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M J Beilby - One of the best experts on this subject based on the ideXlab platform.
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The electrophysiology of salt tolerance in charophytes
Cryptogamie Algologie, 2020Co-Authors: M J Beilby, Virginia A ShepherdAbstract:Lamprothamnium succinctum, charophyte tolerante au seul, croit dans des environnement salins non marins. Chara australis, charophyte sensible au sel, vit en eau douce. Les reponses electro-physiologiques des cellules inter nodales de ces especes a une augmentation de la teneur en Na + de leur milieu sont modelisees et comparees. Les deux charophytes presentent une plus forte conductance de base dans les milieux riches en Na + . Lamprothamnium est capable de maintenir une difference de potentiel (PD) au repos hautement negative par augmentation du taux de protons pompes. Les cellules de Chara, dans un milieu a forte teneur en Na + repondent de facons plus variees. Cependant, meme quant elle se produit, l'augmentation du pompage ne previent pas la depolarisation de la PD membranaire de -243 ± 15 mV (5 cellules) a -188 ± 15 mV (5 cellules), au dela d'un temps d'exposition moyen de 64 mn dans un milieu a forte teneur en Na + . De plus, la pompe a protons devient tres sensible a la fois a la depolarisation et a l'hyperpolarisation imposees a la membrane par la pression du voltage. Une telle inhibition de la pompe entrave le retablissement de la PD negative au repos apres l'application d'une tension ou d'un potentiel d'action spontanee. La signification des petites differences dans un transporteur rendant la plante tolerante au sel est discutee a la lumiere des adaptations evolutives.
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Modelling Oscillations of Membrane Potential Difference
Rhythms in Plants, 2020Co-Authors: M J BeilbyAbstract:The oscillation of the membrane potential difference (PD) is considered in terms of one or more ion transporters changing their conductances. For slow oscillations (period greater than about one minute), the transporters could be identified by employing the current–voltage (I/V) technique. The electrical characteristics of each transporter population were then modeled and the evolution of the model parameters with time obtained. Examples of single transporter type changing against a steady background conductance were the proton pump in the charophyte Chara australis and a putative potassium pump in Ventricaria ventricosa. A detailed modeling was done for the former, but it is in early development for the latter. The hypertonic regulation in the salt-tolerant charophyte Lamprothamnium spp., and an interaction of the proton pump and the proton channel in C. australis are given as examples of two transporters responding to a change in salinity and membrane PD, respectively. A detailed modeling was done for each response. The hypotonic regulation in Lamprothamnium involves a complex interaction of several transporters, initiated by the decrease of the medium salinity. Finally, spontaneous action potentials (APs) in C. australis are shown as the medium salinity is increased. The examples demonstrate the analytical and predictive power of the I/V methodology coupled with the systems biology modeling.
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Salt tolerance at single cell level in giant-celled Characeae.
Frontiers in Plant Science, 2015Co-Authors: M J BeilbyAbstract:Characean plants provide an excellent experimental system for electrophysiology and physiology due to: (i) very large cell size, (ii) position on phylogenetic tree near the origin of land plants and (iii) continuous spectrum from very salt sensitive to very salt tolerant species. A range of experimental techniques is described, some unique to characean plants. Application of these methods provided electrical characteristics of membrane transporters, which dominate the membrane conductance under different outside conditions. With this considerable background knowledge the electrophysiology of salt sensitive and salt tolerant genera can be compared under salt and/or osmotic stress. Both salt tolerant and salt sensitive Characeae show a rise in membrane conductance and simultaneous increase in Na+ influx upon exposure to saline medium. Salt tolerant Chara longifolia and Lamprothamnium sp. exhibit proton pump stimulation upon both turgor decrease and salinity increase, allowing the membrane PD to remain negative. The turgor is regulated through the inward K+ rectifier and 2H+/Cl- symporter. Lamprothamnium plants can survive in hypersaline media up to twice seawater strength and withstand large sudden changes in salinity. Salt-sensitive Chara australis succumbs to 50 - 100 mM NaCl in few days. Cells exhibit no pump stimulation upon turgor decrease and at best transient pump stimulation upon salinity increase. Turgor is not regulated. The membrane PD exhibits characteristic noise upon exposure to salinity. Depolarization of membrane PD to excitation threshold sets off trains of action potentials, leading to further loses of K+ and Cl-. In final stages of salt damage the H+/OH- channels are thought to become the dominant transporter, dissipating the proton gradient and bringing the cell PD close to 0. The differences in transporter electrophysiology and their synergy under osmotic and/or saline stress in salt sensitive and salt tolerant characean cells are discussed in d
