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This paper presents new records and noteworthy data on the following taxa in SE Europe and adjacent regions: mycorrhizal fungus Russula sapinea, parasitic fungus Podosphaera polemonii, saprotrophic fungi Ophiognomonia melanostyla and Plagiostoma apiculatum, diatom alga Nitzschia reskoi, stonewort Nitellopsis obtusa, liverwort Mannia triandra, mosses Buxbaumia viridis and Leptodon smithii, monocots Epipactis purpurata and Orchis × beyrichii and dicots Euphorbia orjeni, Fallopia × bohemica, Nuphar lutea and Saxifraga pedemontana subsp. cymosa.

Despite the importance of action potentials (APs) in plant stress physiology, the molecular identity of Ca2+ channels that initiate APs by passing Ca2+ into the cytoplasm is still unknown in Characean macroalgae. While the Thiel-Beilby mathematical model of AP generation proposes that Ca2+ channels are activated by inositol 1,4,5-trisphosphate (IP3), this hypothesis is controversial because plants do not possess animal IP3 receptor gene homologues. In the present study, we employed the two-electrode current/voltage clamp technique to determine whether IP3 and another inositol phosphate IP6 could modulate the electrogenic parameters of an aquatic macrophyte Nitellopsis obtusa internodal cells. IP3 had no significant effect, whereas IP6 reversibly hyperpolarised the AP excitation threshold which is consistent with the activation of Ca2+ channels. IP6 also shifted the reversal potentials of the Ca2+ and Cl– currents during excitation to negative membrane potential values, indicating altered calcium dynamics in the cytoplasm. These findings suggest the regulation of Ca2+ channels during electrical excitation by IP6 rather than IP3. IP6-induced shift of Ca2+ channel voltage dependence allows a lower magnitude external stressor to initiate electrical signalling, thus turning on various downstream physiological responses.

An unsolved problem of contemporary plant electrophysiology is the identity of Ca2+ channels responsible for the initiation of the action potential. We took a pharmacological approach and applied several Ca2+ channel blockers (verapamil, tetrandrine, and NED-19) on a Characean (Nitellopsis obtusa) algae model system. The impact of the selected pharmaceuticals on the parameters of excitation transients of a single cell was analysed employing the two-electrode voltage clamp technique. It was revealed that tetrandrine exerted no effect, while both verapamil and NED-19 prolonged activation and inactivation durations of the excitatory Cl− current. NED-19 also significantly depolarised the excitation threshold membrane potential and shifted Ca2+ current reversal potential. Thus, NED-19 most specifically targeted Ca2+ channels. A viability assay paired with observations of cytoplasmic streaming revealed that verapamil affected not only Ca2+ channels but also exhibited non-specific effects, which eventually lead to cell death. Since many potential Ca2+ channel blockers exert additional undesirable non-specific effects, our study underlines the necessity to search for new more specific modulators of plant Ca2+ transport systems. It is challenging to isolate transmembrane Ca2+ currents that are activated during the generation of action potentials in plants. We applied several different Ca2+ channel blockers (verapamil, tetrandrine, and NED-19). It was found that, while verapamil and NED-19 did affect Ca2+ currents, non-specific effects were also observed, compromising the usage of these blockers as selective means of distinguishing Ca2+ currents in plants. [ABSTRACT FROM AUTHOR]

