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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 392 (1998), S. 914-916 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Plant growth in the boreal forest, the largest terrestrial biome, is generally limited by the availability of nitrogen. The presumed cause of this limitation is slow mineralization of soil organic nitrogen,. Here we demonstrate, to our knowledge for the first time, the uptake of organic ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 113 (2001), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In this study, we present a rapid, robust and sensitive method for quantification of plant amino acid uptake using universally (U) (13C, 15N)-labelled amino acids and gas chromatography-mass spectrometry (GC-MS). Amino acids were analysed as their tert-butyldimethylsilyl (tBDMS) derivatives and displayed detection limits in the range 10–100 fmol on column, depending on the amino acid. The technique allows for simultaneous detection and quantification of both unlabelled and isotopically labelled species of amino acids. This makes simple quantification of plant amino acid uptake from an isotopically labelled source possible. The analytical variation was low, concerning total amino acid concentrations (relative standard deviation, rsd, less than 5.3%) as well as enrichment of U-13C, 15N-labelled glycine (Gly), arginine (Arg) and glutamic acid (Glu) (rsd〈2.1%). An application of the GC-MS method was conducted on non-mycorrhizal Pinus sylvestris roots supplied with U-13C, 15N-labelled amino acids. Intact, labelled amino acids were traced in root extracts. This provided conclusive evidence of plant root uptake of intact amino acids. Uptake rates of the three amino acids Gly, Glu and Arg in the range 0.5–37.9 μmol g−1 dry weight h−1 were recorded. These rates are comparable with those recorded in earlier studies of amino acid uptake, using other methods, as well as uptake rates measured for nitrate and ammonium.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 111 (2001), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Research on plant nitrogen (N) uptake and metabolism has more or less exclusively concerned inorganic N, particularly nitrate. Nevertheless, recent as well as older studies indicate that plants may have access to organic N sources. Laboratory studies have shown that ectomycorrhizal and ericoid mycorrhizal plants can degrade polymeric N and absorb the resulting products. Recent studies have also shown that some non-mycorrhizal plants are able to absorb amino acids. Moreover, amino acid transporters have been shown to be present in both plant roots and in mycorrhizal hyphae. Although both mycorrhizal and non-mycorrhizal plants appear to have a capacity for absorbing a range of organic N compounds, is this capacity realized in the field? Several lines of evidence show that plants are outcompeted by microorganisms for organic N sources. Such studies, however, have not addressed the issue of spatial and temporal separation between plants and microorganisms. Moreover, competition studies have not been able to separate uptake by symbiotic and non-symbiotic microorganisms. Qualitative assessment of organic N uptake by plants has been performed with dual-labelled glycine in several studies. These studies arrive at different conclusions: some indicate that plants do not absorb this organic N source when competing with other organisms in soil, while others conclude that significant fractions of amino acid N are absorbed as intact amino acid. These variable results may reflect species differences in the ability to absorb glycine as well as differences in experimental conditions and analytical techniques. Although theoretical calculations indicate that organic N might add significant amounts of N to plant N uptake, direct quantitative assessment of the fraction of plant N derived from uptake by organic N sources is a challenge for future research.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Munksgaard International Publishers
    Physiologia plantarum 119 (2003), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Inhibition of nitrogenase (EC 1.18.6.1) activity by O2 has been suggested to be an early response to disturbance in carbon supply to root nodules in the Frankia-Alnus incana symbiosis. Intact nodulated root systems of plants kept in prolonged darkness of 22 h were used to test responses to O2 and short-term N2 deprivation (1 h in Ar:O2). By using a Frankia lacking uptake hydrogenase it was possible to follow nitrogenase activity over time as H2 evolution in a gas exchange system. Respiration was simultaneously recorded as CO2 evolution. Dark-treated plants had lower initial nitrogenase activity in N2:O2 (68% of controls), which declined further during a 1-h period in the assay system in N2:O2 at 21 and 