Plant factories for selenium, new source?
unusually high levels of the cancer-fighting mineral selenium in
their tissues.
Harvesting the plants will create a new source of the nutrient, declining in our food sources, for use in supplements, says the researcher.
Recent research has linked the trace element selenium to reduced risk of prostate cancer. It is also thought to protect from skin cancer. But in Europe, levels of selenium have sharply decreased in the wheat supply because of less selenium in the soil and people may need to supplement their diet with the mineral.
While the mineral is an essential micronutrient for animals, including humans, it is toxic to animals and most plants at high levels. However a few plant species, called selenium hyper-accumulators, have the ability to build up high levels of selenium in their tissues with no ill effects. These plants 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, David Salt and colleagues from Purdue University in the US, produced plants that not only thrive in a selenium-enriched environment but also amass high levels of the selenium-containing MSC in their tissues.
"We now know that this gene works," Salt said. "If you put it into another plant, it will make MSC, and we didn't know that before."
He added that the team is now ready to use genetically modified plants to make the compound for nutritional supplements, "knowing that we have a very, very high likelihood of it working and producing this compound".
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, Salt added.
Two different methods - mass spectroscopy, which relies on extracting compounds from the plant tissue using a variety of solvents and then identifying their chemical nature, and x-ray absorbance spectroscopy (XAS) - were used to confirm the production of MSC in the engineered Arabidopsis.
The research is published in the current issue of BMC Plant Biology (4:1, 28 January 2004).
Other lab studies involving selenium have shown MSC to be the most effective selenium-containing compound in reducing cancer risk in animal models, making it an attractive prospect for eventual use in a nutritional supplement, according to Salt.
But he said the effectiveness of MSC in humans has not yet been tested because of a lack of a good commercial source of the compound.
"We would be very interested in knowing the efficacy of MSC in humans, clearly. The problem has been there's no material to run such an experiment, and that will be an important piece of this story..." Salt continued.
The researcher also suggested that the plants could be used to reduce selenium contamination in certain parts of the world, where agricultural practices result in hazardous levels of the mineral. Fast-growing plants may help to remove large quantities of selenium from the soil.
The research is part of collaboration between Purdue and NuCycle Therapy, a small biotechnology company that develops and sells plant-based nutritional supplements.
