“Talking” Plants: Airborne Chemical Signals

Talking treesJust Keep Talking

The idea of chemical communication among plants has recently gone from being viewed as a fringe idea to an accepted biological phenomenon.

We now know that plants use several different volatile organic compounds not only to send signals from one part of the plant to another part, but also to other nearby plants, to herbivores, and even to predators of those herbivores. (And there are likely more volatile signals that we are unaware of at the present time.)

What are these chemical signals? Where and when are they produced? Do all plants emit such chemicals? And what happens to other plants (and other organisms) when they “smell” these volatile compounds?

Over the next few posts, we’ll explore these and other interesting questions regarding “talking” plants, starting with something minty fresh.

Wintergreen Lifesavers® and Stressed Plants

LifesaversFirst, what is a “stressed” plant?

A plant that’s “stressed” has usually been injured by the physical (cold, heat, drought) or biological (insects, disease-causing microbes) environment.

Such stress often causes the plant to produce an array of defensive compounds. Some of these compounds may help the plant repair itself, some may help to defend the plant, and some may act as chemical signals.

These signals may be produced at the injured part of the plant and travel throughout the plant to trigger systemic defensive mechanisms. Some of these wound signals are volatile, that is, they travel outside the plant.

One such airborne signal is the oil of wintergreen, a.k.a., methyl salicylate.

In 1997, Vladimir Shulaev, Paul Silverman, and Ilya Raskin at Rutgers University first showed that methyl salicylate (MeSA) – in minute quantities – acted as an airborne wound signal in tobacco plants. It may play a similar role in many other plant species. (MeSA is chemically related to acetysalicylic acid, which we know as aspirin.)

Researchers have discovered that plants may emit MeSA in significant quantities into the atmosphere.

Chats1In 2007, they set up specialized instruments (see photo on right) in a walnut grove near Davis, California, to monitor plant emissions of certain volatile organic compounds (VOCs). (These compounds are important because they can combine with industrial emissions to affect pollution. VOCs can also have an influence on local climates.)

To their surprise, they found that the trees emitted significant quantities of MeSA, especially when the plants were stressed by relatively low temperatures and lack of water.

They speculated that the trees use MeSA to trigger defensive responses not only in themselves but also in neighboring plants.

Moreover, these scientists suggested that by monitoring the atmospheric levels of MeSA around groves or fields, farmers may be able to gage the relative stress levels of their crops and respond accordingly.

Next Time: That jasmine tea you’re drinking may be freaking out your houseplants.

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