Cyclosis-related asymmetry of chloroplast–plasma membrane interactions at the margins of illuminated area in <Emphasis Type="Italic">Chara corallina</Emphasis> cells

Cytoplasmic streaming in plant cells is an effective means of intracellular transport. The cycling of ions and metabolites between the cytosol and chloroplasts in illuminated cell regions may alter the cytoplasm composition, while directional flow of this modified cytoplasm may affect the plasma membrane and chloroplast activities in cell regions residing downstream of the illumination area. The impact of local illumination is predicted to be asymmetric because the cell regions located downstream and upstream in the cytoplasmic flow with respect to illumination area would be exposed to flowing cytoplasm whose solute composition was influenced by photosynthetic or dark metabolism. This hypothesis was checked by measuring H⁺-transporting activity of plasmalemma and chlorophyll fluorescence of chloroplasts in shaded regions of Chara corallina internodal cells near opposite borders of illuminated region (white light, beam width 2 mm). Both the apoplastic pH and chlorophyll fluorescence, recorded in shade regions at equal distances from illuminated area, exhibited asymmetric light-on responses depending on orientation of cytoplasmic streaming at the light–shade boundary. In the region where the cytoplasm flowed from illuminated area to the measurement area, the alkaline zone (a zone with high plasma membrane conductance) was formed within 4-min illumination, whereas no alkaline zone was observed in the area where cytoplasm approached the boundary from darkened regions. The results emphasize significance of cyclosis in lateral distribution of a functionally active intermediate capable of affecting the membrane transport across the plasmalemma, the functional activity of chloroplasts, and pattern formation in the plant cell.     

Barrier components acting against osmotic water flow inNitella

In order to check whether or not the layer of chloroplasts densely arranged in the cortical gel of aNitella internode offers substantial resistance to osmotic water flow, a material was prepared which had the cortical gel layer freed from chloroplasts by centrifugation either longitudinal or lateral to the cell axis. The water permeability of the cell remained the same as normal even though the chloroplasts were exfoliated from the cell cortex to the extent of 50% of the total area, showing that the chloroplast layer plays hardly any significant part as a barrier to osmotic flow. Since it is known that the layer of the streaming endoplasm is also negligible as resistance against osmotic water flow (Tasawa and Kamiya, 1965), it is concluded that the major barrier components against osmotic flow in theNitella internode are the cell wall, plasmalemma and/or tonoplast.     

Photo-induced H+ Transport between Chloroplasts and the Cytoplasm in a Protoplasmic Droplet of Characeae

Svintitskikh, V. A., Andrianov, V. K. and Bulychev, A. A. 1985.Photo-induced H⁺ transport between chloroplasts and the cytoplasmin a protoplasmic droplet of Characeae.—J. exp. Bot. 36:1414–1429. The effects of light on the membrane potential and cytoplasmicpH of isolated droplets of protoplasm from Nitella have beenstudied using microcapillary electrodes and pH-sensitive antimonymicro-electrodes. Illumination of chloroplast-containing dropletscaused a change of the membrane potential with a concomitantacidification of both the cytoplasm and the outer medium, butit had no effect on the electrical resistance of the surfacemembrane. Treatment of protoplasmic droplets with uncouplers(NH₄Cl and CCCP) resulted in a complete inhibition of the light-inducedacidification of the cytoplasm, whereas the energy transferinhibitor DCCD had no effect. A correlation between the formationof a pH gradient across the thylakoid membrane and the acidificationof the cytoplasm was explicable in terms of the assumption ofrestricted spatial communication between the intra-thylakoidvolume and the cytoplasm in intact chloroplast. The photo-inducedacidification of the boundary layer of an external medium wasmarkedly stimulated under the action of inhibitors of H⁺-ATPaseDCCD and DES. These findings suggest that the active extrusionof H⁺ from the cytoplasm into the external medium is not drivenby an ATPase, although H+-conducting channels of membrane ATPaseprovide a pathway for a passive diffusion of protons from outsideinto the cytoplasm Key words: Transport of protons, protoplasmic droplet, intact chloroplasts, Characeae     

The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.     