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formation of extracellular sulphated polysaccharide mucilage on the salt tolerant characeae Lamprothamnium
International Review of Hydrobiology, 2014Co-Authors: Kaire Torn, M J Beilby, Michelle T Casanova, Sabah Al KhazaalyAbstract:The aim of this study was to examine the formation and the distribution of extracelluar sulphated polysaccharide (SP) mucilage on Lamprothamnium cells as a function of growth medium salinity. Six Lamprothamnium species were gathered from nine locations in South Australia, Victoria and NSW. The salinity of the original habitats varied from 2 to 41g/L. Alcian Blue staining at low pH was employed to measure the coverage of SP on the thalli. The basal (older) internodes generally exhibited SP coverage between 80 and 100% (in one case 5%) regardless of salinity. In young (apical) internodes the SP coveragewas lower, between 2 and 90%, again independent of salinity. Controlled salinity experiments confirmed that all cells developed SP cover with time, even cells in 0 and very low salinities. The rate of SP development on basal internodes increased with salinity. Similar trends could be seen in apical internodes, but the overall rate was slower, possibly influenced by cell development. A temporary loss of SP mucilage was observed upon planting cuttings at low salinities and low external sulphate concentrations. The SP mucilage was found on all the surveyed Lamprothamnium species. The SP coverage increased with cell age irrespective of growth medium salinity. The results are discussed with reference to the evolution of salt tolerance and the role of SP in different plant groups.
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modelling ion transporters at the time of hypertonic regulation in Lamprothamnium succinctum characeae charophyceae
2007Co-Authors: Sabah Al Khazaaly, M J BeilbyAbstract:exposed to a step from 1 /6 to ⅓ artificial seawater (ASW) and to equivalent osmotic increase by addition of sorbitol (Sorbitol ASW). In each case we observed the membrane potential difference (PD) becoming transiently more negative. The steady state membrane PD of cells in 1 /6 ASW was -133 10 mV (9 cells). The maximum membrane PD in ⅓ ASW of -145 10 mV (7 cells) was reached in 110 91 minutes after the start of the hypertonic stress. The control cells for the Sorbitol ASW experiments were in K + state with membrane PD of -96 10 mV (9 cells) in 1 /6 ASW. The maximum membrane PD in Sorbitol ASW of -151 10 mV (5 cells) was reached after 148 74 minutes. The modelling was implemented by fitting the Two State HGSS (Hansen, Gradmann, Sanders and Slayman) model to the proton pump. The GHK (Goldmann, Hodgkin and Katz) model supplemented by the Boltzmann distribution was employed to fit the large conductance K + channels, dominating the membrane conductance in the K + state, and the inward and outward rectifiers. An empirical model was fitted to the background current. Modelling resolved the hypertonic response to changes in the proton pump, background conductance, the half-activation potential and sometimes the gating charge of the inward rectifier. The pump model parameters k 0 io and κoi (in s -1 ) increased from 4500 and 180 in 1 /6 ASW to 5000 and 850 in ⅓ ASW, respectively. The background conductance increased from 6.3 S/m 2 in 1 /6 ASW to 9.6 S/m 2 in ⅓ ASW. The half-activation PD for the inward rectifier depolarised from -330 to -310 mV. In Sorbitol ASW the pump was activated with maximal k 0 io and κoi (in s -1 ) of 35000 and 55. The background conductance decreased from 2.75 S/m 2 in 1 /6 ASW to 2.0 S/m 2 in Sorbitol ASW. The half-activation PD for the inward rectifier depolarised from -380 to -355 mV. Therefore, the turgor decrease alone initiated the response of the inward rectifier and the proton pump. The increase in salinity was responsible for the rise in the background conductance. The responses of the transporters as function of time in ⅓ ASW and Sorbitol ASW were modelled, starting with the control in either pump state or K + state. While there was a great variability from cell to cell in the timing of the different transporters, the inward rectifier activation at more positive PDs preceded the maximum pump activation. The experiments described here are a part of detailed analysis of the salt tolerance mechanisms at the single cell level. The identity of the salinity stress detector and the signalling cascades activating the regulatory ion transporters are unknown in any plant system. Using charophytes as an experimental system provides another advantage of comparison between salt-tolerant genera (such as Lamprothamnium) and salt-sensitive ones (such as Chara).
Adriana García - One of the best experts on this subject based on the ideXlab platform.
