From: george anderson  <georgea3@e...>
Date: Mon Jan 22, 2001 9:56pm
Subject: Re: phenolic exudations


RE:    edererthomas@8...
> Why do the plantlets exudate these phenolic compounds ?
> How can I prevent this ?

an excellent question and one that is under considerable research lately.
the simple answer is that the plants dont like to be eaten by bugs (an
inconvience, at best; deadly, at worst).  evolution has provided plants 
with defense mechanism to deter the bugs.  the phenols and alkaloids are 
examples of this since the bugs dont like the way they taste.  when a bug 
eates a leaf, signaling chemicals which are usually compartmentalized 
in the plant cell are released starting a cascade of response which is 
eventually expressed by activating (otherwise silent) genes.  the 
eventual gene products result in the production of unapetizing chemicals 
(like phenols, whose concentrations become highly elevated).

practically, people doint tissue culture try to minimize this by adding
charcoal to the media (to absorb the phenols but they also absorb the
components of the media changing their final concentrations in an 
nonuniform manner), or replating often into clean media, and there is 
some published work using inhibitors of polyoxidase enzymes.

the fact that you sometimes see this effect in some samples and not 
others could be the result of the fact that this defense system is 
inducable in somewhat the same fashion as immunity is induced in people 
(ie vacines). so if the plant that you are trying to culture has led a 
hard life and been predated by many eating bugs, one might reasonably 
assume that more phenols will be produced (since the defense genes have 
been unsilenced) when you chop it up and try to culture.

for additional reference, there is a nice symposium of papers in the
proceedings of the  national academy of sciences last year (sorry i 
cant give you the specific reference.
i am in the process of resurfacing the wood floor in my house and my 
library is stacked in piles-i cant find anything without tempting a 
disaster) on the similarity of plant defense and animal defense (ie 
antibody) mechanisms.
one more intresting fact is lerners resent publication that animal
antibodies are capable of producing reactive oxygen species (ie O2*) 
which can oxidize HCL into HOCL (which is what the active agent in 
bleach is).

cheers
gma