of Tall goldenrod (Solidago altissima)a North American species of the goldenrod family Asteraceaecan recognize other nearby plants without touching them by sensing the proportion of far-red light reflected from their leaves. When goldenrod is eaten by herbivores, it adapts its response based on whether other plants are nearby. Are such flexible, real-time adaptive responses a sign of plant intelligence?
In the context of behavioral ecology, plant responses to environmental stressors are increasingly being studied. This is especially true for plant responses to herbivores, which mediate direct and indirect defense and tolerance. These seemingly adaptive changes in plant defense phenotypes in the context of other environmental conditions have prompted discussion of such responses as intelligent behavior. In their paper, Kessler and Mueller explore the concept of plant intelligence and some of its predictions regarding chemical signaling in plant interactions with other organisms. Image courtesy of Becky.
“There are over 70 published definitions of intelligence, and even within specific fields there is no consensus on what it is,” says chemical ecologist Professor André Kessler. Cornell University.
“Many people believe that intelligence requires a central nervous system, and that electrical signals act as the medium for information processing.”
“Some plant biologists equate the plant's vascular system with a central nervous system, arguing that there is some centralized entity within the plant that allows it to process and respond to information.”
But Kessler and his colleague, Michael Mueller, a doctoral student at Cornell University, disagree.
“Although electrical signals are clearly seen in plants, there is no solid evidence of any homology with the nervous system, but the question is how important they are to the plant's ability to process environmental signals,” Professor Kessler said.
To make the case for plant intelligence, the authors narrowed the definition down to its most basic element: the ability to solve problems toward a specific goal based on information obtained from the environment.
As a case study, Kessler points to previous research looking at goldenrod and its response to being eaten by pests.
When beetle larvae feed on goldenrod leaves, the plant releases chemicals that let the insects know the plant is damaged and a poor food source.
These airborne chemicals, called volatile organic compounds (VOCs), are also absorbed by nearby goldenrod plants, causing them to develop their own defenses against the beetle larvae.
In this way, goldenrod attracts herbivores to nearby areas, dispersing damage.
In 2022, Professor Kessler and his co-authors Experiments were conducted To show that Solidago altissima They can also detect a higher proportion of far-red light reflected from the leaves of nearby plants.
If nearby plants are feeding on goldenrods by beetles, the goldenrod will grow faster in an effort to withstand the herbivores, but it will also start producing defensive compounds that help the plant fight off the pests.
In the absence of neighboring plants, plants do not accelerate their growth when eaten, and their chemical response to herbivores is significantly different, but they can still survive a significant amount of herbivore attack.
“This fits into our definition of intelligence: plants change their standard behaviour in response to information they receive from the environment,” Professor Kessler says.
“Neighboring goldenrods also become intelligent when they detect VOCs that signal the presence of pests.”
“Volatile emissions from nearby areas are a harbinger of future herbivore occurrence.”
“They can use cues from the environment to predict future situations and act accordingly.”
“Applying the concept of intelligence to plants could generate new hypotheses about the mechanisms and functions of plant chemical communication and may even change people's ideas about what intelligence actually means.”
“The latter idea is timely because artificial intelligence is a hot topic right now. For example, at least for now, artificial intelligence doesn't solve problems toward a goal.”
“Artificial intelligence is not even intelligent according to our definition of intelligence. Artificial intelligence is based on patterns it identifies from the information it has access to.”
“The idea that interests us comes from mathematicians in the 1920s who proposed that plants might function like beehives.”
“In this case, each cell acts like an individual bee, and the whole plant resembles a hive.”
“That means the plant brain is the whole plant, without any central coordination.”
“Instead of electrical signals, chemical signals are transmitted throughout the superorganism.”
“Work by other researchers has shown that all plant cells have a wide range of light spectrum recognition and sensory molecules to detect very specific volatile compounds emanating from nearby plants.”
“They can sniff out their environment with great precision, and as far as we know, all cells can do that.”
“Cells may be specialized, but they all recognize the same things, communicate through chemical signals, and trigger collective responses in growth and metabolism.”
“The idea is very appealing to me.”
Team paper Published in the journal Plant signaling and behavior.
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Andre Kessler & Michael B. Mueller. Induced resistance to herbivores and intelligent plants. Plant signaling and behaviorPublished online April 30, 2024, doi: 10.1080/15592324.2024.2345985
