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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Transport of Sugars to Developing Embryos Is Not via the Bulk Endosperm in Oilseed Rape Seeds^1,[W],[OA]

Departments of Metabolic Biology (E.R.M.-S., M.J.P., L.M.H., A.M.S., S.R.) and Cell and Developmental Biology (K.F.), John Innes Centre, Norwich NR4 7UH, United Kingdom; and Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom (W.K.)

The fate of sucrose (Suc) supplied via the phloem to developing oilseed rape (Brassica napus) seeds has been investigated by supplying [¹⁴C]Suc to pedicels of detached, developing siliques. The method gives high, sustained rates of lipid synthesis in developing embryos within the silique comparable with those on the intact plant. At very early developmental stages (3 d after anthesis), the liquid fraction that occupies most of the interior of the seed has a very high hexose-to-Suc ratio and [¹⁴C]Suc entering the seeds is rapidly converted to hexoses. Between 3 and 12 d after anthesis, the hexose-to-Suc ratio of the liquid fraction of the seed remains high, but the fraction of [¹⁴C]Suc converted to hexose falls dramatically. Instead, most of the [¹⁴C]Suc entering the seed is rapidly converted to products in the growing embryo. These data, together with light and nuclear magnetic resonance microscopy, reveal complex compartmentation of sugar metabolism and transport within the seed during development. The bulk of the sugar in the liquid fraction of the seed is probably contained within the central vacuole of the endosperm. This sugar is not in contact with the embryo and is not on the path taken by carbon from the phloem to the embryo. These findings have important implications for the sugar switch model of embryo development and for understanding the relationship between the embryo and the surrounding endosperm.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Alison M. Smith (alison.smith{at}bbsrc.ac.uk).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.124644

^* Corresponding author; e-mail alison.smith{at}bbsrc.ac.uk.

Received June 11, 2008; accepted June 13, 2008; published June 18, 2008.