Pathway of ammonia assimilation in illuminated Lemna minor

Rhodes, David; Sims, A. P.; Folkes, B. F.

doi:10.1016/0031-9422(80)83182-7

Cited by 63 publications

(49 citation statements)

References 24 publications

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“…However, the pattern of 5N labelling in the major amino acids in this study differed from the pattern of 5N labelling in major amino acids of ammonia assimilation by the GDH pathway in Candida utilis (Sims & Folkes, 1964), in which glutamate was initially more highly labelled than any other amino acid. Our results also differed from the pattern of labelling in the major amino acids of ammonia assimilation by the GSlGOGAT pathway in Lemna minor (Rhodes et al, 1980) and barley roots (Fentem et al, 1983), which showed that glutamine-amide was the first highly labelled compound.…”

Section: N Uptakecontrasting

confidence: 99%

“…nidulans differs from the previous observations on Lernna minor and barley roots (Fentem et al, 1983;Lewis et al, 1983;Rhodes et al, 1980). Although substantial activity of NADP-GDH was detected in these plants, ammonia was assimilated solely by the GS/GOGAT pathway.…”

Section: Mathematical Modelling Of' N Labellingcontrasting

confidence: 92%

“…nidulans were derived from the flux equation of Rhodes et al (1980). Initially, the theoretical 5N labelling curve for the amide group of glutamine was constructed and compared with the experimental data (Fig.…”

Section: Mathematical Modelling Of' N Labellingmentioning

confidence: 99%

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Ammonia Assimilation by Aspergillus nidulans: [15N]Ammonia Study

Kusnan

Klug²,

Fock³

1989

Microbiology

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~~~l 5N kinetic labelling studies were done on liquid cultures of wild-type Aspergillus nidulans. The labelling pattern of major amino acids under 'steady state' conditions suggests that glutamate and glutamine-amide are the early products of ammonia assimilation in A . nidulans. In the presence of phosphinothricin, an inhibitor or glutamine synthetase, 5N labelling of glutamate, alanine and aspartate was maintained whereas the labelling of glutamine was low. This pattern of labelling is consistent with ammonia assimilation into glutamate via the glutamate dehydrogenase pathway. In the presence of azaserine, an inhibitor of glutamate synthase, glutamate was initially more highly labelled than any other amino acid, whereas its concentration declined. Isotope also accumulated in glutamine. Observations with these two inhibitors suggest that ammonia assimilation can occur concurrently via the glutamine synthetase/glutamate synthase and the glutamate dehydrogenase pathways in low-ammoniagrown A . nidulans. From a simple model it was estimated that about half of the glutamate was synthesized via the glutamate dehydrogenase pathway; the other half was formed from glutamine via the glutamate synthase pathway. The transfer coefficients of nine other amino acids were also determined.

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Section: N Uptakecontrasting

confidence: 99%

Section: Mathematical Modelling Of' N Labellingcontrasting

confidence: 92%

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Ammonia Assimilation by Aspergillus nidulans: [15N]Ammonia Study

Kusnan

Klug²,

Fock³

1989

Microbiology

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“…Such an approach has been successfully applied to cultures of Candida utilis growing under steady state conditions (3,21), demonstrating that in this organism the greater proportion of ammonia taken up from the medium is assimilated via GDH. Comparable studies with cultures of Lemna minor gave labeling data consistent with a two-compartment model in which ammonia is assimilated solely via the GS/glutamate synthase route (18 Sepaation of Nitrogen Compounds. NH3 in plant extracts was separated from nitrate and amino acids by passage through a column (0.5 x 2.0 cm) of Dowex 50W-X8 (400 mesh) sodium form equilibrated with 10 mm sodium acetate, pH 6.2.…”

Section: Methodsmentioning

confidence: 52%

Ammonia Assimilation in the Roots of Nitrate- and Ammonia-Grown Hordeum Vulgare (cv Golden Promise)

Fentem¹,

Lea²,

Stewart³

1983

Plant Physiol.

