共查询到20条相似文献,搜索用时 687 毫秒
1.
We demonstrate in this work that HCO
inf3
sup–
uptake in the marine macroalga Ulva sp. features functional resemblances to anion transport mediated by anion exchangers of mammalian cell membranes. The evidence is based on (i) competitive inhibition of photosynthesis by the classical red-blood-cell anion-exchange blockers 4,4-dinitrostilbene-2,2-disulfonate and 4-nitro-4-isothiocyanostilbene-2,2-disulfonate under conditions where HCO
inf3
sup–
, but not CO2, was the inorganic carbon form taken up; (ii) inhibition of HCO
inf3
–
uptake by pyridoxal phospate, indicating the involvement of lysine residues in the binding/translocation of HCO
inf3
sup–
; and (iii) inhibition of HCO
inf3
sup–
(but not of CO2) uptake by exofacial trypsin treatments, indicating the functional involvement of a plasmalemma protein. It is suggested that HCO
inf3
sup–
uptake mediated by such a putative anion transporter can be a fundamental step in providing inorganic carbon for the CO2-concentrating system of marine marcoalgae in an environment where the HCO
inf3
sup–
concentration is high, but the CO2 concentration and rates of uncatalyzed HCO
inf3
sup–
dehydration are low.Abbreviations CI
ionorganic carbon
- DIDS
4,4-diisothiocyanostilbene-2,2-disulfonate
- DNDS
4,4-dinitrostilbene-2,2-disulfonate
- NIDS
4-nitro-4-isothiocyanostilbene-2,2-disulfonate
- PLP
pyridoxal phosphate
- Rubisco
ribulose-1,5-bisphosphate carboxylase-oxygenase 相似文献
2.
Palmaria palmata, which is able to use HCO
inf3
sup–
as a carbon source for photosynthesis, and Lomentaria articulata, which is dependent on diffusive uptake of dissolved CO2, were grown under constant light and light with sunflecks designed to model wave-induced fluctuations of near-shore underwater light. Both species exhibited significantly increased stable carbon isotope discrimination (more negative values of 13C relative to PDB) when grown with sunflecks. More negative 13C values were associated with decreased growth rate of P. palmata but not of L. articulata. The contrasting effects of sunflecks on the carbon-use characteristics of the two species are discussed in terms of the energetic cost of HCO
inf3
sup–
use and the susceptibility of CO2 diffusion-dependent species to photoinhibition. 相似文献
3.
Water chemistry and periphyton in an alpine wetland 总被引:2,自引:0,他引:2
Dale Toetz 《Hydrobiologia》1995,312(2):93-105
Remote high elevation sites are thought to be good sites to monitor global change and anthropogenic effects on ecosystems. This study was conducted during 1987–1990 in a high elevation wetland (3593 m) located in the Green Lakes Valley, Front Range, Colorado (USA). Salix spp. was the dominant riparian species in this 2 ha. wetland. Small shallow pools (<0.5 m depth) constituted a water area of 236 m3. The major source of water during the study period was snowmelt. The wetland had a well defined outlet and inlet, although an undetermined amount of water entered as groundwater from the snow patch above. Outlet discharge was 424–460 m3 during the month of July and declined thereafter as water input from the snowpatch declined. Inlet discharge was 67% of outlet discharge. Water temperatures in the outlet were always less than 6.8°C, pH 6.0–6.3, and mean conductivity 30.8 µS cm–1. Both NO
inf3
sup–
and SO
inf4
sup–2
were higher in the inlet thanin the outlet. Dominant cations in the inlet and outlet waters were Ca+2 Mg+2 > K+ + Na+; dominant anions were SO
inf4
sup–2
HCO
inf3
sup–
> NO
inf3
sup–
Cl–. Nutrient limitation by P was demonstrated once using nutrient diffusing substrata. No limitation could be shown for NO
inf3
sup–
, HCO
inf3
sup–
, or Fe+EDTA. Slow colonization rates of periphyton on tiles were attributed to low temperatures and/or ultraviolet radiation. However, interannual differences in biomass on tiles were as much as 300% after 35 days. A minimum of 16–54 samples would be needed to detect a significant interannual change in biomass on tiles after 35 days assuming that the extreme case for periphyton patchiness. Global climate change is likely to affect discharge and water temperature in this wetland which hill have direct and indirect affects on population dynamics and ecosystem function. 相似文献
4.
