For more than 20 hours, sunflower seedlings at Tel Aviv University bent toward blue light from changing directions—sometimes growing toward a weaker source after brighter beams canceled each other out.
The movement offers a glimpse of how plants make sense of their surroundings without a brain or nervous system. A team at Tel Aviv University says plants can combine light signals gathered at different points along a stem, using local responses rather than a central control center. The findings help explain how a plant chooses a direction to grow when light comes from more than one place.
Light receptors sit mainly in the stem’s outer layer. In the researchers’ model, each area senses light nearby and turns its intensity into a biological signal. The signals are then combined to guide the stem’s growth. Because a plant’s response is nonlinear, a light source twice as strong does not necessarily produce a signal twice as strong.
To test the idea, the team exposed sunflower seedlings to blue light of different intensities and directions, and recorded their movement for more than 20 hours. In one set of tests, seedlings received light from a single source and then from two sources facing each other. They grew toward the stronger source, but the amount they bent did not match a simple, direct comparison of the two light intensities. A mathematical model developed by the researchers predicted both the strength and direction of the bending under different lighting conditions.
The researchers then set up two equally strong sources opposite each other, along with a weaker third source at a right angle. The opposing strong lights largely canceled one another’s effect, and the seedlings grew toward the weaker light. That result supports the idea that plants combine signals from different directions, rather than simply following the brightest beam.
The model also points to a subtle twist: a plant’s growth direction may differ slightly from the actual direction of the strongest light. The team describes this as an “optical illusion,” though the phrase does not mean that plants see images. Instead, the signals gathered and processed across the stem can make the direction of greatest perceived illumination differ from the physical direction of maximum light. The predicted distortions are small, and natural fluctuations in the seedlings’ movement meant the team could not measure them directly in this experiment.
The study was conducted by Aharon Kempinski, Dr. Amir Porat, Dr. Mathieu Rivière and Professor Yasmine Meroz, of Tel Aviv University’s School of Plant Sciences and Food Security and its Center for the Physics and Chemistry of Living Systems. It was published in the Proceedings of the National Academy of Sciences in 2026. Meroz said the same principle of distributed sensing could be relevant beyond plants, including in cells and bacteria. Further work may show how simple local signals help living systems respond to complex surroundings—without a central command center.