The assimilation of ammonium by barley roots

Lewis, O. A. M.; Chadwick, S.; Withers, Julie M.

doi:10.1007/bf00409136

Cited by 34 publications

(14 citation statements)

References 12 publications

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“…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: 93%

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: Mathematical Modelling Of' N Labellingcontrasting

confidence: 93%

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

Kusnan

Klug²,

Fock³

1989

Microbiology

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“…Tables II and III). An approach to discriminating between GS/GOGAT and GDH pathways of NH4' assimilation is to employ the potent inhibitor of GS, MSX (6,7,13,20,25 (Fig. 3) and shoots (Fig.…”

Section: Nh4+ Assimilation Kinetics In the Presence Andmentioning

confidence: 99%

“…Much biochemical and genetic evidence supports this conclusion. First, potent inhibitors of GS and GOGAT block ammonia assimilation (6,7,13,20,28). Second, '3N and 'sN kinetic evidence indicates that glutamine-amide is the generally the first and most heavily labeled product of NH4' assimilation, and that glutamine carries a large percentage of the total N flux of plant tissue (15,21,22,24,26,31).…”

mentioning

confidence: 99%

Kinetics of ¹⁵NH₄⁺ Assimilation in Zea mays

Magalhães¹,

Ju²,

Rich³

et al. 1990

Plant Physiol.

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In higher plants it is now generally considered that glutamate dehydrogenase (GDH) plays only a small or negligible role in ammonia assimilation. To test this specific point, comparative studies of 15NH4+ assimilation were undertaken with a GDH1-null mutant of Zea mays and a related (but not strictly isogenic) GDHIpositive wild type from which this mutant was derived. The kinetics of 15NH4+ assimilation into free amino acids and total reduced nitrogen were monitored in both roots and shoots of 2-week-old seedlings supplied with 5 millimolar 99% (15NH4)2S04 via the aerated root medium in hydroponic culture over a 24-h period. The GDHI-null mutant, with a 10-to 15-fold lower total root GDH activity in comparison to the wild type, was found to exhibit a 40 to 50% lower rate of 15NH4+ assimilation into total reduced nitrogen. Observed rates of root ammonium assimilation were 5.9 and 3.1 micromoles per hour per gram fresh weight for the wild type and mutant, respectively. The lower rate of 15NH4+ assimilation in the mutant was associated with lower rates of labeling of several free amino acids (including glutamate, glutamine-amino N, aspartate, asparagine-amino N, and alanine) in both roots and shoots of the mutant in comparison to the wild type. Qualitatively, these labeling kinetics appear consistent with a reduced flux of 15N via glutamate in the GDHI-null mutant.However, the responses of the two genotypes to the potent inhibitor of glutamine synthetase, methionine sulfoximine, and differences in morphology of the two genotypes (particularly a lower shoot:root ratio in the GDH1-null mutant) urge caution in concluding that GDH1 is solely responsible for these differences in ammonia assimilation rate.

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“…It has been established, however, that in vascular plants ammonium assimilation occurs almost exclusively via the GS-GOGAT cycle (Miflin & Lea, 1976, 1980Fentem, Lea & Stewart, 1983;Lewis, Chadwick & Withers, 1983). Much less is known about the relative importance of the two potential pathways for assimilation of ammonium by algae; the few detailed studies carried out so far with microalgae indicate that ammonium assimilation is not an exclusive function of any one of these pathways.…”

Section: Introductionmentioning

confidence: 99%

PATHWAYS OF AMMONIUM ASSIMILATION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS NAEG.

Ahmad

Hellebust

1986

New Phytologist

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SUMMARYGlutamine synthetase (GS) and NADPH-glutamate dehydrogenase (GDH) are key enzymes for ammonium assimilation in Stichococcus bacillaris Naeg. (UTEX 314). Cells growing with different concentrations of nitrate and ammonium contain activities of both GS and NADPH-GDH in excess of required nitrogen assimilation rates under autotrophic as well as heterotrophic conditions. The activity of GS increases 2 to 3 fold, and NADPH-GDH 10 to 15 fold when the concentration of ammonium in the medium is lowered from 2 to 0*2 mM, or when nitrate is present as the nitrogen source. The activity of ferredoxin-dependent glutamate synthase (GOGAT) is similar to, or high than that of GS. In this alga. NADPH-GDH has a low Kf or ammonium (1-6 mM), and is capable of functioning effectively over the pH range occurring in the chloroplast stroma. A possible role of NADPH-GDH in nitrogen assimilation by S. bacillaris is supported by the observation that the alga grows normally in the presence of methionine sulphoximine (MSX), when high levels of this enzyme are present, while GS is almost completely inhibited. Stichococcus bacillaris also contains high activities of NADH-GDH, but the Kj^ for ammonium of this GDH (33 mM) appears too high for it to function effectively in nitrogen assimilation. The activity of NADH-GDH increases 3 to 5 fold when cells growing photoautotrophically are transferred to heterotrophic conditions, suggesting a catabolic role for this enzyme.

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The assimilation of ammonium by barley roots

Cited by 34 publications

References 12 publications

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

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

Kinetics of ¹⁵NH₄⁺ Assimilation in Zea mays

PATHWAYS OF AMMONIUM ASSIMILATION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS NAEG.

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The assimilation of ammonium by barley roots

Cited by 34 publications

References 12 publications

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

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

Kinetics of 15NH4+ Assimilation in Zea mays

PATHWAYS OF AMMONIUM ASSIMILATION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS NAEG.

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Kinetics of ¹⁵NH₄⁺ Assimilation in Zea mays