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1.
2.
Summary Models for active Cl transport across epithelia are often assumed to be universal although they are based on detailed studies of a relatively small number of epithelia from vertebrate animals. Epithelial Cl transport is also important in many invertebrates, but little is known regarding its cellular mechanisms. We used short-circuit current, tracer fluxes and ion substitutions to investigate the basic properties of Cl absorption by locust hindgut, an epithelium which is ideally suited for transport studies. Serosal addition of 1mm adenosine 35-cyclic monophosphate (cAMP), a known stimulant of Cl transport in this tissue, increased short-circuit current (I
sc) and net reabsorptive36Cl flux (J
net
Cl
) by 1000%. Cl absorption did not exhibit an exchange diffusion component and was highly selective over all anions tested except Br. Several predictions of Na- and HCO3-coupled models for Cl transport were tested: Cl-dependentI
sc was not affected by sodium removal (<0.05mm) during the first 75 min. Also, a large stimulation ofJ
net
Cl
was elicited by cAMP when recta were bathed for 6 hr in nominally Na-free saline (<0.001 to 0.2mm) and there was no correlation between Cl transport rate and the presence of micromolar quantities of Na contamination. Increased unidirectional influx of36Cl into rectal tissue during cAMP-stimulation was not accompanied by a comparable uptake of22Na.J
net
Cl
was independent of exogenous CO2 and HCO3, but was strongly dependent on the presence of K. These results suggest that the major fraction of Cl transport across this insect epithelium occurs by an unusual K-dependent mechanism that does not directly require Na or HCO3. 相似文献
3.
John F. White 《The Journal of membrane biology》1986,92(1):75-89
Summary The characteristics of Cl– movement across luminal and basolateral membranes ofAmphiuma intestinal absorptive cells were studied using Cl–-sensitive microelectrodes and tracer36Cl techniques. Intracellular Cl– activity (a
Cl
i
) was unchanged when serosal Cl– was replaced; when luminal Cl– was replaced cell Cl– was rapidly lost. Accordingly, the steady statea
Cl
i
could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86mM,a
Cl
i
rose in a linear manner, the mucosal membrane hyperpolarized, and the transepithelial voltage became serosa negative. In contrast, the rate of Cl– transport from the cell into the serosal medium, measured as the SITS-inhibitable portion of the Cl– absorptive flux, attained a maximum whena
Cl
i
reached an apparent value of 17mm, indicating the presence of a saturable, serosal transport step. The stilbeneinsensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. Intracellulara
Cl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account.a
Cl
i
was unaffected by Na replacement, removal of medium K, or elevation of medium HCO
3
–
. Mucosae labeled with36Cl lost isotope into both luminal and serosal media at the same rate and from compartments of equal capacity. Lowering luminal [Cl] or addition of theophylline enhanced luminal Cl– efflux. It is concluded that a conductive Cl leak pathway is present in the luminal membrane. Serosal transfer is by a saturable, stilbene-inhibitable pathway. Luminal Cl– entry appears to be passive, but an electrogenic uptake cannot be discounted. 相似文献
4.
The fate of15N-ammonium sulphate fertilizer that was applied to four lysimeters in the 1990/91 summer was studied over three consecutive growing seasons during which either maize or wheat was grown. Aboveground portions of15N-labelled maize plants from the first harvest were applied to four other lysimeters at 5 t ha–1. Two lysimeters in each of the sets of four were assigned a low and a high moisture treatment using irrigation. In both moisture treatments, plant recovery of fertilizer-15N in the first season was 27% and a further 2% was recovered by plants during the next two seasons. During the second and third seasons, total recovery of15N by aboveground plant portions from lysimeters that received15N-labelled maize material was equivalent to 2.5% of applied fertilizer-15N. This corresponded to ca. 18% recovery of the15N added in maize material. Leaching of fertilizer-N over the three growing seasons did not exceed 0.3% in total. During the first season, a maximum of 0.25 kg N ha–1, equivalent to 0.25% of the applied fertilizer-N, was leached in the high moisture treatment. This represented 1.8% of the nitrate load in leachates. Less than 0.002% of the applied fertilizer-N was leached in the low moisture treatment during the first season. 相似文献
5.
Summary This study concerns the properties of rapid K+ and Cl transport pathways that are present in the (H++K+)-ATPase membrane from stimulated, and secreting, gastric oxyntic cells. Ion permeabilities in the isolated stimulation-associated vesicles were monitored via the rates of H+ efflux under conditions of exclusive H+/K+ counterflux or H+–Cl co-efflux, as well as by comparison of equilibration rates for86Rb and36Cl under conditions of equilibrium exchange and unidirectional salt flux. These latter studies suggest that Rb+ and Cl pathways are conductive and independent. In spite of the functional independence of the ion pathways, several divalent cations inhibit Rb+ and Cl isotopic exchange as well as the H+ efflux that is dependent on either K+ or anion (Cl, SCN, NO2) fluxes. Zn2+ is the more potent inhibitor, reducing by 50% the sensitive component of K+, Cl, and NO2 fluxes at about 20 m; Mn2+ has a similar effect at 200 m. Ni2+ and Co2+ were roughly equipotent to Mn2+ while Mg2+ and Ca2+ had not inhibitory effect. These results suggest that the stimulation-induced permeabilities, while functioning independently, may be physically linked, i.e., residing within a single entity. In similar studies carried out in (H++K+)-ATPase vesicles obtained from nonstimulated cells, no vestiges of sensitivity to the inhibitory divalent cations could be detected. The implications of these findings for the physiology of the oxyntic cell in the context of a model for membrane fusion are discussed. 相似文献
6.
Summary The potential dependence of unidirectional36Cl fluxes through toad skin revealed activation of a conductive pathway in the physiological region of transepithelial potentials. Activation of the conductance was dependent on the presence of Cl– or Br– in the external bathing solution, but was independent of whether the external bath was NaCl-Ringer's, NaCl-Ringer's with amiloride, KCl-Ringer's or choline Cl-Ringer's To partition the routes of the conductive Cl– ion flow, we measured in the isolated epithelium with double-barrelled microelectrodes apical membrane potentialV
a
, and intracellular Cl– activity,a
Cl
c
, of the principal cells indentified by differential interference contrast microscopy. Under short-circuit conditionsI
sc=27.0±2.0 A/cm2, with NaCl-Ringer's bathing both surfaces,V
a was –67.9±3.8mV (mean ±se,n=24, six preparations) anda
Cl
c
was 18.0±0.9mM in skins from animals adapted to distilled water. BothV
a anda
Cl
a
were found to be positively correlated withI
sc (r=0.66 andr=0.70, respectively). In eight epithelia from animals adapted to dry milieu/tap waterV
a anda
Cl
c
were measured with KCl Ringer's on the outside during activation and deactivation of the transepithelial Cl– conductance (G
Cl) by voltage clamping the transepithelial potential (V) at 40 mV (mucosa positive) and –100 mV. AtV=40 mV; i.e. whenG
Cl was deactivated,V
a
was –70.1±5.0 mV (n=15, eight preparations) anda
Cl
c
was 40.0±3.8mm. The fractional apical membrane resistance (fR
a) was 0.69±0.03. Clamping toV=–100 mV led to an instantaneous change ofV
a
to 31.3±5.6 mV (cell interior positive with respect to the mucosal bath), whereas neithera
Cl
c
norfR
a changed significantly within a 2 to 5-min period during whichG
Cl increased by 1.19±0.10 mS/cm2. WhenV was stepped back to 40 mV,V
a
instantaneously shifted to –67.8±3.9 mV whilea
Cl
c
andfR
a remained constant during deactivation ofG
Cl. Similar results were obtained in epithelia impaled from the serosal side. In 12 skins from animals adapted to either tap water or distilled water the density of mitochondria-rich (D
MRC) cells was estimated and correlated with the Cl current (I
Cl though the fully activated (V=–100mV) Cl– conductance). A highly significant correlation was revealed (r=–0.96) with a slope of –2.6 nA/m.r. (mitochondria-rich cell and an I-axis intercept not significantly different from zero. In summary, the voltage-dependent Cl currents were not reflected infR
a anda
Cl
a
of the principal cells but showed a correlation with the m.r. cell density. We conclude that the pricipal cells do not contribute significantly to the voltage-dependent Cl conductance. 相似文献
7.
