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1.
Smith, J. R., Smith, F. A. and Walker, N. A. 1987. Potassiumtransport across the membrane of Chara. I. The relationshipbetween radioactive tracer influx and electrical conductance.J.exp. Bot. 38:731751. The 42K influx () and the electrical conductance (Gm) were measured simultaneously for the membraneof internodal cells of Chara australis as a function of theexternal [KCl] (K?. In bathing solutions of pH = 5?0, progressively increased from 20?5to 430?60 nmol m2 s1 and Gm increased from 0?36?0?02to 3?8?0?8 S m2 when K? was increased from 0?1 to 10mol m3. The resting membrane potential difference (p.d.)was approximately -135 mV for low K? and approached the expectedNernst equilibrium p.d. for K+ ions when K? > 1?0 mol m3.Measurements of 36Cl influx suggested that the 42K influx waspredominantly electrogenic. The equivalent Goldman permeabilityto K+ ions (Pk) was approximately 2030 nm s1 anddid not vary significantly with increasing K?. The equivalentconductance attributable to the electrogenic transport of K+ ions was calculated from assuming passive, independent diffusionof K+ ions and the ratio was found to be typically close to one. It was also found that themagnitudes of and Gm measuredsimultaneously for each individual cell were also well correlatedfor K? 1?0 mol m3, and that the slope of the line ofbest fit was close to one. For each K? it was found that theconductance not attributable to K+ translocation and presumablyassociated primarily with the transport of protons or theirequivalents was typically 0?20?5 Sm2. For K? >1?0 mol m3 the results indicated that the transport ofK+ ions was essentially independent, i.e. there was no evidencefor flux interactions. The results also indicated that the equivalentconductance derived from the measured 42K influx could usefullyindicate the fraction of the electrical conductance attributableto the translocation of K+ ions. Key words: Potassium, conductance, influx 相似文献
2.
Temperature and salinity effect on growth and chemical composition of Gyrodinium aureolum Hulburt in culture 总被引:1,自引:0,他引:1
A factorial experiment shows highly significant effects of temperature(12 522.5°C) and salinity (17.834 S) on thegrowth rate of Gyrodinium aureolum, with a significant temperature-salinityinteraction. The maximum growth rate of G aureolum is measuredto 0.61 div. day1 at 20°C and 22.3 S. Gyrodiniumaureolum does not grow at temperatures :10 °C or 25°Cand at salinities 12 S. The cellular content of carbon (C) andnitrogen (N) and the elemental ratios N/C, P/C and N/P are significantlyaffected by the temperature The cellular content of phosphorus(P) and the elemental ratios P/C and N/P vary significantlywith salinity Significant temperature-salinity interactionsare found for the cellular content of carbon, nitrogen and phosphorus.Variations in the N/P ratio indicate that G.aureolum has a largestorage capacity for phosphorus It is suggested that temperatureis one important limiting factor in the initiation of bloomsof G.aureolum in north European waters. 相似文献
3.
The freezing behaviour and relative importance of heterogeneousice nuclei in affecting supercooling of Citrus sinensis fruitswere studied. The size of an ice nucleation active (INA) Pseudomonassyringae pool inhabiting fruits was positively correlated withthe nucleation temperature (NT) of the plant tissue, with amean of 369 log colony forming units (CFU) fruit1 atNT25C. The INA bacterial pool was responsible for 23%of the nucleation events occurring at this temperature, and29% were attributed to an additional nucleating source. Thelatter was sensitive to bacterial ice nucleation inhibitors,it occupied a different microniche from that of P. syringaenuclei, yet was neither a fungus nor any of the bacterial strainsever reported as active. Treatment with an ice nucleation inactivebacterium antagonistic to INA bacteria, a lentil lectin, a protease,and guanidine reduced mean nucleation temperatures (MNT) offruits to 258, 266, 421, and452C,respectively, compared to a MNT167C for the controls.Thus, the citrus-associated nucleator apparently contained activeproteinaceous components but was void of carbohydrate-like groupsreportedly encountered at or near the bacterial ice nucleatingsite. Despite the different origins of citrus nuclei, bacterialnucleation inhibitors reduced nucleation in the field by 50%at NT25C, an effect probably exerted throughthe proteinaceous site possessed by both nuclei. Key words: Citrus, ice nucleation, INA bacteria, supercooling 相似文献
4.
