MAGNETIC RESONANCE IMAGING: A NON-DESTRUCTIVE APPROACH FOR DETECTION OF XYLEM BLOCKAGES IN XYLELLA FASTIDIOSA INFECTED GRAPEVINES

• Author(s): Labavitch, John; Shackel, Ken; Greve, Carl; Matthews, Mark; Perez, Alonso; Walton, Jeffrey;
• Abstract: It is conventionally thought that multiplication of the xylem-limited bacterium Xylella fastidiosa (Xf) within xylem vessels is the sole factor responsible for the blockage of water movement in grapevines (Vitis vinifera L.) affected by Pierces disease (PD). However, results from our studies have provided substantial support for the idea that vessel obstructions, and likely other aspects of the PD syndrome, result from the grapevines active responses to the presence of Xf, rather than to the direct action of the bacterium. The use of magnetic resonance imaging ((1)H-MRI) to observe the distribution of water within the xylem has allowed us to test the role of the plant hormone ethylene in promoting xylem obstruction development, and the consequent reduction in vine water transport. In both infected and ethylene-exposed plants, MRI shows that an important proportion of the xylem vessels become progressively air-embolized (the magnetic signal is lost from these vessels) after the treatments. The loss of xylem water-transporting function, assessed by MRI, has been also correlated with a decrease in stem specific hydraulic conductivities ((K)S() and the presence of tyloses in the lumen of water conduits. We propose that ethylene) may be involved in a series of cellular events that allows the plant to sense the presence of Xf and stimulates a plant response that includes the production of tyloses and gels, perhaps in an effort to slow systemic movement of the bacteria.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium