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The sunflower dance party

In their growth, the sunflowers "dance" so as not to hide the sun from each other. The surprising study sheds light on a scientific puzzle that has occupied researchers since Darwin's day

Dr. Yasmin Maroz in the hothouse. Photo: Tel Aviv University spokeswoman
Dr. Yasmin Maroz in the sunflower greenhouse. Photo: Tel Aviv University spokesperson

A new study by Tel Aviv University, in collaboration with the University of Colorado Boulder in the USA, revealed that plants that grow in a dense environment, with each plant casting a shadow on its neighbor, find a collective solution with the help of random movements that help them find optimal growth directions. In this way, the study sheds light on a scientific puzzle that has occupied researchers since the days of Darwin.

The surprising research was conducted under the leadership of Prof. Yasmin Maroz from the School of Plant Sciences and Food Security at Tel Aviv University, in collaboration with Prof. Orit Peleg from the University of Colorado Boulder in the USA. The study was published in the prestigious journal Physical Review X.

Prof. Maroz explains: "Previous studies have shown that if sunflowers are planted in a field at a very high density, when they shade each other, they grow in a zigzag pattern - one forward and one back - so as not to be in each other's shadow. Thus they grow side by side in an optimal way to maximize the solar flux, and therefore photosynthesis, on a collective level. In fact, plants know how to distinguish between the shadow of a building, for example, and the green shadow of a leaf. If it's the shadow of a building - they usually don't bother to grow otherwise, because they have nothing to do about it. But if it is the shadow of a plant, they will grow in the direction away from the shadow."

In the current study, the researchers decided to examine the question of how the sunflowers know how to get along in an optimal way and they analyzed the dynamics of the sunflowers in the laboratory while they get along in a zig-zag pattern. Prof. Maroz and her team grew sunflowers in high density and photographed them growing. The camera took pictures of the sunflowers every few minutes, and then the pictures were run together in fast motion (time lapse) to create a kind of video. The researchers followed the movement of each individual sunflower - and saw that they were "dancing" a lot.

According to the researchers, Darwin was the first to recognize that plants - all plants - grow in a kind of cyclical movement (called circumnutations), between rotational and random, including the stems and roots. But until today - with the exception of a few cases such as climbing plants, which grow in huge circular movements to look for something to grab onto - it was not clear whether it was a bug or a feature. Why would the plant invest energy to grow in rotations?

Prof. Maroz: "As part of our research, we conducted a physical analysis that refers to the behavior of each sunflower within the sunflower collective and we saw that the sunflowers 'dance' to find the best angle not to hide from each other. We quantified the movement statistically and showed through computer simulations that the random movements optimize shadow finding collectively. In addition, it was also very surprising to discover that the distribution of the "steps" of the sunflowers was very wide, a distribution of three orders of magnitude, from zero displacement to a movement of two cm every few minutes in one direction or another."

In conclusion, Prof. Maroz adds: "The plant takes advantage of the fact that it has both small and slow steps and large and fast ones, and the range of steps is such that it allows it to get along in the best possible way. That is, if the range of steps was smaller or larger - the arrangement would be expressed in more mutual shading and therefore in less photosynthesis. What is it similar to? for a crowded dance party. Everyone moved a little to the right and a little to the left, without planning in advance and without asking out loud 'Excuse me, can you move a little?' Even the individuals within a dance party should use large and small movements to a certain extent, since if they move too much they will hurt the other dancers, but if they move too little - the crowding problem will not be solved, it will be very crowded in one corner of the square and empty on the other side. The sunflowers show a similar dynamic of communication - a combination of response to the shade of neighboring plants - along with random movements regardless of external stimuli."

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