Background In this review, we summarize data concerning action potentials (APs) – long-distance electrical signals in Characean algae and liverworts. These lineages are key in understanding the mechanisms of plant terrestrialization. Liverworts are postulated to be pioneer land plants, whereas aquatic charophytes are considered the closest relatives to land plants. The drastic change of the habitat was coupled with the adaptation of signalling systems to the new environment. Scope APs fulfil the 'all-or-nothing' law, exhibit refractory periods and propagate with a uniform velocity. Their ion mechanism in the algae and liverworts consists of a Ca2+ influx (from external and internal stores) followed by/coincident with a Cl– efflux, which both evoke the membrane potential depolarization, and a K+ efflux leading to repolarization. The molecular identity of ion channels responsible for these fluxes remains unknown. Publication of the Chara braunii and Marchantia polymorpha genomes opened up new possibilities for studying the molecular basis of APs. Here we present the list of genes which can participate in AP electrogenesis. We also point out the differences between these plant species, e.g. the absence of Ca2+-permeable glutamate receptors (GLRs) and Cl–-permeable SLAC1 channel homologues in the Chara genome. Both these channels play a vital role in long-distance signalling in liverworts and vascular plants. Among the common properties of APs in liverworts and higher plants is their duration (dozens of seconds) and the speed of propagation (mm s–1), which are much slower than in the algae (seconds, and dozens of mm s–1, respectively). Conclusions Future studies with combined application of electrophysiological and molecular techniques should unravel the ion channel proteins responsible for AP generation, their regulation and transduction of those signals to physiological responses. This should also help to understand the adaptation of the signalling systems to the land environment and further evolution of APs in vascular plants. [ABSTRACT FROM AUTHOR]

Lake Scugog is an important headwater to the Trent Severn-Waterway in Ontario, Canada. In recent years, notable ecosystem-level changes have occurred coinciding with the emergence of the non-native invasive charophyte Nitellopsis obtusa. Despite N. obtusa arriving in North America in the early 1970s, studies documenting the impact of N. obtusa on invaded ecosystems are scarce. Given the increasing dominance of N. obtusa in inland waters of the Great Lakes basin, we investigated the ecosystem-level impacts of N. obtusa in Lake Scugog over a 3-year period. We show for the first time a strong association between N. obtusa occurrence and biomass with benthic anoxia in this shallow, polymictic lake. Benthic dissolved oxygen concentrations were significantly lower (p-value < 0.001) at sites with N. obtusa compared to sites without N. obtusa. Additionally, N. obtusa biomass was a negative predictor of near-bed oxygen concentration (R2 = 0.59, p-value < 0.001). Knowing that anoxia can promote the internal loading of phosphorus, we measured soluble reactive phosphorus (SRP) in the pore-water of sediments at each site, and found N. obtusa biomass explained 90% of sediment pore-water SRP (R2 = 0.90, p-value < 0.001). These notable associations between N. obtusa and key lake elements indicates that N. obtusa may be acting as an ecosystem engineer in invaded lakes by altering the biogeochemical fate of oxygen and phosphorus.

The recovery or reconstruction of aquatic vegetation has recently been reported as a result of water quality improvement after anthropogenic eutrophication. The objectives of this study were: to investigate long-term trends in aquatic vegetation abundance in relation to decreasing water fertility and to present new directions in changes of the submerged aquatic vegetation structure, species richness, and biodiversity in Lake Kuźnickie (western Poland) with the perspective of the last 40 years (1978–2018). Lake Kuźnickie is an example of water quality improvement taking place without any additional reclamation measures, except a reduction in nutrient discharge into the lake from its direct catchment. Currently, the study lake represents a mesotrophic status. The Trophy State Index evidenced a decrease in the lake’s fertility compared to previous decades. The water quality improvement manifests in a significant reduction in the total phosphorus concentration. An analysis of the spatial changes in the phytolittoral evidenced a decrease in rush vegetation between 1978 and 2018 by over 2 ha. In the period 1978–2018, the aquatic vegetation structure in Lake Kuźnickie underwent significant reconstruction. Currently, charophytes play a much greater role in the lake compared to the last 40 years, contributing to the maintenance of the lake’s high water quality. Moreover, the endangered charophyte Lychnothamnus barbatus has recovered. Concurrently, however, the biodiversity and species richness of the submerged vegetation has decreased. At present, only four species dominate in the lake, including two charophytes L. barbatus, Nitellopsis obtusa, and two vascular plants Ceratophyllum demersum and Myriophyllum spicatum. Over 40 years, Lake Kuźnickie has changed from a eutrophic lake dominated by vascular plants to a mesotrophic lake with a codominant contribution by charophytes. The lake is characterized by good water quality, optimal for the development of aquatic vegetation, especially charophytes.