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Gyrogonites and oospores, complementary viewpoints to improve the study of the charophytes (Charales)
Aquatic Botany, 2020Co-Authors: Ingeborg Soulié-märsche, Adriana GarcíaAbstract:a b s t r a c t Charophytes (Charales) are multicellular algae growing in fresh- to hypersaline waters and recorded as fossils by their oospores (formed by resistant organic walls) and gyrogonites (formed by intracellular calcification of the spiral cells surrounding the oospore). Preservation of oospores is mostly restricted to Late Pleistocene-Holocene sediments, whereas calcareous gyrogonites provide the fossil record of charo- phytes since the Late Silurian (425 Ma) and constitute the only link between living and fossil charophytes. Oospores and gyrogonites represent successive developmental stages occurring after fertilisation of the oogonia; however, gyrogonites do not develop in the extant genera Nitella and Tolypella section Tolypella of Tribe Nitelleae, and in most species of the subgenus Charopsis. For Tribe Chareae and Sphaerochara (Tolypella section Rothia), gyrogonites display more useful characters than the oospores, allowing easy identification of the extant genera Nitellopsis, Lychnothamnus, Lamprothamnium, Sphaerochara and Chara subgenus Chara. Determination to species level, and in particular the study of plastic species, needs a statistical approach. Extant oospores/gyrogonites can be used as modern analogues to infer palaeo- hydrological conditions and record past biodiversity. The ecological requirements of the living species provide important information for the restoration/conservation of wetlands and their management, and contribute to the reconstruction of Quaternary palaeoenvironments. The aim of the present paper is to highlight the importance of the gyrogonite, especially when studying extant charophytes, the application of both gyrogonites and oospores to palaeoenvironmental reconstructions, and to provide an accurate terminology and determination criteria for their study.
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trace element and stable isotope chemistry of gyrogonites of the euryhaline charophyte Lamprothamnium
Aquatic Botany, 2015Co-Authors: Allan R. Chivas, Adriana GarcíaAbstract:Abstract Within the broader plant kingdom, charophytes, as forerunners to higher plants, and with links to algae, precipitate calcium carbonate in their vegetative and female reproductive structures. We performed experimental cultures to understand the partitioning of Mg/Ca and Sr/Ca and oxygen-isotopes between gyrogonites (the calcified fruiting body) and host water. Such relationships, if systematic, could be utilised to investigate the past environments of water bodies using the chemistry of preserved fossil gyrogonites. The euryhaline charophyte Lamprothamnium cf. succinctum was cultured at 15, 20, 25 and 30 °C and at salinities of 15, 20, 25 and 35 PSU (g/L, total dissolved solids). Among this matrix of conditions, thallus extension rates demonstrate optimal growth at 25 °C and 35 PSU. The carbonate phase in the gyrogonites is high-magnesium calcite with up to 18 mol% Mg. The Mg/Ca ratios of the gyrogonites are related to growth temperature, whereas Sr/Ca ratios do not appear to have any significant correlation to temperature. Variations in salinity, at conservative chemistry, do not affect the minor-element chemistry of the gyrogonites. The δ18O values of gyrogonites show complex but linear relationships as a function of both the temperature (∼ −0.10‰/°C) of the host water and of salinity. This seemingly dual control on gyrogonite δ18O values will make them difficult to apply, in isolation, to the fossil record. A combination of Mg/Ca, Sr/Ca and δ18O may assist in palaeoenvironmental interpretation, although additional techniques (e.g. Ba/Ca and Na/Ca) not yet developed for charophytes, may be required. The δ18O values of cultured gyrogonites are difficult to fully explain, largely because of the paucity of information on the biochemical processes involved in their calcification. However, the KD values for both Mg/Ca and Sr/Ca vary only by 10% about a mean value of 0.038 and 0.46, respectively, over the temperature range 15–25 °C. Accordingly, measurement of these ratios in fossil Lamprothamnium may provide reasonable estimates of the Mg/Ca and Sr/Ca ratios of past waters.
