The Secret Language of Plants

How damaged plants communicate with their neighbours

Trigger Warning - Vegans don’t continue reading

In the complex and interconnected world of nature, communication is often seen as a trait that is exclusive to animals. Plants are perceived as silent, static entities when in fact they possess their own sophisticated means of conveying vital information to each other.

When you sit in a peaceful garden or lush forest, it may seem serene but beneath this tranquil exterior, there is a constant, unseen exchange of information happening at a biochemical level. Especially when a vegan is on the prowl. Ok, I’ll stop with the vegan jokes. I know some vegans so I can’t be a veganist!

This biochemical communication was examined in a recent study published in Nature - Green leaf volatile sensory calcium transduction in Arabidopsis.

The scientists discovered that when a plant is damaged, whether by the relentless nibbling of a vegan (last one, I promise), I meant herbivore or the sudden rupture caused by mechanical forces, it doesn’t suffer in silence. Instead, it releases a cocktail of volatile organic compounds (VOCs) into the air. These VOCs are not random emissions but are potent chemical signals, specifically designed to convey distress and alert neighbouring plants of impending danger.

A single tear in a leaf can set off this silent alarm, reverberating through the plant community. Green leaf volatiles (GLVs) are a group of compounds produced almost instantaneously when the plant suffers physical damage. These volatiles, primarily composed of six-carbon (C6) compounds like alcohols and aldehydes are not mere by-products of damage. They are critical messengers, swiftly produced within seconds of an attack, thanks to a complex biochemical dance that starts with fatty acids in the damaged leaf.

But the role of GLVs extends beyond mere signalling. They serve a dual protective function - directly repelling herbivores while attracting predators of these herbivores. This multifaceted role is a testament to the evolutionary ingenuity of plants. By emitting these compounds, a damaged plant not only safeguards itself but also acts as a sentinel for its neighbours.

How do undamaged plants perceive and respond to the distress signals emitted by their damaged pals?

The core of this response lies in the plant’s ability to detect and react to specific VOCs, notably the GLVs. Using cutting-edge imaging techniques, the scientists observed the fascinating phenomenon in real time. When the undamaged plant they were watching was exposed to VOCs from a damaged plant, they exhibited a rapid increase in calcium levels within their cells. This calcium influx is a deliberate response, signalling the activation of the plant’s internal defence mechanisms.

This cascade of molecular events goes beyond a mere increase in calcium levels. It triggers a series of genetic and biochemical changes within the plant. The expression of certain genes, particularly those associated with stress and defence, is altered, priming the plant to better withstand potential attacks or environmental stresses.

What is truly remarkable is the specificity and rapidity of this response. The plants are able to discern between different VOCs and react accordingly, showing a level of sensitivity and adaptation that is astounding. This response is not just about survival in the face of immediate threats. It also represents a form of ‘plant memory’ where the exposure to these VOCs primes the plants to respond more effectively to future stresses.

Even more amazingly, when undamaged plants encounter these volatiles, they don’t just passively receive them; they engage in a dynamic, responsive process. The reaction within the plants is not uniform by varies depending on the concentration of these volatiles. This nuanced response suggests a sophisticated sensory mechanism, where plants can gauge the intensity of the threat based on the concentration of GLVs in the environment.

The story becomes even more intriguing when we consider the spatial aspect of this response. The scientists observed that the reaction to GLVs is localised. When a part of the plant is exposed to these volatiles, the response - a surge in cellular calcium levels - is confined to that specific area. This localised reaction is a strategic move, allowing the plant to allocate its defensive resources efficiently. It suggests that plants can pinpoint where the threat is likely to occur and concentrate their defensive efforts in that area.

But if the response to GLVs is localised, how does the rest of the plant prepare for potential threats? This is where the concept of ‘systemic acquired resistance’ comes into play. While the immediate response to GLVs is localised, it also serves as a primer for the entire plant. It prepares the plant for a faster and stronger response to future attacks, not just in the exposed area but throughout the entire organism.

The study also looks at the crucial role the stomata plays in this intricate process. These tiny structures, often overlooked, play a pivotal role in how plants perceive and react to the signals sent by their damaged friends.

Stomata are not just passive openings for gas exchange; they are active participants in the plant’s sensory network. When GLVs are released into the air by a damaged plants, they don’t just diffuse aimlessly. They are purposefully channelled through the stomata of neighbouring plants, acting as a direct line of communication. This process is akin to a key unlocking a door, where the GLVs are the key and the stomata are the gateway to the plant’s internal defence mechanisms.

Once inside, these GLVs trigger a cascade of responses. The increase in cellular calcium levels, as discussed above, begins here. But the role of stomata goes beyond just letting in these chemical signals. They also play a part in the plant’s electrical signalling. When exposed to GLVs, changes in the leaf’s surface potential are observed, indicating a complex interaction between chemical and electrical signals within the plant.

This stomatal involvement adds another layer of sophistication to the plant’s response system. It suggests that plants can regulate their sensory intake, opening and closing their stomata not just for breathing but also for ‘listening’ to their environment. This ability to control the influx of external signals allows plants to modulate their responses based on the intensity and nature of the threat.

The scientists were able to observe all this communication by genetically engineering a plant to glow when it ‘talked’.

By introducing a special gene that produces a glow-in-the-dark protein, which lights up in the presence of calcium, they transformed these plants into living sensors. Whenever these modified plants sensed distress signals in the form of certain airborne chemicals released by their damaged neighbours, their cells would light up. This glow, visible under a special microscope, acted like a real-time map of the plant’s internal alarm system, revealing how and when the plants responded to the cries for help from their leafy kin.

To conclude, this fascinating experiment reveals a hidden, yet vibrant world where plants are not silent bystanders but active participants in their environment. This research not only deepens our understanding of plant biology but also opens new avenues for agricultural innovation, where harnessing these silent conversations could lead to more resilient crops, using fewer pesticides.