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PLANTS INTERACTING WITH OTHER ORGANISMS

Xylella fastidiosa Infection and Ethylene Exposure Result in Xylem and Water Movement Disruption in Grapevine Shoots^1,[OA]

Department of Plant Sciences (A.G.P.-D., L.C.G., K.A.S., J.M.L.) and Nuclear Magnetic Resonance Facility (J.H.W.), University of California, Davis, California 95616

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) affected by Pierce's disease. However, results from our studies have provided substantial support for the idea that vessel obstructions, and likely other aspects of the Pierce's disease syndrome, result from the grapevine's active responses to the presence of Xf, rather than to the direct action of the bacterium. The use of magnetic resonance imaging (MRI) to observe the distribution of water within the xylem has allowed us to follow nondestructively the development of vascular system obstructions subsequent to inoculation of grapevines with Xf. Because we have hypothesized a role for ethylene produced in vines following infection, the impact of vine ethylene exposure on obstruction development was also followed using MRI. In both infected and ethylene-exposed plants, MRI shows that an important proportion of the xylem vessels become progressively air embolized after the treatments. The loss of xylem water-transporting function, assessed by MRI, has been also correlated with a decrease in stem-specific hydraulic conductivity (K_S) and the presence of tyloses in the lumens of obstructed water conduits. We have observed that the ethylene production of leaves from infected grapevines is greater than that from healthy vines and, therefore, propose that ethylene may be involved in a series of cellular events that coordinates the vine's response to the pathogen.

² Present address: Departamento de Fruticultura y Enología, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: John M. Labavitch (jmlabavitch{at}ucdavis.edu).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.087023

^* Corresponding author; e-mail jmlabavitch{at}ucdavis.edu; fax 530–752–2278.

Received July 21, 2006; accepted December 1, 2006; published December 22, 2006.

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