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PubMed1992

Substrate specificity of Saccharomyces cerevisiae myristoyl-CoA: protein N-myristoyltransferase. Analysis of fatty acid analogs containing carbonyl groups, nitrogen heteroatoms, and nitrogen heterocycles in an in vitro enzyme assay and subsequent identification of inhibitors of human immunodeficiency virus I replication.

Covalent attachment of myristic acid (C14:0) to the amino-terminal glycine residue of a variety of eukaryotic cellular and viral proteins can have a profound influence on their biological properties. The enzyme that catalyzes this modification, myristoyl-CoA-protein N-myristoyltransferase (NMT), has been identified as a potential target for antiviral and antifungal therapy. Its reaction mechanism is ordered Bi Bi with myristoyl-CoA binding occurring before binding of peptide and CoA release preceding release of myristoylpeptide. Perturbations in the binding of its acyl-CoA substrate would therefore be expected to have an important influence on catalysis. We have synthesized 56 analogs of myristic acid (C14:0) to further characterize the acyl-CoA binding site of Saccharomyces cerevisiae NMT. The activity of fatty acid analogs was assessed using a coupled in vitro assay system that employed the reportedly nonspecific Pseudomonas acyl-CoA synthetase, purified S. cerevisiae NMT, and octapeptide substrates derived from residues 2-9 of the catalytic subunit of cyclic AMP-dependent protein kinase and the Pr55gag polyprotein precursor of human immunodeficiency virus I (HIV-I). Analysis of ketocarbonyl-, ester-, and amide-containing myristic acid analogs (the latter in two isomeric arrangements, the acylamino acid (-CO-NH-) and the amide (-NH-CO)) indicated that the enzyme's binding site is able to accommodate a dipolar protrusion from C4 through C13. This includes the region of the acyl chain occurring near C5-C6 (numbered from carboxyl) that appears to be bound in a bent conformation of 140-150 degrees. The activities of NMT's acyl-CoA substrates decrease with increasing polarity. This relationship was particularly apparent from an analysis of a series of analogs in which the hydrocarbon chain was terminated by (i) an azido group or (ii) one of three nitrogen heterocycles (imidazole, triazole, and tetrazole) alkylated at either nitrogen or carbon. This inverse relationship between polarity and activity was confirmed after comparison of the activities of the closely related ester- or amide-containing tetradecanoyl-CoA derivatives. Members from all of the analog series were surveyed to determine whether they could inhibit replication of human immunodeficiency virus I (HIV-I), a retrovirus that depends upon N-myristoylation of its Pr55gag for propagation. 12-Azidododecanoic acid was the most active analog tested, producing a 60-90% inhibition of viral production in both acutely and chronically infected T-lymphocyte cell lines at a concentration of 10-50 microM without associated cellular toxicity.

Acyltransferases↗
PubMed2005

[Effects of simulated nitrogen deposition on weeds growth and nitrogen uptake].

In this paper, a greenhouse experiment was conducted to study the responses of different functional groups weeds to simulated nitrogen deposition (4.0 g N.m(-2).yr(-1)). Native weed species Poa annua, Lolium perenne, Avena fatua, Medicago lupulina, Trifolium repens, Plantago virginica, Veronica didyma, Echinochloa crusgalli var. mitis, Eleusine indica and Amaranthus spinosus in orchard ecosystem were used test materials, and their above-and underground biomass and nitrogen uptake were measured. The results showed that under simulated N deposition, the total biomass, shoot biomass and root biomass of all weed species tended increase, while the total biomass was differed for different functional groups of weeds. The biomass of C4 grass, legumes and C3 grass was significantly increased under N deposition, while that of C3 and C4 forbs was not significantly impacted. The root/shoot biomass ratio of Avena fatua and Plantago virginica was enhanced by N deposition, but that of Poa annu, Lolium perenne, Medicago lupulina, Trifolium repens and Amarathus spinosus was not impacted significantly. N deposition had no significant effect on plant N concentration, but significantly enhanced the N uptake of all test weed species except Amarathus spinosus, Poa annua and Veronica didyma. was suggested that the further increase of N deposition might speed up the changes of the community structure weed species due to their different responses to N deposition.

Avena↗
PubMed2005

Cereal area and nitrogen use efficiency are drivers of future nitrogen fertilizer consumption.

At a global scale, cereal yields and fertilizer N consumption have increased in a near-linear fashion during the past 40 years and are highly correlated with one another. However, large differences exist in historical trends of N fertilizer usage and nitrogen use efficiency (NUE) among regions, countries, and crops. The reasons for these differences must be understood to estimate future N fertilizer requirements. Global nitrogen needs will depend on: (i) changes in cropped cereal area and the associated yield increases required to meet increasing cereal demand from population and income growth, and (ii) changes in NUE at the farm level. Our analysis indicates that the anticipated 38% increase in global cereal demand by 2025 can be met by a 30% increase in N use on cereals, provided that the steady decline in cereal harvest area is halted and the yield response to applied N can be increased by 20%. If losses of cereal cropping area continue at the rate of the past 20 years (-0.33% per year) and NUE cannot be increased substantially, a 60% increase in global N use on cereals would be required to meet cereal demand. Interventions to increase NUE and reduce N losses to the environment must be accomplished at the farm- or field-scale through a combination of improved technologies and carefully crafted local policies that contribute to the adoption of improved N management; uniform regional or national directives are unlikey to be effective at both sustaining yield increases and improving NUE. Examples from several countries show that increases in NUE at rates of 1% per year or more can be achieved if adequate investments are made in research and extension. Failure to arrest the decrease in cereal crop area and to improve NUE in the world's most important agricultural systems will likely cause severe damage to environmental services at local, regional, and global scales due to a large increase in reactive N load in the environment.

Crops, Agricultural↗
PubMed2005

Global assessment of nitrogen fertilizer: the SCOPE/IGBP nitrogen fertilizer rapid assessment project.

Nitrogen (N) availability is a key role in food and fiber production. Providing plant-available N through synthetic fertilizer in the 20th and early 21st century has been a major contributor to the increased production required to feed and clothe the growing human population. To continue to meet the global demands and to minimize environmental problems, significant improvements are needed in the efficiency with which fertilizer N is utilized within production systems. There are still major uncertainties regarding the fate of fertilizer N added to agricultural soils and the potential for reducing losses to the environment. Enhancing the technical and economic efficiency of fertilizer N is seen to promote a favorable situation for both agricultural production and the environment, and this has provided much of the impetus for a new N fertilizer project. To address this important issue, a rapid assessment project on N fertilizer (NFRAP) was conducted by SCOPE (the Scientific Committee on Problems of the Environment) during late 2003 and early 2004. This was the first formal project of the International Nitrogen Initiative (INI). As part of this assessment, a successful international workshop was held in Kampala, Uganda on 12 -16 January, 2004. This workshop brought together scientists from around the world to assess the fate of synthetic fertilizer N in the context of overall N inputs to agricultural systems, with a view to enhancing the efficiency of N use and reducing negative impacts on the environment. Regionalization of the assessment highlighted the problems of too little N for crop production to meet the nutrient requirements of sub-Saharan Africa and the oversupply of N in the major rice-growing areas of China. The results of the assessment are presented in a book (SCOPE 65) which is now available to provide a basis for further discussions on N fertilizer.

Crops, Agricultural↗
PubMed2006

[Effects of land use type on soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen contents in Karst region of South China].

A total of 721 surface (0-20 cm) soil samples were collected from the paddy field, upland, and woodland in the Karst region of Dacai, Huanjiang County, Guangxi Province, and the contents of their organic carbon (Oc ), total nitrogen (TN), microbial biomass carbon (Bc) , and microbial biomass nitrogen (BN) were determined. The results showed that the Oc and BN contents and soil pH value showed the trend of paddy field = woodland > upland, while TN and Bc contents had the trend of woodland > paddy field > upland. There was a significant positive correlation between Bc and Oc, and between B5 and TN. Soil microbial biomass C and N had rapid responses to the changes of land use type, which could be used as the sensitive biological indicators in evaluating soil quality and fertility in Karst region.

