Internodal Cells Of Nitellopsis Obtusa Research Articles

Biomarker identification of isolated compartments of the cell wall, cytoplasm and vacuole from the internodal cell of characean Nitellopsis obtusa.

Cells of characean algae are attractive for plant cell physiologists because of their large size and their close relation to higher plant cells. The objective of our study was to evaluate the purity of the compartments (cell wall, cytoplasm with plastids, mitochondria, nuclei and endomembrane system, and vacuole) separated mechanically from the internodal cells of Nitellopsis obtusa using enzymatic markers. These included α-mannosidase and malate dehydrogenase, vacuolar and cytoplasmic enzymes, respectively. The biomarkers applied revealed the degree of compartment contamination with the material from unwanted cell parts. The cell wall was contaminated slightly by vacuole and cytoplasm residuals, respectively by 12.3 and 1.96% of corresponding biomarker activities. Relatively high activity of vacuolar marker in the cell wall could be associated with the cell vacuoles in the multicellular structure of the nodes. The biomarkers confirmed highly purified vacuolar (99.5%) and cytoplasmic (86.7%) compartments. Purity estimation of the cell fractions enabled reevaluating nCuO related Cu concentrations in the compartments of charophyte cell. The internalisation of CuO nanoparticles in N. obtusa cell occurred already after 0.5h. In general, the approach seems to be useful for assessing the accumulation and distribution of various xenobiotics and/or metabolites within plant cell. All this justifies N.obtusa internodal cells as a model organism for modern studies in cell biology and nanotoxicology.

Effect of sodium humate on membrane potential in internodal cells of Nitellopsis obtusa

Membrane potential and resistance changes in <em>Nitellopsis obtusa</em> induced by Na-humate as a function of external pH were investigated. The administration of Na-humate at concentrations of 12.5, 25, 50 and 100 mg dm<sup>-3</sup> brought about a hyperpolarization of the membrane potential and a drop of d.c. resistance in the pH range between 4.0 and 9.0. Depolarization of the membrane potential induced by low pH was counteracted by Na-humate. The electrophysiological effects of Na-humate are compared with those of IAA.

The effect of aluminium on bioelectrical activity of the Nitellopsis obtusa cell membrane after H+-ATPase inhibition

AbstractAluminium induced membrane potential (Em) changes and potential changes during repolarization phase of the action potential (AP) in the internodal cells of Nitellopsis obtusa after blocking H+-ATPase activity by DCCD were investigated. Micromolar concentrations of DCCD are sufficient to give complete and irreversible inhibition of proton pumping. The membrane potential was measured by conventional glass-microelectrode technique. We found that the half-amplitude pulse duration differs significantly between standard conditions, after DCCD application, and after H+-ATPase blocking and subsequent Al3+ treatment: 4.9, 7.7 and 17.2 seconds, respectively. We propose that in the short term (2 hours) treatment of Al3+, the decrease in membrane potential was compensated for by H+-ATPase activity. Blocking H+-ATPase activity by DCCD can enhance the influence of Al3+ on the bioelectrical activity of cell membranes.

Physiological and hemolytic toxicity of some aminophosphonates.

The effect of novel synthesized aminophosphonates on membrane potential and electrical conductance of internodal cells of Nitellopsis obtusa and hemolysis of erythrocytes (RBC) was studied. It was found that those the organophosphorous compounds, when present at 10-100 microM concentrations, caused depolarization and increased electrical conductance of alga membranes. They also influenced fluidity of erythrocyte membranes. When used at higher concentrations aminophosphonates caused hemolysis of RBC. The changes observed depended on structural features of the aminophosphonates, i.e., substituents at the carbon, phosphorus and nitrogen atoms, and, most probably, may be the result of direct interaction of the aminophosphonates with the lipid phase of the plasma membrane and the induced structural changes. Two modes of interaction are proposed.