Net O2 evolution, gross CO2 uptake and net HCO
inf3
su–
uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO2 concentrations. Regardless of the CO2 concentration during growth, all cells had the capacity to transport both CO2 and HCO
inf3
su–
; however, the activity of HCO
inf3
su–
transport was more than twofold higher than CO2 transport even in cyanobacteria grown at high concentration of inorganic carbon (Ci = CO2 + HCO
inf3
su–
). In low-Ci cells, the affinities of CO2 and HCO
inf3
su–
transport for their substrates were about 5 (CO2 uptake) and 10 (HCO
inf3
su–
uptake) times higher than in high-Ci cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated Ci pool reached 18, 32 and 55 mM in high-Ci, air-grown and low-Ci cells, respectively, when measured at 1 mM external Ci. Photosynthetic O2 evolution, maximal CO2 and HCO
inf3
su–
transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO2 provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO2 concentrations. Transport studies with high-Ci cells revealed that CO2 and HCO
inf3
su–
uptake were equally inhibited when CO2 fixation was reduced by the addition of glycolaldehyde. In contrast, in low-Ci cells steady-state CO2 transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO2 and HCO
inf3
su–
uptake as well as O2 evolution in both cell types. In high-Ci cells, the degree of inhibition was similar for HCO
inf3
su–
transport and O2 evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO2 was much more sensitive to the inhibitor than HCO
inf3
su–
transport, with an apparent I50 value of around 250 M ethoxyzolamide for CO2 uptake. The implications of our results are discussed with respect to Ci utilisation in the marine Synechococcus strain.Abbreviations Chl
chlorophyll
- Ci
inorganic carbon (CO2 + HCO
inf3
su–
)
- CA
carbonic anhydrase
- CCM
CO2-concentrating mechanism
- EZA
ethoxyzolamide
- GA
glycolaldehyde
- K1/2
concentration required for half-maximal response
- Rubisco
ribulose-1,5,-bisphosphate carboxylase-oxygenase
D.S. is a recipient of a research fellowship from the Deutsche Forschungsgemeinschaft (D.F.G.). In addition, we are grateful to Donald A. Bryant, Department of Molecular and Cell Biology and Center of Biomolecular Structure Function, Pennsylvania State University, USA, for sending us the wild-type strain of Synechococcus PCC7002. 相似文献
5.
The decline and disappearance of Littorella uniflora from oligotrophic waters which have become eutrophic has been associated with shading or reduced CO2 supply. However NO
inf3
sup–
concentrations can reach very high levels (100–2000 mmol m–3 compared with <1–3 in oligotrophic habitats). To investigate the impact of NO
inf3
sup–
loading alone, plants were grown under three NO
inf3
sup–
regimes (very low, near-natural and high). The interactive effects of NO
inf3
sup–
and photon flux density (low and high regimes) on N assimilation and accumulation, CO2 concentrating mechanisms, C3 photosynthesis and growth were also examined. The results were unexpected. Increased NO
inf3
sup–
supply had very little effect on photosynthetic capacity, crassulacean acid metabolism (CAM) or lacunal CO2 concentrations ([CO2]i), although there was considerable plasticity with respect to light regime. In contrast, increased NO
inf3
sup–
supply resulted in a marked accumulation of NO
inf3
sup–
, free amino acids and soluble protein in shoots and roots (up to 25 mol m–3, 30 mol m–3 and 9 mg g–1 fresh weight respectively in roots), while fresh weight and relative growth rate were reduced. Total N content even under the very low NO
inf3
sup–
regime (1.6–2.3%) was mid-range for aquatic and terrestrial species (and 3.1–4.3% under the high NO
inf3
sup–
regime). These findings, together with field data, suggest that L. uniflora is not growth limited by low NO
inf3
sup–
supply in natural oligotophic habitats, due not to an efficient photosynthetic nitrogen use but to a slow growth rate, a low N requirement and to the use of storage to avoid N stress. However the increased NO
inf3
sup–
concentrations in eutrophic environments seem likely have detrimental effects on the long-term survival of L. uniflora, possibly as a consequence of N accumulation. 相似文献
6.
Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m3 Tm–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m–2 d–1) were obtained at a density of 2.5 g FW 1–1 and at a DIN inflow rate of 1.7 g DIN m–2 d–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M–2 d–1), and minimum in winter (1.1 g DIN m–2 d–1) with a yearly average DIN uptake rate of 1.77 g DIN m–2 d–1 At yearly average DIN removal efficiency (2.0 g DIN m–2 d–1, if winter period is excluded), 153 m2 of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN=
dissolved inorganic nitrogen (NH
inf4
sup+
+ NO
inf3
sup–
+ NO
inf2
sup–
);
- FW=
fresh weight;
- DW=
dry weight;
- PFD=
photon flux density;
- V=
DIN uptake rate 相似文献
7.
J. Michael Robinson 《Photosynthesis research》1994,40(1):119-125
A problem often encountered when assaying mesophyll cell isolates prepared from mature soybean leaves, was that of poor reproducibility in rates of net 14CO2 photoassimilation and NO2
– photoreduction. It was known that soybean source leaves repeatedly displayed their most active net CO2 photoassimilation in the period from attainment of maximal leaf area to approximately two to five days subsequent to that point. Advantage was taken of the fact that when soybean leaflets of each leaf reach their maximal area they also have reached their maximal leaf length from base to tip. This facilitates a more rapid determination of the point in time in which leaflet areas had reached Amax. Soybean plants (Glycine max cv. Williams) were propagated in the growth chamber with a 12 h light-12 h dark cycle, 25C, 65% RH, and 700 microeinsteins per meter squared per second. At 24 d post-emergence, the third leaf (numbered acropetally from the unifoliates) of each plant had just attained maximum leaflet areas (110 cm2) and lengths (13 cm). For this study, leaf mesophyll cells were enzymatically isolated, using commercially prepared pectinase, from leaflet sets of leaves selected from each of the second, third, and fourth leaf positions. Maximal rates of net 14CO2 photoassimilation (with 5 mM HCO3
–) for the second, third and fourth leaf (leaflet) isolates were, respectively, 27.0, 57.0, and 41.7 mol 14CO2 assimilated per milligram chlorophyll per hour; simultaneously maximal rates of NO
inf2
sup–
photoreduction (1 mM NO
inf2
sup–
) were, respectively, 4.4, 8.1, and 0.0 mol NO
inf2
sup–
reduced per milligram chlorophyll per hour. These studies made it clear that in order repeatedly to attain reproducible maximal rates of leaf cell isolate net 14CO2 photoassimilation and NO
inf2
sup–
photoreduction, it always was necessary to select the newest, fully expanded leaves (e.g. leaf number 3) for cell isolation. Leaves from several plants only were pooled if they were excised from identically the same node on each of the plants.Abbreviations Amax -
maximum leaflet (trifoliolate) area attained during ontogeny
- CO2 -
CO2 gas dissolved in solution
- HCO
inf3
sup–
-
bicarbonate
- Lmax -
maximum leaf blade length (midvein) attained during ontogeny
- NiRase -
chloroplast nitrite reductase (reduced ferredoxin)
- NiPR -
nitrite photoreduction
- PE -
post-emergence
- Pn -
net CO2 photoassimilation (for leaflets and mesophyll cell isolates)
- PPRC -
pentose phosphate reductive cycle 相似文献
8.
Geoffrey W. Garnham Geoffrey A. Codd Geoffrey M. Gadd 《Applied microbiology and biotechnology》1992,37(5):679-684
Summary Accumulation of [99Tc]pertechnetate ions (99TcO4
–) by the freshwater microalgae Chlorella emersonii, Chlamydomonas reinhardtii and Scenedesmus obliquus has been characterized. In all three species, accumulation consisted of a single rapid energy-independent phase (biosorption), and no energy-dependent accumulation was observed. Biosorption of 99TcO
inf4
sup–
by all three species was concentration dependent, followed a Freundlich adsorption isotherm, and was dependent on pH with increased accumulation by cells with decreasing external pH. Elevated external NaCl concentrations also caused increased accumulation of 99TcO
inf4
sup–
by the cells, as did increased external osmotic potential. Concentrations of K+, Mg2+ and Ca2+ increased accumulation of 99TcO
inf4
sup–
, but concentrations of HCO
inf3
sup–
, SO
inf4
sup2–
and CO
inf3
sup2–
decreased 99TcO
inf4
sup–
accumulation by the cells. Most of the 99TcO
inf4
sup–
accumulated by all three species was easily desorbed by 10 mm buffers at various pH values, 0.5 m NaCl, 10 mm Na2CO3 or 10 mm Na2SO4. No differences in the amount of desorption were observed between the various desorption agents used.
