Metals and metalloids play a key role in plant and other biological systems as some of them are essential to living organisms\r\nand all can be toxic at high concentrations. It is therefore important to understand how they are accumulated, complexed\r\nand transported within plants. In situ imaging of metal distribution at physiological relevant concentrations in highly\r\nhydrated biological systems is technically challenging. In the case of roots, this is mainly due to the possibility of artifacts\r\narising during sample preparation such as cross sectioning. Synchrotron x-ray fluorescence microtomography has been\r\nused to obtain virtual cross sections of elemental distributions. However, traditionally this technique requires long data\r\nacquisition times. This has prohibited its application to highly hydrated biological samples which suffer both radiation\r\ndamage and dehydration during extended analysis. However, recent advances in fast detectors coupled with powerful data\r\nacquisition approaches and suitable sample preparation methods can circumvent this problem. We demonstrate the\r\nheightened potential of this technique by imaging the distribution of nickel and zinc in hydrated plant roots. Although 3D\r\ntomography was still impeded by radiation damage, we successfully collected 2D tomograms of hydrated plant roots\r\nexposed to environmentally relevant metal concentrations for short periods of time. To our knowledge, this is the first\r\npublished example of the possibilities offered by a new generation of fast fluorescence detectors to investigate metal and\r\nmetalloid distribution in radiation-sensitive, biological samples.
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