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2.
Summary The presence of a Ca2+ channel in the plasmalemma of tonoplast-freeNitellopsis obtusa cells was demonstrated and its characteristics were studied using current- and voltage-clamp techniques. A long-lasting inward membrane current (I m ), recorded using a step voltage clamp, consisted of a single component without time-dependent inactivation. Increasing either [Ca2+] o or [Cl] o 1) enhanced the maximum amplitude of inwardI m ((I m ) p ) and 2) shifted the peak voltage ((V m ) p ) at(I m ) p to more positive values under ramp-shaped voltage clamping and 3) depolarized the peak value of action potentials. This behavior is consistent with predictions based on the Nernst equation for Ca2+ but not for Cl. DIDS (4,4-diisothiocyano-2,2-disulfonic acid stilbene) did not suppress(I m ) p in tonoplast-free cells, in contrast with its effect on normal cells. La3+ and nifedipine blocked(I m ) p irreversibly. On the other hand, Ca2+ channel agonist, BAY K 8644 irreversibly enhanced(I m ) p . Both Sr2+ influx and K+ efflux increased upon excitation. The charge carried by Sr2+ influx was compensated for by K+ efflux. It is concluded that only the Ca2+ channel is activated during plasmalemma excitation in tonoplast-free cells. In terms of the magnitude of(I m ) p , Sr2+ could replace Ca2+, but Mn2+, Mg2+ and Ba2+ could not. External pH affected(I m ) p and the membrane conductance (g m ) at(I m ) p ((g m ) p ). Increasing the external ionic strength caused increases in both(I m ) p and(g m ) p , and shifted(V m ) p to positive values. At the same time, Sr2+ influx increased. Thus Ca2+ channel activation seems to be enhanced by increasing external ionic strength. The possible involvement of surface potential is discussed.  相似文献   

3.
Clostridium sporogenes MD1 grew rapidly with peptides and amino acids as an energy source at pH 6.7. However, the proton motive force (p) was only –25 mV, and protonophores did not inhibit growth. When extracellular pH was decreased with HCl, the chemical gradient of protons (ZpH) and the electrical membrane potential () increased. The p was –125 mV at pH 4.7, even though growth was not observed. At pH 6.7, glucose addition did not cause an increase in growth rate, but increased to –70 mV. Protein synthesis inhibitors also significantly increased . Non-growing, arginine-energized cells had a of –80 mV at pH 6.7 or pH 4.7, but was not detected if the F1F0 ATPase was inhibited. Arginine-energized cells initiated growth if other amino acids were added at pH 6.7, and and ATP declined. At pH 4.7, ATP production remained high. However, growth could not be initiated, and neither nor the intracellular ATP concentration declined. Based on these results, it appears that C. sporogenes MD1 does not need a large p to grow, and p appears to serve as a mechanism of ATP dissipation or energy spilling.Mandatory disclaimer: Proprietary or brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product, and exclusion of others that may be suitable.  相似文献   

4.
The high pH state of Chara plasmalemma (Bisson, M.A., Walker, N.A. 1980. J. Membrane Biol. 56:1-7) was investigated to obtain detailed current-voltage (I/V) and conductance-voltage (G/V) characteristics in the pH range 7.5 to 12. The resting conductance started to increase at a pH as low as 8.5, doubling at pH 9.5, but the most notable increases occurred between pH 10.5 and 11.5, as observed previously (Bisson, M.A., Walker, N.A. 1980. J. Membrane Biol. 56:1-7; Bisson, M.A., Walker, N.A. 1981. J. Exp. Bot. 32:951-971). The slopes (and shapes) of the I/V curves varied even over minutes, suggesting a shifting population of open channels. Possible contributions of the permeabilities to H+ and OH-, PH and POH, respectively, to the increase in membrane conductance were calculated in the pH range 8.5 to 12. If PH is the main cause for the increase in conductance, it would have to rise by three orders of magnitude between pH 8.5 and 11.5, implying an enormous increase in the open-channel population as pH rises. On the other hand, a comparatively constant POH over that pH range would result in an increase in conductance due to the rise of OH- concentration. This indicates unchanging open-channel population. The transient excitation conductances at pH 7.5 and 11.5 were compared at a range of membrane PD (potential difference) levels. At more positive PD levels (near 0) the transient conductances showed little change as pH was increased. However, near the excitation threshold the conductance at high pH was slower to reach peak and its amplitude was diminished compared to that at neutral pH. This effect was found to be partially due to the pH change itself and partially due to less negative membrane PD at high pH. The changes in excitation transients developed gradually as pH of the medium was increased. These findings are discussed with a recent model of excitation in mind (Shiina, T., Tazawa, M. 1988. J. Membrane Biol. 106:135-139).  相似文献   

