Inside the garden, methyl jasmonate is the sweetest scent around. Rising off jasmine flowers, the compound's sultry perfume stops pollinators and people alike. But sweetness can be deceiving: When plants are wounded by hungry herbivores, that same scent, shot from the leaves, serves as an SOS.
In fact, the emerging biochemistry of floral scent confirms what researchers have long suspected: Plants are versatile perfumers, flinging similar--and in some cases, identical--chemicals into the air to turn organisms on or off, depending on the situation. "Think of plant volatiles as a language," says Jim Tumlinson of the U.S. Department of Agriculture's Agricultural Research Service in Gainesville, Florida. "If you put them together into one message, you have a scent that attracts pollinators. Put together another way, you have a scent that attracts natural enemies of herbivores threatening a plant."
It's been about 20 years since entomologist Jack Schultz of Pennsylvania State University, University Park, and then-student Ian Baldwin first proposed that "talking trees"--in that case, damaged poplars and maples--could signal distress to their neighbors with airborne chemicals. Scientists scoffed. But last year, Baldwin--now director of molecular ecology at the Max Planck Institute for Chemical Ecology in Jena, Germany--and graduate student André Kessler reported in Science the first field evidence for indirect plant volatile defenses against herbivores (16 March 2001).
Working in southwestern Utah's Great Basin desert, Baldwin and Kessler found that tobacco plants under assault from caterpillars, leaf bugs, and flea beetles naturally release three compounds that can cut this herbivore activity by more than 90%. Now, Baldwin is looking for the genes behind these plant defense volatiles. "What is it that controls volatile release?" he asks.
Plant scents also attract human grazers. Researchers have recently identified key volatiles that flavor sweet basil and strawberries, among other edible plants. Last November in Plant Physiology, Eran Pichersky of the University of Michigan, Ann Arbor, and his colleagues reported engineering tomatoes with S-linalool, a scent and flavor volatile also found in flowers, with the ultimate goal of improving both scent and taste. In fact, he adds, new plant volatiles--and uses--continue to emerge.
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