[MPWG] NEWS: Self-medicating plants! (fwd)

[Olivia Kwong]

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In Fight Against Pathogens, Calcium Helps Plants Make Their Own Aspirin
05.01.2009
Calcium builds strong bones, good teeth—and healthy plants, according to a
new study from Washington State University.

Experiments show that calcium, when bound to a protein called calmodulin,
prompts plants to make salicylic acid (SA) when threatened by infection or
other danger. SA is a close chemical relative of aspirin. In plants, SA
acts as a signal molecule that kicks off a series of reactions that help
defend against external threats.
...more about:
> Aspirin > AtSR1 > Calcium > Pathogen > pathogens > plant cell > Plants >
salicylic > signal molecule
That plants make salicylic acid has been known for more than 100 years,
said B.W. Poovaiah, Regents Professor and director of the study, but the
role of calcium in signaling a plant to make SA has not been known before.

“We are now beginning to understand the molecular mechanism connecting the
calcium/calmodulin signaling to plant immunity,” said Poovaiah.

The study will appear in an upcoming issue of the journal Nature and is now
available online at http://dx.doi.org/10.1038/nature07612.

Poovaiah said that in controlling salicylic acid level, calcium acts like a
gatekeeper within the cells of a plant, directing incoming information and
helping the plant respond to such dangers as pathogen attacks. Normal,
healthy plants have a low level of SA in their cells. That level rises when
the plant is threatened by infection or environmental stress.

“When we expect danger, we try to take precautions,” said Poovaiah. “Plants
cannot run away. Plants have to turn on their built-in system to protect
themselves. The plant has to produce different signal molecules. One of
them is salicylic acid.”

According to lead author, assistant research professor Liqun Du, SA sets
off defensive measures within the plant, such as the “hypersensitive
reaction” in which cells around an infection site die, forming a barrier
that keeps the pathogen from invading deeper into the plant. That provides
protection against the immediate threat. SA also activates the plant’s
systemic acquired resistance, a form of immunity that protects the plant
from further pathogen attacks.

But a rise in SA levels also causes the plant to slow its growth, perhaps
saving its strength for the battle against the pathogen. That sets up a
challenging situation for both the plant—grow faster or protect myself
better?—and farmers, who might view SA as a tool to protect their plants
from disease. A plant that makes high levels of SA all the time will be
safe from infection but will grow slowly. A plant that makes little or no
SA will grow like gangbusters but be very susceptible to infection.

“It’s a fine balance,” said Du. “Too much is bad; too little is bad.”

Working with the small mustard plant Arabidopsis thaliana, Poovaiah’s
research team showed that the key step in this balancing act is the
interaction between calcium/calmodulin and a protein called AtSR1, which
suppresses the production of salicylic acid. Stress or infection causes a
spike in calcium within the plant cells, which, in combination with
calmodulin, acts as a specific signal controlling the activity of AtSR1 and
the formation of SA.

In an environment with few pathogens, a plant will have low levels of SA.
The plant lets its guard down and devotes more resources to growth. If it
becomes infected, SA production goes up, and the plant dials back its
growth and puts more resources into defense.

The importance of AtSR1 was especially clear in experiments in which plants
were engineered to have more or less AtSR1 than normal. Plants that have
extra AtSR1 make almost no SA. They grow larger and faster than a normal
plant, but easily succumb to infection. Plants that lack the gene for AtSR1
develop high levels of SA and deploy their immune responses all the time.
They are nearly impervious to infection, but small in size. The same is
true of plants whose AtSR1 has been changed so it cannot bind to
calcium/calmodulin, demonstrating the crucial role played in this system by
calcium and calmodulin.

The paper is titled “Calcium/Calmodulin Regulates Salicylic Acid-mediated
Immune Response in Plants through AtSR1/CAMTA3.”
Joe Poovaiah | Source: Newswise Science News
Further information: www.wsu.edu

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Threatened plants emit ‘aspirin’
From The Times
September 19, 2008
http://www.timesonline.co.uk/tol/news/world/us_and_americas/article4783497.ece


Washington Forest plants subjected to stresses such as drought emit an
aspirin-like chemical that can be detected in the air above them, American
scientists have discovered.

Thomas Karl, the lead researcher at the US National Centre for Atmospheric
Research, believes that the chemical, methyl salicylate, may be a sort of
immune system response. “Plants can produce their own mix of aspirin-like
chemicals, triggering the formation of proteins that boost their
biochemical defences and reduce injury,” he says in the journal
Biogeosciences.

The chemical can be sensed by other plants and may be a means of
communication. Previous studies have shown that plants being eaten by
animals produce chemicals that are sensed by other plants nearby. (AP)