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Plants Smell Danger

Plants Smell Danger Insect on goldenrod plant
Photo Credit: Walter Siegmund [GFDL or CC-BY-SA-3.0-2.5-2.0-1.0], via Wikimedia Commons

A type of plant can sense mating chemicals from fruit flies, and builds up its defenses when it does.


Transcript

Plants that sniff out threats. I’m Bob Hirshon and this is Science Update.

Male fruit flies use chemical odors to attract mates. But to plants called goldenrods, these amorous scents spell danger. That’s because after the flies mate, the females lay their eggs in the goldenrod’s stem, damaging the plant. Penn State University entomologist Mark Mescher and his colleagues found that goldenrod plants can actually detect the fruit fly smell. And when they do, they build up their defenses accordingly.

Mescher:
So the plant is actually producing toxins and so forth, that are defending itself against the herbivores, and we can see that that’s stronger in plants that have previously been exposed to this odor.

It’s already known that some plants can detect distress chemicals from nearby plants that are being attacked by insects. But this is the first time a plant’s been shown to respond to a chemical from the enemy itself. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Plants can’t talk or make noise, but they can communicate with one another, and we’re learning more about how they do it all the time. Thirty years ago, a study published in the journal Science revealed that poplar and maple trees release certain chemicals when attacked by insects, and that healthy trees nearby responded to these chemicals by building up anti-pest defenses. Other plants communicate by exchanging chemical signals through their leaves, stems, or roots. And it’s not just plants that are involved: Tomato plants, when attacked by caterpillars, send out a signal that attracts caterpillar-eating wasps.

So, we know that plants can signal other plants, and helpful insects. But this is the first known case of a plant detecting chemicals from a harmful pest—chemicals which serve an entirely different purpose to the fruit flies that release them. For the fruit flies, the chemicals are romantic perfumes that attract mates. But after they mate, females deposit their eggs in the goldenrod’s stem. When the eggs hatch a few weeks later, the stem develops a bulging growth called a gall, which impairs its ability to germinate.

In other words, flies trying to mate nearby spell bad news for goldenrod plants. So over the years, the plants have developed a clever adaptation: they can detect and respond to the fly chemicals that signal that mating is about to take place. By the time the flies come to lay their eggs, the goldenrods have built up protective chemicals that protect them from damage.

You might ask why the plants don’t simply carry this level of protection all the time. It’s a good question, and no one knows the precise answer. But in cases like this, evolutionary biologists usually assume that there’s some kind of cost to producing these defensive chemicals at higher levels. For example, it may take resources away from the plant’s other essential functions. That would explain why they scale up the protection only when it’s needed.

Now try and answer these questions:

  1. What are some ways that plants communicate?
  2. What’s new and different about the findings of this study?
  3. Why do the plants use the fly’s mating chemicals as a cue to build up their defenses?
You may want to check out the January 4, 2013, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: Why we might be better tree climbers than we think, what ancient wells can tell us about Neolithic technology, plants that sense pests, and exploring the growing link between fructose consumption and obesity.
 

Learn about other forms of plant communication in the Science Updates Eavesdropping Plants, Plant Kin Help, and Atmospheric Aspirin.

Nematode worms communicate chemically as well. Learn more in Worm Language.


Going Further


For Educators

Learn about other forms of plant communication in the Science Updates Eavesdropping PlantsPlant Kin Help, and Atmospheric Aspirin.

Nematode worms communicate chemically as well. Learn more in Worm Language.


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