Abstracts now available online - Euro Fed Lipid

P4
Carbohydrate metabolism in developing linseed embryos
Stéphanie Troufflard 1 , Stephen Rawsthorne 2 , Jean-Charles Portais 3 , Albrecht Roscher 1
1
Génie Enzymatique et Cellulaire UMR CNRS 6022, Université de Picardie, Amiens,
France
2
Department of Metabolic Biology, John Innes Centre, Norwich, UK
3 Laboratoire de Biotechnologies-Bioprocédés UMR CNRS-INSA 5504 INRA 792, INSA,
Toulouse, France
Lipid accumulation in oilseeds depends on the efficient conversion of photosynthetic
sugars into fatty acids. However, offer and demand to not always coincide, due to daynight
cycles on the one hand and to developmental shifts on the other hand.
Discrepancies between offer and demand can be buffered by temporary carbohydrate
stores inside the embryo. For example, it has been shown that developing rapeseed
(Brassica napus L.) embryos accumulate starch in the days prior to the onset of
maximal lipid synthesis, and that this starch subsequently disappears in favour of
storage lipids [1].
We first analysed carbohydrate dynamics in developing linseed (Linum usitatissimum
L.) embryos on a developmental timescale by measuring the storage product contents
over time. Contrary to rapeseed, linseed accumulates very little starch, and the rate of
net starch degradation is about a hundredfold lower than the rate of lipid synthesis [2].
In a second approach, the capacity of isolated linseed plastids to synthesise starch was
tested. When fed with [1- 14 C]-glucose 6-phosphate, the isolated plastids surprisingly
synthesise starch at a rate which is nearly a hundred times higher than the net rate of
synthesis in planta [2].
Thirdly, the metabolism of [1- 13 C]-glucose by excised linseed embryos was directly
followed by in vivo NMR. The label was incorporated into sucrose allowing to assess the
rate of sucrose synthesis and the sucrose pool turnover. Label incorporation into fatty
acids however occurred much faster suggesting that most of the incoming sugar
bypasses the sucrose pool, and the latter might rather serve as a buffer on a timescale
of several hours. Label analysis in the starch pool after the incubation period showed
that the starch pool, too, is renewed in less than a day.
[1] P.J. Eastmond and S. Rawsthorne, Plant Physiol. 122, 767 (2000)
[2] S. Troufflard et al., Proceedings 16 th Intern. Symp. Plant Lipids, Budapest (2004)