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Xylem Water Distribution in Woody Plants Visualized with a Cryo-scanning Electron Microscope
Published on: June 20, 2019
Hydraulic disruption and passive migration by a bacterial pathogen in oak tree xylem
Andrew J McElrone1, Susan Jackson, Piotr Habdas
1USDA-ARS Crops Pathology and Genetics Research Unit, University of California, Davis, CA 95616, USA. ajmcelrone@ucdavis.edu
Journal of Experimental Botany
|May 20, 2008
Summary
Xylella fastidiosa (Xf) causes leaf scorch by degrading xylem pit membranes, leading to embolism and hydraulic failure. Large pit pores in oak xylem facilitate Xf migration and susceptibility to disease.
Area of Science:
- Plant Pathology
- Plant Physiology
- Forest Science
Background:
- Xylella fastidiosa (Xf) is a bacterial pathogen causing widespread leaf scorch in various ecosystems.
- The mechanisms of Xf-induced hydraulic disruption and xylem colonization are not fully understood across all hosts.
Purpose of the Study:
- To investigate the functional and structural xylem characteristics in healthy and Xf-infected Quercus species.
- To elucidate the role of xylem structure in Xf pathogen spread and disease development.
Main Methods:
- Quantified hydraulic conductivity (K(s)) and embolism in petioles of healthy and Xf-infected oak species (Q. palustris, Q. rubra).
- Assessed pit membrane porosity using cavitation vulnerability data, SEM, microsphere injection, and air seeding thresholds.
- Examined xylem structure in different organs of healthy and infected trees.
Main Results:
- Hydraulic conductivity significantly decreased in Xf-infected petioles, reaching zero at symptom onset.
- Embolism levels were up to 3.7 times higher in infected petioles before K(s) reduction, linked to pit membrane degradation.
- Four methods confirmed frequent large pit membrane pores in oak xylem, exceeding Xf diameter.
Conclusions:
- Pit membrane degradation and subsequent embolism are key factors in Xf-induced hydraulic failure.
- Large pit pores in Quercus species facilitate systemic Xf colonization within the xylem network.
- Xylem structural traits contribute to the high susceptibility of these oak species to bacterial leaf scorch.
Keywords:
CavitationXylella fastidiosaembolismhydraulic conductivityvascular pathogensxylem-limited bacteriaMore Related Videos
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