Correspondence to: G. M. Gadd 相似文献
9.
Denis Lemoine Thierry Jouenne Guy-Alain Junter 《Applied microbiology and biotechnology》1991,36(2):257-264
Summary A double-chambered bioreactor based on a composite immobilized-cell gel layer/microporous membrane structure was applied to the continuous denitrification of high-nitrate water. Immobilized denitrifying bacteria (Pseudomonas denitrificans) were provided with separate flows of nitrate and carbon (C) nutrient, with no contamination of the treated water by cell leakage from the gel. Using acetate (7.5 mm) as a C source and a C/N ratio of 3 (mol/mol), specific denitrification rates ranging from 15 to 25 g NO
inf3
sup–
· h–1 · – cm–2 membrane surface (50–85 g NO
inf3
sup–
· h–1 · cm–3 gel) were obtained. The denitrifying activity remained stable for several months. At the flow rate used (10 cm3 · h–1), the effluents contained noticeable amounts of NO
inf2
sup–
ions but the treated water remained uncontaminated by the carbon nutrient. Most NO
inf2
sup–
ions disappeared from the treated water in a second reactor connected in series. When fed with an unchlorinated sludge supernatant as C nutrient, immobilized bacteria performed efficient denitrification of water for only 3 weeks. Diffusion experiments showed that acetate ions diffused much less rapidly than NO
inf3
sup–
or NO
inf2
sup–
ions through the composite structure. Further developments of the system are considered. 相似文献
10.
Diurnal variation in hydrological variables and dissolved inorganic nutrients such as PO
inf4
sup3–
-P, N O
inf2
sup–
-N, NO
inf3
sup–
-N and NH
inf4
sup+
-N were studied in three interconnected biotopes including freshwater, marine and mangrove brackish water of the Kakinada coastal zone, Andhra Pradesh. Samples were collected at intervals of 3 hours, for a period of 24 hours. In the marine environment salinity varied from 26 to 32 whereas in the mangrove waters it fluctuated from 12 to 20 and in both biotopes salinity showed bimodal type of oscillation. Dissolved oxygen content was high in the mangrove waters during day time but decreased rapidly during the night hours. In the marine environment POf4
p3–-P concentration varied from 0.345 to 1.195 g at l–1, NO
inf3
sup–
-N from 1.03 to 6.62 g at l–1 and NO
inf2
sup–
-N from 0.086 to 0.506 g at l–1. The highest and the lowest concentrations of PO
inf4
sup3–
-P, NO
inf3
sup–
-N, NO
inf2
sup–
-N recorded in the mangrove waters were 0.790 and 0.325 g at l–1, 7.10 and 1.60 g at l–1 and 0.278 and 0.060 g at l–1, respectively. The concentration of PO
inf4
sup3–
-P, NO
inf3
sup–
-N and NO
inf2
sup–
-N were high in the freshwater canal, the maximum and minimum values being 1.110 and 0.730 g at l–1, 26.40 and 9.98 g at l–1 and 0.520 and 0.252 g at l–1 respectively. The concentration of ammonia was relatively high in the mangrove water. Gross and net primary production in the mangrove water was 4 times higher than in the marine biotope. There was no export of dissolved nutrients from the mangrove environment to the adjacent marine waters. 相似文献
11.
