Dr. Ingrid Pickering
Canada Research Chair in Molecular Environmental Science
On the Great Plains of North America grows a purple-flowered plant called two-grooved milk vetch, or locoweed. When cattle eat it, it interferes with their nervous systems, causing in severe cases a set of symptoms called the blind staggers.
These symptoms are caused by the plant’s tendency to accumulate selenium in its tissues. While this is bad news for ranchers, it offers promise in the emerging field of phytoremediation, where plants are used to clean up contaminated soils.
Dr. Ingrid Pickering is using synchrotron-based x-ray absorption spectroscopy (XAFS) to find out how locoweed handles high levels of selenium without poisoning itself.
“These hyperaccumulators store a huge amount of selenium,” Dr. Pickering says. “That is of interest if you have a high selenium area and you want to clean it up.”
Dr. Pickering is using XAFS to look at a plant’s inner molecular workings in vivo, in their natural state. Samples can literally be put into the experimental hutch at the synchrotron, tested, then removed unharmed to continue growing.
Hyperaccumulator plants are typically quite small and grow slowly. However, understanding how they sequester metals is the first step in potentially transferring the trait into crops with high growth rates and biomass. Dr. Pickering collaborates with researchers in the U.S. working to identify the genes that govern hyperaccumulation. This could lead to high-biomass plants that clean up contaminated soil.
According to Dr. Pickering, a synchrotron is essential for this type of research. For example, for microprobe experiments, the beam size is only a few microns wide - a small fraction of the width of a human hair. At this scale, every photon counts, and nothing but a synchrotron can produce xrays of sufficient brilliance. The XAFS beamline at the Canadian Light Source promises even greater resolution.
“With this technique, you have a tiny beam - about five microns across,” she says. “With the CLS we should have many more photons and the ability to go to much smaller beams.”
Pickering was also part of a team that discovered the reason behind a peculiar biochemical effect: if you administer a lethal dose of selenium together with a lethal dose of arsenic, they will somehow cancel each other out. XAFS revealed the reason why.
“The chemical reason for that, which we were able to show using x-ray absorption spectroscopy, is that it forms this really unusual molecule where the arsenic is bound to one selenium and to two sulphurs,” she says.
This knowledge has practical implications for areas of the world such as Bangladesh, where groundwater supplies are contaminated with arsenic. There, people have symptoms that have been attributed to arsenic poisoning - symptoms that are also consistent with selenium deficiency. While selenium is toxic in higher doses, the body needs this element for a healthy immune system and other critical functions. The hypothesis is the arsenic in the water is binding with the selenium and leaching it from the body, causing a deficiency. If this idea is correct, selenium supplements in the diet might improve the health of Bangladeshis.