Analysis of the transport activity of barley sucrose transporter HvSUT1

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

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

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 K0.5 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 K0.5 values were measured. The apparent affinity for all substrates was dependent on membrane potential and pH with lower K0.5 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. JSPP

Original languageEnglish (US)
Pages (from-to)1666-1673
Number of pages8
JournalPlant and Cell Physiology
Volume46
Issue number10
DOIs
StatePublished - Oct 2005

Fingerprint

Glucosides
Hordeum
glucosides
Sucrose
transporters
barley
sucrose
Arbutin
membrane potential
Membrane Potentials
Oocytes
oocytes
hydroquinone
Maltose
Xenopus laevis
maltose
substrate specificity
Substrate Specificity
filling period
Arabidopsis

Keywords

  • Electrophysiology
  • Hordeum vulgare
  • HvSUT1
  • Oocyte expression
  • Sucrose transporter

Cite this

Analysis of the transport activity of barley sucrose transporter HvSUT1. / Sivitz, Alicia B.; Reinders, Anke; Ward, John M.

In: Plant and Cell Physiology, Vol. 46, No. 10, 10.2005, p. 1666-1673.

Research output: Contribution to journalArticle

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AB - 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 K0.5 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 K0.5 values were measured. The apparent affinity for all substrates was dependent on membrane potential and pH with lower K0.5 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. JSPP

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