Plant Vasculature - Recent Work:
Refereed journal articles:
1.) The physiological implications of primary xylem organization in two ferns
Craig R. Broderson, Lindsey C. Roark, Jarmila Pittermann
Department of Ecology & Evolutionary Biology, University of California, Santa Cruz, CA, USA
Xylem structure and function are well described in woody plants, but the implications of xylem organization in less-derived plants such as ferns are poorly understood. Here, two ferns with contrasting phenology and xylem organization were selected to investigate how xylem dysfunction affects hydraulic conductivity and stomatal conductance (g(s)). The drought-deciduous pioneer species, Pteridium aquilinum, exhibits fronds composed of 25 to 37 highly integrated vascular bundles with many connections, high g(s) and moderate cavitation resistance (P50 = -2.23 MPa). By contrast, the evergreen Woodwardia fimbriata exhibits sectored fronds with 3 to 5 vascular bundles and infrequent connections, low g(s) and high resistance to cavitation (P50 = -5.21 MPa). Xylem-specific conductivity was significantly higher in P. aqulinium in part due to its wide, efficient conduits that supply its rapidly transpiring pinnae. These trade-offs imply that the contrasting xylem organization of these ferns mirrors their divergent life history strategies. Greater hydraulic connectivity and g(s) promote rapid seasonal growth, but come with the risk of increased vulnerability to cavitation in P. aquilinum, while the conservative xylem organization of W. fimbriata leads to slower growth but greater drought tolerance and frond longevity.
Citation: C.R. Brodersen, L.C. Roark, and J. Pittermann, "The physiological implications of primary xylem organization in two ferns," Plant, Cell and Environment 35, 1898 (2012).
2.) Automated analysis of three-dimensional xylem networks using high-resolution computed tomography
Craig R. Brodersen1, Eric F. Lee1,2, Brendan Choat3, Steven Jansen4, Ronald J. Phillips2, Kenneth A. Shackel5, Andrew J. McElrone1,6 and Mark A. Matthews1
1Department of Viticulture and Enology, University of California, Davis, CA, USA; 2Department of Chemical Engineering and Materials Science, University of California, Davis, CA, USA; 3Hawkesbury Institute for the Environment, University of Western Sydney, Sydney, NSW 2753, Australia; 4Institute of Systematic Botany and Ecology, Ulm University, Ulm, Germany; 5Department of Plant Science, University of California, Davis, CA, USA; 6USDA-ARS, Crops Pathology and Genetics Research Unit, Davis, CA 95616, USA
Connections between xylem vessels represent important links in the vascular network, but the complexity of three-dimensional (3D) organization has been difficult to access. 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 tomography scans of grapevine (Vitis vinifera) stems, although the method could be applied to other species. Manual and automated analyses of vessel networks yielded similar results, with the automated method generating orders of magnitude more data in a fraction of the time. In 4.5-mm-long internode sections, all vessels and all intervessel connections among 115 vessels were located, and the connections were analyzed for their radial distribution, orientation, and predicted shared wall area. Intervessel connections were more frequent in lateral than in dorsal/ventral zones. The TANAX-reconstructed network, 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.
Citation: Brodersen C. R., Lee E. F., Choat B., Jansen S., Phillips R. J., Shackel K. A., McElrone A. J. and Matthews, M. A. (2011). Automated analysis of three-dimensional xylem networks using high-resolution computed tomography. New Phytologist, 191: 1168–1179.
3.) The Dynamics of Embolism Repair in Xylem: In Vivo Visualizations Using High-Resolution Computed Tomography
Craig R. Brodersen1, Andrew J. McElrone1,3, Brendan Choat4, Mark A. Matthews1, and Kenneth A. Shackel2
1Department of Viticulture and Enology and 2Department of Plant Sciences, University of California, Davis, California 95616; 3United States Department of Agriculture-Agricultural Research Service, Crops Pathology and Genetics Research Unit, Davis, California 95616 (A.J.M.); 4Research School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia
Water moves through plants under tension and in a thermodynamically metastable state, leaving the nonliving vessels that transport this water vulnerable to blockage by gas embolisms. Failure to reestablish flow in embolized vessels can lead to systemic loss of hydraulic conductivity and ultimately death. Most plants have developed a mechanism to restore vessel functionality by refilling embolized vessels, but the details of this process in vessel networks under tension have remained unclear for decades. Here we present, to our knowledge, the first in vivo visualization and quantification of the refilling process for any species using high-resolution x-ray computed tomography. Successful vessel refilling in grapevine (Vitis vinifera) was dependent on water influx from surrounding living tissue at a rate of 6 3 1024 mm s21, with individual droplets expanding over time, filling vessels, and forcing the dissolution of entrapped gas. Both filling and draining processes could be observed in the same vessel, indicating that successful refilling requires hydraulic isolation from tensions that would otherwise prevent embolism repair. Our study demonstrates that despite the presence of tensions in the bulk xylem, plants are able to restore hydraulic conductivity in the xylem.
Citation: Broderson C.R., McElrone A.J., Choat B., Matthews M.A. and Shackel K.A. (2010), The dynamics of Embolism Repair in Xylem: In Vivo Visualizations Using High-Resolution Computed Tomography. Plant Physiology, 154: 1088-1095. doi:
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