Protoplast hexose carrier activity is a determinate of genotypic difference in hexose storage in tomato fruit

Authors

  • Y.-L. RUAN,

    1. Department of Biological Sciences, The University of Newcastle, Callaghan, Newcastle, NSW 2308, Australia
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    • *

      Department of Cellular and Molecular Biology and Department of Plant Pathology, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL32611-0680, USA.

  • J.W. PATRICK,

    Corresponding author
    1. Department of Biological Sciences, The University of Newcastle, Callaghan, Newcastle, NSW 2308, Australia
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  • C. BRADY

    1. Department of Biological Sciences, The University of Newcastle, Callaghan, Newcastle, NSW 2308, Australia
    2. CSIRO. Division of Horticulture, North Ryde, NSW 2113, Australia
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J. W. Patrick, Department of Biological Sciences, The University of Newcastle, Callaghan, Newcastle, NSW 2308, Australia.

ABSTRACT

Post-phloem sugar transport in developing tomato (Lycopersicon esculentum Mill. cv. Flora-Dade) fruit follows an apoplastic route during the rapid phase of sugar accumulation. The pathway is characterized by sugar retrieval by the storage parenchyma cells from the fruit apoplast. Two tomato genotypes differing in fruit hexose content were compared in terms of the transport and transfer processes controlling fruit sugar levels. The genotypic difference in fruit sugar content was independent of photoassimilate export from source leaves. Discs of pericarp tissue were cultured in a medium based on analyses of the fruit apoplastic sap. The cultured discs maintained a composition, a relative growth rate and a respiration rate similar to those of the pericarp tissue of intact fruit. Estimates of hexose fluxes into metabolic and storage pools suggested that membrane transport regulated the genotypic difference in hexose accumulation. Short-term [14C]hexose uptake experiments demonstrated a genotypic difference in Vmax for glucose, fructose and 3-O-methyl-glucose, and this difference was abolished in the presence of the inhibitor p-chloromercuribenzenesulphonic acid (PCMBS). The results support the hypothesis that the activity of energized hexose carriers on the plasma membranes of storage parenchyma cells is a significant determinate of the genotypic difference in hexose accumulation.

Abbreviations
ABA

γ-aminobutyric acid

DAA

days after anthesis

DW

dry weight

FW

fresh weight

Mes

2-(N-morpholino) ethanesulphonic acid

3-OMG

3-O-methylglucose

PCMBS

p-chloromercuribenzenesulphonic acid

Pipes

Piperazene-N,N-bis[2-ethanesulphonic acid]

PS

photosynthesis

RGR

relative growth rate

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