All three races of Neotricula aperta, an epilithic, schistosometransmitting, snail of the Mekong and Mul rivers of NortheastThailand and southern Laos, were found to take up acetate froma dilute solution. After 48 h incubation the mean specific netuptake rates (µmol1 g1 h1), from750 µM acetate, were: 1.86, -race; 1.39, ß-raceand 3.25, y-race. Over 48 h the snails were able to achievereductions in the ambient acetate concentration of up to 60%.Incubations under bacteriostatis suggested that bacteria arenot involved in the uptake of acetate by N. aperta. The uptakecharacteristics conform to the Michaelis-Menten model. The transportconstants, Jmax (µmol1 g1 h1) andKt (µM) were 1.10 and 102 respectively (-race). Racialdifferences in uptake characteristics are discussed in relationto micro-habitat differences. HPLC indicated concentrations of acetate in y-N. aperta microhabitatsof around 325 µM. This suggests a pool size sufficientto satisfy only 6% of the snail's basal metabolic rate (BMR).Levels within the epilithic aufwuchs, however, are probablyhigh enough to provide for more than 50% of the BMR. The possible role of acetate in the energy metabolism of N.aperta is discussed. Short-chain carboxylic acids (such as acetate),arising from the decomposition of the aufwuchs, could representsources of fermentable organics that may be taken up by N. apertasnails and used to supplement their nutrition during times offood shortage. However, further investigations involving 14C-labellingtechniques are required. The findings of this investigationhave implications for the chemical ecology and life-cycle ofN. aperta. (Received 16 June 1994; accepted 28 July 1994) 相似文献
5.
In Trifolium repens L. there were immediate transient depolarizationsof the membrane electropotential (Evo) when KH2PO4 was addedto phosphate-free media, but these were of the same magnitudeas the controls (K2SO4 and KCI). Furthermore, the extents ofdepolarization were the same as the expected effect of the addedK+ calculated using the Goldman equation. There was no significantdepolarization on adding H3PO4 to buffered media. Consequently,there was no evidence for a depolarization caused by phosphate.This result provides evidence that the H+H2PO4 symportin roots of T. repens operates with a stoichiometry of 1: 1. In a group of control plants ( + P plants) and a group whichwere stressed by reducing the supply of phosphate ( Pplants), the P plants had lower values for Evo than+P plants ( 118 mV and 130 mV, respectively).The absence of phosphate from the measurement media also reducedEvo (mean effect = 9 mV). A significant difference in Evo between P and + P plants persisted when phosphate was addedto P plants. The electropotential difference acrossthe tonoplast (Evo) in P plants became more positivewith time. Key words: White clover, membrane transport, roots, tonoplast, symport 相似文献
6.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m3 CaCl2 r, P, Y and were20.7±4.6 µm min1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min1MPa1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m3 KC1 these parametersbecame 12.3±3.5 µm min1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min1MPa1. After 24 h osmotic adjustment in 150 mol m3mannitol/0.5 mol m3 CaCl2 r= 19.6±4.2 µmmin1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min1 MPa01, respectively.After 24 h growth in 350 mol m3 mannitol/0.5 mol m3CaCl2 r= 13.3±4.1 µm min1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min1MPa1. During osmotic adjustment in 200 mol m3mannitol/0.5 mol m3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min1MPa1. Therefore, Y and are influenced by 10 mol m3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur 相似文献
7.
Enhanced suicidal death of erythrocytes from gene-targeted mice lacking the Cl-/HCO(3)(-) exchanger AE1 总被引:2,自引:0,他引:2
Akel A Wagner CA Kovacikova J Kasinathan RS Kiedaisch V Koka S Alper SL Bernhardt I Wieder T Huber SM Lang F 《American journal of physiology. Cell physiology》2007,292(5):C1759-C1767
Genetic defects of anion exchanger 1 (AE1) may lead to spherocytic erythrocyte morphology, severe hemolytic anemia, and/or cation leak. In normal erythrocytes, osmotic shock, Cl removal, and energy depletion activate Ca2+-permeable cation channels with Ca2+-induced suicidal erythrocyte death, i.e., surface exposure of phosphatidylserine, cell shrinkage, and membrane blebbing, all features typical for apoptosis of nucleated cells. The present experiments explored whether AE1 deficiency favors suicidal erythrocyte death. Peripheral blood erythrocyte numbers were significantly smaller in gene-targeted mice lacking AE1 (AE1/ mice) than in their wild-type littermates (AE1+/+ mice) despite increased percentages of reticulocytes (AE1/: 49%, AE1+/+: 2%), an indicator of enhanced erythropoiesis. Annexin binding, reflecting phosphatidylserine exposure, was significantly larger in AE1/erythrocytes/reticulocytes (10%) than in AE1+/+ erythrocytes (1%). Osmotic shock (addition of 400 mM sucrose), Cl removal (replacement with gluconate), or energy depletion (removal of glucose) led to significantly stronger annexin binding in AE1/ erythrocytes/reticulocytes than in AE1+/+ erythrocytes. The increase of annexin binding following exposure to the Ca2+ ionophore ionomycin (1 µM) was, however, similar in AE1/ and in AE1+/+ erythrocytes. Fluo3 fluorescence revealed markedly increased cytosolic Ca2+ permeability in AE1/ erythrocytes/reticulocytes. Clearance of carboxyfluorescein diacetate succinimidyl ester-labeled erythrocytes/reticulocytes from circulating blood was more rapid in AE1/ mice than in AE1+/+ mice and was accelerated by ionomycin treatment in both genotypes. In conclusion, lack of AE1 is associated with enhanced Ca2+ entry and subsequent scrambling of cell membrane phospholipids. annexin; cell volume; osmolarity; phosphatidylserine; energy depletion 相似文献
8.
