Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

• Published in: Plant physiology (Bethesda) 2007, Vol.143 (1), p.530-539
• Main Authors: Purnell, Matthew Peter, Botella, José Ramon
• Format: Article
• Language: English
• Subjects: Amides; Amination; Ammonium; Biological and medical sciences; Corn; Dehydrogenase; Dehydrogenases; Enzymes; Fundamental and applied biological sciences. Psychology; Glutamate Dehydrogenase (NADP+) - physiology; Glutamate-Ammonia Ligase - antagonists & inhibitors; Glutamic Acid - metabolism; Herbicides; Herbicides - pharmacology; Isoenzymes - physiology; Leaves; Metabolism; Nicotiana - drug effects; Nicotiana - enzymology; Nicotiana - genetics; Nitrogen; Nitrogen metabolism; Plant Leaves - enzymology; Plant Leaves - genetics; Plant Leaves - metabolism; Plant physiology and development; Plant roots; Plant Roots - enzymology; Plant Roots - genetics; Plant Roots - metabolism; Plants; Plants, Genetically Modified - drug effects; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - metabolism; Quaternary ammonium compounds; Quaternary Ammonium Compounds - metabolism; Roots; Systems Biology, Molecular Biology, and Gene Regulation; Transgenic plants
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.106.091330

Glutamate (Glu) dehydrogenase (GDH, EC 1.4.1.2-1.4.1.4) catalyzes in vitro the reversible amination of 2-oxoglutarate to Glu. The in vivo direction(s) of the GDH reaction in higher plants and hence the role(s) of this enzyme is unclear, a situation confounded by the existence of isoenzymes comprised totally of either GDH β- (isoenzyme 1) or α- (isoenzyme 7) subunits, as well as another five α-β isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [¹⁵N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [¹⁵N]ammonium (NH₄⁺) accumulation rate in these lines was elevated approximately 65% compared with a null segregant control line, indicating that isoenzyme 1 catabolizes Glu in roots. Leaf glutamine synthetase (GS) was inhibited with a GS-specific herbicide to quantify any contribution by GDH toward photorespiratory NH₄⁺ reassimilation. Transgenic line S49-H did not show enhanced resistance to the herbicide, indicating that the large pool of isoenzyme 1 in S49-H leaves was unable to compensate for GS and suggesting that isoenzyme 1 does not assimilate NH₄⁺ in vivo.