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1.
Use of permeabilised cells of Chara corallina provides a uniqueopportunity to study the electrical characteristics of the tonoplastwhilst being able to control ionic conditions on the outsideof the membrane. Current-voltage (I/V) analysis over wide voltagespans, and admittance measurements at 5 Hz showed that manypermeabilised cells had a similar conductance and capacitanceto the tonoplast of intact cells. Cells developed two regionsof negative-slope conductance upon addition of external Cl,which suggests the existence of potential-dependent Clchannels in the Chara tonoplast. With Cl concentrationssimilar to those expected in vivo, the resting potential wasmore sensitive to changes in external K+ than Cl; however,a decrease in external K+ did not significantly alter the shapeof the I/V relation.
1Present address: Biopysics Laboratory, School of BiologicalSciences, A12, University of Sydney, Sydney, N.S.W., 2006, Australia
2Permanent address: Department of botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan (Received May 6, 1987; Accepted September 21, 1987) 相似文献
2.
The effects of light/dark on anion fluxes in isolated guardcells of Commelina communis L. have been studied, using 82Brand 36Cl. Transfer of open guard cells from light to dark hasno effect on the 82Br influx, but produces a marked transientstimulation of 82Br or 36Cl efflux, similar to the effect ofsuch transfer on the 86Rb fluxes, and to the effects on both86Rb and 82Br fluxes of adding ABA. On return of guard cellsto light, after the transient, there is a further reductionin Cl/Br efflux. It is argued that control of a specific processof ion extrusion is important in regulating the ability of guardcells to stay open. In three out of four batches of steady-statetissue labelled with 82Br, the plasmalemma fluxes were highenough, relative to the tonoplast fluxes, for the efflux kineticsto be separable into two exponential components, allowing estimationof bromide contents in cytoplasm and vacuole (Qc and Qv), andfluxes at plasmalemma and tonoplast. With opening in light,Qc increased by 3.9 ± 0.4 pmol mm2 µm1and Qy by 5.2 ± 0.6 pmol mm2 µm1(change in content per mm2 of epidermis perµm change inaperture). Using rough estimates for the volumes of cytoplasmand vacuole these figures suggest that at 6.1 µm in thedark the concentrations were about 63 mol m3 in the cytoplasmand 35 mol m3 in the vacuole, rising to about 185 molm3 in the cytoplasm and 125 mol m3 in the vacuole,at 16.7 µm aperture in light. Neither increase can providean adequate increase in salt concentration to account for theosmotic change required, and some solute other than potassiumsalt must also be involved. In one experiment with 82Br andin the only experiment with 36Cl the plasmalemma flux was lower,and not high enough relative to the tonoplast flux to allowseparation of two phases in the efflux curves, and calculationof cytoplasmic and vacuolar contents and fluxes. The effectsof transfer from light to dark were, nevertheless, similar inboth types of tissue. Key words: Commelina communis L., Light/dark effects, Anion fluxes, Guard cells 相似文献
3.
Homble F. 1985. Effect of sodium, potassium, calcium, magnesiumand tetraethylammonium on the transient voltage response toa galvanostatic step and of the temperature on the steady membraneconductance of Chara corallina: A further evidence for the involvementof potassium in the fast time variant conductance.J.exp. Bot. 36: 16031611. Potassium channels of Chara corallina have an activation energyof 36±1 kJ mol1 and 50±2 kJ mol1at temperatures higher and lower than 15°C respectively.The fast time variant conductance property of potassium channelsis insensitive to sodium and magnesium ions and is depressedby the presence of calcium, potassium and tetraethylammoniumions. It is suggested that in Chara two different kinds of potassiumchannels exist, each kind being distinguished by their kineticsand their response to calcium and magnesium ions. Key words: Chara corallina, membrane conductance, potassium channels, temperature 相似文献
4.
