Goldenrod plants can sense other nearby plants through the ratio of far-red light and adjust 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 information about the environment. His research shows that goldenrod sends out chemicals that signal neighboring plants to mount defenses against pests. This adaptive behavior and communication through volatile organic compounds suggests 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 sense other nearby plants without ever touching them by sensing the ratios of far-red light reflected from the leaves. When goldenrod is eaten by herbivores, it adjusts its response depending on whether another plant is nearby. Is this kind of flexible, adaptive, real-time response a sign of plant intelligence?
This is not an easy question to answer, but Andre Kessler, a chemical ecologist, argues for plant intelligence in a recent journal article Plant signaling and behavior.
Defining intelligence in plants
“There are more than 70 definitions that are published for intelligence, and there is no consensus on what it is, even within the 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 liken plant vascular systems to central nervous systems and suggest that some sort of centralized entity within the plant allows them to process information and respond. But Kessler strongly disagrees with this idea.
Goldenrod plant.
“There is no good evidence for any of the homologies with the nervous system, although we clearly see electrical signaling in plants, but the question is how important is this signaling to the plant’s ability to process environmental stimuli?” He said.
Arguing for plant intelligence, Kessler and co-author Michael Mueller, a PhD student in his lab, narrowed their definition down to its most basic elements: “The ability to solve problems based on information you get from the environment. to a specific goal,” Kessler said.
As a case study, Kessler points to his earlier research examining goldenrod and its response when eaten by pests. When beetle larvae eat goldenrod leaves, the plant releases a chemical that tells the insect that the plant is damaged and a poor food source. These airborne chemicals, called volatile organic compounds (VOCs), are also picked up by neighboring goldenrod plants, leading them to develop their own defenses against the beetle larvae. In this way, the goldenrod moves the herbivores to its neighbors and distributes the damage.
Experiments and observations
In a 2022 journal article Plants, Kessler and co-author Alexander Chautá, Ph.D. ’21 conducted experiments which showed 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 herbivore tolerance by growing faster, but also start producing defense compounds that help the plants fight off insect pests. When no neighbors are present, the plants do not resort to accelerated growth when consumed, and the chemical responses to herbivores are markedly different, although they still tolerate relatively large numbers of herbivores.
“That would fit our definition of intelligence,” Kessler said. “Depending on the information the plant receives from the environment, it changes its default behavior.”
Neighboring goldenrods also display intelligence when they sense VOCs that signal the presence of a pest. “The fugitive emissions coming from a neighbor predict future herbivory,” Kessler said. “They can use the environmental cue to predict the future situation and then act accordingly.”
Applying the concept of intelligence to plants can inspire new hypotheses about the mechanisms and functions of plant chemical communication, while also shifting people’s thinking about what intelligence really means, Kessler said.
The last thought is current, as Artificial Intelligence is a current topic of interest. For example, according to him, artificial intelligence does not solve problems towards the goal, at least not yet. “Artificial intelligence, by our definition of intelligence, is not even intelligent,” he said. Instead, it is based on patterns it identifies in the information it has access to.
The idea that interests Kessler came from mathematicians in the 1920s who suggested that plants might function more like beehives. In this case, each cell functions as a separate bee, and the whole plant is analogous to a beehive.
“This means that the brain in the plant 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 a broad perception of the light spectrum and sensory molecules to detect very specific volatile compounds originating from neighboring plants.
“They sense their environment very precisely; every single cell can do that, as far as we know,” he said. Cells can be specialized, but they also all sense the same things and communicate through chemical signaling to trigger a collective response in growth or metabolism. “The idea is very appealing to me,” he said.
Reference: “Induced Herbivory Resistance and the Intelligent Plant” by André Kessler and Michael B. Mueller, 30 Apr 2024, Plant signaling and behavior.
DOI: 10.1080/15592324.2024.2345985
The paper was supported by a grant from the Fund of New Phytologists.