A Ras-related NTP-binding protein was partially purified froma membrane fraction derived from the mycelia of Neurospora crassa.[-32P]ATP and [-32P]GTP were incubated with mem brane and solublefractions which were then irradiated with UV light to inducecrosslinking of tightly bound nucleotides. After SDS-polyacrylamidegel electrophoresis, blotting onto a nitrocellulose filter andautoradiography it was apparent that most of the proteins thatbound [-32P]-GTP also bound [-32P]ATP. Pretreatment of the membranefraction with Ras-specific antibody effectively blocked thebinding of [-32P]ATP and [-32P]GTP to several ATP-GTP-bindingproteins. The band of a protein with a molecular weight of 26kDa on the SDS-polyacrylamide gel cross-reacted strongly withthe Ras-specific antibody. The protein was extracted from thegel and further purified by repeated gel electrophoresis. Thepurified protein bound [-32P]ATP, [-32P]-GTP, [-32P]CTP and[-32P]UTP at 1.6x10 M and was autophosphorylated in thepresence of [-32P]ATP and [-32P]GTP at 1.7x10 M. Pretreatmentof the protein with Ras-specific antibody partially blockedthe autophosphorylation in the presence of these nucleotides.The binding of [-32P]ATP to the NTP-binding protein was blockedby addition of ATP at 104103 M. ATP ata concentration of 104 M prevented the binding of [-32P]to a greater extent than did GTP at the same concentration.Binding of [-32P]CTP and [-32P]UTP to the protein was also observed. (Received October 7, 1991; Accepted July 14, 1992) 相似文献
9.
Ethylene and Ethane Production in 2,4-D Treated and Salt Treated Tobacco Tissue Cultures 总被引:1,自引:0,他引:1
Gas chromatography was used to measure ethylene (ethene) andethane production by tobacco (Nicotiana tabacum cv. Wisconsinno. 38) callus tissues grown on media containing inorganic saltsaccording to Murashige and Skoog (1962), sucrose, myo-inositol,thiamine-HCl kinetic according to Linsmaier and Skoog (1965),and either 2,4-dichiorophenoxyacetic acid (2,4-D) in the range0100 mgl1 or 2 mgl1 indoi-3-ylacetic acidplus NaCl in the range 0200 Meq l1. Ethylene productionrates were high (> 500 nl h1 g1 fresh weight)initially in all treatments. Subsequently, ethylene productiondeclined in rapidly growing cultures but remained high in moderatelyand severely 2,4-D (> 0·5 mgl1) stressed andin severely NaCl (150 Meql1) stressed cultures. Highinitial rates of ethane production (> 200 nl h1 g1fresh weight) were obtained under conditions of severe stresscaused by 2,4-D or NaCl but not in control or moderately inhibitedcultures. With further incubation ethane production declinedin the severely stressed cultures. It is concluded that ethyleneproduction can be used as an index of moderate 2,4-D stressand severe NaCl stress by virtue of the high persisting ratesof ethylene production in stressed cultures. Ethane productioncan be used as an early index of severe stress caused by either2,4-D or NaCl in vitro. Nicotiana tabacum L., tobacco, ethylene, ethenen, ethane, 2,4-dichlorophenoxyacetic acid, auxin, stress, callus tissue 相似文献
10.
