Plasma Membrane Of Plant Cells Research Articles

The Conductance of the Plasmalemma for CO2

Permeability coefficients (PS values) for CO2 of the plasma membrane (PM) of the unicellular green algae Eremosphaera viridis, Dunaliella parva, and Dunaliella acidophila, and of mesophyll protoplasts isolated from Valerianella locusta were determined from 14CO2 uptake experiments using the rapid separation of cells by the silicone oil layer centrifugation technique. The experimental PS values were compared with calculated numbers obtained by interpolation of Collander plots, which are based on lipid solubility and molecular size, for D. parva cells, mesophyll protoplasts isolated from Spinacia oleracea, mesophyll cells and guard cells of Valerianella, and guard cell protoplasts isolated from Vicia faba. The conductivity of algal plasma membranes for CO2 varies between 0.1 and 9 × 10−6 m s−1, whereas for the plasmalemma of cells and protoplasts isolated from leaves of higher plants values between 0.3 and 11 × 10−6 m s−1 were measured. By assuming that these measurements are representative for plants and algae in general, it is concluded that the CO2 conductivity of algal PM is of the same order of magnitude as that of the higher plant cell PM. Ps values of plasma membranes for CO2 are lower than those for SO2, but are in the same order of magnitude as those measured for H2O. On the basis of these results it is concluded that theoretical values of about 3000 × 10−6 m s−1 believed to be representative for higher plant cells (Nobel, 1983) and which are frequently used for computer-based models of photosynthesis, lack experimental confirmation and represent considerable overestimations. However, with several systems, including higher plant cells, the conductance of the PM for CO2 was significantly higher in light than in darkness. This suggests that in light, additional mechanisms for CO2 uptake such as facilitated diffusion or active uptake may operate in parallel with diffusional uptake.

Adsorption of Al 3+ to phosphatidylcholine vesicles

Aluminum toxicity to soil and aquatic organisms is widespread, but the mechanisms of toxicity are unknown. To understand these mechanisms, it is important to know how aluminum reacts with cell surfaces. In this report, we studied adsorption of Al 3+ to liposomes composed of phosphatidylcholine, the most abundant phospholipid in plasma membranes of eukaryotic cells. Our equilibrium dialysis and electrophoresis experiments both showed that Al 3+ has a 560-fold higher affinity for the phosphatidylcholine surface than Ca 2+. Unlike previous reports for adsorption of divalent metals, adsorption of Al 3+ to phosphatidylcholine was predicted only approximately by the Stern model. Adsorption of AlF 2+ and AlF 2 + to the surface was not detectable at the activities we used. From our data, we calculate that Al 3+ at 5 × 10 −6 activity could neutralize the surface charge on plant cell plasma membranes and cause a surface potential shift from −30 to +11 mV. This is consistent with non-specific Al 3+ inhibition of cation uptake by root cells. Al 3+ adsorption to phosphatidylcholine may also play a role in aluminum uptake into cytoplasm by endocytosis.

Involvement of ion channels and active transport in osmoregulation and signaling of higher plant cells

The transport of inorganic and organic ions across the plasma membrane and organelle membranes of higher plants by ion channels, electrogenic pumps and co-transporters is essential to vital processes such as osmoregulation, growth, development, signal transduction and the storage of solutes. Recent studies have led to the identification of specialized transport proteins in the plasma membrane and vacuolar membrane of higher plant cells. Here we have integrated the functional aspects of these membrane proteins into a model which proposes a novel basis for ion transport processes involved in the regulation of gas exchange in leaves.

RGD-dependent linkage between plant cell wall and plasma membrane: consequences for growth.

