McElrone Andrew J, Choat Brendan, Parkinson Dilworth Y, MacDowell Alastair A, Brodersen Craig R
U.S. Department of Agriculture, USA.
J Vis Exp. 2013 Apr 5(74):50162. doi: 10.3791/50162.
High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique with sub-micron resolution capability that is now being used to evaluate the structure and function of plant xylem network in three dimensions (3D) (e.g. Brodersen et al. 2010; 2011; 2012a,b). HRCT imaging is based on the same principles as medical CT systems, but a high intensity synchrotron x-ray source results in higher spatial resolution and decreased image acquisition time. Here, we demonstrate in detail how synchrotron-based HRCT (performed at the Advanced Light Source-LBNL Berkeley, CA, USA) in combination with Avizo software (VSG Inc., Burlington, MA, USA) is being used to explore plant xylem in excised tissue and living plants. This new imaging tool allows users to move beyond traditional static, 2D light or electron micrographs and study samples using virtual serial sections in any plane. An infinite number of slices in any orientation can be made on the same sample, a feature that is physically impossible using traditional microscopy methods. Results demonstrate that HRCT can be applied to both herbaceous and woody plant species, and a range of plant organs (i.e. leaves, petioles, stems, trunks, roots). Figures presented here help demonstrate both a range of representative plant vascular anatomy and the type of detail extracted from HRCT datasets, including scans for coast redwood (Sequoia sempervirens), walnut (Juglans spp.), oak (Quercus spp.), and maple (Acer spp.) tree saplings to sunflowers (Helianthus annuus), grapevines (Vitis spp.), and ferns (Pteridium aquilinum and Woodwardia fimbriata). Excised and dried samples from woody species are easiest to scan and typically yield the best images. However, recent improvements (i.e. more rapid scans and sample stabilization) have made it possible to use this visualization technique on green tissues (e.g. petioles) and in living plants. On occasion some shrinkage of hydrated green plant tissues will cause images to blur and methods to avoid these issues are described. These recent advances with HRCT provide promising new insights into plant vascular function.
高分辨率X射线计算机断层扫描（HRCT）是一种具有亚微米分辨率能力的非破坏性诊断成像技术，目前正用于三维（3D）评估植物木质部网络的结构和功能（例如Brodersen等人，2010年；2011年；2012a，b）。HRCT成像基于与医学CT系统相同的原理，但高强度同步加速器X射线源可实现更高的空间分辨率并缩短图像采集时间。在此，我们详细展示了基于同步加速器的HRCT（在美国加利福尼亚州伯克利市劳伦斯伯克利国家实验室的先进光源进行）与Avizo软件（美国马萨诸塞州伯灵顿市VSG公司）相结合，如何用于探索离体组织和活体植物中的植物木质部。这种新的成像工具使用户能够超越传统的静态二维光学或电子显微照片，使用任意平面的虚拟连续切片来研究样本。可以在同一样本上制作任意方向的无数切片，这是传统显微镜方法在物理上无法实现的功能。结果表明，HRCT可应用于草本和木本植物物种以及一系列植物器官（即叶子、叶柄、茎、树干、根）。此处展示的图片有助于说明一系列具有代表性的植物维管解剖结构以及从HRCT数据集中提取的细节类型，包括对海岸红杉（北美红杉）、核桃（胡桃属物种）、橡树（栎属物种）和枫树（槭属物种）树苗到向日葵（向日葵）、葡萄藤（葡萄属物种）以及蕨类植物（欧洲蕨和条纹乌毛蕨）的扫描。木本物种的离体干燥样本最易于扫描，通常能产生最佳图像。然而，最近的改进（即更快的扫描和样本稳定）使得在绿色组织（如叶柄）和活体植物上使用这种可视化技术成为可能。偶尔，水合绿色植物组织的一些收缩会导致图像模糊，本文描述了避免这些问题的方法。HRCT的这些最新进展为植物维管功能提供了有前景的新见解。
