Agent that triggers immune response in plants is...( Although plants lack humans' T cells...)

Although plants lack humans' T cells and other immune-function cells to signal and fight infection, scientists have known for more than 100 years that plants still somehow signal that they have been attacked in order to trigger a plantwide resistance. Now, researchers at the Boyce Thompson Institute for Plant Research (BTI) on the Cornell campus have identified the elusive signal in the process: methyl salicylate, an aspirin-like compound that alerts a plant's immune system to shift into high gear.

This phenomenon is called systemic acquired resistance and is known to require movement of a signal from the site of infection to uninfected parts of the plant.

The findings are published in the Oct. 5 issue of Science.

"By finally identifying a signal that moves from an infection site to activate defenses throughout the plant, as well as the enzymes that regulate the level of this signal, we may be in a position to alter the signal in a way that enhances a plant's ability to defend itself," said BTI senior scientist Daniel F. Klessig, an adjunct professor in plant pathology at Cornell, who conducted the work with Sang-Wook Park and other BTI colleagues.

Their approach, using gene technology to enhance plant immunity, could have wide consequences, boosting crop production and reducing pesticide use.

Methyl salicylate is a modified form of salicylic acid (SA), which has been used for centuries to relieve fever, pain and inflammation, first through the use of willow bark and, since 1889, with aspirin, still the most widely used drug worldwide.

In the 1990s, Klessig's research group reported that SA and nitric oxide are two critical defense-signaling molecules in plants, as well as playing important roles in human health. Then, in 2003 and 2005, the group reported in the Proceedings of the National Academy of Sciences that an enzyme, salicylic acid-binding protein 2 (SABP2), is required for systemic acquired resistance and converts methyl salicyl
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