Inorganic-carbon transport was investigated in the eukaryotic marine microalgaeStichococcus minor, Nannochloropsis oculata and aMonallantus sp. Photosynthetic O2 evolution at constant inorganic-carbon concentration but varying pH showed thatS. minor had a greater capacity for CO2 rather than HCO
3
–
utilization but forN. oculata andMonallantus HCO
3
–
was the preferred source of inorganic carbon. All three microalgae had a low affinity for CO2 as shown by the measurement of inorganic-carbon-dependent photosynthetic O2 evolution at pH 5.0. At pH 8.3, where HCO
3
–
is the predominant form of inorganic carbon, the concentration of inorganic carbon required for half-maximal rate of photosynthetic O2 evolution [K
0.5 (CO2)] was 53 M forMonallantus sp. and 125 M forN. oculata, values compatible with HCO
3
–
transport. Neither extra- nor intracellular carbonic anhydrase was detected in these three microalgal species. It is concluded that these microalgae lack a specific transport system for CO2 but that HCO
3
–
transport occurs inN. oculata andMonallantus, and in the absence of intracellular carbonic anhydrase the conversion of HCO
3
–
to CO2 may be facilitated by the internal pH of the cell. 相似文献
12.
Wei-Min Wu Robert F. Hickey Mahendra K. Jain J. Gregory Zeikus 《Archives of microbiology》1993,159(1):57-65
Accumulation of formate to millimolar levels was observed during the growth of Methanobacterium formicicum species on H2–CO2. Hydrogen was also produced during formate metabolism by M. formicicum. The amount of formate accumulated in the medium or the amount H2 released in gas phase was influenced by the bicarbonate concentration. The formate hydrogenlyase system was constitutive but regulated by formate. When methanogenesis was inhibited by addition of 2-bromoethane sulfonate, M. formicicum synthesized formate from H2 plus HCO
inf3
sup-
or produced H2 from formate to a steady-state level at which point the Gibbs free energy (G) available for formate synthesis or H2 production was approximately -2 to -3 kJ/reaction. Formate conversion to methane was inhibited in the presence of high H2 pressure. The relative rates of conversion of formate and H2 were apparently controlled by the G available for formate synthesis, hydrogen production, methane production from formate and methane production from H2. Results from 14C-tracer tests indicated that a rapid isotopic exchange between HCOO- and HCO
inf3
sup-
occurred during the growth of M. formicicum on H2–CO2. Data from metabolism of 14C-labelled formate to methane suggested that formate was initially split to H2 and HCO
inf3
sup-
and then subsequently converted to methane. When molybdate was replaced with tungstate in the growth media, the growth of M. formicicum strain MF on H2–CO2 was inhibited although production of methane was not Formate synthesis from H2 was also inhibited. 相似文献
13.
14.
The ability of several high arctic plant species to utilize nitrate nitrogen under field conditions 总被引:2,自引:0,他引:2
The ability to utilize NO
inf3
sup–
in seven high arctic plant species from Truelove Lowland, Devon Island, Canada was investigated, using an in vivo assay of maximum potential nitrate reductase (NR) activity and applications of 15N. Plant species were selected on the basis of being characteristic of nutrient-poor and nutrient-rich habitats. In all species leaves were the dominant site of NR activity. Root NR activity was negligible in all species except Saxifraga cernua. NO
inf3
sup–
availability per se did not appear to limit NR activity of the species typically found on nutrient-poor sites (Dryas integrifolia, Saxifraga oppositifolia, and Salix arctica), or in Cerastium alpinum, as leaf NR activities remained low, even after NO
inf3
sup–
addition. 15NO
inf3
sup–
uptake was limited in D. integrifolia and Salix arctica. However, the lack of field induction of NR activity in C. alpinum and Saxifraga oppositifolia was not due to restricted nitrate uptake, as 15NO
inf3
sup–
labelled NO
inf3
sup–
entered the roots and shoots of both species. Leaf NR activity rates were low in three of the species typical of nutrient-rich habitats (O. digyna, P. radicatum and Saxifraga cernua), sampled from a site containing low soil NO
inf3
sup–
. Additions of NO
inf3
sup–
significantly increased leaf NR activity in these latter species, suggesting that potential NR activity was limited by the availability of NO
inf3
sup–
. 15N labelled NO
inf3
sup–
was taken up by O. digyna. P. radicatum and Saxifraga cernua. Although two species (D. integrifolia and Salix arctica) showed little utilization of NO
inf3
sup–
, we concluded that five of the seven selected high arctic plant species (C. alpinum, O. digyna, P. radicatum, Saxifraga cernua and Saxifraga oppositifolia) do have the potential to utilize NO
inf3
sup–
as a nitrogen source under field conditions, with the highest potential to utilize NO
inf3
sup–
occurring in three of the species typically found on fertile habitats. 相似文献
15.
