In vivo and in vitro metabolomic analysis of anaerobic rice coleoptiles revealed unexpected pathways

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Abstract

The ability of the rice (Oryza sativa L.) seedling to tolerate extended hypoxia during submergence is largely attributed to the biochemical adaptation of its coleoptile. Rice coleoptiles are capable of sustaining ATP production and cytoplasmic pH, unlike flood-sensitive organs, such as maize shoots. Fermentation reactions leading to the production of ethanol, alanine, succinate, and γ-aminobutyrate (GAB) are active in both types of tissues and thus may not account for the difference in tolerance. We have shown previously that rice coleoptiles undergo nitrate reduction and metabolism, which is efficient in alleviating cytoplasmic acidosis and regenerating NAD. Here, we employed 13C-2-acetate tracer methods with in vivo 13C NMR measurement, including in vivo isotopomer analysis, to probe the tricarboxylic acid (TCA) cycle and interacting pathways in rice coleoptiles during anaerobiosis. We found that the TCA cycle underwent multiple turns based on the metabolic scrambling of 13C label patterns in glutamine and malate. The in vivo kinetics of the 13C label incorporation into glutamic acid, glutamine, and GAB supports a separate pool of glutamate that was derived from the glutamate dehydrogenase reaction and subsequently decarboxylated to yield GAB. Both reactions consume additional H+ and/or NADH. Moreover, the higher rate of 13C enrichment at C-3 than C-2 of malate suggests the contribution of the glyoxylate cycle to malate synthesis, which could replenish the TCA cycle carbons diverted to GAB, glutamate, and glutamine synthesis. All of the above reactions contribute to the maintenance of glycolysis for energy production.

Original languageEnglish
Pages (from-to)787-793
Number of pages7
JournalRussian Journal of Plant Physiology
Volume50
Issue number6
DOIs
StatePublished - Nov 2003

Keywords

  • C isotopomer analysis
  • Anaerobiosis
  • Glycolysis
  • Glyoxylate cycle
  • In vivo NMR
  • Metabolite profiling
  • Oryza sativa
  • TCA cycle

ASJC Scopus subject areas

  • Plant Science

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