Subject: Plants vs. Predators

From: [email-masked] (Aregula )
Date: 13 May 1995 17:36:36 GMT

I am trying to find out what ways do plants protect themselves against
predators(insects, animals).  I know of different natural poisons they
use, but there do not seem to be many ways they can defend themselves
against pests.  Does anyone know of any natural defense mechanisms
plants of general variety use?

Any comments would be appreciated.
Thank you.

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From: [email-masked] (EJGOLD)
Date: 16 May 1995 20:45:56 -0400

=Subject: Plants vs. Predators
=From: [email-masked] (Aregula )
=Date: 13 May 1995 17:36:36 GMT
=Message-ID: <[email-masked]>
=I am trying to find out what ways do plants protect themselves against
=predators(insects, animals).  I know of different natural poisons they
=use, but there do not seem to be many ways they can defend themselves
=against pests.  Does anyone know of any natural defense mechanisms
=plants of general variety use?
=Any comments would be appreciated.
=Thank you.

One of many defense mechanisms:
Pubescence. Many plants have varying degrees of 'hairyness'. These fine
'hairs' hold smaller sucking-type insects (like aphids) away from the
outer layer of cells which make up the plant, therefore the insect cannot
suck fluid from the cells.

EJ

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From: [email-masked] (T CRANCUE)
Date: 17 May 1995 02:35:57 -0400

One of the most important, but most overlooked, plant adaptations to
defend against animal predators may the development of a plant structure
extremely high in fiber. Fiber, being highly indigestable by most animals,
is an excellent inhibitor to animals. A few animals have found a way to
enter this niche food source including cows and some monkeys, both having
adapted specialized foreguts to handle the digestion of fiber by a
bacterial colony which in turn provides the ingesting animal with food as
a biproduct. These same animals are often able to utilize plants employing
another protection, namely toxins. The bacteria in the foregut break down
the toxins allowing the animal to survive when ingesting foods that would
normally kill other animals. You should also consider other more obvious
protection mechanisms like thorns, spines, thistles, the fur-like hairy
fibers on some cacti, etc.

While plants don't seem to react to attack, there is evidence that if a
single plant is damaged, either by an animal or the blow of an axe, the
chemical balance of trees surrounding the damaged tree changes. You could
say that they "sense" this damage and make moves to adjust their chemical
states to the best advantage during an attack. This "sense" is probably a
simple chemical reaction to the release of chemicals from the damaged
tree.

Hope this helps!

--TCC

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From: [email-masked] (Maarten van Helden)
Date: 18 May 1995 10:03:06 GMT

In article <[email-masked]>, [email-masked] says...
 snip snip

>simple chemical reaction to the release of chemicals from the damaged

Hello out there, you seem to have overlooked some of the latest discoveries. 
When a plant is attacked by an insect it can start to produce compounds 
like phenolics which deter an insect/predator. This is a very important 
phenomena eventhough the underlyiing mechanism is not very well understood. 
Moreover there have been a number of papers which describe that an 
phytophagous organism, while eating from a plant induces the production of 
volatile compounds by the plant, which then attract predators of the 
phytophagous attacker. You might say that the plants "cry for help". Since the 
first discovery of this phenomena some years ago a large number of examples 
has been found. The volatile compounds are often attacker specific and 
therefore also attract only the specific predators !!
Some recent publications even suggest that neighbouring plants might join the 
chorus and produce these volatiles even though they are not damaged 
themselves. For more info: contact Marcel Dicke at 
"[email-masked]"  

++++++++++++++++++++++++++++++++++++++++++++++++++++++++
||\\  //||  Maarten van Helden
|| \\// ||  Dept. of Entomology
||  \/  ||  Wageningen Agricultural University
||||||||||  Binnenhaven 7, 6709 PD
||      ||  Wageningen, the Netherlands
||      ||  Tel +31-8370-85118 Fax +31-8370-84821
||      ||  Email: <[email-masked]>
     
++++++++++++++++++++++++++++++++++++++++++++++++++++++++

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From: [email-masked] (Marcel Dicke)
Date: 18 May 1995 12:39:01 GMT

>Any comments would be appreciated.

Plants can have two basic types of defense:
1. The best-known type is DIRECT defense that affects the herbivore 
directly. This comprises e.g. the use of toxins, digestibility reducers,
hairs, spikes etc. etc.
2. The second type has been studied since the 1980s and is becoming very 
well documented. It is INDIRECT defense, where the plant affects the
effectiveness of carnivorous enemies of plant attacking organisms.
INDIRECT defense can comprise shelters that are used by carnivores
(e.g. the horns of the bullhorn acacia are used as nesting sites by ants
that defend the plant). A more spectacular aspect is that plants RESPOND
to being damaged by herbivorous mites or insects by starting to produce
volatile chemicals that lure the carnivorous enemies of the herbivores.
The plant can disseminate very specific blends of volatiles, e.g.
plants can emit different blends when damaged by different species of
herbivores.
Moreover, the plant sends out the SOS-signals from infested leaves as well
as from uninfested leaves (systemic response).
As also mentioned by Maarten van Helden, there is now evidence that also
uninfested neighbouring plants become attractive to carnivores after being
exposed to the SOS-signals from their infested neighbour.

For more information:
Dicke, M. 1994. Local and systemic production of volatile herbivore-induced
     plant terpenoids: their role in plant-carnivore mutualism. J. Plant
     Physiol. 143: 465-472.
Mattiacci et al. 1995. beta-glucosidase: elicitor of herbivore-induced 
     plant odors that attract host searching parasitic wasps. Proc. Natl.
     Acad. Sci. USA 92: 2036-2040.
Bruin et al. 1995. Do plants tap SOS-signals from their infested 
     neighbours? Trends in Ecology and Evolution 10: 167-170.

Marcel Dicke