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1.
Differential filtration was used to apportion [32p]orthophosphate(P1) uptake to predominantly bacterial (<3 µm) or algal(>3 µm) components of Lake Kinneret microplankton.Bacteria generally showed preferential 32Pi uptake in comparisonwith algae. Nevertheless, in most cases, the relative proportionof 32P counts retained on 3 µm filters was greater thanthe proportion of 14C counts from heterotrophic bacterial incorporationof [14Clglucose, indicating that algae were competing for Piwith bacteria with some measure of success. Most time courseexperiments did not show any consistent transfer of 32P frombacteria to algae. The addition of a bacterial inhibitor (garamycin)caused a relative increase in the proportion of algal to bacterial32Pi uptake. Added organic P substrates lowered the amount of32Pi uptake and appeared to be preferentially utilized by bacteria.Apparent residence times for Pi in Lake Kinneret ranged from0.4 h (prior to overturn) to 17.4 h during bomothermy. Despitelow ambient Pi concentrations, P limitation in Lake Kinneretis not as extreme as in many other aquatic environments. 相似文献
2.
Differential uptake of orthophosphate and organic phosphorus substrates by bacteria and algae in Lake Kinneret 总被引:6,自引:0,他引:6
The availability of six organic phosphorus substrates (OPS)to serve as sources of this nutrient for natural populationsof phytoplanktonic algae and bacteria was tested by measuringthe degree to which the organic substrates decreased uptakeof [32P]orthophosphate (32Pi). When added to samples of LakeKinneret water, six organo-phosphorus compounds usually loweredthe amount of 32Pi] taken up by microplankton retained on 0.2-µfilters.In contrast, OPS addition generally stimulated 32Pi uptake intothe mainly algal fraction (>3 µm), indicating thatthe bacteria were mostly responsible for utilising OPS. Thesparing effect of OPS addition on 32P1 uptake was very fast,suggestingthat the micro-organisms possessed constitutive or rapidly inducedenzyme systems to exploit the OPS.The results of this studyindicate that a significant flux of phosphorus may pass viaDOP into microbiota, especially bacteria, in some aquatic systems. 相似文献
3.
Ca2+ influx through alpha1S DHPR may play a role in regulating Ca2+ release from RyR1 in skeletal muscle 总被引:1,自引:0,他引:1
Shtifman A Paolini C López JR Allen PD Protasi F 《American journal of physiology. Cell physiology》2004,287(1):C73-C78
Skeletal muscle fiber types differ in their contents of total phosphate, which includes inorganic phosphate (Pi) and high-energy organic pools of ATP and phosphocreatine (PCr). At steady state, uptake of Pi into the cell must equal the rate of efflux, which is expected to be a function of intracellular Pi concentration. We measured 32P-labeled Pi uptake rates in different muscle fiber types to determine whether they are proportional to cellular Pi content. Pi uptake rates in isolated, perfused rat hindlimb muscles were linear over time and highest in soleus (2.42 ± 0.17 µmol·g1·h1), lower in red gastrocnemius (1.31 ± 0.11 µmol·g1·h1), and lowest in white gastrocnemius (0.49 ± 0.06 µmol·g1·h1). Reasonably similar rates were obtained in vivo. Pi uptake rates at plasma Pi concentrations of 0.31.7 mM confirm that the Pi uptake process is nearly saturated at normal plasma Pi levels. Pi uptake rate correlated with cellular Pi content (r = 0.99) but varied inversely with total phosphate content. Sodium-phosphate cotransporter (PiT-1) protein expression in soleus and red gastrocnemius were similar to each other and seven- to eightfold greater than PiT-1 expression in white gastrocnemius. That the PiT-1 expression pattern did not match the pattern of Pi uptake across fiber types implies that other factors are involved in regulating Pi uptake in skeletal muscle. Furthermore, fractional turnover of the cellular Pi pool (0.67, 0.57, and 0.33 h1 in soleus, red gastrocnemius, and white gastrocnemius, respectively) varies among fiber types, indicating differential management of intracellular Pi, likely due to differences in resistance to Pi efflux from the fiber. inorganic phosphate; sodium-inorganic phosphate transporters; PiT-2; inorganic phosphate efflux 相似文献
4.