Soybean (Glycine max [L.] Merr. cv. Mandarin) root cells (SB-1 cell line) grown in suspension culture containing Glycyl-Arginyl-Glycyl-Aspartyl-Seryl-Proline (GRGDSP) (0.25 mg/ml), a synthetic peptide containing the RGD sequence found in many extracellular matrix adhesive proteins, demonstrated (a) significantly enhanced growth rate, and (b) aberrant cell wall/plasma membrane interactions and organization. Substitution of the Asp (D) by a Glu (E) amino acid in the hexapeptide, or inversion of the RGD sequence to GDR, abolished the morphological and growth effects observed for GRGDSP in plant cells. Immunoblots, which were prepared from beta-octylglucoside extracts of whole soybean cells and protoplasts, probed with polyclonal antibodies raised against human vitronectin receptor (hVNR) complex, demonstrated a single band with an apparent molecular mass of 70-72 kD. Chromatography of beta-octylglucoside extracts of SB-1 cells on a Gly-Arg-Gly-Asp-Ser-Pro-Lys-Sepharose affinity column demonstrated the retention of a single 70-72 kD polypeptide that reacted specifically with anti-hVNR antiserum. In contradistinction, no cross-reactivity was observed with antifibronectin receptor antiserum. Epifluorescence microscopy of whole soybean cells, after moderate treatment with pectinase, demonstrated punctate fluorescent patches at the cell membrane/wall boundary when probed with anti-hVNR and rhodamine-derivatized secondary antibodies. We propose that coordination and control of plant cell division and proper cell wall biosynthesis may be mediated by an RGD-dependent recognition system in which RGD binding protein(s) promote cell membrane-cell wall attachment.

On Possible Functions of Electron Transport in the Plasmalemma of Plant Cells

Summary Electron transport has now been established to occur not only in membranes of chloroplasts or mitochondria but also in the plasma membranes of prokaryotes and eukaryotes. Here the basis reactions and reaction participants of electron transport in the plasma membrane of plant cells - the plasmalemma - are reviewed and hypotheses on its functioning are presented and discussed. The question is addressed in what respect electron transport at the plasmalemma is involved in bioenergetics, growth, and other cellular processes of plants.

A fast and high-current voltage clamp device for biophysical investigations

A fast voltage clamp circuit is described which permits the electrical potential difference of the plasma membrane of large plant cells to be controlled in less than 1 ms. It can supply a large current.

Plasma membrane alteration during bacteria-induced hypersensitive reaction in tobacco suspension cells as monitored by intracellular accumulation of fluorescein

Alteration of plant cell plasma membrane lipid phase during bacteria-induced hypersensitive reaction has been reported. To improve the detection of membrane lipid phase alteration during bacteria-induced hypersensitive reaction we monitored the accumulation of the fluorescent molecule fluorescein, from added fluorescein diacetate. Cells exposed to fluorescein diacetate accumulate fluorescein by rapid diffusion of fluorescein diacetate through the lipid phase of the plasma membrane and intracellular release of the acetate moieties by enzymes having esterase activity. Therefore, alterations of the lipid phase which affect fluorescein accumulation by changing the diffusion rate of fluorescein diacetate through the membrane can be monitored. The hypersensitive reaction was induced in tobacco suspension cultured cells by addition of the pathogenic bacterium, Pseudomonas syringae pv. syringae . Dramatic reduction of fluorescein accumulation was observed after 2 h. Tobacco cells exposed to a Tn5 insertion mutant of the pathogen, which does not induce the hypersensitive reaction, or the compatible pathogen Pseudomonas syringae pv. tabaci , did not show a reduction in fluorescein accumulation. Evaluation of possible mechanisms indicated that decreased fluorescein accumulation resulted from decreased membrane permeability to fluorescein diacetate. Since fluorescein diacetate is a lipid-soluble, non-polar molecule, the lowered plasma membrane permeability to fluorescein diacetate implies that alteration of plasma membrane lipid phase occurs during the hypersensitive reaction of tobacco to P. syringae pv. syringae .

Dependence of thermodynamic efficiency of proton pumps on frequency of oscillatory concentration of ATP.