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Quaternary and extant euryhaline Lamprothamnium Groves (Charales) from Australia: Gyrogonite morphology and paleolimnological significance
Journal of Paleolimnology, 2004Co-Authors: Adriana García, Allan R. ChivasAbstract:Charophytes are very common in Australian modern and Quaternary waterbodies, and are quite commonly incorrectly reported as “ Chara ” sp. or Lamprothamnium papulosum (Wallroth) Groves. This paper is the first attempt at the identification of the widespread euryhaline genus Lamprothamnium in Australia, and its use as a paleoenvironmental indicator. Lamprothamnium is distributed worldwide in all continents, except north and central America. The Australian environment, characterized by increasing aridity during the last 500 ka, has an abundance of saline lakes. We sampled 30 modern lakes and identified extant Lamprothamnium macropogon (A. Braun) Ophel and Lamprothamnium succinctum (A. Braun in Ascherson) Wood. Fossil gyrogonites, from lacustrine sediments ∼65 ka old from Madigan Gulf, Lake Eyre, were identified as Lamprothamnium williamsii sp. nov. We applied statistical analysis (analysis of variance, ANOVA) to the morphometry of the gyrogonites from one fossil and three living Lamprothamnium populations. The ANOVA test suggests all the populations are different, including two separate populations of extant L. macropogon , interpreted in this case as the expression of ecophenotypic variability. Lamprothamnium is a useful paleoenvironmental indicator because it indicates a non-marine environment with varying salinity ranging from fresh (usually 2–3 g l^−1) to 70 g l^−1, and water bodies holding water for at least 70 consecutive days. Collectively, these parameters provide important information in the study of ephemeral habitats.
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Lamprothamnium heraldii sp nov charales charophyta from australia the first dioecious representative of the genus
Phycologia, 2003Co-Authors: Adriana García, Michelle T CasanovaAbstract:Abstract Lamprothamnium heraldii A. Garcia & Casanova sp. nov. (Charales, Charophyta) is a dioecious species collected in Australia. Its dioecious nature and the characteristics of its reproductive organs separate it from other species of the genus. The habit of the male and female plants is similar, and their vegetative morphology is similar in many respects to that of the monoecious species. However, the new species has larger antheridia and oogonia, larger coronula cells on the oogonium, a smaller number of striae and circumvolutions in the oospores and gyrogonites, and different gyrogonite morphology. The new species has been found in ephemeral lakes from the Paroo region in north-western New South Wales (NSW) and south-western Queensland, at the eastern margin of central Australia. Lake Gidgee, NSW, was chosen as the type locality. Lamprothamnium heraldii was also collected from Palaeo Lake, NSW, and Mid-Blue Lake and Lower Bell Lake, Queensland. These habitats are characterized by fluctuating salini...
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the charophyte Lamprothamnium succinctum as an environmental indicator a holocene example from tom thumbs lagoon eastern australia
Alcheringa, 2002Co-Authors: Adriana García, Brian G Jones, Bryan E Chenhall, Colin V MurraywallaceAbstract:The palaeobiota from a middle to late Holocene succession in Tom Thumbs Lagoon, N.S.W., Australia, reflects a range of environmental conditions caused by sea-level changes and active estuarine sedimentation. At the base of the succession (∼ −0.4 m AHD) a thin bed, containing molluscs dated at 6.7 ka B.P. by radiocarbon and amino acid racemisation, and foraminifers is indicative of open estuarine conditions. From +0.35 m AHD towards the top of the sequence the charophyte Lamprothamnium succinctum occurs in subrecent deposits. This species is characterised here by statistical measurements, and new characters are described and illustrated. The charophytes record a drop in sea level and the establishment of a lower salinity artificial wetland. The investigation has also established that decalcification in charophytes can be related to acidification produced by the release of organic acids, aggravated after 1928 by anthropogenic pollution.
Virginia A Shepherd - One of the best experts on this subject based on the ideXlab platform.
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The electrophysiology of salt tolerance in charophytes
Cryptogamie Algologie, 2020Co-Authors: M J Beilby, Virginia A ShepherdAbstract:Lamprothamnium succinctum, charophyte tolerante au seul, croit dans des environnement salins non marins. Chara australis, charophyte sensible au sel, vit en eau douce. Les reponses electro-physiologiques des cellules inter nodales de ces especes a une augmentation de la teneur en Na + de leur milieu sont modelisees et comparees. Les deux charophytes presentent une plus forte conductance de base dans les milieux riches en Na + . Lamprothamnium est capable de maintenir une difference de potentiel (PD) au repos hautement negative par augmentation du taux de protons pompes. Les cellules de Chara, dans un milieu a forte teneur en Na + repondent de facons plus variees. Cependant, meme quant elle se produit, l'augmentation du pompage ne previent pas la depolarisation de la PD membranaire de -243 ± 15 mV (5 cellules) a -188 ± 15 mV (5 cellules), au dela d'un temps d'exposition moyen de 64 mn dans un milieu a forte teneur en Na + . De plus, la pompe a protons devient tres sensible a la fois a la depolarisation et a l'hyperpolarisation imposees a la membrane par la pression du voltage. Une telle inhibition de la pompe entrave le retablissement de la PD negative au repos apres l'application d'une tension ou d'un potentiel d'action spontanee. La signification des petites differences dans un transporteur rendant la plante tolerante au sel est discutee a la lumiere des adaptations evolutives.
