Plants, “cognitive organisms”. Vibrations from the drops can serve as a warning signal and accelerate plant growth. Research offers the first direct proof that seeds act based on sounds.
The gentle sound of rain can act as a warning sign for seeds waiting to germinate. This is what the work of researchers at the Massachusetts Institute of Technology (MIT), in the United States, indicates.
In practice, it is as if the seeds feel or “hear” the rain through the vibrations it produces. Scientists have discovered that some of them germinate faster.
To reach this conclusion, MIT researchers carried out tests with rice seeds. They found that the acoustic vibrations from the raindrops brought the seeds out of dormancy and caused them to sprout sooner than they would have under other conditions.
The results were in Scientific Reports, and offer the first direct proof that plant seeds can detect sounds and act based on them.
Like “a jet engine in the air”
The researchers exposed thousands of rice seeds to controlled drops of water, simulating rains of different intensities, from light to heavy. The seeds were submerged in shallow water — typical conditions for rice cultivation.
Seeds exposed to the sound of falling drops germinated 30% to 40% faster than seeds kept silent.
It all comes down to physics. When a raindrop hits water or the ground, the pressure it causes creates vibrations — or “pressure waves” — which propagate and can be perceived as sound. In water, these vibrations can be particularly intense.
Nicholas Makris, an MIT researcher and co-author of the study, compares the pressure waves captured by the seeds, just a few centimeters from the impact of a raindrop, to the sound that a person hears “a few meters from a jet engine in the air”.
Do seeds “hear” the rain?
It is known that plants respond to a variety of environmental stimuli. Some react to touch, others to chemicals, and most to light. Science has also demonstrated that they may be able to detect gravity.
In the case of raindrops, the idea that plants “hear” suggests that there is a part of the plant that is “listening” and acting cognitively based on what it “hears.” And there is some truth to this.
Other studies suggest that plant seeds may have “decision centers”which function as small “plant brains”.
“We know that plants are true living organisms,” explains Frantisek Baluska, professor emeritus of plant physiology and plant cell biology at the University of Bonn. “Plants are asserting themselves as cognitive organisms.”
Just like the idea of plants hearing rain, plants do not think in the same way that we humans understand “thinking”. But, according to Baluska, it is possible that seeds decide about germination based on a form of “cognitive evaluation”.
Gravity sensitivity
The study authors believe that the vibrations act on small internal structures known as statoliths. These dense organelles, similar to grains of sand, are present inside plant cells and help to detect gravity.
The statoliths are deposited at the bottom of the cells, allowing the seed to know which direction is up and down — thus, the roots grow downwards and the stems grow upwards.
However, the team’s research suggests that the energy from rain-induced vibrations interferes with the normal functioning of statoliths.
Seeds that respond to these vibrations are likely to be near the surface, where moisture is available, but not so deep that emerging sprouts cannot reach the light. This means the sound of rain can help them assess whether they are in an ideal position to grow.
“Human hearing is adapted to be advantageous to humans,” says Makris. “What we discovered is that plant seeds and seedlings do something that appears to be advantageous for them as well.”
According to the researcher, it is likely that seeds from other plants respond to the sound of rain in a similar way.