This paper describes experiments designed to investigate theeffects of increases in external osmotic pressure on the electrophysiologicalbehaviour of the plasmalemma in cells of the brackish-wateralga, Chara inflata. The electrical conductance of the plasmalemmaof these cells of, due to the diffusion of ions, consists mainlyof K+, Cl and leak components. The addition of sorbitolat concentrations in the range 40280 mol m3 tothe external solution bathing the cells, progressively and reversiblydepolarized the cell membrane and increased the total membraneconductance, chiefly due to increases in each of the separateionic conductances. At concentrations higher than about 280mol m3 when the cells became plasmolysed, the effectsof sorbitol on the electrical properties of the cell ceasedto be fully reversible. When the membrane electrical potentialdifference is stepped in a negative direction with a voltage-clamp,the resulting inward current has voltage-dependent componentsconsisting of an inactivating K+ current, an activating Clcurrent and a constant leak current. The addition of sorbitolto the external solution modified these currents by increasingtheir magnitude, by increasing the half-time of the inactivationof the K+ current, and by decreasing the half-time of activationof the Cl current. Key words: Chara inflata, osmotic effects, K+ and Cl currents 相似文献
5.
Using permeabilized characean cells in which the ionic conditionsat the cytoplasmic side of the tonoplast are easily controlled,effects of Ca2+ ion on tonoplast potential were examined. Whenthe cell was treated with 1 µM Ca2+, the tonoplast potential(EM became positive in a complicated manner in Chara corallinawhile it simply became negative in Nitella axilliformis. Whenthe cell was treated with 9-antracenecarboxylic acid, a Cl-channelinhibitor, Em became more negative and the response of Em toCa2+ was significantly suppressed. It is suggested that Ca2+activates Cl-channel at a low concentration and inactivatesat a higher one in C. corallina while it simply inactivate Cl-channelin N. axilliformis.
1Present address: Biological Laboratory, The University of theAir, Wakaba 2-11, Wakaba, 260 Japan. (Received August 22, 1988; Accepted December 26, 1988) 相似文献
6.
Ion Fluxes in 'Isolated' Guard Cells of Commelina communis L. 总被引:4,自引:0,他引:4
Ion fluxes have been measured in isolated guardcells of Commelina communis L. using 86RbCl and K82Br, in epidermalstrips in which all cells other than guard cells have been killedby treatment at low pH. To avoid problems of slow free spaceexchange most fluxes have been measured at pH 3.9, at whichstomata open well in K(Rb) Cl(Br) and are stable for many hours.At pH 3.9 the intracellular 86Rb exchanged as a single compartmentwith a half-time of 23 h, independent of external concentration(Co). The influx of 86Rb rose with concentration, to a Vmaxof about 23 pmol mm2 h1. The efflux curve of 82Brcould be well fitted by two exponential terms, with half-timesof 38 min (independent of Co), and 535 h (falling withincreasing Co). Bromide contents of cytoplasm and vacuole (Qcand Qv), and fluxes at plasmalemma and tonoplast, were calculatedfrom the efflux kinetics. Over Co 2060 mM, as the apertureincreased from 7 µm to 17 µm, the tonoplast flux(0.511.5 pmol mm2h1) was always much lessthan the plasmalemma flux (777 pmol mm2 h1).Qc and Qv both increased with aperture. The increase in Qc of10.3 pmol mm2 µm1 is adequate to accountfor the osmotic changes required to change the aperture, aspreviously estimated. However, the change in vacuolar contentof only 5.9 pmol mm2 µm1 is much too smallto account for the osmotic changes required, or to balance thecytoplasmic changes. It appears therefore that increasing KBroutside not only increases the cytoplasmic salt content, andthe Br flux at the tonoplast, but also stimulates the vacuolaraccumulation of some other solute. 相似文献
7.
