Goldenrod plants can sense other nearby plants through reports of far-red light and adapt their responses when eaten by herbivores, suggesting a form of plant intelligence. Andre Kessler, a chemical ecologist, argues for plant intelligence by defining it as the ability to solve problems based on environmental information. His research shows that goldenrod releases chemicals to signal neighboring plants to produce defenses against pests. This adaptive behavior and communication via volatile organic compounds shows that plants can process information and respond flexibly to their environment, challenging traditional notions of intelligence. Credit: SciTechDaily.com
New research shows that goldenrod plants demonstrate a form of intelligence by tailoring their responses to herbivores based on the presence of neighboring plants and environmental cues, challenging traditional definitions of intelligence.
Goldenrod can perceive other nearby plants without touching them by sensing the reports of very red light reflected from the leaves. When goldenrod is eaten by herbivores, it adapts its response based on whether or not another plant is nearby. Is this kind of flexible, real-time, adaptive response a sign of intelligence in plants?
The question is not easy to answer, but Andre Kessler, a chemical ecologist, makes a case for plant intelligence in a recent journal paper. Signaling and plant behavior.
Defining intelligence in plants
“There are more than 70 definitions that have been published for intelligence, and there is no agreement on what it is, even within a given field,” said Kessler, a professor in the Department of Ecology and Evolutionary Biology in the College of Agriculture and Life Sciences.
Many people believe that intelligence requires a central nervous system, with electrical signals acting as a medium for information processing. Some plant biologists equate plant vascular systems with central nervous systems and propose that some kind of centralized entity in plants allows them to process information and respond. But Kessler disagrees with this idea.
A goldenrod plant.
“There is no good evidence for any homology with the nervous system, even though we clearly see electrical signaling in plants, but the question is how important is that signaling to a plant’s ability to process environmental signals?” he said.
To make their case for plant intelligence, Kessler and co-author Michael Mueller, a doctoral student in his lab, narrowed their definition down to the most basic elements: “The ability to solve problems based on information you get from the environment. , toward a specific goal,” Kessler said.
As a case study, Kessler points to his previous research investigating goldenrod and its responses to being eaten by pests. When leaf beetle larvae eat goldenrod leaves, the plant releases a chemical that informs the insect that the plant is damaged and is a poor food source. These airborne chemicals, called volatile organic compounds (VOCs), are also taken up by neighboring goldenrod plants, prompting them to produce their own defenses against the beetle larvae. In this way, golden rods move herbivores to neighbors and spread damage.
Experiments and Observations
In a 2022 paper in the journal Plants, Kessler and co-author Alexander Chautá, Ph.D. ’21, experiments were conducted to show that goldenrod can also perceive higher ratios of far-red light reflected from the leaves of neighboring plants. When neighbors are present and goldenrods are eaten by beetles, they invest more in tolerating the herbivore by growing faster, but also begin to produce defensive compounds that help plants fight insect pests. When there are no neighbors present, plants do not use accelerated growth when eaten, and chemical responses to herbivores are markedly different, although they still tolerate fairly high amounts of herbivory.
“That would fit our definition of intelligence,” Kessler said. “Depending on the information it receives from the environment, the plant changes its default behavior.”
Neighboring goldenrod also display intelligence when they perceive VOCs that signal the presence of a pest. “Volatile emission from a neighbor is predictive of future herbivory,” Kessler said. “They can use an environmental cue to predict a future situation and then act on it.”
Applying the concept of intelligence to plants could inspire new hypotheses about the mechanisms and functions of plant chemical communication, while also shifting people’s thinking about what intelligence actually means, Kessler said.
The last idea is timely, since artificial intelligence is a current topic of interest. For example, he said, artificial intelligence doesn’t solve problems toward a goal, at least not yet. “Artificial intelligence, by our definition of intelligence, is not even intelligent,” he said. Rather, it is based on the patterns it identifies in the information it can access.
An idea that interests Kessler came from mathematicians in the 1920s who proposed that perhaps plants functioned more like beehives. In this case, each cell functions as an individual bee, and the whole plant is analogous to a hive.
“What that means is that the brain in the factory is the whole plant without the need for central coordination,” Kessler said.
Instead of electrical signaling, there is chemical signaling throughout the superorganism. Studies by other researchers have shown that each plant cell has broad spectrum light perception and sensory molecules to detect very specific volatile compounds coming from neighboring plants.
“They can smell their environment very accurately; every single cell can do that, as far as we know,” he said. Cells may be specialized, but they also perceive all the same things, and they communicate through chemical signaling to trigger a collective response in growth or metabolism. “This idea is very attractive to me,” he said.
Reference: “Induced Herbivore Resistance and Smart Plants” by André Kessler and Michael B. Mueller, 30 Apr 2024, Signaling and plant behavior.
DOI: 10.1080/15592324.2024.2345985
The work was supported by a grant from the New Fitologist Fund.