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.
The research was led by Harsh Bais, assistant professor of plant and soil sciences at UD, former postdoctoral researcher Thimmaraju Rudrappa, who is now a research scientist at the DuPont Co., Kirk Czymmek, associate professor of biological sciences and director of UD's Bio-Imaging Center, and Paul Par, a biochemist at Texas Tech University.
The study is reported in the November issue of Plant Physiology and also is featured on the journal's cover. Rudrappa is the lead author of the research paper.
"Plants are a lot smarter than we give them credit for," says Bais from his laboratory at the Delaware Biotechnology Institute.
"People think that plants, rooted in the ground, are just sitting ducks when it comes to attack by harmful fungi or bacteria, but we've found that plants have ways of seeking external help," he notes.
In a series of laboratory experiments, the scientists infected the leaves of the small flowering plant Arabidopsis thaliana with a pathogenic bacterium, Pseudomonas syringae. Within a few days, the leaves of the infected plants began yellowing and showing other symptoms of disease.
However, the infected plants whose roots had been inoculated with the beneficial microbe Bacillus subtilis were perfectly healthy.
Farmers often add B. subtilis to the soil to boost plant immunity. It forms a protective biofilm around plant roots and also has antimicrobial properti
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University of Delaware