Glutamine Synthetases of Higher Plants

McNally, Sheila F.; Hirel, Bertrand; Gadal, Pierre; Mann, A. F.; Stewart, George R.

doi:10.1104/pp.72.1.22

Cited by 289 publications

(136 citation statements)

References 11 publications

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“…Furthermore, the rates of ammonia fixation measured in chloroplasts isolated from spinach and pea leaves (4,19,22) are adequate to support the refixation of ammonia released during photorespiration under ambient atmospheric conditions. Since the chloroplastic isoform of GS is the predominant GS component in leaves of C3 plants (12), one can conclude from the above evidence that the chloroplast is the major site for the reassimilation of photorespiratory ammonia via the chloroplastic GS/GOGAT pathway.…”

Section: Resultsmentioning

confidence: 98%

“…High rates of ammonia assimilation have been observed in spinach and pea chloroplasts and this activity appears to involve the GS/GOGAT pathway (1,4,14,19,22), even though the chloroplast also contains a NADP-specific GDH (9). Since the chloroplastic isoform of GS appears to be predominant in leaves of C3 plants (12) the assimilation of ammonia during photorespiration (7,18,23,24) would therefore be expected to take place predominantly in the chloroplast (2,23).…”

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confidence: 99%

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¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

Woo

Boyle²,

Flügge³

et al. 1987

Plant Physiol.

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The direct incorporation of`5NH4Cl into amino acids in illuminated spinach (Spinacia okracea L.) chloroplasts in the presence of 2-oxoglutarate plus malate was determined. The amido-N of glutamine was the most highly labeled N-atom during "5NH4 assimilation in the presence of malate. In 4 minutes the '5N-label of the amido-N of glutamine was 37% enriched. In contrast, values obtained for both the N-atom of glutamate and the amino-N of glutamine were only about 20% while that of the Natom of aspartate was only 3%. The addition of malate during the assimilation of '5N11CI and Nal5N02 greatly increased the '5N-label into glutamine but did not qualitatively change the order of the incorporation of '5N-label into all the amino acids examined. This evidence indicates the direct involvement of the glutamine synthetase/glutamate synthase pathway for ammonia and nitrite assimilation in isolated chloroplasts. The addition of malate or succinate during ammonia assimilation also led to more than 3-fold increase in ['4q2-oxoglutarate In leaves of higher plants the GS/GOGAT2 pathway is the primary route for the assimilation of ammonia (8,13,16,18,24). High rates of ammonia assimilation have been observed in spinach and pea chloroplasts and this activity appears to involve the GS/GOGAT pathway (1,4,14,19,22), even though the chloroplast also contains a NADP-specific GDH (9). Since the chloroplastic isoform of GS appears to be predominant in leaves of C3 plants (12) the assimilation of ammonia during photorespiration (7,18,23,24) would therefore be expected to take place predominantly in the chloroplast (2,23).In recent studies we have shown that the rates of (NH3, 19,22). These dicarboxylates were also found to partially relieve the inhibition of 2-OG transport by NH4Cl in the light (21). It is now possible to explain the above discrepancies by a two-translocator model for 2-OG and glutamate transport during NH3 assimilation in chloroplasts (5, 20). However, the fate of the assimilated N during ammonia assimilation in isolated chloroplasts under these conditions has never been established. It is not known whether the observed stimulation of 2-OG transport by dicarboxylates in the presence of NH4Cl is directly coupled to ammonia assimilation via GS/ GOGAT and glutamate export in the chloroplast. The present study examines and provides direct evidence for the involvement ofthe GS/GOGAT pathway for the assimilation of '5NH4Cl and Na'5N02 in spinach chloroplasts in the presence and absence of malate. Malate also increased the rate of 15N incorporation into glutamine and glutamate. The results further show that the increase in 2-OG transport in the presence of a dicarboxylate also led to increased amino acid synthesis and glutamate export from the chloroplast. MATERIALS AND METHODSMeasurements of "5N-Incorporation. The isolation of intact chloroplasts from spinach (Spinacia oleracea L.) leaves was as described (3). '5N-Labeling studies (in duplicates) were carried out in an O2 electrode reaction chamber in an assay mediu...

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Section: Resultsmentioning

confidence: 98%

mentioning

confidence: 99%

¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

Woo

Boyle²,

Flügge³

et al. 1987

Plant Physiol.