In order to evaluate the utilization of variable ATP concentration produced by an oscillatory reaction (as in anaerobic glycolysis), we analyze the thermodynamic efficiency of power output of a cyclic, ATP-driven proton pump found in the plasma membrane of plant cells. The model used includes the coupling of potassium and calcium ion transport. Oscillations in the concentration of ATP can lead to either increases or decreases in efficiency compared to that at constant ATP concentration, with corresponding decreases and increases in dissipation in the irreversible processes of the proton pump, depending on the frequency of the oscillations. Variations of imposed frequencies induce, in the periodic response, variations of phase shifts between the components of the total membrane current, which consist of the pump's proton current and the currents of potassium and calcium ions. Increases in efficiency are attained when the phase shifts are such that maxima (or minima) in the proton pump current and membrane potential occur simultaneously.

Nodulin-26, a peribacteroid membrane nodulin is expressed independently of the development of the peribacteroid compartment.

The peribacteroid membrane (pbm) of root nodules is derived from the plant cell plasma membrane but contains in addition several nodule-specific host proteins (nodulins). Antibodies raised against purified pbm of soybean were used to immunoprecipitate polysomes to isolate an RNA fraction that served as a template for the synthesis of a cDNA probe for screening a nodule-specific cDNA library. Clone p1B1 was found to encode a 26.5 kDa polypeptide (nodulin-26) which is immunoprecipitable specifically with the anti-pbm serum. Nodulin-26 has features of a transmembrane protein and its structure differs from that of nodulin-24 which appears to be a surface protein of pbm. The expression of these two pbm nodulins was examined in nodules induced by Bradyrhizobium japonicum Tn5 mutants that arrest nodule development at different stages of pbm biosynthesis. Nodules that do not show release of bacteria from the infection thread express nodulin-24 at a very low level. In contrast, the expression of nodulin-26 occurs fully in nodules that form infection threads only and is not affected by the release of bacteria from the threads.

Activity of the Ethylene-forming Enzyme Measured in vivo at Different Cell potentials

Summary Activity of the ethylene-forming enzyme (EFE) has been determined in hypocotyl segments of mung bean ( Vigna radiata L.) and in discs of red beet ( Beta vulgaris L.) at the same time as the plasma membrane potential difference, measured with a microelectrode, has been progressively reduced by titration with the protonophores 2,4-dinitrophenol and carbonyl cyanide m-chloropheny1hydrazone and with KCl. Treatment with the protonophores affected EFE activity in both the mung bean hypocotyls and in the beet discs, although in different ways in the two tissues, while the depolarisation resulting from KCl treatment did not affect the EFE activity of either tissue. The results obtained are not consistent with the proposal of John (1983, FEBS Letters 152, 141) that a potential-dependent EFE activity is located at the plasma membrane of plant cells.

Monoclonal antibodies to antigens in the peribacteroid membrane from Rhizobium-induced root nodules of pea cross-react with plasma membranes and Golgi bodies.

Three rat hybridoma lines that produced monoclonal antibodies reacting with the peribacteroid membrane from Pisum sativum were isolated, and these all appeared to recognize the same antigenic structure. Using one of these monoclonal antibodies, AFRC MAC 64, electron microscopy of immunogold-stained thin sections of nodule tissue revealed that the antigen, present in the peribacteroid membrane, was also found in the plant plasma membranes and in the Golgi bodies, but not in the endoplasmic reticulum. When peribacteroid membrane proteins were separated by SDS-polyacrylamide gel electrophoresis and transferred to nitrocellulose by electro-blotting, it was found that MAC 64 bound to a series of protease-sensitive bands that migrated in the mol. wt. range 50-85 K. The epitope was sensitive to periodate oxidation and its structure may therefore involve the carbohydrate component of a membrane glycoprotein. We suggest that this structure originates in the Golgi apparatus and is subsequently transferred to the peribacteroid membranes and plasma membranes. The monoclonal antibody also reacted with peribacteroid membranes from nodules of Vicia and lupin, and with plasma membranes and Golgi membranes from uninfected plant cells, including root tip cells from onion (Allium cepa), indicating that the antigen is highly conserved in the plasma membranes of plant cells.

