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Your Environment. Your Health.

How Plants Take Up and Distribute Metals

Mary Lou Guerinot, Ph.D.

October 26, 2017

Mary Lou Guerinot, Ph.D.

Guerinot is the Ronald and Deborah Harris Professor of the Sciences at Dartmouth College. In 2016, she was elected to the National Academy of Sciences for her outstanding contributions to research.
(Photo courtesy of Dartmouth College)

Research by NIEHS grantee Mary Lou Guerinot, Ph.D., is answering important questions about how plants absorb metals from the soil. She is identifying plant genes responsible for uptake of toxic metals such as arsenic, as well as iron and other nutrients, with the goal of making rice and other edible plants safer and more nutritious.

"We try to find plants that contain more or less of certain metals. We then use different genetic techniques to figure out what genes cause these differences," said Guerinot, a professor of biological sciences at Dartmouth College. "This will help us understand how the process of metal uptake works to see if we can change it."

Investigating arsenic in rice

As part of the Dartmouth College Superfund Research Program (SRP) Center, Guerinot is conducting research on arsenic uptake, transport, and storage in plants, such as rice.

Synchrotron x-ray imaging on an Arabidopsis leaf highlighting zinc

Using synchrotron x-ray fluorescence technology, Guerinot and her research team found that zinc, shown in white, accumulates in small clusters throughout the Arabidopsis leaf.
(Photo courtesy of Dartmouth College)

C-FARR paper
One of the C-FARR papers focuses on how arsenic in the soil and water is taken up by crop plants. (Image reproduced from Punshon et. al 2017)

Dartmouth SRP Center researchers have led efforts to learn how arsenic ends up in food and to identify food products with relatively high amounts of arsenic. In one study of U.S. women, researchers found that consumption of about half a cup of cooked rice per day led to urinary levels of arsenic comparable to drinking 1 liter per day of water containing 10 micrograms of arsenic, the current U.S. maximum contaminant level. Researchers have also uncovered high levels of arsenic in organic brown rice syrup.

Guerinot is identifying genes associated with the uptake of arsenic into plants as well as genes that may be linked to the flux of arsenic from the root back out into the soil.

"If we can identify genes involved in the efflux of arsenic in rice, we can screen through different rice varieties to see which types have the genes of interest and would likely accumulate less arsenic," Guerinot said.

In a study of rice grains grown at four international field sites, Guerinot and her colleagues found candidate genes associated with grain concentrations of arsenic. By measuring grain arsenic concentrations across multiple sites, they have also identified varieties of rice that have lower levels of arsenic.

Using advanced techniques to understand metal uptake and distribution

Guerinot has also been investigating how iron migrates into plants and has identified key genes involved in this process. Her research also has applications in environmental clean-up where plants can be used to remove toxic metals from the soil, a method known as phytoremediation.

Advanced imaging techniques allow Guerinot and her team to visualize the distribution of metals in plants, which helps them to better understand how the metals are taken up. In 2015, one of their images was recognized as part of the Federation of American Societies for Experimental Biology BioArt competition. The image shows where zinc accumulation takes place in a leaf from the model organism Arabidopsis.

They are also separating out cell layers in the root to determine if genes in different cell types may impact the uptake of metals in the root.

"We normally take the entire root and extract RNA to look at the expression of different genes," said Guerinot. "This advanced method helps us see if genes are only expressed in certain cell types, which simply cannot be determined when looking at the whole root."

Forming collaborations to extend the reach of research

As part of the Dartmouth SRP Center, Guerinot co-leads the Collaborative on Food with Arsenic and associated Risk and Regulation (C-FARR), a network of scientists who study the fate of arsenic in food and resulting exposure to humans.

C-FARR convened a team of scientists and stakeholders to gather and analyze data and publish a series of papers related to sources of arsenic and human exposure via food consumption. The five resulting C-FARR papers were published in a Virtual Special Section in the journal Science of the Total Environment.

In one article in the Special Section, Guerinot and colleagues discuss the importance of understanding the sources of arsenic in crop plants and the influence of arsenic cycle dynamics, and how these factors are key to reducing the current crop uptake of arsenic, thereby preventing exposure in the future.

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