How They Talk, Listen, and Remember
A stroll through a still, quiet forest is actually a walk through a hub of constant conversation, all happening just beyond our normal perception.
For centuries, plants were viewed as passive automatons, simply growing and reacting to their environment through basic mechanics. Today, a scientific revolution is overturning that centuries-old belief. Research has revealed that plants are sessile, highly sensitive organisms that actively assess their surroundings, estimate energy needs for goals, and take measures to control environmental resources 1 . They perceive themselves, distinguish between self and non-self, and protect their territory 1 . This is all possible because plants are masters of biosemiotics—the science of signs and communication in living systems. They engage in constant, sophisticated conversations, both within their own bodies and with the world around them.
This article delves into the hidden world of plant communication, exploring the chemical vocabulary, electrical signals, and pressure waves that form the foundation of the plant kingdom's secret language.
The old view of plants as growth automatons has been replaced by a new understanding: the coordination of their growth and development is only possible through the use of signs, not pure mechanics 1 . In this context, a "sign" is anything that stands for something else for some living being. A chemical molecule, for instance, can function as a signal, a messenger, or a memory medium 1 .
Plant communication is a multilevel phenomenon, occurring in three main spheres 1 :
A core principle of biosemiotics is that the same signal can have different meanings in different contexts. The plant hormone auxin, for example, is a versatile sign. It acts as a neurotransmitter in synaptic-like cell-cell communication, helps plants react to light and gravity, functions as an electrical synchronization signal, and promotes growth and cell division 1 . Its meaning is not in its chemical structure alone, but in the pragmatic context of its use.
Within the plant itself
Between plants of same/different species
Between plants and other organisms
The chemical communication within and between plants is remarkably complex, involving a vast molecular vocabulary. Scientists have identified over 20 different groups of molecules with communicatory functions, with an estimated 100,000 different substances known as secondary metabolites active in the root zone alone 1 .
| Signal Molecule | Primary Function | Context-Dependent Role |
|---|---|---|
| Auxin | Growth hormone; promotes cell division and elongation. | Functions as a neurotransmitter, electrical signal, and positional signal during organogenesis 1 . |
| Sugars | Primary energy source and building block. | Act as crucial messengers telling guard cells to open stomata to let in CO₂ for photosynthesis 3 . |
| Ethylene & Jasmonate | Growth regulation and fruit ripening. | In combination with peptide systemin, they activate effective defense responses against injury 1 . |
| Nitric Oxide (NO) | Traditionally associated with disease resistance. | Has regulatory functions in numerous other processes, including germination, growth, and reproduction 1 . |
| Serotonin | Human neurotransmitter. | In plants, it shapes the microbial community around roots, promoting or suppressing certain microbes based on nutrient availability 6 . |
This molecular language is not limited to internal plant communication. Plants release these compounds into the air and soil to send messages. For instance, when a plant is attacked by a pest, it may release volatile organic compounds (VOCs) that act as an early warning system for neighboring plants, allowing them to pre-emptively ramp up their defenses 9 . Recent research has even identified specific receptors in plants, like a "nose" in petunias, that can detect these VOCs with high selectivity, ensuring the message is received clearly 9 .
For over a hundred years, a central mystery puzzled plant scientists: how do plants internally transmit signals from one part to another to coordinate a response to stressors like a caterpillar bite or drought? Some hypothesized it was via hormones; others suggested mechanical signals.
In 2025, a team from the Center for Research on Programmable Plant Systems (CROPPS) published a study that finally provided a unified answer 2 5 . They solved this century-old conundrum by identifying internal pressure changes within the plant's vasculature as the key driver.
The researchers developed a predictive model and framework to explain signal transmission. The core of their methodology involved 2 :
The model revealed that this mass flow of fluid acts as a courier service, carrying two types of signals 2 5 :
This discovery was a major leap forward. It provided a mechanistic understanding of how both local and long-distance signals are transmitted, integrating mechanical and chemical signaling into one coherent process 2 .
| Stress Event | Immediate Physical Effect | Downstream Signal Carried | Plant's Ultimate Response |
|---|---|---|---|
| Caterpillar Bite | Pressure change in leaf vasculature. | Mass flow carries jasmonate-like chemicals; Calcium ions released. | Production of toxic or repellant compounds; genetic defense activation. |
| Drought Onset | Shift in water pressure balance in stems and roots. | Hydraulic signals and abscisic acid hormone distribution. | Stomatal closure to conserve water; altered growth patterns. |
Caterpillar bite or drought
In vascular system
Chemical & mechanical signals
Toxin production or water conservation
To decode the hidden language of plants, scientists rely on a sophisticated toolkit. The following essential materials and reagents are fundamental to research in this field, from studying whole-plant physiology to molecular biology.
| Research Reagent / Tool | Function in Research |
|---|---|
| Apoplast Fluid Extraction | Allows researchers to carefully extract and analyze the chemical cocktail of metabolites present in the space between plant cells, which is the highway for many communicatory signals 3 . |
| Metabolomics Profiling | A technique used to identify and quantify the hundreds of unique metabolites (like sugars and maleic acid) in extracted apoplast fluid, helping pinpoint potential signaling molecules 3 . |
| Model Organisms (e.g., Arabidopsis thaliana, Vicia faba) | These well-studied plants, with fully sequenced genomes, serve as standard subjects for experiments, allowing for reproducible results and genetic manipulation 3 . |
| Plant Electrophysiology Tools | Used to measure the electrical signals that plants use to communicate, providing real-time data on plant responses to stress 9 . |
| Genetically Encoded Reporters (e.g., for Calcium) | Tools that make plants glow or fluoresce when specific ions like calcium are released, allowing scientists to visualize signal propagation in real-time 2 . |
The implications of understanding plant communication are profound, particularly for agriculture. The ultimate vision of research groups like CROPPS is to create a two-way communication system between plants and farmers 2 5 . Imagine "reporter plants" that change color or fluoresce under UV light when they need water, enabling perfectly timed irrigation 2 5 . Conversely, a farmer could inform crops of an upcoming dry spell, prompting the plants to pre-emptively conserve water.
This future is already taking shape. Swiss startup Vivent, for example, uses plant electrophysiology to monitor crop health in real time, detecting root infections by nematodes long before visible symptoms appear 9 . Other researchers are exploring how to boost natural underground fungal networks—the "Wood Wide Web"—that allow plants to exchange nutrients and information, potentially reducing the need for artificial fertilizers 9 .
As we continue to listen in on the quiet conversations of the plant world, we are not just satisfying scientific curiosity. We are learning the rules of a language that could help us build a more sustainable and resilient future, one where we can finally hear what the forests have been saying all along.