Grass SOS

Grass SOS Photo Credit: aussigall via flickr

Researchers find that the smell of cut grass serves a purpose.


Chemical distress signals. I’m Bob Hirshon and this is Science Update.

The sweet smell of newly cut grass may be a cry for help, according to Texas A&M plant pathologist Mike Kolomiets. He says that before there were lawnmowers, blades of grass were most likely to be cut by the jaws of hungry caterpillars and other herbivores. The strong smelling compound released by the grass attracts parasitoid wasps.

Michael Kolomiets:
So they come to the plant that is being chewed upon by insect herbivores, and lay eggs in caterpillars’ body. And those are parasitoid wasps.

In a study published in The Plant Journal, Kolomiets and his colleagues showed that mutant plants that couldn’t produce the smell compound were ignored by wasps, no matter how many caterpillars were chewing on them. He says scientists are just beginning to understand the role these volatile organic compounds play in both plants and animals. I’m Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

Research into how, or if, plants can communicate is still a relatively new area of inquiry. In recent years, however, scientists have discovered that plants release various chemicals that can act as signals to other plants and, it turns out, to animals.

Dr. Kolomiets and his colleagues are trying to understand how molecular signals function in plants. It appears that when some plants are cut or injured, they produce a hormone (jasmonate) that works to defend the plant against insects. They also can signal distress through the release of volatile organic compounds (VOCs), which are one of a number of chemicals that evaporate or vaporize readily. When an injured plant releases a group of VOCs called green leaf volatiles, they lure beneficial insects to the plants, in this case parasitoid wasps, who respond and lay their eggs in the insects attacking the plant.

What happens, though, if a plant does not have these green leaf volatiles? In the case of some mutant corn plants that did not have the green leaf volatiles, Dr. Kolomiets discovered through lab and field tests that the parasitoid wasps ignored them after they were cut and damaged during testing. According to Dr. Kolomiets, “We have proven that when you delete these volatiles, parasitoid wasps are no longer attracted to that plant, even when an insect chews on the leaf. So this volatile is required to attract parasitoids."

There are two roles, then, for the green leaf volatiles:

  1. They activate the jasmonate hormone, which involves activation of defenses against insects on the plant.
  2. They attract parasitoid wasps. They come to the plant that is being chewed up by insect herbivores and lay eggs in the caterpillar’s body.

But why would scientists be interested in finding out how plants react when they are injured or cut? It turns out that how plants react to stress has an impact on how well they could survive drought or infestations. If scientists can determine exactly what happens to plants when they are injured or cut, it may help plant breeders know how to develop new varieties that are more resistant to insects and drought.

Now try and answer these questions:

  1. What is the the new element in this research?
  2. What are VOCs? How do they work?
  3. What might this research lead to?

You may want to check out these other resources:

In Eavesdropping Plants, you can learn about a study that offers an example of the many sophisticated ways that a plant can respond to its environment.

When people feel stressed, their hearts start beating fast, they breathe harder, and their stomach ties in knots. But what happens when trees get stressed? You can find out in Atmospheric Aspirin.

Going Further

For Educators

In addition to the Science Updates mentioned, you can extend the concepts in this lesson by helping your students explore other examples of how organisms use some unique survival strategies in Periodical Cicada Survival and Cicada Emergence.

Your students also can learn more about beneficial insects by reading Beneficial Lawn Insects, from the University of Massachusetts–Amherst.

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