Multi-scale Control of Structural Functionality in Plant

Plant tissues display structural organization that is intimately related with the specific tissue's functionality. A unique functionality in plants is organ motion. Although plants are not exactly known to move much, many species actuallly have the ability to orient or fold their leaves in order to optimize photosynthesis or ward off herbivores. Leaf actuation is executed by pulvini—joint-like motor organs that operate like hydraulically powered hinges. In the mimosa leaf, pulvini are incorporated at multiple locations in the compound leaf allowing it to rapidly and efficiently fold upon touch. To understand the mechanical principles underlying the execution of the rapid motion, we investigated pulvinus structure at tissue and cell scales. We found that circumferential hoop reinforcements present at various length scales optimize the translation of hydraulic changes into motion. Specialized cell wall structures and epidermis morphologies direct tissue swelling into directed organ shape changes. These findings provide insight into the role of cell wall structure in plant motor strategies, underscore the hierarchical, emergent nature of biomechanical systems, and highlight design principles that can inform the development of biologically inspired soft actuators.