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Plant Physiol, January 2003, Vol. 131, pp. 228-236
Metabolism of Sugars in the Endosperm of Developing Seeds of
Oilseed Rape1
Lionel M.
Hill,*
Edward R.
Morley-Smith, and
Stephen
Rawsthorne
Department of Metabolic Biology, John Innes Centre, Norwich
Research Park, Colney, Norfolk NR4 7UH, United Kingdom
The sugars in the endosperm of a developing seed have many
potential roles, including the supply of carbon to the developing embryo and controlling gene expression in it. Our understanding of
their metabolism is, however, fragmentary and is confined to a very few
species (especially Vicia spp.). To develop a
quantitative understanding of the regulation of sugars in seeds of
oilseed rape (Brassica napus), we measured relevant
enzyme activities, the sizes of the pools of sugars in the liquid
endosperm, and the flux of sugars from the endosperm into the embryo.
The concentrations of hexose sugars in the liquid endosperm decreased,
and sucrose (Suc) increased through development. The overall osmotic
potential also fell. The timing of the changes was not precise enough
to determine whether they signaled the onset of rapid accumulation of
storage products. Changes in endosperm invertase activity were complex
and quantitatively do not explain the changes in sugars. The embryo can
metabolize hexose sugars in addition to Suc, and possibly at higher
rates. Therefore, in addition to invertase, the growing embryo itself
has a potential to influence the balance of sugars in the endosperm.
The activity of Suc synthase in the embryo was greater than that of
invertase during development. This observation and a higher activity of
fructokinase than glucokinase in the embryo are both consistent with
the embryo using Suc as a carbon source.
1
This work was supported by the Biotechnology and
Biological Sciences Research Council (Core Strategic Grant). E.R.M.-S.
was partially supported by a Nuffield/John Innes Foundation Scholarship.
*
Corresponding author; e-mail lionel.hill{at}bbsrc.ac.uk; fax
44-1603-450014.
© 2003 American Society of Plant Biologists
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