INRAE researchers prove proprioception drives active straightening in poplar stems

Researchers from INRAE and Université Clermont Auvergne demonstrated that young poplar trees actively correct stem curvature using internal proprioception rather than passive mechanical recoil alone, according to a study published in New Phytologist doi.orgNew Phytologistdoi.orgOpen source ↗. The team investigated whether trees rely on curvature sensing to control autotropic movements when external spatial references are removed.

To separate proprioception from gravitropic and phototropic responses, scientists grew hybrid poplars (Populus tremula × alba) horizontally until gravitropic stimuli induced upward bending via tension wood. After roughly ten days, once bending was established, the bent specimens were transferred to a dedicated clinostat system housed inside an omnidirectional illumination sphere. This suspended gravitropic orientation and directional light cues on demand, leaving internal curvature sensing as the only directional signal available to the plant doi.orgNew Phytologistdoi.orgOpen source ↗.

Antagonistic Wood Formation

Quantitative analysis of the stems revealed that the poplars initiated active counter-curving, progressively straightening over several weeks doi.orgNew Phytologistdoi.orgOpen source ↗. The production of tension wood on the original upper surface halted inside the test environment. Instead, new tension wood developed systematically along the convex side of the curved stem, exerting tensile force to pull the axis back into alignment until straightness was achieved doi.orgNew Phytologistdoi.orgOpen source ↗.

This pattern indicates that tension wood functions analogously to an antagonistic muscle system, shifting position dynamically based on internal mechanical feedback. Anatomical cross-sections confirmed identical structural features in the tension wood layers formed during both the bending and counter-curving stages doi.orgNew Phytologistdoi.orgOpen source ↗.

Feedback Control Dynamics

The experimental data enabled researchers to formulate the curvature-dependent control law governing this response and measure proprioceptive sensitivity doi.orgNew Phytologistdoi.orgOpen source ↗. Historically, textbook models assumed that reaction wood in dicot stems forms exclusively in response to gravity. The authors showed that stem posture regulation instead relies on a balance between gravitropic and proprioceptive feedback loops doi.orgNew Phytologistdoi.orgOpen source ↗.