Poison Ivy

Podcast

Poison Ivy

Transcript

What puts the itch in poison ivy? I'm Bob Hirshon and this is Science Update.

Perhaps a recent hike in the woods prompted Tim Appenzeller of Washington, D.C. to ask why touching poison ivy makes you itch. We asked weed scientist Joe Neal of North Carolina State University. He says poison ivy gets its itching power from compounds called urushiols.

Neal:

And all of the poison ivy, poison oak, poison sumacs, have these compounds in their leaves, their stems, their fruit, their flowers and the roots, and even the wood of the vines. This material causes allergic dermatitis.

That means that once urushiol is absorbed through the skin, it causes itching and inflammation, as the immune system tries to get rid of the substance. Dr. Neal says that no one really knows why poison ivy developed this kind of defense, but it may be to keep from being eaten.

Neal:

If you're itching to ask a science question, call us at 1-800-WHY-ISIT. If we use it on the show you'll get a free Science Update mug. For the American Association For The Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Despite the fact that they cannot move around, plants are hardly defenseless. Plants have effective chemical defenses specifically designed to deter animals from eating them. Some of these toxic chemicals simply discourage a plant predator by making the plant unpalatable; others can sicken or even kill the animal. In some cases the compounds fend off predators only until the plant has matured; then the toxicity decreases so that the fruit can be eaten, and the seeds dispersed.

You could use this Science Update to begin a study of the amazing diversity of chemical substances found in plants, or more generally, to the defense mechanisms that plants and animals use to protect themselves from predators.

Now try to answer the following questions:

1. What causes people to itch once they've been exposed to poison ivy?
2. What role does the immune system play in the allergic reaction?
3. Why would a plant produce an irritant? What evolutionary advantage would this plant have?
4. What defenses do animals have to keep from being eaten? How many of these animal defenses require mobility? Do you think plants or animals would have a greater reliance on chemical defenses? Why?
5. Can you think of a way in which a toxic chemical might help a plant protect itself from other plants?

Going Further

For an introduction to poisonous and allergenic plants, go to Poisonous and Allergenic Plants from the University of Maryland's Undergraduate Program in Plant Biology. This set of lecture notes provides a broad overview of the topic, as well as links to relevant photos and articles.

For general information on poison ivy, go to Poison Ivy: Prevention and Treatment from the InteliHealth website.

For a lesson that explores how the immune system functions in a variety of allergic reactions, go to the Science NetLinks lesson entitled The Allergy Chronicles.