The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO2-concentrations between 200 and 1200 µmolmol-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO2 balance, usingnitrous oxide (N2O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO2 concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyPmax 5-9 g m-2 h-1 CO2 uptake; ratio Pmax/LAI 1·5-3 gm-2 h-1; light compensation point 32-86 µmol s-1 m-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol-1 and CO2 compensation point 18-54 µmolmol-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO2, CO2 balance, CO2 use efficiency, cucumber, Cucumis sativus L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas 相似文献
5.
Kinetic Characterization of Two Phosphate Uptake Systems with Different Affinities in Suspension-Cultured Catharanthus roseus Protoplasts 总被引:2,自引:0,他引:2
We studied the kinetics of inorganic phosphate (P1) uptake from0.11,000 µM P1 by protoplasts from suspension-culturedcells of Catharanthus roseus (L.) G. Don. Concentration dependenceof [32P]P1 uptake revealed two kinetically different uptakesystems, a high-affinity system and a low-affinity system, withKm values of 3.0 and 47 µM, respectively. Protoplastsfrom cells grown in Pi-rich media had a medium level of thelow-affinity activity and a very low level of the high-affinityactivity. It appeared low-affinity system is expressed constitutively,while the high-affinity system is regulated by the availabilityof Pi. When cells grown in a Pi-rich media were transferredto Pi-depleted media, the high-affinity activity increased significantlyafter 2 d, but the low-affinity activity was barely changed.Upon addition of 10 mM Pi, the high level of the high-affinityactivity fell to almost undetectable level in 1d. Both uptakesystems exhibited maximum activity between pH 5 and 6.
1 Present address: Tokyo Research Laboratories, Kyowa HakkoKogyo Co., Ltd., 3-6-6 Asahi-cho, Machida, Tokyo, 194 Japan. 相似文献
6.
Nitrogen dynamics in lower Narragansett Bay, Rhode Island. I. Uptake by size-fractionated phytoplankton populations 总被引:1,自引:0,他引:1
The contribution of nanoplankton (< 10 µm fraction)to winter spring (1977 78) and summer (1978,1979) phytoplankton nitrogen dynamics in lower NarragansettBay was estimated from ammonium, nitrate and urea uptake ratesmeasured by 15N tracer methods. During the winter spring,an average of 80% of chlorophyll a and nitrogen uptake was associatedwith phytoplankton retained by a 10 µm screen. In contrast,means of 51 58% of the summer chlorophyll a standingcrops and 64 70% of nitrogen uptake were associatedwith cells passing a 10 µm screen. Specific uptake ratesof winter spring nanoplankton populations were consistentlylower than those of the total population. Specific uptake ratesof fractionated and unfractionated summer populations were notsignificantly different. Ammonium uptake averaged between 50and 67% of the total nitrogen uptake for both the total populationand the < 10µm fraction. The total population and the10 µm fraction displayed similar preferences for individualnitrogen species. Though composed of smaller cells, flagellatedominated nanoplankton assemblages may not necessarily takeup nitrogen at faster rates than diatom dominated assemblagesof larger phytoplankters in natural populations.
1Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia 相似文献
7.
Studies were conducted over a 13 month period at four pelagicsites in eutrophic Lake Okeechobee, Florida (USA), in orderto quantify carbon (C) uptake rates by size-fractionated phytoplankton,and subsequent transfers of C to zooplankton. This was accomplishedusing laboratory 14C tracer methods and natural plankton assemblages.The annual biomass of picoplankton (<2 µm), nanoplankton(220 µm) and microplankton (<20 µm averaged60, 389 and 100 µg C 11 respectively, while correspondingrates of C uptake averaged 7, 51 and 13 µg C11h1. The biomass of microzooplankton (40200 µm)and macrozooplankton (<200 µm averaged 18 and 60 µgC 11, respectively, while C uptake rates by these herbivoregroups averaged 2 and 3 µg C 11 h1. Therewere no strong seasonal patterns in any of the plankton metrics.The ratio of zooplankton to phytoplankton C uptake averaged7% over the course of the study. This low value is typical ofthat observed in eutrophic temperate lakes with small zooplanktonand large inedible phytoplankton, and indicates ineffectiveC transfer in the grazing food chain. On a single occasion,there was a high density (<40 11) of Daphnia lumholrzii,a large-bodied exotic cladoceran. At that time, zooplanktoncommunity C uptake was <20 µg C 11 h1and the ratio of zooplankton to phytoplankton C uptake was near30%. If D.lumholrzii proliferates in Lake Okeechobee and theother Florida lakes where it has recently been observed, itmay substantially alter planktonic C dynamics. 相似文献
8.
