Trees can sense their own posture and adjust their growth to remain upright, a capacity known as proprioception that was once associated only with animals. Researchers demonstrated in 2012 that plants also possess this ability, and new experiments show how trees use tension wood as part of an internal sensorimotor system to correct the shape of their stems.
Separating proprioception from gravity and light
Plants use several sources of information to guide their growth. They respond to gravity, detect the direction of sunlight and monitor the shape and position of their stems. Although scientists had established that plants could detect their own form, the biological process that translated this information into physical movement remained unclear.
In 2012, researchers working with INRAE demonstrated that plants have proprioception (Bastian R. et al., PNAS). Further research examined how this internal sense enables plants to monitor their posture and adjust their growth to become as straight as possible (Mouria et al., Science).
To study proprioception independently of external signals, researchers needed to remove the directional information normally provided by gravity and light. They placed a young tree horizontally on a platform that rotated on its axis inside a sphere illuminated evenly from all directions.
The rotating platform prevented the tree from receiving a consistent directional signal from gravity, while the uniform lighting removed clues about which way it should grow. This setup allowed the researchers to examine how the tree responded to its own shape without relying on the environmental signals that normally influence growth.
Tension wood helps the stem 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 type 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 rotating system. Over the following weeks, the stems did not retain their curved form. Instead, they slowly straightened and became almost straight again.
To determine why, the team examined the wood that formed during the straightening process. The original tension wood on the top of the stem stopped developing once the experimental conditions were introduced. At the same time, tension wood began to form on the opposite side.
The newly formed wood appeared to generate a pulling force in the opposite direction, much like an opposing muscle. As the two forces interacted, the curved stem gradually returned toward a straight shape.
The production of tension wood involves complex cellular processes. The findings indicate that a tree’s internal perception of its own shape regulates this process, helping determine where tension develops so the tree can correct its posture.
A more versatile role for tension wood
Scientists had 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 base of trees growing on mountain slopes, where trunks must curve to maintain an upright position.
The new research suggests that tension wood has a broader role. It can develop on the opposite side of the stem and generate force in different directions, resembling the opposing muscle groups animals use to maintain posture and control movement.
The finding points to sophisticated growth-regulation systems in trees. Trees 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 their posture.
Implications for forests, crops and wood quality
The ability to sense and modify posture can help trees recover from environmental disturbances. Storms, landslides and other extreme events can bend or displace trees, making the ability to regain an upright position 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. Identifying plants with particularly effective proprioception could help researchers select varieties that grow straighter, maintain better posture and produce higher-quality wood.
In agriculture, the same knowledge could contribute to the development of grain varieties that are less likely to collapse before harvest. This problem, known as lodging, can cause significant yield losses when crops fall over near the end of the growing season.
The research could also help improve 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, 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 value of combining expertise from different scientific fields to understand the complex ways plants interact with their environment.
INRAE Research Engineer Felix Hartmann highlighted the collaborative work behind the discovery:
“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
