Plant and Cell Physiology Advance Access originally published online on March 15, 2008
Plant and Cell Physiology 2008 49(5):691-703; doi:10.1093/pcp/pcn044
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Metabolite Profiling Reveals Distinct Changes in Carbon and Nitrogen Metabolism in Phosphate-Deficient Barley Plants (Hordeum vulgare L.)
1Australian Centre for Plant Functional Genomics, The University of Adelaide, Waite Campus, PMB1, Glen Osmond, South Australia, 5064, Australia
2Australian Centre for Plant Functional Genomics, School of Botany, The University of Melbourne, Victoria, 3010, Australia
3Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Golm, Germany
4Molecular Plant Breeding Cooperative Research Centre, The University of Adelaide, South Australia, 5005, Australia
5Metabolomics Australia, School of Botany, The University of Melbourne, Victoria, 3010, Australia
*Corresponding author: E-mail, chunyuan.huang{at}adelaide.edu.au; Fax, +61-8-8303-7102.
| Abstract |
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Plants modify metabolic processes for adaptation to low phosphate (P) conditions. Whilst transcriptomic analyses show that P deficiency changes hundreds of genes related to various metabolic processes, there is limited information available for global metabolite changes of P-deficient plants, especially for cereals. As changes in metabolites are the ultimate readout of changes in gene expression, we profiled polar metabolites from both shoots and roots of P-deficient barley (Hordeum vulgare) using gas chromatography–mass spectrometry (GC-MS). The results showed that mildly P-deficient plants accumulated di- and trisaccharides (sucrose, maltose, raffinose and 6-kestose), especially in shoots. Severe P deficiency increased the levels of metabolites related to ammonium metabolism in addition to di- and trisaccharides, but reduced the levels of phosphorylated intermediates (glucose-6-P, fructose-6-P, inositol-1-P and glycerol-3-P) and organic acids (
-ketoglutarate, succinate, fumarate and malate). The results revealed that P-deficient plants modify carbohydrate metabolism initially to reduce P consumption, and salvage P from small P-containing metabolites when P deficiency is severe, which consequently reduced levels of organic acids in the tricarboxylic acid (TCA) cycle. The extent of the effect of severe P deficiency on ammonium metabolism was also revealed by liquid chromatography–mass spectrometry (LC-MS) quantitative analysis of free amino acids. A sharp increase in the concentrations of glutamine and asparagine was observed in both shoots and roots of severely P-deficient plants. Based on these data, a strategy for improving the ability of cereals to adapt to low P environments is proposed that involves alteration in partitioning of carbohydrates into organic acids and amino acids to enable more efficient utilization of carbon in P-deficient plants.
Keywords: Ammonium - Barley (Hordeum vulgare L.) - Carbohydrate - Metabolite profile - Phosphate deficiency
Abbreviations: GC-MS, gas chromatography–mass spectrometry; LC-MS, liquid chromatography–mass spectrometry; TCA, tricarboxylic acid.
(Received February 21, 2008; Accepted March 13, 2008)
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