Goldenrod has the remarkable ability to detect other plants nearby without physical contact, using far-red light ratios reflected off leaves. When this plant is consumed by herbivores, it can adjust its response based on the presence of neighboring plants. Is this flexible, real-time, adaptive behavior a demonstration of intelligence in plants?
Answering this question is challenging, but chemical ecologist Andre Kessler presents a case for plant intelligence in a recent article in the Plant Signaling and Behavior journal.
“There are more than 70 definitions that are published for intelligence, and there is no agreement on what it is, even within a given field,” said Kessler, professor in the Department of Ecology and Evolutionary Biology in the College of Agriculture and Life Sciences.
Many believe that intelligence requires a central nervous system through which electrical signals serve as the information processing conduits. Some plant biologists draw parallels between plant vascular systems and central nervous systems, suggesting the presence of a centralized entity in plants that enables information processing and response. However, Kessler vehemently opposes this proposition.
“There is no good evidence for any of the homologies with the nervous system, even though we clearly see electrical signaling in plants, but the question is how important is that signaling for a plant’s ability to process environmental cues?” He said.
Kessler and his co-author, Michael Mueller, have argued for plant intelligence by defining it as the ability to solve problems based on environmental information toward a specific goal. In a notable case study, Kessler highlights his prior research on goldenrod and its reactions to pest consumption.
When leaf beetle larvae feed on goldenrod leaves, the plant releases a chemical signal that alerts the insect to the damaged state of the plant and its unsuitability as a food source. These airborne chemicals, known as volatile organic compounds (VOCs), are also detected by neighboring goldenrod plants, prompting them to initiate their own defenses against the beetle larvae. Consequently, goldenrod effectively redirects herbivores to neighboring plants and mitigates damage distribution.
In a recent 2022 study published in the journal Plants, Kessler and Alexander Chautá, Ph.D. ’21, carried out experiments demonstrating that goldenrod has the ability to detect higher far-red light ratios reflected off leaves of neighboring plants.
When goldenrods are consumed by beetles in the presence of neighboring plants, they demonstrate an increased investment in tolerating the herbivore by accelerating growth and producing defensive compounds that aid in fending off insect pests. In the absence of neighboring plants, goldenrods do not exhibit the same accelerated growth response when consumed, and their chemical reactions to herbivores are notably different, although they still display high tolerance to herbivory.
“This would fit our definition of intelligence,” Kessler said. “Depending on the information it receives from the environment, the plant changes its standard behavior.”
Neighboring goldenrod also exhibit intelligence when they perceive VOCs that signal the presence of a pest. “The volatile emission coming 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 that.”
The exploration of plant intelligence can lead to new theories about plant chemical communication and broaden our understanding of intelligence. This shift in perspective is especially relevant now, given the widespread interest in artificial intelligence.
Although artificial intelligence currently operates based on patterns of inaccessible information rather than problem-solving toward a goal, it prompts us to reconsider our definition of intelligence. Kessler finds the comparison of plant function to beehive mechanisms thought-provoking, likening each cell to an individual bee and the entire plant to a hive.
“What that means is, the brain in the plant is the entire plant without central coordination,” Kessler said.
The superorganism relies on chemical signaling rather than electrical signaling. Research indicates that every plant cell can perceive a wide range of light spectra and detect specific volatile compounds from nearby plants. This chemical communication system demonstrates the interconnectedness and complexity of plant life.
“They can smell out their environment very precisely; every single cell can do it, as far as we know. Cells might be specialized, but they also all perceive the same things, and they communicate via chemical signaling to trigger a collective response in growth or metabolism. “That idea is very appealing to me,” he said.
Journal reference:
André Kessler & Michael B. Mueller. Induced resistance to herbivory and the intelligent plant. Plant Signaling & Behavior, 2024. DOI: 10.1080/15592324.2024.2345985
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