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2478580538 ca063478e2 bSmells Like Trouble

If you’re crunching on a Wintergreen Lifesaver®, while drinking a cup of jasmine tea, you may be totally “freaking out” your nearby house plants.

Why?

Because you’re disseminating two volatile organic compounds known to have significant effects on plants, you may be inadvertently turning on hundreds of defense-related genes in your plants.

The two organic compounds in question are methyl salicylate (a.k.a., oil of wintergreen), which was discussed in the previous post, and methyl jasmonate (MeJA).

It turns out that MeJA was one of the first compounds implicated in plant-to-plant communication. In 1990, Bud Ryan and colleagues at Washington State University reported (ref. 1 below) that MeJA produced by sagebrush plants was able to elicit chemical defenses in adjacent tomato plants. Subsequent studies showed that many biotic and abiotic stresses (particularly herbivory and wounding) cause some plants to release MeJA into the air.

We now know the plants used both MeJA and methyl salicylate (MeSA) as volatile wound signals that can quickly travel from a wounded leaf or stem, for example, to other parts of the plant. (e.g., ref. 2 below) These airborne signals can enter the plant via the stomates. Once inside, they trigger a cascade of cellular signaling events that results in the production of defensive chemicals such as phytoalexins and protease inhibitors. Both of these compounds help protect the plant against disease-causing microbes.

While we are on the subject of airborne wound signals, let’s not forget that the gaseous plant hormone ethylene also plays a role in eliciting wound responses in plants, though it’s likely more well-known as promoting fruit ripening.

Such airborne wound signals can travel much faster throughout the plant than chemical signals that travel through the plant’s vascular system (phloem). Thus the plant is able to more quickly muster chemical defenses against potential attacks, which may increase its chances of survival.

Heard It Through The Grapevine

One of the interesting side effects of using airborne wound signals is that other plants may be able to “eavesdrop” and to benefit from their wounded neighbor.

It’s been shown that even minuscule levels of MeJA and MeSA can affect plants up to several feet away from the source.

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This raises all sorts of interesting ecological and evolutionary questions. If other plants are able to “eavesdrop” and benefit from airborne wound signals, wouldn’t plants then be providing help to potential competitors?

Indeed, one of the early criticisms of the research on MeJA was that experiments were done entirely in enclosed greenhouses. Thus, these results may not have had relevance to the “real world”.

Recent experiments addressing this question have shown that the presence of nearby wounded plants in the field may indeed increase disease resistance of adjacent plants.
This effect also seems to work across species, although there is some evidence to suggest that this effect works best among closely related plants.

Surprisingly, some have speculated that such airborne wound signals may participate in kin selection in plants. (e.g., see ref. 4 below) Such kin selection has historically been limited to animals. But new evidence suggests that plants may favor their relatives by “talking” to them and alerting them of danger, more so than to non-relatives.

Sap is thicker than water?

Next time: A parasitic plant sniffs out its victims.

References

1. Farmer, E. E. and C. A. Ryan (1990) “Interplant communication: Airborne methyl jasmonate induces synthesis of proteinase inhibitors in plant leaves.” Proceedings of the National Academy of Sciences (USA), Vol. 87, pp. 7713-7716. (Full Text)

2. Reymond, P. and E. E. Farmer (1998) “Jasmonate and salicylate as global signals for defense gene
expression.” Current Opinion in Plant Biology, Vol. 1, pp. 404–411. (Full Text – PDF)

3. Farmer, E. E. (2001) “Surface-to-air signals.” Nature, Vol. 411, pp. 854-856.

4. Karban, R. and K. Shiojiri (2010) “Identity recognition and plant behavior.”
Plant Signaling & Behavior, Vol. 5, pp. 854-855. (Full Text)

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