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the characteristics of ca activated cl channels of the salt tolerant charophyte Lamprothamnium
Plant Cell and Environment, 2006Co-Authors: M J Beilby, Virginia A ShepherdAbstract:The dependence of the Ca++-activated Cl– channels on potential difference (PD) was extracted from current–voltage (I/V) profiles recorded at the time of hypotonic regulation while the large conductance (G) K+ channels were blocked by tetraethylammonium (TEA). The total clamp current (I) was dominated by the Cl–I, iCl, with small contribution from the background I (ibackground). The iCl was fitted by the Goldman–Hodgkin–Katz (GHK) model with enhanced PD dependence simulated by Boltzmann probability distributions. The ibackground was modelled by an empirical equation. The iCl responded to PD changes within tens of milliseconds. The G maxima were located between −20 and −150 mV. The Cl– channel number and channel permeability parameter, NClPCl, decreased as a function of time in a hypotonic medium (from 0.45 × 10−7 to 0.17 × 10−7 ms−1 in 19 min), with the positive half activation PD, V50+, shifting from +35 to −65 mV, and the negative half activation PD, V50–, shifting from −134 to −310 mV. The fitted Cl– concentration [Cl–]cyt at the time of hypotonic regulation indicated rapid equalization of vacuolar and cytoplasmic concentrations. Excellent data obtained under similar experimental conditions in a previous study enabled us to infer [Ca++]cyt influences on the Cl– channel characteristics. Thick sulphated polysaccharide mucilage, found on Lamprothamnium cells acclimated to more saline media, eliminated the activation of the iCl at the time of the hypotonic regulation. This effect was reversed by the application of the enzyme heparinase. The characteristics of the iCl were found to be consistent with a component of the excitation Is at the time of the action potential (AP). The short duration of the excitation transients was contrasted with that of the hypotonic regulation. The mechanisms for Cl– channel activation (and hence the Ca++ channel activation) were considered.
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The characteristics of Ca++‐activated Cl– channels of the salt‐tolerant charophyte Lamprothamnium
Plant Cell and Environment, 2006Co-Authors: M J Beilby, Virginia A ShepherdAbstract:The dependence of the Ca++-activated Cl– channels on potential difference (PD) was extracted from current–voltage (I/V) profiles recorded at the time of hypotonic regulation while the large conductance (G) K+ channels were blocked by tetraethylammonium (TEA). The total clamp current (I) was dominated by the Cl–I, iCl, with small contribution from the background I (ibackground). The iCl was fitted by the Goldman–Hodgkin–Katz (GHK) model with enhanced PD dependence simulated by Boltzmann probability distributions. The ibackground was modelled by an empirical equation. The iCl responded to PD changes within tens of milliseconds. The G maxima were located between −20 and −150 mV. The Cl– channel number and channel permeability parameter, NClPCl, decreased as a function of time in a hypotonic medium (from 0.45 × 10−7 to 0.17 × 10−7 ms−1 in 19 min), with the positive half activation PD, V50+, shifting from +35 to −65 mV, and the negative half activation PD, V50–, shifting from −134 to −310 mV. The fitted Cl– concentration [Cl–]cyt at the time of hypotonic regulation indicated rapid equalization of vacuolar and cytoplasmic concentrations. Excellent data obtained under similar experimental conditions in a previous study enabled us to infer [Ca++]cyt influences on the Cl– channel characteristics. Thick sulphated polysaccharide mucilage, found on Lamprothamnium cells acclimated to more saline media, eliminated the activation of the iCl at the time of the hypotonic regulation. This effect was reversed by the application of the enzyme heparinase. The characteristics of the iCl were found to be consistent with a component of the excitation Is at the time of the action potential (AP). The short duration of the excitation transients was contrasted with that of the hypotonic regulation. The mechanisms for Cl– channel activation (and hence the Ca++ channel activation) were considered.
