Martin Heil and his team at the Center for Research and Advanced Studies in Irapuato, Mexico, have been studying wild lima beans (Phaseolus lunatus) for the past several years to further explore this question. Heil knew that scientists had observed that when a lima bean plant is eaten by beetles, it responds in two ways. The leaves that are being eaten by the insects release a mixture of volatile chemicals into the air, and the flowers (though not directly attacked by the beetles) produce a nectar that attracts beetle-eating arthropods. Early in his career at the turn of the millennium, Heil had worked at the Max Planck Institute for Chemical Ecology in Jena, Germany, the same institute where Baldwin was (and still is) a director, and like Baldwin before him Heil wondered why it was that lima beans emitted these chemicals.
Heil and his colleagues placed lima bean plants that had been attacked by beetles next to plants that had been isolated from the beetles and monitored the air around different leaves. They chose a total of four leaves from three different plants: from a single plant that had been attacked with beetles they chose two leaves, one leaf that had been eaten and another that was not; a leaf from a neighboring but healthy “uninfested” plant; and a leaf from a plant that had been kept isolated from any contact with beetles or infested plants. They identified the volatile chemical in the air surrounding each leaf using an advanced technique known as gas chromatography/mass spectrometry (often featured on the show CSI and employed by perfume companies when they are developing a new fragrance).
Heil found that the air emitted from the foraged and the healthy leaves on the same plant contained essentially identical volatiles, whereas the air around the control leaf was clear of these gases. In addition, the air around the healthy leaves from the lima beans that neighbored beetle-infested plants also contained the same volatile chemicals as those detected from the foraged plants. The healthy plants were also less likely to be eaten by beetles.
But Heil was not convinced that damaged plants “talk” to other plants to warn them against impending attack. Rather he proposed that the neighboring plant must be practicing a form of olfactory eavesdropping on an internal signal actually intended for other leaves on the same plant.
Heil modified his experimental setup in a simple, albeit ingenious, way to test his hypothesis. He kept the two plants next to each other but enclosed the attacked leaves in plastic bags for 24 hours. When he checked the same four types of leaves as in the first experiment, the results were different. While the attacked leaf continued to emit the same chemical as it did before, the other leaves on the same vine and neighboring vines now resembled the control plant; the air around the leaves was clear.
Heil and his team opened the bag around the attacked leaf, and with the help of a small ventilator usually used on tiny microchips to help cool computers, they blew the air in one of two directions: either toward the neighboring leaves farther up the vine or away from the vine and into the open. They checked the gases coming out of the leaves higher up the stem and measured how much nectar they produced. The leaves blown with air coming from the attacked leaf started to emit the same gases themselves, and they also produced nectar. The leaves that were not exposed to the air from the attacked leaf remained the same.
The results were significant because they revealed that the gases emitted from an attacked leaf are necessary for the same plant to protect its other leaves from future attacks. In other words, when a leaf is attacked by an insect or by bacteria, it releases odors that warn its brother leaves to protect themselves against imminent attack, similar to guard towers on the Great Wall of China lighting fires to warn of an oncoming assault.
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Add CommentThis is awesome!!
Reply | Report Abuse | Link to thisThis is awesome!!
Reply | Report Abuse | Link to thisRe: "other flora throughout our natural world respond to pheromones, just as we do. Plants detect a volatile chemical in the air, and they convert this signal (albeit nerve-free) into a physiological response. Surely this could be considered olfaction."
Reply | Report Abuse | Link to thisThe concept of human pheromones has been challenged -- even by olfactory researchers like Richard L. Doty in his book "The Great Pheromone Myth." Cearly, however, the concept is one of olfactory/pheromonal communication that must occur for any species of plant or animal to survive. Nutrient chemicals, for example, calibrate invidual survival via their epigentic effects on intracellular signaling. The nutrients metabolize to pheromones that standardize and control reproduction.
The common molecular mechanisms place the human pheromone-deniers in a catagory that could only be reserved for those who think that plant odors (as in food odors) do not have the same epigenetic effects on intracellular signaling as pheromones do in species from microbes to man. How (e.g.,on earth) could humans not produce and respond to pheromones. Are we evolutionarily adapted outliers due to random mutations, or is our behavior consistent with the epigenetic effects of nutrient chemicals and pheromones on pre-existing genetic variability across all species?
Oh my God! I love this article. I have watched this plant my whole life and I could never find any information on it, so I always called it what my American Indian (Shawnee) mother called it - 'Love Tangle'. It always infested a weed (which is popular in South Central West Virginia), my brother and I called, 'Sword Weed'; strip the leaves off the Sword Weed (if you can withstand the pungent smell) and the stem is strong enough to use as a sword in play (I always won by brother in sward play because he was two-years younger than me.). We had tomatoes growing in a garden beside the Sword Weed and the Dodder always preferred the Sword Weed. The Sword Weed is a very pungent plant, more so than the tomato, but since the Sword Weed has no beneficial medical properties, we Indians had no interest in it. I have never seen the Dodder bloom because the Squirting Cucumber (Touch-Me-Not) always chocked it out and killed it before harvest, or blooming time.
Reply | Report Abuse | Link to thisThis is the best article I have read on SciAm. My complements to the author, Daniel Chamovitz.