Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Chara”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1994

Role of the microtubule cytoskeleton in gravisensing Chara rhizoids.

The arrangement of the microtubule cytoskeleton in tip-growing and gravisensing Chara rhizoids has been documented by immunofluorescence microscopy. Predominantly axially oriented undulating bundles of cortical microtubules were found in the basal zone of the rhizoids and colocalized with the microfilament bundles underlying the cytoplasmic streaming. Microtubules penetrate the subapical zone, forming a three-dimensional network that envelops the nucleus and organelles. Microtubules are present up to 5 to 10 microns basal from the apical cytoplasmic region containing the statoliths. No microtubules were found in the apical zone of the rhizoid which is the site of tip growth and gravitropism. Depolymerization of microtubules by application of oryzalin does not affect cytoplasmic streaming and gravitropic growth until the relatively stationary and polarly organized apical and subapical cytoplasm is converted into streaming cytoplasm. When the statoliths and the apical cytoplasm are included in the cytoplasmic streaming, tip growth and gravitropism are stopped. Oryzalin-induced disruption of the microtubule cytoskeleton also results in a rearrangement of the dense network of apical and subapical microfilaments into thicker bundles, whereas disruption of the microfilament cytoskeleton by cytochalasin D had no effect on the organization of the microtubule cytoskeleton. It is, therefore, concluded that the arrangement of microtubules is essential for the polar cytoplasmic zonation and the functionally polar organization of the actin cytoskeleton which is responsible for the motile processes in rhizoids. Microtubules are not involved in the primary events of gravitropism in Chara rhizoids.

Chlorophyta↗
PubMed1993

Autoradiographic studies on 3H-fucose incorporation into manubria and its translocation to antheridial space during spermatogenesis in Chara vulgaris L.

The internal space of antheridium in Chara vulgaris L. is filled with the PAS-positive polysaccharide mucilage. It is produced and secreted by non-generative, polyploidal cells--manubria. Autoradiographic studies with the use of 3H-fucose have shown that this precursor is incorporated into polysaccharidial compounds at the manubrium surface. The dynamics of this process is different in proliferative phase than after symplasmic isolation of antheridium. The translocation of mucilage into antheridial space is very intensive, especially at the older developmental stages of antheridium. The data obtained after 12-hour postincubation indicated secondary metabolic changes of mucilage. The decrease in total radioactivity per investigated section is most intensive by the end of spermatogenesis. These facts seem to confirm the assumption about nutritive role of mucilage filling Chara antheridium during the process of spermatogenesis.

Autoradiography↗
PubMed1977

The role of histones in the restriction of chromatin activity in successive stages of development of the antheridial filaments of Chara vulgaris L.

The binding of 3H actinomycin D(3H AMD) was studied autoradiographically and the extinction following Feulgen's reaction at short (5 minutes) hydrolysis in 1N HCl was investigated cytophotometrically in 4 successive (4-, 8-, 16-, and 32-cell) generations of synchronously dividing antheridial filaments of Chara vulgaris L. Four stages of interphase, i.e. early and late S and early and late G2 were taken into consideration in each generation. The intensity of 3H AMD binding, except for early S, declines gradually in successive generations, i.e. in the developmental stages of antheridial filaments. Each generation reveals the highest radioactivity in the cells of early G2. Removal of lysine-rich histones in late G2 is the more effective for enhancing 3H AMD binding the more advanced is the stage of development of antheridial filaments. In early phase S extraction of arginine- or lysine-rich histones stimulates the binding of 3H AMD in the same degree. When all histones are removed, differences in the intensity of 3H AMD binding between particular generations of antheridial filaments disappear altogether. After a 5 minutes hydrolysis Feulgen's reaction reveales mainly loose chromatin, whereas after 16 minutes compact chromatin predominates. Removal of lysin-rich histones brings about an increased extinction after a 5 minutes hydrolysis in all phases of the cell cycle and in all developmental stages of antheridial filaments. After 5 minutes of hydrolysis, the extinction value per nuclear area in all experimental series, despite identical DNA content, undergoes a gradual reduction with the diminishing nuclear volume in the successive generations of antheridial filaments. This reduction is correlated with a decreased intensity of 3H AMD binding. The obtained data indicate that a decline in chromatin cativity in successive developmental stages of antheridial filaments of Chara vulgaris L. is caused by the progressing condensation of chromatin for which lysin-rich histones are responsible.