Using the method of impedance spectroscopy, we studied the change regularities in the three electrical characteristics of Nitellopsis obtusa cells: potential φm, resistance Rm, capacity Cm, while modifying the transport properties of the plasma membrane (PM). The average values of these quantities for 100 cells under standard conditions were φм = -171±0,4 mV Rм = 3.8±0,15 Om∙m2, Cm=0,9±0,05 μf∙cm-2, respectively. Between Rm and φm has been established a linear dependence of Rm =0,032-0,03φm with a coefficient correlation r = 0,67. The activity of K+ ions in the cell cytoplasm, measured using K+ -sensitive microelectrodes, was ak +=104±6 mM. In the conducting state, in cells with | φм |> 170 mV, were observed K+- channels of inward rectification and in cells with |φм|<170 mV-K+- channels of outward rektification. At 10 and 100-fold increase of the K+ content in the medium, and modulation of the protein phase content in the PM, См change wasn’t observed. Consequently, the contribution of the protein phase in PM is insignificant for См. The exogenous effects of low concentrations of lipophilic modifiers of dimethyl sulfoxide, dicyclohexylcarbodiimide and the K+ channel blocker Co2 + caused a change of Cm by 20-30%, an increase in φm within 30 mV at a constant Rm, which indicated the relationship between electrogenic activity and lability of structuralpolarization PM properties. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

The recovery or reconstruction of aquatic vegetation has recently been reported as a result of water quality improvement after anthropogenic eutrophication. The objectives of this study were: to investigate long-term trends in aquatic vegetation abundance in relation to decreasing water fertility and to present new directions in changes of the submerged aquatic vegetation structure, species richness, and biodiversity in Lake Kuznickie (western Poland) with the perspective of the last 40 years (1978-2018). Lake Kuznickie is an example of water quality improvement taking place without any additional reclamation measures, except a reduction in nutrient discharge into the lake from its direct catchment. Currently, the study lake represents a mesotrophic status. The Trophy State Index evidenced a decrease in the lake's fertility compared to previous decades. The water quality improvement manifests in a significant reduction in the total phosphorus concentration. An analysis of the spatial changes in the phytolittoral evidenced a decrease in rush vegetation between 1978 and 2018 by over 2 ha. In the period 1978-2018, the aquatic vegetation structure in Lake Kuznickie underwent significant reconstruction. Currently, charophytes play a much greater role in the lake compared to the last 40 years, contributing to the maintenance of the lake's high water quality. Moreover, the endangered charophyte Lychnothamnus barbatus has recovered. Concurrently, however, the biodiversity and species richness of the submerged vegetation has decreased. At present, only four species dominate in the lake, including two charophytes L. barbatus, Nitellopsis obtusa, and two vascular plants Ceratophyllum demersum and Myriophyllum spicatum. Over 40 years, Lake Kuznickie has changed from a eutrophic lake dominated by vascular plants to a mesotrophic lake with a codominant contribution by charophytes. The lake is characterized by good water quality, optimal for the development of aquatic vegetation, especially charophytes. [ABSTRACT FROM AUTHOR]

Often facilitated by human-mediated pathways, aquatic invasive species are a threat to the health and biodiversity of global ecosystems. We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes. As an example, we use the green alga Nitellopsis obtusa, also known as starry stonewort, an aquatic invasive species affecting the Great Lakes region in the United States and Canada. The movement of algal fragments via human-mediated pathways (i.e., watercraft) has been hypothesized as the primary driver of starry stonewort invasion. We used survey data collected at boat ramps during the 2013 and 2014 open-water seasons to describe the flow of watercraft from Lake Koronis, where N. obtusa was first detected in Minnesota, to other lakes in the state. Our results suggest that the risk of N. obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes. Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts. [ABSTRACT FROM AUTHOR]

