Plants have an astonishing biochemical communication network

Researchers at Purdue University have made significant strides in understanding plant communication through chemical signals, revealing their intricate language.

Plants, incapable of movement, have evolved unique mechanisms for survival and communication, particularly through Volatile Organic Compounds (VOCs).

These compounds serve as distress signals, warning neighboring plants of potential dangers, such as insect attacks or diseases.

Roots to receptors: The plant communication network

Natalia Dudareva, a Distinguished Professor at Purdue in the departments of Biochemistry and Horticulture and Landscape Architecture, emphasizes the importance of VOCs in plant communication.

She describes it as a form of immunization, where plants primed by these signals respond more vigorously to threats, despite showing no visible changes under normal conditions.

“Plants inform neighboring plants about pathogen attacks. It looks almost like immunization. Under normal conditions, you don’t see any changes in the receiver plant. But as soon as a receiver plant is infected, it responds much faster. It’s prepared for response,” explained Dudareva.

How plants use VOCs as invisible signals

The concept of plants communicating through VOCs is not new to science, but the mechanisms behind this communication have remained largely unexplored due to the lack of identifiable markers.

However, recent discoveries by Dudareva and her team have shed light on this process. Their research has documented how petunias produce volatiles to sterilize parts of their flowers, protecting against microbial invasion.

This discovery, first published in 2019, also introduced stigma size as a reliable marker for studying inter-organ communication in plants.

Shannon Stirling, a Ph.D. student at Purdue and the study’s lead author, has contributed significantly to this research.

Karrikins and plant communication

Through meticulous analysis, including measurements of stigma size affected by exposure to VOCs, Stirling’s work has helped establish a consistent trend in the communication process.

“There are a lot of sugars on the stigma, especially in petunias. It means that bacteria will grow very nicely without these volatiles present,” Dudareva explained.

“But if the stigma does not receive tube-produced volatiles, it’s also smaller. This was interorgan communication. Now we had a good marker — stigma size — to study this communication process,” she concluded.

This trend is further supported by genetic studies that pinpointed a karrikin-like signaling pathway as a crucial element in this communication.

Karrikins, interestingly, are compounds not produced by plants but are associated with smoke or fire exposure, raising intriguing questions about plant evolutionary biology.

Selectivity of plant receptors

The study also highlights the exceptional selectivity of plant receptors, particularly in recognizing specific sesquiterpene compounds.

Matthew Bergman, a postdoctoral researcher and co-author of the study, points out the receptor’s ability to differentiate between mirror images of compounds, emphasizing the precision of this signaling system in avoiding false triggers.

“The plant produces many different volatile compounds and is exposed to plenty of others,” Bergman said. “It’s quite remarkable how selective and specific this receptor is exclusively for this signal being sent from the tubes. Such specificity ensures that no other volatile signals are getting by. There’s no false signaling.”

Secrets of plant pistils and stigmas

Stirling’s expertise in protein manipulation has been pivotal in identifying the interactions between signaling molecules and receptors. The process involves delicate techniques to modify protein levels in petunia pistils, a challenging task given the small size of these organs.

“Pistils and stigmas are small. They’re a little difficult to work with because of their size,” Stirling said. “Even the sheer amount of stigmas you need to get enough sample for anything is quite large because they don’t weigh much.”

This methodological breakthrough could pave the way for further discoveries in plant signaling and communication.

Petunias, with their vivid colors and fragrances, are more than just a visual delight. As Bergman notes, their value extends into the realm of scientific research, serving as an effective model for understanding complex biological processes.

Plant talk as both an art and a science

In summary, this fascinating research has peeled back the layers of mystery surrounding plant communication. These brilliant scientists discovered how petunias, through the sophisticated use of volatile organic compounds, communicate threats to their neighbors. This communication, in turn, effectively immunizes them against potential dangers.

This study highlights the intricacies of plant signaling pathways, particularly through the discovery of the karrikin-like signaling mechanism and the precise receptor specificity for sesquiterpene compounds, while setting the stage for future research in plant biology.

By advancing our understanding of these complex communication systems, scientists unlock new possibilities for enhancing plant resilience and health, paving the way for agricultural innovations and environmental conservation strategies.

More about Volatile Organic Compounds (VOCs) and plant communication

As discussed above, Volatile Organic Compounds (VOCs) represent a vast group of chemicals that plants and other organisms naturally emit. These compounds easily evaporate at room temperature, making them a significant part of the air we breathe.

In the plant kingdom, VOCs serve as critical components in a sophisticated communication network. They play pivotal roles in attracting pollinators, deterring herbivores, and signaling neighboring plants about environmental stressors.

Role of VOCs in plant communication

Plants utilize VOCs to convey vital information to their surroundings. This form of communication is especially crucial in responding to threats such as herbivore attacks or disease.

When a plant gets damaged, it releases specific VOCs into the air. These signals can directly repel pests or attract natural enemies of the pests, such as predators or parasitoids, effectively reducing the damage to the plant.

Moreover, VOCs are not just about defense. They are instrumental in forming symbiotic relationships and facilitating plant-to-plant interactions.

For example, when one plant is attacked, neighboring plants can detect the VOCs released and preemptively bolster their own defenses, a phenomenon known as “priming.” This capability suggests a level of interconnectedness and communal support among plant populations.

VOCs in attracting pollinators and symbiosis

Beyond defense, plants produce VOCs to lure pollinators. These chemical signals can attract specific insects or animals, ensuring the plant’s reproductive success.

The diverse array of scents and odors produced by flowers is primarily due to VOCs, tailored to appeal to the plant’s pollinators, whether they be bees, birds, or bats.

Furthermore, VOCs facilitate symbiotic relationships between plants and microorganisms. Certain VOCs can attract beneficial microbes that help the plant absorb nutrients more efficiently or provide resistance against pathogens.

This interaction underscores the complexity of VOCs in plant ecology, extending beyond plant-to-plant communication to encompass a broader ecological network.

Impact of VOCs on ecosystem dynamics

The exchange of VOCs among plants and between plants and other organisms significantly influences ecosystem dynamics. It affects plant competition, biodiversity, and the structure of plant communities.

VOCs can mediate the outcome of plant interactions, determining which species dominate in certain conditions and contributing to the overall health and resilience of ecosystems.

VOCs and future study on plant communication

As discussed above, Volatile Organic Compounds are more than mere byproducts of plant metabolism. They are vital communicative tools that plants use to interact with their environment.

Through the release of VOCs, plants can defend against predators, attract pollinators, and communicate with neighboring flora, showcasing a sophisticated level of interaction that mirrors the complexity of animal communication networks.

As research in this field progresses, we continue to uncover the depth and breadth of plant communication, revealing an intricate world where plants are far from passive entities in their ecosystems.

This study, which appears in the March 22, 2024, issue of the journal Science, is a collaborative effort involving scientists from Purdue, Université Jean Monnet Saint-Etienne in France, and the University of California-Davis.

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