title: Cell wall-degrading enzymes enlarge the pore size of intervessel pit membranes in healthy and Xylella fastidiosa-infected grapevines.
abstract: The pit membrane (PM) is a primary cell wall barrier that separates adjacent xylem water conduits, limiting the spread of xylem-localized pathogens and air embolisms from one conduit to the next. This paper provides a characterization of the size of the pores in the PMs of grapevine (Vitis vinifera). The PM porosity (PMP) of stems infected with the bacterium Xylella fastidiosa was compared with the PMP of healthy stems. Stems were infused with pressurized water and flow rates were determined; gold particles of known size were introduced with the water to assist in determining the size of PM pores. The effect of introducing trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), oligogalacturonides, and polygalacturonic acid into stems on water flux via the xylem was also measured. The possibility that cell wall-degrading enzymes could alter the pore sizes, thus facilitating the ability of X. fastidiosa to cross the PMs, was tested. Two cell wall-degrading enzymes likely to be produced by X. fastidiosa (polygalactuoronase and endo-1,4- beta -glucanase) were infused into stems, and particle passage tests were performed to check for changes in PMP. Scanning electron microscopy of control and enzyme-infused stem segments revealed that the combination of enzymes opened holes in PMs, probably explaining enzyme impacts on PMP and how a small X. fastidiosa population, introduced into grapevines by insect vectors, can multiply and spread throughout the vine and cause Pierce's disease.
authors.affiliation: Department of Plant Sciences, University of California, Davis, California 95616-8780, USA.
authors.forename: Alonso G
authors.initials: AG
authors.lastname: Pérez-Donoso
authors.forename: Qiang
authors.initials: Q
authors.lastname: Sun
authors.forename: M Caroline
authors.initials: MC
authors.lastname: Roper
authors.forename: L Carl
authors.initials: LC
authors.lastname: Greve
authors.forename: Bruce
authors.initials: B
authors.lastname: Kirkpatrick
authors.forename: John M
authors.initials: JM
authors.lastname: Labavitch
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure; D002473:Cell Wall / Q000648:ultrastructure*; D002480:Cellulase / Q000235:genetics / Q000378:metabolism*; D004492:Edetic Acid / Q000031:analogs & derivatives; D004791:Enzyme Inhibitors / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D010935:Plant Diseases; D010940:Plant Proteins / Q000378:metabolism; D018547:Plant Stems / Q000382:microbiology / Q000648:ultrastructure; D030821:Plants, Genetically Modified / Q000382:microbiology / Q000648:ultrastructure; D011096:Polygalacturonase / Q000235:genetics / Q000378:metabolism; D016062:Porosity; D027843:Vitis / Q000378:metabolism / Q000382:microbiology* / Q000648:ultrastructure; D014867:Water; D044167:Xylella / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D052584:Xylem / Q000382:microbiology / Q000648:ultrastructure
chemical_list: D004791:Enzyme Inhibitors; C081479:PGIP protein, plant; D010940:Plant Proteins; D014867:Water; C005390:CDTA; D004492:Edetic Acid; D011096:Polygalacturonase; D002480:Cellulase