Agriculture↗
PubMedDate not supplied

Novel, delta-opioid receptor-selective peptide antagonists: demonstration of a possible opioid interaction in the absence of a protonated nitrogen and attempts to locate the protonated nitrogen site.

We have recently (Rónai et al., 1992) introduced a family of novel delta-opioid receptor-selective peptide antagonists, based on the Tyr-Pro-Gly-Phe-Leu-Thr structure, where the nitrogen accepts substituents that make protonation possible (e.g. diallyl) as well as substituents (e.g. t-Boc) where protonation cannot occur. In this paper, we present the details of a design strategy where the structurally closely related biologically active and inactive compounds are suggestive of conformational requirements of action. Furthermore, since even those derivatives of the antagonist peptides where the N-terminus was free were either devoid of opioid agonist activity or were extremely weak agonists, it is suggested that these antagonists do not interact with the conventional "opioid nitrogen site". To find this "conventional" site, a number of N-substituted (phenylglycyl-, alpha-Boc-lysyl-, alpha-Phe-beta-alanyl-) derivatives of Tyr-Pro-Gly-Phe-Leu-Thr hexapeptide were synthesized and their biological activities were determined in the mouse vas deferens bioassay.

Amino Acid Sequence↗
PubMed2026

Wheat breeding during and after the "green revolution" contributed to the reduced use of elite nitrogen metabolism alleles linked to nitrogen use efficiency.

The wheat "Green Revolution (GR)" that occurred from the 1960s to the 1970s significantly enhanced the harvest index and resistance to lodging, thereby increasing grain production, but at the cost of reduced nitrogen (N) use efficiency (NUE) in wheat. The NUE of wheat is mainly regulated by N metabolism genes (NMGs). However, the evolutionary process of NMGs during GR and post-GR wheat breeding, as well as which of them affect NUE, remains unclear. Here, we collected 265 wheat varieties that were released before, during, and after the GR and investigated grain yield per plant and 24 other traits under different N supply conditions. Next, we identified the genotypes of these wheat varieties using a 100 K targeted sequencing array. Then, we systematically analyzed the signatures in the genomes of GR and post-GR released varieties compared with pre-GR released varieties through population divergence (Fst) and nucleotide diversity (π) ratio analyses, and found that 41 NMGs were located within the selective sweep regions during the GR and post-GR breeding. We further identified 118 quantitative trait loci (QTLs) involved in regulating NUE through genome-wide association studies (GWAS). Four NMGs-NRT1 AND PEPTIDE TRANSPORTER FAMILY 2.7-D (TaNPF2.7-D), TaNPF2.3-D, TaNPF2.7 L-D, and QUASIMODO2-B (TaQUA2-B)-were located within overlapping regions of selective sweeps and NUE-related QTLs. Notably, the elite haplotypes of these genes for NUE are less utilized in GR and post-GR released cultivars. Furthermore, we found that TaNPF2.7-D positively regulates nitrate exudation as well as the wheat development. Collectively, our findings uncover an important reason for the reduction in NUE in modern cultivars and provide a valuable resource for improving wheat NUE.

Triticum↗
PubMed1975

A comparison of nitrogen mustard, vincristine, procarbazine, and prednisone (MOPP) vs. nitrogen mustard in advanced Hodgkin's disease.

A randomized study of patients with advanced Hodgkin's disease was designed to determine whether the improved therapeutic effectiveness of combination chemotherapy was due to the use of a combination of drugs or might be achieved with a single agent if given as intensively and for as long a period. A combination of nitrogen mustard, vincristine, procarbazine, and prednisone (MOPP) was compared with nitrogen mustard (HN2) alone. Treatment with both regimens was given to tolerance on cylic basis and was continued for six cycles of treatment. Sixty-one evaluable patients were treated with MOPP and 47 with HN2. The complete remission rate of 47.5% with MOPP was significantly better than the 12.8% with HN2 (p less than .05). Complete remission lasted a median of 15 months after MOPP and 12 months after HN2. The survival of patients initially treated with MOPP was significantly better than that of those initially treated with HN2.