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tolerant charophyte Lamprothamnium
2006Co-Authors: M J Beilby, Virginia A ShepherdAbstract:The dependence of the Ca ++ + + -activated Cl - channels on potential difference (PD) was extracted from current-volt- age ( I/V ) profiles recorded at the time of hypotonic regu- lation while the large conductance ( G ) K + channels were blocked by tetraethylammonium (TEA). The total clamp current ( I ) was dominated by the Cl - I , i Cl , with small con- tribution from the background I ( i background ). The i Cl was fitted by the Goldman-Hodgkin-Katz (GHK) model with enhanced PD dependence simulated by Boltzmann proba- bility distributions. The i background was modelled by an empir- ical equation. The i Cl responded to PD changes within tens of milliseconds. The G maxima were located between − 20 and − 150 mV. The Cl - channel number and channel perme- ability parameter, N Cl P Cl , decreased as a function of time in a hypotonic medium (from 0.45 × 10 − − − 7 to 0.17 × 10 − 7 ms − 1 in 19 min), with the positive half activation PD, V 50+ , shifting from + + + 35 to − 65 mV, and the negative half activation PD,
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Mechanosensory ion channels in charophyte cells: the response to touch and salinity stress.
European Biophysics Journal, 2002Co-Authors: Virginia A Shepherd, M J Beilby, Teruo ShimmenAbstract:Mechanosensitive (MS) ion channels are activated by mechanical stress and then transduce this information into electrical signals. These channels are involved in the growth, development and response to environmental stress in higher plants. Detailed analyses of the electrophysiology in higher plants are difficult because such plants are composed of complex tissues. The large cells of the charophytes facilitate electrophysiological measurements and allow us to study MS ion channels at the level of single cells. We draw parallels between the process of touch-perception in freshwater Chara, and the turgor-regulating response to osmotic shock in salt-tolerant Lamprothamnium. In terms of electrophysiology, these responses can be considered in three stages: (1) stimulus perception, (2) signal transmission and (3) induction of response. In Chara the first stage is due to the receptor potential (RPD), a transient depolarization with a critical threshold that triggers action potentials, which are responsible for stages (2) and (3). Receptor potentials are generated by MS ion channels. Action potentials involve a transient influx of Ca2+ to the cytoplasm, effluxes of K+ and Cl– and a temporary decrease of turgor pressure. Reducing cell turgor increases sensitivity to mechanical stimulation. In Lamprothamnium, a hypotonic shock produces an extended depolarization that resembles an extended RPD and is responsive to osmotic rather than ionic changes. Like the action potential, a critical threshold depolarization triggers Ca2+ influx, opening of Ca2+-sensitive Cl– channels and K+ channels; effluxes that last over an hour and result in turgor regulation. These processes show us, in primal form and at the level of single cells, how mechanoperception occurs in higher plants. Recent progress in research into the role of MS ion channels in the freshwater and salt-tolerant Characeae is reviewed and the relevance of these findings to plants in general is considered.
V A Shepherd - One of the best experts on this subject based on the ideXlab platform.
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COHERENT DOMAINS IN THE STREAMING CYTOPLASM OF A GIANT ALGAL CELL
Water and the Cell, 2020Co-Authors: V A ShepherdAbstract:Giant internodal cells of the charophyte Lamprothamnium respond to hypotonic shock with an extended action potential and transient cessation of cytoplasmic streaming. The macro-structure of streaming cytoplasm was analysed before, during, and after hypotonic shock. Streaming cytoplasm contains coherent, cloud-like macroscopic domains, whose perimeter varies from hundreds to many thousands of micrometres. Some domains avidly associate with the fluorochrome 6-carboxyfluorescein (6CF), and others do not. The 6CF-labelled domains are recognisable through many cycles of streaming, despite constantly changing irregular edges. Domain perimeters were described by a fractal dimension of 4/3, the exponent of a power law fitted to a log-log plot of domain perimeter-area. Following hypotonic shock, the stable pattern of coherent domains enters an unstable phase of coalescence, and discrete domains subsequently amalgamate into stable, extended domains. Instability is associated with Ca2+ influx and Cl- efflux, and a large increase in cell conductance. The electrophysiological K+ state, with greatly reduced conductance, is associated with the new, amalgamated stable state. The results support a concept of cytoplasm as a sponge-like percolation cluster, undergoing transition from discrete to extended domains. Results are discussed in terms of published theories concerning co-operative behaviour of supramolecular water-ion-protein complexes
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Electrophysiology of Turgor Regulation in Marine Siphonous Green Algae
The Journal of Membrane Biology, 2006Co-Authors: M. A. Bisson, M.j. Beilby, V A ShepherdAbstract:We review electrophysiological measures of turgor regulation in some siphonous green algae, primarily the giant-celled marine algae, Valonia and Ventricaria , with particular comparison to the well studied charophyte algae Chara and Lamprothamnium. The siphonous green algae have a less negative plasma membrane potential, and are unlikely to have a proton-based chemiosmotic transport system, dominated by active electrogenic K^+ uptake. We also make note of the unusual cellular structure of the siphonous green algae. Hypertonic stress, due to increased external osmotic pressure, is accompanied by positive-going potential difference ( PD ), increase in conductance, and slow turgor regulation. The relationship between these is not yet resolved, but may involve changes in K^+ conductance ( G _K) or active K^+ transport at both membranes. Hypotonic turgor regulation, in response to decreased external osmotic pressure, is ∼3 times faster than hypertonic turgor regulation. It is accompanied by a negative-going PD , although conductance also increases. The conductance increase and the magnitude of the PD change are strongly correlated with the magnitude of hypotonic stress.