At that work is shown the absence change of electrical capacity plasma membrane Nitellopsis obtusa cells in the presence of polypeptide antibiotics valinomisine and gramisidine. The absence effect of polypeptide antibiotics on capacity accompanied with change of electrogenic activity and conductivity of plasma membrane. The results of investigations discussed on that point of, the capacity is characteristic of lipid phase of biomembranes. [ABSTRACT FROM AUTHOR]

Early detection of aquatic invasive species, such as Nitellopsis obtusa, is often critical to reduce their long- term negative effects. This macroalga resembles native taxa and can invade deep locations in littoral zones of lakes in North America. Studies in which effects of Nitellopsis on macrophyte communities were quantified are rare.We surveyed 4 lakes in central New York where Nitellopsis is present to document whether macrophyte communities are negatively affected by this invasive macroalgae and to test whether Nitellopsis was found more frequently in deeper- than in shallow-water habitats. We found lower macrophyte species richness when Nitellopsis was abundant. This pattern was consistent at 3 water depths (shallow [>1 m], intermediate [1-2 m], and deep [>2m]). Macrophyte biomasses (total, including native and other nonnative species, and only native species) were significantly lower in quadrats with greater abundance of Nitellopsis. Nitellopsis biomass exceeded the combined biomass of macrophytes in some lakes. Nitellopsis was present more frequently in deeper than in shallow water in 2 of the study lakes. Our results suggest that Nitellopsis can have negative effects on macrophyte communities and indicate that this taxon can become dominant in littoral zones of invaded lakes. It is more likely to be present in deeper water, which may prevent casual observation, so personnel responsible for monitoring programs should establish protocols and methods tailored to detect this spreading, cryptic invasive species. [ABSTRACT FROM AUTHOR]

The amplitudes of oscillation changes of potential and electrical resistance of Nitellopsis obtusa cell membranes differing from each other in their individual evolution stages were determined. The first, third and fifth cells from the tops of the plants were collected for measurements and only those characterised by rhythmical changes in potential and electrical conductivity of membranes (which revealed one or simultaneously 2-3 types of oscillations) were selected. Visible dependence of the amplitude of investigated changes on developmental stages of the cells, correlating with the intensity of metabolic transformations, was established.

The dependence of the amplitude of oscillatory changes in the electrical resistance of Nitellopsis obtusa cell membranes on the vegetation season of these plants is determined. The measurements were made on third cells from the tips of the plants which showed at least one type of oscillation in the resistance. A clear dependence of the amplitude of the studied changes on the vegetation season, especially on the maturity and rest stages of the plants, was found. These results as well as the observed changes in the characteristics of oscillations in the resistance, caused by sudden changes in the temperature of the cell surrounding, indicate a relationship between the oscillatory behaviour and the intensity of metabolic changes in the cells.

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The charophytic green alga Nitellopsis obtusa was first reported in the New World in the St. Lawrence River in 1978. Since that time, N. obtusa has been reported from inland lakes throughout Michigan, northern Indiana, and western New York and has been listed as an aggressive invasive species by the United States Geological Survey. This study addresses the distribution of N. obtusa by surveying 390 waterbodies throughout New York. Previous reports are confirmed and new localities are presented, including new reports from five counties (Franklin, Ontario, Seneca, Wayne, and Yates). In total, N. obtusa was found in 17 counties at 31 sites, including 16 inland lakes, seven sites in the St. Lawrence River, and eight sites in Lake Ontario. [ABSTRACT FROM AUTHOR]

