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Environmental Factor, December 2012

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Guerinot discusses metal uptake, transport, and accumulation in plants

By Sara Mishamandani

Mary Lou Guerinot, Ph.D.

Guerinot is the Ronald and Deborah Harris Professor of the Sciences at Dartmouth College. She has served as chair of the Department of Biological Sciences, as Associate Dean of the Faculty for the Sciences, and as Vice Provost. (Photo courtesy of Steve McCaw)

Guerinot and Carlin

DERT Program Administrator Danielle Carlin, Ph.D., left, hosted Guerinot’s lecture at NIEHS. (Photo courtesy of Steve McCaw)

Understanding the way plants absorb and distribute metals, such as iron and arsenic, may help to improve environmental and human health, said Dartmouth College professor and Superfund Research Program (SRP) grantee Mary Lou Guerinot, Ph.D., during her Oct. 25 lecture at NIEHS. Her talk was part of the Keystone Science Lecture Seminar Series, sponsored by the NIEHS Division of Extramural Research and Training (DERT).

In her lecture, “Ionome to Genome: Gene Discovery in Aid of Plant Nutrition, Human Health, and Environmental Remediation,” Guerinot discussed techniques to better understand the genes and mechanisms involved in metal uptake and distribution in plants. She introduced and described ionomics, or the study of the complete set of mineral nutrients and trace elements found within a living organism.

Guerinot’s group measures metal ion abundance in plants, using inductively coupled plasma mass spectroscopy (ICP-MS). ICP-MS uses high temperature to both ionize and atomize metals present in a sample, to prepare them for detection in a spectrometer, providing accurate measurements of overall metal content.

Her group also investigates where the metal ions are localized within the plant, using synchrotron X-ray fluorescence microspectroscopy. This method takes advantage of the fluorescent light released when X-rays interact with the outer electrons of a metal atom. The wavelength of the emitted light determines the type and location of the metals within a sample.

Iron accumulation in plants and nutrition

Guerinot’s group analyzes plant iron content to search for mutants that can more readily absorb iron, and to determine the genes associated with iron uptake. The group identified several promising plant lines that accumulate more iron in their seeds than other plants, and are using them to better understand the genes responsible for the uptake.

“Because extreme poverty limits access to food for much of the world’s population, it is important that affordable food be as nutritious as possible,” said Guerinot.

Iron deficiency is the most common human nutritional disorder. She explained that understanding the genetic propensity of a plant to absorb iron will help develop ways to fortify foods with iron, improving nutrient content.

Understanding arsenic in rice

Guerinot also discussed her research on harmful metal uptake in edible plants, such as arsenic and cadmium in rice. This work is being done at the Dartmouth SRP center, which focuses on the fate and transport of arsenic, as well as arsenic exposure and associated health effects.

Previous research at the Dartmouth SRP, led by Brian Jackson, Ph.D., uncovered high levels of inorganic arsenic in organic brown rice syrup. Another Dartmouth SRP grantee, Margaret Karagas, Ph.D., discovered that consumption of around a half cup per day of cooked rice had levels of arsenic comparable to drinking 1 liter per day of water containing 10 micrograms of arsenic, the current U.S. maximum contaminant limit. This research revealed the need to monitor arsenic in foods and develop guidelines for arsenic concentrations.

Guerinot uses the same laboratory techniques she uses to investigate iron in plants to determine abundance and localization of arsenic in rice.

Finding rice cultivars that don’t take up arsenic

Guerinot’s research group evaluated more than 300 rice cultivars grown in multiple locations, and performed field trials, in varied arsenic soils, to see how much of the arsenic concentration was due to the environment and how much was due to genotype. The results showed a genetic basis for arsenic accumulation.

“We are trying to find rice cultivars that restrict arsenic accumulation in the grain,” said Guerinot. “We think it is the simplest, fastest, and most cost effective approach to solve the problem of arsenic contamination of rice and rice-based products.”

Discovering this genetic variation may help breed cultivars low in grain arsenic, leading to reduced human exposure to arsenic from rice.

(Sara Mishamandani is a research and communication specialist for MDB, Inc., a contractor for the NIEHS Superfund Research Program, Worker Education and Training Program, and Division of Extramural Research and Training.)

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