M. C. J. Laima 《Biogeochemistry》1994,27(2):83-95
The release of NH
4
+
and15N-labelled NH
4
+
by one-step KCl extraction was assessed in different types of coastal marine sediments. KCl was efficient to extract NH
4
+
from sandy sediments and less efficient in silt sediments, where an extended extraction period was required for obtaining a maximum NH
4
+
yield. Extraction at 0 or 20 °C had only a little effect on the efficiency of KCl. KCl gave always non complete recovery of15NH
4
+
in silt sediments. However, the added label could be fully recovered by addition of 80 mol·cm–3 exogenous NH
4
+
prior to KCl, or when NaCl or ASW replaced KCl.15NH
4
+
was added to non-biological silt sediment, which was incubated at 0 °C up to 16 hours, to see the effect of physical processes on the partition of15NH4 among porewater (29–49%) exchangeable (9–30%) and non-extractable, organic bound pools (24–42%). Total15N recovery was approximately 100%. KCl failed to remove15NH4 which entered to unknown, bound pools in sediment. Only shortly after addition of15N (0.1 h), the extraction period resulted in significantly different15N recoveries (P < 0.05) in KCl extractable NH
4
+
, 17% versus 9% of label was recovered after 1 min or 60 min extraction of sediment, respectively. Two hours of incubation time were required for complete equilibrium of15NH
4
+
among porewater, exchangeable and organic bound pools. Sediments (silt) to which15NH
4
+
has been added in order to measure NH
4
+
turn-over and KCl is used as extractant, should be incubated for at least 2 hours, before taking a zero-time sample. 相似文献
8.
William Breuer 《The Journal of membrane biology》1989,107(1):35-42
Summary The basolateral membrane of the thick ascending loop of Henle (TALH) of the mammalian kidney is highly enriched in Na+/K+ ATPase and has been shown by electrophysiological methods to be highly conductive to Cl–. In order to study the Cl– conductive pathways, membrane vesicles were isolated from the TALH-containing region of the porcine kidney, the red outer medulla, and Cl– channel activity was determined by a36Cl uptake assay where the uptake of the radioactive tracer is driven by the membrane potential (positive inside) generated by an outward Cl– gradient. The accumulation of36Cl– inside the vesicles was found to be dependent on the intravesicular Cl– concentration and was abolished by clamping the membrane potential with valinomycin. The latter finding indicated the involvement of conductive pathways. Cl– channel activity was also observed using a fluorescent potential-sensitive carbocyanine dye, which detected a diffusion potential induced by an imposed inward Cl– gradient. The anion selectivity of the channels was Cl–>NO
3
–
=I– gluconate. Among the Cl– transport inhibitors tested, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPAB), 4,4-diisothiocyano-stilbene-2,2-disulfonate (DIDS), and diphenylamine-2-carboxylate (DPC) showed IC50 of 110, 200 and 550 m, respectively. Inhibition of36Cl uptake by NPPAB and two other structural analogues was fully reversible, whereas that by DIDS was not. The nonreactive analogue of DIDS, 4,4-dinitrostilbene-2,2-disulfonate (DNDS), was considerably less inhibitory than DIDS (25% inhibition at 200 m). The irreversible inhibition by DIDS was prevented by NPPAB, whereas DPC was ineffective, consistent with its low inhibitory potency. It is proposed that NPPAB and DIDS bind to the same or functionally related site on the Cl– channel protein. 相似文献
9.
Contributions to nitrogen leaching and pasture uptake by autumn-applied dairy effluent and ammonium fertilizer labeled with 15N isotope 总被引:1,自引:0,他引:1
The objective of this study was to compare the N leaching loss and pasture N uptake from autumn-applied dairy shed effluent
and ammonium fertilizer (NH4Cl) labeled with 15N, using intact soil lysimeters (80 cm diameter, 120 cm depth). The soil used was a sandy loam, and the pasture was a mixture
of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The DSE and NH4Cl were applied twice annually in autumn (May) and late spring (November), each at 200 kg N ha-1. The N applied in May 1996 was labeled with 15N. The lysimeters were either spray or flood irrigated during the summer.
