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  • From: "Tradingpost" <tradingpost@lobo.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] Plant Biologists Discover Plant Defenses Against Insects
  • Date: Sun, 25 Jan 2009 14:39:51 -0700


Plant Biologists Discover Plant Defenses Against Insects
http://www.sciencedaily.com/videos/2007/0906-plants_under_attack.htm

September 1, 2007 — Plant biologists have identified the strategy used by
plants to recognize an attack. When insects ingest parts of a plant
digestion turns proteins into a peptide elicitor, which is secreted back
into the plant during subsequent feedings. The plant recognizes this
elicitor and launches its defensive chemistry.

Posies and plants may look peaceful, but flowers and veggies are waging war
on their enemies.

"They're actually doing a lot more than me and you are because they're
static, because they can't run and hide when something is attacking them,"
said Eric Schmelz, plant physiologist with the USDA.

He said the best way to protect our crops is to figure out how they protect
themselves.

"What we're studying is how plants are using these chemicals to help to
defend themselves," Schmelz said. These chemicals call to other bugs for
help. Plants can't feel a caterpillar munching on it, but it recognizes the
chemicals from the digestive juices from the caterpillar's mouth. Sensing
something is wrong, the plant releases odors to attract other bugs to get
rid of the problem. "A tiny bite from a very small caterpillar will start
this process going," Schmelz explains.

Researchers hope to learn more about the chemical process plants use to
protect themselves. This information may help lower the use of pesticides.

"If we can have a plant that is producing a stronger defensive reaction
once it's chewed on, that pest may no longer be a problem. We might not
need pesticides," Schmelz said.

Not only can bugs detect the odors plants emit for protection, but many
farmers notice when army worms are in their cornfield. They smell very
sweet. And plants react to each attack differently, emitting different
odors to attract different bugs to help defend them.

BACKGROUND: Plants seem like the most peaceful of organisms, but they
nonetheless have their own form of defense mechanisms: they emit toxins or
volatile chemicals in response to plant-eating insects. For the first time,
researchers at the US Department of Agriculture's Center for Medical,
Agricultural, and Veterinary Entomology in Gainesville, Florida, have
identified how plants known when they are under attack. Ultimately, their
work could lead to the development and genetic manipulation of plants with
improved protection against pests.

THE BEST DEFENSE: Proteins already present in the plants are eaten by the
attacking insects. Digesting the proteins, the insects convert this food
into a new type of chemical, which is in turn secreted back onto plants in
later feedings. The plants recognize these secretions as a type of 'SOS'
signal, and launch their telltale defensive chemistry. Although researchers
have long known that some plants can distinguish between different insect
attackers, they had not been able to fully describe all the potential
interactions. There are, after all, at least four million kinds of insects
and 230,000 flowering plant species, and the plant defense signals can
occur at trace levels that are too small to easily detect or isolate. Prior
research showed that bacteria and fungi, for example, can trigger a variety
of chemical warning signals in plants, which respond by increasing hormones
to regulate defensive responses. But until now, researchers didn't know
which chemical signals act as alarms, or how. It turns out that the
attacking insect's digestive enzymes may interact with the plant,
generating a defensive response.

THE KEY INGREDIENT: The USDA scientists spent three years analyzing the
biochemical response of the cowpea, a type of legume favored by an insect
known as the fall armyworm. They conducted over 10,000 leaf bioassays,
collecting just a few microliters at a time until they amassed a full liter
of caterpillar secretions. They identified a specific class of small
peptide 'elicitors', or plant defense signals that help plants react to
insect attack. One in particular, an 11-amino acid peptide called inceptin,
plays a pivotal warning role in cowpea plants under attack by armyworms.
The USDA researchers also identified two related but less abundant peptide
fragments that provoke similar defense responses in cowpea, and a third
with no apparent effect. Furthermore, they showed that inceptin and related
peptides spark a cascade of phytohormone increases in cowpea to trigger its
defenses, and identified critical features of the protein's structure that
enable it to function as a plant defense signal.





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