A U.S. Department of Agriculture (USDA) scientist in California has opened a window into the vascular networks of a number of crops by adapting computed tomography (CT) scan technology to the study of plants.

Andrew McElrone, a plant physiologist with USDA's Agricultural Research Service (ARS)  in Davis, Calif., is using the technology to study how water and pathogens move through a plant's vascular tissue called xylem. ARS is USDA's principal intramural scientific research agency.

The xylem consists of tube-like elements that play a major role in the plant's growth and survival. When a plant takes up water from its roots, water passes through these tubes as if it were sipping water through a straw, and it uses thousands of these tubes in the process.

Drought conditions increase tension on the water in healthy xylem tubes, making them more susceptible to the formation of air bubbles, called embolisms, which interrupt the water flow and lead to damage or even death of the vine.

Being able to study embolism formation and the connections between xylem tissues in fine detail will help scientists determine how plants respond to water stress and other changing conditions. It also should assist in efforts to breed crops better equipped to tolerate drought and resist disease.

Some pathogens target the xylem tissue and spread by moving through it. Using the CT technology, McElrone found that a key to infection susceptibility is the presence of specialized "bridge cells" that serve as connections between xylem tubes.

His research has shown that how well the bridge cells link the xylem tubes could contribute to how the bacterial pathogen that causes Pierce's disease-which results in major damage in vineyards-will move through a grapevine. Grapevines susceptible to Pierce's disease have more bridge cells, which may allow pathogens to pass through them more easily.

McElrone has a manuscript accepted in the Journal of Visualized Experiments with an accompanying film that demonstrates the CT scanning technique for other scientists. Much of McElrone's work has focused on grapevines, but he is working with other researchers to use the technology to study other crops, including walnuts, sunflowers, citrus, and blueberries.

www.ars.usda.gov