17% O2, but not at 13% O2. When dark-treated plants were deprived of N2 at 21 and 17% O2 nitrogenase activity declined rapidly to 61 and 74%, respectively, after 20 min, compared with control plants continuously kept in their normal light regime. In contrast, there was no decline in dark-treated plants at 13% O2, and only a smaller and temporary decline in control plants at 21% O2. When dark-treated plants were kept at 21% O2 during 45 min prior to N2 deprivation at 17% O2 the decline was abolished. This supports the idea that the decline in nitrogenase activity observed in N2:O2 at 21% O2 and during N2 deprivation was caused by O2, which affected a sensitive nodule fraction. Nodule contents of the amino acids Gln and Cit decreased during N2 deprivation, suggesting decreased assimilation of NH4+. Contents of ATP and ADP in nodules were not affected by short-term N2 deprivation. ATP/ADP ratios were about 5 indicating a highly aerobic metabolism in the root nodule. We conclude that nitrogenase activity of Alnus plants exposed to prolonged darkness becomes more sensitive to inactivation by O2. It seemed that dark-treated plants could not adjust their nodule metabolism at higher perceived pO2 and during cessation of NH4+ production.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 70 (1987), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine (Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3−, no such increase could be detected in the needles. Detached seedlings placed in NO3− solution showed increasing NR activities with increasing NO3− concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2− (g fresh weight)−1 h−1 to about 400 nmol NO2− (g fresh weight)−1 h−1. This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2− (g fresh weight)−1 h−1. Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx-fumigated seedlings compared to corresponding controls.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Small birch plants (Betula pendula Roth.) were grown at different rates of exponentially increasing nitrogen supply. This resulted in plants with different relative growth rates and different internal nitrogen concentrations. Within a nitrogen treatment, both of these variables remained constant with time.Free amino acids were measured in leaves and roots of the seedlings at two different harvests. At greater nitrogen supply, higher concentrations of total amino acid nitrogen were found in roots and leaves. The ratio of amino acid nitrogen to total nitrogen was low albeit greater at higher nitrogen supply. Higher concentrations of amino acid nitrogen were mainly due to high concentrations of citrulline, glutamine, γ-aminobuitric acid and arginine.Greater leaf concentrations of amino acid nitrogen at higher nitrogen supply may be related lo increased concentrations in the xylem sap and/or may be indicative of small excesses of nitrogen with respect to current nitrogen usage in protein synthesis.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature biotechnology 22 (2004), S. 455-458 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Selectable markers enable transgenic plants or cells to be identified after transformation. They can be divided into positive and negative markers conferring a selective advantage or disadvantage, respectively. We present a marker gene, dao1, encoding D-amino acid oxidase (DAAO, EC 1.4.3.3) that ...
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 110 (1997), S. 487-492 
    ISSN: 1432-1939
    Keywords: Key words Understorey boreal plants  ;   Nitrogen storage  ;  Free amino acids  ;  Soluble and insoluble proteins  ;  Nitrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Storage forms of N were studied in below-ground structures of nine boreal forest understorey plants. The ericaceous shrubs Vacciniumvitis-idaea and V.myrtillus, the fern Gymnocarpium dryopteris, the grass Deschampsia flexuosa, and the herbs Epilobium angustifolium, Maianthemum bifolium, Solidago virgaurea, Geranium sylvaticum and Trientalis europaea were sampled in early summer and late autumn from plots fertilised with a complete mixture of nutrients and from non-fertilised control plots. Concentrations of total nitrogen, insoluble and soluble proteins, free amino acids and nitrate were measured, and changes in absolute and relative concentrations of these N fractions between early summer and late autumn were used to identify the forms in which the plants store N. In all species studied, the concentration of free amino acids increased both between summer and autumn and in response to fertilisation, while the concentration of protein N increased only in response to fertilisation. Thus, free amino acids appear to have a central role in N storage. In all of the species except G. dryopteris, D. flexuosa and S. virgaurea, arginine dominated the pool of free amino acids and thus arginine was the major form of stored N in most species. In D. flexuosa and S. virgurea, however, asparagine and arginine together were the major forms of stored N, while glutamine was the major free amino acid, and N storage form, in G. dryopteris.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 99 (1994), S. 290-296 
