title: Routes of pyruvate synthesis in phosphorus-deficient lupin roots and nodules.
abstract: 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.
authors.affiliation: Department of Environmental Sciences, Applied Sciences Faculty, Cape Peninsula University of Technology, PO Box 652, Cape Town SA-8000, South Africa.
authors.forename: M R
authors.initials: MR
authors.lastname: Le Roux
authors.forename: C L
authors.initials: CL
authors.lastname: Ward
authors.forename: F C
authors.initials: FC
authors.lastname: Botha
authors.forename: A J
authors.initials: AJ
authors.lastname: Valentine
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D002250:Carbon Radioisotopes; D031297:Lupinus / Q000378:metabolism* / Q000382:microbiology; D008293:Malates / Q000378:metabolism; D010758:Phosphorus / Q000172:deficiency* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology; D011773:Pyruvates / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D008293:Malates; D011773:Pyruvates; D010758:Phosphorus; D000249:Adenosine Monophosphate; C030298:malic acid