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Modeling the Current-Voltage Characteristics of Charophyte Membranes. II. The Effect of Salinity on Membranes of Lamprothamnium papulosum
The Journal of Membrane Biology, 2001Co-Authors: M.j. Beilby, V A ShepherdAbstract:Lamprothamnium is a salt-tolerant charophyte that inhabits a broad range of saline environments. The electrical characteristics of Lamprothamnium cell membranes were modeled in environments of different salinity: full seawater (SW), 0.5 SW, 0.4 SW, and 0.2 SW. The cells were voltage-clamped to obtain the I/V (current-voltage) and G/V (conductance-voltage) profiles of the cell membranes. Cells growing at the different salinities exhibited one of three types of I/V profiles (states): pump-, background- and K^+-states. This study concentrates on the pump- and background-states. Curved (pump-dominated) I/V characteristics were found in cells with resting membrane PDs (potential differences) of −219 ± 12 mV (in 0.2 SW: 6 cells, 16 profiles), −161 ± 12 mV (in 0.4 SW: 6 cells, 7 profiles), −151 ± 12 mV (in 0.5 SW: 6 cells, 12 profiles) and −137 ± 12 mV (in full SW: 8 cells, 13 profiles). The linear I/V characteristics of the background-state were found in cells with resting PDs of −107 ± 12 mV (in 0.4 SW: 7 cells, 12 profiles), −108 ± 12 mV (in 0.5 SW: 7 cells, 10 profiles) and −104 ± 12 mV (in full SW: 3 cells, 5 profiles). The resting conductance ( G ) of the cells progressively increased with salinity, from 0.5 S·m^−2 (in 0.2 SW) to 22.0 S·m^−2 (in full SW). The pump peak conductance only rose from 2 S·m^−2 (0.2 SW) to 5 S·m^−2 (full SW), accounting for the increasingly depolarized resting PD observed in cells in more saline media. Upon exposure to hypertonic medium, both the pump and an inward K^+ rectifier were stimulated. The modeling of the I/V profiles identified the inward K^+ rectifier as an early electrical response to hypertonic challenge.
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modeling the current voltage characteristics of charophyte membranes ii the effect of salinity on membranes of Lamprothamnium papulosum
The Journal of Membrane Biology, 2001Co-Authors: M J Beilby, V A ShepherdAbstract:Lamprothamnium is a salt-tolerant charophyte that inhabits a broad range of saline environments. The electrical characteristics of Lamprothamnium cell membranes were modeled in environments of different salinity: full seawater (SW), 0.5 SW, 0.4 SW, and 0.2 SW. The cells were voltage-clamped to obtain the I/V (current-voltage) and G/V (conductance-voltage) profiles of the cell membranes. Cells growing at the different salinities exhibited one of three types of I/V profiles (states): pump-, background- and K+-states. This study concentrates on the pump- and background-states. Curved (pump-dominated) I/V characteristics were found in cells with resting membrane PDs (potential differences) of −219 ± 12 mV (in 0.2 SW: 6 cells, 16 profiles), −161 ± 12 mV (in 0.4 SW: 6 cells, 7 profiles), −151 ± 12 mV (in 0.5 SW: 6 cells, 12 profiles) and −137 ± 12 mV (in full SW: 8 cells, 13 profiles). The linear I/V characteristics of the background-state were found in cells with resting PDs of −107 ± 12 mV (in 0.4 SW: 7 cells, 12 profiles), −108 ± 12 mV (in 0.5 SW: 7 cells, 10 profiles) and −104 ± 12 mV (in full SW: 3 cells, 5 profiles). The resting conductance (G) of the cells progressively increased with salinity, from 0.5 S·m−2 (in 0.2 SW) to 22.0 S·m−2 (in full SW). The pump peak conductance only rose from 2 S·m−2 (0.2 SW) to 5 S·m−2 (full SW), accounting for the increasingly depolarized resting PD observed in cells in more saline media.