Journal of Plankton Research, 11, 12731295, 1989. The values of P/U0 (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 12891290) and severalequations (footnote b of Table I; p. 1290, lines 34)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studiedaGnathobaseof trunklimb number. bP = 8µU0/(b(1 21nt + 1/6(t2) - 1/144(t4))), whereP = pressure drop in dyn cm2, =3.1416, U0 = fluid velocityin cm s1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s1cm2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm2 (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm2 (with fluid velocity of 0.07 cms1) allocates only 2171 ergs h1 to filtrationof a total energy expenditure of 104 ergs h1 [filtrationenergy (ergs h1) = area (cm2) x pressure drop (dyn cm2)x 3600 (s h1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h1) = respiration(0.05 µl O2 ind1 h1 consumed; Gophen, 1976)x conversion factor (2 x 105 ergs µl1 O2). Withan estimated 0.034 mm2 in filter area, fluid velocity of 0.041cm s1 and respiration of 1.8 x 104 ergs h1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s1for Ceriodaphnia, 0.2 cm s1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s1 for Ceriodaphnia and 0.041 cm s1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection. 相似文献
11.
Factors controlling primary production in a hypertrophic lake (Hartbeespoort Dam, South Africa) 总被引:5,自引:0,他引:5
The physical factors controlling algal primary production weredemonstrated from data collected for a hypertrophic lake. Amaxranged between 12.4 and 5916 mg C m3 h1. Arealrates (A) varied between 46.9 and 3381 mg C m2 h1.The factors permitting and controlling production were subjectivelyseparated into two categories. In category 1, nutrients (N +P), which were in overabundance, permitted large standing cropsof Microcystis aeruginosa to develop (>1000 µg chla 11). Wind patterns determined the dramatic spatialand temporal changes in algal standing crop which could dropto 2.7 µg chl a 11. In category 2 were the factorswhich affected the rate processes. The buoyancy mechanism ofMicrocystis usually kept the alga in the euphotic zone. A powerrelationship (r = 0.92, n = 54) between A and Amax/min showedthat with increasing phytoplankton vertical stratification,Amax was increasingly important in the integral. The saturationparameter IK and photosynthetic capacity were temperature dependent.Variations of A were significantly related to changes in watercolumn stability (g cm cm2) because both axes of thephotosynthesis depth-profile were affected by stability changes. 相似文献
12.
Pseudomonas aeruginosa inhibits endocytic recycling of CFTR in polarized human airway epithelial cells 总被引:1,自引:0,他引:1
Swiatecka-Urban A Moreau-Marquis S Maceachran DP Connolly JP Stanton CR Su JR Barnaby R O'toole GA Stanton BA 《American journal of physiology. Cell physiology》2006,290(3):C862-C872
The most common mutation in the CFTR gene in individuals with cystic fibrosis (CF), F508, leads to the absence of CFTR Cl channels in the apical plasma membrane, which in turn results in impairment of mucociliary clearance, the first line of defense against inhaled bacteria. Pseudomonas aeruginosa is particularly successful at colonizing and chronically infecting the lungs and is responsible for the majority of morbidity and mortality in patients with CF. Rescue of F508-CFTR by reduced temperature or chemical means reveals that the protein is at least partially functional as a Cl channel. Thus current research efforts have focused on identification of drugs that restore the presence of CFTR in the apical membrane to alleviate the symptoms of CF. Because little is known about the effects of P. aeruginosa on CFTR in the apical membrane, whether P. aeruginosa will affect the efficacy of new drugs designed to restore the plasma membrane expression of CFTR is unknown. Accordingly, the objective of the present study was to determine whether P. aeruginosa affects CFTR-mediated Cl secretion in polarized human airway epithelial cells. We report herein that a cell-free filtrate of P. aeruginosa reduced CFTR-mediated transepithelial Cl secretion by inhibiting the endocytic recycling of CFTR and thus the number of WT-CFTR and F508-CFTR Cl channels in the apical membrane in polarized human airway epithelial cells. These data suggest that chronic infection with P. aeruginosa may interfere with therapeutic strategies aimed at increasing the apical membrane expression of F508-CFTR. cystic fibrosis 相似文献
13.
Primary production was measured for 7 years, using the in situ14C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m3. The maximum volumetric rate of production(Amax) was 12->8800 mg C m3 h1 with areal productions(A) of 69->3300 mg C m2 h1 for euphotic zonedepths of <0.58.4 m. The intrinsic parameters of phytoplanktonproduction (, Amax/B, Ik) indicated that the phytoplankton populationwas adapted to high light levels. Both Amax/B and Ik were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm2 h1,while the measured rate was 2.5 g Cm2 h1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis. 相似文献
14.
Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves 总被引:1,自引:0,他引:1
The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 1219 days' duration reachedchl concentrations of 1050 µg1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30100 µE m2S1and the growth rate was reduced by about 30% at 5001000µE m2S1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm2S1 chl/C ratios were also below maximum at PFDsbelow 4050 µE m2S1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)1h1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1sat (160330 µE m2S1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for Isat (560 µE m2S1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes. 相似文献
15.
Effects of light flux density (LFD) during growth and uptakeassay on induction of transport system and kinetics of transport were studied using the Azolla pinnata-Anabaena azollae association (Azolla). Theinduction and uptake kinetics of the transport system were determined using an automated system that measuredthe NO3 concentration in the growth medium as a function oftime, using an on-line high performance liquid chromatograph(HPLC) with a UV-VIS detector. Full induction of the transport system required about 1.5 to 2.0 h and occurred without any apparent lag phase,regardless of the LFD provided. The level of induction of transport of Azolla grown at 600 µmol m2s1 LFD was higher than for that grown at 100 µmolm2 s1. Similarly, 600 µmol m1 s1LFD during the assay resulted in a higher level of inductionthan did 100 umol m2 s1. An increase in the LFDeither during the growth or the assay period increased the uptake rate; however, an increase in LFD duringthe latter period had greater effect. Azolla grown and assayedat 600 umol m2 s1 had the highest uptake rate. The uptake rate at 50 cm3 m3ambient CO2 concentration was initially higher than at 305 cm3m3, but the uptake rate decreased rapidly with time andeventually dropped below that at 305 cm3 m3 CO2. Thesedata suggest that the energy required for transport in Azolla may bypass the photosynthetic CO2 fixationand carbon-cycling. Key words: carbon dioxide, concentration dependence, light flux density, uptake 相似文献
16.
Micropropagation of Pissardi Plum 总被引:2,自引:0,他引:2
An efficient medium for multiplication of Prunus cerasifera,J. F. Ehrh. cv. Atropurpurea, Pissardi plum, consistedof Linsmaier-Skoog basal medium (LS) supplemented with 3% sucrose,10mg 11 N4-(2-isopentenyl) adenine (2iP), and 162 mg11 phloroglucinol (Phl). Phl in the medium significantlyenhanced growth (P < 0.1 %) over cultures maintained on LSmedium with 10 mg 11 2iP and no Phl. Plantlets were rootedon a half-strength Murashige-Skoog (MS) medium supplementedwith 0.2 mg 11 indole-3-butyric acid (IBA). Prunus cerasifera, Pissardi plum, micropropagation, phloroglucinol, N6-(2-isopentenyl) adenine 相似文献
17.
Diel vertical studies of zooplankton community filtration rates(CFR) were undertaken in situ over two annual cycles in a shelteredbay of Lake le Roux, a large silt-laden oligotrophic reservoirin the arid subtropics of South Africa. The grazer communitywas dominated by a copepod, Meradiaptomus meridianus, whileDaphnia gibba. D. barbara and Moina brachiara accounted forthe balance. Spot estimates of CFR varied from 0.1 to 75% d1( = 12.2) in the upper 10 m, while depth-integrated values ranged seasonally from 0.1 to 15% d1 ( = 7.4). Most variation in CFR was attributable toseasonal changes in grazer biomass (0408, = 58.2 µg 11 or 31000, 360 mg m2 dry wt), and temperature (1222C). Thesevariables are used to construct multiple linear regression modelsfor the prediction of CFR in this system. Some higher CFR values(up to 260% d1 were measured in wanner (up to 26.5C)surface waters with an unusually rich zooplankion (786 rg 11).No significant did vertical changes in CFR or grazer biomasswere observed. Both variables declined sharply with depth. Inorganicturbidity dominated the seston, and algal carbon probably accountedon average for less than about 20% of the total POC available.The feeding responses of this turbid-water community were generallyconsistent with observations made on other assemblages, apartfrom seemingly high specific filtration rates which, atypically,were inversely related to temperature. 相似文献
18.
The luciferin-luciferase method was used to determine ATP extractedfrom darkmaintained and light-exposed samples of the green algaChlorella pyrenoidosa and of the blue-green alga Anacystis nidulans.A few measurements on Synechococcus lividus (a bluegreen thermophile,clone 65?C) are also reported.