The autumn-applied DSE resulted in lower N leaching losses compared with NH4Cl. However, the N applied in the autumn had a higher potential for leaching than N applied in late spring. Between 4.5–8.1%
of the 15N-labeled mineral N in the DSE and 15.1–18.8% of the 15N-labeled NH4Cl applied in the autumn were leached within a year of application. Of the annual N leaching losses in the DSE treatments
(16.0–26.9 kg N ha-1), a fifth (20.3–22.9%) was from the mineral N fraction of the DSE applied in the autumn, with the remaining larger proportion
from the organic fraction of the DSE, soil N and N applied in spring. In the NH4Cl treatments, more than half (53.8–64.8%) of the annual N leaching loss (55.9–57.6 kg N ha-1) was derived from the autumn-applied NH4Cl. DSE was as effective as NH4Cl in stimulating pasture production. Since only 4.4–4.5% of the annual herbage N uptake in the DSE treatment and 12.3–13.3%
in the NH4Cl treatment were derived from the autumn-applied mineral N, large proportions of the annual herbage N uptake must have been
derived from the N applied in spring, the organic N fraction in the DSE, soil N and N fixed by clover. The recoveries of 15N in the herbage were similar between the DSE and the NH4Cl treatments, but those in the leachate were over 50% less from the DSE than from the NH4Cl treatment. The lower leaching loss of 15N in the DSE treatment was attributed to the stimulated microbial activities and increased immobilization following the application
of DSE.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
In monocropped cereal systems, annual N inputs from non-fertilizer sources may be more than 30 kg ha-1. We examined the possibility that these inputs are due to biological N2 fixation (BNF) associated with roots or decomposing residues. Wheat was grown under greenhouse conditions in pots (34 cm
long by 10 cm diameter) containing soil from a plot cropped to spring wheat since 1911 without fertilization. The roots and
soil were sealed from the atmosphere and exposed to a15N2-enriched atmosphere for three to four weeks during vegetative, reproductive or post-reproductive stages. This technique permitted
detection of as little as 1 μg fixed N plant-1 in plant material and 40 μg fixed N plant-1 in soil. No fixation of15N2 occurred during either of the first two labelling periods. In the final labelling period, straw returned to the soil was
significantly enriched in15N, especially in a pot with a higher soil moisture content. Total BNF in this pot was 13 μg N plant-1, or about 30 g N ha-1. In a separate experiment with soil from the same plot, we detected BNF only when soil was amended with glucose at a high
soil moisture content. Measured associative BNF was insufficient to account for observed N gains under field conditions.
Lethbridge Research Centre contribution no. 3879488.
Lethbridge Research Centre contribution no. 3879488. 相似文献
11.
Alfalfa (Medicago sativa L.) was grown in greenhouse sand culture to examine the effect of salinity composition and concentration on Se accumulation
by plants. In a 2×2×4 factorial experiment, salinity was added as either C1− or SO
4
2−
salts to the irrigating solution to achieve an electrical conductivity of 0.5, 1.5–3.0, or 6.0 dS m−1. Selenium was added to the nutrient solution at a concentration of 0.25 or 1.0 mg Se(VI)I−1. Following the third cutting, the roots were washed and all plant material analyzed for dry weight and Se. Plant biomass
production decreased with additions of either Se or salinity, regardless of composition. In the presence of Se, the yield
reduction was greater with Cl− salinity than with SO
4
2−
salinity. Plant Se accumulation was reduced from 948 mg Se kg−1 to 6 mg Se kg−1 in the presence of SO
4
2−
salts (0.5 mmol SO
4
2−
l−1
vs. 40 mmol SO
4
2−
l−1) due to an apparent Se(VI) −SO
4
2−
antagonism. This Se−SO
4
2−
antagonism prevented accumulation of Se and reduced Se-induced toxicity. A lesser antagonistic effect on Se accumulation
was observed between Cl−, and Se. A synergistic interaction between SO
4
2−
and Se(VI) increased plant S concentrations in the presence of the relatively low basal SO
4
2−
concentrations but not at the higher solution SO
4
2−
concentrations. In many areas, soil and water containing high Se concentrations also contain large amounts of SO
4
2−
. The occurrence of SO
4
2−
with Se reduces plant accumulation of Se(VI) and may lower the risk of Se overexposure to animals feeding on forage material
grown in high Se−SO
4
2−
regions. 相似文献
12.