Drug Evaluation↗
PubMed1989

Proposal of a new formula to calculate total urinary nitrogen from urea urinary nitrogen.

Urea urinary nitrogen (UUN) and total urinary nitrogen (TUN) were determined in 15 patients to study their relationship mainly in highly catabolic patients. The subjects were: 7 multiple trauma, 3 autologous bone-marrow transplant, 1 tetanus, 4 postcholecystectomy patients; 180 determination were made, 111 of which in highly catabolic phase (TUN > 15 g/day). TUN and UUN are well correlated (r = 0.9742; p < 0.001) in the range 3 to 52 g/ day of TUN. Urea represents the 83.2 +/- 9.4% (M +/- SD). A double-linear formula to calculate TUN from UUN is proposed (for UUN 15 g/ day: TUN = UUN x 1.17 + 0.7; for UUN > 15 g/ day: TUN = UUN + 4). The least square procedure was used to compare the differences between measured and calculated TUN, and the results obtained with the proposed double-linear formula were compared with that obtained employing pre-existing formulas (Lee's and Mackenzie's). Considering all ranges of values studied (3-52 g of TUN) the results obtained were significantly different (p < 0.005); dividing the levels of TUN in 15 g; 16-29 g and 30 g, the results were always better, but the statistical significancy was not always reached.

Journal Article↗
PubMed1988

Effects of nitrogen dioxide on leaf chlorophyll and nitrogen content of soybean.

One-month-old soybean (Glycine max [L.] Merrill), cultivar 'Williams', plants were exposed to nitrogen dioxide (0.1, 0.2, 0.3 and 0.5 ppm) and carbon filtered air (control), 7 h per day, for 5 days, under a controlled environment. Leaf chlorophyll content (Ch a, Ch b, and total Ch content) and foliar nitrogen content (%N) were determined before and after the exposure. The influence of NO(2) treatments up to 0.3 ppm on leaf chlorophyll content was negligible although a stimulatory effect was evident in Ch a and total Ch content with 0.2 ppm NO(2). Marked decline in Ch content was observed with 0.5 ppm treatment; the reductions in Ch a and total Ch were 45% and 47%, respectively. Foliar-N contents of plants treated with 0.2 and 0.3 ppm NO(2) were higher than the control; plants exposed to 0.5 ppm NO(2) showed a 41% reduction in foliar-N compared to pre-exposure values.

Journal Article↗
PubMed2000

Comparison of drought tolerance in nitrogen-fixing and inorganic nitrogen-grown common beans.

In this work, we evaluated how the use of alternative N sources affects drought-stress tolerance in common beans. To this end, plants were cultivated employing either N(2) fixation or two levels of inorganic nitrogen: 1 mM NH(4)NO(3) (limiting) or 10 mM NH(4)NO(3) (sufficient). Drought was imposed by withholding watering at 30 days after planting (DAP) - coinciding with flowering. At 20 DAP, growth and N content were significantly higher in NH(4)NO(3)-sufficient plants than in N(2)-fixing and NH(4)NO(3)-limited beans. At later times, only N(2)-fixing and NH(4)NO(3)-sufficient plants continued assimilating N and growing, with the NH(4)NO(3)-sufficient plants being consistently bigger. After 10 days of stress (40 DAP), desiccation was evident, but only NH(4)NO(3)-sufficient plants suffered drought-induced senescence. After 20 days of stress (50 DAP), N content increased in NH(4)NO(3)-sufficient but not in N(2)-fixing beans, despite the latter's lesser state of wilt. Pod dry weight dropped 43% in NH(4)NO(3)-sufficient beans with respect to well-watered plants, while remaining constant in N(2)-fixing beans. Under drought conditions, the number of pods limited pod yield regardless of the nitrogen source used; nevertheless, the translocation of soluble matter to pods continued in both NH(4)NO(3)-sufficient and N(2)-fixing beans. We conclude that common beans grown under conditions of N(2) fixation were more drought tolerant than those provided with sufficient levels of NH(4)NO(3). The most stress-sensitive traits in these plants were the incorporation of N into their shoots and the number of pods remaining on them.