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“…DL-Phosphinothricin (DL-PPT) and &hydroxylysine have been identified as potent inhibitors of GS [I], but the action of these inhibitors has been studied only with crude preparations of GS. However, it has been shown that GS occurs as two isoforms in plants: GSl in the cytosol and GS2 in the chloroplast [2,3]. We have therefore examined the inhibition ,of GS isoforms by DL-PPT and &hydroxylysine to see if there is any differential sensitivity of the two enzyme forms.…”

Section: Introductionmentioning

confidence: 99%

“…We have therefore examined the inhibition ,of GS isoforms by DL-PPT and &hydroxylysine to see if there is any differential sensitivity of the two enzyme forms. Furthermore, in view of the demonstrated variations in the relative proportions of GSl and GS2 between species [3], we have examined the effects of DL-PPT on the GS isoforms from a range of plant species. Plants were chosen to represent crop and major attendant weed pairs in the hope that any variation in inhibition sensitivity might offer clues to selective herbicide design.…”

Section: Introductionmentioning

confidence: 99%

Kinetic analysis of glutamine synthetases from various plants

Acaster

Weitzman

1985

FEBS Letters

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Glutamine synthetase (GS) was partially purified from the leaves of 7 plant species and the relative contributions of two isoforms, GSl and GS2, were determined. Only 3 species, Zea mays, Hordeurn vulgare and Triticum aesticum, contained detectable levels of GS 1. K, values for glutamate and ATP of the various GS isolates were all within a narrow range. Both GS isoforms may be inhibited by phosphinothricin, competitively with glutamate. &Hydroxylysine also inhibited both isoforms but acted uncompetitively. The kinetic parameters of GS isolated from all 7 species showed a remarkable similarity.Glutamine synthetase Phosphinothricin &Hydroxylysine

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“…Thus, the principal function of the chloroplastic GOGAT cycle is the reassimilation of NH3 generated by photorespiration (3, 31). The chloroplastic GOGAT cycle involves operation of the ferredoxin-dependent GOGAT and the GS isoenzyme located in the chloroplast stroma (15,19).Several previous studies have examined ['4C]glutamate metabolism in leaves. Jordan and Givan (12) studied the role played by light in controlling the metabolism of ['4C]glutamate in leaves of Viciafaba and showed that the glutamine-synthetase inhibitor MSO not only prevented glutamine synthesis but also led to rapid metabolism ofglutamate by decarboxylation, deamination, and oxidation via the tricarboxylic acid cycle (cf.…”

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confidence: 99%

Glutamic Acid Metabolism and the Photorespiratory Nitrogen Cycle in Wheat Leaves

Walker¹,

Givan²,

Keys³

1984

Plant Physiol.

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The effects of methionine sulfoximine and ammonium chloride on ll4q glutamate metabolism in excised leaves of Triticum aesti'um were investipted. Glutamine The amount of NH3 generated by photorespiratory oxidation of glycine is several-fold greater than the amount produced through reduction of NO3-(5, 14, 25). Thus, the principal function of the chloroplastic GOGAT cycle is the reassimilation of NH3 generated by photorespiration (3, 31). The chloroplastic GOGAT cycle involves operation of the ferredoxin-dependent GOGAT and the GS isoenzyme located in the chloroplast stroma (15,19).Several previous studies have examined ['4C]glutamate metabolism in leaves. Jordan and Givan (12) studied the role played by light in controlling the metabolism of ['4C]glutamate in leaves of Viciafaba and showed that the glutamine-synthetase inhibitor MSO not only prevented glutamine synthesis but also led to rapid metabolism ofglutamate by decarboxylation, deamination, and oxidation via the tricarboxylic acid cycle (cf. 17). Franz et al. (5) subsequently found that total levels ofglutamate declined markedly in oat leaves when GS was inhibited, but they provided no information on the products or pathway of glutamate utilization.The inhibition of GS with MSO leads to large accumulations of NH3 in plant tissues (e.g. 22, 27). Elsewhere K. A. Walker, A. J. Keys, and C. V. Givan (in preparation) describe the effects of ammonium and MSO on rates and products of '4C02 assimilation in wheat leaves. A major goal of the present investigation was to distinguish between those effects of MSO that result principally from elevated tissue levels of NH3 per se and those that are specifically the result of blocked NH3 assimilation. Particular attention has been paid to metabolic interactions between glutamate and the tricarboxylic acid cycle and to the effects of light on operation of the tricarboxylic acid cycle.

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Glutamine Synthetases of Higher Plants

Cited by 289 publications

References 11 publications

¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

Kinetic analysis of glutamine synthetases from various plants

Glutamic Acid Metabolism and the Photorespiratory Nitrogen Cycle in Wheat Leaves

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Glutamine Synthetases of Higher Plants

Cited by 289 publications

References 11 publications

15N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

15N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

Kinetic analysis of glutamine synthetases from various plants

Glutamic Acid Metabolism and the Photorespiratory Nitrogen Cycle in Wheat Leaves

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¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light

¹⁵N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light