Development of CAT Scan Technology for Analysis of Xylem Structure and Function

Although intervessel connections are essential for radial and tangential movement of water and solutes in xylem conduits, little is known about their prevalence or distribution because of the difficulty in analyzing the complex three dimensional (3D) nature of the xylem network.  This study describes the development of a custom software package called TANAX (Tomography-derived Automated Network Analysis of Xylem) that automatically extracts vessel dimensions and the distribution of intervessel connections from High Resolution Computed Assisted Tomography (aka CAT) scans.  Manual and automated analyses of vessel networks in grapevine (Vitis vinifera L.) stems yielded similar results, with the automated method generating orders of magnitude more data in a fraction of the time.  In 4.5 mm internode sections, all vessels and all intervessel connections among 115 vessels were located, and the connections were analyzed for their radial distribution, orientation, and shared wall (pit) area.  Intervessel connections were more frequent in lateral than in dorsal/ventral zones and more commonly oriented radially than tangentially.  PHAST reconstructed the conduit network with its connections, and in combination with commercial software was used to visualize vessel networks in 3D.  The 3D volume renderings of vessel networks were freely rotated for observation from any angle, and the 4.5 µm virtual serial sections were capable of being viewed in any plane, revealing aspects of vessel organization not possible with traditional serial sections.  This methodology, including CAT scans and custom software for xylem network analysis, should be useful for building accurate network models for studies of stem hydraulics and plant water use.