Journal Article↗
PubMed1999

Total skin electron beam therapy with or without adjuvant topical nitrogen mustard or nitrogen mustard alone as initial treatment of T2 and T3 mycosis fungoides.

PURPOSE: To compare the efficacy of total skin electron beam therapy (TSEBT) with or without adjuvant topical nitrogen mustard (+/- HN2) with topical nitrogen mustard (HN2) alone as initial management of T2 and T3 mycosis fungoides (MF). METHODS AND MATERIALS: A retrospective analysis of 148 patients presenting to Stanford from January, 1970 through January, 1995 within 4 months of pathologic diagnosis of MF. Fifty-five patients with T2 and 27 with T3 disease received TSEBT +/- HN2. Fifty-four patients with T2 and 12 with T3 disease received HN2 alone. Boosts with radiotherapy were usually administered to cutaneous tumors of patients with T3 disease. RESULTS: TSEBT +/- HN2 yielded significantly higher complete response (CR) rates than did HN2 alone in patients with T2 and T3 disease (76% vs 39%, p = 0.03 for T2, and 44% vs 8%, p < 0.05 for T3, respectively). In T2 disease, treatment with adjuvant HN2 was associated with a longer freedom from relapse following TSEBT when compared to observation following a CR to TSEBT (p = 0.068). However, no significant differences in survival were observed for different management programs for T2 or T3 disease. In T2 disease, both TSEBT and HN2 were as effective as salvage therapy as when utilized as initial therapy. However, salvage therapy in T3 disease was rarely effective. Limited tumor involvement in T3 disease did not correlate with improved survival compared to more generalized tumorous disease. MF contributed to 27% and 68% of deaths in patients with T2 and T3 disease, respectively. CONCLUSION: Because of high response rates, management of significantly symptomatic or extensive T2 MF should include TSEBT, and adjuvant HN2 should be administered after a CR to TSEBT. Patients with T2 disease who fail TSEBT or HN2 can be salvaged with the other modality. TSEBT is also an effective treatment for T3 disease. The small subset of patients with limited T3 disease may also be treated with HN2 and local radiotherapy to the tumors. Further investigations are necessary to improve the overall outcome for T3 mycosis fungoides.

Administration, Topical↗
PubMed2002

Coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) and (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2): the effect of alkylating the nitrogen bridge on ligand bridging versus chelating behavior.

The coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(R)P(C(6)H(5))(2) [R = H (dppa); R = CH(3) (dppma)] has been investigated by (31)P NMR and electrospray mass spectrometry (ESMS). Species observed by (31)P NMR include Ag(2)(mu-dppa)(2+), Ag(2)(mu-dppa)(2)(2+), Ag(2)(mu-dppa)(3)(2+), Ag(2)(mu-dppma)(2+), Ag(2)(mu-dppma)(2)(2+), and Ag(eta(2)-dppma)(2)(+). Species observed by ESMS at low cone voltages were Ag(2)(dppa)(2)(2+), Ag(2)(dppa)(3)(2+), Ag(2)(dppma)(2)(2+), and Ag(dppma)(2)(+). (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2) showed a strong tendency to chelate, while (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) preferred to bridge. Differences in the bridging versus chelating behavior of the ligands are assigned to the Thorpe-Ingold effect, where the methyl group on nitrogen sterically interacts with the phenyl groups on phosphorus. The crystal structure of the three-coordinate dinuclear silver(I) complex (Ag(2)[(C(6)H(5))(2)PN(H)P(C(6)H(5))(2)](3))(BF(4))(2) has been determined. Bond distances include Ag-Ag = 2.812(1) A, Ag(1)-P(av) = 2.492(3) A, and Ag(2)-P(av) = 2.509(3) A. The compound crystallizes in the monoclinic space group Cc at 294 K, with a = 18.102(4)(o), Z = 4, V = 7261(3) A(3), R = 0.0503, and R(W) = 0.0670.

