Regulation of Glutamate Dehydrogenase Activity in Relation to Carbon Limitation and Protein Catabolism in Carrot Cell Suspension Cultures

Robinson, Sharon A.; Stewart, George R.; Phillips, Richard D.

doi:10.1104/pp.98.3.1190

Cited by 112 publications

(81 citation statements)

References 19 publications

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“…in C sinks, during darkness, and during C starvation of explants) and repressed by a high cellular C to N ratio (e.g. in C sources, during light, and during supply of Suc to explants; Melo-Oliveira et al, 1996;Turano et al, 1997;Ficarelli et al, 1999;Masclaux et al, 2000;Masclaux-Daubresse et al, 2002;Tercé-Laforgue et al, 2004b), agreeing with GDH activity data (Restivo et al, 1989;Robinson et al, 1992;Masclaux et al, 2000;Morkunas et al, 2000;Tercé-Laforgue et al, 2004b). In source leaves, both subunits are localized to mitochondria of phloem companion cells.…”

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confidence: 74%

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

Purnell

Botella

2006

Plant Physiol.

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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 b-(isoenzyme 1) or a-(isoenzyme 7) subunits, as well as another five a-b isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [ 15 N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [ 15 N]ammonium (NH 4 1 ) 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 NH 4 1 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 NH 4 1 in vivo.The intricate linkage of plant C and N metabolism requires constant balancing at the cellular level. Fundamentally, this involves orchestrating cellular levels of three metabolites: ammonium (NH 4

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supporting

confidence: 74%

“…Conversely, if GDH operates in the catabolic direction, it may help alter cellular C to N ratios and/or fuel the TCA cycle under conditions of C deficit (Rhodes et al, 1989;Robinson et al, 1991Robinson et al, , 1992Aubert et al, 2001;Loulakakis and RoubelakisAngelakis, 2001;Miflin and Habash, 2002;Dubois et al, 2003;Skopelitis et al, 2006).…”

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confidence: 99%

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

Purnell

Botella

2006

Plant Physiol.

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“…It is estimated that up to onethird of the Glu-dependent respiratory rates in isolated mitochondria can be attributed to the GDH deamination reaction (Aubert et al, 2001). The carbon flow from Glu oxidation becomes important under conditions of carbon limitation in darkness (Scheible et al, 2000) and carbohydrate starvation (Robinson et al, 1992;Turano, 1998). Also, the transition of young leaves to old leaves is characterized in part by a decrease in Suc (Masclaux et al, 2000).…”

Section: Discussionmentioning

confidence: 99%

Glutamine Synthetase-Glutamate Synthase Pathway and Glutamate Dehydrogenase Play Distinct Roles in the Sink-Source Nitrogen Cycle in Tobacco

et al. 2006

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Glutamate (Glu) metabolism and amino acid translocation were investigated in the young and old leaves of tobacco (Nicotiana tabacum L. cv Xanthi) using [15N]ammonium and [2-15N]Glu tracers. Regardless of leaf age, [15N]ammonium assimilation occurred via glutamine synthetase (GS; EC 6.1.1.3) and Glu synthase (ferredoxin [Fd]-GOGAT; EC 1.4.7.1; NADH-GOGAT; EC 1.4.1.14), both in the light and darkness, and it did not depend on Glu dehydrogenase (GDH; EC 1.4.1.2). The [15N]ammonium and ammonium accumulation patterns support the role of GDH in the deamination of [2-15N]Glu to provide 2-oxoglutarate and [15N]ammonium. In the dark, excess [15N]ammonium was incorporated into asparagine that served as an additional detoxification molecule. The constant Glu levels in the phloem sap suggested that Glu was continuously synthesized and supplied into the phloem regardless of leaf age. Further study using transgenic tobacco lines, harboring the promoter of the GLU1 gene (encoding Arabidopsis [Arabidopsis thaliana] Fd-GOGAT) fused to a GUS reporter gene, revealed that the expression of Fd-GOGAT remained higher in young leaves compared to old leaves, and higher in the veins compared to the mesophyll. Confocal laser-scanning microscopy localized the Fd-GOGAT protein to the phloem companion cells-sieve element complex in the leaf veins. The results are consistent with a role of Fd-GOGAT in supplying Glu for the synthesis and transport of amino acids. Taken together, the data provide evidence that the GS-GOGAT pathway and GDH play distinct roles in the source-sink nitrogen cycle of tobacco leaves.

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“…Results from studies of GDH in carrot cell suspension cultures grown in limiting amounts of carbon also suggest that GDH is involved in the catabolism of Glu to form a-ketoglutarate (Robinson et al, 1991(Robinson et al, , 1992. GDH activity increased in Suc-starved cells, and the addition of SUC resulted in a rapid decrease in GDH activity.…”

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confidence: 91%

Characterization and Expression of NAD(H)-Dependent Glutamate Dehydrogenase Genes in Arabidopsis

et al. 1997

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Two distinct cDNA clones encoding NAD(H)-dependent glutamate dehydrogenase (NAD[H]-GDH) in Arabidopsis thaliana were identified and sequenced. The genes corresponding to these cDNA clones were designated GDH1 and GDH2. Analysis of the deduced amino acid sequences suggest that both gene products contain putative mitochondrial transit polypeptides and NAD(H)- and α--ketoglutarate-binding domains. Subcellular fractionation confirmed the mitochondrial location of the NAD(H)-GDH isoenzymes. In addition, a putative EF-hand loop, shown to be associated with Ca2+ binding, was identified in the GDH2 gene product but not in the GDH1 gene product. GDH1 encodes a 43.0-kD polypeptide, designated α-, and GDH2 encodes a 42.5-kD polypeptide, designated [beta]. The two subunits combine in different ratios to form seven NAD(H)-GDH isoenzymes. The slowest-migrating isoenzyme in a native gel, GDH1, is a homohexamer composed of α- subunits, and the fastest-migrating isoenzyme, GDH7, is a homohexamer composed of [beta] subunits. GDH isoenzymes 2 through 6 are heterohexamers composed of different ratios of α- and [beta] subunits. NAD(H)-GDH isoenzyme patterns varied among different plant organs and in leaves of plants irrigated with different nitrogen sources or subjected to darkness for 4 d. Conversely, there were little or no measurable changes in isoenzyme patterns in roots of plants treated with different nitrogen sources. In most instances, changes in isoenzyme patterns were correlated with relative differences in the level of α- and [beta] subunits. Likewise, the relative difference in the level of α- or [beta] subunits was correlated with changes in the level of GDH1 or GDH2 transcript detected in each sample, suggesting that NAD(H)-GDH activity is controlled at least in part at the transcriptional level.

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Regulation of Glutamate Dehydrogenase Activity in Relation to Carbon Limitation and Protein Catabolism in Carrot Cell Suspension Cultures

Cited by 112 publications

References 19 publications

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

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

Glutamine Synthetase-Glutamate Synthase Pathway and Glutamate Dehydrogenase Play Distinct Roles in the Sink-Source Nitrogen Cycle in Tobacco

Characterization and Expression of NAD(H)-Dependent Glutamate Dehydrogenase Genes in Arabidopsis

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