The replacement of autochthonous tree species by invasive ones in coastal zones of freshwater bodies induces additional alteration of hydrochemical and microbiological characteristics due to decomposition of fallen leaves of non-indigenous species, which can lead to ecotoxic response of the littoral biota. Leaves of invasive to Lithuania boxelder maple ( Acer negundo ) and autochthonous black alder ( Alnus glutinosa ) lost more than half of biomass and released stable amount of DOC (60–70 mg/L) throughout 90-day mesocosm experiment under aerobic conditions. This, along with the relatively small BOD 7 values detected after some variation within the first month confirms effective biodegradation by fungi and bacteria. The ambient water was more enriched with different forms of N and P by decomposing boxelder maple than by alder leaves. During the first month, both leachates were more toxic to charophyte ( Nitellopsis obtusa ) at mortality and membrane depolarization levels, while later to two crustacean species. Biomarker response, H + -ATPase activity in membrane preparations from N. obtusa , was stronger for A. negundo . Generally, boxelder maple leaf leachates were more toxic to tested hydrobionts and this coincides with previous study on leaves of the same pair of tree species conducted under microaerobic conditions (Krevš et al., 2013). [ABSTRACT FROM AUTHOR]

The impact of low-dose ionizing radiation on the electrical signalling pattern and membrane properties of the characea Nitellopsis obtusa was examined using conventional glass-microelectrode and voltage-clamp techniques. The giant cell was exposed to a ubiquitous radionuclide of high biological importance - tritium - for low-dose irradiation. Tritium was applied as tritiated water with an activity concentration of 15 kBq L-1 (an external dose rate that is approximately 0.05 μGy h-1 above the background radiation level); experiments indicated that this was the lowest effective concentration. Investigating the dynamics of electrical excitation of the plasma membrane (action potential) showed that exposing Characeae to tritium for half an hour prolonged the repolarization phase of the action potential by approximately 35%: the repolarization rate decreased from 39.2 ± 3.1 mV s-1 to 25.5 ± 1,8 mV s-1 due to tritium. Voltage-clamp measurements showed that the tritium exposure decreased the Cl- efflux and Ca2+ influx involved in generating an action potential by approximately 27% (Δ = 12.4 ± 1.1 μA cm-2) and 64% (Δ = -5.3 ± 0.4 μA cm-2), respectively. The measured alterations in the action potential dynamics and in the chloride and calcium ion transport due to the exogenous low-dose tritium exposure provide the basis for predicting possible further impairments of plasma membrane regulatory functions, which subsequently disturb essential physiological processes of the plant cell. [ABSTRACT FROM AUTHOR]

The hornwort Ceratophyllum demersum is a loosely attached to the bottom or free-floating vascular macrophyte, which builds dense stands in nutrient-rich waters. The hornwort stands are usually monospecific communities with a negligible contribution of other aquatic plants. However, some published literature data and our own observations evidenced the co-occurrence of densely growing Ceratophyllum and other macrophytes, including charophytes, which by contrast to hornwort are indicative of clear and less productive waters. Thus, the aim of this study was to identify the charophyte species growing in C. demersum stands and to define the environmental conditions promoting this co-occurrence. In 18 natural lakes of Western Poland, 60 stands of Ceratophyllum demersum were studied in the years 2001-2005. A total of 25 species built the studied stands. As many as eight charophyte species, 13 vascular plants, two moss species and one filamentous alga co-occurred with C. demersum. Among charophytes rare to Poland Chara polyacantha and Nitella gracilis were identified. Nitellopsis obtusa and Chara globularis revealed the highest frequencies along with Myriophyllum spicatum. Morphology of lakes combined with water quality, particularly transparency, appeared to regulate the coexistence of charophytes and C. demersum, macrophytes usually competing with each other. [ABSTRACT FROM AUTHOR]

