Beyond stiffness: extensometry in plant growth and morphogenesis

Plant growth is a mechanical process in which turgor-generated tension stretches the cell wall, while irreversible expansion depends on wall relaxation, creep, and yielding. Plant biomechanics can be investigated using a wide range of techniques, often integrated with computational modeling. Yet these methods differ in the scale, direction, and loading mode they probe. This review highlights the distinctive role of extensometry in measuring living tissue responses to controlled in-plane tension, a loading mode closely related to the tensile state generated during turgor-driven expansion. Apparent tensile modulus and rupture characterize resistance and failure, whereas creep and stress relaxation probe time-dependent behavior more closely related to irreversible wall expansion. Tensile experiments can also quantify recovery, residual strain, anisotropy, and work to failure. Optical tracking, confocal imaging, and finite element modeling help connect these sample-scale responses to local deformation and tissue structure. At the same time, tensile data require careful interpretation because apparent tissue stiffness integrates wall material behavior with turgor, cell geometry and patterning, wall thickness, hydration, and boundary conditions. Here, we discuss applications in different plant organs and cell wall mutants and highlight open hardware, automated imaging, and multiscale modeling as routes toward a more quantitative plant mechanobiology. We outline how paired loading and recovery protocols, constitutive models, and independent measurements can constrain reversible deformation, persistent strain, and growth-relevant parameters.