Potassium transport has been studied in the marine euryhalinealga, Enteromorpha intestimlis cultured in seawater and in low-salinitymedium (Artificial Cape Banks Spring Water, ACBSW; 25·5mol m3 Cl, 20·4 mol m3 Na+, 0·5mol m3 K+). K+ fluxes were measured using 42K+ and 86Rb+although 86Rb+ does not act as an efficient K+ analogue in thisplant. 42K+ experiments on seawater plants typically exhibiteda single protoplasmic exchange phase whereas 86Rb+ exhibitedtwo exchange phases. Compartmental analysis of 86Rb+ effluxexperiments on seawater-grown Enteromorpha plants were usedto deduce the intracellular partition of K+ between the cytoplasm(279±38 mMolal) and vacuole (405±68 mMolal). Theplasmalemma K+ flux in plants in seawater was greater in thelight than in the dark (563±108 nmol m2 s1versus 389±66·7 nmol m2 s1). Inlow-salinity plants, separate cytoplasmic and vacuolar exchangephases were apparent. Analysis of 42K+ efflux experiments onlow-salinity plants yielded a cytoplasmic K+ of 222±38mMolal and a vacuolar K+ of 82±11 mMolal. The plasmalemmaand tonoplast flux was 23±4·5 nmol m2 s1. The Nernst equation showed that, although K+ was close to electrochemicalequilibrium, active accumulation of K+ across the plasmalemmaoccurred in plants in seawater and ACBSW both in the light anddark. K+ was also actively transported inwards across the tonoplastin low-salinity plants. The electrochemical potential for K+across the plasmalemma ranged from 2·41±0·60kJ mol1 in plants grown in seawater in the light to 5·79±0·87kJ mol1 for plants in ACBSW in the light. Although K+is close to electrochemical equilibrium, the flux of K+ in plantsin both seawater and ACBSW media is high, hence the power consumptionof K+ transport is high. The permeability of K+ (PK+) was significantlyhigher in the light than in the dark in plants in seawater (about7·0 versus 2·5 nm s1) but in plants inlow-salinity (ACBSW) medium the permeability was independentof light (about 12 nm s1). The energy requirements ofactive K+ transport by ATP-dependent pumps is discussed. Key words: Enteromorpha, Potassium transport, Ionic relations, Saltwater, Low salinity, Thermodynamics 相似文献
8.
Salinity-induced Malate Accumulation in Chara 总被引:3,自引:0,他引:3
Ion absorption by Chara corallina from solutions containingpredominantly KC1 or RbCl at up to 100 mol m3 resultedin accumulation of salts and turgor regulation. Turgor regulationdid not occur in solutions containing Na+ or Li+salts. Duringion absorption from various salts of K+ and Rb+ vacuolar cationconcentration exceeded Cl concentration. This differencewas shown to be balanced by the synthesis and accumulation ofmalate. Vacuolar malate concentration reached 48 mol m3,with accumulation occurring at rates of up to 0.45 mol m3h1. Malate accumulation was inhibited by low externalpH and was dependent upon external HCO3 concentration.The synthesis of malic acid and its subsequent dissociationimposed a severe acid load on the cell. Biophysical regulationof cellular pH was achieved by a H+efflux at a rate of about40 nmol m2 s1from the cell. The results presentedargue against cytoplasmic Cl, HCO3 or pH regulatingmalate accumulation in Chara and it is suggested that malatetransport across the tonoplast may regulate malate accumulation. Key words: Malate, Chara corallina, pH regulation, salinity 相似文献
9.
Internodal cells of Chara australis were subjected to two consecutiveintracellular perfusions with a Ca2+-free EGTA medium whichdisintegrated the tonoplast within about 10 minutes and thenwith a Ca2+-buffered medium. All perfusion media usually contained1 mM ATP. To stop the electrogenic pump, the internode was depletedof intracellular ATP. The excitability of the plasmalemma wasnot significantly influenced by intracellular free Ca2+ concentrationsup to 104 M. To trigger action potentials, minimum currentdensities of 1 to 2 µA cm2 had to be applied atall tested Ca2+ concentrations. In the absence of cytoplasmicATP, excitability was completely lost at all Ca2+ concentrations.
1 Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, D-5300 Bonn, FRG. (Received September 22, 1984; Accepted March 6, 1985) 相似文献
10.
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
11.
