In Vivo and In Vitro Metabolomic Analysis of Anaerobic Rice Coleoptiles Revealed Unexpected Pathways

Fan, T.W.M. and Lane, A.N. and Higashi, R.M. (2003) In Vivo and In Vitro Metabolomic Analysis of Anaerobic Rice Coleoptiles Revealed Unexpected Pathways. Russian Journal of Plant Physiology, 50 (6). pp. 787-793.

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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.

Item Type: Article
Additional Information: UC Davis Center for Ecological Health Research (U.S. EPA no. R819658) and Dr. Vic Claassen for providing the funds for GCMS instrumentation.
Uncontrolled Keywords: Oryza sativa, anaerobiosis, in vivo NMR, metabolite profiling, 13C isotopomer analysis, glycolysis, TCA cycle, glyoxylate cycle
Author Affiliation: Department of Land, Air, and Water Resources, University of California, One Shields Ave, Davis, CA, 95616, USA and 2. Department of Chemistry, University of Louisville, S. Brook St., Louisville, KY, 40208, USA
Subjects: Crop Improvement
Divisions: Other Crops
Depositing User: Mr Siva Shankar
Date Deposited: 21 Dec 2012 05:37
Last Modified: 21 Dec 2012 05:37
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