Short‐term regulation of cytosolic Ca2+, cytosolic pH and vacuolar pH under NaCl stress in the charophyte alga Nitellopsis obtusa

ABSTRACTIsolated characean internodal cells of Nitellopsis obtusa can be stored in artificial pond water for many days, but they cannot survive in 100mol m−3 NaCl solution unless more than several mol m−3 Ca2+ is added. Short‐term effects of NaCl stress on the cytosolic concentration of Ca2+ ([Ca2+]c), cytosolic pH (pHc) and vacuolar pH (pHv) were studied in relation to the external concentration of Ca2+ ([Ca2+]e). Changes in [Ca2+]c were measured with light emission from a Ca2+‐sensitive photoprotein, semisynthetic fch‐aequorin which had been injected into the cytosol. Both pHc and pHv were measured with double‐barrelled pH‐sensitive microelectrodes. When internodal cells were treated with 100 mol m−3 NaCl (0–1 mol m−3 NaCl (0.1 mol m−3 [Ca2+]e), [Ca2+]c increased and then recovered to the original level within 60 min. The time course of the transient change in [Ca2+]c was not influenced by the level of [Ca2+]c (0.1 and 10 mol m−3). In some cases, the transient increase in [Ca2+]c was induced only by increasing external osmotic pressure with sorbitol. In response to treatment with 100 mol m−3 NaCl (0.1 mol m−3 [Ca2+]c), pHc decreased by 0.1–0.2 units after 10min but recovered after 30–60 min, while pHv increased by 0.4–0.5 units after 2–50 min and tended to recover after 60 min. The initial changes in both pHc and pHv were suppressed when [Ca2+]e was raised from 0.1 to 10mol m−3. These results show that the charophyte alga Nitellopsis can regulate [Ca2+]c, pHc and pHv under NaCl stress in the short term and that the protective effect of Ca2+ on salinity stress is apparently unrelated to perturbation of Ca2+ and pH homeostasis.

Nature of the water channels in the internodal cells ofNitellopsis

The hydraulic resistance was measured on internodal cells of Nitellopsis obtusa using the method of transcellular osmosis. The hydraulic resistance was approximately 2.65 pm-1 sec Pa, which corresponds to an osmotic permeability of 101.75 microns sec-1 (at 20 degrees C). p-Chloromercuriphenyl sulfonic acid (pCMPS) (0.1-1 mM, 60 min) reversibly increases the hydraulic resistance in a concentration-dependent manner. pCMPS does not have any effect on the cellular osmotic pressure. pCMPS increases the activation energy of water movement from 16.84 to 32.64 kJ mol-1, indicating that it inhibits water movement by modifying a low resistance pathway. pCMPS specifically increases the hydraulic resistance to exosmosis, but does not influence endosmosis. By contrast, nonyltriethylammonium (C9), a blocking agent of K+ channels, increases the hydraulic resistance to endosmosis, but does not affect that to exosmosis. These data support the hypothesis that water moves through membrane proteins in characean internodal cells and further that the polarity of water movement may be a consequence of the differential gating of membrane proteins on the endo- and exoosmotic ends.

Effects of quaternary ammonium salts on membrane potential and electric conductance in internodal cells of Nitellopsis obtusa

Effects of quaternary ammonium salts on membrane potential and electric conductance in internodal cells of Nitellopsis obtusa

Effects of UV‐C radiation on membrane potential and electric conductance in internodal cells of Nitellopsis obtusa

Effects of 253.7 nm ultraviolet radiation on membrane potential and conductance in internodal cells of Nitellopsis obtusa were studied. The radiation caused transient depolarization of plasmalemma and tonoplast and simultaneous increase in electric conductance. These effects were partly reversible and the degree of the recovery depended on the duration of the exposure. In cells with potential difference (between vacuole and external medium) more negative than – 140 mV, the radiation induced an action potential. The hyperpolarized state created by visible light and indole‐3‐acetic acid was fully suppressed by the radiation. The results are discussed taking into account the data for Chara corallina obtained by C. J. Doughty and A. B. Hope. It is suggested that 253.7 nm radiation inhibits electrogenic proton pumps in the plasmalemma and activates the Cl− channels.

Temperature dependence of the membrane resistance in Characeae cells

Changes in the electrical resistance of internodal cells of Nitellopsis obtusa (Desv. in Lois) J. Gr. and Lychnothamnus barbatus (Meyen) Leonh., produced by short‐lasting temperature changes (3‐min intervals) in the range of 4⇌48°C were measured. In the whole temperature range examined the electrical resistance of the cell membranes underwent from 5 to 9 distinct changes; the overall changes were approximately hyperbolic, while in certain narrow temperature ranges they were non‐monotonic, and in others linear. Arrhenius plots of these dependencies provide data which suggest a specific, stepwise character of changes in the permeability to ions, produced by temperature alterations and probably connected with corresponding modifications of cell membrane fluidity. This seems to support the view that the cell membranes of the examined plant species may exist in different, discrete, physiological states characteristic of certain temperature ranges.