Nitellopsis obtusa ( Charales, Charophyceae) are widely distributed from Europe to Asia; however, this species has been recorded in only the five lakes in central Honshu in Japan. This species was thought to be extinct in Japan, but was rediscovered in limited areas of Lake Kawaguchi in central Honshu. More recently, we discovered more Japanese populations of N. obtusa in Lake Biwa in western Honshu, and it became clear that the species had a broader distribution in Japan than originally believed. In addition, although only male or female thalli have been collected at each lake, both male and female thalli were found from Lake Biwa. This is the first report of a potentially sexual population of N. obtusa in Japan. The DNA sequences of three chloroplast DNA markers, including both coding and non-coding regions, were identical in all specimens from Lake Kawaguchi and Lake Nojiri ( Central Honshu), and differed from those of Lake Biwa and German specimens. Although Japanese and German specimens were genetically similar, Japanese specimens displayed considerable genetic diversity according to locality. [ABSTRACT FROM AUTHOR]

Objectives: Our living environment is composed of mixed pollution. Consequently, the combination of toxic elements may produce either new kinds of harmful products or induce further toxicity in the already existing ones. Thus, living organism response to combined contamination could differ from additive toxicity hypothesis or the effect of a single pollutant. This is especially true for the low-dose ionizing radiation which is able to sensitize organisms to other contaminants. Nowadays aluminum and tritium appear to be widespread pollutants due to the development of new technologies and nuclear energy. Plants, similar to animals, employ electrical signals in the integration of their responses to the environmental stress. The electrical properties of plant cells have a substantial influence on the maintenance of ion transport involved in intracellular regulation, signal transduction, other processes essential for plant's survival. Therefore, we conducted an electrophysiological investigation to identify alteration in bioelectrical activity of a charophyte cell. This study could provide essential understanding of the primer cell response to the combined pollution of aluminum and tritium, expressed in complex interference into the electrogenesis of intact plant cell in appropriate environmental context. Methods: Conventional intracellular methods of microelectrodes and voltage clamp technique was applied to investigate the impact of combined exogenous exposure to aluminum and tritium on the bioelectrical properties of the plant cell plasma membrane. Results: The combination of aluminum and tritium was found to cause significant changes in transient Cl-, Ca2+, and K+ currents involved in the generation of action potential in plants in comparison with those evoked by single aluminum. Conclusions: Charophyte cells provide a unique model system for electrophysiological investigation of the plasma membrane properties. The observed phenomena of modifying action of tritium on aluminum toxicity gives a better understanding of the biological behavior of both naturally occurring contaminants in the environment and provides an approach to predict that tritium as a source of ionizing radiation could be considered alongside with acidity as an important factor for aluminum toxicity expression in plants. Thus, comprehensive studies are necessary for elucidating the mechanisms of interaction of aluminum and tritium and also other ionizing radiation sources, paying particular attention to the investigation of aluminum toxicity in conditions of potential excessive radiation and higher background radiation, accidental radioactive pollution, radioactive waste disposals, human dealing with medical and occupational exposure. [ABSTRACT FROM AUTHOR]

Throughout 90-day biodegradation under microaerobic conditions, invasive to Lithuania species boxelder maple (Acer negundo) leaves lost 1.5-fold more biomass than that of autochthonous black alder (Alnus glutinosa), releasing higher contents of N tot, ammonium and generating higher BOD7. Boxelder maple leaf leachates were characterized by higher total bacterial numbers and colony numbers of heterotrophic and cellulose-decomposing bacteria than those of black alder. The higher toxicity of A. negundo aqueous extracts and leachates to charophyte cell (Nitellopsis obtusa), the inhabitant of clean lakes, were manifested at mortality and membrane depolarization levels, while the effect on H+-ATPase activity in membrane preparations from the same algae was stronger in case of A. glutinosa. Duckweed (Lemna minor), a bioindicator of eutrophic waters, was more sensitive to leaf leachates of A. glutinosa. Fallen leaves and leaf litter leachates from invasive and native species of trees, which enter water body, affect differently microbial biodestruction and aquatic vegetation in freshwater systems. [Copyright &y& Elsevier]

The article offers information on the investigation for nitellopsis obtuse Desvaux (Desv.) J. Groves species of genus nitellopsis hy in Bangladesh. It states that the plant, which has common name of starry stonewort, is a dioecious type and grows by up to 14 centimeters (cm) high in deep green color. It adds that the plant, which is distributed in Europe, Asia, and Africa, is from freshwater lotic habitat. It also says that the plant does not produce oospores and has very low fructification.