The permeability (P) of a lipophilic cation, triphenylmethylphosphonium(TPMP+) which is frequently used as a membrane potential probe,has been measured in Chara australis (Charophyceae). PTPMP+across biological membranes is usually thought to be very highbut this is not the case across the plasmalemma of Chara. Thepermeability of TPMP+ across the plasmalemma was found to betypical of inorganic cations, about 1.0 nm s1. Estimateswere made of the permeability of lipophilic cations across someother cell membranes, based on previously published work. Thepermeability of TPMP+ across the plasma membranes of the redalga, Griffithsia monilis and the blue-green alga, Anabaenavariabilis was about 25 nm s1. The permeabilityof TPMP+ across the plasma membranes of eukaryotes and prokaryotesappears to be similar. The permeability of lipophilic cationsacross the cristae of isolated mitochondria are exceptionallyhigh, about 170 nm s1. TPMP+ did not behave as a thiamineanalogue in Chara, unlike in the case of yeast. The means ofentry of TPMP+ into the Chara cell, driven by the electrochemicalgradient across the plasmalemma, has not been identified. Thepresence of a second lipophilic cation probe, DDA+ (dibenzyldimethylammonium),caused a decrease in the uptake flux of TPMP+; this suggeststhat the two lipophilic cations compete for the same site atthe surface of the plasmalemma. Key words: Chara australis, TPMP+, Permeability, Lipophilic cation 相似文献
12.
Membrane potential and resistance, each of which was the sumof those of the plasmalemma and tonoplast, measured in the coenocyticthallus of Boergesenia forbesii were 6.7 mv inside positiveand 2.8 k.cm2, respectively. Protoplasm squeezed from the thallus into artificial sea water(ASW) formed numerous spherical bodies, which are termed aplanospore-likecells (simply "spores"). The following electrical propertiesof the "spores" 2040 hr after squeezing were obtained:potential difference (p.d.) across plasmalemma (Eco) was 66mv ( means inside negative), plasmalemma resistance 665cm2, p.d. across the tonoplast (Evc) +73 mv, and tonoplast resistance2.6 k.cm2. Tenfold increase in external [K+] caused +45 mv changein Eco and +17 mv in Evc. The plasmalemma was entirely depolarizedin Ca++-free ASW or ASW containing Triton X-100. When the "spore" was immersed in potassium-rich (277 mil) ASW,Eco was almost zero and the tonoplast showed two states (I andII, Eve about +70 mv and +20 mv, respectively). Evc went backand forth between the two states spontaneously or when a smallcurrent was applied. In most cases oscillatory changes in Evcoccurred after the lapse of a long time in the K+-rich sea water.Membrane resistances in states I and II were 5 and 9 k.cm2,respectively. (Received July 11, 1977; ) 相似文献
13.
In response to hypotonic treatment internodal cells of the brackishwater Characeae Lamprothamnium regulate turgor pressure by releasingK+ and Cl, accompanying membrane depolarization and atransient increase in membrane electrical conductance (Okazakiet al. 1984b). The hypothesis that a transient increase in cytoplasmicfree Ca2+ concentration ([Ca2+]c) caused by hypotonic treatmenttriggers release of K+ and Cl from the cell (Okazakiand Tazawa 1986a, b, c) was tested using tonoplast-removed cells.These cells did not regulate turgor pressure. The plasmalemmaconductance remained almost constant for a change in the intracellularfree Ca2+ concentration ([Ca2+],) from 106 to 102mol?m3. The results suggest that some cytoplasmic Ca2+-sensitizingsoluble components, which work as mediators to activate K+ and/orCl channels in the plasmalemma and/or the tonoplast,were lost after desintegration of the tonoplast. The plasmalemmapotential was depolarized under high [Ca2+]i. However, no membranedepolarization was observed upon hypotonic treatment. Sincemembrane depolarization has been suggsted to occur under normal[Ca2+]c in intact cells (Okazaki and Tazawa 1986a, b), its absencesuggests that some cytoplasmic factors, which induce the membranedepolarization in a Ca2+-independent manner, are lost in tonoplast-removedcells.
1 Present address: Department of Biology, Osaka Medical College,Sawaragi-cho 2-41, Takatsuki, Osaka 569, Japan. (Received October 22, 1986; Accepted March 31, 1987) 相似文献
14.