Ultrastructure of infection-thread development during the infection of soybean by Rhizobium japonicum

The location and topography of infection sites in soybean (Glycine max (L.) Merr.) root hairs spot-inoculated with Rhizobium japonicum have been studied at the ultrastructural level. Infections commonly developed at sites created when the induced deformation of an emerging root hair caused a portion of the root-hair cell wall to press against an adjacent epidermal cell, entrapping rhizobia within the pocket between the two host cells. Infections were initiated by bacteria which became embedded in the mucigel in the enclosed groove. Infection-thread formation in soybean appears to involve degradation of mucigel material and localized disruption of the outer layer of the folded hair cell wall by one or more entrapped rhizobia. Rhizobia at the site of penetration are separated from the host cytoplasm by the host plasmalemma and by a layer of wall material that appears similar or identical to the normal inner layer of the hair cell wall. Proliferation of the bacteria results in an irregular, wall-bound sac near the site of penetration. Tubular infection threads, bounded by wall material of the same appearance as that surrounding the sac, emerge from the sac to carry rhizobia roughly single-file into the hair cell. Growing regions of the infection sac or thread are surrounded by host cytoplasm with high concentrations of organelles associated with synthesis and deposition of membrane and cell-wall material. The threads follow a highly irregular path toward the base of the hair cell. Threads commonly run along the base of the hair cell for some distance, and may branch and penetrate into subjacent cortical cells at several points in a manner analagous to the initial penetration of the root hair.     

Role of cyclosis in asymmetric formation of alkaline zones at the boundaries of illuminated region in <Emphasis Type="Italic">Chara</Emphasis> cells

The role of cytoplasmic streaming in pattern formation at the plasma membrane and chloroplast layer was examined with Chara corallina Klein ex Willd. cells exposed to nonuniform illumination. Our hypothesis was that the exchange of ions and metabolites between the chloroplasts and the cytoplasm in the illuminated cell area alters the composition of the cytosol while the flow of modified cytoplasm induces asymmetrical changes in the plasmalemmal transport and fluorescence of chloroplasts in the adjacent shaded areas. The hypothesis was tested by measuring the H⁺-transporting activity of plasmalemma and non-photochemical quenching (NPQ) in shaded areas of Chara cells at distances of 1–5 mm on either side of the illuminated region (white light, 1000 μmol/(m² s), beam width 2 mm). When measured at equal distances on opposite sides from the illuminated region, both pH and NPQ changes differed considerably depending on the direction of cytoplasmic movement at the light-shade boundary. In the region where the cytoplasm flowed out of irradiated area, the formation of alkaline zone (the plasma membrane domain with a high H⁺-conductance) and NPQ in chloroplasts was observed. In the vicinity of light-shade boundary where the flow was directed from the shade to the illuminated area, neither alkaline zone nor NPQ were formed. The results demonstrate the significance of cyclosis in the transfer of physiologically active intermediate that affects the membrane transport, the functional activity of chloroplasts, and the pattern formation in the plant cell.     

Intracellular Mobilization of Ca2+ and Inhibition of Cytoplasmic Streaming Induced by Transcellular Osmosis in Internodal Cells of Nitella flexilis

When transcellular osmosis was induced in internodal cells ofNitella flexilis that had been rendered inexcitable by treatmentwith KCl or EGTA, the rate of cytoplasmic streaming was reducedand the membrane was depolarized. In both KCl- and EGTA-treatedcells, the endoosmosis induced a significant increase in theconcentration of Ca²⁺ in the cytoplasm, which was demonstratedby monitoring the emission of light from aequorin that had beeninjected into the cytoplasm. When transcellular osmosis was induced in tonoplast-free cells,in which the intracellular Ca²⁺ concentration had been stabilizedat a very low level by treatment with the Ca²⁺-chelating agentEGTA, no change in the rate of cytoplasmic streaming on theendoosmosis side was observed. Hydration of the cytoplasm in the absence of endoosmosis wasinduced by direct introduction of a hypotonic medium into thevacuole by intracellular perfusion. The results mimicked theinhibition of streaming induced by transcellular osmosis. During transcellular osmosis, chloroplasts on the endoosmosisside swelled as a result of dilution of the cell sap. Swellingof chloroplasts was demonstrated to be unrelated to the inhibitionof streaming, since streaming was retarded at sites from whichchloroplasts had been removed. It is suggested that hydration of the cytoplasm triggers themobilization of Ca²⁺ from internal stores and causes an increasein the level of cytoplasmic Ca²⁺ that is responsible for theinhibition of streaming. Possible mechanisms for the osmosis-inducedincreases in the level of Ca²⁺ in the cytoplasm are discussed. (Received January 11, 1993; Accepted November 8, 1993)     

