brown stuff secreted by plants??

K N and P J Harris ecoli at cix.compulink.co.uk
Fri Mar 29 16:18:19 EST 1996


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> bionet/plants #801, from ajt at rri.sari.ac.uk, 2235 chars, Thu  28 Mar 
1996 19:02:02 +0
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> Article: 9322 of bionet.plants
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> Subject: Re: brown stuff secreted by plants??
> Message-ID: <315AE22A.6357 at rri.sari.ac.uk>
> From: Tony Travis <ajt at rri.sari.ac.uk>
> Date: Thu, 28 Mar 1996 19:02:02 +0000
> References: <4ip494$g5g at sunca.ncaur.gov>
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> Chris Skory wrote:
> > 
> > This question will probably reveal my ignorance in plant physiology,
> > but, I was curious what general types of compounds do plants secrete
> > from their roots.   I ask this because I saw some plants (eg 
lettuce,
> > carrots, etc) growing in sterile medium the other day.  The medium
> > became increasingly more turbid and brown as the culture grew.  Is
> > this protein, alkaloids or some other secondary metabolite.  Any
> > help would be appreciated.
> 
> Plant roots are adapted for the uptake of water and minerals.  They do 
> not normally 'secrete' anything as such but the root 'cap' is sloughed 
> off as the root penetrates the soil or other medium it is growing 
> through.
> 
> This has important consequences for interaction between the plant and 
> soil microorganisms, but it may also release soluble phenolic 
compounds 
> amongst other things into a sterile medium.  These phenolic compounds 
> would turn brown and be insoluble when oxidised.
> 
> Of course, if the roots are growing in a sterile _solution_ then no 
> sloughing of the root cap will occur. The cells in the root cap will 
> simply degenerate and lose their contents into the medium.  However, 
if 
> the sterile medium is exposed to light then you may just be seeing the 
> growth of algae - if it's not sterile any more ...
> 
>  Tony.
> --
> Dr. A.J.Travis,                     |  mailto:ajt at rri.sari.ac.uk
> Rowett Research Institute,          |    
http://www.rri.sari.ac.uk/~ajt
> Greenburn Road, Bucksburn,          |   phone:+44 (0)1224 712751
> Aberdeen AB2 9SB, Scotland, UK.     |     fax:+44 (0)1224 716687
Root exudates don't exist.
This is strong stuff. Albert Rovira, Jim Lynch and a whole host of other 
soil microbiologists had better just pack up their tents and retreat.
Time lapse photographs of root exudation taken at Long Ashton (copies 
still available) are not real. Those who claim that between 5% and 25% 
of the total photosynthate can be released as exudates are wrong ?
Supporting references would be most welocome.
Peter Harris,
department of Soil Science,
The University of Reading,




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