We humans are quick to assume that other species are simpler, less complex and capable than we are.  One of our assumptions has been that plants are  passive beings.  They simply grow where they’re planted, defenseless against external threats like an  infestation of insects.

     But plants are proving more capable of defending themselves than we used to think.  Research shows that they are even able to ’warn’ their fellow plants of danger.  For example, in an experiment that included two similar groups of willow trees, a scientist infested one group of the trees with caterpillars.  The other group he left alone.  After two weeks, he plucked leaves from the infested trees and fed them to caterpillars in his lab.  The caterpillars grew very slowly.  When he fed caterpillars a diet of leaves from the non-infested willows, those caterpillars also grew slowly. 

     Upon closer examination, the scientist learned that both groups of willows had flooded their leaves with an unsavory chemical that discourages caterpillar growth.  Not only did the infested group defend themselves by making their leaves unappetizing to the caterpillars, but the trees also, the scientist surmised, communicated a danger signal to the non-infested trees.  The latter group responded to the signal by producing the same chemical to make their own leaves unappealing to caterpillars.

     In another experiment, a scientist potted 45 young poplars.  Thirty of the trees were placed together in an isolated chamber.  The other 15 were put into another isolated chamber, far from the first one.  The scientist ripped the leaves of 15 of the trees  in the first chamber, but left the other 15 trees in that chamber untouched.  Nor did he interfere with the leaves on the trees in the distant chamber.

     After 52 hours, the scientist analyzed leaves from all 45 trees for phenolics, noxious compounds that insects disdain.  The leaves from both the ripped and non-ripped trees in the first chamber showed a significant increase in phenolics, while the leaves of the untouched trees in the distant chamber showed no increase in the compounds.  The research suggests that the trees whose leaves were ripped, reacted to the damage not only by making their leaves unpalatable, but also by ‘tipping off’ the nearby undamaged trees of the need to defend against danger.

     Other scientists have studied the emissions of many plants and trees of the aspirin-like chemical methyl salicylate.  The chemical, emitted when a plant is threatened, such as during an attack by harmful insects, seems to have two benefits.   One is to attract beneficial insects that kill the ones that are attacking the plant.  The other benefit, scientists believe, is to ‘warn’ nearby plants to prepare for a pathogen in the environment.

     I am excited that scientists keep turning up new information about complexities in the natural world, complexities that help us to move away from our simplistic view that what we can observe of the natural world is the way it is, and toward a deeper understanding and appreciation for the intricacies and complexities that are all around us.–April Moore

This entry was posted on Wednesday, May 20th, 2009 at 8:48 am and is filed under Insights and Visions on the State of the Earth. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.