It may seem like a fantastical scene straight out of “The Lord of the Rings,” but real-life trees on Earth have the ability to communicate and warn each other of danger. A recent study has shed light on this phenomenon, revealing that injured plants emit certain chemical compounds that can infiltrate nearby healthy plants and activate defenses within their cells. This newfound understanding could have significant implications for scientists and farmers, allowing them to fortify plants against future threats such as insect attacks and drought.
The study, published in Nature Communications, marks the first time researchers have been able to visualize plant-to-plant communication. By harnessing this system, scientists hope to inform entire plants to activate different stress responses in anticipation of future threats or environmental challenges.
The concept of “talking” trees gained traction in the 1980s when ecologists observed that trees under attack by insects began producing chemicals that made their leaves unappetizing and indigestible. Even more intriguingly, healthy trees of the same species located nearby, with no root connections to the damaged trees, exhibited the same chemical defenses. This led scientists to speculate that trees communicated with each other through the air, a phenomenon now known as plant eavesdropping.
Over the past four decades, researchers have observed this cell-to-cell communication in over 30 plant species. However, until now, they were unsure which compounds were crucial and how they were sensed. The recent study has helped answer some of these long-standing questions.
While plants lack ears and eyes, previous research has demonstrated that they communicate with their environment by emitting volatile organic compounds, which we can smell. These compounds serve various functions, including attracting pollinators and defending against predators. When a plant is injured, it releases a specific class of compounds known as green leafy volatiles. These compounds are emitted by almost every green plant with leaves and are produced in response to physical damage.
In the study, researchers manually crushed leaves and placed caterpillars on Arabidopsis mustard or tomato plants, triggering the emission of various green leafy volatiles. They then exposed healthy plants to these compounds to observe their reactions. To track the plants’ responses, the team genetically modified them to fluoresce calcium ions when activated inside their cells. Calcium signaling is crucial for cellular functions in various organisms, including humans.
The researchers discovered that only two specific green leafy volatiles increased calcium ions inside the plant cells, signaling the activation of defense responses. Furthermore, they found that calcium signaling occurred first in the guard cells that form the plant’s leaf pores, known as stomata. This finding indicates that the compounds are absorbed into the plant’s inner tissues and cannot simply seep through its surface.
According to the study’s senior author, Masatsugu Toyota, calcium signaling acts as a switch, triggering the plant’s defense responses. Once the signaling increases, the plant enhances the production of certain gene expressions that provide protection. For example, the plant may produce proteins that deter insects from consuming them, ultimately leading to the insects experiencing digestive problems.
With this newfound knowledge, researchers believe it may be possible to immunize plants against threats and stressors before they occur, akin to giving a vaccine to a plant. By exposing healthy plants to insect-affected plants or the associated green leafy volatiles, farmers could enhance their genetic defenses, reducing the need for pesticides. Additionally, this revelation could help plants become more resilient during droughts by signaling the plants to retain more water.
The implications of this study are far-reaching, planting the seeds for future research. For instance, scientists are eager to understand why only two specific green leafy volatiles can enter the stomata and trigger calcium signaling. Identifying the receptors in plants specific to these compounds’ chemical structure is the next step in unraveling this mystery.
Furthermore, in response to insect attacks, plants can produce specific responses based on the species of herbivore feeding on them. This impressive behavior is an area of focus for plant ecologist André Kessler, who believes it raises questions about our understanding of intelligence and how plants navigate their surroundings.
The study on plant communication has opened new avenues of exploration, demonstrating that the natural world is far more complex and interconnected than previously imagined. By unlocking the secrets of how plants communicate, scientists are gaining a broader perspective on the intricacies of the natural world and our place within it.
