Amino Acid Interconversion in Germinating Seeds

Lea, Peter J.; Joy, K. W.

doi:10.1007/978-1-4684-1167-6_5

Cited by 25 publications

(15 citation statements)

References 110 publications

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“…We suggest that the three GS isoenzymes fulfil different metabolic roles as the leaf develops from the plumule stage, which represents a sink for carbon and nitrogen supplied by the cotyledons, into a mature, photosynthesising leaf. In the germinating seed, mobilisation of the cotyledonary storage proteins leads to the release of ammonium, firstly in the cotyledons and later in the developing embryo, which must then be reassimilated via GS [25]. The gln-~ gene is the predominantly expressed GS gene both in plumules at this early stage (Figs.…”

Section: Differential Expression Of the Gs Gene Family In Developing mentioning

confidence: 99%

Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Cock

Watson

et al. 1991

Plant Mol Biol

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Glutamine synthetase (GS) activity increased over three-fold in developing primary leaves of Phaseolus vulgaris L. This increase was shown to be the result of differential expression of three members of the GS gene family: gln-alpha and gln-beta, which encode cytosolic GS polypeptides, and gln-delta, which encodes the chloroplast-located GS. The gln-delta gene was the most highly expressed GS gene and was regulated in a complex manner with two different transcripts accumulating differentially during leaf development. This gene was expressed weakly in the dark and was induced strongly by light; this induction was shown not to be an indirect effect of photorespiration. In the long term, gln-delta showed increased expression in photorespiring compared with non-photorespiring leaves. However, in the short term, there was no induction of gln-delta following transfer of plants to photorespiratory conditions. These results suggest that regulation of gln-delta by photorespiration was the result of indirect, long-term effects on cellular metabolism. In general, in all these experiments, analysis of cytosolic versus chloroplastic GS polypeptides and of the GS isoenzyme profiles showed the same pattern of changes in abundance as that observed for the mRNAs suggesting that regulation of GS gene expression occurred primarily at the mRNA level. However, it was noteworthy that the delta isoenzyme remained at a high abundance in older leaves, grown in both light and dark, despite a decrease in abundance of gln-delta mRNA.

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Section: Differential Expression Of the Gs Gene Family In Developing mentioning

confidence: 99%

Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Cock

Watson

et al. 1991

Plant Mol Biol

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“…In particular, mobilization of nitrogen reserves as a source of energy and nutrients to supply expanding new tissue is proposed to take part in the control of germination (Garciarubio et al 1997). Several analytical works based on 14 C labeling showed that amino acids in germinating seeds contribute a large amount of carbon substrate to the respiratory system and sugar synthesis, as shown in gluconeogenic oilseeds such as castor bean (Lea and Joy 1983). Considerable inter-conversion of amino acids occurs following storage-protein hydrolysis in germinating seeds (Lea and Joy 1983).…”

Section: Introductionmentioning

confidence: 99%

Respective roles of the glutamine synthetase/glutamate synthase cycle and glutamate dehydrogenase in ammonium and amino acid metabolism during germination and post-germinative growth in the model legume Medicago truncatula

Glévarec

Bouton

Jaspard

et al. 2004

Planta

103

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Our objective was to determine the respective roles of the couple glutamine synthetase/glutamate synthase (GS/GOGAT) and glutamate dehydrogenase (GDH) in ammonium and amino acid metabolism during germination and post-germinative growth in the model legume Medicago truncatula Gaertn. For this aim, amino acids were analyzed by HPLC and changes in gene expression of several enzymes involved in N and C metabolism were studied by real-time quantitative reverse transcription-polymerase chain reaction. Among the enzymes studied, GDH showed the highest increase in gene expression (80-fold), specifically in the embryo axis and concomitant with the increase in ammonium content during post-germinative growth. In cotyledons, GDH gene expression was very low. Although in vitro GDH aminating activity was several times higher than its deaminating activity, in vivo 15NH4 incorporation into amino acids was completely inhibited by methionine sulfoximine, a GS inhibitor, indicating that GDH is not involved in ammonium assimilation/detoxification. Changes in the expressions of GS and GOGAT isoforms revealed that GS1b (EC 6.3.1.2) in concert with NADH-dependent GOGAT (EC 1.4.1.14) constitute the major route of assimilation of ammonium derived from reserve mobilization and glutamic acid/glutamine synthesis in germinating M. truncatula seeds. However, during post-germinative growth, although germination was held in darkness, expression of GS2 and Fd-GOGAT (EC 1.4.7.1) increased and expression of GS1b decreased in cotyledons but not in the embryo axis. 2-Oxoglutarate, the substrate of the transamination reaction, was provided by the cytosolic isoform of isocitrate dehydrogenase (EC 1.1.1.42). We suggest that GDH during post-germinative growth, specifically in the developing embryo axis, contributes to ammonium delivery to GS for glutamine synthesis in the absence of primary NO3- assimilation. Interestingly, this reaction also produces reducing power (NADH) in organs deprived of photosynthesis.

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“…The ammonia released is reassimilated into organic form via GS for nitrogen transport to the developing seedling (14). To determine the role of each "twin" GS gene in this developmental context, the gene-specific 3' Sl- Figure 2.…”

Section: Northern Blot Analysismentioning

confidence: 99%

“…In plants, GS assimilates ammonia generated from a number of different processes including the reduction of soil nitrate, photorespiration, and atmospheric dinitrogen reduced in nitrogen-fixing nodules of legumes. GS activity has also been shown to increase dramatically in cotyledons during germination where large amounts of glutamine are synthesized for nitrogen transport to the developing seedling (14). Molecular analysis of the GS genes in P. sativum has uncovered a multigene family whose individual members encode a single chloroplast GS2 polypeptide, and several distinct cytosolic GS GM07982. in the nucleus (26,27).…”

mentioning

confidence: 99%

Developmentally Regulated Expression of the Gene Family for Cytosolic Glutamine Synthetase in Pisum sativum

Walker

Coruzzi

1989

Plant Physiol.

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In Pisum sativum, two classes of genes encode distinct isoforms of cytosolic glutamine synthetase (GS). The first class comprises two nearly identical or "twin" GS genes (GS341 and GS132), while the second comprises a single GS gene (GS299) distinct in both coding and noncoding regions from the "twin" GS genes. Gene-specific analyses were used to monitor the individual contribution of each gene for cytosolic GS during root nodule development and in cotyledons during germination, two contexts where large amounts of ammonia must be assimilated by GS for nitrogen transport. mRNAs corresponding to all three genes for cytosolic GS were shown to accumulate coordinately during a time course of nodule development. All the GS mRNAs also accumulate to wild-type levels in mutant nodules formed by a nifD strain of Rhizobium leguminosarum indicating that induced GS expression in pea root nodules does not depend on the production of ammonia. Distinct pattems of expression for the two classes of GS genes were observed in certain mutant root nodules and most dramatically in cotyledons of germinating seedlings. The different pattems of expression between the two classes of genes for cytosolic GS suggests that their distinct gene products may serve nonoverlapping functions during pea development.

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Amino Acid Interconversion in Germinating Seeds

Cited by 25 publications

References 110 publications

Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Respective roles of the glutamine synthetase/glutamate synthase cycle and glutamate dehydrogenase in ammonium and amino acid metabolism during germination and post-germinative growth in the model legume Medicago truncatula

Developmentally Regulated Expression of the Gene Family for Cytosolic Glutamine Synthetase in Pisum sativum

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