Bioelectrical reactions of Nitellopsis obtusa induced by indole‐3‐acetic acid

The complex of bioelectrical paramenters (membrane potential, membrane resistance and capacitance) of internodal cells of Nitellopsis obtusa was measured over a wide range of IAA concentration (10−10 to 10−4M) with two intracellular microelectrodes. Primary effects of IAA at a concentration as low as 10−10M were observed. The optimum range of IAA action was from 10−9 to 10−6M. The type of IAA‐induced electroresponse depended on the initial level of membrane potential, which characterized the energetic state of the plasmalemma. In the energized state (ca −200 mV) N. obtusa cells appeared to have 3 typical reactions: hyperpolarization (membrane potential less than K+‐equilibrium potential), depolarization (membrane potential higher than K+‐potential) and absence of response at K+‐electrochemical equilibrium. Membrane capacitance was found constant at 0.74 ± 0.05 μF cm−2, but membrane resistance increased up to 50% independently of the sign of the electrogenic reaction. Increase of membrance capacitance and decrease of the membrane resistance was a feature of the de‐energized state (ca −135 mV) and may be explained by lower viscosity of membrane lipids, which interacted with IAA. The complex of parameter, including cytoplasmic steaming taken as an indicator of energy supply, is discussed as indicating slow IAA penetration combined with a primary action of IAA on the plasmalemma receptor sites.

Effect of intracellular Ca2+ on membrane potential and membrane resistance in tonoplast-free cells ofNitellopsis obtusa

Internodal cells ofNitellopsis obtusa were made tonoplast-free by intracellular perfusion of the vacuole with medium containing 5 mM EGTA. Next, the cells were perfused with media of various Ca2+ concentrations and the plasma membrane potential (Em) and resistance (Rm) were measured by the open-vacuole method.

Impedance of Nitellopsis obtusa Cells at Low Frequencies

Measurements of impedance were made on the internodal cells of Nitellopsis obtusa with the aid of external electrodes and current frequencies of from 20 to 1000 Hz. The analysis of the results points to the fact that the resistance (r) and capacity (c) of the membrane and the specific resistance (p) of the interior of the cell are constant in the range of the frequencies used. The values of r, c, and p are: r = 26-2 k£i cm2; c = 0-55 pF cm-2; p = 78 I2 cm. The observed dispersion of the resistance and capacity of the system investigated at low frequencies is a result of its complex structure, which consists of several phases with different electrical parameters. These phases are: the membranes, the cytoplasm, the vacuolar sap, the external solution, and the electrodes.

The Measurements of the Membrane Resistance ofCharaceaeby Alternating and Direct Currents

The internodal cells of Nitellopsis obtusa, Chara brauni, and Nitella flexilis were investigated quasi-simultaneously by direct and alternating currents with a frequency range from 1 to 1000 Hz. The membrane resistance obtained with a.c. was significantly lower than that obtained with d.c. We suggest that the discrepancies in the results obtained can be accounted for in terms of a three-layer model of the cell membrane.

Permeability of the Plasmalemma as Compared with that of the Tonoplast

In recent years there has been an increasing tendency to regard the tonoplast as the decisive diffusion barrier of the protoplast. The plasmalemma has been assumed to be more or less freely permeable, especially to ions (Brooks 4, Arisz 1, Epstein 8, Briggs and Robertson 3, Sutcliffe 12). This view is, however, based on observations which are far from unequivocal.In the following we shall try to elucidate the question of the relative permeability and susceptibility of the two plasma membranes towards sodium hydroxide and sodium carbonate. The tests were made on internodal cells of Nitellopsis obtusa, staminal hairs of Tradescantia virginiana and T. zcbrina and epidermal cells of Allium cepa var. sanguinetim. These cells show protoplasmic streaming and either contain anthocyanins or were stained with neutral red.In these experiments the plasmalemma, or some other layer outside the streaming part of the protoplasm, is assumed to be more or less impermeable towards sodium hydroxide as long as protoplasmic streaming is going on in the cells lying in the strongly alkaline solution. On the other hand, by the time the colour of the cell sap changes a considerable amount of NaOH must have passed through the whole protoplast, including both plasmalemma and tonoplast. The principal object of the experiments was, therefore, to compare (a) the time necessary to stop the protoplasmic streaming, irreversibly, with (b) the time required for the colour of the vacuole to change either to yellow (neutral red) or to blue (anthocyanin).