Developmental and Structural Section
Sun, Q. , Pérez-Donoso, A. , Roper, M.C. , Greve, L.C. , Kirkpatrick, B.C. , Labavitch, J.M. .
Cell wall composition and porosity of intervessel pit membranes in grape stems and possible mechanisms of systemic movement of Xylella fastidiosa, causal pathogen of Pierce’s disease of grape.
Intervessel pit membranes consist of a middle lamella and primary cell walls of two adjacent vessels and are believed to be structural barriers for systemic spread of xylem-limited Xylella fastidiosa in grapevines. Since the Xylella genome includes genes which encode the cell wall degrading enzymes endo-1,4-Î²-glucanase (EGase) and polygalacturonase (PG), we proposed that Xylella uses these enzymes to digest the intervessel pit membranes and clear the barrier that limits systemic spread of the bacterial population. To test this hypothesis, we firstly investigated cell wall composition of pit membranes with monoclonal cell wall antibodies and found that pit membranes contained homogalacturonans and fucosylated xyloglucan. Tests of pit membrane porosity involving xylem infusion with suspensions of colloidal gold particles of known sizes indicated that introduction of either of EGase or PG alone did not increase pit membrane porosity appreciably, but when the two enzymes were introduced together the combination of the two enzymes increased pit membrane porosity substantially. When the xylem conduits were flushed with EGase and PG, electron microscope examination revealed pit membrane gaps of greater size than Xylella cells. Therefore, the present report suggests that the digestion of wall components in the pit membrane facilitates the systemic distribution of Xylella in grapevines.
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1 - University of California Davis, Department of Plant Sciences, One Shields Avenue, Davis, California, 95616, USA
2 - University of California Davis, Department of Plant Pathology, One Shields Avenue, Davis, California, 95616, USA
cell wall composition
Presentation Type: Poster:Posters for Sections
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM