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UC Berkeley researchers have found that certain genetically modified plants
accumulate selenium four times faster than their wild-type counterparts,
raising a viable alternative for eradicating high levels of toxic
contaminants in California soils, February 2005 by Stephanie Pace.

?Phytoremediation, the use of plants to clean up the environment, can help
remove the selenium, but the thing that?s holding people up from using
plants more widely is that, by and large, they work slowly,? said Norman
Terry, UC Berkeley professor of plant and microbial biology in the College
of Natural Resources and director of the study.

Researchers from the Agricultural Research Service (ARS) of the U.S.
Department of Agriculture joined forces with Terry in a 6-week trial to
determine if transgenic plants perform better than wild type, or genetically
unaltered, plants in cleaning up soil polluted by selenium.

?We?re trying to create designer plants to really step up selenium uptake
and accumulation,? Terry said.

The transgenic plants were engineered to produce three types of enzymes:
adenosine triphosphate sulfurylase (APS), gamma-glutamyl cysteine synthetase
(ECS) and glutathione synthetase (GS). The first, APS, proved to be the most
important in converting selenate, an oxygenated form of selenium, into a
non-toxic form of selenium, which allowed the plant to accumulate large
doses of the contaminant without incurring harm.

?By testing these transgenic plants in the field, we can find out whether
this approach works or not,? Terry said.

The trial consisted of transplanting the three types of transgenic plants
and wild-type control plants into four field plots. Two contained sediment
from the highly selenium-contaminated San Luis Drain and the other two
contained clean soil.

The APS plant line accumulated 4.3 times more selenium than the wild-type
plants, while the ECS and GS plant lines accumulated 2.8 and 2.3 times more
selenium, respectively. In the field trial, the GS lines were shown to have
tolerated the contaminant so well that they grew 80 percent as well as GS
plants in clean soil.

Researchers minimized the escape of genes from the transgenic plants to wild
mustards in the area. Workers were specifically trained to go through the
fields every morning and nip off any emerging flowers at the bud to prevent
gene-bearing pollen from fertilizing wild mustards. Also, aerial surveys
were conducted to ensure that no other mustard-related plant species were
being grown in the vicinity.

?It is important for all experimenters carrying out field trials to be
scrupulously careful to avoid gene flow to other plants,? Terry said. ?In
this case however, I believe the genes we used should be relatively harmless
since they are found normally in all plants and are essential to the uptake
and assimilation of the nutrient sulfur.?

According to Terry, this research paves the way for establishing
phytoremediation as an important cost-effective and efficient way of
environmental cleanup.

?The importance of this research is that it establishes proof-of-concept,?
Terry said. ?This is the first time that anyone has been able to show that
it is indeed possible to genetically engineer plants to be better at
pollutant removal under real-world conditions; that is, in the field itself
rather than in the lab or the greenhouse.?

There are other uses for selenium-saturated plants aside from
contaminant-removal. Because much of California is deficient in selenium,
farmers have had to supplement their cattle or sheep artificially with
selenium tablets. Now, with Terry?s research, farmers could use
selenium-saturated plants as nutritional supplements in animal feed or to
enhance soil.

Terry wants to use his current research to generate transgenic plants that
not only take up more selenium, but also convert it to non-toxic volatile
forms that pass harmlessly into the atmosphere.

?Our goal is to increase selenium uptake rates to 10, 100 or even 1,000-fold
so that 10 years of pollutant-removal work could be accomplished in one to
two years,? Terry said. ?The most exciting aspect of our current research is
that it will encourage researchers to genetically engineer plants for the
removal of many other types of pollutants including heavy metals like
cadmium or mercury, or even toxic organic compounds such as PCBs and
dioxins.?

[www.dailycal.org]

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