Something to Chew on; January 1994; Scientific American Magazine; by Leutwyler; 1 Page(s)

By chewing on the bark of a white willow tree, Edmund Stone, an 18th-century Anglican clergyman, discovered the analgesic merits of salicylic acid, the active ingredient in aspirin. No one, no matter how grateful for pain relief, has yet fathomed why Stone was gnawing on willow bark. But a possible reason why the willow and other plants produce this versatile compound has been discovered. A team from the Agricultural Biotechnology Research Unit at Ciba-Geigy has shown that the accumulation of salicylic acid in plant tissue after an infection is essential for prompting a crucial immune response, called systemic acquired resistance (SAR).

The two main defenses a plant inherits to fight disease are known as vertical resistance and horizontal resistance. Vertical resistance acts against individual agents of disease. Horizontal resistance, a category to which SAR belongs, is mounted against a wide array of related plant pathogens. It works by stalling fungal, bacterial or viral proliferation and activity. Because horizontal resistance protects against many kinds of plant pathogens, the ability to mobilize SAR in the absence of an actual infection could bolster a plant¿s ability to ward off disease. "One of our goals is to develop chemicals to spray on plants that will actually trigger a plant to be healthy," says John Ryals, the project¿s research director.