Issue Date: September 29, 2008
Plants' Chemical SOS
Walnut trees under stress fill the air with significant quantities of methyl salicylate, an ester of salicylic acid, according to a report in Biogeosciences (2008, 5, 1287). This chemical warning system could help farmers identify ailing crops before visible indicators such as dead leaves appear. Thomas Karl and coworkers of the National Center for Atmospheric Research, in Boulder, Colo., accidentally detected airborne methyl salicylate when attempting to monitor levels of climate-influencing volatile organic compounds (VOCs) in the air over a California walnut grove. Until this study, researchers had never detected airborne methyl salicylate in an ecosystem, even though it is a key component in oil of wintergreen, produced by certain herbs. The team measured VOC levels in the grove with a specially designed tower equipped with a mass spectrometer. Methyl salicylate readings spiked during cold or dry periods, suggesting that the plants were sending out a distress signal. Lab research by other groups has shown that plants build their defenses when methyl salicylate-emitting neighbors are nearby. The field study suggests that plants use methyl salicylate to trigger an ecosystem-wide immune response, the authors write.
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