Scientists Develop Potential Anti-Carcinogen Plant

Selenium may be at the root of cancer prevention

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This photograph shows the presence of two different selenium compounds in living plant tissue. The image on the left shows a high concentration of MSC, the selenium compound shown to have anti-cancer properties, in one of the plant's leaves. The image on the right highlights a different selenium compound in the same leaf. The image was obtained using X-ray absorbance spectroscopy to visualize concentrations of selenium. Red indicates regions of high concentration. Blue and green indicate lower concentration. (Ingrid Pickering/Proceedings of the National Academy of Science)

A Purdue University researcher has successfully engineered plants that may not only lead to the production of anti-carcinogenic nutritional supplements, but also may be used to remove excess selenium from agricultural fields.

By introducing a gene that makes plants tolerate selenium, David Salt, professor of plant molecular physiology at Purdue, West Lafayette, Ind., has developed plants capable of building up unusually high levels of a selenium compound in their tissues. Salt's interest in selenium stems in part from recent research sponsored by the National Institutes of Health showing that selenium can reduce the risk of developing prostate cancer by 60 percent.

Selenium, a mineral that occurs naturally in the soil in some parts of the world, is an essential micronutrient for animals, including humans, but is toxic to animals and most plants at high levels.

However, a few plant species have the ability to build up high levels of selenium in their tissues with no ill effects. These plants, called selenium hyper-accumulators, convert selenium taken up from the soil into a non-toxic form called methylselenocysteine, or MSC.

By inserting the gene responsible for this conversion into Arabidopsis thaliana, a model lab plant that does not tolerate selenium, Salt and his colleagues produced plants that not only thrive in a selenium-enriched environment but also amass high levels of the selenium-containing MSC in their tissues.

The plants that naturally hyper-accumulate selenium would not be good candidates for use as a supplement because they often produce other compounds that may have toxic effects in humans, says Salt.

Salt and his colleagues used two different methods to verify the production of MSC in the engineered Arabidopsis. The first method, mass spectroscopy, relies on extracting compounds from the plant tissue using a variety of solvents, then running those compounds through a machine that identifies their chemical nature.

The other method they used was X-ray absorbance spectroscopy, or XAS, which identifies the various forms of selenium in living plant tissue and can also provide a spatial map of where in the plant these selenium compounds are located.

Both techniques confirmed the presence of MSC in the engineered plants, Salt says.

Another very different aspect of the research is the possibility of developing plants that remove contaminants from the environment. Selenium contamination, for example, is a major problem in certain parts of the world, including the agricultural region of California's San Joaquin valley, Salt says. Selenium occurs naturally in the soil in that part of the country, but agricultural practices build that selenium to hazardous levels, he says.

A possible solution lies in the potential to engineer fast-growing plants capable of removing large quantities of selenium from the soil. Now that he and his colleagues have successfully produced a selenium-hyper-accumulating Arabidopsis, they have the tools to develop a plant that would be a good candidate for removing selenium from the soil.

For more information, call 765-494-4600 or visit www.purdue.edu.

— Purdue University