Why Do Plants Move? Scientists Solve an Old Mystery That Baffled Charles Darwin

A study has found that sunflowers’ erratic movements help them locate sunlight, providing insights into plant behavior and potential agricultural benefits.

In a new study, physicists from the United States and Israel may have found an explanation for a strange behavior in plant growth, a mystery that puzzled Charles Darwin himself during the last decades of his life.

To many humans, plants may seem stationary and even a little dull. But green things actually move a lot. If you watch a time-lapse video of a sunflower seedling sprouting from the soil, for example, it doesn’t grow straight up. Instead, as the sunflower grows, its crown spins in circles, twists into a spiral, and generally wriggles—albeit very slowly.

Now, researchers led by Orit Peleg of the University of Colorado Boulder and Yasmin Meroz of Tel Aviv University have discovered a role for these chaotic movements, also known as “rotation.” In greenhouse experiments and computer simulations, the group showed that sunflowers use rotation to search their surroundings for patches of sunlight.

“A lot of people don’t really take into account the motion of plants, because as humans we typically view plants at the wrong frame rate,” said Peleg, a co-author of the study and an associate professor in the BioFrontiers Institute and the Department of Computer Science.

The team published its results on August 15 in the journal Physical Review X.

These findings may one day help farmers come up with new strategies for growing a range of crops in more efficient arrangements.

“Our team does a lot of work on social interactions in insect swarms and other animal groups,” said Chantal Nguyen, lead author and postdoctoral researcher at BioFrontiers.

“But this research is particularly interesting because we see similar dynamics in plants. They are rooted in the ground.”

Darwin’s Choice

Plants don’t usually move like animals, Nguyen added, but instead move by growing in different directions over time. This phenomenon fascinated Darwin long after his return from his voyage on the battleship Beagle. According to historical accounts.

In the 1860s, Darwin, who was suffering from a series of illnesses that limited his mobility, spent days observing the plants in his home. He planted seeds of cucumbers and other plants. ClassThen they tracked how their crowns moved from day to day — and the resulting maps looked random and crazy.

“I have a lot of fun with my curls – it’s just the kind of annoying work that suits me.” Written to a friend in 1863.

Whether Darwin was amused or not, he could not explain why some of his hair was twisted.

It’s a mystery that also baffles Meroz, a physicist by training. One study conducted in 2017 This research pointed her in the right direction. In the study, scientists led by the University of Buenos Aires grew rows of sunflowers in cramped conditions. They discovered that the plants naturally and consistently arranged themselves in a zigzag pattern, almost like the teeth of a zipper. This arrangement likely helps the plants maximize their access to sunlight as a group.

Meroz wondered if plant vibrations could be the engine driving such patterns in plant growth.

“For climbing plants, it’s clearly about finding supports to cling to,” said Meroz, a professor of plant science and food security. “But for other plants, it’s not clear why it’s worth it.”

Here comes the sun

To find out, she and her colleagues planted five week-old sunflowers in rows. Then, like Darwin before them, they mapped how the plants moved over the course of a week.

Next, Nguyen and Bligh developed a computer program to analyze the patterns that govern sunflower growth. The researchers were also able to use computer simulations to see what would happen if the sunflowers moved more or less — in other words, if they moved randomly or in a slow, steady pattern.

The group found that if the digital plants didn’t move at all, they would all lean away from each other in a straight line. By contrast, if they moved a lot, they would grow in a random pattern. But if they moved with just the right amount of randomness, the sunflowers formed that distinctive zigzag shape that in real plants provides ample access to sunlight. The plants seem to swivel around to find where the best light is coming from, and then grow in that direction, Nguyen explained.

“When you add a little bit of noise to the system, it allows the plant to explore its surroundings and settle into those configurations that allow each plant to find the maximum amount of light exposure. That results in this beautiful zigzag pattern that we see,” she said.

In future experiments, the researchers will test how sunflowers grow in more complex arrangements. For her part, Meroz is happy to see plants getting some recognition for their mobility and impact.

“If we all lived on the same time scales as plants, you could walk down the street and see them moving,” she said. “Maybe we would all have plants as pets.”

Reference: “Noisy circles facilitate self-organized shade avoidance in sunflowers” ​​by Chantal Nguyen, Emre Dromi, Aharon Kempinski, Gabriela E. C. Gal, Orit Peleg, and Yasmin Meroz, August 15, 2024, Physical Review X.
DOI: 10.1103/PhysRevX.14.031027