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Leaves of young maize plants are wounded. Their defense mechanisms are then activated by adding insect oral secretions. The volatile compounds can subsequently be transferred from one plant to another using glass bottles and a special airflow system, and defense responses can then be determined in real-time.
Photo Credit: © Kastriot Bajaktari
Scientific Frontline: Extended "At a Glance" Summary: Volatile-Mediated Plant Defenses
The Core Concept: Uninjured neighboring plants detect rapidly transmitted green leaf volatiles from an attacked plant and release their own defensive compounds even earlier than the damaged plant itself.
Key Distinction/Mechanism: Contrary to the expectation that injured plants would emit secondary defensive compounds first, damaged leaves quickly close their stomata to prevent water loss. Meanwhile, undamaged neighboring plants keep their stomata open, allowing them to freely synthesize and release defensive volatiles immediately upon sensing the initial chemical warning.
Origin/History: A study published in the Proceedings of the National Academy of Sciences on October 28, 2026, by researchers at the Institute of Plant Sciences at the University of Bern, documented this phenomenon using automated mass spectrometry.
Major Frameworks/Components:
- Green leaf volatiles: Act as the rapid, primary chemical warning signals emitted from wound sites within seconds to minutes of an attack.
- Stomatal regulation: The physiological opening and closing of leaf pores, which dictates a plant's physical capacity to emit synthesized defensive compounds.
- Isotopic labeling: The use of heavy carbon isotopes to conclusively prove that neighboring plants synthesize their own defensive compounds rather than simply reflecting the wounded plant's emissions.
- Multitrophic signaling: The ecological framework in which plant-emitted volatiles serve as "guide signals" to attract beneficial insects that prey on herbivorous pests.
Branches of Science: Plant Physiology, Chemical Ecology, Molecular Botany, and Agricultural Science.
Future Application: This mechanism could be harnessed to develop targeted agricultural strategies that activate the natural defenses of crop plants, significantly reducing the need for synthetic pesticides.
Why It Matters: This discovery reveals a highly synchronized chemical communication network in which undamaged neighboring plants act as early amplifiers of defensive signals, better protecting entire plant populations from pest infestations.
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| Dr. Tristan Cofer places a maize plant in a glass bottle to measure its volatile emissions. Photo Credit: © Kastriot Bajaktari |
Plants detect volatiles from their attacked neighbors and respond by activating their own defenses. Previously, it was unclear how quickly these reactions occur in direct comparison to the attacked plant, and which volatiles are responsible.
Researchers at the Institute of Plant Sciences at the University of Bern have now shown for the first time that uninjured maize plants release certain defensive compounds even earlier than their injured neighbors. At first glance, this almost seems like telepathy. How can a neighboring plant react faster to an attack than the damaged plant itself? The solution to this puzzle lies in the identity of the volatiles transmitted between the plants.
Simulated caterpillar feeding triggers a defense response
For their experiments, the researchers connected two maize plants via a controlled airflow. On one plant, they simulated caterpillar feeding by scratching the leaf and applying caterpillar oral secretions. The second plant remained undamaged and received the volatiles from the first plant via the airflow. An automated measurement system—combining a mass spectrometer with a specially developed automated sampling system—recorded the release of volatile emissions every 15 minutes. In addition, the team examined defense hormones, gene activation, the levels of volatiles in the leaves, and the opening of the plants’ stomata—through which they absorb and release volatiles.
“We had expected the undamaged neighboring plants to react somewhat later than the plants that were directly attacked, since they first have to absorb and process the volatiles from the injured plant,” says Dr. Matthias Erb of the Institute of Plant Sciences at the University of Bern. “The fact that they released many defensive compounds faster than the attacked plant itself seemed contradictory at first.”
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The mass spectrometer measures volatile compounds in real time. It automatically moves between the various sources of volatile compounds, making it possible to analyze over 100 plants in less than 30 minutes. This system was developed in collaboration with external partners at the University of Bern and is the only one of its kind in the world.
Photo Credit: © Kastriot Bajaktari
The smell of freshly cut grass as a warning signal
Eventually, the scientists found the solution. Genetically modified maize plants lacking certain volatiles were the key. “Our experiments with these plants showed that so-called green leaf volatiles are necessary for the neighbors’ rapid defense response,” explains Dr. Tristan Cofer, the study’s first author. These green leaf volatiles are released by injured plants from the wound sites within seconds to minutes, long before other defensive volatiles are produced and released. The neighboring plants detect them as an early chemical warning signal and subsequently begin to produce the other defensive volatiles. Labeling one of these volatiles with a heavy carbon isotope provided direct evidence that the neighboring plants synthesize it themselves and then release it more quickly than the source plants.
Open stomata could explain the head start
It was also surprising that the neighboring plants did not increase defense hormone levels or volatile production earlier. “The difference seems to lie primarily in the release,” says Cofer. Damaged leaves quickly close their stomata, presumably to limit water loss. The undamaged neighboring plants initially keep these tiny openings on the leaf surface open and may therefore be able to release their volatiles earlier. However, direct evidence of the causal role of the stomata is still lacking. It could also be that the neighboring plants transport their volatiles out of the cells more quickly.
New questions for plant protection
Undamaged neighboring plants thus become additional sources of defensive compounds early on. “We want to understand whether undamaged neighboring plants reinforce the defense of the attacked plant and whether their defensive compounds help beneficial insects locate pests,” says Erb. Infested plants attract natural enemies of the pests with scents. If undamaged neighboring plants amplify the scent signal from the infested plant, beneficial insects could be attracted from farther away and find the infested plant via the undamaged “guide plant.” In the long term, understanding these various, sequential processes could help activate the natural defenses of crop plants in a more targeted manner and reduce pesticide use. The researchers still need to investigate whether the observed head start in the release of defensive compounds plays a major role in the field.
Funding: The study was supported by the Swiss National Science Foundation, the State Secretariat for Education, Research, and Innovation (SERI) as part of replacement funding for an ERC Consolidator Grant, and the University of Bern.
Published in journal: Proceedings of the National Academy of Science
Authors: Tristan M. Cofer, Lingfei Hu, Gaetan Glauser, and Matthias Erb
Source/Credit: University of Bern
Edited by: Scientific Frontline
Reference Number: bot102926_01