Autoradiography↗
PubMed1996

Autoradiographic studies on mucilage synthesis in Chara vulgaris antheridium with the use of 3H-fucose in total darkness and light.

Autoradiographic studies with 3H-fucose have shown that this precursor of polysaccharide compounds is incorporated into manubria and antheridial mucilage of Chara vulgaris both in the light and in the darkness. The dynamics of this process is lower in total darkness. The decrease in overall labelling of antheridium (manubria and mucilage) reflects secondary metabolic changes both in proliferative phase and in spermiogenesis. The pulse (2 and 5 min) incubations with the isotope confirm the intensive mucilage translocation which at later developmental stages is more dynamic than at earlier ones. It can explain previously observed decrease in manubria radioactivity at later stages after long (40 min) incubation, because PAS-positive polysaccharide synthesis is simultaneous with their fast translocation to the antheridial space. The present and previous autoradiographic and cytophotometric data taken altogether confirm the assumption about a nutritive role of mucilage filling Chara antheridium during the process of spermatogenesis.

Autoradiography↗
PubMed1997

Extract from maturing antheridia of Chara induces increased condensation of mitotic chromosomes in root meristem cells.

Serving as the incubation medium for root meristems of Allium cepa and Melandrium noctiflorum, crude extracts obtained from maturing male sex organs of Chara tomentosa induce: (1) increased condensation (with both shortening and thickening) of prophase, metaphase and anaphase chromosomes, (2) disarrangement of metaphase plates and aberrant segregation of chromosomes during anaphase, and (3) abnormal decondensation of chromosomes at telophase. Numerous resemblances that exist between the natural processes occurring in male sex organs of Chara and root meristem cells from antheridial extract-treated seedlings suggest the existence of a diffusible condensation-promoting factor, responsible for the reorganization of chromatin.

Cell Count↗
PubMed2005

Proteomic identification of putative plasmodesmatal proteins from Chara corallina.

Plasmodesmata are channels that bridge the cell walls of plant cells, allowing regulated transport of molecules between neighbouring cells. We have used a proteomic strategy to identify putative plasmodesmata-associated proteins in the giant-celled green alga Chara corallina. Proteins were extracted from the plasmodesmata-rich nodal complexes and the middle of the long internodal cells, which do not contain plasmodesmata. Comparison of protein spot patterns generated by two-dimensional gel electrophoresis of both the soluble and cell wall fractions from the two cell types was done. Fifty-eight spots that were common to the nodal and internodal soluble fractions were analysed by matrix assisted laser desorption/ionisation-time of flight mass spectrometry, and peptide mass fingerprint data were used to search the database. Matches were made to four of these spots, in each case to housekeeping proteins. Further, a number of nodal specific spots were identified, 11 from the soluble fraction and nine from the wall fraction. These spots were excised from the gels and analysed by liquid chromatography tandem mass spectrometry to obtain peptide sequence. Database searches suggest that these spots include homologues to previously identified plasmodesmata-associated proteins cp-wap13 and heat shock cognate 70, as well as RNA-binding proteins, eukaryotic initiation factor 4A and a beta-1,3-glucanase. Several spots remained unidentified providing exciting new candidate plasmodesmata-associated proteins.

Amino Acid Sequence↗
PubMed2004

Effect of a single excitation stimulus on photosynthetic activity and light-dependent pH banding in Chara cells.

Using pH microelectrodes and a Microscopy PAM (pulse-amplitude modulated) chlorophyll fluorometer, it is shown that a propagation of an action potential in Chara corallina leads to transient suppression of spatially periodic pH profiles along the illuminated cell. The suppression was manifested as a large pH decrease in the alkaline zones and a slight pH increase in the acid zones. The propagating action potential diminished the maximum yield of chlorophyll fluorescence (F(m)') in the alkaline cell regions, as well as the quantum yield of photosystem II photochemistry, without affecting F(m)' in the acid cell regions. The results indicate an interference of membrane excitation in the mechanisms responsible for pH banding patterns in Characean algae. Apparently, the electrical excitation of the plasma membrane in the alkaline cell regions initiates a pathway that can modulate membrane events at the thylakoid membrane.

