Study contributes to research addressing malnutrition and iron
deficiency
Dartmouth biologists are leading a research team that has learned where and
how some plant seeds store iron, a valuable discovery for scientists working to
improve the iron content of plants. This research helps address the worldwide
issues of iron deficiency and malnutrition. Their findings were published
online on Nov. 2 at ScienceExpress,
the advance publication site for the journal Science.
Professor of Biological Sciences Mary Lou Guerinot (center) with Sun A Kim
(left) and Tracy Punshon, both postdoctoral fellows at Dartmouth. (Photo by
Joseph Mehling '69)
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The team found that iron is stored in the developing vascular system of the
seed of Arabidopsis, a model plant used in research; in particular, iron is
stored in the vacuole, a plant cell's central storage site. The researchers
also learned that this localization is dependent on a protein called VIT1,
shown to transport iron into the vacuole.
Professor of Biological Sciences Mary Lou
Guerinot, the principal investigator on the study, says, "Iron
deficiency is the most common human nutritional disorder in the world today,
afflicting more than three billion people worldwide. Most of these people rely
on plants for their dietary iron. However, plants are not high in iron, and the
limited availability of iron in the soil can limit plant growth. Our study
certainly suggests that iron storage in the vacuole is a promising and, before
now, largely unexplored target for increasing the iron content of
seeds."
The researchers combined traditional mutant analysis (turning on and off the
VIT1 protein) with a powerful X-ray imaging technique to create a map of where
iron is localized in the seed. Guerinot was surprised by the findings because
most studies on iron storage focus on the protein ferritin. This paper reveals
how important it is to look beyond ferritin to understand how iron is stored by
plants. The researchers say that their study suggests that the stored iron in
the vacuole is an important source of iron for developing seedlings. Seedlings
that do not express the VIT1 protein grow poorly when iron is limited.
"We have demonstrated the usefulness of synchrotron X-ray fluorescence
microtomography to look inside a seed," says Guerinot. "This
technique is noninvasive and requires no sample preparation. We think our work
will open the way for many more biologists to use this technique to examine the
spatial distribution of metals in samples of interest." The imaging was
carried out at the Department of Energy's National Synchrotron Light Source at
Brookhaven National Laboratory.
Other authors on the paper include Sun A Kim and Tracy Punshon, both
postdoctoral fellows at Dartmouth; Antonio Lanzirotti of the University of
Chicago; Liangtao Li and Jerry Kaplan from the University of Utah School of
Medicine; José Alonso from North Carolina State University; and Joseph Ecker
with the Salk Institute for Biological Studies.
This research was supported by grants from the National Science Foundation and the National Institutes of Health. Tracy Punshon was
supported by a training fellowship provided by the National Institute of
Environmental Health Sciences Superfund Basic Research
Program Project through Dartmouth's Center for Environmental
Health Sciences.
By SUSAN KNAPP
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