    ISSN: 1432-1939
    Keywords: Arginine ; Conifers ; Nitrogen deposition and removal ; δ15N ; Protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The concentrations of arginine, protein and total nitrogen (N) and the abundance of15N were measured in 3-and 4-year-old needles of Scots pine trees fertilized with either 0 (C), 36 (N1) or 73 (N2) kg N ha-1 year-1 annually for 22 years (average doses of N). Remaining green needles and needles that were shed were compared and removal of N from total, protein and arginine pools was calculated. Earlier investigations had shown that high arginine concentrations are found in needles of trees that have an excessive N supply (Näsholm and Ericsson 1990). This study aimed to elucidate the fate of the accumulated arginine during needle senescence. It was speculated that a low removal of arginine during senescence would implicate that the primary function of arginine is in N detoxification and not in N storage. Moreover, litter quality would be altered if needles are shed with high concentrations of arginine and this might affect the turnover of N in forest ecosystems. In remaining green needles, the concentration of total N increased with increasing N supply. Protein N concentrations were higher in fertilized trees, but did not differ between the two N treatments. Arginine N was low in C and N1 trees but high in N2 trees. Senescent needles from C and N1 trees had about equal total N concentrations while in N2 trees this concentration was significantly higher. Protein N in senescent needles did not differ between treatments. Arginine N, however, was less than 0.1 mg g−1 dw in C and N1 trees but was higher than 1.5 mg g−1 dw in N2 trees. Removal of N was highest in N1 trees followed by C trees while N2 trees removed least N from senescing needles. The high concentration of total N in senescent needles from N2 trees was to a great extent explained by a high arginine concentration. The δ15N value of remaining, green needles was higher (less negative) in N2 trees than in C and N1 trees. The same pattern was found for senescent needles. Comparisons of δ15N values between remaining, green and senescent needles within each treatment showed a significant increase in δ15N for all treatments during senescence possibly indicating losses of N as NH3 (g) from needles during senescence. It is concluded that arginine, accumulated in response to high N supply, is retranslocated only to a small extent during needle senescence. The ecological and physiological implications of this finding are discussed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2285
    Keywords: Nitrogen saturation ; Forest decline ; Norway spruce ; Mineral nutrient ratio ; Survey method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This study evaluated the utility of free arginine concentrations as a possible alternative to mineral nutrient concentrations as an indicator of mineral nutrient imbalances in Norway spruce [Picea abies (L.) Karst.]. The concentrations of mineral nutrients and arginine were measured in the needles of spruce trees from two areas in Sweden, one with high (15–30 kg ha–1 year–1) airborne N deposition, and one with lower (1–4 kg ha–1 year–1) deposition. The spruce needles from the area with high deposition in southern Sweden had elevated concentrations of free arginine, especially on peat sites. No increase in concentrations was found in the low deposition area in northern Sweden. The arginine concentrations on different sampling occasions were consistent for each site and for individual trees. Trees on peat sites in the south seemed to suffer from P deficiency in relation to N availability. A tendency for K deficiency in needles from peat sites was also found. Needles from trees on mor plots showed acceptable levels of these nutrient elements. Sites in the northern area showed low N concentrations, but the ratios between the different mineral elements analyzed in this study and N were within ranges normally found. A low P/N ratio correlated to high free arginine concentration. The threshold for elevated arginine concentrations is crossed when P/N ratios drop below 0.07–0.08. A tendency for increased arginine levels when ratios between N and the other mineral elements are low was also found, although it was not as strong as that for the P/N ratio. The results are discussed in relation to mineral nutrient imbalances in spruce stands caused by airborne deposition.
    Type of Medium: Electronic Resource
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