Trees can sense their own shape and adjust their growth to remain upright, a capacity known as proprioception that was once thought to exist only in animals. Research by INRAE scientists has now shown how this internal sense guides the formation of tension wood, allowing a bent stem to straighten even when gravity and directional light are removed from the experiment.
How scientists identified trees’ hidden sense
Plants use several types of information to guide their growth. They respond to gravity, detect the direction of sunlight and monitor the shape and position of their stems. In 2012, researchers working with INRAE demonstrated that plants possess proprioception, or an ability to sense their own position and shape (Bastian R. et al., PNAS). Later work established that plants could detect their own form, but the biological process that converted this information into physical movement remained unclear (Mouria et al., Science).
To study proprioception independently of other signals, the researchers needed to remove the directional cues provided by gravity and light. They placed a young tree horizontally on a platform that rotated it around its axis inside a sphere illuminated evenly from all directions.
The rotating platform prevented the trees from receiving a consistent directional signal from gravity, while the uniform lighting removed clues about which direction they should grow. This arrangement enabled the researchers to examine how the trees responded to their own shape without relying on the environmental signals that normally influence growth.
Muscle-like wood helps trees straighten
The experiment began with young poplar trees positioned horizontally. As each tree grew, its stem gradually curved upward and its top moved back toward a vertical position.
This response depends on a specialized form of wood called tension wood. Unlike ordinary wood, tension wood can generate pulling forces as it develops. When it forms along the upper side of a stem, it acts somewhat like a contracting muscle, pulling the stem upward and bending it.
After about 10 days, when the trees had begun to bend noticeably, the researchers transferred them to the experimental setup. Over the following weeks, the stems slowly straightened and became almost straight again instead of retaining their curved shape.
To determine what caused this change, the team examined the wood that formed during the straightening process. They found that the original tension wood on the upper side of the stem stopped developing after the experimental conditions were introduced. At the same time, tension wood began to form on the opposite side.
The newly formed wood appeared to act like an opposing muscle, generating a pulling force in the opposite direction. As the two forces interacted, the curved stem gradually returned to a straighter shape.
The production of tension wood involves complex biological processes controlled at the cellular level. The findings indicate that a tree’s internal sense of its own shape regulates this process, helping determine where tension wood develops to correct the plant’s posture.
A more versatile role for tension wood
Scientists previously thought that tension wood formed only on the upper side of a stem, where it helped pull the stem upward. This is particularly evident near the bases of trees growing on mountain slopes, whose trunks must curve to maintain an upright position.
The new research suggests that tension wood has a more flexible role. It can develop on the opposite side of a stem and generate force in different directions, similar to the opposing muscle groups animals use to maintain posture and control movement.
The finding points to sophisticated growth-regulation systems in trees. Plants combine information about their surroundings, including light and gravity, with an internal awareness of their own shape. By processing these signals, they can regulate where tension develops and adjust the position of the stem.
Why the discovery matters for forests and agriculture
The ability to sense and modify body shape may be particularly important when trees experience environmental disturbances. Strong storms, landslides and other extreme events can bend or shift trees, making the ability to regain an upright posture important to their resilience.
Understanding this mechanism could become increasingly valuable as climate change exposes forests to more extreme conditions.
The findings may also have practical applications in forestry and agriculture. By identifying plants with especially effective proprioception, scientists might be able to select varieties that grow straighter, maintain better posture and produce higher-quality wood.
In agriculture, the same knowledge could help researchers develop grain crops that are less likely to collapse before harvest. This problem, known as lodging, can cause significant yield losses when crops fall over toward the end of the growing season.
The research could also contribute to improving wood quality. Poorly coordinated formation of tension wood can create excessive internal stresses in a tree, affecting the properties of the resulting timber.
Bruno Moulia, an INRAE research director, said:
“What we have discovered is a genuine sensorimotor loop operating in the woody part of the tree! Poor coordination in the continuous activation of tension wood can result in excessive internal tension, which can affect the quality of the wood. These discoveries therefore reshape more applied research aimed at improving the quality of wood… and the aim of getting as straight and relaxed a tree as possible, no matter what life brings!”
The study also underscores the importance of combining expertise from different scientific fields to understand the complex ways plants interact with their environment.
INRAE research engineer Felix Hartmann emphasized the collaborative effort behind the work:
“Uncovering the amazing abilities of trees requires tremendous ingenuity, and this project achieved that by bringing together researchers from different fields with complementary skills and perspectives. This will take time and patience, but these interdisciplinary discoveries show that the effort is worth it.”
Source: www.sciencedaily.com