ScienceDaily (Oct. 17, 2008) — Researchers at the University of Delaware have discovered that when the leaf of a plant is under attack by a pathogen, it can send out an S.O.S. to the roots for help, and the roots will respond by secreting an acid that brings beneficial bacteria to the rescue.

The finding quashes the misperception that plants are “sitting ducks”--at the mercy of passing pathogens--and sheds new light on a sophisticated signaling system inside plants that rivals the nervous system in humans and animals.