Abstract: Starting in the middle of the 1970s, submerged macrophytes began to disappear from shallow Lake Warniak due to feeding pressure by grass carp (Ctenopharyngodon idella). In the middle of the 1980s, the lake was stocked with seston-feeding silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis). By 1993, the biomass of silverhead carp and bighead carp had declined. This allowed charophytes to recolonize the bottom of the lake. The main charophyte species at this time were Chara globularis and Chara rudis. Since then, five other stonewort species have been found: Chara contraria, C. filiformis, C. tomentosa, C. aspera and Nitellopsis obtusa. Seventeen species of aquatic angiosperms have also been found. There were distinct changes in the relative abundance and spatial distribution of particular species. C. rudis developed most intensely in the shallow parts of the lake near the southern and western shores. C. globularis gradually took over the deeper central part of the lake. In 2001, C. rudis began to retreat again. The relative abundance and spatial distribution of charophytes was correlated to water clarity (r =0.87, p <0.05), total phosphorus level (r =−0.78; p <0.05), and chlorophyll a content (r =−0.79; p <0.05). [Copyright &y& Elsevier]

The principal aim of the work is to determine possibilities of using a model system that in vitro registers changes in membrane functional activity as a toxicity biomarker of water media. Functional activity was evaluated according to the proton pump (K+, Mg2+-ATPase) activity of Nitellopsis obtusa cell membrane structures. 50 % inhibition of K+, Mg2+-ATPase activity (IC50) was measured in membrane preparations and sensitivity of both freshly isolated and frozen microsome fractions for xenobiotics was investigated. Sensitivity of frozen frozen (-8 °C) microsomal fraction (49±17 μM, n=8) did not significantly (p=0.05) differ from that of freshly isolated one (37±31 μM, n=12), as confirmed by a reference procedure with CuSO4. Sensitivity of frozen microsomal fraction did not change while stored in a fridge for at least 40 days, moreover, the variability of the ATPase activity inhibition endpoint values was less in relation to freshly isolated microsomal fraction. Applying the above-described model systems (H+-ATPase inhibition and electrophysiological characteristics), toxicity of water media under different conditions and at different distances from pollution sources was evaluated in the environment. [ABSTRACT FROM AUTHOR]

The effect of prolonged illumination (60 min) with photosynthetically active monochromatic radiation of low intensity (3 µmol m−2 s−1) and high intensity (60 µmol m−2 s−1), corresponding to the physiological conditions and light stress conditions, respectively, was studied in the algae Nitellopsis obtusa. Illumination of Nitellopsis obtusa cells with strong light was associated with activation of the xanthophyll cycle, manifested by the deepoxidation of violaxanthin and accumulation of antheraxanthin and zeaxanthin. At the same time, the efficient singlet excitation quenching in the photosynthetic apparatus was activated, as demonstrated by the decrease in the intensity of the chlorophyll a fluorescence emission by ca 50 %. The difference of the fluorescence excitation spectra recorded before and after the light treatment match the difference absorption spectrum of the xanthophyll cycle pigments. The illumination with low light intensity resulted also in the chlorophyll a fluorescence quenching but the effect was very small (less than 10 %). The fluorescence quenching is interpreted in terms of the energy transfer between the Qy energy level of chlorophyll a and the 21 Ag − energy level of zeaxanthin. The singlet energy levels of carotenoids, corresponding to the green spectral region, are also taken into consideration in the interpretation of the excitation energy exchange between the carotenoids and chlorophylls. Possible molecular mechanisms involved in the activation of the strong and the weak excitation quenching, including violaxanthin isomerization, and possible physiological functions of such pathways of energy transfer are discussed. [ABSTRACT FROM AUTHOR]