5.
The effect of prolonged illumination (60 min) with photosynthetically active monochromatic radiation of low intensity (3 μmol m−2 s−1) and high intensity (60 μmol m−2 s−1), corresponding to the physiological conditions and light stress conditions, respectively, was studied in the algae Nitellopsis obtusa. Illumination of Nitellopsis obtusa cells with strong light was associated with activation of the xanthophyll cycle, manifested by the deepoxidation of violaxanthin and accumulation of antheraxanthin and zeaxanthin. At the same time, the efficient singlet excitation quenching in the photosynthetic apparatus was activated, as demonstrated by the decrease in the intensity of the chlorophyll a fluorescence emission by ca 50 %. The difference of the fluorescence excitation spectra recorded before and after the light treatment match the difference absorption spectrum of the xanthophyll cycle pigments. The illumination with low light intensity resulted also in the chlorophyll a fluorescence quenching but the effect was very small (less than 10 %). The fluorescence quenching is interpreted in terms of the energy transfer between the Qy energy level of chlorophyll a and the 21 Ag energy level of zeaxanthin. The singlet energy levels of carotenoids, corresponding to the green spectral region, are also taken into consideration in the interpretation of the excitation energy exchange between the carotenoids and chlorophylls. Possible molecular mechanisms involved in the activation of the strong and the weak excitation quenching, including violaxanthin isomerization, and possible physiological functions of such pathways of energy transfer are discussed.  相似文献   

6.
The food pathogen Bacillus cereus is likely to encounter acidic environments (i) in food when organic acids are added for preservation purposes, and (ii) during the stomachal transit of aliments. In order to characterise the acid stress response of B. cereus ATCC14579, cells were grown in chemostat at different pH values (pHo from 9.0 to 5.5) and different growth rates (μ from 0.1 to 0.8 h−1), and were submitted to acid shock at pH 4.0. Cells grown at low pHo were adapted to acid media and induced a significant acid tolerance response (ATR). The ATR induced was modulated by both pHo and μ, and the μ effect was more marked at pHo 5.5. Intracellular pH (pHi) was affected by both pHo and μ. At a pHo above 6, the pHi decreased with the decrease of pHo and the increase of μ. At pHo 5.5, pHi was higher compared to pHo 6.0, suggesting that mechanisms of pHi homeostasis were induced. The acid survival of B. cereus required protein neo-synthesis and the capacity of cells to maintain their pHi and ΔpH (pHi - pHo). Haemolysin BL and non-haemolytic enterotoxin production were both influenced by pHo and μ.  相似文献   