Effect of Cl on Cd uptake by Swiss chard in nutrient solutions 总被引:6,自引:1,他引:5
Swiss chard (Beta vulgaris L., cv. Fordhook Giant) was grown in nutrient solution with Cl concentrations varying between 0.01 mM and 120 mM. Solution Na concentration and ionic strength were maintained in all treatments by compensating with NaNO3. All solutions contained Cd (50 nM, spiked with 109Cd). Three different Cd2+ buffering systems were used. In one experiment, Cd2+ activity was unbuffered; its activity decreased with increased Cl concentration as a result of the formation of CdCln
2–n species. In the other experiments, Cd2+ activity was buffered by the chelator nitrilotriacetate (NTA, 50 M) and ethylene-bis-(oxyethylenenitrilo)-tetraacetate (EGTA, 50 M) at about 10–9
M and 10–11
M, respectively. Plant growth was generally unaffected by increasing Cl concentrations in the three experiments. In unbuffered solutions, Cd concentrations in plant tissue decreased significantly (p<0.01) (approximately 2.4-fold) as solution Cl concentration increased from 0.01 mM to 120 mM. However, this decrease was smaller in magnitude than the 4.7-fold decrease in Cd2+ activity as calculated by the GEOCHEM-PC program for the same range of Cl concentrations. In solutions where Cd2+ activity was buffered by NTA, Cd concentrations in plant tissue increased approximately 1.4-fold with increasing Cl concentration in solution, while the Cd2+ activity was calculated to decrease 1.3-fold. In solutions where Cd2+ activity was buffered by EGTA, Cd concentrations in the roots increased 1.3-fold with increasing Cl concentration in solution but there was no effect of Cl on shoot Cd concentrations. The data suggest that either CdCln
2–nspecies can be taken up by plant roots or that Cl enhances uptake of Cd2+ through enhanced diffusion of the uncomplexed metal to uptake sites.Abbreviations DAS
days after sowing
- EGTA
ethylene-bis-(oxyethylenenitrilo)-tetraacetate
- HBED
N,N-bis(2-hydroxybenzyl)-ethylenediamine-N,N-diacetate
- NTA
nitrilotriacetate 相似文献
13.
Donna L. Payne Bernice Adeleye Donna J. Hunt Barbara J. Stoecker 《Biological trace element research》1996,53(1-3):1-6
Optimum concentration of Cr for infant formulas has not been established. Such components as soy protein or supplemental Fe
could influence absorption and retention. Suckling rat pups were used to evaluate the influence of three commercial formulas
and human milk, all of which had been incubated with51CrCl3 for 1 h, on the uptake and retention of the added51Cr. After fasting 3 h, the pups were intubated with a single dose of 25 μCi51CrCl3 in either a cow's milk-based formula, an Fe-supplemented cow's milk-based formula, a soy-based formula, or human milk. Six
hours later,51Cr was counted in five organs, thymus, blood, and total urine. Absorption of51Cr was low. At 6 h, percent51Cr in blood was <0.2% of the dose, and total51Cr excretion in urine was <1.8%. The uptake and retention of51Cr and its concentration in any of the organs, thymus, blood, and urine were not influenced by different types of formula
or by human milk. 相似文献
14.
Summary Wheat plants that were grown for 30 days in flowing nutrient solution were transferred to CaSO4 solution, and water stress was developed by increasing the evaporative demand on the tops and decreasing the amount of the root system in the solution. The stress was maintained for 3 or 9 h. Uptake of36Cl by the plants was measured immediately after removal of the stress and at intervals up to 36 h later.The water potential of the leaves ranged from –5 bar in the control to –12 bar in stressed plants. Stressed plants transpired less water after removal of the stress than did unstressed plants.Chloride uptake immediately after the removal of water stress was unaffected by the stress, but when measurements were made 36 h later previously stressed plants absorbed only 2 M h–1 chloride compared to 7 M h–1 for unstressed plants. 相似文献
15.
Lupins, canola, ryegrass and wheat fertilized with Na2
35SO4 and either 15NH4Cl or K15NO3(N:S=10:1), were grown in the field in unconfined microplots, and the sources of N and S (fertilizer, soil, atmosphere, seed)
in plant tops during crop development were estimated. Modelled estimates of the proportion of lupin N derived from the atmosphere,
which were obtained independently of reference plants, were used to calculate the proportion of lupin N derived from the soil.