H+‐translocating ATPases of the plasma membrane and tonoplast of plant cells

H⁺‐translocating ATPases of the plasma membrane and tonoplast of plant cells

Oriented ?rosette? alignment during cellulose formation in mung bean hypocotyl

Cell-wall microfibrils formed on the surface of plant cells may be either deposited without obvious order, as in primary wall formation of higher plants, or in parallel orientations, as during secondary wall formation of higher plants and in the crossed microfibrillar layers in various algae. The mechanism of orientation is an actual cytological theme with controversial hypotheses trying to correlate components of the cytoskeleton with the microfibril orientation [1, 2]. Mainly based on inhibitor experiments, there is broad agreement that in most cases microtubules play a key role in the orientation mechanism. With the recent freeze-fracture findings of "roset te" particle complexes in the plasma membrane of a variety of cellulose forming algae, moss, fern and some higher plant systems (reviews in [3, 5]), it has become rather probable that these rosette structures, and perhaps associated "terminal globules" in the other half of the membrane, are involved in cellulose microfibril formation, or even are the synthases themselves ([3-8], for discussion see [3, 4]). We now have freeze-fractured the plasma membrane of higher plant cells involved in secondary wall formation to check for the possible existence of oriented rosette arrangements during the deposition of parallel wall microfibrils. We used mung beans (Vigna radiata (L.) Wilczek) cultivated for 6 days with twice daily watering. The hypocotyl was cut into thin slices, and immediately after sectioning was frozen between double replica holders in nitrogen slush. The further procedures were as described [3]. The plasmatic fracture face (PF) of the plasma membrane of (not further defined) cells with parallel microfibril arrangement (as judged from the microfibril imprints) was relatively rich in rosettes, and showed unequal particle density depending on the region of the cell surface. Some rosettes did not show a correlated position with respect to other rosettes, but quite frequently the rosettes occurred in tracks (Fig. 1 a). There was no regular distance between the individual rosettes in such a track, and the alignment was somewhat zigzag, with up to ca. 50 nm lateral deviation from the extrapolated center line of such a track following a microfibril imprint (arrows). This arrangement would allow cooperation of adjacent rosettes in formation of microfibril bands, if each rosette would form a 3.5 nm elementary microfibril (Fig. 1 b) as postulated earlier [3]. It furthermore would allow formation of many parallel microfibrils. The adjacent tracks of rosettes were often, but not always, in parallel, and not with regular spacing to the neighbour track. These findings of an oriented arrangement of rosettes in mung bean plasma membranes are the first such case for a higher plant system, and lend further support to the postulated role of rosettes in cellulose microfibril formation [3-8]. There are some indications that individual rosettes arranged in lines also occur in the basal parts of Funaria caulonema cells [8]. The arrangement of rosettes in tracks somewhat resembles the rows of rosettes involved in formation of the parallel microfibrils in Closterium, but there the groups of rosettes show equal center-to-center spacing [5]. From a variety of experimental data, mainly involving serial section analyses of cortical microtubule arrangement with respect to microfibril orientation after inhibition of the crystallization process, it has become rather

Proton Motive Potential Difference Across the Plasma Membrane of Plant Cells: a Comparison of Cultured Cells and Protoplasts From Italian Ryegrass (Lolium multiflorum Lam.) Endosperm

The electrochemical proton gradient (ΔμH+) was measured across the plasma membranes of ryegrass (Lolium multiflorum Lam.) endosperm cells grown in suspension culture. The pH gradient (ΔpH) and the transmembrane electrical potential (ΔΨ) of cells and protoplasts were compared. The pH gradient (ΔpH) was measured from the distribution of acetylsalicylic acid and 5,5-dimethyloxazolidine and the membrane potential (ΔΨ) was calculated from the distribution of the lipophilic tetraphenylphosphonium cation (TPP+) between the cells and medium. The protoplasts and cells maintained a similar ΔpH. At the external pH of the growth medium (pH 5.5), the cytoplasmic pH was about 7. Under these conditions the ΔΨ was -60 mV (negative inside) for cells and -46 mV for protoplasts. ΔpH and ΔΨ have values which vary reciprocally depending on the external pH. The main contributor to ΔμH+ at pH 4.0 is ΔpH whereas, at pH 7.0, ΔΨ is the main component. The external K+ concentration influences the cytoplasmic pH significantly only at the higher external pH values.