Journal Article↗
PubMed2001

Laser absorption spectroscopy diagnostics of nitrogen-containing radicals in low-pressure hydrocarbon flames doped with nitrogen oxides.

Absolute concentration profiles of NH2 and HNO have been measured in low-pressure methane/air flat flames doped with small amounts of NO and N2O. Addition of a small amount of nitrogen oxides does not alter significantly the flame speeds, temperature profiles and other parameters of the relatively well-understood methane/air flames. Intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS) are high-sensitivity techniques used to measure absolute concentrations of minor species in flames. In this work ICLAS is used to monitor NH2 and HNO, whereas CRDS is used for temperature measurements using OH spectra in the UV range. The (090)-(000) and (080)-(000) bands of the A2A1-X2B1 electronic transition of NH2 and (100)-(000) and (011)-(000) bands of the A1A"-X1A' transition of HNO are used. Methane flames of different equivalence ratios are used. NH2 and HNO are observed in the flame as well as in the zone surrounding the flame, closer to the walls of the low-pressure chamber where the burner is located. An absorption originating from the species in this zone can affect substantially the results of line-of-sight experiments. A slow flow of nitrogen through the optical window holders was added in order to separate the spectra of HNO originating from the central flame zone. Calculations based on the commonly used GRI-Mech chemical mechanism predict two maxima in the HNO concentration profile in the NO doped flames. The first is located in the vicinity of the burner, and the second is closer to the luminescence flame zone. We were able to observe the first maximum, and its measured location agrees well with prediction. On the other hand, GRI-Mech strongly underpredicts the observed absolute concentration of HNO in this maximum. The measured absolute concentrations of NH2 are in reasonable agreement with the GRI-Mech predictions.

Journal Article↗
PubMedDate not supplied

Quantitation of biomarkers of exposure to nitrogen mustards in urine from rats dosed with nitrogen mustards and from an unexposed human population.

The nitrogen mustards bis(2-chloroethyl)ethylamine (HN1), bis(2-chloroethyl)methylamine (HN2), and tris(2-chloroethyl)amine (HN3) have the potential to be used as chemical terrorism agents because of their extreme vesicant properties. We modified a previously reported method to incorporate automated solid-phase extraction, improve chromatography, and include the urinary metabolite for HN3. The improved method was used to measure levels of the urinary metabolites N-ethyldiethanolamine (EDEA), N-methyldiethanolamine (MDEA), and triethanolamine (TEA) in rats dosed with HN1, HN2, and HN3, respectively, and to establish background levels of EDEA, MDEA, and TEA in human urine samples from a population with no known exposure to nitrogen mustards. Rat dosing experiments confirmed that EDEA, MDEA, and TEA could be detected in urine for at least 48 h after exposure to HN1, HN2, and HN3, respectively. Substantial amounts of EDEA (89 ng/mL), MDEA (170 ng/mL), and TEA (1105 ng/mL) were measured in the urine of rats exposed to 10 mg HN1, HN2, and HN3, respectively, 48 h after exposure. The background concentrations for TEA in the human population ranged from below the limit of detection (LOD 3 ng/mL) to approximately 6500 ng/mL. Neither EDEA (LOD 0.4 ng/mL) nor MDEA (LOD 0.8 ng/mL) was detected above the LOD in the human samples.

Administration, Cutaneous↗
PubMed1987

The Nitrogen Use Efficiency of C(3) and C(4) Plants: I. Leaf Nitrogen, Growth, and Biomass Partitioning in Chenopodium album (L.) and Amaranthus retroflexus (L.).