Total uptake of N and S and uptake of labelled N and S increased during crop development. Total uptake of S by canola was
higher than lupins, but labelled S uptake by lupins exceeded uptake by canola. The form of N applied had no effect on uptake
of labelled and unlabelled forms of N or S. Ratios of labelled to unlabelled S and ratios of labelled to unlabelled N derived
from soil sources decreased during growth, and were less for S than for N for each crop at each sampling time. Although ratios
of labelled to unlabelled soil-derived N were similar between crops at 155, 176 and 190 days after sowing, ratios of labelled
to unlabelled S for lupins were higher than for the reference crops and declined during this period. The ratios of labelled
to unlabelled S in lupins and the reference plants therefore bore no relationship either to ratios of labelled to unlabelled
soil-derived N in the plants, or to total S uptake by the plants. Therefore the hypothesis that equal ratios of labelled N
to unlabelled soil-derived N in legumes (Rleg) and reference plants (Rref) would be indicated by equal ratios of labelled to unlabelled S was not supported by the data. The results therefore show
that the accuracy of reference plant-derived values of Rleg cannot be evaluated by labelling with 35S. 相似文献
16.
Summary The kinetic of15N2 diffusion has been measured in a system similar to that for the estimation of N2 fixation in plant microorganism associations cultivated in soil. The15N2 enrichment of the soil atmosphere reached an homogenous value one hour after injection of15N2 and is identical to that obtained by calculation, indicating that no adsorption occurs in the soil particles.
Diffusion du15N2 dans le sol pendant la mesure de fixation biologique de l'azote
Résumé La cinétique de diffusion du15N2 est mesurée sur un système identique à ceux pouvant être utilisés pour la mesure de fixation de l'azote chez les associations plantes-microorganismes cultivées sur sol. L'enrichissement homogène de l'atmosphère du sol est obtenu une heure environ après l'injection de15N2 et correspond à l'enrichissement calculé, ce qui indique qu'aucune adsorption n'a lieu dans les particules du sol.相似文献
17.
Assessing Nitrification and Denitrification in the Seine River and Estuary Using Chemical and Isotopic Techniques 总被引:4,自引:0,他引:4
Mathieu Sebilo Gilles Billen Bernhard Mayer Daniel Billiou Micheline Grably Josette Garnier André Mariotti 《Ecosystems》2006,9(4):564-577
Downstream from metropolitan Paris (France), a large amount of ammonium is discharged into the Seine River by the effluents
of the wastewater treatment plant at Achères. To assess the extent of nitrification and denitrification in the water column,
concentrations and isotopic compositions of ammonium (δ15N–NH4+) and nitrate (δ15N–NO3−, δ18O–NO3−) were measured during summer low-flow conditions along the lower Seine and its estuary. The results indicated that most of
the ammonium released from the wastewater treatment plant is nitrified in the lower Seine River and its upper estuary, but
there was no evidence for water-column denitrification. In the lower part of the estuary, however, concentration and isotopic
data for nitrate were not consistent with simple mixing between riverine and marine nitrate. A significant departure of the
nitrate isotopic composition from what would be expected from simple mixing of freshwater and marine nitrates suggested coupled
nitrification and denitrification in the water, in spite of the apparent conservative behavior of nitrate. Denitrification
rates of approximately 0.02 mg N/L/h were estimated for this part of the estuary. 相似文献
18.
Quantitative and Qualitative Aspects of Dissolved Organic Carbon Leached from Senescent Plants in an Oligotrophic Wetland 总被引:1,自引:0,他引:1
Nagamitsu Maie Rudolf Jaffé Toshikazu Miyoshi Daniel L. Childers 《Biogeochemistry》2006,78(3):285-314
We conducted a series of experiments whereby dissolved organic matter (DOM) was leached from various wetland and estuarine
plants, namely sawgrass (Cladium jamaicense), spikerush (Eleocharis cellulosa), red mangrove (Rhizophora mangle), cattail (Typha domingensis), periphyton (dry and wet mat), and a seagrass (turtle grass; Thalassia testudinum). All are abundant in the Florida Coastal Everglades (FCE) except for cattail, but this species has a potential to proliferate
in this environment. Senescent plant samples were immersed into ultrapure water with and without addition of 0.1% NaN3 (w/ and w/o NaN3, respectively) for 36 days. We replaced the water every 3 days. The amount of dissolved organic carbon (DOC), sugars, and
phenols in the leachates were analyzed. The contribution of plant leachates to the ultrafiltered high molecular weight fraction
of DOM (>1 kDa; UDOM) in natural waters in the FCE was also investigated. UDOM in plant leachates was obtained by tangential
flow ultrafiltration and its carbon and phenolic compound compositions were analyzed using solid state 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy and thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH thermochemolysis), respectively.
