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771.
B. Jongsareejit R. N. Z. A. Rahman S. Fujiwara T. Imanaka 《Molecular & general genetics : MGG》1997,254(6):635-642
The gltA gene encoding a glutamate synthase (GOGAT) from the hyperthermophilic archaeon Pyrococcus sp. KOD1 was cloned as a 6.6 kb HindIII-BamHI fragment. Sequence analysis indicates that gltA encodes a 481- amino acid protein (53 269 Da). The deduced amino acid sequence of KOD1-GltA includes conserved regions that
are found in the small subunits of bacterial GOGAT: two cysteine clusters, an adenylate-binding consensus sequence and an
FAD-binding consensus sequence. However, no sequences homologous to the large subunit of bacterial GOGAT were found in the
upstream or downstream regions. In order to examine whether GltA alone can act as a functional GOGAT, GltA was overexpressed
in Escherichia coli BL21 (DE3) cells using an expression plasmid. GltA was purified to homogeneity and shown to be functional as a homotetramer
of approximately 205 kDa, which is equivalent to the molecular weight of the native GOGAT from KOD1, thus indicating that
KOD1-GOGAT is the smallest known active GOGAT. GltA is capable of both glutamine-dependent and ammonia-dependent synthesis
of glutamate. Synthesis of glutamate by KOD1-GltA required NADPH, indicating that this enzyme is an NADPH-GOGAT (EC 1.4.1.13).
The optimum pH for both activities was 6.5. However, GltA exhibited different optimum temperatures for activity depending
on the reaction assayed (glutamine-dependent reaction, 80° C; ammonia-dependent reaction, 90° C).
Received: 30 October 1996 / Accepted: 13 January 1997 相似文献
772.
A number of Tn5 mutants were isolated which were unable to fix nitrogen and showed enhanced ammonium repression of the nitrate/nitrite assimilation
genes. They also had reduced nitrate reductase activity under fully inducing conditions. Insertions were localized within
the nifB gene, and inability to fix nitrogen was shown to be due to disruption of the nifB gene. However, enhanced ammonium repression proved to be the result of constitutive expression of the downstream nifO gene from an `out' promoter present in Tn5. Our results suggest that molybdenum metabolism might function as a regulatory factor that acts through the nitrate reductase.
Received: 4 December 1996 / Accepted: 27 March 1997 相似文献
773.
The molecular characteristics of markers in the chromosome region surrounding the supernodulation gene (nts-1) of soybean (Glycine max L. Merr.) were investigated in 187 F2 plants from a cross of G. max cv. Bragg (nts) and G. soja PI468.397 (wild-type nodulation). RFLP marker pUTG-132a, linked tightly (0.7±0.5 cM) to nts-1, was converted to a PCR marker. The polymorphism resides within a 1.72 kb PstI fragment and consists of an 832 bp insertion in G. max relative to the wild progenitor G. soja. The insertion is flanked by a 35 bp direct duplication that was found only once in G. soja. Data suggest that the pUTG-132a sequence exists only once in the genome, which is compatible with the recessive nature of
nts-1. Accordingly, pUTG-132a is a valuable marker for map-based cloning. Another RFLP marker, pA-381, was mapped 4.8 cM distal
to nts-1. Marker order, established by Maximum Likelihood Analysis, placed nts-1 between pUTG-132a and pA-381. To generate additional molecular markers, a segregating F2 population was analysed using bulked segregant analysis (BSA) and single oligonucleotide primer-based PCR (DNA amplification
fingerprinting; DAF). PCR marker pcr5-4L was mapped to soybean linkage group H and sequenced. The data revealed (i) recombination
events and marker order in the nts-1 region; (ii) the molecular nature and cause of polymorphisms in linked molecular markers; (iii) a low density of polymorphisms
around nts-1, and (iv) diploidy of the distal region of linkage group H of soybean.
Received: 18 January 1996 / Accepted: 9 October 1996 相似文献
774.
Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? 总被引:7,自引:0,他引:7
S. Zanetti U. A. Hartwig C. van Kessel A. Lüscher T. Hebeisen M. Frehner B. U. Fischer G. R. Hendrey H. Blum J. Nösberger 《Oecologia》1997,112(1):17-25
The extent of the response of plant growth to atmospheric CO2 enrichment depends on the availability of resources other than CO2. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO2 response of plants. The effect of elevated CO2 (60 Pa) partial pressure (pCO2) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems
were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO2, the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual
N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N-limited biomass production)
under elevated pCO2, the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO2 than under ambient pCO2 in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO2 was evoked indirectly by a reduction of plant-available N. For L. perenne grown in association with T. repens and exposed to elevated pCO2, there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained
by an increased apparent transfer of N from the associated N2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under
elevated pCO2. All the additional N yielded was due to symbiotically fixed N. Through the presence of an N2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation
under elevated pCO2.
Received: 11 November 1996 / Accepted: 20 May 1997 相似文献
775.
Christopher Neill Marisa C. Piccolo Carlos C. Cerri Paul A. Steudler Jerry M. Melillo Marciano Brito 《Oecologia》1997,110(2):243-252
Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO3 ?-N and total inorganic N concentrations than pasture soils, but substantial NO3 ?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing. 相似文献
776.
The objective of the present study was to assess whether, in barley, nitrogen supply limits the rate of leaf elongation through
a reduction in (relative) cell elongation rate and whether this is attributable to a reduced turgor, a reduced availability
of osmolytes or, by implication, changed wall properties. Plants were grown on full-strength Hoagland solution (“Hoagland”-plants),
or on N-deficient Hoagland solution while receiving N at a relative addition rate of 16 or 8% N · plant-N−1 · d−1 (“16%-” and “8%-plants”). Hoagland-plants were demand-limited, whereas 16%- and 8%-plants were supply-limited in N. Third
leaves were analysed for leaf elongation rate and final epidermal cell length, and, within the basal growing region, for the
spatial distribution of relative segmental elongation rates (RSER, pin-pricking method), epidermal cell turgor (cell-pressure
probe), osmotic pressure (OP, picolitre osmometry) and water potential (Ψ). During the development of the third leaf, plants
grew at relative growth rates (relative increase in fresh weight ) of 18.2, 15.6 and 8.1% · d−1 (Hoagland-, 16%- and 8%-plants, respectively). Final leaf length and leaf elongation rate were highest in Hoagland plants
(ca. 34.1 cm and 2.33–2.60 mm · h−1, respectively), intermediate in 16%- plants (31.0 cm and 1.89–1.96 mm · h−1) and lowest in 8%-plants (29.4 cm and 1.41–1.58 mm · h−1). These differences were accompanied by only small differences in final cell length, but large differences in cell-flux rates
(146, 187 and 201 cells · cell-file−1 · d−1 in 8%-, 16%- and Hoagland-plants, respectively). The length of the growth zone (32–38 mm) was not much affected by N-levels
(and nutrient technique). A decrease in RSER in the growth zone distal to 10 mm produced the significant effect of N-levels
on leaf elongation rate. In all treatments, cell turgor was almost constant throughout the growing region, as were cell OP
and Ψ in 16%- and 8%-plants. In Hoagland-plants, however, cell OP increased by ca. 0.1 MPa within the zone of highest elongation
rates and, as a consequence, cell Ψ decreased simultaneously by 0.1 MPa. Cell Ψ increased considerably where elongation ceased.
Within the zone where differences in RSERs were highest between treatments (10–34 mm from base) average turgor was lowest,
OP highest and Ψ most negative in Hoagland- compared to 8%- and 16%-plants (P < 0.001), but not significantly different between 8%- and 16%-plants.
Received: 9 January 1997 / Accepted: 6 March 1997 相似文献
777.
1. Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain.
2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover.
3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg–1 , values typical of nutrient-replete stands of C4 plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level.
4. The vegetation accumulated 377, 51 and 1136kgha–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km2 of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low-water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain. 相似文献
2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover.
3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg
4. The vegetation accumulated 377, 51 and 1136kgha
778.
CO_2倍增对紫花苜蓿碳、氮同化与分配的影响 总被引:6,自引:0,他引:6
本文简要报道CO2倍增下紫花苜蓿碳素积累、氮素的吸收与生物固氮及其产物在地上、地下部分配的特性1 材料和方法在北京香山中国科学院植物研究所植物园试验区,建立了两个高2.8m、直径2.2m的钢管支撑的圆柱状开顶式薄膜培养室,由底部向室内连续通气,保证培养室内每分钟换气3次。对照室通入正常空气(350×10-6,1×CO2),处理室通入CO2加倍的空气(700×10-6,2×CO2)。室内CO2浓度经红外CO2分析仪(QGD-07型,北京分析仪器厂产品)测定,24h内均可保持在350×10-6及70… 相似文献
779.
Net primary production and light use efficiency in a mixed coniferous forest in Sweden 总被引:5,自引:0,他引:5
FREDERIK LAGERGREN LARS EKLUNDH ACHIM GRELLE MATTIAS LUNDBLAD MEELIS MÖLDER HARRY LANKREIJER & ANDERS LINDROTH 《Plant, cell & environment》2005,28(3):412-423
Simple light use efficiency (ɛ) models of net primary production (NPP) have recently been given great attention (NPP = ɛ × absorbed photosynthetically active radiation). The underlying relationships have, however, not been much studied on a time step less than a month. In this study daily NPP was estimated as the sum of net ecosystem exchange (NEE) and heterotrophic respiration (Rh) of a mixed pine and spruce forest in Sweden. NEE was measured by eddy correlation technique and Rh was estimated from measurements of forest floor respiration (Rf) and the root share of Rf. The total yearly NPP was on average 810 g C m−2 year−1 for 3 years and yearly ɛ was between 0.58 and 0.71 g C MJ−1, which is high in comparison with other studies. There was a seasonal trend in ɛ with a relatively constant level of approximately 0.90 g C MJ−1 from April to September Daily NPP did not increase for daily intercepted radiation above 6 MJ m−2 d−1, indicating that between-years variation in NPP is not directly dependent on total Qi. The light was most efficiently used at an average daytime temperature of around 15 °C. At daytime vapour pressure deficit above 1400 Pa ɛ was reduced by approximately 50%. 相似文献
780.
Luca Bragazza Juul Limpens† Renato Gerdol Philippe Grosvernier‡ Michal Hájek§ Tomá Hájek¶ Petra Hajkova§ Ina Hansen Paola Iacumin Lado Kutnar†† Håkan Rydin‡‡ Teemu Tahvanainen§§ 《Global Change Biology》2005,11(1):106-114
Alteration of the global nitrogen (N) cycle because of human‐enhanced N fixation is a major concern particularly for those ecosystems that are nutrient poor by nature. Because Sphagnum‐dominated mires are exclusively fed by wet and dry atmospheric deposition, they are assumed to be very sensitive to increased atmospheric N input. We assessed the consequences of increased atmospheric N deposition on total N concentration, N retention ability, and δ15N isotopic signature of Sphagnum plants collected in 16 ombrotrophic mires across 11 European countries. The mires spanned a gradient of atmospheric N deposition from about 0.1 up to about 2 g m?2 yr?1. Mean N concentration in Sphagnum capitula was about 6 mg g?1 in less polluted mires and about 13 mg g?1 in highly N‐polluted mires. The relative difference in N concentration between capitulum and stem decreased with increasing atmospheric N deposition, suggesting a possible metabolic mechanism that reduces excessive N accumulation in the capitulum. Sphagnum plants showed lower rates of N absorption under increasing atmospheric N deposition, indicating N saturation in Sphagnum tissues. The latter probably is related to a shift from N‐limited conditions to limitation by other nutrients. The capacity of the Sphagnum layer to filter atmospheric N deposition decreased exponentially along the depositional gradient resulting in enrichment of the mire pore water with inorganic N forms (i.e., NO3?+NH4+). Sphagnum plants had δ15N signatures ranging from about ?8‰ to about ?3‰. The isotopic signatures were rather related to the ratio of reduced to oxidized N forms in atmospheric deposition than to total amount of atmospheric N deposition, indicating that δ15N signature of Sphagnum plants can be used as an integrated measure of δ15N signature of atmospheric precipitation. Indeed, mires located in areas characterized by greater emissions of NH3 (i.e., mainly affected by agricultural activities) had Sphagnum plants with a lower δ15N signature compared with mires located in areas dominated by NOx emissions (i.e., mainly affected by industrial activities). 相似文献