February 1, 2005
By Flora Mauch,
A plant that cleans toxic
substances from soils and turns the matter into
nutraceutical—does it sound to good to be true? Thanks to a team
at the Center for
Plant Environmental Stress Physiology in West Lafayette it
may soon become reality.
Phytoremediation is an emerging
science, which when translated means using plants to remove
contaminants from soils, thus cleansing the environment. In many
cases, researches use the root system of a given plant as a
huge, subterranean sponge, which soaks up impurities such as
crude oil or heavy metals.
Another element that can be absorbed by plants is selenium.
Selenium is a metal found in natural deposits and is an
essential nutrient at low levels. It is known that selenium
accumulates in living tissues. When people are exposed to above
normal doses for relatively short periods of time, it has been
found to cause health effects such as, damage to the peripheral
nervous system, fatigue and irritability.
Selenium compounds are released in the air during the combustion
of coal and petroleum fuels, during the smelting and refining of
other metals or can be the result of natural geological
processes. Sites rich in selenium are situated for example in
soils in the high plains of northern Nebraska and the Dakotas.
Interestingly, there is a selenium accumulating plant called
Astragalus bisulcatus, which has the ability to turn toxic
selenium into a compound with cancer preventing qualities
called, Methylselenocysteine (MeSeCys). While studying A.
bisulcatus, Dr. Salt’s research team at the Center for Plant
Environmental Stress Physiology at West Lafayette, studied an
enzyme called selenocysteine methyltransferase (SMT) that
provided A. bisulcatus with the ability to convert
selenium into MeSeCys.
Recognizing the value of this enzyme, the researchers in West
Lafayette characterized its properties, in order to develop
plants not only with ability to cleanse selenium, but also an
enhanced ability to biosynthesize MeSeCys. In this way the
research team expected to obtain an efficient plant based source
of the anti-carcinogenic compound.
Ideally, Dr. Salt needed to have a plant that would be edible,
grow fast and produce MeSeCys when growing in the presence of
selenium. Since, A. bisulcatus only could grow relatively
slow and contains compounds that are toxic to humans, Dr. Salt’s
group needed to search elsewhere.
Hence, Dr. Salt’s lab is in the process of generating
genetically modified mustard plants, expressing the A.
bisulcatus selenocysteine methyltransferase (SMT) gene.
According to Dr. Ellis, a researcher in Dr. Salt’s lab, a first
step towards this goal has already been taken.
“While our SMT transgenics have increased selenium tolerance and
accumulation when grown on selenite, they have no increase in
selenium tolerance or accumulation when grown on selenate. These
plants are the first step to producing plants that could be used
Dr. Ellis continued with, “We are currently conducting
experiments with the goal of understanding how A. bisulcatus
selenium hyperaccumulators reduce large amounts of selenate. If
successful, we can use this knowledge to create transgenic
plants that could be potentially used for selenium
The research team of Dr. Salt envisions the genetically
engineered mustard plants being used as a nutraceutical and
offered to people in pill form. However, Dr. Ellis cautions,
“While methylselenocysteine can potentially be beneficial at
some doses, consuming too much can be toxic.”
However, we can look forward to a new type of phytoremediation
that will provide not only a cleaner environment, but also be of
great use for human health.
Flora Mauch is a Science Writer for Checkbiotech in Basel,
Switzerland and is currently studying Biology.