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Science 311 (5762): 803-

Copyright © 2006 by the American Association for the Advancement of Science

The Invisible Bouquet

Pamela J. Hines

Of the thousands of different metabolites that plants can produce, many form a cloud around the plant. These volatile compounds reflect the metabolic complexity of plants and also serve a diversity of functions. Volatile compounds signal opportunity to insects, pathogens, and pollinators alike. In a classic case of "the enemy of my enemy is my friend," plants being nibbled on by insect herbivores can produce volatile signals that call in other insects to prey on the herbivores. For plants that flower at night, volatiles may be a better signal than floral color or shape to draw in the best insect pollinators. Volatile signals are also read by neighboring plants and reinterpreted as instructions to adjust their own defenses. Through olfaction and, secondarily, through the combination of taste and olfaction, which we interpret as flavor, volatiles signal to mammals that what's nearby may be food or foul. Some volatile compounds have biochemical functions, such as the antimicrobial activity of the spice clove. The prevalence of clove and similar spices in traditional food recipes has much to do with the value of these spices for preserving food in pre-refrigeration human history. That these spices also deliver a unique flavor through their volatility serves as well as an overt signal of the (hopefully) better quality of the food so prepared.

In this special issue, we explore various notes of this aromatic story. Lund and Bohlmann (p. 804) discuss how genome, environment, and cultivation practices shape the suite of volatiles that eventually give each bottle of wine its unique flavor. Kaiser (p. 806) illustrates how effectively certain plants and fungi can mimic each other, poaching on their insect partnerships by using volatile signals. Pichersky et al. (p. 808) describe the biochemistry and the evolutionary forces that combine to produce the complex suite of volatiles. Baldwin et al. (p. 812) explain how plants eavesdrop on their neighbors to adjust their own reactions to ecosystem changes. And finally, Goff and Klee (p. 815) put forth a hypothesis about how volatiles fine-tune or misdirect our human responses to food.

In related online resources, a Science of Aging Knowledge Environment (SAGE KE) Perspective by Rawson explores the nature of age-related olfactory loss and how it might be prevented. Information at Science's Signal Transduction Knowledge Environment (STKE) highlights plant signaling by the volatile plant hormone jasmonate (see the Connections Maps by the Farmer lab), and a Teaching Resource by Laskowski shows an animated model of the regulation of gene expression by auxin. In an STKE Perspective, Vogt focuses attention on the evolution of olfactory receptors and the molecular mechanisms for perceiving odorants.



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