Some time ago, on the internet, came information about how plants can feel hurt when they’re cut. Well, this new study further backs this up. 

In this new research, scientists from Tel Aviv University found that tomato and tobacco plants emit sounds when they’re under stress. The plants don’t only make this sound when the stem is cut off; they “scream” when they’re thirsty as well.  

The scream is not like a toned-down mandrake cry, if that’s what you’re imagining right now, it’s more like a popped bubble wrap. And, we can detect it from more than a meter (39.3 inches) away, particularly when they need water. 

According to scientists, it’s hard for us humans to detect the sound because the frequency of the noises is too high, but animals like insects or some mammals, and possibly other plants, can hear it.  

This means 1) that the plants can “talk” with their surroundings far more than we realize, and 2) farmers are now able to tell when their crop needs some attention by “listening in.” 

Stress in plants 

The researchers found out that the the plants “vocalize” is comparable in volume to normal human conversation. 

Senior author Professor Lilach Hadany said, “Even in a quiet field, there are actually sounds that we don’t hear, and those sounds carry information. There are animals that can hear these sounds, so there is the possibility that a lot of acoustic interaction is occurring.” 

Previous research has noted ultrasonic vibrations from plants. Hadany’s study is the first evidence of the airborne sound. And with this fact, plants have become more relevant for other organisms in the environment. 

“Plants interact with insects and other animals all the time, and many of these organisms use sound for communication, so it would be very suboptimal for plants to not use sound at all,” Hadany said. 

The team used microphones to record healthy and stressed tomato and tobacco plants. First, they did it in a soundproofed acoustic chamber and then in a noisier greenhouse environment. To make the plants stressed, they used two methods: not watering them for several days and cutting their stems. 

After recording the plants, the team trained a machine-learning algorithm to differentiate between unstressed plants, thirsty plants, and cut plants. They found that stressed plants are noisier than unstressed plants. Not unlike some of us, eh? 

Per the researchers, a single stressed plant emits about 30 to 50 pops or clicks per hour at seemingly random intervals. Plants that are fine don’t emit that many sounds. “When tomatoes are not stressed at all, they are very quiet,” Hadany said. 

Plants that are thirsty emit sounds before they are visibly parched. The frequency of their sounds peaks after five days with no water before decreasing again as the plants dried up completely. 

 

 

Different sounds from plants 

The researchers have trained the machine-learning algorithm to tell the difference between stress from dehydration or cutting, as well as finding out whether the sounds come from a tomato or tobacco plant. 

And although the team tested only two types of plants (as tomato and tobacco are easier to grow in the lab), they’ve also recorded sounds from other plant species. 

“We found that many plants – corn, wheat, grape, and cactus plants, for example – emit sounds when they are stressed,” Hadany said.  

The researchers are still not sure about the exact mechanism behind the noises, but they suggest that it might be caused by the formation and bursting of air bubbles in the plant’s vascular system. 

They also don’t know if the plants produce the sounds to “talk” with each other or other organisms. However, the scientists believe that the sounds’ existence has big ecological and evolutionary implications. 

“It’s possible that other organisms could have evolved to hear and respond to these sounds. For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision,” Hadany said. 

Previously, Hadany and her team showed that plants increase the concentration of sugar in their nectar when they “hear” the sounds made by pollinators. Other previous studies have shown that plants change their gene expression in response to sounds. 

“If other plants have information about stress before it actually occurs, they could prepare,” Hadany said. 

Listening to plants in the future 

The research team suggests that sound detection and recordings of plants might be useful in agricultural irrigation systems. We can monitor crop hydration status and help distribute water more efficiently. 

Co-senior author Professor Yossi Yovel said that there’s actually a lot of ultrasound around us. A lot of living things around us produce sounds we can’t hear. However, plants making airborne sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds. 

“We are currently investigating the responses of other organisms, both animals and plants, to these sounds, and we’re also exploring our ability to identify and interpret the sounds in completely natural environments,” Hadany explained about her plans. 

 

 

Plants sending alarm about danger 

Of course, this isn’t the first time that researchers have shown how plants are not silent and are able to feel threatened. In a 2020 study published in Nature Plants, researchers from the Salk Institute showed how plants respond to a hormone called jasmonic acid or jasmonate. 

With this knowledge, the researchers hoped that we can better prepare crops so they can be more robust, more able to withstand assault, particularly in times of climate change, as we can ensure proper growth and development. 

In this study, the researchers examined Arabidopsis thaliana because the plant’s genome has been well characterized. Just a little info, A. Thaliana is a small flowering plant in the mustard family. 

Now, jasmonate isn’t exclusive to this plant only, and rather throughout the plant kingdom. And, it’s known to be an important part of plants’ defense response against attacks from fungi and insects. 

But, the researchers at the time wanted to precisely understand what happens after jasmonic acid is perceived by the plant. 

By using different computational approaches, the researchers could identify genes that are important for the plant’s response to jasmonic acid and for cellular cross-communication with other plant hormone pathways. 

Co-first author Mark Zander then said, “We now have this very comprehensive picture of which genes are turned on and off during a plant’s defense response. With the availability of CRISPR gene editing, these kinds of details can be useful for breeding crops that are able to better withstand attacks from pests.” 

 

Sources

https://talker.news/2023/03/30/plants-scream-and-cry-when-theyre-stressed-or-thirsty-study/   

https://www.sciencedaily.com/releases/2020/03/200313155308.htm