Ammonia assimilation in lupin nodules

Scott, David B.; Farnden, Kevin J. F.; Robertson, John

doi:10.1038/263703a0

Cited by 125 publications

(58 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The study indicated that the proportion of nitrogen as ureide in sap was a relatively stable quantity, Most recent evidence suggests that the amide group ofglutamine is the initial product of ammonia assimilation after N2 fixation or NO3 reduction (12) and that this nitrogen serves directly in the synthesis of glutamate (18), and in the synthesis of the amide group of asparagine by a transamidation reaction with aspartate (19). Ureide formation based on purine biosynthesis requires two atoms of amide nitrogen, either as glutamine or asparagine (7,17), and a N atom of aspartate to form three of the four N atoms of allantoin and allantoic acid (4), so synthesis of these compounds could be envisaged as competitive with asparagine formation.…”

Section: Methodsmentioning

confidence: 99%

Nitrogen Nutrition and Xylem Transport of Nitrogen in Ureide-producing Grain Legumes

Pate¹,

Atkins²,

White³

et al. 1980

Plant Physiol.

150

View full text Add to dashboard Cite

Xylem sap composition was examined in nodulated and nonnodulated cowpea ( Vigna unguicd L.I Walp.) plants receiving a range of levels of NO3 and in eight other ureide-forming legumes udlizing NO3 or N2 as sole source of nitrogen. A 15N dilution technique determined the proportions of plant nitrogen derived from N2 in the nodulated cowpeas fed NO. Xylem sap composition of N03-fed, nodulated cowpea varied predictably with the relative extents to which N2 and NO3 were being utilized. The ratios of asparagine to glutamine (N/N) and of NO3 to ureide (N/N) in xylem sap increased with increasing dependence on NO3 whereas per cent of xylem nitrogen as ureide and the ratio of ureide plus glutamine to asparagine plus NO3 (N/N) in xylem sap increased with increasing dependence on N2 fixation. The amounts of NO3 and ureides stored in leaflets, stems plus petioles, and roots of cowpea varied in a complex manner with level of NO3 and the presence or absence of N2 fixation. All species showed higher proportions of organic nitrogen as ureide and several-fold lower ratios of asparagine to glutamine in their xylem sap when relying on N2 than when utilizing NO3. In nodulated (minus nitrate) cowpea and mung bean (Vigna radiata [L.1 Wilczek) the percentage of xylem nitrogen as ureide remained constant during growth but the ratio of asparagine to glutamine varied considerably. The biochemical significance of the above differences in xylem sap compositdon was discussed.A number of legumes, especially tropical species, synthesize allantoin and allantoic acid from currently fixed N2 in nodules and use these compounds for transport and storage of N (1, 3, 6, 10). In soybean (Glycine max [L.] Merr.) the ureides are more prominent in nodulated plants than in plants grown with NO3 or NH4 salts (8, 11), suggesting a special association between N2 fixation and ureide formation (9), and the possibility of using ureide levels in plant tissues or transport fluids to determine the extent to which a field-grown crop is relying on symbiosis as opposed to combined forms of N from soil or fertilizer. This paper describes xylem sap composition of N2 and N03-fed cowpea (Vigna unguiculata [L.] Walp.) and of other grain legumes which form ureides, and suggests how compositional features of the sap might be used to evaluate the N2-fixing status of nodulated plants grown in the presence of NO3. MATERIALS AND METHODSThe species studied were cowpea (V. unguiculata [L.] Plants were grown in pots of heat sterilized sand during summer in a naturally lit glasshouse maintained within the temperature range 20-35 C by supplementary heating (night) and evaporative cooling (day). One set of plants of each species was inoculated with an effective Rhizobium (strain CB437, for soybean, strain NGR234 for horse gram, and strain CB756 for all other species) and grown with a N-free culture solution. A matching set of uninoculated plants received culture solution containing 10 mM NO3. By using this level of NO3, sterile sand and effective surface sterilization of s...

show abstract

Section: Methodsmentioning

confidence: 99%

Nitrogen Nutrition and Xylem Transport of Nitrogen in Ureide-producing Grain Legumes

Pate¹,

Atkins²,

White³

et al. 1980

Plant Physiol.

150

View full text Add to dashboard Cite

show abstract

“…The results from numerous in vivo studies with metabolic inhibitors (14) and from in vitro enzymic analyses (9)(10)(11)14) have established glutamine-linked asparagine synthesis in higher plants, although the pathway providing the carbon skeleton to asparagine remains open (I 1). In most legumes so far considered, asparagine is the principal assimilation product of symbiotic nitrogen fixation (7,8,10,16).…”

mentioning

confidence: 99%

“…In most legumes so far considered, asparagine is the principal assimilation product of symbiotic nitrogen fixation (7,8,10,16). Scott et al (10) found glutamine-linked asparagine synthetase in the cytosol fraction of lupin nodules and proposed a sequence for asparagine formation from atmospheric nitrogen fixed by nodule bacteroids. Bleeding sap of soybean nodules also contains high concentrations of asparagine (16), indicating the presence of active asparagine synthesizing and transporting systems in soybean nodules.…”

mentioning

confidence: 99%

Asparagine Formation in Soybean Nodules

Fujihara¹,

Yamaguchi²

1980

Plant Physiol.