Anion-Sensitive, H+-Pumping ATPase in Membrane Vesicles from Oat Roots

H(+)-pumping ATPases were detected in microsomal vesicles of oat (Avena sativa L. var Lang) roots using [(14)C]methylamine distribution or quinacrine fluorescent quenching. Methylamine (MeA) accumulation into vesicles and quinacrine quench were specifically dependent on Mg,ATP. Both activities reflected formation of a proton gradient (DeltapH) (acid inside) as carbonyl cyanide m-chlorophenylhydrazone, nigericin (in the presence of K(+)), or gramicidin decreased MeA uptake or increased quinacrine fluorescence. The properties of H(+) pumping as measured by MeA uptake were characterized. The K(m) (app) for ATP was about 0.1 millimolar. Mg,GTP and Mg, pyrophosphate were 19% and 30% as effective as Mg,ATP. MeA uptake was inhibited by N,N'-dicyclohexylcarbodiimide and was mostly insensitive to oligomycin, vanadate, or copper. ATP-dependent MeA was stimulated by anions with decreasing order of potency of Cl(-) > Br(-) > NO(3) (-) > SO(4) (2-), iminodiacetate, benzene sulfonate. Anion stimulation of H(+) pumping was caused in part by the ability of permeant anions to dissipate the electrical potential and in part by a specific requirement of Cl(-) by a H(+) -pumping ATPase. A pH gradient, probably caused by a Donnan potential, could be dissipated by K(+) in the presence or absence of ATP. MeA uptake was enriched in vesicles of relatively low density and showed a parallel distribution with vanadate-insensitive ATPase activity on a continuous dextran gradient. DeltapH as measured by quinacrine quench was partially vanadate-sensitive. These results show that plant membranes have at least two types of H(+) -pumping ATPases. One is vanadate-sensitive and probably enriched in the plasma membrane. One is vanadate-resistant, anion-sensitive and has many properties characteristic of a vacuolar ATPase. These results are consistent with the presence of electrogenic H(+) pumps at the plasma membrane and tonoplast of higher plant cells.

The coupling of ethylene biosynthesis to a transmembrane, electrogenic proton flux

It is proposed that the reactions which lead to the generation of ethylene from 1-aminocyclopropane—1-carboxylic acid are arranged asymmetrically in the plasma membrane of plant cells so that ethylene biosynthesis is coupled to an inwardly directed, electrogenic flow of protons. According to this model a membrane potential (outside positive is required for ethylene biosynthesis. This proposed requirement is indicated by previous observations of a marked sensitivity of ethylene biosynthesis to the protonophore 2,4-dinitrophenol, and by its unusually strict dependence on membrane integrity.

Phytochrome induces photoreversible calcium fluxes in a purified mitochondrial fraction from oats

Previous studies have indicated that phytochrome regulates Ca(2+) fluxes across the plasma membrane of plant cells. In this study we investigated whether phytochrome can also regulate such fluxes across mitochondrial membranes, using the Ca(2+)-sensitive dye murexide to monitor the uptake and release of Ca(2+) by mitochondria. The results showed that Ca(2+) fluxes in these organelles could be photoreversibly altered, red light diminishing the net uptake rate and far-red light restoring this rate to its dark control level. Treatment of the mitochondria with ruthenium red blocked their Ca(2+) uptake. In the presence of this inhibitor, red light induced a net efflux of Ca(2+) from the mitochondria, and subsequent far-red light reduced this efflux to nearly zero, the dark control level. Light-induced rate changes in Ca(2+) flux, both with and without the inhibitor, persisted for several minutes in the dark and remained photoreversible through several irradiations for as long as 30 min. The purity of the mitochondrial preparation was judged to be about 80% by electron microscopic morphometry; most of the phytochrome present was localized on the mitochondria in the preparation by using immunocytochemical methods. Taken together with previous findings, the results suggest that red light activation of phytochrome would initiate an increase in the cytosolic Ca(2+) concentration. The results are integrated with the fact that calmodulin is a component of plant cell cytoplasms to construct a model postulating that phytochrome directs photomorphogenesis in part through its regulation of Ca(2+) and calmodulin-controlled enzyme activities.

