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Materials 2014, 7(4), 3160-3175; doi:10.3390/ma7043160
Article

Quantitative X-ray Elemental Imaging in Plant Materials at the Subcellular Level with a Transmission Electron Microscope: Applications and Limitations

1
, 2
, 2
 and 2,*
1 College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, China 2 Forstbotanik und Baumphysiologie, Büsgen-Institute, Georg-August Universität Göttingen, Göttingen 37077, Germany
* Author to whom correspondence should be addressed.
Received: 5 February 2014 / Revised: 10 March 2014 / Accepted: 11 April 2014 / Published: 21 April 2014
(This article belongs to the Section Biomaterials)
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Abstract

Energy-dispersive X-ray microanalysis (EDX) is a technique for determining the distribution of elements in various materials. Here, we report a protocol for high-spatial-resolution X-ray elemental imaging and quantification in plant tissues at subcellular levels with a scanning transmission electron microscope (STEM). Calibration standards were established by producing agar blocks loaded with increasing KCl or NaCl concentrations. TEM-EDX images showed that the salts were evenly distributed in the agar matrix, but tended to aggregate at high concentrations. The mean intensities of K+, Cl, and Na+ derived from elemental images were linearly correlated to the concentrations of these elements in the agar, over the entire concentration range tested (R > 0.916). We applied this method to plant root tissues. X-ray images were acquired at an actual resolution of 50 nm ´ 50 nm to 100 nm ´ 100 nm. We found that cell walls exhibited higher elemental concentrations than vacuoles. Plants exposed to salt stress showed dramatic accumulation of Na+ and Cl in the transport tissues, and reached levels similar to those applied in the external solution (300 mM). The advantage of TEM-EDX mapping was the high-spatial-resolution achieved for imaging elemental distributions in a particular area with simultaneous quantitative analyses of multiple target elements.
Keywords: TEM; EDX; agar standard; Populus euphratica; root; cortex; cell wall; vacuole; xylem vessel; salt tolerance TEM; EDX; agar standard; Populus euphratica; root; cortex; cell wall; vacuole; xylem vessel; salt tolerance
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Chen, S.; Diekmann, H.; Janz, D.; Polle, A. Quantitative X-ray Elemental Imaging in Plant Materials at the Subcellular Level with a Transmission Electron Microscope: Applications and Limitations. Materials 2014, 7, 3160-3175.

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