Even before water reaches them, the sound of droplets triggers germination in rice plants

By K. R. Callaway edited by Claire Cameron

Rain sounds maybe soothing for humans, but for plants, the pitter-patter of droplets is more like a jarring morning alarm. As water falls onto soil or water, the vibrations are far stronger underground than on the surface, and new research suggests plants take advantage of this wake-up call.

The sound of rain spurs rice seeds to sprout up to 40 percent faster than they would otherwise, according to a study published today in Scientific Reports. The results mark the first direct evidence that plants sense the sound of the world around them and respond to it. And it’s likely that seeds from other plant species behave in the same way, the authors say.

“What this study is saying is that the seeds can sense sound in ways that can help them survive,” said study co-author Nicholas Makris, a professor of mechanical engineering at the Massachusetts Institute of Technology, in a statement.

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Just how much plants can sense in the world around them has long puzzled researchers. There’s evidence to suggest that plants might have the ability to “think,” “see,” “hear” and make sounds, but scientists have only rarely observed a cause-and-effect relationship that reveals our flora friends responding to their environment in real time. In the new study, the researchers home in on the relationship between sound and germination.

In plants, cellular structures called statoliths are responsible for external sensing. These structures are envelopes of starch that shift and settle at the bottom of plant cells, helping the organisms to detect changes in their position and stability—and to tell germinating seeds in which direction to grow their roots. Makris and his team theorized that rain sounds underwater might produce large enough vibrations to jostle the statoliths and possibly spur germination in rice seeds.

The researchers exposed about 8,000 rice seeds submerged in water—their preferred growing condition—to rain sounds. The team found the noise spurred these seeds to germinate between 30 and 40 percent faster than seeds that were kept in identical—but quiet—conditions. It’s possible there is a biological advantage to being able to sense rain in this way, Makris and his co-author argue.

“It has to do with the fact that water is denser than air, so the same drop makes larger pressure waves underwater,” Makris said. “So, if you’re a seed that’s within a few centimeters of a raindrop’s impact, the kind of sound pressures that you would experience in water or in the ground are equivalent to what you’d be subject to within a few meters of a jet engine in the air.”

Makris and his co-author, Cadine Navarro, want to further investigate whether other environmental cues, such as wind, could be sensed by plants in similar ways.