The effect of applied nitrogen (N) on the growth, leaf expansion rate, biomass partitioning and leaf N levels of Chenopodium album (C(3)) and Amaranthus retroflexus (C(4)) were investigated. At a given applied N level, C. album had 50% greater leaf N per unit area (N(a)) than A. retroflexus. Nitrate accumulated at lower N(a) in A. retroflexus than C. album. A. retroflexus was more productive than C. album at high N, but C. album was more productive at low N. At high applied N, nitrogen use efficiency (NUE), expressed either as net assimilation rate (NAR) per unit N or relative growth rate per unit N, was greater in A. retroflexus than C. album. However, at low applied N, C. album had a greater NUE on both an NAR and growth basis than A. retroflexus. The leaf area partitioning coefficient was similar in the species at high N, but was greater in A. retroflexus than C. album at low N. At low N, greater leaf area partitioning apparently lowered leaf N in A. retroflexus to levels at which necrosis occurred. In C. album by contrast, leaf area partitioning declined to a greater degree with declining N than it did in A. retroflexus, so that leaf N did not decline as much. Consequently, low N C. album plants did not lose leaf area to necrosis and had a greater NAR and NUE at low applied N than A. retroflexus.

Journal Article↗
PubMed1989

Phosphorus-31 and Nitrogen- 14 NMR Studies of the Uptake of Phosphorus and Nitrogen Compounds in the Marine Macroalgae Ulva lactuca.

Cytoplasmic phosphomonoesters and inorganic phosphate, as well as vacuolar inorganic phosphate and polyphosphates, gave rise to the major peaks in (31)P nuclear magnetic resonance (NMR) spectra of the marine macroalgae Enteromorpha sp., Ceramium sp., and Ulva lactuca which were collected from the sea. In contrast, NMR-visible polyphosphates were lacking in Pylaiella sp. and intracellular vacuolar phosphate seemed to act as the main phosphorus store in this organism. In laboratory experiments, polyphosphates decreased in growing U. lactuca which was cultivated in continuous light under phosphate-deficient conditions. In contrast, the same organism cultivated in seawater with added phosphate and ammonium, accumulated phosphate mainly in the form of polyphosphates. When nitrate was provided as the only nitrogen source, accumulation of polyphosphates in the algae decreased with increasing external nitrate concentration. From the chemical shift of the cytoplasmic Pi peak, the cytoplasmic pH of superfused preparations of Ulva was estimated at 7.2. The vacuolar pH, determined from the chemical shifts of the vacuolar Pi and the terminal polyphosphate peaks, was between 5.5 and 6.0. The intracellular nitrate and ammonium levels in U. lactuca were determined by (14)N NMR. Both nitrogen sources were taken up and stored intracellularly; however, the uptake of ammonium was much faster than that of nitrate.

Journal Article↗
PubMed2007

Burkholderia phymatum is a highly effective nitrogen-fixing symbiont of Mimosa spp. and fixes nitrogen ex planta.

* The ability of Burkholderia phymatum STM815 to effectively nodulate Mimosa spp., and to fix nitrogen ex planta, was compared with that of the known Mimosa symbiont Cupriavidus taiwanensis LMG19424. * Both strains were equally effective symbionts of M. pudica, but nodules formed by STM815 had greater nitrogenase activity. STM815 was shown to have a broader host range across the genus Mimosa than LMG19424, nodulating 30 out of 31 species, 21 of these effectively. LMG19424 effectively nodulated only nine species. GFP-marked variants were used to visualise symbiont presence within nodules. * STM815 gave significant acetylene reduction assay (ARA) activity in semisolid JMV medium ex planta, but no ARA activity was detected with LMG19424. 16S rDNA sequences of two isolates originally from Mimosa nodules in Papua New Guinea (NGR114 and NGR195A) identified them as Burkholderia phymatum also, with nodA, nodC and nifH genes of NGR195A identical to those of STM815. * B. phymatum is therefore an effective Mimosa symbiont with a broad host range, and is the first reported beta-rhizobial strain to fix nitrogen in free-living culture.

Bacterial Proteins↗