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Modeling the Current-Voltage Characteristics of Charophyte Membranes. II.* The Effect of Salinity on Membranes of Lamprothamnium papulosum
The Journal of Membrane Biology, 2001Co-Authors: M J Beilby, V A ShepherdAbstract:Lamprothamnium is a salt-tolerant charophyte that inhabits a broad range of saline environments. The electrical characteristics of Lamprothamnium cell membranes were modeled in environments of different salinity: full seawater (SW), 0.5 SW, 0.4 SW, and 0.2 SW. The cells were voltage-clamped to obtain the I/V (current-voltage) and G/V (conductance-voltage) profiles of the cell membranes. Cells growing at the different salinities exhibited one of three types of I/V profiles (states): pump-, background- and K+-states. This study concentrates on the pump- and background-states. Curved (pump-dominated) I/V characteristics were found in cells with resting membrane PDs (potential differences) of −219 ± 12 mV (in 0.2 SW: 6 cells, 16 profiles), −161 ± 12 mV (in 0.4 SW: 6 cells, 7 profiles), −151 ± 12 mV (in 0.5 SW: 6 cells, 12 profiles) and −137 ± 12 mV (in full SW: 8 cells, 13 profiles). The linear I/V characteristics of the background-state were found in cells with resting PDs of −107 ± 12 mV (in 0.4 SW: 7 cells, 12 profiles), −108 ± 12 mV (in 0.5 SW: 7 cells, 10 profiles) and −104 ± 12 mV (in full SW: 3 cells, 5 profiles). The resting conductance (G) of the cells progressively increased with salinity, from 0.5 S·m−2 (in 0.2 SW) to 22.0 S·m−2 (in full SW). The pump peak conductance only rose from 2 S·m−2 (0.2 SW) to 5 S·m−2 (full SW), accounting for the increasingly depolarized resting PD observed in cells in more saline media.
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Spatial heterogeneity of macrophytes in Lake Gallocanta (Aragón, NE Spain)
Hydrobiologia, 1993Co-Authors: Francisco A. Comín, Xavier Rodó, Margarita MenéndezAbstract:The spatial distribution of macrophytes ( Ruppia drepanensis ) Tineo and Lamprothamnium papulosum (Wallr.) J. Gr. was studied along transects perpendicular to the shoreline in Lake Gallocanta (Aragón, NE Spain) in 1988 and 1990. In the shallow zone, a gradient from the shoreline to offshore waters was clear: Small R. drepanensis plants were the only colonizers of nearshore waters affected by wave action and desiccation. R. drepanensis and L. papulosum coexisted at intermediate depths in the shallow zone. L. papulosum reached higher biomasses than R. drepanensis in the deepest parts of the shallow zone. In the deepest zone of the lake, stands of the two species did not overlap. Individual plants of R. drepanensis occured patchily within a sparse prairie of L. papulosum . This spatial pattern was observed at different lake levels, suggesting that macrophytes are adapted to fluctuations of environmental conditions. In very shallow water the macrophytes decay as indicated by negative net production and low chlorophyll a /chlorophyll b and plant K^+ concentration/water K^+ concentration ratios.
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Spatial heterogeneity of macrophytes in Lake Gallocanta (Aragón, NE Spain)
Hydrobiologia, 1993Co-Authors: Francisco A. Comín, Xavier Rodó, Margarita MenéndezAbstract:The spatial distribution of macrophytes (Ruppia drepanensis Tineo and Lamprothamnium papulosum (Wallr.) J. Gr. was studied along transects perpendicular to the shoreline in Lake Gallocanta (Aragon, NE Spain) in 1988 and 1990. In the shallow zone, a gradient from the shoreline to offshore waters was clear: Small R. drepanensis plants were the only colonizers of near shore waters affected by wave action and desiccation. R. drepanensis and L. papulosum coexisted at intermediate depths in the shallow zone. L. papulosum reached higher biomasses than R. drepanensis in the deepest parts of the shallow zone. In the deepest zone of the lake, stands of the two species did not overlap. Individual plants of R. drepanensis occured patchily within a sparse prairie of L. papulosum.
