A tree might look like it’s stuck in place, quietly suffering whatever weather comes. But below that stillness is a remarkable system for sensing, responding and correcting its own posture. But new research suggests that trees can sense when their stems are bent, and turn on a biological process that works much like opposing muscles to bring them back into alignment. Scientists from INRAE and the University Clermont Auvergne have unveiled yet another sophisticated strategy by which plants respond to their environment, and to the shape of their own bodies, by demonstrating how this process operates in young trees. The study published by Phys Org, states that ‘Proprioception’ is the sense of the position of the different parts of the body. In animals, it coordinates muscles and joints, enabling movement and posture maintenance. For a long time it was thought that this is something plants cannot do. However, in 2012, an INRAE research team showed that plants can perceive their own shape and use this information to control their posture. But the biological mechanism for that ability was not understood. An important piece of the puzzle is provided by a new study in New Phytologist. Scientists have discovered that trees can use information about the curvature of their stems to regulate when they produce tension wood, a special wood that generates forces that can change the direction of a stem.
A lab built to shut out the outside world
To study proprioception alone, the researchers had to remove other cues that normally affect a tree’s growth. Trees always respond to gravity and the direction of incoming light, which can tell a plant how it is oriented. Scientists, in turn, made a peculiar experimental environment: a horizontal platform rotating about its own axis inside a sphere illuminated uniformly from all sides. Light came equally from all directions, so there were no directional cues, and gravity was canceled out. And all they had left was their ability to see their own curvature.
The wood that is like muscle
The researchers examined the wood formed in this phase and found that the tension wood which had formed previously on the upper side, stopped forming.
The scientists started out by laying young poplar trees down horizontally. Over the years the trees grew upwards, their tops at last pointing to the vertical. The tension wood formation on the upper side of the stem produced that movement. That specialized tissue pulls the stem into a curve upward. Once the desired curvature had been reached (after 10 days or so) the trees were transferred into the experimental apparatus. Then, in the weeks that followed, something unexpected occurred. Slowly the stems grew straight. The researchers examined the wood formed in this phase and found that the tension wood which had formed previously on the upper side, stopped forming. Instead, the same tension wood started to develop on the other side of the stem.
A hostility system for equilibrium
The finding suggests that tension wood can act in opposite directions, in a similar way as antagonistic muscles in animals. Tension wood, in the first place, pulls a bent stem up. When the tree feels the shape has changed enough the process switches to the other side of the tree, creating force in the other direction, which gradually brings the stem back to a straighter position. This disproves the long-held assumption that tension wood only develops on the upper side of a leaning stem. The process is regulated at the cellular level through several stages and the research shows that proprioception is central in determining where the specialized wood forms.
Why is tree balance important
The findings suggest that trees do more than just respond to environmental signals such as gravity and light. They also monitor their own structure, combining information about their environment with information about their shape. This ability could be especially important when trees are disturbed by storms, landslides, or other extreme events. Being able to change their posture could help them to recover from being knocked and stay stable. The finding could also have practical implications for agriculture and forestry. Understanding plant proprioception could ultimately help scientists select or create upright crops, potentially reducing lodging in cereal crops, researchers suggest. For forestry, the mechanism could offer new insight into tree development of internal stresses and their effects on wood quality.
A new approach to plant hardiness
The study offers a surprising glimpse of trees as living things capable of sensing their own shapes, processing that data and orchestrating a physical reaction. What looks like a dead trunk is actually part of an active biological feedback loop. Specialized wood pulls in opposite directions. This means the tree can be constantly working toward the posture that best suits its circumstances. The discovery deepens scientists’ understanding of plant intelligence and resilience.Images Courtesy: istock
