If you think plants can't tell you're touching them, you may want to think again. In fact, a gentle tap or squeeze may trigger a kind of "911" call to all of the plant's cells, placing it on red alert.
"Squeezing the leaves probably gives the plant the feeling that it's already in the jaws of an insect," says Frank J. Turano, a molecular biologist.
A group of students from Eleanor Roosevelt High School in Greenbelt, Md., helped Turano show that even a gentle pat can send a plant's stress levels off the chart.
To a plant, these gentle taps may seem like the soft steps of an approaching insect, sneaking in for a bite to eat. Turano credits the students with helping set the stage for learning how plants make their 911 calls.
Talking, and even singing, to plants to see how they respond is a common science fair project, he notes. But results have been mixed.
Turano's studies suggest maybe it's because students just aren't using the right form of communication. Maybe, the trick is to stop talking and just reach out and touch the plant.
Then, let it do the talking back.
That's what happened when Turano asked the Greenbelt high schoolers to touch the plants at 1-, 2-, 5- and 15-minute intervals. The object of this touchy-feely experiment was a type of wild mustard plant called Arabidopsis thaliana (Uh-rab-ih-DOP-sis thal-ee-ANN-uh). By the way, the picture at left is a test-tube grown plant, not the one used in Turano's experiments.
Turano found that the students' touching set off high levels of two substances called amino acids. They signal that the plant is really stressed out.
It may happen something like this: touching triggers the amino acids' release. They in turn set off a chain reaction that unlocks a gate-like area on cell walls, called receptors.
Through this receptor gate flows a stream of electrically charged molecules called ions. They become part of the 911 call that rapidly alerts other cells--from the plant's top down to its roots. It's probably a long distance call, but one that Ma Nature doesn't charge for (after all, the plant is stressed enough as it is).
Turano says it's possible the plant's long distance calling may send messages a bit like that of our own nervous system.
More research is needed to prove this is what actually happens in plants. For now, it's a hypothesis, he says. Instead of electrical, for example, the plant's SOS signals may turn out to be chemical.
So why worry about plant SOS signals anyway?
At ARS' Climate Stress Laboratory in Beltsville, Turano's job was to find out how plants handle--or don't handle--stress. This can result from severe heat or cold, dryness or flooding or damage from chewing insects, says Turano (he's now a professor at George Washington University in Washington, D.C.).
Eventually, the findings may help plant breeders find ways to breed crop plants that don't get so stressed out.
For the farmer, that could mean more crop to sell as food, fiber or livestock feed and less to throw away.
The stress research could also mean better-adapted trees, beautiful shrubs, flowers and houseplants.
Hopefully, they won't mind being touched--or maybe it's the singing that really bugs them.
--By Don Comis, Information Staff, Agricultural Research Service.