Journal Article

Analysis of the Transport Activity of Barley Sucrose Transporter HvSUT1

Alicia B. Sivitz, Anke Reinders and John M. Ward

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 10, pages 1666-1673
Published in print October 2005 | ISSN: 0032-0781
Published online October 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci182
Analysis of the Transport Activity of Barley Sucrose Transporter HvSUT1

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  • Biochemistry
  • Molecular and Cell Biology
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Localization studies indicate that barley (Hordeum vulgare) sucrose transporter HvSUT1 functions in sucrose uptake into seeds during grain filling. To further understand the physiological function of HvSUT1, we have expressed the HvSUT1 cDNA in Xenopus laevis oocytes and analyzed the transport activity by two-electrode voltage clamping. Consistent with a H+-coupled transport mechanism, sucrose induced large inward currents in HvSUT1-expressing oocytes with a K 0.5 of 3.8 mM at pH 5.0 and a membrane potential of –157 mV. Of 21 other sugars tested, four glucosides were also transported by HvSUT1. These glucosides were maltose, salicin (2-(hydroxymethyl) phenyl β-d-glucoside), α-phenylglucoside and α-paranitrophenylglucoside. Kinetic analysis of transport of these substrates by HvSUT1 was performed and K 0.5 values were measured. The apparent affinity for all substrates was dependent on membrane potential and pH with lower K 0.5 values at lower external pH and more negative membrane potentials. HvSUT1 was more selective for α-glucosides over β-glucosides than the Arabidopsis sucrose transporter AtSUC2. Several substrates transported by AtSUC2 (β-phenylglucoside, β-paranitrophenylglucoside, α-methylglucoside, turanose, and arbutin (hydroquinone β-d-glucoside)) showed low or undetectable transport by HvSUT1. Of these, β-paranitrophenylglucoside inhibited sucrose transport by HvSUT1 indicating that it interacts with the transporter while arbutin and α-methyl glucoside did not inhibit. The results demonstrate significant differences in substrate specificity between HvSUT1 and AtSUC2.

Keywords: Electrophysiology; Hordeum vulgare; HvSUT1; Oocyte expression; Sucrose transporter

Journal Article.  4863 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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