February 21, 2006 | David F. Coppedge

Of Talking Trees and Plant Perfumes


It’s not just Middle Earth where the trees talk. The forests of Regular Earth have a language, too: a chemical language called the “invisible bouquet” by Pamela J. Hines, introducing a special series of articles on plant communication in Science.1

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.

The “aromatic story” of plant volatiles is described in detail in three papers in the same issue of Science. Pichersky, Noel and Dudareva characterize the complex chemistry of many of these compounds produced by plants as “nature’s diversity and ingenuity.”2 These compounds don’t just happen; they are constructed in complex stepwise fashion like technical lab work in organic chemistry, involving methylation, acylation, oxidation/reduction, and formation of aromatic rings. Plants have specialized enzymes for these tasks. The authors’ description of the assembly of compounds that make roses smell sweet is mind-numbingly technical. What’s more, the compounds are produced by specialized cells, containing storage vacuoles and mechanisms for timed release into the air. Though the authors believe these processes evolved by gene duplication and diversification, they note that “Convergent evolution is often responsible for the ability of distally related species to synthesize the same volatile.”

Whether or not one agrees with that hypothesis, it must surely be surprising to learn that we know of 1,000 such compounds so far, with probably many times that waiting to be discovered. Other estimates in the magazine suggest tens of thousands or hundreds of thousands of primary and secondary metabolite chemicals made by plants, all with diverse biological properties and functions. How plants manufacture, store and emit these chemicals is a neglected area of study, the authors say. Another paper Baldwin et al.3 actually mentions “talking trees” –

Plants may “eavesdrop” on volatile organic compounds (VOCs) released by herbivore-attacked neighbors to activate defenses before being attacked themselves. Transcriptome and signal cascade analyses of VOC-exposed plants suggest that plants eavesdrop to prime direct and indirect defenses and to hone competitive abilities. Advances in research on VOC biosynthesis and perception have facilitated the production of plants that are genetically “deaf” to particular VOCs or “mute” in elements of their volatile vocabulary. Such plants, together with advances in VOC analytical instrumentation, will allow researchers to determine whether fluency enhances the fitness of plants in natural communities.

The phrase “talking trees” has actually been used by scientists to explain interplant communication; whether it is talking or eavesdropping may just be a point of view. Experiments have shown that plants rendered “deaf” to these signals are more susceptible to harm.

The last of the series of special articles on plant volatiles is of interest to us humans. Why do spices attract our taste buds? It may be that our own sense of smell is keen to which plants are healthy and which are toxic. Stephen Goff and Harry Klee4 investigated whether plant volatiles provide clues for health and nutritional value. There is evidence that “the important flavor-related volatiles are derived from essential nutrients.” They add, “Although a single fruit or vegetable synthesizes several hundred volatiles, only a small subset generates the ‘flavor fingerprint’ that helps animals and humans recognize appropriate foods and avoid poor or dangerous food choices.” Maybe we all need to practice a lost skill, and start sniffing more intently in the woods or in the supermarket.

1Pamela J. Hines, “The Invisible Bouquet,” Science 10 February 2006: Vol. 311. no. 5762, p. 803, DOI: 10.1126/science.311.5762.803.
2Pichersky, Noel and Dudareva, “Biosynthesis of Plant Volatiles: Nature’s Diversity and Ingenuity,” Science 10 February 2006: Vol. 311. no. 5762, pp. 808 – 811, DOI: 10.1126/science.1118510.
3Baldwin et al., “Volatile Signaling in Plant-Plant Interactions: ‘Talking Trees’ in the Genomics Era,” Science 10 February 2006: Vol. 311. no. 5762, pp. 812 – 815, DOI: 10.1126/science.1118446.
4Stephen A. Goff and Harry J. Klee, “Plant Volatile Compounds: Sensory Cues for Health and Nutritional Value?”, Science 10 February 2006: Vol. 311. no. 5762, pp. 815 – 819, DOI: 10.1126/science.1112614.

Had you ever given much thought to this amazing phenomenon? If you have ever studied organic chemistry, you know how complicated synthesis of particular compounds can be. Plants do this kind of synthesis in hundreds of thousands of ways, easily and purposefully, via complex enzymes. The enzymes, furthermore, do not just perform at random in the cell, but deliver their messaging molecules with storage and emission machinery. This is all in addition to the sophisticated “interplant internet” processes that keep the individual plant in touch with itself (11/09/2004, 08/12/2005).

Animal and human olfactory senses also require extremely sophisticated mechanisms for detecting, transmitting and decoding these signals (08/31/2005, 06/07/2005). The whole picture is one of rich symbiosis involving numerous organisms working together to maintain a rich and diverse ecology.

The “warfare of nature” metaphor may be misleading (plants being “attacked” by insects, etc.; see 07/04/2003 “Metaphors Bewitch You”). It may be more appropriate to think of these interactions as checks and balances in a homeostatic system. In a dynamic world (picture ice hockey players with everyone in motion), there need to be ways to accelerate some processes and put the brakes on others. Catastrophic imbalances that lead to devastation or extinction may reflect not so much on the design of an originally perfect creation, but on the judgment of a cursed world.

Evolutionists want us to believe that all this complexity and interconnectedness is the result of blind, unguided, processes that managed to accumulate single benefits of rare beneficial mistakes here and there. This story should remind us of how improbable that explanation is. As usual, the evolutionists failed to offer detailed scenarios of how the enzymes, vacuoles, emitters and sensory organs evolved. They merely assumed that they did, somehow, even to the absurd length of invoking that old hand-waving trick, “convergent evolution.”

Don’t let the fallacies of fallible humans ruin your day. Plant volatiles enrich our lives and make the world beautiful and informative. Get out and smell the roses and tomatoes.

It was hip during the new age fad to talk to your house plants. Whether they listened to your words or not is debatable, but they might have been eavesdropping on your own VOCs. Your wilting ficus or rhododendron might be trying to tell you something.

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Categories: Amazing Facts, Botany

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