Fisher T.R.; Morrissey K.M.; Carlson P.R.; Alves L.F.; Melack J.M. 《Journal of plankton research》1988,10(1):7-29
Uptake of ammonium and nitrate by plankton was measured in tropicalLake Calado, Brazil. Nitrate uptake was strongly influencedby light and was light saturated at {small tilde}340 µEm2 s1. In contrast, uptake of ammonium was lessinfluenced by light, and saturated at {small tilde}250 µEm2 s1. Uptake rates of both forms of nitrogenwere inhibited by up to 80% at light intensities higher thanthose required for saturation. Concentrations of ammonium andnitrate also had a strong influence on uptake rates. Half-saturationconstants (0.35 µM) were usually greater than ambientconcentrations (0.10.6 µM), indicating that uptakerates at ambient concentrations were less than one-half of thesaturated rates. Ammonium is the more important type of inorganicnitrogen for plankton of Lake Calado because nitrate concentrationsremain low to undetectable except during periodic inputs ofnitrate-rich water from the Amazon River. Using the observeddependence of uptake on concentration and light, maximum uptakerates per unit chlorophyll were computed to be in reasonableagreement with rates derived from PBm values for carbon uptake.
1 Present address: Florida Department of Natural Resources,Marine Research Laboratory, St Petersburg, FL 33701, USA 相似文献
9.
Dark uptake of inorganic 14C by offshore plankton was measuredat two depths at 36 stations in the Atlantic Ocean from 52°Sto 26°N, mainly along 30°W. The samples were incubatedfor 2 h with and without inhibition of biological activity withHgCl2. In addition, six time course experiments were performed.The mean dark uptake rate varied from 0.68 to 4.82 (µmolC m3 h1 over the transect and showed a significantpositive relationship with chlorophyll a. The dark uptake wasusually >5% of the maximum photosynthetic capacity (Pm),and higher values relative to Pm were associated with low valuesof Pm and not with high absolute dark values. A linear relationshipbetween dark uptake and Pm was found with a background value(y-axis intercept) of 0.51 (µmol C m3 h1and a slope of 0.77% of Pm. A major fraction of the dark signal,6680% of the total signal, persisted in bottles treatedwith HgCl2, indicating that most of the dark signal was independentof biological activity. Time course experiments showed a lineardark uptake with time for the first hours, whereafter the uptakeceased. At stations with low concentrations of inorganic nitrogen[>1 (µmol (NH4++NO3)], a second stage was observedafter 38 h, probably due to an increase in bacterialactivity. The results suggest three mechanisms for the darkvalue in short-term incubations in oligotrophic waters. A backgroundvalue independent of biomass and incubation time which was thedominant part of the dark signal in samples with very low phytoplanktonbiomass (>0.3 p-g Chi a 1"). Another important part was residualsof 14C associated with plankton, probably adsorbed to compoundsinside the cells. This fraction was dominant in short-term incubationsat chlorophyll concentrations >0.3 p.g Chi a H. Active uptakeby living cells (total minus HgCl2 uptake) wasonly a minor part of the dark signal in short-term incubations,but dominated at longer incubation time (>39 h), probablydriven by an increase in bacterial activity. A significant enhancementof the non-photosynthetic uptake of 14C was observed in light,probably associated with a carbon-concentrating mechanism inphytoplankton or light stimulation of ß-carboxylationactivity. The results strongly suggest that dark values shouldbe subtracted from the light uptake. This correction is particularlyimportant when photosynthetic rates are low, e.g. at low lightor in short-term incubations where a time-zero background becomesa significant part of the total uptake in light.
