X-Ray Computed Microtomography and Investigations of Wood Structure and the Vascular Cambium

X-ray computed microtomography (µCT) provides an important complement to optical imaging for understanding the three-dimensional (3D) organization and function of xylem and wood. Unlike conventional sectioning, µCT is a non-destructive process that produces high-quality data sets that can be rotated, resliced and, following image segmentation, quantified. We highlight examples in which quantitative processing of 3D µCT sets has provided quantitative understanding of xylem and wood including the development and refilling of xylem embolisms, tree ring analyses and the development of interlocked grain. We also highlight two ways through which the µCT imaging of wood, and plants in general, will be improved. While the current staining protocols for plants are non-specific, developments in specific labeling techniques, including modifications of traditional electron microscopy stains for cell walls and recent developments in µCT imaging in non-plant specimens for studying antibody labeling and transgenes, should allow significant improvements in the imaging of xylem and wood by µCT. We also highlight machine learning which is already facilitating improvements in image segmentation and quantification of µCT data sets. When coupled with the recent advances in molecular genetics of the vascular cambium, these improvements in µCT should dramatically increase our understanding of xylem formation.