7.
The voltage-clamp technique was used to study Ca2+ and Cl transient currents in the plasmalemma of tonoplast-free and intact Chara corallina cells. In tonoplast-free cells [perfused medium with ethylene glycol bis(2-aminoethyl ether)tetraacetic acid] long-term inward and outward currents through Ca channels consisted of two components: with and without time-dependent inactivation. The voltage dependence of the Ca channel activation ratio was found to be sigmoid-shaped, with about –140-mV activation threshold, reaching a plateau at V>50 mV. As the voltage increased, the characteristic activation time decreased from approximately 103 ms in the threshold region to approximately 10 ms in the positive region. The positive pulse-activated channels can then be completely deactivated, which is recorded by the Ca2+ tail currents, at below-threshold negative voltages with millisecond-range time constants. This tail current is used for fast and brief Ca2+ injection into tonoplast-free and intact cells, to activate the chloride channels by Ca2+ . When cells are perfused with EDTA-containing medium in the presence of excess Mg2+, this method of injection allows the free submembrane Ca2+ concentration, [Ca2+]c, to be raised rapidly to several tens of micromoles per liter. Then a chloride component is recorded in the inward tail current, with the amplitude proportional to . When Ca2+ is thus injected into an intact cell, it induces an inward current in the voltage-clamped plasmalemma, having activation–inactivation kinetics qualitatively resembling that in EDTA-perfused cells, but a considerably higher amplitude and duration (approximately 10 A m–2 and inact~0.5 s at –200 mV). Analysis of our data and theoretical considerations indicate that the [Ca2+]c rise during cell excitation is caused mainly by Ca2+ entry through plasmalemma Ca channels rather than by Ca2+ release from intracellular stores.  相似文献   

8.
The fluorescence of the voltage sensitive dye, diS-C3-(5), has been analyzed by means of synchronous excitation spectroscopy. Using this rather rare fluorescence technique we have been able to distinguish between the slightly shifted spectra of diS-C3-(5) fluorescence from cells and from the supernatant. It has been found that diS-C3-(5) fluorescence in the supernatant can be selectively monitored at exc = 630 nm and em= 650 nm, while the cell associated fluorescence can be observed at exc= 690 nm and em = 710 nm. A modified theory for the diSC3-(5) fluorescence response to the membrane potential is presented, according to which a linear relationship exists between the logarithmic increment of the dye fluorescence intensity in the supernatant, In I/I°, and the underlying change in the plasma membrane potential, p=pp. The theory has been tested on human myeloid leukemia cells (line ML-1) in which membrane potential changes were induced by valinomycin clamping in various K+ gradients. It has been demonstrated that the membrane potential change, p,can be measured on an absolute scale. Offprint requests to: J. Plasek  相似文献   

9.
Summary The current-voltage curve of theChara membrane was obtained by applying a slow ramp de- and hyperpolarization by use of voltage clamp. By inhibiting the electrogenic pump with 50m DCCD (dicyclohexylcarbodiimide), theI–V curve approached a steady state within 100 min, which gave thei d -V curve of the passive diffusion channel. Thei p -V curve of the electrogenic pump channel was obtained by subtracting the latter from the former. With the increase of external pH, thei d -V curve showed only a slight change, while thei p -V curve of the pump channel showed almost a parallel shift, in the hyperpolarizing direction, along the voltage axis in the pH range between 6.5 and 7.5. The sigmoidali p -V curve in this pH range could be simulated satisfactorily with the five-state model reported previously (U. Kishimoto, N. Kami-ike, Y. Takeuchi & T. Ohkawa,J. Membrane Biol. 80:175–183, 1984) as well as with a lumped two-state model presented in this report. The analysis based on these models suggests that the electrogenic pump of theChara membrane is mainly a 2H+/1ATP pump. The forward rate constant in the voltage-dependent step increased with the increase of external pH, while the backward one decreased. On the other hand, the forward rate constant in the voltage-independent step remained almost unchanged with the increase of external pH, while the backward one increased markedly. The pump conductance at the resting membrane potential showed either a slight increase or a decrease with the increase of external pH, depending on the sample. Nevertheless, the pump current showed generally a slight increase with the increase of external pH.  相似文献   

10.
Z. Wang  J. Shen  F. Zhang 《Plant and Soil》2006,287(1-2):247-256
The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 μM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 μmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.  相似文献   