Elaboration of cellulose fibrils by Agrobacterium tumefaciens during attachment to carrot cells.

The attachment of virulent strains of Agrobacterium tumefaciens to plant cells is the first step in the bacterial induction of tumors. Binding of A. tumefaciens to carrot tissue culture cells occurred as a two-step process. The initial step was the attachment of the bacteria to the plant cell wall. Living plant cells were not required. Bacterial attachment to heat-killed or glutaraldehyde-fixed carrot cells proceeded with only slightly altered kinetics and unaltered bacterial strain specificity. After the bacteria bound to the carrot cell surface, scanning electron microscopy showed that fibrils developed, surrounded the bacteria, and anchored them to the plant cell surface. These fibrils were synthesized by the bacteria and not by the plant cell since they were also made after the attachment of A. tumefaciens to dead carrot cells and since under some conditions the bacteria synthesized fibrils in the absence of plant cells. Calcofluor staining, acid hydrolysis, enzymatic digestion studies, and infrared spectroscopy showed that the fibrils were composed of cellulose. The formation of these cellulose fibrils occurred during the attachment of virulent strains of A. tumefaciens to plant cells in vitro. The fibrils anchored the bacteria to the plant cell surface and entrapped additional bacteria. The multiplication of entrapped and attached bacteria resulted in the formation of large clusters of bacteria held close to the plant cell wall and plasma membrane by cellulose fibrils. This high concentration of bacteria may facilitate transfer of Ti plasmid deoxyribonucleic acid to the plant cell resulting in the formation of tumors.

Electrogenic membrane transport in plants a review

This review treats some examples of electrogenic transport across the outer plasmamembrane (plasmalemma) of plant cells. The selection includes primary active uniport by membrane ATPases (e.g., the proton pump), secondary active transport of hexoses by proton-dependent cotransport, and passive uniport of amines. Primacy is given to the presentation of electrophysiological data and to the discussion of voltage-dependence of the transport mechanisms.

Membranes in lupin root nodules. I. The role of Golgi bodies in the biogenesis of infection threads and peribacteroid membranes.

The process of infection of lupin nodule cells by rhizobia was examined using thin-section and freeze-fracture electron-microscopic techniques to characterize the properties of different membranes and to establish relationships between them. The membranes of the Golgi bodies and the endoplasmic reticulum stained with zinc iodide-osmium tetroxide but not with phosphotungstic acid or silver. By contrast the infection thread membranes, peribacteroid membranes, plasma membranes and membranes of cytoplasmic vesicles did not stain with zinc iodide-osmium tetroxide but stained with phosphotungstic acid and silver. The peribacteroid membranes and plasma membranes are, however, different from each other since the particle density on the E face of freeze-fracture replicas of plasma membranes was twice that on the E face of the peribacteroid membranes. An examination of the tips of the infection threads in the cytoplasm of the plant cells, showed that the rhizobia bud off from the infection threads enclosed in the infection thread membranes. The rhizobia continue to divide still surrounded by membranes of plant origin, namely the peribacteroid membranes. Cytoplasmic vesicles are observed in both thin-section and freeze-fracture preparations of nodule tissue closely associated with, and apparently produced by, Golgi bodies. Formation of the walls and membranes of the infection threads and of the peribacteroid membranes involves fusion of the cytoplasmic vesicles with these membranes. It is proposed that the process of infection of plant cells in lupin nodules involves a change in the function of the Golgi body system for the biogenesis of plant cell walls and plasma membranes to include the synthesis of the walls and membranes of the infection threads and also the peribacteroid membranes.