Planta

, Volume 219, Issue 1, pp 176–184 | Cite as

Expression and localisation analysis of the wheat sucrose transporter TaSUT1 in vegetative tissues

  • N. Aoki
  • G. N. Scofield
  • X.-D. Wang
  • J. W. Patrick
  • C. E. Offler
  • R. T. Furbank
Original Article

Abstract

Previously we reported the isolation of three sucrose transporter genes, TaSUT1A, 1B and 1D, all expressed at high levels in the developing grains of hexaploid wheat (Triticum aestivum L.), but also in a variety of other tissues [N. Aoki et al. (2002) Plant Mol Biol 50:453–462]. In order to further characterise the expression of the TaSUT1 genes in wheat plants, we have analysed TaSUT1 expression in their vegetative tissues using semi-quantitative reverse transcription–polymerase chain reaction, in situ hybridisation and immunolocalisation. The three TaSUT1 genes, which encode 98% identical SUT proteins, all appeared to be expressed at the same level in leaf blades, leaf sheaths and internodes, as well as developing grains, of hexaploid wheat. In mature leaf blades, TaSUT1 protein localised to the plasma membrane of phloem sieve elements in all classes of veins. In contrast, TaSUT1 mRNA was found to be localised to phloem companion cells. A similar localisation pattern for TaSUT1 protein was observed in veins of leaf sheaths and internodes. These results suggest that the wheat SUT1 has a transport function in enucleate sieve elements, in both veins responsible for loading photoassimilates, and in veins for axial transport. Furthermore, transport of the fluorescent dye carboxyfluorescein was used to investigate symplasmic connectivity between sieve element–companion cell complexes and non-phloem cells. Observations in source leaves indicated that sieve element–companion cell complexes of minor veins were symplasmically restricted, suggesting a role of TaSUT1 in apoplasmic phloem loading. In contrast, the dye was able to move symplasmically out of the phloem in internodes. In these circumstances TaSUT1 may also have a role in retrieving sucrose leaked to the phloem apoplasm.

Keywords

Phloem function Sieve element–companion cell complex Sucrose transporter Triticum 

Abbreviations

CF(DA)

6-Carboxyfluorescein (diacetate)

CLSM

Confocal laser-scanning microscopy

DAPI

4′,6-Diamidino-2-phenyindole

DIG

Digoxigenin

FITC

Fluorescein 5(6)-isothiocyanate

SE–CCC

Sieve element–companion cell complex

SUT

Sucrose transporter

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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • N. Aoki
    • 1
  • G. N. Scofield
    • 1
  • X.-D. Wang
    • 2
  • J. W. Patrick
    • 2
  • C. E. Offler
    • 2
  • R. T. Furbank
    • 1
  1. 1.CSIRO Plant IndustryCanberraAustralia
  2. 2.School of Environmental and Life SciencesUniversity of NewcastleCallaghanAustralia

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