Action Potentials↗
PubMed2005

Voltage-gated calcium and Ca2+-activated chloride channels and Ca2+ transients: voltage-clamp studies of perfused and intact cells of Chara.

The voltage-clamp technique was used to study Ca(2+) and Cl(-) transient currents in the plasmalemma of tonoplast-free and intact Chara corallina cells. In tonoplast-free cells [perfused medium with ethylene glycol bis(2-aminoethyl ether)tetraacetic acid] long-term inward and outward currents through Ca channels consisted of two components: with and without time-dependent inactivation. The voltage dependence of the Ca channel activation ratio was found to be sigmoid-shaped, with about -140-mV activation threshold, reaching a plateau at V>50 mV. As the voltage increased, the characteristic activation time decreased from approximately 10(3) ms in the threshold region to approximately 10 ms in the positive region. The positive pulse-activated channels can then be completely deactivated, which is recorded by the Ca(2+) tail currents, at below-threshold negative voltages with millisecond-range time constants. This tail current is used for fast and brief Ca(2+) injection into tonoplast-free and intact cells, to activate the chloride channels by Ca(2+) . When cells are perfused with EDTA-containing medium in the presence of excess Mg(2+), this method of injection allows the free submembrane Ca(2+) concentration, [Ca(2+)](c), to be raised rapidly to several tens of micromoles per liter. Then a chloride component is recorded in the inward tail current, with the amplitude proportional to [see text]. When Ca(2+) is thus injected into an intact cell, it induces an inward current in the voltage-clamped plasmalemma, having activation-inactivation kinetics qualitatively resembling that in EDTA-perfused cells, but a considerably higher amplitude and duration (approximately 10 A m(-2) and tau(inact)~0.5 s at -200 mV). Analysis of our data and theoretical considerations indicate that the [Ca(2+)](c) rise during cell excitation is caused mainly by Ca(2+) entry through plasmalemma Ca channels rather than by Ca(2+) release from intracellular stores.

Calcium↗
PubMed2004

Studies on semipermeability and electrical characteristics in membranes of Chara cells fixed with glutaraldehyde.

When internodal cells of Chara corallina were incubated in a solution containing 1% glutaraldehyde, an increase in intracellular osmolality was observed, and this indicates that the plasma membrane maintained its semipermeability. The effect on the membrane potential was studied. Although the active component generated by the electrogenic proton pump was lost, the passive component (more negative than -100 mV) was maintained during glutaraldehyde treatment for more than 1-2 h. The membrane resistance increased significantly. It was found that the tonoplasts also maintained their semipermeability during glutaraldehyde treatment.

Cell Membrane Permeability↗
PubMed2003

Recombinant motor domain constructs of Chara corallina myosin display fast motility and high ATPase activity.

The mechanism and structural features that are responsible for the fast motility of Chara corallina myosin (CCM) have not been elucidated, so far. The low yields of native CCM that can be purified to homogeneity were the major reason for this. Here, we describe the expression of recombinant CCM motor domains, which support the fast movement of actin filaments in an in vitro motility assay. A CCM motor domain without light chain binding site moved actin filaments at a velocity of 8.8 microm/s at 30 degrees C and a CCM motor domain with an artificial lever arm consisting of two alpha-actinin repeats moved actin filaments at 16.2 microm/s. Both constructs displayed high actin-activated ATPase activities ( approximately 500 Pi/s/head), which is indicative of a very fast hydrolysis step. Our results provide an excellent system to dissect the specific structural and functional features that distinguish the myosin responsible for fast cytoplasmic streaming.

Adenosine Triphosphatases↗
PubMed2004

Enhancing the staggered fluctuations of an actin filament sliding on Chara myosin.

We examined both longitudinal and transversal fluctuations of displacements of an actin filament sliding upon Chara myosin molecules. Although the magnitude of transversal fluctuations remained rather independent of ATP concentration, the longitudinal ones were found to increase their magnitude as the concentration increased. In addition, the longitudinal fluctuations gradually increased as the sliding velocity of the filament increased.

Actin Cytoskeleton↗
PubMed2006

Excitation-induced dynamics of external pH pattern in Chara corallina cells and its dependence on external calcium concentration.