11.
Ionselective microelectrode method was used to study changes of pH in transmitting tissue of style in Petunia hybrida (Hort.). Effect of pollination and pollen tube growth were examined. Subsequently solutions of ions and various stimulators or blockers of ion channels were applied on pollinated styles to examine the possible role of ion channels in pH stabilisation. It was confirmed in the present study that: (1) there is a pH gradient in the transmitting tissue of a petunia unpollinated style with the stigma region being more acidic; (2) pollination causes further acidification of transmitting tissue: (3) the gradient of pH first vanishes at 24 h after pollination then is reversed up to 72 h after pollination; (4) active transport of ions plays an important role in pH regulation in transmitting tissue. The presented results confirm the role of pH changes and Ca2+ as a mediator in controlling proton influx into the apoplast of the transmitting tissue during pollen tube growth.  相似文献   

12.
Venturicidin behaves as an orthodox energy transfer inhibitor in intact cells of Rhodopseudomonas capsulata as judged by the following criteria. 1. It led to inhibition of respiration. Inhibition was relieved by low concentrations of uncoupling agent. 2. It enhanced light-induced and oxygen dependent H+ efflux. 3. It stimulated light-induced and oxygen dependent carotenoid band shifts. The rate of decay of the band shifts after short flash excitation was decreased in the presence of venturicidin. 4. It stimulated light-induced and oxygen dependent butyltriphenylphosphonium uptake. 5. It inhibited the rise in cellular ATP concentration accompanying either photosynthesis or respiration.  相似文献   

13.
Michael R. Blatt 《Planta》1988,174(2):187-200
Fusicoccin (FC) is commonly thought to promote electrogenic H+ extrusion through its action on the H+-ATPase of the plant plasma membrane. Nonetheless, essential support from rigorous electrophysiological analysis has remained largely absent. The present investigation surveys the effects of FC on the charge transport properties at the membrane of a higher-plant cell — stomatal guard cells of Vicia faba L. — for which the electrical geometry is defined, and from which the voltage-dependent kinetic characteristic for the pump has been identified. Current-voltage (I-V) relations of the guard cells were determined before and during treatments with FC, and during brief exposures to NaCN plus salicylhydroxamic acid. Responses of the pump and of the ensemble of secondary transport processes were identified in the whole-membrane conductance-voltage relations and in the difference-current-voltage (dI-V) characteristic for the pump. In 0.1 mM K+, exposure to 10 M FC shifted guard-cell potentials negative by 29–61 mV. Current-and conductance-voltage profiles indicated limited changes in the pump I-V characteristic, an observation which was confirmed through explicit kinetic analysis of pump dI-V relations. However, the voltage response was accompanied by a 1.5-to 2.6-fold fall in membrane conductance. These results challenge conventional views of fusicoccin action by ascribing the electrical responses to reduced current passage through secondary transport pathways as well as to enhanced electrogenic ion pumping.Abbreviations and symbols Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - SHAM salicylhydroxamic acid - FC fusicoccin - V m free-running membrane potential - G m membrane slope conductance at V m - (d)I-V (difference) current-voltage (relation) - G-V slope conductance-voltage (relation)  相似文献   

14.
The intracellular pH of the halotolerant green algae Dunaliella tertiolecta, was determined by the distribution of 5,5-dimethyl-2(14C)-oxalolidine-2,5-dione (DMO) between the cell and the surrounding medium. 5,5-dimethyl-2(14C)oxalolidine-2,4-dione was not metabolized by the algal cells. The intracellular pH of Dunaliella tertiolecta was 6.8 in the dark and 7.4 in the light. During a salt stress, after two hours, the intracellular pH was increased by 0.2 pH units in both light and dark. The salt stressed cells maintained a constant pH of about 7.5 over the pH range of 6.5 to 8.5. Because of the relatively low permeability coefficient of the plasma membrane for DMO, this technique does not permit rapid pH determinations during the induction period after a salt stress. The magnitude of the salt induced pH changes measured 2 h after the salt stress implies a minor importance of this alkalization in this time range, but does not exclude a larger importance of pH changes for osmoregulation during the induction period.Abbreviations Chl chlorophyll - DMO 5,5-dimethyl-2(14C)oxalolidine-2,4-dione - PCV packed cell volume - SDS sodium dodecyl sulfate  相似文献   

