Inference of mechanical forces through 3D reconstruction of the closing motion in venus flytrap leaves.

Venus flytrap (Dionaea muscipula) leaves exhibit an exceptionally rapid closing motion that occurs within one second. The rapid closure of outwardly curved leaves is thought to be driven by snap-buckling instability-a rapid transition of an elastic system from one state to another. However, the ability of leaves that do not curve outward to also close suggests that the mechanics of leaf closure are complex and need to be understood using three-dimensional (3D) kinematics. We therefore developed a 3D reconstruction method to quantify the curvatures and displacements of leaf blades using two high-speed cameras. We then reconstructed a 3D surface mesh of the leaf, which revealed that the changes in curvature are spatiotemporally heterogeneous. We inferred the stretching and curvature elastic energies of the reconstructed surface, determining that the mechanical forces associated with in-plane deformation become significant in the peripheral regions of the leaf. This was true among different samples; however, the components of the energy profiles varied for each sample. The novelty of this study is that we could infer the elastic energy and the corresponding mechanical forces during closing motion. Our mechanical inference method will be useful for examining the deformation processes of various curved plant structures.