Plants Cry; Here’s Why!
Photo via The New York Times.
Plants and Dawson students have one thing in common: they both cry when they are stressed. Researchers have recently made the shocking discovery that plants might literally express their sadness using airborne sounds. In order to prove this, the scientific journal Cell carried out an experiment that was officially published in early April.
During the course of their study, researchers monitored the physiological characteristics of tomato and tobacco plants while analysing ultrasonic noises the plants produced in an acoustic room and a greenhouse. The purpose of this procedure was to better understand the interactions between plants and their environment and whether it could further advancements in the agricultural field. The results concluded that plants produce certain sounds – ranging from clicks to pops – that can be indicators of distress in plants. In fact, tests reveal that thirsty plants respond audibly differently than plants that have been cut out and analysed. These sounds could be intercepted by mammals and small insects from up to 3-5 meters away from the plant source. Instead of using vocal cords, it is hypothesised that plants produce such sounds by cavitation - a change in pressure or movement of air bubbles found within their water vessels. Plants exposed to imminent stimuli that trigger distress would respond in tiny bubble bursts inside the plant’s vascular system, which would produce mini-shock waves and a popping sound, relatively similar to the mechanism in your joints when you crack your knuckles.
It’s important to report that plants do not solely rely on audible communication to interact with their environment. Their main form of communication is by emitting chemicals. Other interactions include behavioural responses such as increasing their nectar production in response to the sound of approaching pollinators. To communicate with one another, plants release chemicals from their roots into the soil. This process occurs in the plant-root zone, called the rhizosphere. Here, all other organisms receive signals from the emitted tiny chemical known as root exudates.
For a better understanding of plant behaviour, here’s some historical context on Darwinian biological research. In the 1880s, the famous biologist Charles Darwin experimented on plant roots to investigate their response. He concluded that the roots’ tips plant root tips have a brain-like structure guiding the various movements while taking in impulses from the sensory organs; light, gravity, chemicals, and sound are just a few stimuli that a root’s tip may detect and react to. It then sends out signals that trigger actions in plants, like growth, directional movement, and the production and release of certain gases. Furthermore, Darwin analysed chemical signalling in plant communication. He demonstrated how soluble chemicals (created at the expanding shoot's tip of barley seedlings) were carried down the stems and induced stem curvature and cell division. These chemical cues are now understood to be hormones called auxins, produced by plants that encourage the growth of longer, curved stems, which migrate throughout the body of plants and are crucial to shaping and growth patterns.
As mentioned above, plants communicate with their environmental stimuli by movement! This movement occurs in order to get important information about their surroundings, react accordingly, and share this information with other plants using clear signals. Such information consists of daylight, temperature, gravity, water, nutrient resources, dangers, and so on. In addition to root communication, gaseous substances known as volatile organic compounds (VOCs) serve as chemical messengers between organisms. They are the most common kind of chemical signals that plants emit. These small molecules are gases formed from the producing plant and are easily diffused into the atmosphere. For instance, methyl jasmonate (MeJA), one of the most prevalent plant VOCs, is produced and emitted by plants that have been injured, such as when an animal tries to consume it. When MeJA is produced by an attacked plant, it travels via the air to nearby plants and to unaffected areas of the same plant. There, it activates defence systems in unaffected neighbours.
Plants and Dawson students have something else in common: they are great communicators, exploring their environment and expressing their emotions (hopefully). Whether they communicate acoustically or chemically, plant behaviour is slowly starting to be analysed by biology researchers. Such studies are highly beneficial in the agricultural sector as the workers would be able to act more appropriately to their plants’ needs. So, next time you see a plant, maybe consider talking to it. It might talk back.
If you are curious, some recordings of the cry noises have been published along with the research. The following link presents several recordings of the clicking/popping sound in different situations, such as a tomato plant’s response to thirst.