Barley Mutants Lacking Chloroplast Glutamine Synthetase—Biochemical and Genetic Analysis

Wallsgrove, R. M.; Turner, J. C.; Hall, N. P.; Kendall, A. C.; Bright, S. W. J.

doi:10.1104/pp.83.1.155

Cited by 343 publications

(248 citation statements)

References 11 publications

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“…Furthermore, molecular studies have shown that under photorespiratory conditions the gene encoding the chloroplast isoenzyme of GS was induced 4-fold (Edwards and Coruzzi, 1989). These results support the earlier findings of Wallsgrove et al (1987), which suggested that GS/GOGAT played a key role in the reassimilation of ammonia released during photorespiration. However, GDH may play a complementary role to GS/GOGAT in the reassimilation of excess ammonia released during stress conditions or during specific stages of development (Yamaya et al, 1986;Rhodes et al, 1989; for review, see Stewart et al, 1980;Srivastava and Singh, 1987).…”

supporting

confidence: 81%

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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supporting

confidence: 81%

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

et al. 1997

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“…The activity of the promoter for chloroplast GS2 predominantly in photosynthetic cell types is consistent with findings that chloroplast GS2 functions in the reassimilation of photorespiratory ammonia (7,17) and in the assimilation of reduced nitrite in plastids (8). Previous analysis of photorespiratory mutants revealed that plants that lacked chloroplast GS2 were nonviable when grown under photorespiratory conditions even though they contained normal levels of cytosolic GS (7).…”

Section: Discussionsupporting

confidence: 60%

“…Early biochemical data revealed that GS functions in the assimilation of ammonia generated by numerous plant processes, which include seed germination (4,5), photorespiration (6,7), nitrite reduction (8), nitrogen-fixation in root nodules (9,10), and primary ammonia assimilation from the soil (11). An analysis of the GS genes in several species has revealed a strong correlation of individual GS gene expression with specific aspects of plant development (12)(13)(14)(15)(16)(17)(18).…”

mentioning

confidence: 99%

Cell-specific expression in transgenic plants reveals nonoverlapping roles for chloroplast and cytosolic glutamine synthetase.

Edwards

Walker

Coruzzi

1990

Proc. Natl. Acad. Sci. U.S.A.

210

123

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Chloroplast and cytosolic isoforms of glutamine synthetase (GS; EC 6.3.1.2) are encoded by separate nuclear genes in plants. Here we report that the promoters for chloroplast GS2 and cytosolic GS3A of Pisum sahvum confer nonoverlapping, cell-specific expression patterns on the j8-glucuronidase (GUS) reporter gene in transgenic tobacco. The promoter for chloroplast GS2 directs GUS expression within photosynthetic cell types (e.g., palisade parenchymal cells of the leaf blade, chlorenchymal cells of the midrib and stem, and photosynthetic cells of tobacco cotyledons). The promoter for chloroplast GS2 retains the ability to confer light-regulated gene expression in the heterologous transgenic tobacco system in a manner analogous to the light-regulated expression of the cognate gene for chloroplast GS2 in pea. These expression patterns reflect the physiological role of the chloroplast GS2 isoform in the assimilation of ammonia generated by nitrite reduction and photorespiration. In contrast, the promoter for cytosolic GS3A directs expression of GUS specifically within the phloem elements in all organs of mature plants. This phloem-speciflic expression pattern suggests that the cytosolic GS3A isoenzyme functions to generate glutamine for intercellular nitrogen transport. In germinating seedlings, the intense expression of the cytosolic GS3A-GUS transgene in the vasculature of cotyledons reveals a role for cytosolic GS in the mobilization of seed storage reserves. The distinct, cell-specific patterns of expression conferred by the promoters for chloroplast GS2 and cytosolic GS3A indicate that the corresponding GS isoforms perform separate metabolic functions.In higher plants, many steps in nitrogen metabolism occur in multiple subcellular compartments. For example, many amino acid biosynthetic isoenzymes are located in the cytosol as well as in the mitochondria or chloroplasts. The relative function of many amino acid biosynthetic isoenzymes has been difficult to assess due to inadequate fractionation of organelle and cytoplasm components, overlapping activity profiles, and immunological cross-reactivity (1, 2). Consequently, it is unclear whether these isoenzymes carry out redundant or distinct roles in plant metabolism.The best-studied example of a plant amino acid biosynthetic enzyme shown to occur as multiple isoforms is glutamine synthetase (GS; EC 6.3.1.2) (3). Early biochemical data revealed that GS functions in the assimilation of ammonia generated by numerous plant processes, which include seed germination (4, 5), photorespiration (6, 7), nitrite reduction (8), nitrogen-fixation in root nodules (9, 10), and primary ammonia assimilation from the soil (11). An analysis of the GS genes in several species has revealed a strong correlation of individual GS gene expression with specific aspects of plant development (12)(13)(14)(15)(16)(17)(18). Recent sequence analysis of GS cDNAs from Pisum sativum and Phaseolus vulgaris has shown that chloroplast and cytosolic GS are encoded by separate but similar nuclea...

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“…1 within mesophyll cells (Keys et al, 1978). GS2 is crucial for the reassimilation of this NH 4 1 , because mutants lacking this enzyme accumulate NH 4 1 and die (Wallsgrove et al, 1987). Although GDH activity is usually very low in mesophyll cells compared with GS2 (Bechtold et al, 1998), several studies have provided evidence that mesophyll GDH may reassimilate small amounts of photorespiratory NH 4 1 (Hartmann and Ehmke, 1980;Neeman et al, 1985;Yamaya et al, 1986 1 ] produce more labeled Glu and Gln than controls (Ameziane et al, 2000;Mungur et al, 2005).…”

Section: Gdh Isoenzyme 1 In Roots Catabolizes Glumentioning

confidence: 99%

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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Barley Mutants Lacking Chloroplast Glutamine Synthetase—Biochemical and Genetic Analysis

Cited by 343 publications

References 11 publications

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

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

Cell-specific expression in transgenic plants reveals nonoverlapping roles for chloroplast and cytosolic glutamine synthetase.

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

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