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JXB Advance Access originally published online on February 13, 2007
Journal of Experimental Botany 2007 58(6):1321-1332; doi:10.1093/jxb/erl297
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Characterization of ADP-glucose transport across the cereal endosperm amyloplast envelope

Caroline G. Bowsher1, Edward F. A. L. Scrase-Field1, Sergio Esposito2, Michael J. Emes3 and Ian J. Tetlow3,*

1Faculty of Life Sciences, 3.614 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
2Dipartmento di Biologia Vegetale, University of Naples (Federico II), Via Foria 223, 80139, Naples, Italy
3Department of Molecular and Cellular Biology, College of Biological Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1

* To whom correspondence should be addressed. E-mail: itetlow{at}uoguelph.ca

Most of the carbon used for starch biosynthesis in cereal endosperms is derived from ADP-glucose (ADP-Glc) synthesized by extra-plastidial AGPase activity, and imported directly across the amyloplast envelope. The properties of the wheat endosperm amyloplast ADP-Glc transporter were analysed with respect to substrate kinetics and specificities using reconstituted amyloplast envelope proteins in a proteoliposome-based assay system, as well as with isolated intact organelles. Experiments with liposomes showed that ADP-Glc transport was dependent on counter-exchange with other adenylates. Rates of ADP-Glc transport were highest with ADP and AMP as counter-exchange substrates, and kinetic analysis revealed that the transport system has a similar affinity for ADP and AMP. Measurement of ADP and AMP efflux from intact amyloplasts showed that, under conditions of ADP-Glc-dependent starch biosynthesis, ADP is exported from the plastid at a rate equal to that of ADP-Glc utilization by starch synthases. Photo-affinity labelling of amyloplast membranes with the substrate analogue 8-azido-[{alpha}-32P]ADP-Glc showed that the polypeptide involved in substrate binding is an integral membrane protein of 38 kDa. This study shows that the ADP-Glc transporter in cereal endosperm amyloplasts imports ADP-Glc in exchange for ADP which is produced as a by-product of the starch synthase reaction inside the plastid.

Key words: ADP-glucose transport, amylopectin, amyloplasts, amylose, starch synthesis

Received 2 August 2006; Revised 7 December 2006 Accepted 11 December 2006


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[Abstract] [Full Text] [PDF]


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