Routes of pyruvate synthesis in phosphorus-deficient lupin roots and nodules

Authors

  • M. R. Le Roux,

    1. Department of Environmental Sciences, Applied Sciences Faculty, Cape Peninsula University of Technology, PO Box 652, Cape Town SA−8000, South Africa;
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  • C. L. Ward,

    1. Erasmus University Medical Centre, Department of Cell Biology and Genetics, PO Box 1738, NL−3000 DR, Rotterdam, the Netherlands;
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  • F. C. Botha,

    1. South African Sugar Association Experiment Station, Private bag X02, Mount Edgecombe, SA−4300, South Africa
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  • A. J. Valentine

    Corresponding author
    1. Department of Environmental Sciences, Applied Sciences Faculty, Cape Peninsula University of Technology, PO Box 652, Cape Town SA−8000, South Africa;
    • Author for correspondence: A. J. Valentine Tel: +27 21 4603200 Fax: +27 21 4603193 Email: alexvalentine@mac.com

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Summary

  • • Here, nodulated lupins (Lupinus angustifolius (cv Wonga)) were hydroponically grown at low phosphate (LP) or adequate phosphate (HP).
  • • Routes of pyruvate synthesis were assessed in phosphorus (P)-starved roots and nodules, because P-starvation can enhance metabolism of phosphoenolpyruvate (PEP) via the nonadenylate-requiring PEP carboxylase (PEPc) route. Since nodules and roots may not experience the same degree of P stress, it was postulated that decreases in metabolic inorganic phosphorus (Pi) of either organ, should favour more pyruvate being synthesized from PEPc-derived malate.
  • • Compared with HP roots, the LP roots had a 50% decline in Pi concentrations and 55% higher ADP : ATP ratios. However, LP nodules maintained constant Pi levels and unchanged ADP : ATP ratios, relative to HP nodules. The LP roots had greater PEP metabolism via PEPc and synthesized more pyruvate from PEPc-derived malate. In nodules, P supply did not influence PEPc activities or levels of malate-derived pyruvate.
  • • These results indicate that nodules were more efficient than roots in maintaining optimal metabolic Pi and adenylate levels during LP supply. This caused an increase in PEPc-derived pyruvate synthesis in LP roots, but not in LP nodules.

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