Plant Articles
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“Common Scents: Plants Constantly Catch a Whiff of Their Neighbors’ Perfume”Scientific American, May 22, 2012http://www.scientificamerican.com/article.cfm?id=what-a-plant-smells&page=2Summary
This article describes recent findings about pheromonal interaction among plants and their neighbors. Cuscuta pentagona, more commonly known as dodder, is a plant of unusual appearance, comprised of an orange vine and small white flowers. It does not have leaves, and since it is not green it does not contain chlorophyll, and therefore is unable to carry out photosynthesis. What makes it especially peculiar it the fact that is a parasitic heterotroph; it needs a host organism in order to survive. After a dodder seed begins to grow, its shoot tip acts like a hand, searching around its environment for the leaf of a nearby plant. The dodder’s plant of choice appears to be the tomato plant. Once it locates the leaf, the microprojection of the dodder burrows into the soil and locates the tomato plant’s stem. It then coils around the stem and sinks its probing microprojections into the phloem tissue of the plant stem. The dodder has now created a tube by which it can rob its neighbor plant of nutrients. Consuela De Moraes, a scientist at Penn State, performed several experiments investigating the behavior of Cuscuta. Her work showed that dodder will always grow toward a tomato plant, no matter what the situation. This led Moraes to believe that the dodder “actually smelled the tomato” (Scientific American). She placed a dodder plant in a sealed box and a tomato plant in another sealed box. She connected the two boxes with a tube so that air could be exchanged. Sure enough, the dodder grew toward the tube connecting it to the tomato box. Moraes then created a tomato “perfume” to test if the dodder really could smell the tomato plant. She soaked cotton swabs with a tomato extract and placed these in a dodder’s pot, along with the solvents she created the tomato perfume with as a control. Once again, the dodder grew toward the tomato. Another experiment placed a dodder between a wheat plant and a tomato plant; still the dodder grew toward the tomato. Reasons behind this include pheromones and chemical odors. Tomato plants give off three volatile chemicals that attract the dodder, while wheat only harbors one. Wheat also contains an acetate that the dodder retracts from.
Another interesting experiment in plant communication is an experiment in 1983 testing communication between trees. Two scientists from the University of Washington observed that when caterpillars infected a willow tree, the other trees near it often remained healthy. They decided that somehow the infected tree was able to send a pheromone to the healthy trees, warning them of the caterpillar threat. Several other scientists performed experiments investigating the quality of the air around healthy plants and plants infected with caterpillars. They deduced that when a leaf is damaged, it develops higher levels of caterpillar-repelling chemicals, and pheromones pertaining to these chemicals are released, alerting nearby trees. Yet another team of scientists concluded that this was a form of “olfactory eavesdropping,” and the pheromonal signal was meant for the rest of the leaves on the infected plant that were still healthy, warning them and effecting the production of caterpillar-inhibiting chemicals. Other plants “eavesdropped” on the pheromonal signal and odors released, and followed the infected plant’s instructions.