Ohad, A. | Search bioRxiv

bioRxiv2026

Circumnutations drive embodied mechanical sensing and support selection in twining plants

Climbing plants use self-generated oscillatory movements called circumnutations to search their environment for supports to attach to. Yet little is known about what information these movements provide. Here we show that circumnutations enable climbing plants to actively assess the mechanical stability of a newly encountered support and determine whether to initiate twining. Analogous to whisking in mammals, circumnutating shoots generate predictable mechanical loading that probes support resistance. Force measurements of freely circumnutating bean shoots reveal that contact forces follow a characteristic sinusoidal pattern. We develop a minimal physical model of this system, and experimentally informed simulations recover the measured force trajectories. We find that the stem-support interaction is captured by a simple torque balance between external loading and the intrinsic bending moment of the stem, equivalent to a cantilever beam with a rotating load. Analysis of force trajectories, supported by experimentally informed simulations, shows that force amplitude is set by stem stiffness and geometry, whereas the characteristic timescale is governed by the circumnutation rate. Twining occurs only after the stem reaches a critical torque threshold, corresponding to a threshold deformation of the stem that likely serves as the mechanical trigger for twining initiation, reflecting both sufficient support stability and a minimal geometric overshoot required for grasp. Motorized-stage experiments further demonstrate that increasing the effective circumnutation rate accelerates twining initiation to minutes, whereas reducing it can suppress twining despite prolonged contact. Together, these results establish embodied mechanical sensing in plants and show how morphology and self-generated motion enable support selection without centralized control.

biophysics↗

bioRxiv2025

Dual-Axial Force Measurements of Non-Tethered Plants

Growing plants are remarkable at negotiating obstacles in their unstructured and changing environments. Measuring the mechanical interactions of growing plants with surrounding objects is a critical step towards deciphering thigmotropic responses underpinning complex growth strategies. Yet, available force-measurement systems have limited capacity to capture weak (sub-mN) forces in freely moving plant organs - such as the forces applied by a growing shoot pushing at an obstacle. We developed a measurement system based on the deflection of a pendulum by a freely moving shoot. Crucially, unlike many force-measurement systems, the organ is not tethered to the device. Moreover, force is measured along two axes, as opposed to one axis in commonly used methods such as cantilevers. Orthogonal cameras track the 3D position of the rod and shoot, yielding the rod deflection angle and, using a mechanical torque equilibrium equation, allowing to extract the force applied by the plant over time. This system is relevant for measuring weak forces in macro-sized systems (such as growth or turgor pressures), and the force detection range can be tuned by altering rod mass and length. We demonstrate the system with bean (Phaseolus vulgaris) shoots, measuring the forces they apply on a candidate support during inherent circumnutation movements, prior to twining. Such measurements lay the foundations for deciphering how climbing plants assess whether to twine or not - an open question since Darwins first observations.

biophysics↗