Present address: National Environmental Research Institute,Department of Marine Ecology and Microbiology, Frederiksborgvej399, PO Box 358, DK-4000 Roskilde, Denmark 相似文献
10.
The uptake of the rubidium ion by well-washed disks of carrotparenchyma has been determined at 0·2° C and 25°C., in the presence and absence of 104M. dinitrophenol,from solutions of rubidium chloride containing 0·5 and5·0 meq./l. Readily-exchangeable and non-exchangeablefractions were separately indentified. The lowering of temperature and application of DNP reduced themagnitude of both ion fractions at each of the two concentrationsof rubidium chloride. Despite the fact that the uptake of ionsinto an exchangeable form at 5·0 meq./l. was about 3times greater, the combined effect of low temperature and thepresence of DNP reduced this fraction by a relatively constantabsolute amount. Under the same conditions the uptake of ionsinto a non-exchangeable form from each concentration was reducedby approximately the same percentage. Over a 6-hour period the rate of uptake of rubidium into a non-exchangeableform at 25° C. was relatively constant, whereas at 0·2°C. there was an initial rapid uptake lasting for about 60 minutesfollowed by a slow steady uptake. The Q10 of this latter processmeasured after 360 minutes was 2·3. It is concluded that an appreciable part of the capacity ofthe tissue to hold ions by exchange is dependent on concurrentmetabolism. The significance of measurements of exchangeability in the interpretationof mechanisms of ion uptake is discussed. 相似文献
11.
Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (45µm diameter) alone or in combination with Peridinium trochoideum(1618 µm diameter) at concentrations of 0.150.70mm3 x 11. Grazing rates (ml x zooid1 x 24 h 1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC1x 24 h1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (106 µm3x zooid1 x 24 h1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC1 x 24 h1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m3) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day.
1Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5 相似文献
12.
Duneclift, S., U. Wells, and J. Widdicombe. Estimationof thickness of airway surface liquid in ferret trachea in vitro. J. Appl. Physiol. 83(3): 761-767, 1997.The tracheae of ferrets and rabbits were mounted in vitro inorgan baths. While the tracheae were liquid filled, the permeabilitycoefficient ( P) was determined, and then while thetracheae were air filled, the percent clearance for99mTc-labeleddiethylenetriaminepentaacetic acid (DTPA) was determined. The thicknessof airway surface liquid (ASL) was estimated by three methods.1) The initial concentration of99mTc-DTPA and the total amount of99mTc-DTPA (the sum of thatentering the outside medium, that draining from the trachea, and thatwashed out at the end of 40 min) gave the initial volume of ASL andthus its thickness. Mean values were 45.7 µm for the ferret and 41.9 µm for the rabbit. 2) Estimates ofASL thickness at the end of the 40-min period, based on the final99mTc-DTPA concentration and theamount in the washout, were 42.9 µm for ferret and 45.4 µm forrabbit. 3) The ratio of Pto percent clearance gave mean ASL thickness values of 49.2 µm forthe ferret and 40.3 µm for the rabbit. Thus three separate methodsfor determining ASL thickness give very similar results, with means inthe range 40-49 µm. Administration of methacholine or atropineto ferret tracheae did not significantly change ASL thickness. 相似文献
13.
Inorganic phosphorus uptake and regeneration in the OkhotskSea waters were investigated in JulyAugust 1994 withthe use of radioisotopic techniques. The rates of PO4-P uptakeby microplankton in the upper mixed layer were between 1.5 and6.6 µg P l-1 day-1 (average 2.75) in areas of diatom dominance,and between 0.68 and 1.68 µg P l-1 day-1 (average 1.16)in areas of intense warming and summer phytoplankton minimum.The residence time of PO4-P standing stock in water at differentstations varied between 1.5 and 24 days (mean 9 days). The shareof bacterioplankton contributing to total PO4-P uptake was 50%in areas of the summer phytoplankton minimum and 2030%in areas of diatom dominance. The PO4-P regeneration rate wasmeasured first time experimentally in the temperate sea. Itsrates varied from 0.30 to 1.65 µg P l-1 day-1. In areasof diatom dominance, it compensated with 3060% of PO4-Puptake. In zones of summer phytoplankton minimum and in thelayers of deep chlorophyll maxima at 1025 m depths, thePO4-P regeneration rate often exceeded its uptake. Primary phytoplanktonproduction correlated well with PO4-P uptake values in the uppermixed layer, while no correlation was found between primaryproduction and the ambient PO4-P content in water. 相似文献
14.
