brown stuff secreted by plants??

Tony Travis ajt at
Thu Mar 28 14:02:02 EST 1996

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 

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 ...

Dr. A.J.Travis,                     |  mailto:ajt at
Rowett Research Institute,          |
Greenburn Road, Bucksburn,          |   phone:+44 (0)1224 712751
Aberdeen AB2 9SB, Scotland, UK.     |     fax:+44 (0)1224 716687

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