The active species of CO2 , i.e. CO2 or HCO
3
–
–(H2CO3) utilized by enzymes catalyzing ferredoxin-linked carboxylation reactions was determined. The enzyme investigated was pyruvate synthase from Clostridium pasteurianum (EC 1.2.7.1; Pyruvate: ferredoxin oxidoreductase). Data were obtained which were compatible with those expected if CO2 is the active species.The dissociation constant (K
S) of the enzyme-CO2 complex was measured. At pH 7.2 K
Sfor CO2 of pyruvate synthase was found to be approximately 5 mM.Abbreviations Fd
ferredoxin
No distinctions are made between CO2, H2CO3, HCO
3
–
and CO
3
=
when the symbol CO2 is used. 相似文献
16.
Nitrogen and phosphorus uptake by the Brazilian kelp Laminaria abyssalis (Phaeophyta) in culture 总被引:1,自引:1,他引:0
The uptake of ammonium, nitrate and phosphate by laboratory-grown young sporophytes of Laminaria abyssalis was measured in a perturbed system (batch mode) at 18 °C and 35 ± 5 µE m–2 s–1 photon flux density. Uptake of all appeared to follow saturation-type nutrient uptake kinetics. The NO
inf3
sup–
(K
s = 14.0 µM, V
max = 5.0 µmol h–1 g–1 dry wt) and NH
inf4
sup+
(K
s = 4.6 µM, V
max= 2.0 µmol h–1 g–1 dry wt) were taken up simultaneously, although NH
inf4
sup+
was taken up more rapidly. Values of K
3 and V
max for phosphate were, respectively, 2.21 µM and 0.83 µmol h–1 g–1 dry wt. Nitrate and phosphate were both consumed in similar rates (V
max /Ks 0.37) at low concentrations. NH
inf4
sup+
, thus, might be a more efficient form of N fertilizer if artificial enrichment of seawater is used. 相似文献
17.
Gotthold Gäbel Susanne Vogler Holger Martens 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(4):419-426
Summary Unidirectional 22Na+ and 36Cl– fluxes were determined in short-circuited, stripped rumen mucosa from sheep by using the Ussing chamber technique. In both CO2/HCO
–
3
-containing and CO2/HCO
–
3
-free solutions, replacement of gluconate by short-chain fatty acids (SCFA, 39 mM) significantly enhanced mucosal-toserosal Na+ absorption without affecting the Cl– transport in the same direction. Short-chain fatty acid stimulation of Na+ transport was at least partly independent of Cl– and could almost completely be abolished by 1 mM mucosal amiloride, while stimulation of Na+ transport was enhanced by lowering the mucosal pH from 7.3 to 6.5. Similar to the SCFA action, raising the PCO2 in the mucosal bathing solution led to an increase in the amiloride-sensitive mucosal-to-serosal Na+ flux. Along with its effect on sodium transport, raising the PCO2 also stimulated chloride transport. The results are best explained by a model in which undissociated SCFA and/or CO2 permeate the cell membrane and produce a raise in intracellular H+ concentration. This stimulates an apical Na+/H+ exchange, leading to increased Na+ transport. The stimulatory effect of CO2 on Cl– transport is probably mediated by a Cl–/HCO
–
3
exchange mechanism in the apical membrane. Binding of SCFA anions to that exchange as described for the rat distal colon (Binder and Mehta 1989) probably does not play a major role in the rumen.Abbreviations
DIDS
4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid
-
G
t
transepithelial conductance (mS·cm-2)
-
HSCFA
undissociated short-chain fatty acids
-
J
ms
mucosal-to-serosal flux (Eq · cm-2 · h-1)
-
J
net
net flux (Eq · cm-2 · h-1)
-
J
sm
serosal-to-mucosal flux (Eq · cm-2 · h-1)
-
PD
transepithelial potential difference (mV)
-
SCFA
dissociated short-chain fatty acids
-
SCFA
short-chain fatty acids 相似文献
18.