Potassium Transport Across the Membranes of Chara: IV. INTERACTIONS WITH OTHER CATIONS 总被引:3,自引:0,他引:3
Smith, J. R. and Kerr, R. J. 1987. Potassium transport acrossthe membranes of Chara. IV. Interactions with other cations.J.exp. Bot. 38: 788799. The 42K influx () and the membrane electrical conductance (Gm were measured simultaneously forintemodal cells of Chara australis bathed in solutions containingdifferent concentrations of various cationic species. It wasfound that the potassium permeability (Pk,) of the membranewas reduced significantly when the bathing [CaSO4 exceeded 01mol m1. Concentrations of tetra-ethylammonium ions (TEA)exceeding 0?3 mol m3 were found to reduce significantlyboth and , but even high concentrations (10 mol m3)usually did not reduce the fluxes by more than a factor of 3.Na+ ions were found to be capable of reducing PK by a factorof 5?6 to a value of 4 nm s1. This appeared to be aminimum value for PK which was not reduced even if several inhibitorycations were present simultaneously. This suggests that possiblyonly one of two different modes of K+ transport can be inhibitedby cations. The possible geometry of the inhibitable K+ channelis briefly discussed and the implications of the presence ofNa+ and Ca2+ ions in many common bathing solutions are considered. Key words: Potassium, calcium, tetraethylammonium, inhibition 相似文献
15.
The vacuolar pH (pHv) and the cytoplasmic pH (pHc) of the marinegiant-celled green alga Chaetomorpha darwinii were measuredby pH microelectrode techniques on extracted vacuolar sap, andby the [I4C]DMO distribution method respectively. Equilibrationof DMO occurred with a half-time of about 2 h, with an apparentPDMO of 3.6 x 105 cm s1, but the vacuolar concentrationof free, undissociated DMO was always less than the externalconcentration. The explanation offered for freshwater giant-celledalgae of net DMO leakage across the plasmalemma cannotapply to Chaetomorpha darwinii, since electrically-driven DMOexit from the cytoplasm should be similar across the plasmalemmaand the tonoplast in these cells with large, vacuole-positivepotential differences across the tonoplast. pHc was accordinglycomputed assuming either tonoplast or plasmalemma equilibrationof DMO, with correction for DMO metabolism within the cell.pHc was 8.08.3 in the light in artificial seawater (pHoabout 8.0), was some 0.5 units lower in the dark, and was slightlylower with an external pH of 7. Vacuolar pH was 6.56.9,without consistent effects of illumination or of external pHof 7 rather than 8. While µH+ at the tonoplast was similarto that in giant-celled freshwater algae (although with a greatercontribution from relative to pH), µH+ at the plasmalemmawas less than 8 kJ mol1, i.e. less than one-third ofthe value in freshwater green algae. µNa+ was some 13kJ mol1 at the plasmalemma. The possibility that theprimary active transport process at the plasmalemma of Chaetomorphadarwinii (and certain other marine algae) is Na+ efflux ratherthan H+ efflux is discussed. 相似文献
16.
With the use of voltage clamp and current clamp techniques thesupposition was proved that during the hyperpolarizing response(HR) N. obtusa cells generate active electromotive force (emf)at the expense of metabolic energy. Threshold inward currentsent through the plasmalemma of the cell which was depolarizedwith 100 mol m3 KG resulted in the HR with the transferof the membrane's excitable units from the high-conductive stateto the low-conductive state. During the HR the membrane potentialVm increased from 135±10 mV to 290±15mV, the membrane resistance increased from 3.3±1.5 kOhmcm2 to 5.8±1.2 kOhm cm2 and the membrane emf Em increasedfrom 20±4 mV to 93± 15 mV. Changesin the external concentration of K, Na+, Cl andH did not affect the patterns of HR. Cells which weredepolarized by light also generated HR (in normal medium) whichwas accompanied with the increase of Vm, Rm and Em. The highvalue of Em generated during the HR can be explained only withthe involvement of active electrogenic charge transfer acrossthe membrane. 0.05 mol m3 DCCD added to the externalmedium inhibited the HR in both cases. Key words: Active ion transport, Hyperpolarizing response, Nitellopsis obtusa 相似文献
17.