View full text Add to dashboard Cite

ABSTRACT'5NH4+ and I'5N1(amide)-glutamine externally supplied to detached nodules from soybean plants (cv. Tamanishiki) were incorporated within nodule tissues by vacuum infiltration and metabolized to various nitrogen compounds during 60 minutes of incubation time. In the case of 15NH4+-feeding, the 15N abundance ratio was highest in the amide nitrogen of glutamine, followed by glutamate and the amide nitrogen of asparagine. In '5N content (micrograms excess 15N), the amide nitrogen of asparagine was most highly enriched after 60 minutes. 1"NH4+ was also appreciably assimilated into alanine.When 115NI(amide)-glutamine was fed to detached nodules, 15N was almost entirely in the amide nitrogen of asparagine. The result indicates the presence of active glutamine-linked asparagine synthesizing systems in soybean root nodules.The results from numerous in vivo studies with metabolic inhibitors (14) and from in vitro enzymic analyses (9-11, 14) have established glutamine-linked asparagine synthesis in higher plants, although the pathway providing the carbon skeleton to asparagine remains open (I 1). In most legumes so far considered, asparagine is the principal assimilation product of symbiotic nitrogen fixation (7,8,10,16). Scott et al. (10) found glutamine-linked asparagine synthetase in the cytosol fraction of lupin nodules and proposed a sequence for asparagine formation from atmospheric nitrogen fixed by nodule bacteroids. Bleeding sap of soybean nodules also contains high concentrations of asparagine (16), indicating the presence of active asparagine synthesizing and transporting systems in soybean nodules. Extensive attempts by Streeter (12) to demonstrate asparagine biosynthesis from various radioactive precursors have, however, failed, possibly because of the presence of a very active asparaginase in soybean nodules (12). We observed that soybean nodule bacteroids had a high ability to transform asparagine to aspartate (unpublished data). The existence of such an active asparagine-decomposing system in nodules makes in vitro enzymic or tracer studies on asparagine synthesis difficult. In the present in vivo tracer study, asparagine formation in soybean nodules was examined especially in regard to the source of the amide nitrogen of asparagine.The data from isotopic analysis in this communication clearly Ar, and incubated at 30 C for I h. Reaction was terminated by the addition of 2 ml cold 0.4 N HC104 to each vial. The contents of the vials were immediately transferred into a cold mortar, ground with a pestle, washed into a centrifuge tube, and centrifuged at 15,000g for 30 min at 0 C. The acid precipitate was washed in cold 0.2 N HC104, centrifuged again, and the combined supernatant fluid was neutralized to pH 6.5. The cleared solution was used for the fractionation of each nitrogen constituent.Separation of Nitrogen Compounds and Conversion to Ammonia. The supernatant solution was shaken vigorously with I o (w/ v) of Permutit for several min and centrifuged at l0,OOOg for 10 min. The ammonia free supernata...

show abstract

“…In addition, unlike some plants [12], yeast does not accumulate endogenous asparagine ; this amino acid concentration is indeed one of the lowest.…”

Section: Conclusion and Discussionmentioning

confidence: 88%

Two Asparagine Synthetases in Saccharomyces cerevisiae

Ramos

Wiame

1980

Eur J Biochem

View full text Add to dashboard Cite

In Saccharomyces cerevisiaeL‐asparagine auxotrophy, resulting from a lack of L‐asparagine synthesis, needs simultaneous defects in two genes. This unusual situation is shown to result from the occurrence of two L‐asparagine synthetases. The meaning of this duplication remains obscure. The properties of the two enzymes are remarkably similar: both have a molecular weight of 150000 and they exhibit a slight repression and a similar inhibition by asparagine. Neither one is located in mitochondria and both are probably cytosolic. Their identification so far lies only in their behaviour on ion‐exchange chromatography and in the encoding genes.

show abstract

Ammonia assimilation in lupin nodules

Cited by 125 publications

References 13 publications

Nitrogen Nutrition and Xylem Transport of Nitrogen in Ureide-producing Grain Legumes

Nitrogen Nutrition and Xylem Transport of Nitrogen in Ureide-producing Grain Legumes

Asparagine Formation in Soybean Nodules

Two Asparagine Synthetases in Saccharomyces cerevisiae

Contact Info

Product

Resources

About