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to be reached on the pathway of ammonia assimilation. Thus, 15N-feeding experiments with both root (17, 27) and shoot (8) tissues, and studies using 13N (13,22) in which glutamine was initially more highly labeled than glutamate, have been interpreted as being consistent with ammonia assimilation via the GS/glutamate synthase route. Similarly, experiments in which glutamate was initially more highly labeled than glutamine (6, 8) have been interpreted as being at least qualitatively consistent with assimilation via GDH. Such conclusions are, however, speculative in the absence of information on the number and relative sizes of the glutamate and glutamine pools in the tissues concerned.The purpose of these studies was to obtain kinetic labehling data from experiments in which Hordeum seedlings, growing under steady state conditions, were fed '5N-labeled ammonia or nitrate.Attempts were then made to apply a quantitative analysis to the 15N incorporation patterns in ammonia-fed barley roots. MATERIALS AND METHODSNumerous studies have demonstrated that both roots and leaves of higher plants possess the enzymic potential for the assimilation of ammonia either via the direct reductive amination of 2-oxoglutarate, catalyzed by GDH2 or via the combined action of GS and glutamate synthase (23). The now widely held belief that the GS/ glutamate synthase pathway is solely responsible for ammonia assimilation in these tissues (15) Growth of Plants. The growth system used was a 'continuous flow' water culture system. Seeds of Hordeum vulgare L. var.Golden Promise were soaked overnight in running tap water, with aeration, before sowing on sections of Netlon mesh covered with muslin and stretched over the top of lengths of plastic guttering filled with culture solution. Culture solution was cycled through the gutters from a large reservoir by means of a pump. The flow of nutrient solution through the gutters was adjusted to a rate sufficient to prevent the concentrations of nutrient in the gutters differing from those in the reservoir due to uptake by the plants. Seedlings were subjected to a 14-h daylight regime, with a light intensity of 4.95 J cm -2 h-' at the level of the plants, and a constant temperature of 23°C. The nutrient solution used was a modified one-quarter strength Long Ashton solution (4). Nitrogen was supplied either as potassium nitrate or ammonium chloride. The volume of the reservoir was chosen to prevent the concentration of ammonia or nitrate in the culture solution from being reduced by more than 10% over a 24-h period. Labeling studies were performed on 9-d-old seedlings. At the start of a '5N-labeling experiient, the pump was stopped, and the gutters were rapidly drained and refilled with culture solution containing the nitrogen source labeled at 96% 15N atom abundance. The reservoir was exchanged for one containing the labeled nitrogen source, and the pump was restarted. The plants were sampled by removing individual sections of Netlon mesh.Extraction of Soluble Nitrogen Pools. Root and shoot tissues...

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“…If NADP-GDH, present at high levels, was the only enzyme operative in the fixation of ammonia, a steeper increase in [ SN]glutamate would have occurred. Therefore, not only NADP-GDH but also GS must have been involved in primary ammonia fixation to form [ SN]glutamate as well as glutamine with the amide group preferentially labelled (Rhodes et al, 1980). When metabolized via GOGAT, the large glutamine pool of S. semiglobutu will, especially in the early phase of l5NH4C1 assimilation, dilute glutamate with 14N and cause the observed lag phage of glutamate labelling.…”

Section: )mentioning

confidence: 99%

The involvement of glutamate dehydrogenase and glutamine synthetase/glutamate synthase in ammonia assimilation by the basidiomycete fungus Stropharia semiglobata

Schwartz

Misri

Fock

1991

Journal of General Microbiology

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~When grown on ammonia as sole nitrogen source, the basidiomycete fungus Stropharia semigfobatu assimilated nitrogen via glutamate dehydrogenase (GDH). The two isoenzymes of GDH were both repressed by increasing concentrations of ammonia, but NADP-GDH (EC 1.4.1.4) was far more active than NAD-GDH (EC 1.4.1.2). Glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (GOGAT; EC 1.4.7.1) were also active in S. semigfobatu and these enzyme activities were independent of the ammonia concentration in the suspension. From enzyme activity and lSN-labelling studies of amino acids, it is concluded that both GDH and GS/GOGAT contribute to ammonia assimilation in this fungus.

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Pathway of ammonia assimilation in illuminated Lemna minor

Cited by 63 publications

References 24 publications

Ammonia Assimilation by Aspergillus nidulans: [15N]Ammonia Study

Ammonia Assimilation by Aspergillus nidulans: [15N]Ammonia Study

Ammonia Assimilation in the Roots of Nitrate- and Ammonia-Grown Hordeum Vulgare (cv Golden Promise)

The involvement of glutamate dehydrogenase and glutamine synthetase/glutamate synthase in ammonia assimilation by the basidiomycete fungus Stropharia semiglobata

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