Subject: brown stuff secreted by plants??

From: [email-masked] (Chris Skory)
Date: 20 Mar 1996 14:21:24 GMT

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.

Chris Skory
[email-masked]

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From: [email-masked](Michael L Roginsky )
Date: 25 Mar 1996 21:51:45 GMT

In <[email-masked]> [email-masked] (Chris Skory)
>help would be appreciated.

It appears that the "sterile medium" has been compromised. In plant
hydroponics, the growing medium is enriched with soluble nutrients and
circulated over again. You may have a spore culture started, or a
bacterial invasion. Check it out under the microscope!

Micro, not a microbe!

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From: Tony Travis <[email-masked]>
Date: Thu, 28 Mar 1996 19:02:02 +0000

> 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:[email-masked]
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

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From: [email-masked] ("K N and P J Harris")
Date: Fri, 29 Mar 1996 21:18:19 GMT

> ==========
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1996 19:02:02 +0
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> Subject: Re: brown stuff secreted by plants??
> Message-ID: <[email-masked]>
> From: Tony Travis <[email-masked]>
> Date: Thu, 28 Mar 1996 19:02:02 +0000
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> Chris Skory wrote:
> > 
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,