The influence of cell excitation and external calcium level on the dynamics of light-induced pH bands along the length of Chara corallina cells is studied in the present paper. Generation of an action potential (AP) transiently quenched these pH patterns, which was more pronounced at 0.05-0.1 mM Ca2+ than at higher concentrations of Ca2+ (0.6-2 mM) in the medium. After transient smoothing of the pH bands, some alkaline peaks reemerged at slightly shifted positions in media with low Ca2+ concentrations, while at high Ca2+ concentrations, the alkaline spots reappeared exactly at their initial positions. This Ca2+ dependency has been revealed by both digital imaging and pH microelectrodes. The stabilizing effect of external Ca2+ on the locations of recovering alkaline peaks is supposedly due to formation of a physically heterogeneous environment around the cell owing to precipitation of CaCO3 in the alkaline zones at high Ca2+ during illumination. The elevation of local pH by dissolving CaCO3 facilitates the reappearance of alkaline spots at their initial locations after temporal suppression caused by cell excitation. At low Ca2+ concentrations, when the solubility product of CaCO3 is not attained, the alkaline peaks are not stabilized by CaCO3 dissolution and may appear at random locations.

Calcium↗
PubMed2005

Turgor pressure moves polysaccharides into growing cell walls of Chara corallina.

BACKGROUND AND AIMS: Plant growth involves pressure-driven cell enlargement generally accompanied by deposition of new cell wall. New polysaccharides are secreted by the plasma membrane but their subsequent entry into the wall is obscure. Therefore, polysaccharides and gold colloids of various sizes were presented to the inner wall face as though they were secreted by the plasma membrane. METHODS: Primary cell walls were isolated from growing internodes of Chara corallina and one end was attached to a glass capillary. Solutions of dextran or suspensions of gold colloids were pushed into the lumen by oil in the capillary. The oil did not enter the wall, and the solution or suspension was pressed against the inner wall face, pressurized at various 'artificial' P (turgor pressure), and polymer or colloid movement through the wall was monitored. KEY RESULTS: Interstices in the wall matrix had a diameter of about 4.6 nm measured at high P with gold colloids. Small solute (0.8 nm) readily moved through these interstices unaffected by P. Dextrans of 3.5 nm diameter moved faster at higher P while dextran of 9 nm scarcely entered unless high P was present. Dextran of 11 nm did not enter unless P was above a threshold, and dextran of 27 nm did not enter at P as high as 0.5 MPa. The walls filtered the dextrans, which became concentrated against the inner wall face, and most polymer movement occurred after P stabilized and bulk flow ended. CONCLUSIONS: P created a steep gradient in concentration and mechanical force at the inner wall face that moved large polymers into small wall openings apparently by starting a polymer end or deforming the polymer mechanically at the inner wall face. This movement occurred at P generally accepted to extend the walls for growth.

Cell Wall↗
PubMed2006

Calcium pectate chemistry controls growth rate of Chara corallina.

Pectin, a normal constituent of cell walls, caused growth rates to accelerate to the rates in living cells when supplied externally to isolated cell walls of Chara corallina. Because this activity was not reported previously, the activity was investigated. Turgor pressure (P) was maintained in isolated walls or living cells using a pressure probe in culture medium. Pectin from various sources was supplied to the medium. Ca and Mg were the dominant inorganic elements in the wall. EGTA or pectin in the culture medium extracted moderate amounts of wall Ca and essentially all the wall Mg, and wall growth accelerated. Removing the external EGTA or pectin and replacing with fresh medium returned growth to the original rate. A high concentration of Ca2+ quenched the accelerating activity of EGTA or pectin and caused gelling of the pectin, physically inhibiting wall growth. Low pH had little effect. After the Mg had been removed, Ca-pectate in the wall bore the longitudinal load imposed by P. Removal of this Ca caused the wall to burst. Live cells and isolated walls reacted similarly. It was concluded that Ca cross-links between neighbouring pectin molecules were strong wall bonds that controlled wall growth rates. The central role of Ca-pectate chemistry was illustrated by removing Ca cross-links with new pectin (wall "loosening"), replacing vacated cross-links with new Ca2+ ("Ca2+-tightening"), or adding new cross-links with new Ca-pectate that gelled ("gel tightening"). These findings establish a molecular model for growth that includes wall deposition and assembly for sustained growth activity.

