7.16 When under attack, plants call for bacterial backup
By Matt Ford | Published:
October 21, 2008 - 11:42AM CT
When most animals are under attack, they can simply get up and move; they have the option of fight or flight. Plants, on the other hand, don't really have two options; I suppose they're faced with a fight or die situation. New research from my alma mater, the University of Delaware, has shown that certain plants, when under attack from microbial invaders, can call on bacteria to do the fighting for them.
Inset image credit: University of
Delaware/Thimmaraju Rudrappa
Set to be published in the
November edition of Plant Physiology, the Delaware team examined the response
of Arabidopsis thaliana to an invasion by the bacterium Pseudomonas syringae. Plants in the
control group withererd and had their leaves yellow a few days after being
infected. In the experimental population, the plants had their roots inoculated
with the beneficial bacterium Bacillus subtilis; these plants were
perfectly healthy even days after the infection by the harmful microbe.
The addition of B.
subtilis is not a novel idea, as farmers use it to boost the immunity of their
plants. It is known to form a biofilm around plant roots and has antimicrobial
properties, according to a co-author of the paper, Harsh Bais. However, in this
work, the researchers were able detect the transmission of a
"long-distance signal" from the plant leaves to the B. subtilis
in the soil. The signal went via the roots, which responded by secreting malic
acid, a carbon-rich chemical used to attract the helpful bacterium backup.
By tagging the helpful
bacterium and using confocal microscopy, the researchers were able to
conclusively determine that the response in the roots occurred because of what
was happening at the leaves. The team has not yet determined the entire
signaling process from leaf to root, but are working on it using pathogen-associated
molecular markers. According to Prof. Bais, "plants can't move from where
they are, so the only way they can accrue good neighbors is through
chemistry."
Plant Physiology,
2008. Upcoming.
