Ducla, J.; Di Fino, L.; Mentzelopoulou, A.; Talide, L.; Besten, M.; Bernacka-Wojcik, I.; Arbring Sjöström, T.; Zahid, N.; Jämtgard, S.; Stavrinidou, E.; Niittylä, T.; Sprakel, J.; Marhavy, P.

The plant-to-plant communication of damage is vital for plants to mount pre-emptive defensive responses in the face of threats. A variety of threats to the well-being of plants are found below ground; yet how plant roots activate inter-plant communication is largely unclear. Here we demonstrate that a wounded root rapidly releases protons (H+), that travel faster than any other \"known\" soluble biochemical signal due to a specialised diffusion mechanism. Within seconds after damage, cells in neighbouring unwounded roots sense the acidification and activate tissue-specific Ca2+ damage signalling. In turn, this triggers a differential growth response allowing the unwounded root to avoid the site of a potential threat. Our results reveal a non-canonical rapid response mechanism for inter-plant communication based on ultrafast proton diffusion.