The maximum yield of DOC leached from plants over the 36-day incubations ranged from 13.0 to 55.2 g C kg−1 dry weight. This amount was lower in w/o NaN3 treatments (more DOC was consumed by microbes than produced) except for periphyton. During the first 2 weeks of the 5 week
incubation period, 60–85% of the total amount of DOC was leached, and exponential decay models fit the leaching rates except
for periphyton w/o NaN3. Leached DOC (w/ NaN3) contained different concentrations of sugars and phenols depending on the plant types (1.09–7.22 and 0.38–12.4 g C kg−1 dry weight, respectively), and those biomolecules comprised 8–34% and 4–28% of the total DOC, respectively. This result shows
that polyphenols that readily leach from senescent plants can be an important source of chromophoric DOM (CDOM) in wetland
environments. The O-alkyl C was found to be the major C form (55±9%) of UDOM in plant leachates as determined by 13C CPMAS NMR. The relative abundance of alkyl C and carbonyl C was consistently lower in plant-leached UDOM than that in natural
water UDOM in the FCE, which suggests that these constituents increase in relative abundance during diagenetic processing.
TMAH thermochemolysis analysis revealed that the phenolic composition was different among the UDOM leached from different
plants, and was expected to serve as a source indicator of UDOM in natural water. Polyphenols are, however, very reactive
and photosensitive in aquatic environments, and thus may loose their plant-specific molecular characteristics shortly. Our
study suggests that variations in vegetative cover across a wetland landscape will affect the quantity and quality of DOM
leached into the water, and such differences in DOM characteristics may affect other biogeochemical processes. 相似文献
19.
Vibeke Secher Dam Donna MB Boedtkjer Christian Aalkjaer Vladimir Matchkov 《Channels (Austin, Tex.)》2014,8(4):361-369
The presence of Ca2+-activated Cl– currents (ICl(Ca)) in vascular smooth muscle cells (VSMCs) is well established. ICl(Ca) are supposedly important for arterial contraction by linking changes in [Ca2+]i and membrane depolarization. Bestrophins and some members of the TMEM16 protein family were recently associated with ICl(Ca). Two distinct ICl(Ca) are characterized in VSMCs; the cGMP-dependent ICl(Ca) dependent upon bestrophin expression and the ‘classical’ Ca2+-activated Cl– current, which is bestrophin-independent. Interestingly, TMEM16A is essential for both the cGMP-dependent and the classical ICl(Ca). Furthermore, TMEM16A has a role in arterial contraction while bestrophins do not. TMEM16A’s role in the contractile response cannot be explained however only by a simple suppression of the depolarization by Cl– channels. It is suggested that TMEM16A expression modulates voltage-gated Ca2+ influx in a voltage-independent manner and recent studies also demonstrate a complex role of TMEM16A in modulating other membrane proteins. 相似文献
20.
A14C labeling apparatus was developed to permit the labeling of four-year-old Ponderosa pine with14CO2 in the field. The labeling system is a completely closed canopy system with14CO2 monitored by a GM tube ratemeter apparatus. The level of14CO2 corresponding to ambient levels is monitored by a microloggercomputer which controls a14CO2 generating system. The generated14CO2 is mixed in the canopy by circulating the atmosphere with 12V diaphram pumps. The portable system requires little operator
attention.
At approximately monthly intervals over a one-year period two four-year-old Ponderosa pine trees were labeled for three to
five days using this labeling apparatus. After an assimilate distribution period, one tree was excavated and analyzed for14C distribution. During late spring and early summer most of the carbon assimilated (>60%) was found in the active growing
tips and new needles, with little being allocated to the roots (<10%) or woody material (<20%). During mid to late fall there
was an increase in root labeling along with an increase in carbon going to woody material. Over the winter period, most of
the fixed carbon (65%) resided in the older leaves. The early spring labeling period showed another pulse of root labeling
along with some labeling of woody tissues. 相似文献