Simultaneous Measurement of the Bioelectric Potential of the Cell Wall and the Vacuoles during the Oscillatory Response to the Nitella Cell

Simultaneous measurements of bioelectric potentials of the vacuole and cell wall in cells of Nitella mucronata were made by inserting glass microelectrodes into the vacuole and cell wall respeclively. During the oscillation of the bioelectric potential of the vacuole. induced by sudden changes of the external bathing solution or by the impalement of the cell with a microelectrode. the cell wall potential also exhibited fluctuations of variable intensities in phase and concomitant with spikes of the vacuolar potential oscillation. However, the polarity of the pulses of the cell wall potential was reverse to that of the spikes of the vacuolar potential. These results suggest that the same event is registered at both sides of the plasmalemma membrane across which these phenomena are occurring. The results also support the voltage clamp and tracer flux measurements on these cells which indicate that during the generation of single action potentials, induced by current, the plasma lemma transiently increases its permeability to Cl^? and K⁺ ions expelling them from the cell. The variable intensity of the transient hyperpolarizations of the cell wall potential is explained by the distance of the microelectrode in the cell wall from the plasmalemma.     

Proton flows across the plasma membrane in microperforated characean internodes: tonoplast injury and involvement of cytoplasmic streaming

Microperforation of characean cell wall with a glass micropipette in the absence of the tonoplast impalement was found to cause rapid alkalinization of the apoplast by 2–3 pH units, which may rigidify the cell wall structure, thus protecting the cell from further injury. A similar but a deeper insertion of a microneedle, associated with piercing the tonoplast and with an action potential generation, led to a considerable delay in the apoplast alkalinization without affecting the amplitude of the eventual increase in pH. The retardation by the mechanically elicited action potential of the incision-mediated pH transients in the apoplast contrasted sharply to the enhancement of these pH transients by the action potential triggered electrically before the microperforation. Hence, the delay of the apoplast alkalinization was not related to basic ionic mechanisms of plant action potentials. Measurements of the vacuolar pH after mechanical elicitation of an action potential indicate that the tonoplast piercing was accompanied by leakage of protons from the vacuole into the cytoplasm, which may strongly acidify the cytoplasm around the wounded area, thus collapsing the driving force for H⁺ influx from the medium into the cytoplasm. The lag period preceding the onset of external alkalinization was found linearly related to the duration of temporal cessation of cytoplasmic streaming. The results suggest that the delayed alkalinization of the apoplast in the region of tonoplast wounding reflects the localized recovery of the proton motive force across the plasmalemma during replacement of the acidic cytoplasm with fresh portions of unimpaired cytoplasm upon restoration of cytoplasmic streaming.     

Ultrastructure and Development of Oil Idioblasts in Annona muricata L.

