Typically, plants grow in crowded environments, where neighboring plants shade each other while competing for light. The presence of neighbors varies over space and time, and plants have evolved the ability to detect neighbors and grow away from their shade. While it is generally acknowledged that these responses aid plants in increasing their individual light exposure, it is not clear how they manage to find collectively beneficial solutions. Here we seek a mechanistic understanding of the spontaneous self-organized pattern formation in sunflower arrays that are mediated by shade avoidance.

Our analysis reveals that circumnutations—inherent oscillatory plant movements—provide random perturbations that conform to a bounded random walk. These movements are characterized by a remarkably broad distribution of velocities, covering 3 orders of magnitude. In motile animal systems, such velocity distributions are frequently associated with enhanced exploration and other behavioral processes, suggesting that circumnutations may serve as functional noise. To test our hypothesis, we develop a minimal model of interacting growing disks, informed by experiments, and find that the observed breadth of the velocity distribution underpins an optimized arrangement with minimal shading, balancing exploration of possible solutions and exploitation of available light. These findings represent the first report of broadly distributed plant movements and their role as functional noise, providing a conceptual framework for investigating plant navigation based on task-oriented processes, optimization, and active sensing.

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C. Nguyen, I. Dromi, A. Kempinski, G.E.C. Gall, O. Peleg, Y. Meroz
Noisy Circumnutations Facilitate Self-Organized Shade Avoidance in Sunflowers
PRX 14, 031027 (2024)