people and animals are not the only ones who can smell. plants are also able to perceive odors（气味） , but they process them in a very different way . while insects or mammals smell odors within a second of exposure, plants require much longer exposure times to respond. then using this information, they react effectively to the odors emitted by infected or 1 neighboring plants in order to increase their resistance to pest insects or disease. the new study by sarai giron-calva, from the department of 2 engineering at cinvestav-irapuato in mexico, and colleagues is published online in springer's journal of chemical ecology. odors emitted by stressed plants can induce（诱导） resistance to disease in healthy neighbors. while this so-called 'talking trees' phenomenon was identified more than 20 years ago, the 3 by which plants smell and process odors 4 unclear.
to establish both the dose of odors and length of exposure which are required to induce resistance against 5 infection in plants, the authors exposed lima bean plants to different concentrations of two odor compounds -- nonanal and methyl salicylate (mesa). both compounds are known to enhance resistance to bacterial disease in lima beans. they then measured the plants' resistance to the pathogen, after both 6 and 24 hours.
in the case of nonanal, plant resistance was significantly increased after both 6 and 24 hours. furthermore, there was no difference in induced resistance between the two concentrations of the odor. in contrast, the authors found that the lima bean plants mounted a high level of resistance to bacterial infection after exposure to mesa over an entire day, but not after short exposure of 6 hours. after 24 hours of exposure, the low concentration of mesa was as effective at inducing resistance to the pathogen（病原体） as the higher concentrations.
the researchers conclude: "in contrast to insect or mammals which can respond to odors within a second of exposure, the 'nose' of plants works in a fundamentally different way to perceive odors. plant to plant signaling in this instance is likely to involve the accumulation of odors in the receiving plant over a long period of time."
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