Water transport

Jon Monroe monroejd at jmu.edu
Thu Apr 8 09:21:54 EST 1999


Jim,

Great question!  I'm looking forward to the replies.  On one point I have a
comment:

>In the case of Moore, et al.'s commentary, why would cold nights cause the
>conversion of starch to sucrose?

The regulation of starch degradation is not very well understood, but it
happens in leaves shortly after the sun goes down every day, and it happens
in potatoes that are stored at low temperatures.  Perhaps some combination
of these mechanisms is operating in maple trees on cold nights.  (During
the cold winter of '77-'78 in northern Ohio our root cellar was much colder
than it normally was and we had to eat awful "sweet" white potatos for
weeks!)

I just searched on PubMed (http://www.ncbi.nlm.nih.gov/PubMed/medline.html)
using the key words: "starch", "degradation", "cold", and "plant" I found
this abstract:

****
Nat Biotechnol 1998 May;16(5):473-7  Inhibition of a starch-granule-bound
protein leads to modified starch and repression of cold sweetening.
Lorberth R, Ritte G, Willmitzer L, Kossmann J.

We have cloned a gene involved in starch metabolism that was identified by
the ability of its product to bind to potato starch granules. Reduction in
the protein level of transgenic potatoes leads to a reduction in the
phosphate content of the starch. The complementary result is obtained when
the protein is expressed in Escherichia coli, as this leads to an increased
phosphate content of the glycogen. It is possible that this protein is
responsible for the incorporation of phosphate into starch-like glucans, a
process that is not understood at the biochemical level. The reduced
phosphate content in potato starch has some secondary effects on its
degradability, as the respective plants show a starch excess phenotype in
leaves and a reduction in cold-sweetening in tubers.
****

There are other citations among the 21 hits that look relevant...

Jon

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  Jonathan Monroe
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  Department of Biology
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  James Madison University
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