The ultrastructure and development of oil idioblasts in theshoot apex and leaves in Annona muricata L. are described, andthree arbitrary developmental stages are distinguished: cellsin which no additional cell wall layers have been depositedagainst the initial primary cell wall, possessing an electron-translucentcytoplasm and distinct plastids which lack thylakoids (stage1); cells in which a suberized layer has been deposited againstthe primary wall (stage 2, the cytoplasm resembles that of thepreceding stage), and cells in which an additional inner walllayer has been deposited against the suberized layer, whichincreases in thickness with development (stage 3). In this stagean oil cavity is formed, surrounded by the plasmalemma, andattached to a bell-like protrusion of the inner wall layer,the cupule. A complex membranous structure occurs next to thecupule. Smooth tubular endoplasmic reticulum (ER), appearingas linearly arranged tubules, and groups of crystalline bodieswith an almost hexagonal outline are present. The final stagewas further subdivided into three subgroups (a, b, c) basedon the extent of the oil cavity, its contents, and the compositionof the cytoplasm, and increasing thickness of the inner walllayer. The oil is probably synthesized in the plastids, releasedinto the cytoplasm, and then passed through the plasmalemmasurrounding the oil cavity. Oil idioblasts, Annona muricata L., suberized layer, inner wall layer, oil cavity, cupule, smooth tubular ER, crystalline bodies     

Participation of Ca2+ in cessation of cytoplasmic streaming induced by membrane excitation inCharaceae internodal cells

Summary The mechanism of the cessation of cytoplasmic streaming upon membrane excitation inCharaceae internodal cells was investigated.Cell fragments containing only cytoplasm were prepared by collecting the endoplasm at one cell end by centrifugation. In such cell fragments lacking the tonoplast, an action potential induced streaming cessation, indicating that an action potential at the plasmalemma alone is enough to stop the streaming.The active rotation of chloroplasts passively flowing together with the endoplasm also stopped simultaneously with the streaming cessation upon excitation. The time lag or interval between the rotation cessation and the electrical stimulation for inducing the action potential increased with the distance of the chloroplasts from the cortex. The time lag was about 1 second/15 m, suggesting that an agent causing the rotation cessation is diffused throughout the endoplasm.Using internodes whose tonoplast was removed by replacing the cell sap with EGTA-containing solution (tonoplast-free cells,Tazawa et al. 1976), we investigated the streaming rate with respect to the internal Ca²⁺ concentration. The rate was roughly identical to that of normal cells at a Ca²⁺ concentration of less than 10^–7 M. It decreased with an increase in the internal Ca²⁺ concentration and was zero at 1 mM Ca²⁺.The above results, together with the two facts that Ca²⁺ reversibly inhibits chloroplast rotation (Hayama andTazawa, unpublished) and the streaming in tonoplast-free cells does not stop upon excitation (Tazawa et al. 1976), lead us to conclude that a transient increase in the Ca²⁺ concentration in the cytoplasm directly stops the cytoplasmic streaming. Both Ca influxes across the resting and active membranes were roughly proportional to the external Ca²⁺ concentration, which did not affect the rate of streaming recovery. Based on these results, several possibilities for the increase in Ca²⁺ concentration in the cytoplasm causing streaming cessation were discussed.     

The Membrane Potential of Enzymatically Isolated Nitella expansa Protoplasts as Compared with their Intact Cells

With the enzymatically isolated Nitella protoplasts, sufficientinsertions of micro-electrodes to make a stable measurementof the membrane potential by the conventional method could notbe made because of an ‘elasticity’ of the outermembrane. We developed an effective method in which a micro-electrodecould be inserted after the outer membrane was punctured bypassing an electrical impulse through the micro-electrode. Inthis method, Ca ions play a crucial role in the ‘punching’and ‘healing’ processes of the protoplast membrane. The effects of the cations K⁺, Na⁺, Ca²⁺ and the anions Cl^–,, , on the membrane potentials of Nitella expansa protoplasts were compared with those of intactcells. The membrane potential of protoplasts was less negativethan that of intact cells when concentrations of Na or K, inthe presence of Ca, were below certain levels which increasedwith increasing Ca concentration; and it tended to become identicalto that of intact cells when Na or K concentrations were beyondthose levels. Beyond those levels for K the membrane potentialsof both protoplasts and intact cells typically seemed to bethe Nernst potentials in the presence of 0•1 to 30 molm^–3 Ca²⁺. However, for Na, the difference in potentialsbetween intact cells and protoplasts decreased at much higherconcentrations than for K. Increase of Ca always gave less negativeprotoplast potentials than those in intact cells. Replacementof Ca by Mg did not change the membrane potential of intactcells, although it was deleterious to protoplasts. The cellwall potential of intact cells was also measured by the micro-electrodetechnique and was revealed as a simple Donnan potential, assumingthe fixed negative charge density of 0•8 equivalent perdm³. The membrane potential of intact cells seems to be a significantreflection of the plasmalemma potential which is thought tobe measured directly in their protoplasts in terms of ionicselectivity and concentration dependency of the ion speciesexamined. In addition, increased sensitivity to calcium in protoplastpotentials compared to intact cells is suggested, though themembrane potential of intact cells seems to be largely preservedin their enzymatically isolated protoplasts. Key words: Membrane potential, protoplasts, Nitella expansa, cell wall potential     