Meng XJ Timmer RT Gunn RB Abercrombie RF 《American journal of physiology. Cell physiology》2000,278(6):C1183-C1190
ATP-dependent 45Ca uptake in rat brainmicrosomes was measured in intracellular-like media containingdifferent concentrations of PO4 and oxalate. In the absenceof divalent anions, there was a transient 45Caaccumulation, lasting only a few minutes. Addition of PO4did not change the initial accumulation but added a second stage that increased with PO4 concentration. Accumulation during thesecond stage was inhibited by the following anion transport inhibitors: niflumic acid (50 µM),4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS; 250 µM),and DIDS (3-5 µM); accumulation during the initial stage wasunaffected. Higher concentrations of DIDS (100 µM), however,inhibited the initial stage as well. Uptake was unaffected by 20 mM Na,an activator, or 1 mM arsenate, an inhibitor of Na-PO4 cotransport. An oxalate-supported 45Ca uptake was larger,less sensitive to DIDS, and enhanced by the catalytic subunit ofprotein kinase A (40 U/ml). Combinations of PO4 and oxalatehad activating and inhibitory effects that could be explained byPO4 inhibition of an oxalate-dependent pathway, but notvice versa. These results support the existence of separate transportpathways for oxalate and PO4 in brain endoplasmic reticulum. 相似文献
15.
A Comparison between the Uptake of Potassium by Plants from Solutions of Constant Potassium Concentration and during Depletion 总被引:6,自引:0,他引:6
A comparison was made between two methods of measuring the relationshipbetween the external [K+] and the flux of K+ into whole plantsof Lolium perenne and Raphanus sativus. The values of flux obtainedfrom solutions of 1.2 µM K+ held constant around the rootswere three and six times greater for Lolium and Raphanus respectivelythan the values obtained at the same concentration in a depletionexperiment in which the solutions, initially 100 µM K+,were depleted to below 1.2 µM K+ by plant uptake. In thedepletion experiment with Lolium, the flux was higher into plantsgrown at low [K+] than into plants grown at 100 µM eventhough [K+] within the plant was about the same for all groupsof plants. It is suggested that Lolium grown at low [K+] hasan efficient mechanism for K+ uptake which continues to operatefor some time after the plants have been transferred to a higherconcentration. With both species, Km was 1520 µMin the depletion experiment and below 1 µM when concentrationswere held constant. 相似文献
16.
The correlation between the velocities of cytoplasmic streamingand of translocation of 14C-photosynthate and 32P-phosphateassociated radioactivity has been investigated in whole plantsof the green freshwater alga Chara hispida L. Tracer was suppliedto the plant's rhizoid system in a split-chamber. The velocityof cytoplasmic streaming of 52±3.3 µm s1compares with 57±10 µm s1 found for 14C-transportand 32±20 µm s1 found for 32P-transport.There was no indication of intercellular translocation at avelocity faster than visible streaming. Cytochalasin B inhibitedthe translocation of 32P and cytoplasmic streaming. CytochalasinB becomes fully effective in inhibiting streaming and transportafter an incubation time of at least 5 h. Key words: Chara hispida, Cytoplasmic streaming, Intercellular transport 相似文献
17.
