Enzymes of Ammonia Assimilation

Lea, Peter J.; Blackwell, R. D.; Chen, Fengling; Hecht, Ursula

doi:10.1016/b978-0-12-461013-2.50022-8

Cited by 95 publications

(82 citation statements)

References 91 publications

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“…The extraction buffer (pH 8.5) was supplemented by 2% (w\v) PVP to remove phenolic compounds and 20% glycerol (v\v). Extracts were stored at k80mC for a maximum of 2 wk before GS activity was assayed according to Lea et al (1990). The assay was performed at pH 7.5 and 37mC.…”

Section: Plant Tissue Analysesmentioning

confidence: 99%

Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

et al. 1999

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The physiological potential for acquisition of atmospheric ammonia (NH $ ) was investigated in three European meadow grasses (Arrhenatherum elatius, Bromus erectus and Brachypodium pinnatum) competing in chalk grasslands. Experiments were carried out with plants cultivated for about three months on a soil-sand mixture at high root nitrogen supply or in nutrient solutions at low root nitrogen supply. Two different root nitrogen regimes were applied to the solution-grown plants : 130 µmol NO $ plant −" wk −" (approx. 50 kg nitrogen ha −" in three months) ; or 130 µmol NO $ − plus 130 µmol NH % + plant −" wk −" . Each regime was combined with two levels of NH $ fumigation (0 and 70 nmol mol −" air for 24 d). Uptake of gaseous NH $ in the shoots was investigated under controlled environmental conditions including NH $ concentrations ranging from 0 to 30 nmol mol −" air. Concurrently, photosynthesis, glutamine synthetase activity, nitrogen allocation, biomass allocation and apoplastic cation composition were measured. For A. elatius, the influence of photorespiration on NH $ acquisition was also assessed.Independently of plant nitrogen status, ammonia compensation points in A. elatius and B. erectus plants were 0.5 nmol mol −" . The total leaf conductance to NH $ absorption remained constant at increasing NH $ concentrations, showing that the capacity for assimilation was unaltered. Whereas internal factors in the leaves did not cause differences in the potential for NH $ acquisition between the species, other factors of NH $ acquisition were quite different : B. erectus had higher stomatal conductance and, thus, higher NH $ uptake rates per unit leaf area compared to A. elatius and B. pinnatum ; higher stomatal conductances of B. erectus were to a large extent offset by a lower leaf area per plant, resulting from a lower growth rate and thicker leaves than in the two other species. The rate of photorespiration in Arrhenatherum constituted at least 15% of the net photosynthetic rate. Surprisingly, suppression of photorespiration indicated that NH $ uptake was supported by photorespiration. Bromus responded to fumigation with 70 nmol NH $ mol −" air for 24 d by lowering the root : shoot ratio and increasing the nitrogen concentration in the stem dry matter. The total leaf conductance to NH $ uptake decreased in all three species upon exposure to NH $ , while the stomatal conductance was unaffected. The NH $ exposure caused lower apoplastic concentrations of H + , Mg# + and Ca# + in A. elatius and B. erectus.

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Section: Plant Tissue Analysesmentioning

confidence: 99%

Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

et al. 1999

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“…The assimilation of ammonia in higher plants is catalysed by the glutamine synthetase/glutamate synthase pathway (Lea et al, 1990;Miflin and Lea, 1980). In leaves both enzymes are located in the chloroplast and, in light, the ATP and reductant necessary for the respective reactions are generated photochemically (Anderson and Done, 1977).…”

Section: Introductionmentioning

confidence: 99%

Reductant for glutamate synthase in generated by the oxidative pentose phosphate pathway in non‐photosynthetic root plastids

et al. 1992

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SummaryPurified pea root plastids were supplied with glutamine, 2-oxoglutarate and phosphorylated sugars. Formation of glutamate was linear for 75 min and dependent upon the intactness of the organelle. Glucose-6-phosphate and ribose-5-phosphate were the most effective substrates in supporting glutamate synthesis. Flux through the oxidative pentose phosphate pathway during glutamate synthesis in purified plastids was followed by monitoring the release of I4CO2 from [l-'4C]glucose-6-phosphate. I4CO2 evolution from C-1 was dependent upon the presence of both glutamine and 2-oxoglutarate and could be inhibited by the application of azaserine. The data are discussed in view of the role of the oxidative pentose phosphate pathway in non-photosynthetic plastids.

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“…GS activity was measured by the synthetase assay (Lea et al, 1990). NADH-GOGAT was measured spectrophotometrically monitoring NADH absorbance at 340 nm (Groat and Vance, 1981).…”

Section: Enzyme Assaysmentioning

confidence: 99%

“…The GS is crucial in this assimilatory process as it catalyzes the first step in the conversion of inorganic nitrogen (ammonium) into its organic form (glutamine). The amide nitrogen from glutamine is then transferred to 2-oxoglutarate to yield two molecules of glutamate which can serve as GS substrate and so complete the GS/GOGAT cycle (Lea et al, 1990). Much of the fixed nitrogen is rapidly transferred to asparagine that, together with glutamine, is transported in the xylem from the nodule in Lotus spp.…”

Section: Introductionmentioning

confidence: 99%

Glutamine synthetase and glutamate synthase activities in relation to nitrogen fixation in Lotus spp.

Gonnet¹,

Dı́az²

2000

Rev. Bras. Fisiol. Veg.

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-Lotus corniculatus, L. tenuis, L. pedunculatus, and L. subbiflorus inoculated withMesorhizobium loti NZP2037 strain were grown in a growth chamber. The plants dry weight (DW), the nodule fresh weight (FW), the nitrogenase activity, the nodule glutamine synthetase (GS) and glutamate synthase (GOGAT) activities, as well as the leghemoglobin content and the amino acid in the stem were measured 28 days after inoculation. The highest DW of plants was measured in L. tenuis and the highest FW of nodules was measured in L. pedunculatus. Nitrogenase activity in L. tenuis, L. pedunculatus and L. subbiflorus was six fold the activity in L. corniculatus. Nodule GS and GOGAT activities did not follow this same pattern. L. tenuis had the highest values of GS and GOGAT activities in the nodule, and a high nitrogenase activity which is consistent with its high plant DW. The four species of Lotus were compared and no correlation between nitrogen fixation parameters and ammonia assimilation enzymes was found, but the GS/GOGAT ratio has a positive and significant correlation (r 2 =0.82 ** ) with the amino acid content in stems. ADDITIONAL INDEX TERMS:

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Enzymes of Ammonia Assimilation

Cited by 95 publications

References 91 publications

Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

Reductant for glutamate synthase in generated by the oxidative pentose phosphate pathway in non‐photosynthetic root plastids

Glutamine synthetase and glutamate synthase activities in relation to nitrogen fixation in Lotus spp.

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