Permeability of Lipophilic Cations

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). P_TPMP+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 s^–1. 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 2–5 nm s^–1. 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 s^–1. 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     

Light-Triggered Changes of Membrane Potential in Cells of Anthoceros punctatus and their Relation to Activation of Chloroplast ATPase

Post-illumination transients of the membrane potential wererevealed in cells of Anthoceros punctatus upon short (1–2s) irradiation with photosynthetically active light. An initialfast depolarization of the cell by 20–30 mV after a lagperiod of 2 s and a subsequent slow repolarization were recordedwith micro-electrodes positioned both in the chloroplast andin transparent parts of the cell. The potential changes of similarkinetics were also observed upon continuous illumination. Post-illuminationpotential changes were abolished by 3-(3, 4-dichlorophenyl)-l,l-dimethylurea and dicyclohexylcarbodiimide and were stimulatedby the addition of NH₄C1. It is assumed that the light-triggeredpotential change across the plasmalemma of A. punctatus aredetermined by the light activation of chloroplast ATPase. Thisassumption is further supported by observations of post-illuminationtransient increase of the chlorophyll fluorescence in preparationsof A. punctatus. Key words: Cell membrane potential, Chloroplast, Photosynthesis     

The Hyperpolarization of the Chara Membrane at High pH: Effects of External Potassium, Internal pH, and DCCD

At high external pH, the Chara membrane is known to switch toa new state in which the membrane potential is highly negative;it has been characterized as a passive diffusion potential forH⁺ (or 0H^–). DCCD is shown to inhibit the increased conductanceand the highly negative membrane potential associated with thisstate. DCCD also inhibits the plasmalemma H⁺-ATPase, as wellas cytoplasmic streaming. The alkaline state of the membraneis shown to involve a decreased permeability to K⁺; this enhancesthe selectivity for H⁺ (or OH^–) which results from theincreased permeability to H⁺ (or OH^–). Altering the cytoplasmicpH affects the membrane potential at both neutral and alkalinepH. It can also affect the ability of the cell to make the transitionto the alkaline state.     

Ultrastructure of Aerial Hyphae in Linderina pennispora

Ultrathin sections of the aerial hyphae of Linderina pennispora,fixed in glutaraldehyde, show the wall to be composed of anouter electron-dense layer and an inner less-dense one. Thefully developed septum is plugged by electrondense material.A similar septum exists at the base of the pseudophialide. Cytoplasmiccontinuity on both sides of the septum is maintained by theplasmalemma which passes through the septal pore around theperiphery of the plug. Membrane-lined vesicles may occur inthe wall, between the wall and the plasmalemma and internalto the plasmalemma. Ribosome-like particles are numerous inthe cytoplasm and endoplasmic reticulum is virtually absent.     

Effects of Intracellular Vanadate on Electrogenesis, Excitability and Cytoplasmic Streaming in Nitellopsis obtusa

Vanadate, which is known to inhibit the plasma membrane H^$-ATPaseof Neurospora, was applied intracellularly to internodal cellsof Nitellopsis by use of the intracellular perfusion technique.It inhibited electrogenesis and H^$-extrusion, evidence thatthe electrogenic pump of the Characeae plasmalemma is the H^$-extrudingone. The concentration of vanadate for the half-maximal inhibitionof the activity of the pump was 5 µM. The membrane potentialand H^$-extrusion occasionally recovered from vanadate inhibitionsfor reasons that are unknown. Membrane excitability, which isdependent on Mg?ATP, was not inhibited by vanadate, which suggeststhat the ATPase involved with membrane excitability differsfrom that of the H^$ pump. Cytoplasmic streaming took place evenwhen the cell was perfused with the medium containing 1 mM vanadate,which indicates that the vanadate-insensitive actomyosin systemis concerned with the motive force generation of the streaming. (Received August 27, 1981; Accepted April 13, 1982)     