15.
A detailed reaction cycle for cytochrome oxidase, an electron-transport-driven proton pump, has been presented earlier by our research group. The essential feature of the model is that both cytochrome a and CuA must be reduced in order to allow the transition from the electron and proton input state to the output state. The model is thus based on an indirect coupling between electron transfer and proton translocation.In this study, the same model is examined with respect to (1) intrinsic electron and proton leaks and (2) the effect of applying an electrochemical potential gradient on the pump incorporated in a membrane, both with respect to the electrical and chemical components.The model is successfully used to simulate various experimental results. Comparisons of experimental results with simulations based on the model support the existence of electron and proton leaks. The analysis of electron leaks suggests that electron gating is best achieved by varying the reorganization energy rather than by varying the reduction potentials.It is also suggested that both the electrical and chemical components of the electrochemical potential gradient are responsible for the regulation of the enzyme activity. Furthermore, an attempt is made to interpret the seemingly contradictory results obtained when measuring the pH dependence of the reduction potential of cytochrome a. In addition, the simulations support the assumption that protons are pumped by a mechanism that combines a membrane Bohr effect with the transition-state mechanism.Abbreviations R molar gas constant - k B Boltzmann contant - F Faraday constant - e elementary charge - T absolute temperature - transmembrane electrochemical potential gradient - pH transmembrane pH difference - pH1 and pH2 inside (matrix) and outside (cytosol) pH, respectively - transmembrane electrical potential - E m midpoint potential  相似文献   

16.
George S. Espie  Brian Colman 《Planta》1981,153(3):210-216
The intracellular pH of isolated, photosynthetically active mesophyll cells of Asparagus sprengeri Regel has been determined, in the light and dark, by the distribution of the weak acid 5,5-dimethyl-[2-14C]oxazolidine-2,4-dione ([14C]DMO) between the cells and the liquid medium. [14C]DMO was taken up rapidly, reaching equilibrium in 7–10 min of incubation, but was not metabolized by the cells, and intracellular binding of the compound was minimal. The intracellular pH, measured at saturating light fluence and 1.5 mM sodium bicarbonate, was found to remain relatively constant at 6.95–7.21 over the external pH range of 5.5–7.2. Illumination of the cells increased the intracellular pH compared to dark controls. The pH of the cytoplasm, excluding and including the chloroplasts (cytoplasmic and bulk cytoplasmic, respectively) was calculated from the experimentally derived intracellular [14C]DMO concentration and estimates of the vacuolar, chloroplastic and cytoplasmic volumes. The calculated cytoplasmic pH was similar in the light and dark, being 7.75 and 7.74, respectively, while the calculated pH of bulk cytoplasm was 7.85 in the light and 7.49 in the dark. Theoretical analysis indicated that intracellular pH is a good indicator of changes in the bulk cytoplasmic pH but insensitive to changes in vacuolar pH. The external pH optimum for photosynthesis (O2 evolution) of isolated Asparagus cells was pH 7.2. At pH 8.0 photosynthesis was inhibited by 30% and at pH 5.25 by 45%. Inhibition at alkaline pH may be the result of a decrease in the pH gradient between the cells and the medium, causing CO2 limitation in the cell. At acid pH, decrease in internal pH caused by substantial accumulation of inorganic carbon may account for the loss in photosynthetic activity.Abbreviations [14C]DMO 5,5-dimethyl[2-14C]oxazolidine-2,4-dione - pHi overall intracellular pH - pHe pH of external medium  相似文献   

