How slender bamboo reacts to gravitational and external mechanical stimuli: Responses and mechanisms

Bamboo is renowned for its rapid growth rate and striking slenderness. Despite the challenges to mechanical stability posed by its slender structure, bamboo demonstrates an exceptional ability to resist external forces. How does it accomplish this? In this study, we focused on upright plants of Moso bamboo (Phyllostachys edulis), as well as those that were bending naturally or inclined artificially, exploring their responses to gravitational and mechanical stimuli. Artificially inclined bamboo showed remarkable control and reorientation of posture through the independent sensing of local angles at each internode. Strain gauge tests revealed that bamboo possesses growth stress, forming an intrinsic support system. Upright bamboo (UB) plants displayed longitudinal tensile stresses, enhancing their stability amidst disturbances. Non-UB plants exhibited a pronounced asymmetrical stress distribution, with higher tensile stress on one side, which is crucial for maintaining a slanted posture. We detected variability in stress on the opposite side, ranging from low-level tensile stress to compressive stress, demonstrating bamboo's dynamic response to stimuli. Moreover, growth stress was detected at the cellular level, providing a foundation for investigating the origin and generation of growth stress in bamboo. Multiscale studies revealed adaptations across the macroscopic appearance, microscopic structure, and physiological functions of bamboo in response to gravitational and external mechanical stimuli, which are closely linked to mechanical responses, thereby ensuring efficient growth and stability.