Two-dimensional X-ray fluorescence image of total Fe (a) and As (b) in a whole mount of a Fe plaque-free rice root grown in well-weathered soil. Panels (c–h) are higher resolution images of the yellow box in panel (a) that show the Fe (c), arsenite (As(III)) (d), and arsenate (As(V)i) (e) distribution where a lateral root has formed from the main root, and panels (f–h) are tricolor plots that show the localization of As(III) in relation to As(V)i and Fe (f), K (g), and S (h). All colormap units are in pg cm−2, with a maximum of 200 for Fe and 0.75 for As, and show that lateral root junctions are hotspots of As(III)i entering the vascular tissue. [Seyfferth, A. L., et al. 2017.]
X-ray fluorescence imaging (XRF), or x-ray spectromicroscopy, maps the distributions of elements and chemical species of interest within biological samples. Synchrotron XRF (SXRF) can provide detailed images of element speciation to a resolution of 0.5 µm per pixel, a sensitivity beyond desktop XRF, electron microprobe, or other elemental imaging techniques. SXRF resources supported by the DOE Office of Biological and Environmental Research (BER) can image phosphorus through most elements in the periodic table. Sample requirements and preparation are minimal, allowing the flexibility to explore diverse scientific questions and to design unique user experiments. SXRF beamlines use a combination of methods, ranging from mapping an area at a particular x-ray energy (that corresponds to the excitation of an element) to identifying the oxidation state and chemistry of a particular element to using a technique called x-ray absorption near edge structure (XANES) spectroscopy.
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Seyfferth, A. L., et al. 2017. "Evidence for the Root-Uptake of Arsenite at Lateral Root Junctions and Root Apices in Rice (Oryza sativa L.)," Soils 1(1), 3. DOI: 10.3390/soils1010003.
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