There’s long been a theory that talking to plants can help them grow better. But what if plants themselves could “talk” to each other? That’s a question that André Kessler, professor of ecology and evolutionary biology, and his research team addressed over a 12-year study that examined plant-to-plant communication in goldenrod.
According to their research, published Sept. 23 in Current Biology, plants actually do have a way of talking to each other. Their messages come embedded in the form of airborne chemicals known as volatile organic compounds (VOCs), which transfer information among plants.
The project looked at Solidago altissima, a species of goldenrod native to the Northeast, and monitored the impact of a specific herbivore: the goldenrod leaf beetle.
The big finding in the study is what Kessler calls “open-channel communication.” Based on their genotypes, different plants have different smells. But when plants come under attack from pests like the goldenrod leaf beetle, their smells – carried by VOCs – become more similar.
“So they kind of converge on the same language, or the same warning signs, to share the information freely,” Kessler said. “The exchange of information becomes independent of how closely related the plant is to its neighbor.”
The research found that neighboring plants pick up on warning VOCs and prepare for the perceived threat, such as an oncoming insect pest. Said Kessler: “A (VOC) emitted by one plant can be picked up by another plant, and they can either ready their defenses or they may actually directly induce those defenses.”
However, their goodwill toward plant neighbors only works on an if-you-see-something-say-something basis and when, as a result of the communication, pest pressure is equally distributed across the plant population. Plants in populations without herbivores do not freely share information with their neighbors. Instead, they maintain a private channel with their closest kin through VOC emissions that induce resistance – but only in those relatives or plant parts distant from the damage site on the same plant.
“We code our language if we want to keep it private, and that’s exactly what happens there, but on a chemical level,” Kessler said. “That analogy is striking and not what we expected.”
“What we very often see when plants get attacked by pathogens or herbivores is, they change their metabolism,” Kessler said. “But it’s not a random change – in fact, those chemical and metabolic changes are also helping them cope with those attackers. It’s very much like our immune system: Though plants don’t have antibodies like we have, they can fight back with pretty nasty chemistry.”
That chemistry includes defensive compounds. “Some of the VOCs can be attractive to predacious insects, or parasitoids, which then come in and kill the herbivore, and the plant is saved. We call that indirect defense,” Kessler said.
Another defense mechanism is the VOCs themselves. Previous research from Kessler’s team found that insect larvae avoid plants that emit these warning VOCs, regardless of whether the plants have already been damaged.
Such findings could have practical applications around the world.
“For a long time, people have thought about using plant-to-plant interactions in organic agriculture to protect crop plants, especially when you have intercropping systems,” Kessler said. “We are involved in work on a system in Kenya – called ‘push-pull’ and developed by the International Center for Insect Physiology and Ecology – which is based on manipulating the flow of information to control a pest in corn fields.”
Co-lead authors were Aino Kalske, from the department of biology at the University of Turku, Finland; and Kaori Shiojiri, from the department of agriculture at Ryukoku University, Japan. Also contributing was Kimberly Morrell, Ph.D. ’15, formerly of the Kessler lab and now a research entomologist at Bayer Crop Science.
Other contributors were from Monash University, Australia; and Akita Prefectural University, Japan.