- The light-minus-dark ATP levels (ATP) from aerobic cells ofChlorella and Anacystis were negative; however, ATP from Synechococcuswas positive. Large positive ATP was obtained in regularly grown(RG: moderate light) Chlorella treated with oligomycin; darklevels were reduced, light levels remained essentially unaffected.In high-light exposed (HLE) Chlorella, oligomycin reduced bothlight and dark ATP levels, but positive ATP was still obtained.However, in Anacystis, which has a different organization ofthylakoid membrane, oligomycin severely reduced both the lightand the dark ATP levels and the ATP remained negative.
- Theoligomycin (12 µM) treated Chlorella and the untreatedAnacystis and Synechococcus show the presence of cyclic photophosphorylationunder conditions in which the non-cyclic electron flow fromphotosystem II to photosystem I is blocked by 10 µM 3-(3,4-dichlorophenyl)-l,l-dimethylurea(DCMU), or not allowed to operate by the absence of CO2. Cyclicphotophosphorylation ranged from 1030% of the maximumATP in RG, to 4050% in HLE Chlorella. In RG Chlorella,cyclic and non-cyclic (in the absence of DCMU) photophosphorylation(ATP) saturate at about 103 ergs cm2 sec1 and104 ergs cm2 sec1 and 104 ergs cm2 sec1red (>640 nm) light, respectively; a lag was observed inthe light curve.
- In Chlorella, the addition of the photosystemI electron acceptormethyl viologen (MV; 1 mM) increased ATPby twofold. Furtheraddition of DCMU (25 µm) reduced thisto the level observedwith DCMU alone. If 1 mM reduced dichlorophenolindophenol orphenazine methosulphate (DCPIPH2 or PMSH2, respectively)wasadded along with DCMU, the ATP level was 3040% ofthecontrol. Further addition of MV increased the JATP to be7080%of that of the control. These and other resultsconfirm thepresence of both non-cyclic and cyclic photophosphorylationin vivo, the former predominating in Chlorella, and the latterin Anacystis and Synechococcus.
19.
Duhamel TA Green HJ Perco JG Ouyang J 《American journal of physiology. Cell physiology》2006,291(4):C607-C617
We employed a glycogen-depleting session of exercise followed by a low-carbohydrate (CHO) diet to investigate modifications that occur in muscle sarcoplasmic reticulum (SR) Ca2+-cycling properties compared with low-CHO diet alone. SR properties were assessed in nine untrained males [peak aerobic power (O2 peak) = 43.6 ± 2.6 (SE) ml·kg1·min1] during prolonged cycle exercise to fatigue performed at 58% O2 peak after 4 days of low-CHO diet (Lo CHO) and after glycogen-depleting exercise plus 4 days of low-CHO (Ex+Lo CHO). Compared with Lo CHO, Ex+Lo CHO resulted in 12% lower (P < 0.05) resting maximal Ca2+-ATPase activity (Vmax = 174 ± 12 vs. 153 ± 10 µmol·g protein1·min1) and smaller reduction in Vmax induced during exercise. A similar effect was observed for Ca2+ uptake. The Hill coefficient, defined as slope of the relationship between cytosolic free Ca2+ concentration and Ca2+-ATPase activity, was higher (P < 0.05) at rest (2.07 ± 0.15 vs. 1.90 ± 0.10) with Ex+Lo CHO, an effect that persisted throughout the exercise. The coupling ratio, defined as the ratio of Ca2+ uptake to Vmax, was 2330% elevated (P < 0.05) at rest and during the first 60 min of exercise with Ex+Lo CHO. The 27 and 34% reductions (P < 0.05) in phase 1 and phase 2 Ca2+ release, respectively, observed during exercise with Lo CHO were not altered by Ex+Lo CHO. These results indicate that when prolonged exercise precedes a short-term Lo CHO diet, Ca2+ sequestration properties and efficiency are improved compared with those during Lo CHO alone. calcium cycling; vastus lateralis; contractile activity; glycogen; phosphorylation potential 相似文献
20.
Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. 42K fluxes and the electrical current as a functionof membrane voltage.J. exp. Bot. 38: 752777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the 42K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK+ ions. There was thus no evidence for the interaction of K+ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K+ ions.When the external [K+] = 10 mol m3, the average valueof was 0?85 for Vm > 125 mV and 07?5 for Vm <150 mV. When the external [K+] = 0?1 mol m3, was 0?6 for Vm < 80 mV and 0?1 for Vm > 250mV. It was also found that the conductance associated with K+transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio 相似文献