Internodal cells of Chara australis can accumulate ammoniumto high concentrations (10 to 70 mol m3) in their vacuoles.When Cl is included in the bathing solution, changesin the cellular concentrations of ammonium, K+, Cl andNa+ have been shown to meet the requirements for electroneutralityand to account for the changes in vacuolar osmotic pressureassociated with ammonium uptake. If accumulation occurs in theabsence of external Cl, however; changes in the inorganicions do not meet these criteria. Malate is found in the vacuolesof cells accumulating amine in the absence of external Cland its presence (at 0·5 to 8·5 mol m3)allows us to account for electroneutrality and for changes inthe osmotic potential. Key words: Malate, Chara, electroneutrality, ammonium 相似文献
18.
The water-relations parameters of Chara inflata cells were determineddirectly using the micro pressure probe technique. The turgorpressure of cells in artificial pond water (0 = 0.06 MPa) wasabout 0.65 MPa and the half-time (T1/2) for water exchange wasabout 6.5 s. The calculated values of the hydraulic conductivity(LP) were in the range 12 ? 106m s1 (MPa)1.The volumetric elastic modulus () was 32.8 MPa for turgor rangingfrom 0.77 to 0.82 MPa. Large changes in the water-relations parameters and the electricalproperties of the membrane occurred when the turgor was decreasedto low values. These changes included: (i) a decrease in theT1/2 for water exchange, (ii) an increase in LP and (iii) depolarizationof the membrane potential difference (Vm). The micro pressure probe, which enabled the turgor pressureof the cell to be altered, was used in combination with thevoltage-clamp technique to determine the relationship betweenK+ and Cl conductances of the plasmalemma and the cellturgor. The K+ conductance increased reversibly as the turgorwas reduced in the range 0 to 0.6 MPa and the Cl -conductanceincreased as the turgor was reduced in the range 0.1 to 0.5MPa. It is suggested that these pressure-dependent K+ and Clconductances may have a dual role in electrical events and thenon-electrical responses such as changes in the cell volume. Key words: Chara inflata, membrane conductances, ion channels, water-relations parameters 相似文献
19.
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
20.
GYENES M.; ANDRIANOV V. K.; BULYCHEV A. A.; KURELLA G. A. 《Journal of experimental botany》1978,29(5):1185-1195
The effects of light on the pH in the vacuole and the electricpotential difference across the plasmalemma and the tonoplastof Nitellopsis obtusa were investigated by means of conventionaland H+-specific glass or antimony microelectrodes. Illuminationis found to bring about a decrease in the pH of the vacuolarsap by 0.10.5 units concomitant with a depolarizationof the cell. The light-induced changes of the potential differenceand the vacuolar pH depend in different ways on the pH of theexternal medium (pHo). At pHo 9.0 cells exhibit great light-inducedpotential changes (up to 100 mV), but only small pH changesof the vacuolar sap. At neutral or slightly acidic pHo valuesthe amplitude of the light-induced pH changes in the vacuoleincreases up to 0.30.5 pH units, but the amplitudes ofthe potential changes at the plasmalemma are relatively small.At pHo 9.0 a transient acidification of the medium is observedupon illumination whereas at lower pH values light-induced alkalinizationwas only seen. Transfer of the cells from pHo 9.0 to pHo 7.5results in a cell hyperpolarization by 6080 mV and adecrease of the vacuolar pH by 0.40.5 units under lightconditions but has no significant effect on the potential andthe vacuolar pH in the darkness. It is proposed that mechanismsof active H+ extrusion from the cytoplasm are located both inthe plasmalemma and the tonoplast. The observed acidificationin the vacuole appears to be determined by a light-induced increaseof the concentration of H+ in the cytoplasm. The H+ conductionof the plasmalemma seems to increase on illumination. The patternof the light-induced H+ fluxes across the tonoplast and theplasmalemma depends crucially on the extent of the light-inducedchanges in the H+ conductance and on the electrochemical gradientfor H+ at the plasmalemma. 相似文献