Documents: Kidz Korner:

10 Neat Things About How Plants Talk
by Dorothy Dobbie
February 5, 2012

1. Help me! Help me!

"I speak for the plants, For the plants have no tongues," observed the Lorax in Dr. Seuss' book, but nevertheless, it is now agreed that plants do communicate, and urgently, when they are under attack. At the very least, they send out puffs of chemical signals to each other and to symbiotic insects, bacteria and fungi. Sometimes, these signals are aimed at the attacker, discouraging it by becoming unappetizing or toxic. Sometimes the signals are aimed at enemies of the attacker, attracting predators to help deal with the invaders.

2. Humans can get the message.

Farmers can detect when their corn crop is under attack by army worms, because the plants emit a sweet odour. The farmer then musters additional defences to help the plants. Not that we should be surprised. Plants have been manipulating human behaviour for eons. We call that manipulation gardening or farming. Huh!

3. Hey! Don't I know you?

Plants can recognize themselves and their own clones. Plants under attack communicate quickly with their cuttings, emitting signals that elicit chemical defences in the cuttings without physical contact.

4. Plant! Heal thyself.

Plants produce antibiotics to ward off bacterial infections. This is in addition to the pesticides they produce to deter insects. One mechanism for triggering these reactions occurs when certain insects bite into a plant. The insect's digestive juices turn proteins into peptide elicitors which are re-injected in the plant with the insect's next bite.

5. Thick skinned.

People and other animals are not the only ones with skin. Plants too have an epidermis that protects vulnerable cells. These cells are further protected by a waxy coating called a cuticle. Bacteria, viruses, fungi, pathogens and even some insects need to find a way through this first line of defence in order to attack and eat or invade the plant. Some pathogens will enter the plant through stomata, the breathing pores of plants that exist on their skins, especially on the underside of leaves. Some will enter through wounds. Certain fungi secrete an enzyme to penetrate the cuticle.

6. Underground railway.

Plant communication can also occur at ground and even underground levels. Stoloniferous plants, those with above ground "runners" such as strawberries, or underground runners such as goutweed, can obviously move information around, physically. But more interesting is the relationship they form with a type of fungus called mycorrhizae that colonize the roots of plants and spread out over very wide areas. Not only can the fungi convey messages, such as disease resistance and defence signals, from plant to plant, they can also carry food in the form of carbon nutrients.

7. W-waves.

In 1989, a physicist named O.E. Wagner said he had discovered something he calls w-waves when he was looking for electrical impulses as a communication methods between trees. He discovered that when he attacked one of the trees in the experiment with an axe, there was an almost instantaneous response from a neighbouring tree. This happened too fast to be explained by either air-transmitted chemicals or electromagnetic waves. He has since refined this theory to include the interaction between all things in a way that transcends gravity. "There are more things in heaven and earth,Horatio ...".

8. Attack of the spider mites.

In Kyoto, an experiment showed that spider mites released to attack lima beans stimulated several defence mechanisms. In addition to releasing chemical signals that changed the flavour of the beans encouraging the spider mites to move on, they also sent out a call for a predator mite that attacked the spider mites. A similar experiment involving army worms signaled parasitic wasps to come and lay eggs in the caterpillars whose larvae eventually killed the worms by eating them.

9. No use wasting good chemicals.

Plants know the difference between an insect attack and someone or something crushing or damaging leaves in another way. Even though the plant being damaged may have been stimulated enough to emit some chemicals, the plants surrounding it ignored those signals.

10. Do plants eavesdrop on their neighbours?

There is some evidence that certain plants can read the signals of unrelated neighbours of a different species. When sagebrush (Artemisia) were put under attack by herbivores and also when clipped with scissors, the tobacco, (Solonacea) plants growing within 10 cm reacted by producing defence chemicals. The clipped plants responded with lower levels of the chemical than those that were attacked by the herbivores.

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