Scientists have discovered that trees utilize specialized, opposing muscle-like tension wood to actively straighten themselves and monitor their posture, revealing a sophisticated sensorimotor loop operating within woody plant parts.
Isolating Plant Proprioception Inside Rotating Spheres
Trees possess a natural awareness of body position known as proprioception. While this internal sense was once thought to exist exclusively in animals, researchers working with INRAE demonstrated in 2012 through work published in PNAS by Bastien R. et al. that plants share this capability. How plants convert this positional awareness into physical movement remained unknown until recent experiments.
To isolate proprioception from external cues, researchers needed to eliminate the directional signals of gravity and light. Young poplar trees were placed on a horizontal platform that rotated around its axis inside a sphere illuminated equally from every direction. The rotation blocked consistent gravitational signals, while the uniform light removed directional cues.
The experiment began with young poplar trees positioned horizontally. As they grew, their stems curved upward to bring their tips back toward a vertical orientation. This initial movement relied on tension wood forming along the upper side of the stem, generating pulling forces that acted like a contracting muscle.
Activating Opposing Tension Wood Forces
After approximately ten days, once the trees developed a noticeable curve, researchers placed them into the experimental apparatus. The stems slowly straightened until they became nearly straight again. Examining the wood structure revealed that the original tension wood stopped developing when the system activated. At the same time, identical tension wood began forming on the opposite side of the stem.
This newly formed wood acted as an opposing muscle, producing a pulling force in the reverse direction. The opposing forces worked against each other to return the curved stems to a straight shape. The findings show that a tree’s internal sense of its own shape regulates where tension wood develops to correct its posture.
Previously, scientists believed tension wood formed solely on the upper side of stems to pull them upward, a pattern visible near the bases of trees on mountain slopes. The new research proves that tension wood plays a more versatile role by developing on opposing sides and generating forces in different directions, similar to the opposing muscle groups animals use to control movement.
Implications for Forestry and Agriculture
The ability to correct shape is essential when storms, landslides, and extreme weather bend or displace trees. Understanding this mechanism provides practical value for forestry and agriculture. Scientists may be able to select plant varieties that grow straighter, maintain better posture, and produce higher-quality wood.
In agriculture, the same knowledge could help researchers develop cereal crops that resist lodging, a problem where crops fall over near the end of the growing season and cause significant yield losses. Poorly coordinated tension wood can also create excessive internal stresses that affect timber quality.
Bruno Moulia, INRAE research director, explained the significance of the findings regarding wood quality and plant resilience.
What we have uncovered is a genuine sensorimotor loop operating in the woody parts of trees! Poor coordination in the successive activation of tension wood results in excessive internal tension, which can affect wood quality. These findings therefore reshape more applied research aimed at improving wood quality… and at obtaining trees that are as straight and as relaxed as possible, whatever life throws at them!
Félix Hartman, INRAE research engineer, emphasized the collaborative effort behind the discovery.
Revealing the remarkable capabilities of trees requires a great deal of ingenuity. In this project, we achieved it by bringing together researchers from different disciplines, with complementary skills and perspectives. This requires time and perseverance, but these interdisciplinary discoveries show that the effort is worthwhile.
This discovery highlights how combining interdisciplinary expertise unlocks complex plant environmental interactions, providing a foundation for future agricultural and forestry advancements.
