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“HEY, BRO,” SAID THE SAGEBRUSH
IT MAY SOUND unscientific, but in SCIENCE magazine, January 4, 2019, Elizabeth Pennisi asks, ”Do Plants Favor Their Kin?”
In fact, recent research suggests that individual plants may well help their own relatives, in the same way that animal kin, humans included, occasionally display this altruistic behavior. Back in 2007, Canadian biologist Susan Dudley published a paper claiming that the succulent American searocket, Cakile edentula, identified and helped its kin. Sharing a pot with unrelated plants of the same species, a searocket would greatly expand its root system to maximize its own growth. By contrast, planted with a relative, it would leave room for the kin’s roots to develop as well.
Initially received skeptically, the work of biologist Susan Dudley led other scientists to study plant altruism. Image from Science, January 4, 2019.
The Scientific Method. When a thesis is controversial, the scientific process works in both directions: Can it be reproduced? Does a failure of repletion imply some oddity of the methodology? Can the thesis withstand criticism by colleagues?
Arabidopsis thaliana Mustard Leaf Cooperation. AAAS Science writer Elizabeth Pennisi notes, “About eight years ago, Jorge Casal, a plant biologist at the University of Buenos Aires, noticed that Arabidopsis plants growing next to relatives shift their leaves to reduce shading of their neighbors, but don’t do that when the neighbors are unrelated. How they sense the presence of relatives was a mystery, however.”
Arabidopsis thaliana, a member of the mustard family, plays a role in plant biology akin to Drosophila melanogaster, the common fruit fly, in other biological research: Because of their reproductive characteristics, both are model organisms in genetic studies. Image from Brona at en.wikipedia.
Spanish Herb Research. Rubén Torices and colleagues working at the University of Lausanne in Switzerland and the Spanish National Research Council demonstrated kinship cooperation in plant flowering. They grew 770 seedlings of the Spanish herb Moricandia moricandiodes, either alone or with three or six neighbors of varying relatedness. The result: Plants grown with siblings put out more flowers, making them more alluring to pollinators. Pennisi reports, “The floral displays were especially big in plants in the most crowded pots of relatives.”
Sagebrush Seem Caring Too. When injured by herbivores, sagebrush, Artemisia tridentata, emit volatile chemicals that stimulate neighboring sagebrushes to follow suit with chemicals that are toxic to their shared enemies.
Basin sagebrush, Artemisia tridentata, is one of several woody and herbaceus plants native to the North American west. Image by Peemus.
Subsequent research identified that sagebrush are of two chemotypes, one emitting camphor, the other emitting another organic compound called thujone. Researchers found that the chemotypes are inheritable, making them a potential kin-recognition signal.
In 2014, this signal hypothesis was confirmed by applying one volatile compound or the other to one kind of sagebrush or the other. Sure enough, related plants mounted stronger antiherbivore defenses and had less insect damage.
Practical Applications. Chinese researchers studied rice varieties that give off weed-killing chemicals in their roots. Pennisi writes, “In a three-year field test, kin-recognizing versions of these self-protected rice varieties produced a five-percent increase in yield when grown with kin, rather than unrelated plants.”
Other researchers found that when sunflower kin are planted close together, they lean to stay out of each other’s way. Pennisi writes that the researchers “planted 10 to 14 related plants per square meter—an unheard of density for commercial growers—and got up to 47 percent more oil from plants that were allowed to lean away from each other than plants forced to grow straight up.”
Sunflower, Helianthus, comprises some 70 species, almost all of which are native to North America. Image from Science, January 4, 2019.
Research continues, with Pennisi noting, “To some biologists, the emerging picture of communicating, cooperating plants is still based on thin evidence.” However, she also quotes Richard Karban, ecologist at the University of California, Davis, on application of the scientific method: “We are learning that plants are capable of so much more sophisticated behavior than we had thought. It’s really cool stuff.” ds
© Dennis Simanaitis, SimanaitisSays.com, 2019
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