Characterization of transport mechanisms and determinants critical for Na+-dependent Pi symport of the PiT family paralogs human PiT1 and PiT2 总被引:1,自引:0,他引:1
Bøttger P Hede SE Grunnet M Høyer B Klaerke DA Pedersen L 《American journal of physiology. Cell physiology》2006,291(6):C1377-C1387
The general phosphate need in mammalian cells is accommodated by members of the Pi transport (PiT) family (SLC20), which use either Na+ or H+ to mediate inorganic phosphate (Pi) symport. The mammalian PiT paralogs PiT1 and PiT2 are Na+-dependent Pi (NaPi) transporters and are exploited by a group of retroviruses for cell entry. Human PiT1 and PiT2 were characterized by expression in Xenopus laevis oocytes with 32Pi as a traceable Pi source. For PiT1, the Michaelis-Menten constant for Pi was determined as 322.5 ± 124.5 µM. PiT2 was analyzed for the first time and showed positive cooperativity in Pi uptake with a half-maximal activity constant for Pi of 163.5 ± 39.8 µM. PiT1- and PiT2-mediated Na+-dependent Pi uptake functions were not significantly affected by acidic and alkaline pH and displayed similar Na+ dependency patterns. However, only PiT2 was capable of Na+-independent Pi transport at acidic pH. Study of the impact of divalent cations Ca2+ and Mg2+ revealed that Ca2+ was important, but not critical, for NaPi transport function of PiT proteins. To gain insight into the NaPi cotransport function, we analyzed PiT2 and a PiT2 Pi transport knockout mutant using 22Na+ as a traceable Na+ source. Na+ was transported by PiT2 even without Pi in the uptake medium and also when Pi transport function was knocked out. This is the first time decoupling of Pi from Na+ transport has been demonstrated for a PiT family member. Moreover, the results imply that putative transmembrane amino acids E55 and E575 are responsible for linking Pi import to Na+ transport in PiT2. inorganic phosphate transport; retroviral receptor; SLC20 相似文献
18.
Nitric oxide regulates oxygen uptake and hydrogen peroxide release by the isolated beating rat heart 总被引:3,自引:0,他引:3
Poderoso Juan J.; Peralta Jorge G.; Lisdero Constanza L.; Carreras Maria Cecilia; Radisic Marcelo; Schopfer Francisco; Cadenas Enrique; Boveris Alberto 《American journal of physiology. Cell physiology》1998,274(1):C112
Isolated rat heart perfused with 1.5-7.5µM NO solutions or bradykinin, which activates endothelial NOsynthase, showed a dose-dependent decrease in myocardial O2uptake from 3.2 ± 0.3 to 1.6 ± 0.1 (7.5 µM NO, n = 18,P < 0.05) and to 1.2 ± 0.1 µM O2 · min1 · gtissue1 (10 µM bradykinin, n = 10,P < 0.05). Perfused NO concentrations correlated with aninduced release of hydrogen peroxide (H2O2) inthe effluent (r = 0.99, P < 0.01). NO markedlydecreased the O2 uptake of isolated rat heart mitochondria(50% inhibition at 0.4 µM NO, r = 0.99,P < 0.001). Cytochrome spectra in NO-treated submitochondrial particles showed a double inhibition of electron transfer at cytochrome oxidase and between cytochrome b andcytochrome c, which accounts for the effects in O2uptake and H2O2 release. Most NO was bound tomyoglobin; this fact is consistent with NO steady-state concentrationsof 0.1-0.3 µM, which affect mitochondria. In the intact heart,finely adjusted NO concentrations regulate mitochondrial O2uptake and superoxide anion production (reflected byH2O2), which in turn contributes to thephysiological clearance of NO through peroxynitrite formation. 相似文献
19.
- The permeability of unplasmolysed cells of beetroot, v. CrimsonGlobe, was determined from the rate of water loss ofbeet slices on placing in sucrose solutions having O.P. greaterthan the suction pressure of the beet. The absolute values obtainedwere about 0?7µ3 water per µ2 cell-surface per hourper atmosphere osmotic pressure difference, i.e. 0?7 µ/hr./atm.
- The permeability of similar beet cells plasmolysed withintheircell walls was found to be about 13µ/hr./atm.
- Thepermeability of beet cells which had been plasmolysed andallowedto recover was shown to be approximately the same asthat ofunplasmolysed cells.
- The hypothesis is advanced that the increasein water permeabilityon plas-molysis is due to those partsof the plasma-membranewhich had formerly been pressed againstthe micelles of thecell wall becoming free and able to takepart in water transfer.
- The energy requirement for the maintenanceof an excess hydrostaticpressure of five atmospheres withina cell by its vital activitywas shown to be about one-tenthof the total respiratory energyreleased in freshly cut beetslices.
20.
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