The seeds of some plants are “activated” by the sound of rain, as demonstrated by incredible and innovative research led by Massachusetts Institute of Technology (MIT, USA). This discovery can really change our vision of the plant world, which – yes – is always less “static” than we thought until now.
The researchers conducted the experiments, in particular, with rice seeds immersed in shallow water, discovering that the sound of falling drops effectively awakened them from their dormant state, stimulating them to germinate faster than seeds not exposed to the same sound vibrations: these results represent the first direct evidence that seeds and seedlings can perceive sounds in nature.
MIT researchers have also put forward hypotheses to explain how seeds can do this (the scientific community has long suspected that many other types of similar seeds can react to the sound of rain): in fact, they discovered that when a raindrop hits the surface of a puddle or the ground, it generates a sound wave that makes the surrounding environment, including submerged seeds, vibrate.
In particular, they verified that these vibrations can be strong enough to move a seed’s statoliths, tiny organelles sensitive to gravity, enough to orient the roots downwards and the stem upwards.
This mechanism has been known for a long time: statoliths are in fact denser than the cell cytoplasm and can move and sink inside the cell, and when a statolith settles to the bottom, its position on the cell membrane reflects the direction of gravity and indicates where the seed root or shoot should grow.
But scientists have now discovered that if the statolith is moved, this can stimulate more seed growth.
I went back to examine the work carried out by some colleagues in the 1980s who measured the sound of rain under water – says Nicholas Makris, first author of the work – If you check, you will see that it is much louder than in the air. This is because water is denser than air, so the same drop creates larger pressure waves underwater. Consequently, if a seed is a few centimeters from the impact of a raindrop, the type of sound pressure it would experience in water or in the ground is equivalent to that to which it would be subjected to a few meters from a jet engine in flight
To test whether sound waves generated by rain could actually move the statoliths, the researchers conducted experiments with rice seeds, which grow naturally in shallow marshy fields: the team immersed around 8,000 individual rice seeds in shallow trays of water and exposed sections of them to dripping water.
He naturally positioned the seeds at such a distance from the drops that they could only be reached by the sound waves they generate, and varied the size and height of each drop of water to simulate raindrops during light, moderate and intense storms.
Result? The seeds germinated faster: in practice, their statoliths are shaken, and this movement acts as a signal for the seeds and seedlings, stimulating their growth and germination.
“This study shows that seeds can perceive sound in ways that can help them survive,” Makris explains. “The energy from the sound of rain is enough to accelerate a seed’s growth.”
The researchers also suspect that the sound of rain is similar to vibrations generated by other natural phenomena such as wind, and they plan to further this work to study other natural vibrations and sounds that plants might perceive.
On the other hand, plants – and this has been known for some time – have evolved by developing, in order to survive, the ability to perceive and react to environmental stimuli: some species close suddenly upon contact, while others fold in on themselves if exposed to toxic odors. And of course, most of them react to light, leaning towards the sun to encourage growth.
Today we know that they can “feel” the rain: the plant world is increasingly incredible and close to us.
The work was published on Scientific Reports.
Sources: Massachusetts Institute of Technology / Scientific Reports