Gunnar Nygaard 《Hydrobiologia》1991,211(3):195-226
60 desmids were identified from plankton samples collected during 20 years, bimonthly, or monthly in 5 of the years. Only 5 desmids were perennial, performing cell divisions in a frozen lake at PAR at only 5 cal cm –2 day –1, below ice-cover. The greatest number of desmids per 100 ml lake water was found in September; it never exceeded 150. Owing to a concentration of free CO2 of only 0.02 mM l–1 and a HCO
inf3
sup–
concentration of 0.002 mM l–1 the densities of desmid cells were often smaller than 1 cell per 100 ml lake water. A density of 1 cell per 1 ml was attained only by Staurastrum longipes, a desmid showing temporal variation. The relation of the compound phytoplankton quotient to two components of the CO2-system is discussed. Three new taxa are described: Staurastrum brachiatum Ralfs var. bicorne n. var., Staurastrum thomassonii n.sp. and Xanthidium antilopaeum Kütz. f. bimaculatum n.f.. 相似文献
19.
Russell F. Husted Loren H. Cohen Philip R. Steinmetz 《The Journal of membrane biology》1979,47(1):27-37
Summary Bicarbonate is transferred across the serosal (S) membrane of the epithelial cells of the turtle bladder in two directions. Cellular HCO
3
–
generated behind the H+ pump moves across this membrane into the serosal solution. This efflux of HCO
3
–
is inhibited by SITS (4-isothiocyano-4-acetamido-2,2-disulfonic stilbene). When HCO
3
–
is added to the serosal solution it is transported across the epithelium in exchange for absorbed Cl–. This secretory HCO
3
–
flow traverses the serosal cell membrane in the opposite direction. In this study the effects of serosal addition of 5×10–4
m SITS on HCO
3
–
secretion and Cl– absorption were examined. The rate of H+ secretion was brought to zero by an opposing pH gradient, and 20mm HCO
3
–
was added toS. HCO
3
–
secretion, measured by pH stat titration, was equivalent to the increase inMS Cl– flux after HCO
3
–
addition. Neither theSM flux of HCO
3
–
nor theMS flux of Cl– were affected by SITS. In the absence of electrochemical gradients, net Cl– absorption was observed only in the presence of HCO
3
–
in the media; under such conditions, unidirectional and net fluxes of Cl– were not altered by serosal or mucosal SITS. H+ secretion, however, measured simultaneously as the short-circuit current in ouabain-treated bladders decreased markedly after serosal SITS. The inhibition of the efflux of HCO
3
–
in series with the H+ pump and the failure of SITS to affect HCO
3
–
secretion and Cl– absorption suggest that the epithelium contains at least two types of transport systems for bicarbonate in the serosal membrane. 相似文献
20.
We investigated seasonal patterns of photosynthetic responses to CO2 concentrations in Spartina alterniflora Loisel, an aerenchymous halophyte grass, from a salt marsh of the Bay of Fundy (NB, Canada), and from plants grown from rhizome in controlled-environment chambers. From late May to August, CO2 compensation concentrations () of field-grown leaves varied between 2.5–10.7 cm3(CO2) m–3, with a mean of 5.4 cm3(CO2) m–3. From September onwards field leaves showed CO2 compensation concentrations from 6.6–21.1 cm3(CO2) m–3, with a mean of 13.1 cm3 m–3 well into the C3–C4 intermediate range. The seasonal variability in did not result from changing respiration, but rather from a sigmoidal response of net photosynthetic rate (P
N) to applied CO2 concentration, found in all tested leaves but which became more pronounced late in the season. One explanation for the sigmoidal response of P
N to external CO2 concentration could be internal delivery of CO2 from roots and rhizomes to bundle sheath cells via the aerenchyma, but the sigmoidal responses in S. alterniflora persisted out to the tips of leaves, while the aerenchyma extend only to mid-leaf. The sigmoidicity persisted when CO2 response curves were measured from low to high CO2, or from high to low CO2, and even when prolonged acclimation times were used at each CO2 concentration. 相似文献