XYLEM CHEMISTRY MEDIATION OF RESISTANCE TO PIERCE`S DISEASE

• Author(s): Andersen, Peter; Leite, Breno; Ishida, Maria Lucia;
• Abstract: Xylella fastidiosa (Xf) is the causal agent of Pierces disease (PD) of grapevines. The mechanism involved in pathogenecity is largely due to the occlusion of xylem vessels by aggregates of Xf (cells and biofilm. Increasing concentrations of CaCl)2 and (MgCl)2 consistently induced aggregation of Xf in vitro and differences in aggregation patterns occurred when comparing strains of Xf. A solution (100 mg/Liter) of divalent cation (calcium or magnesium) increased Xf aggregation by about 10 fold. A pre-treatment of Xf cells with the reduced form of glutathione (an antioxidant present in the xylem fluid) significantly enhanced the attraction of Xf cells for calcium and resulted in more cell aggregation. By contrast, pre-treatment of cells with oxidized glutathione virtually eliminated aggregation. Our data indicate that cell aggregation and biofilm formation in grapevine vessels may be dependent on: a) the presence of free divalent ions and b) the proper redox environment, which in turn modulates surface characteristics (particularly thiol moieties) of Xf. These results support the contention that Xf pathogenicity mechanisms may involve rapid aggregation in early stages and biofilm formation induced by xylem fluid constituents.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium