共查询到20条相似文献,搜索用时 31 毫秒
1.
Nanetti L Taffi R Vignini A Moroni C Raffaelli F Bacchetti T Silvestrini M Provinciali L Mazzanti L 《Molecular and cellular biochemistry》2007,303(1-2):19-25
Oxidative stress is probably one of the mechanisms involved in neuronal damage induced by ischemia-reperfusion, and the antioxidant
activity of plasma may be an important factor providing protection from neurological damage caused by stroke-associated oxidative
stress. The aim of this study was to investigate the status of oxidative stress, NO and ONOO− levels in patients with atherothrombotic and lacunar acute ischemic stroke and iNOS, eNOS and nitrotyrosine expression in
the same patients. Plasma ONOO− levels were significantly higher in patients than in controls while NO decreases in patients in respect to controls. Densitometric
analysis of bands indicated that iNOS and N-Tyr protein levels were significantly higher in patients in respect to controls.
This study has highlighted a significant NO decrease in our patients compared with controls and this is most probably due
to the increased expression of inducible NO synthase by the effect of thrombotic attack. In fact, the constitutive NO isoforms,
which produce small amounts of NO, are beneficial, while activation of the inducible isoform of NO, which produces much more
NO, causes injury, being its toxicity greatly enhanced by generation of peroxynitrite. The significant ONOO− increase observed in our patients, compared to controls, is most probably due to reaction of NO with O2·−. These findings suggest that free radical production and oxidative stress in ischemic stroke might have a major role in the
pathogenesis of ischemic brain injury. Peroxynitrite might be the main marker of brain damage and neurological impairment
in acute ischemic stroke. 相似文献
2.
Lactate is potentially a major energy source in brain, particularly following hypoxia/ischemia; however, the regulation of
brain lactate metabolism is not well understood. Lactate dehydrogenase (LDH) isozymes in cytosol from primary cultures of
neurons and astrocytes, and freshly isolated synaptic terminals (synaptosomes) from adult rat brain were separated by electrophoresis,
visualized with an activity-based stain, and quantified. The activity and kinetics of LDH were determined in the same preparations.
In synaptosomes, the forward reaction (pyruvate + NADH + H+ → lactate + NAD+), which had a V
max of 1,163 μmol/min/mg protein was 62% of the rate in astrocyte cytoplasm. In contrast, the reverse reaction (lactate + NAD+ → pyruvate + NADH + H+), which had a V
max of 268 μmol/min/mg protein was 237% of the rate in astrocytes. Although the relative distribution was different, all five
isozymes of LDH were present in synaptosomes and primary cultures of cortical neurons and astrocytes from rat brain. LDH1
was 14.1% of the isozyme in synaptic terminals, but only 2.6% and 2.4% in neurons and astrocytes, respectively. LDH5 was considerably
lower in synaptic terminals than in neurons and astrocytes, representing 20.4%, 37.3% and 34.8% of the isozyme in these preparations,
respectively. The distribution of LDH isozymes in primary cultures of cortical neurons does not directly reflect the kinetics
of LDH and the capacity for lactate oxidation. However, the kinetics of LDH in brain are consistent with the possible release
of lactate by astrocytes and oxidative use of lactate for energy in synaptic terminals.
Special issue dedicated to John P. Blass. 相似文献
3.
Blanco Garcia J Aldinucci C Maiorca SM Palmi M Valoti M Buonocore G Pessina GP 《Neurochemical research》2009,34(5):931-941
The NO donor 3-Morpholinosydnonimine (SIN-1) releases NO in the presence of molecular oxygen. In this study, we evaluated
the effect of SIN-1 on mitochondria of rat cortical synaptosomes. We demonstrated in vitro that the amount of ONOO− generated and H2O2 formation directly correlated with SIN-1 concentration. The mean oxygen consumption by synaptosomal mitochondria was approximately
3.8 nmol of O2 min−1 mg−1 protein, which decreased significantly in the presence of SIN-1 1 mM to 2.5 nmol O2 min−1 mg−1. This decrease was not modified by catalase or Trolox, demonstrating that ONOO− was responsible for the effect. The same concentration of SIN-1 caused a significant decrease of ATP production by synaptosomal
mitochondria and depolarized the mitochondrial membrane. Moreover, ROS production increased progressively and was completely
inhibited by pre-incubation of synaptosomes with Trolox. Finally, phosphatidylserine was externalized and, at the same time,
intrasynaptosomal lactate dehydrogenase decreased confirming both, the external membrane breakdown after the addition of SIN-1
and the damage to the synaptosomes. 相似文献
4.
Abstract: The effects of hypoxia, aglycaemia, and hypoxia-aglycaemia on intrasynaptosomal free Ca2+ concentration ([Ca2+]i) have been investigated in rat brain synaptosomes prepared from animals aged 5, 10, 15, 20, 25, and 60 days. After 60 min of hypoxia there was no significant difference, when compared with controls, in basal [Ca2+]i or [Ca2+]i following depolarisation in all of the ages studied. Following 60 min of aglycaemia there was no significant difference from controls in [Ca2+]i of synaptosomes prepared from pups of ≤20 days, although a significant rise in [Ca2+]i was seen in preparations from animals >20 days old. Sixty minutes of hypoxia-aglycaemia led to a significant rise in [Ca2+]i only in preparations from animals 15–60 days old. With both aglycaemia and hypoxia-aglycaemia a progressive increase in the magnitude of the rise in [Ca2+]i was seen with development. These data suggest increases in [Ca2+]i in adult nerve terminals following prolonged aglycaemia and hypoxia-aglycaemia but no change following prolonged hypoxia. In contrast, no significant changes in [Ca2+]i values were apparent in neonatal nerve terminals under any of these conditions. In control synaptosomes with glucose and oxygen freely available, a decrease in resting and depolarised [Ca2+]i during development was seen, suggesting a change in calcium homeostasis within the nerve terminal as the brain develops. It is suggested that the mechanism underlying the relative resistance to ischaemic damage of neonatal brain as compared with adult brain may be related to the regulation of calcium at the nerve ending. 相似文献
5.
In the present study, we evaluated the effect of neutrophil elastase inhibitor, sivelestat sodium hydrate on ischemia–reperfusion
injury in the rat bladder. Rat abdominal aorta was clamping with a small clip to induce ischemia–reperfusion injury in the
bladder. Eight-week-old male Sprague Dawley rats were divided into four groups; sham-operated control rats, 30 min ischemia–60 min
reperfusion (IR) rats, and IR rats treated with 15 or 60 mg/kg of sivelestat sodium hydrate. Sixty minutes prior to induction
of ischemia, sivelestat sodium hydrate was administrated intraperitoneally. Real-time monitoring of blood flow and nitric
oxide (NO) release were measured simultaneously with a laser Doppler flowmeter and an NO-selective electrode, respectively.
The NO2–NO3 and malonaldehyde (MDA) concentrations were measured in the experimental urinary bladders. Clamping of the abdominal aorta,
blood flow was rapidly decreased and NO release was gradually increased. After removing the clip, blood flow was rapidly increased
and NO release was gradually returned to the basal level. These movements of blood flow and NO release were inhibited by treatment
with sivelestat sodium hydrate in a dose-dependent manner. Both NO2–NO3 and MDA concentrations in the bladder were increased by induction of IR, and NO2–NO3 and MDA concentrations were decreased by treatment with high dose of sivelestat sodium hydrate significantly. Our data indicated
that sivelestat sodium hydrate could inhibit increasing NO2–NO3 and MDA concentrations by IR, and it has potentiality protective effects on IR injury in the rat urinary bladder. 相似文献
6.
Shi-Han Zhang Ling-Lin Cai Yun Liu Yao Shi Wei Li 《Applied microbiology and biotechnology》2009,82(3):557-563
The biological reduction of Fe(III) ethylenediaminetetraacetic acid (EDTA) is a key step for NO removal in a chemical absorption–biological
reduction integrated process. Since typical flue gas contain oxygen, NO2
− and NO3
− would be present in the absorption solution after NO absorption. In this paper, the interaction of NO2
−, NO3
−, and Fe(III)EDTA reduction was investigated. The experimental results indicate that the Fe(III)EDTA reduction rate decrease
with the increase of NO2
− or NO3
− addition. In the presence of 10 mM NO2
− or NO3
−, the average reduction rate of Fe(III)EDTA during the first 6-h reaction was 0.076 and 0.17 mM h−1, respectively, compared with 1.07 mM h−1 in the absence of NO2
− and NO3
−. Fe(III)EDTA and either NO2
− or NO3
− reduction occurred simultaneously. Interestingly, the reduction rate of NO2
− or NO3
− was enhanced in presence of Fe(III)EDTA. The inhibition patterns observed during the effect of NO2
− and NO3
− on the Fe(III)EDTA reduction experiments suggest that Escherichia coli can utilize NO2
−, NO3
−, and Fe(III)EDTA as terminal electron acceptors. 相似文献
7.
A sand-culture experiment was conducted to study the influence of a deficiency of and an excess of micronutrients on the uptake
and assimilation of NH
4
+
and NO
3
−
ions by maize. By studying the fate of15N supplied as15NH4NO3 or NH4
15NO3, it was demonstrated that in maize plants NH4−N was absorbed in preference to NO
3
−
−N. The uptake and distribution of N originating from both NH
4
+
and NO
3
−
was considerably modified by deficiency of, or an excess of, micronutrients in the growth medium. The translocation of NH
4
+
−N from roots to shoots was relatively less than that of NO
3
−
−N. Deficiency as well as excessive amounts of micronutrients, in the growth medium, substantially reduced the translocation
of absorbed N into protein. This effect was more pronounced in the case of N supplied as NO
3
−
. Amino-N was the predominant non-protein fraction in which N from both NH
4
+
and NO
3
−
tended to accumulate. The next important non-protein fractions were NO
3
−
−N when N was supplied as NO
3
−
and amide-N when NH
4
+
was the source. The relative accumulation of15N into different protein fractions was also a function of imposed micronutrient levels. 相似文献
8.
Nitrogen (N) pollution is a problem in many large temperate zone rivers, and N retention in river channels is often small
in these systems. To determine the potential for floodplains to act as N sinks during overbank flooding, we combined monitoring,
denitrification assays, and experimental nitrate (NO3− -N) additions to determine how the amount and form of N changed during flooding and the processes responsible for these changes
in the Wisconsin River floodplain (USA). Spring flooding increased N concentrations in the floodplain to levels equal to the
river. As discharge declined and connectivity between the river and floodplain was disrupted, total dissolved N decreased
over 75% from 1.41 mg l−1, equivalent to source water in the Wisconsin River on 14 April 2001, to 0.34 mg l−1 on 22 April 2001. Simultaneously NO3− -N was attenuated almost 100% from 1.09 to <0.002 mg l−1. Unamended sediment denitrification rates were moderate (0–483 μg m−2 h−1) and seasonally variable, and activity was limited by the availability of NO
3− -N on all dates. Two experimental NO3− -N pulse additions to floodplain water bodies confirmed rapid NO3− -N depletion. Over 80% of the observed NO
3− -N decline was caused by hydrologic export for addition #1 but only 22% in addition #2. During the second addition, a significant
fraction (>60%) of NO3− -N mass loss was not attributable to hydrologic losses or conversion to other forms of N, suggesting that denitrification
was likely responsible for most of the NO3− -N disappearance. Floodplain capacity to decrease the dominant fraction of river borne N within days of inundation demonstrates
that the Wisconsin River floodplain was an active N sink, that denitrification often drives N losses, and that enhancing connections
between rivers and their floodplains may enhance overall retention and reduce N exports from large basins. 相似文献
9.
Spatial and Temporal Variability in Sediment Denitrification Within an Agriculturally Influenced Reservoir 总被引:2,自引:1,他引:1
Reservoirs are intrinsically linked to the rivers that feed them, creating a river–reservoir continuum in which water and
sediment inputs are a function of the surrounding watershed land use. We examined the spatial and temporal variability of
sediment denitrification rates by sampling longitudinally along an agriculturally influenced river–reservoir continuum monthly
for 13 months. Sediment denitrification rates ranged from 0 to 63 μg N2O g ash free dry mass of sediments (AFDM)−1 h−1 or 0–2.7 μg N2O g dry mass of sediments (DM)−1 h−1 at reservoir sites, vs. 0–12 μg N2O gAFDM−1 h−1 or 0–0.27 μg N2O gDM−1 h−1 at riverine sites. Temporally, highest denitrification activity traveled through the reservoir from upper reservoir sites
to the dam, following the load of high nitrate (NO3−-N) water associated with spring runoff. Annual mean sediment denitrification rates at different reservoir sites were consistently
higher than at riverine sites, yet significant relationships among theses sites differed when denitrification rates were expressed
per gDM vs. per gAFDM. There was a significant positive relationship between sediment denitrification rates and NO3−-N concentration up to a threshold of 0.88 mg NO3− -N l−1, above which it appeared NO3−-N was no longer limiting. Denitrification assays were amended seasonally with NO3−-N and an organic carbon source (glucose) to determine nutrient limitation of sediment denitrification. While organic carbon
never limited sediment denitrification, all sites were significantly limited by NO3−-N during fall and winter when ambient NO
3−-N was low. 相似文献
10.
T. Rütting D. Huygens C. Müller O. Van Cleemput R. Godoy P. Boeckx 《Biogeochemistry》2008,90(3):243-258
Nitrite (NO2
−) is an intermediate in a variety of soil N cycling processes. However, NO2
− dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics
were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3
−, NH4
+ and NO2
−. Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of
functional links between (1) NH4
+ oxidation, the main process for NO2
− production (nitritation), and NO2
− reduction, and (2) oxidation of soil organic N, the dominant NO3
− production process in this soil, and dissimilatory NO3
− reduction to NH4
+ (DNRA). The production of NH4
+ via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the
rate of DNRA was several magnitudes higher than the rate of other NO3
− reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process
in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic
conditions of this Nothofagus ecosystem. 相似文献
11.
Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges 总被引:4,自引:0,他引:4
Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest
to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO3
−) and nitrite (NO2
−) to methanogenesis. The methanogenic toxicity of the NOx− compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and
hydrogen, was studied. The inhibition was the severest when the NOx− compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis
was evident at the lowest concentrations of added NO2
− tested (7.6–10.2 mg NO2
−-N l−1) or 8.3–121 mg NO3
−-N l−1 of added NO3
−, depending on substrate and inoculum source. The inhibition imparted by NO3
− was not due directly to NO3
− itself, but instead due to reduced intermediates (e.g., NO2
−) formed during the denitrification process. The toxicity of NOx− was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NOx− concentrations; whereas the recovery was only partial at high added NOx− concentrations. The recovery is attributed to the metabolism of the NOx− compounds. The assay substrate had a large impact on the rate of NO2
− metabolism. Hydrogen reduced NO2
− slowly such that NO2
− accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was
inversely proportional to the amount of NOx− compounds added indicating that they were the preferred electron acceptors compared to methanogenesis. 相似文献
12.
Stream export of nitrogen (N) as nitrate (NO3−; the most mobile form of N) from forest ecosystems is thought to be controlled largely by plant uptake of inorganic N, such
that reduced demand for plant N during the non-growing season and following disturbances results in increased stream NO3− export. The roles of microbes and soils in ecosystem N retention are less clear, but are the dominant controls on N export
when plant uptake is low. We used a mass balance approach to investigate soil N retention during winter (December through
March) at the Hubbard Brook Experimental Forest by comparing NO3− inputs (atmospheric deposition), internal production (soil microbial nitrification), and stream output. We focused on months
when plant N uptake is nearly zero and the potential for N export is high. Although winter months accounted for only 10–15%
of annual net nitrification, soil NO3− production (0.8–1.0 g N m−2 winter−1) was much greater than stream export (0.03–0.19 N m−2 winter−1). Soil NO3− retention in two consecutive winters was high (96% of combined NO3− deposition and soil production; year 1) even following severe plant disturbance caused by an ice-storm (84%; year 2) We show
that soil NO3− retention is surprisingly high even when N demand by plants is low. Our study highlights the need to better understand mechanisms
of N retention during the non-growing season to predict how ecosystems will respond to high inputs of atmospheric N, disturbance,
and climate change. 相似文献
13.
Protective effects of antioxidative serotonin derivatives isolated from safflower against postischemic myocardial dysfunction 总被引:4,自引:0,他引:4
Hotta Y Nagatsu A Liu W Muto T Narumiya C Lu X Yajima M Ishikawa N Miyazeki K Kawai N Mizukami H Sakakibara J 《Molecular and cellular biochemistry》2002,238(1-2):151-162
N-(p-Coumaroyl)serotonin (C) and N-feruroylserotonin (F) with antioxidative activity are present in safflower oil. The protective effects of C and F were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Changes in cellular levels of high phosphorous energy, NO and Ca2+ in the heart together with simultaneous recordings of left ventricular developed pressure (LVDP) were monitored by an nitric oxide (NO) electrode, fluorometry and 31P-NMR. The rate of recovery of LVDP from ischemia by reperfusion was 30.8% in the control, while in the presence of C or F a gradual increase to 63.2 or 61.0% was observed. Changes of transient NO signals (TNO) released from heart tissue in one contraction (LVDP) were observed to be upside-down with respect to transient fura-2-Ca2+ signals (TCa) and transient O2 signals detected with a pO2 electrode. At the final stage of ischemia, the intracellular concentration of Ca2+ ([Ca2+]i) and the release of NO increased with no twitching and remained at a high steady level. The addition of C increased the NO level at the end of ischemia compared with the control, but [Ca2+]i during ischemia decreased. On reperfusion, the increased diastolic level of TCa and TNO returned rapidly to the control level with the recovery of LVDP. By in vitro EPR, C and F were found to directly quench the activity of active radicals. Therefore, it is concluded that the antioxidant effects of two derivatives isolated from safflower play an important role in ischemia-reperfusion hearts in close relation with NO. 相似文献
14.
Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess
N loading to aquatic ecosystems. Nitrate (NO3
−) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation,
or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO3
− by coupling its reduction with the oxidation of sulfide to sulfate (SO4
2−). The NO3
− may be reduced to N2 or to NH4
+, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance
of S oxidation as a NO3
− removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO3
− removal and SO4
2− production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The
measured SO4
2− production can account for a significant fraction (25–40%) of the overall NO3
− removal. Addition of 15NO3
− and measurement of 15NH4
+ production using the push–pull method revealed that DNRA was a potentially important process of NO3
− removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO3
−-driven SO4
2− production could be widespread and biogeochemically important in freshwater sediments. Removal of NO3
− by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S)
pollution enhances NO3
− removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously
appreciated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
Aguilar-García A González-Frankenberger B Ramón-Frías T Méndez-Franco BJ Pérez-de la Mora M 《Amino acids》2000,19(1):63-77
Summary. GABA is synthesized within GABA terminals through a highly compartmentalized process in which glial-derived glutamine is
a major precursor and its release is modulated by GABAB autoreceptors. The aim of this work was to ascertain whether or not GABA synthesis and release are coupled in the rat brain
through a GABAB autoreceptor-mediated modulation. It was found that (−)baclofen (30 μM) reduces the K+ stimulated release of [3H]GABA in synaptosomes and prisms (10 μM) from cerebral cortex, while at the same concentrations (−)baclofen failed to modify the synthesis of [3H]GABA from [3H]glutamine in cortical and hypothalamic slices, prisms and in cortical synaptosomes. In this latter preparation, identical
results were observed when (−)baclofen was added to Krebs-Tris media, containing 5 or 15 mM K+ concentration. In agreement with these latter results, glutamic acid decarboxylase (GAD) activity from cortical and hypothalamic
prisms was not affected by 1–100 μM (−)baclofen. Similar results on GABA synthesis were also observed when 1–100 μM 3-aminopropil(methyl)-phosphinic acid or GABA was used instead of (−)baclofen to stimulate GABAB autoreceptors. [3H]GABA release, [3H]GABA synthesis from [3H]glutamine and GAD activity were also insensitive to the action of the GABAB antagonist CGP 52432 (10–100 μM). Likewise, muscimol (0.3–100 μM) did not affect GABA synthesis. Our results indicate that unlike GABA release, GABA synthesis is not modulated by GABAB autoreceptors.
Received August 31, 1999 Accepted September 20, 1999 相似文献
16.
Summary. The fungal toxin cytochalasin D as well as endogenous gelsolin depolymerize filamentous actin which may induce dynamic uncoupling
of membrane ion channels. In vitro application of cytochalasin D reduced NMDA-induced [3H]noradrenaline release from mouse brain neocortical slices by 38%. In gsn deficient neocortical synaptosomes [Ca2+]i increase in response to K+ (30 mM) depolarization was 33% higher than in wild-type. After transient focal cerebral ischemia K+-induced [Ca2+]i increase in neocortical synaptosomes was 56% lower than in synaptosomes prepared from the non-ischemic contralateral hemisphere.
After in vivo pretreatment with cytochalasin D 10 min before MCA occlusion K+-induced [Ca2+]i increase in synaptosomes in vitro prepared 1 h after reperfusion from the ischemic hemisphere was only 25% lower than in contralateral synaptosomes, while
cytochalasin D pretreatment in vivo did not reduce K+-induced [Ca2+]i increase in vitro. Hence, presynaptic Ca2+ influx and subsequently neuronal vulnerability are attenuated by increased and are aggravated by decreased F-actin depolymerization.
Received June 29, 2001 Accepted August 6, 2001 Published online August 9, 2002 相似文献
17.
Nitrogen Transformations in Flowpaths Leading from Soils to Streams in Amazon Forest and Pasture 总被引:1,自引:0,他引:1
Joaquín Chaves Christopher Neill Sonja Germer Sergio Gouveia Neto Alex V. Krusche Adriana Castellanos Bonilla Helmut Elsenbeer 《Ecosystems》2009,12(6):961-972
The modification of large areas of tropical forest to agricultural uses has consequences for the movement of inorganic nitrogen
(N) from land to water. Various biogeochemical pathways in soils and riparian zones can influence the movement and retention
of N within watersheds and affect the quantity exported in streams. We used the concentrations of NO3
− and NH4
+ in different hydrological flowpaths leading from upland soils to streams to investigate inorganic N transformations in adjacent
watersheds containing tropical forest and established cattle pasture in the southwestern Brazilian Amazon Basin. High NO3
− concentrations in forest soil solution relative to groundwater indicated a large removal of N mostly as NO3
− in flowpaths leading from soil to groundwater. Forest groundwater NO3
− concentrations were lower than in other Amazon sites where riparian zones have been implicated as important N sinks. Based
on water budgets for these watersheds, we estimated that 7.3–10.3 kg N ha−1 y−1 was removed from flowpaths between 20 and 100 cm, and 7.1–10.2 kg N ha−1 y−1 was removed below 100 cm and the top of the groundwater. N removal from vertical flowpaths in forest exceeded previously
measured N2O emissions of 3.0 kg N ha−1 y−1 and estimated emissions of NO of 1.4 kg N ha−1 y−1. Potential fates for this large amount of nitrate removal in forest soils include plant uptake, denitrification, and abiotic
N retention. Conversion to pasture shifted the system from dominance by processes producing and consuming NO3
− to one dominated by NH4
+, presumably the product of lower rates of net N mineralization and net nitrification in pasture compared with forest. In
pasture, no hydrological flowpaths contained substantial amounts of NO3
− and estimated N removal from soil vertical flowpaths was 0.2 kg N ha−1 y−1 below the depth of 100 cm. This contrasts with the extent to which agricultural sources dominate N inputs to groundwater
and stream water in many temperate regions. This could change, however, if pasture agriculture in the tropics shifts toward
intensive crop cultivation. 相似文献
18.
Jonathan M. O’Brien Walter K. Dodds Kymberly C. Wilson Justin N. Murdock Jessica Eichmiller 《Biogeochemistry》2007,84(1):31-49
We conducted 15NO3− stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed
to measure nitrate (NO3−) cycling dynamics. Mean ambient NO3− concentrations of the streams ranged from 0.9 to 21,000 μg l−1 NO3−–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two
to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which
stream biota utilized available NO3−-decreased along the gradient of increasing NO3−. Observed functional relationships of biological N transformations (uptake and nitrification) with NO3− concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical
relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase
with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient
of NO3− concentrations, but only accounted for ∼1% of total NO3− uptake. On average, 20% of stream water NO3− was lost to denitrification per km, but the percentage removed in most streams was <5% km−1. Although the rate of cycling was greater in streams with larger NO3− concentrations, the relative proportion of NO3− retained per unit length of stream decreased as NO3− concentration increased. Due to the rapid rate of NO3− turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove
N through denitrification is highly variable. 相似文献
19.
Praveen Nagella Hosakatte Niranjana Murthy 《Plant Cell, Tissue and Organ Culture》2011,104(1):119-124
Withania somnifera is an important medicinal plant that contains withanolides and withaferins, both bioactive compounds. We have tested the
effects of macroelements and nitrogen source in W. somnifera cell suspension cultures with the aim of optimizing the production of biomass and withanolide A. The effects of the macroelements
NH4NO3, KNO3, CaCl2, MgSO4 and KH2PO4 at concentrations of 0.0, 0.5, 1.0, 1.5 and 2.0× strength and of the nitrogen source [NH4
+/NO3
− (mM/mM) ratio of: 0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20,
and 14.38/37.60 (mM)] in Murashige and Skoog medium were tested for biomass and withanolide A production. The highest accumulation
of biomass [147.81 g l−1 fresh weight (FW) and 14.02 g l−1 (dry weight (DW)] was recorded in the medium containing a 0.5× concentration of NH4NO3, and the highest production of withanolide A content was recorded in the medium with 2.0× KNO3 (4.36 mg g−1 DW). The NH4
+/NO3
− ratio also influenced cell growth and withanolide A production, with both parameters being larger when the NO3
− concentration was higher than that of NH4
+. Maximum biomass growth (110.45 g l−1 FW and 9.29 g l−1 DW) was achieved at an NH4
+/NO3
− ratio of 7.19/18.80, while withanolide A production was greatest (3.96 mg g−1 DW) when the NH4
+/NO3
− ratio was 14.38/37.60 mM. 相似文献
20.
The effects of Ca(NO3)2 stress on biomass production, oxidative damage, antioxidant enzymes activities and polyamine contents in roots of grafted
and non-grafted tomato plants were investigated. Results showed that when exposed to 80 mM Ca(NO3)2 stress, the biomass production reduction in non-grafted plants was more significant than that of grafted plants. Under Ca(NO3)2 stress, superoxide anion radical (O2•−) producing rate, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents of non-grafted plants roots were significantly higher than those of grafted plants, however,
nitrate (NO3
−), ammonium (NH4
+) and proline contents, superoxide dismutase (SOD, EC1.15.1.1), peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6) and
arginine decarboxylase (ADC, EC 4.1.1.19) activities of grafted plants roots were significantly higher than those of non-grafted
plants. Regardless of stress, free, conjugated and bound polyamine contents in roots of grafted plants were significantly
higher than those of non-grafted plants. The possible roles of antioxidant enzymes, prolines and polyamines in adaptive mechanism
of tomato roots to Ca(NO3)2 stress were discussed.
Gu-Wen Zhang and Zheng-Lu Liu contributed equally to this work. 相似文献