Mitosis, Cytokinesis and Colony Formation in Pediastrum boryanum

Uninucleate cells of Pediastrum become multinucleate by a seriesof synchronous mitoses. Mitotic nuclei are enclosed by a perinuclearenvelope of endoplasmic reticulum. Cytoplasmic cleavage of themultinucleate cells leads to the production of uninucleate,biflagellate zoospores (zooids) which are subsequently releasedinto a lenticular vesicle through a rupture in the outer layerof the parental cell wall. Within the vesicle, presumably derivedfrom part of the inner layer of parental wall, the zooids swarmactively before aggregating in a planar array. Bands of microtubulesunderlie the plasmalemma of the zooids which, when the zooidsaggregate, are usually coplanar with the newly formed colony.The role of microtubules in patterned colony formation and inthe development of the characteristic horns on peripheral cellsof colonies of Pediastrum is discussed.     

Deterination of Effective Partition Coefficients of Alkali Chlorides by Measurements of Concentration Potential across the Nitella flexilis (L.) Ag. Isolated Cell Wall

We report a study in which we estimate by means of non-equilibriumprocesses the value of an effective partition coefficient, x,a parameter that we use to take into account the non-ideal behaviourof the electrolyte of the external medium in the cell wall space.This parameter is defined by the ratio of the salt partitioncoefficient to the activity of the non-diffusing charges. Tothat purpose, concentration potential in NaCl, LiCI and CuCl₂solutions was measured across an isolated cell wall of Nitellaflexilis at different pH. No significant difference appearedbetween the potential values measured in the presence of NaClor LiCl (pH 5.5, 4.0 and 3.0). At pH 3.0, in CuCl₂ solutions,the Nitella wall behaved as an uncharged membrane. Two methods—high concentrations and least-squares approximation-wereused to calculate from these results the value of the effectivepartition coefficient. Both gave similar values of x At a givenpH, the values of x are independent of the concentration ofthe external medium over a large range of concentration ratios.The activity of the exchange sites was estimated by the experimentallydetermined fraction of absorbed monovalent cations. The ionicconcentrations in the wall space were calculated at pH 5.5 and3.0 by introducing the values of x in the relations which correlatethem to the ionic concentrations in the wall for that givenvalue of the activity of the carboxylate sites. From their values,it appears that the negative fixed charges of the wall werefunctionally shaded by the condensation of a part of the adsorbedmonovalent cations. The activity of the former was, therefore,reduced to a value considerably lower than that estimated bythe cationic exchange capacity during equilibrium processes. Key words: Nitella flexilis (L.) Ag., cell wall, concentration potential, partition coefficient, ion condensation     

Is Calmodulin Involved in Electrophysiology of Chara corallina?

The role of calmodulin in Chara was investigated using the antipsychoticdrug trifluoperazine (TFP), which is known to bind to the calmodulin/Ca⁺⁺complex preventing it from carrying out its normal functions. At low concentration (4.0 µM), TFP had profound and irreversibleeffects on the electrophysiology of Chara plasmalemma. The restingp.d. depolarized and the membrane conductance decreased suggestingan inhibition of the proton pump. After several hours of exposurethe membrane became leaky, as cells deteriorated. The excitation was also affected by TFP. Spontaneous repetitivefiring was observed. The excitation increased in duration andthe action potential peak depolarized to + 20 mV. The cytoplasmic streaming was unaffected by TFP; the streamingrate at the resting potential remained unchanged when TFP wasadded to the medium, stoppage occurred at the time of excitationand the streaming slowly resumed. Key words: Calmodulin, Chara corallina, Proton pump, Cytoplasmic streaming, Current, voltage characteristics