Calcium↗
PubMed2006

Further quantification of the role of internal unstirred layers during the measurement of transport coefficients in giant internodes of Chara by a new stop-flow technique.

A new stop-flow technique was employed to quantify the impact of internal unstirred layers on the measurement of the solute permeability coefficient (P(s)) across the plasma membrane of internodes of the giant-celled alga Chara corallina using a cell pressure probe. During permeation experiments with rapidly permeating solutes (acetone, 2-propanol, and dimethylformamide), the solute concentration inside the cell was estimated and the external medium was adjusted to stop solute transport across the membrane, after which responses in turgor were measured. This allowed estimation of the solute concentration right at the membrane. Stop-flow experiments were also simulated with a computer. Both the stop-flow experiments and simulations provided quantitative data about internal concentration gradients and the contribution of unstirred layers to overall measured values of P(meas)(s) for the three solutes. The stop-flow experimental results agreed with stop-flow simulations assuming that solutes diffused into a completely stagnant cell interior. The effects of internal unstirred layers on the underestimation of membrane P(s) declined with decreasing P(s). They were no bigger than 37% in the presence of the most rapidly permeating solute, acetone (P(meas)(s) =4.2 x 10(-6) m s(-1)), and 14% for the less rapidly permeating dimethylformamide (P(meas)(s) =1.6x10(-6) m s(-1)). It is concluded that, even in the case of rapidly permeating solutes such as isotopic water and, even when making pessimistic assumptions about the internal mixing of solutes, an upper limit for the underestimation of P(s) due to internal unstirred layers was 37%. The data are discussed in terms of recent theoretical estimates of the effect of internal unstirred layers and in terms of some recent criticism of cell pressure probe measurements of water and solute transport coefficients. The current stop-flow data are in line with earlier estimations of the role of unstirred layers in the literature on cell water relations.

Biological Transport↗
PubMed2003

Studies on alkaline band formation in Chara corallina: ameliorating effect of Ca2+ on inhibition induced by osmotic shock.

Although the decrease in cell turgor by application of sorbitol to the external medium did not inhibit the alkaline band formation in Chara corallina, recovery of normal turgor severely inhibited it. Alkaline-loading analysis suggested that the inhibition of alkaline band formation was caused by inhibition of HCO(3)(-) influx but not that of OH(-) efflux. In the presence of 10 mM CaCl(2), the capacity of alkaline band formation was maintained during osmotic treatment. Cells could not form alkaline bands, when plasmolysis was induced by application of sorbitol at a higher concentration. Addition of 10 mM CaCl(2) could ameliorate the inhibition caused by plasmolyis.

Alkalies↗
PubMed2005

Possible involvement of mechanosensitive Ca2+ channels of plasma membrane in mechanoperception in Chara.

When an internodal cell of Chara corallina was stimulated with a mechanical pulse of various amplitudes lasting for 0.1 s (mechanical stimulus), the cell generated a receptor potential, which was highly dependent not only on the strength of the stimulus but also on the extracellular Cl- concentration. Extracellular Ca2+ was indispensable for generating receptor potential, since removal of Ca2+ reversibly inhibited generation of the receptor potential. The cytoplasmic Ca2+ level transiently rose upon mechanical stimulation. The stronger the mechanical stimulus, the larger was the increase in the cytoplasmic level of Ca2+. It is proposed that the first step of receptor potential is an activation of mechanosensitive Ca2+ channels at the plasma membrane.

Calcium Channels↗
PubMed2006

Electrical perception of the 'death message' in Chara: characterization of K+ -induced depolarization.

When the nodal end of an internodal cell of Chara corallina was subjected to a pulse treatment with artificial cell sap, a depolarization lasted in artificial pond water. This depolarization could also be induced by pulse treatment with KCl solution, indicating that K+ in the artificial cell sap is responsible (K+ -induced depolarization). The depolarization was prolonged in the presence of 2 mM KCl and the prolonged depolarization was terminated by supplementing with either CaCl2, MgCl2 or NaCl. These results supported the hypothesis that K+ released from the killed cell is responsible for generation of the wound-induced membrane depolarization.

Calcium↗