Young trees, like all living things, carry an inward sense of their own shape, and a recent study suggests that sense can be translated into the slow, patient work of straightening a bent stem. Bruno Moulia and his colleagues at INRAE found that poplars, once bent, unwound their curves by shifting where a specialized pulling tissue forms, placing it on the opposite side to pull back. It is a quiet reminder that even rooted organisms move their bodies by means of inner balance, and that the ways trees hold themselves upright may one day help humans grow sturdier forests and crops in an increasi
Trees Straighten Themselves Using Opposing 'Muscles' of Tension Wood, Study Finds
Tension wood can form on both sides, pulling a bent stem straight
Mark
So what actually happened to those poplars?
Mimi
They were bent sideways, grew upward with tension wood on the top side, then were put in a rotating, evenly lit sphere. There the stems straightened, because tension wood stopped forming on top and started forming on the opposite side.
Mark
Why does the rotating sphere matter?
Mimi
It strips out gravity and directional light, so the only information left is the tree's own sense of its shape.
Luke
Worth noting the experiment used young poplars. The report doesn't say whether other species, or mature trees, behave the same way.
Mark
Fair. But the muscle comparison, is that literal?
Mimi
It's an analogy. Tension wood pulls, and on opposite sides it pulls in opposite directions, the way paired muscles do.
Luke
Right, and the "opposing muscle" description is the researchers' interpretation of the wood's pattern. Nothing here says trees have anything like nerves or muscle tissue.
Mark
What about the farm side, the lodging of cereal crops?
Mimi
That's a hoped-for application. Selecting varieties with better proprioception could reduce lodging and improve timber.
Luke
Which is still a prospect. No crop or breeding results are reported, so those benefits are unproven.
Mark
So what's solid?
Mimi
That tension wood can form on both sides of a stem and that this corrects posture in the experiment. That overturns the idea it only forms on the upper side.
Le Pouls
- A poplar bent sideways by circumstance struggles to recover its upright posture, and the tension behind that struggle is what the researchers set out to understand.
- Scientists had assumed a tree's pulling tissue formed only on the upper side of a stem, so the discovery of an opposing forming pattern upended a long-held picture.
- Researchers removed gravity and light cues with a rotating, evenly lit sphere, forcing the trees to rely on their own inner sense of shape.
- The stems slowly straightened as pulling tissue on the upper side faded and new tissue rose on the opposite side, so the opposing forces unwound the curve.
- Forestry and farming teams now aim to identify the trees and crops with the strongest inner sense of shape, hoping to breed straighter timber and cereals that resist collapse under harsher storms.
Young trees, like all living things, carry an inward sense of their own shape, and a recent study suggests that sense can be translated into the slow, patient work of straightening a bent stem. Bruno Moulia and his colleagues at INRAE found that poplars, once bent, unwound their curves by shifting where a specialized pulling tissue forms, placing it on the opposite side to pull back. It is a quiet reminder that even rooted organisms move their bodies by means of inner balance, and that the ways trees hold themselves upright may one day help humans grow sturdier forests and crops in an increasingly unsettled climate.
Picture a young poplar lying on its side. Within about ten days its stem has bent upward, its top swinging back toward vertical. A team led by Bruno Moulia of the French research institute INRAE set out to learn how the tree manages that recovery, a process that had been studied but never fully explained.
Plants sense their own shape, a faculty called proprioception, and it helps them grow straight. What remained unknown was how that sensed information becomes physical movement inside woody tissue. To isolate the stem's own sense of form, the researchers placed young trees on a slowly rotating platform inside a sphere lit evenly from every side, removing the cues of gravity and light.
Once the trees had curved upward, they were moved into this apparatus, and over the following weeks their stems slowly straightened. The wood tells the story: tension wood, which pulls like a contracting muscle, stopped forming on the upper side and began forming on the opposite side. Opposing forces then unwound the curve. Scientists had believed this tissue appeared only on one side, so the finding reshapes that picture, suggesting trees combine outside cues with awareness of their own form.
The stakes reach beyond the laboratory. Storms, landslides and other extreme events bend trees, and as climate change brings harsher weather, recovering proper posture grows more important. Forestry could select varieties that grow straighter and yield better wood, and agriculture might breed cereal crops less prone to lodging. Moulia and his colleague Félix Hartman see the work as proof that bringing different disciplines together, though slow, is worth the effort. The next step is to find which plants sense their shape most effectively and put that ability to use in breeding.
Picture a young poplar laid on its side. Within about ten days its stem has bent upward, the top swinging back toward vertical. That is where a group of researchers, led by Bruno Moulia of the French research institute INRAE, started an experiment that has now been reported in Science.
The question was an old one with a missing piece. Scientists already knew plants can sense their own shape, a faculty called proprioception, and that this internal sense helps them grow as straight as possible. What nobody had worked out was how that sensed information turns into physical movement in the woody parts of a tree.
Plants draw on several kinds of information as they grow: the pull of gravity, the direction of light, and the form and position of their own stems. To study the last of these alone, the team had to silence the first two. They built an unusual apparatus in which young trees sat on a horizontal platform rotating around its axis, inside a sphere lit equally from every direction. The rotation denied the trees a steady gravitational cue, and the even light removed any hint of which way was up.
Before entering that system, the poplars were positioned horizontally and allowed to curve upward. That upward bend depends on tension wood, a specialized tissue unlike ordinary wood because it generates pulling force as it develops. Formed along the upper side of a stem, it works much like a contracting muscle, drawing the stem upward.
Once the trees had a noticeable curve, the researchers moved them into the apparatus. Over the following weeks, the stems did not hold their curved shapes. They slowly straightened until they were nearly straight again.
To find out why, the team examined the wood laid down during that period. The original tension wood, on the upper side of the stems, stopped forming once the trees were in the system. At the same time, identical tension wood began forming on the opposite side. That new tissue pulled the other way, and as the two forces opposed each other, the curve unwound. The findings indicate that the tree's internal sense of its shape helps decide where tension wood develops.
This overturns a narrower picture. Scientists had believed tension wood formed only on the upper side of a stem, a pattern easy to see near the bases of trees on mountain slopes, where trunks curve to stand upright. The new work shows it can form on opposing sides and generate forces in different directions, like the opposing muscle groups animals use to hold posture. Trees, it suggests, combine outside information such as light and gravity with an awareness of their own form to steer their growth.
The practical stakes are considerable. Powerful storms, landslides and other extreme events can bend or displace trees, so recovering a proper posture matters for their resilience, a concern that grows as climate change brings harsher conditions. In forestry, identifying plants with especially effective proprioception could help select varieties that grow straighter and yield higher-quality wood. Poorly coordinated tension wood formation can create excessive internal stress in a tree, which may affect the wood's properties. In agriculture, the same knowledge might help develop cereal crops less prone to lodging, the collapse of plants late in the season that can cause significant yield losses.
Moulia called the finding "a genuine sensorimotor loop operating in the woody parts of trees," and said it reshapes applied work aimed at trees "as straight and as relaxed as possible." His colleague Félix Hartman, an INRAE research engineer, stressed that the result came from bringing together researchers from different disciplines, which takes time and perseverance but, he said, proves worthwhile. The next step is to see whether plants with especially effective proprioception can be identified and put to use in breeding.
Citations marquantes
What we have uncovered is a genuine sensorimotor loop operating in the woody parts of trees.— Bruno Moulia, INRAE research director
Interdisciplinary discoveries take time and perseverance, but the effort is worthwhile.— Félix Hartman, INRAE research engineer (paraphrased)
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