Leaves have a hidden sense of touch that relies on their vein networks, new research shows. Yang and colleagues found that leaf veins in the model plant Arabidopsis thaliana can detect gentle mechanical stimulation on their own, without input from other leaf tissues. Their discovery has recently been published in Science Advances.
Using tiny glass beads, the team applied precise mechanical forces to Arabidopsis leaves and veins. They recorded rapid electrical signals produced in response, similar to the action potentials generated by animal nerves. However, unlike animal nerves, the plant vein signals did not follow an all-or-none pattern characteristic of true action potentials.
Surprisingly, the researchers could also trigger electrical activity by stimulating exposed veins they had surgically removed from the rest of the leaf. This response suggests the veins themselves are sensitive to touch rather than relying solely on touch-detecting cells in the outer leaf layers.
Further experiments implicated proton pumps called H+-ATPases in powering the vein electrical responses. Mutant plants lacking key H+-ATPase genes had reduced touch-induced signals. One of these, aha3, produced a protein that was found throughout the vein network and specifically in phloem companion cells.
Why might leaf veins sense touch? One reason might be defence. The authors write:
The fact that mechanostimulation-induced local jasmonate signaling suggests a connection to plant defense. Under some conditions (such as penetration of developmental layer 3 by sucking invertebrates), there may be advantages of locally inducing jasmonate pathway activity. We note, however, that the long recovery periods between full-amplitude touch-response electrical signals might preclude strong stimulation of defenses.Yang et al. 2023
Intriguingly, plants with impaired vein touch-sensitivity also grew more slowly. This result hints that the mechanical sensitivity of veins is tied to their role in transporting nutrients like sugars. The findings reveal veins are not just passive plumbing but dynamic sensory systems finely tuned to the life of the leaf.