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Plant and Cell Physiology Advance Access originally published online on June 10, 2009
Plant and Cell Physiology 2009 50(7):1329-1344; doi:10.1093/pcp/pcp081
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

This article appears in the following Plant and Cell Physiology issue: Special Issue Articles: Omics and Bioinformatics [View the issue table of contents]

Activation of Sucrose Transport in Defoliated Lolium perenne L.: An Example of Apoplastic Phloem Loading Plasticity

Alexandre Berthier1, Marie Desclos1, Véronique Amiard2,4, Annette Morvan-Bertrand1, Barbara Demmig-Adams3, William W. Adams, III3, Robert Turgeon2, Marie-Pascale Prud’homme1 and Nathalie Noiraud-Romy1,*

1UMR INRA-UCBN 950, Ecophysiologie Végétale, Agronomie and nutritions NCS, irba, Esplanade de la Paix, Université de Caen, 14032 Caen Cedex, France
2Department of Plant Biology, Cornell University, Plant Science Building, Ithaca, NY 14853, USA
3Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334, USA

*Corresponding author: E-mail: nathalie.noiraud-romy{at}unicaen.fr; Fax, +33-2-31-56-53-60.


  Abstract

The pathway of carbon phloem loading was examined in leaf tissues of the forage grass Lolium perenne. The effect of defoliation (leaf blade removal) on sucrose transport capacity was assessed in leaf sheaths as the major carbon source for regrowth. The pathway of carbon transport was assessed via a combination of electron microscopy, plasmolysis experiments and plasma membrane vesicles (PMVs) purified by aqueous two-phase partitioning from the microsomal fraction. Results support an apoplastic phloem loading mechanism. Imposition of an artificial proton-motive force to PMVs from leaf sheaths energized an active, transient and saturable uptake of sucrose (Suc). The affinity of Suc carriers for Suc was 580 µM in leaf sheaths of undefoliated plants. Defoliation induced a decrease of Km followed by an increase of Vmax. A transporter was isolated from stubble (including leaf sheaths) cDNA libraries and functionally expressed in yeast. The level of L.perenne SUcrose Transporter 1 (LpSUT1) expression increased in leaf sheaths in response to defoliation. Taken together, the results indicate that Suc transport capacity increased in leaf sheaths of L. perenne in response to leaf blade removal. This increase might imply de novo synthesis of Suc transporters, including LpSUT1, and may represent one of the mechanisms contributing to rapid refoliation.

Keywords: Defoliation - Lolium perenne - Sucrose transport

Abbreviations: CC, companion cell; CCCP, carbonyl cyanide m-chlorophenylhydrazone; DEPC, diethylpyrocarbonate; NEM, N-ethylmaleimide; PC, parenchyma cell; PCMBS, p-chloromercuriphenylsulfonic acid; PEG, polyethylene glycol; PMF, proton-motive force; PMV, plasma membrane vesicle; qPCR; quantitative PCR; RT–PCR, reverse transcription–PCR; SE, sieve element; Suc, sucrose; SUT, sucrose transporter.

4Present address: Centro de Genómica Nutricional Agro acuícola, Unidad de Biotecnología de Plantas, INIA-Carillanca, Casilla 58-D, Temuco, Chile.

(Received March 24, 2009; Accepted June 1, 2009)
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