doctoral student in the 1980s, he started evaluating plants and vegetables for radioactive materials following the Chernobyl nuclear accident.

Then during several trips to India and Sri Lanka, he discovered how resistant the Indian mustard plant was to selenium.

Using genetically modified plants to soak up contaminants from the soil is not a new idea, but it is highly controversial. The fear of transgenic plants pollinating their natural unaltered cousins has led to calls for stringent surveillance.

Banuelos, who personally prefers to stick to the natural wild Indian mustard, said that given the current absorption rate of the transgenic variety, it is unlikely that farmers would go through the hassle of using it.

The increase in absorption capacity may not be worth the risk involved, said Ignacio Chapela, assistant professor at UC Berkeley's department of environment science, policy and management. Chapela has raised concerns before about genetically modified plants.

"It is great to see that these researchers are furthering the understanding of these plants in absorbing selenium. I just hope that they are not releasing these organisms into the environment," he said.

LeDuc, however, said commercial use of transgenic mustard plants is a long way off. She said the transgenic plants carry an antibiotic-resistant gene that could be a cause of worry for many. That will have to go before the plant is made available for commercial use, she said.

"It's not ready yet," she said.

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Source: The Fresno Bee

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