Plants can hear the rain. MIT scientists proved that rice seeds detect the sound of raindrops falling and start to grow up to 40 percent more quickly. The study, published in Scientific Reports, is the first time anyone has directly shown that seeds in a natural setting hear sounds and use them to begin growth.
The idea is surprising but makes a sort of sense. Rain creates strong sound waves that a seed can pick up. Just as a person is woken by the sound of rain on a window, a seed buried in the ground can be ‘jolted’ into activity. But for the seed, this sound is a signal to start growing.
The team specifically looked at rice, because it sprouts in both the ground and in shallow water. They found that seeds that were exposed to sounds like rain sprouted sooner than those in otherwise exactly the same, completely quiet conditions. And this wasn’t a very small difference; it was a quick, noticeable increase in speed.
How scientists tested rain’s sound
To make something like a storm, the researchers put around 8,000 rice seeds in shallow containers. They changed how big the raindrops were and how far they fell, to represent light, medium, and heavy rain. Other groups of seeds were in the same containers, but without the sound of the falling drops.
The outcome was obvious. Seeds that “heard” rainfall sounds sprouted 30 to 40 percent faster than those that heard nothing at all. The team also used hydrophones (things that record sound under water) to actually measure the sound vibrations made by the raindrops as they hit the water.
Inside the seed: statoliths shaken awake
The way this works is inside the plant cells. Statoliths are very small, heavy particles that help plants feel gravity, like grains of sand settling at the bottom of a jar. They tell a seed which way to grow, even when it’s dark.
When rain hits the ground or a puddle, it makes very powerful sound waves. The team says the sound pressure under the water from a raindrop close by can be as loud as standing a few meters from a jet engine in the air! That much energy is enough to shake the statoliths from where they are resting and start growth.
Seeds that were closer to the surface responded to the rain sounds more. This makes sense when you think about how things developed. If a seed is near enough to the surface to hear the rain, it’s probably at a good depth to soak up the water and safely start to grow upwards.
Key findings at a glance
Here’s what the experiments showed most importantly:
– Rice seeds that “heard” rain sounds sprouted 30 to may 40 percent quicker.
– Approximately 8,000 seeds were examined in shallow water.
– The size and distance of the drops were altered to copy a variety of rainstorms.
– Seeds closer to the surface could sense the sound more effectively.
– Hydrophones recorded the sound vibrations.
What researchers plan next
Nicholas Makris, the lead researcher and a professor of mechanical engineering at MIT, says that the study shows seeds can sense sound in ways that help them live. He puts it this way: the energy in the sound of the rain is strong enough to make a seed grow faster.
Makris and Cadine Navarro, who also worked on the study, think that other kinds of seeds might also react in a similar way. They are now going to try to find out if wind and other vibrations in nature have the same effect. For now, they want to emphasize that this is the first direct evidence of seeds hearing natural sounds.
Plants sense more than we think
Plants aren’t just sitting there doing nothing. Some close up quickly when touched (like the touch-me-not plant). Others curl up when they’re exposed to poisonous smells. Most turn toward the light. And many can sense gravity to help their roots and stems grow in the right direction, even without being able to see the sun.
This research now adds sound to that list of things plants can sense. As Makris explained, rain is louder under the water than in the air because water is heavier and makes bigger pressure waves. If you’re a seed just a few centimeters from where a raindrop hits, those waves can be very strong.
The researchers also mention something from Japanese culture. Makris said the findings give a new understanding to a Japanese expression for a time of year called “Falling rain awakens the soil.” In the lab, at least, the rain doesn’t calm the seeds. It wakes them up and tells them to grow.
To sum it up, MIT scientists showed that the sound of rain can speed up the sprouting of rice seeds by 30 to 40 percent, probably by shaking the gravity-sensing statoliths. Why this is important is straightforward: it’s direct proof that seeds can ‘hear’ the world around them. The next step is to find out how much they can hear.
