Tracy Punshon

Former Lab MembersFormer_Lab_Members.html

My research uses synchrotron x-ray fluorescence microspectroscopy (SXRF) and x-ray absorption spectroscopy (XAS) to help characterize the function of genes involved in metal and metalloid transport in plants. I work closely with molecular geneticists to provide elemental images that help in the functional characterization of genes.

Synchrotron x-ray fluorescence microspectroscopy is technique which allows the distribution and abundance of  multiple elements within biological tissues to be imaged non-destructively, without the need for intrusive sample preparation and sectioning. We recently published a Botanical Briefings article in Annals of Botany that explains the technique and its application to metal and metalloid homeostasis research.

I began using SXRF and collaborating with beam line scientist Antonio Lanzirotti at beamline X26A of the National Synchrotron Light Source in 2000. I was investigating the impact of metal and radionuclide contamination on plants, and found a metal signature in the annual rings of willows growing on a former radiological settling basin. In a subsequent paper I used XAS to investigate the speciation of nickel in the annual rings.

When I joined the Guerinot lab in 2005, research was underway on the characterization of VIT1 (Vacuolar Iron Transporter1) in Arabidopsis; which was highly expressed in the seed. Other lines of evidence suggested VIT1 was involved in loading Fe in to the vacuole, but deletion did not change the volume-averaged concentration of Fe in the seed. By collecting three dimensional images of the Fe fluorescence in wild type and knock out mutants we were able to image directly the influence of VIT1. This gene acts in the cells of the embryonic vasculature (in the radicle; the pericycle) to load the vacuole with Fe, presumably in preparation for germination.

We have recently began using similar techniques to search for and characterize genes involved in arsenic transportation to the grain in rice plants. This is a Superfund Basic Research Program funded project that  uses molecular genetics, ionomics, SXRF, XAS mapping and various other speciation techniques offered by Dartmouth College’s Trace Element Analysis Core to understand arsenic homeostasis in rice.

Three-dimensional rendering of the Fe (red) and Mn (green) distribution in a wild type (Columbia-0) Arabidopsis thaliana seed

Movie of Fe Kα fluorescence in an Arabidopsis seed