17.
Effects of changing the cytoplasmic pH on the cytoplasmic streaming, membrane potential and membrane excitability were studied in tonoplast-free cells ofChara australis andNitellopsis obtusa. The cytoplasmic pH was varied by internal perfusion of pH-buffered media.Nitellopsis cells were perfused only once, whileChara cells were perfused twice to control the pH more accurately. In both materials the rate of cytoplasmic streaming was maximum at about pH 7, low at pH 8.5–9 and almost zero at pH 5–5.5. The membrane potential was most negative at about pH 7. InChara the membrane potential supported by Mg·ATP was strongly inhibited at pH 5.5, and almost zero at pH 9, supporting the results obtained by Fujiiet al. (1979) on cells ofChara australis which were perfused once. The action potential could be induced by electrical stimulation inChara at pH 6.0–9.0 and inNitellopsis at pH 6.6–7.9. The membrane resistance ofNitellopsis was high at acidic and neutral pH values and low at alkaline pH, while that ofChara was low at both acidic and alkaline pH values.  相似文献   

18.
Pulvinar motor cells ofPhaseolus vulgaris L display transient depolarization of the membrane potential and a turgor pressure decrease when exposed to a pulse of blue light. To analyze the mechanism of the transient depolarization, the effects of some factors such as anoxia, metabolic inhibitors and specific inhibitors of H+-ATPase have been examined. The findings have led to the conclusion that blue light inactivates the electrogenic H+-pumping ATPase in the plasma membrane of the motor cells. This inactivation seems to suppress ion uptake and decrease the turgor pressure of the motor cells.  相似文献   

19.
The carboxylic ionophore, monensin, rapidly induced cell-wall acidification and a decrease in cytosolic pH when added to maize coleoptiles at low external pH and Na+ concentration. Elongation growth at rates equivalent to those obtained with indole-3-acetic acid was induced for about 1 h. Stimulation of the outwardly directed proton pump apparently occurred, since under the same conditions monensin induced membrane hyperpolarization of maize root rhizodermis cells. When the external pH was high (>8) and Na+ present, monensin treatment caused only minimal changes in membrane potential and cytosolic pH. Although the ionophore transported protons out of the cell, resulting in cell-wall acidification, no elongation growth occurred. However, under identical conditions, indole-3-acetic acid dit induce growth. The data indicates that stimulation of the outwardly directed electrogenic proton pump rather than the subsequent acidification of the cell wall is vital for the induction of elongation growth.Abbreviations CFA2 6-carboxyfluorescein diacetate - FA2 fluorescein diacetate - Hepes 4-(2-hydroxyethyl-1-piperazinepropanesulfonic acid - IAA indole-3-acetic acid - Mes 2-(N-morpholino) ethanesulfonic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol  相似文献   

20.
Oscillations of photosynthesis induced in leaves of Vicia faba L. were accompanied by oscillations not only in the pH of the chloroplast stroma, but also by pH oscillations in the cytosol and in the vacuole of leaf mesophyll cells. Cytosolic pH oscillations were in phase with stromal oscillations, but antiparallel to vacuolar pH oscillations. During maxima of photosynthesis, the cytosolic pH exhibited maxima and the vacuolar pH minima. Vacuolar acidification is interpreted to be the result of energized proton transport from the cytosol into the vacuole. Since the ratio of dihydroxyacetone phosphate to phosphoglycerate is maximal during the peaks of photosynthesis (Stitt et al., 1988, J. Plant Physiol. 133, 133–143; Laisk et al., 1991, Planta 185, 554–562), while the activity of NADP-malic dehydrogenase is highest during minima of photosynthesis (Scheibe and Stitt, 1988, Plant Physiol. Biochem. 26, 473–481), the present data indicate in agreement with earlier observations (Yin et al., 1991, Planta 184, 30–34) that light-dependent cytosolic energization is brought about by the oxidation of dihydroxyacetone phosphate rather than of malate. They also indicate that the over-reduction of the electrontransport chain observed during minima of photosynthesis is relieved not predominantly by oxaloacetate reduction and export of the resulting malate from the chloroplasts but by another reaction, presumably oxygen reduction.Abbreviations CDCF 5-(and 6-)carboxy-2,7-dichlorofluorescein  相似文献   

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