To study the mechanism of aluminium toxicity in plant cells, the effects of aluminium on the electrogenesis of plasma membrane were investigated. We analyzed Al 3+ induced membrane potential (E m ) changes and potential changes during generation of the action potential (AP) in the internodal cells of Nitellopsis obtusa. Al 3+ modified E m decrease significantly. Al 3+ didn't attenuate the amplitude of the action potential too much, though the peak value of the action potential increased. The shift of the second stage of AP repolarization was about 32 mV in positive direction as a result of Al 3+ treatment. Al 3+ has been suggested to affect Ca 2+ homeostasis and H + -ATPase activity. [ABSTRACT FROM AUTHOR]

The toxicity of industrial and urban wastewater (WW) samples collected in Lithuania and Estonia was evaluated by using a suite of biological tests comprising the Algaltoxkit F™ with Selenastrum capricornutum, the Charatox with Nitellopsis obtusa, Daphtoxkit F™ with Daphnia magna, Thamnotoxkit F™ with Thamnocephalus platyurus, Protoxkit F™ with Tetrahymena thermophila and the Microtox® with Vibrio fischeri. The Charatox and Thamnotoxkit F™ tests showed highest relative sensitivity, responding to 80–90% of samples, respectively, and both expressed good discrimination capacity between samples. Principal Component and pairwise correlation analysis allowed to select test-battery consisting of Charatox, Thamnotoxkit™ and Microtox®. The WW toxicity was evaluated by means of cumulative indices such as average toxicity (AvTx) and two indices derived from the PEEP-index (Environ. Toxicol. Water Qual. 8 (1993) 115). In addition to these integrated evaluations of test-battery response, WW toxicity was evaluated according to the most sensitive test (MST) in the battery. The linear regression analysis between cumulative toxicity indices and chemical-based indices (derived from comparison of WW chemical concentrations and their respective maximum allowable concentration) revealed positive linear relationships (r2=0.7–0.8), while toxicity evaluation based on the MST was less positively related with chemical analysis data (r2=0.5–0.6). Although better coincidence between the toxicity and chemical-based assessments was achieved when information from all tests in the battery was assembled, the prediction of toxicity from chemical data was still limited. In search of suitable test-battery for the screening of certain type of WWs, a preliminary study comprising excessive suite of tests might be useful. [Copyright &y& Elsevier]

The decomposition of urea by Nitellopsis obtusa from Characeae was investigated. The intact cells were exposed to the inhibition by two typical urease inhibitors: boric acid and fluoride ion, used as a criterion to define if urease or UAL-ase is responsible for the ureolytic activity of the algae. It was found that boric acid and fluoride ion are simple competitive and slow-binding competitive inhibitors of Nitellopsis obtusa enzyme respectively, which is the response characteristic of urease. The inhibition constants equal to 2.3 and 0.1 mM for boric acid and fluoride ion, when compared to those of jack bean urease, indicate that in the observed kinetic behaviour of Nitellopsis obtusa urease partake transport processes taking place in the intact cells. [ABSTRACT FROM AUTHOR]

Oscillatory changes of the electrical resistance across the nodal complex of Nitellopsis obtusa (Desv. in Lois) J. Gr. were observed in experiments performed for 40-150 mm with the use of external electrodes and microelectrodes. Three main patterns of node resistance oscillations were similar to those found for membrane potential and resistance. The presented findings indicate an oscillatory behaviour of the plasmodesmata system at the node, which may be connected with e.g. pulsatile variations in the number of open plasmodesmata. [ABSTRACT FROM AUTHOR]

Oscillatory changes in electrical parameters of cells of Nitellopsis obtusa (Desv. in Lois)J. Gr. and Nitella flexilis f. Atkahensis R. D. W, particularly in the membrane potential, were investigated with external Ag/AgCl electrodes. Three main types of oscillations were observed The measurements were carried out on 30 cells with the application of an inhibitor of cytoplasmic streaming (procaine) and revealed that there was no direct correlation between cytoplasmic streaming and oscillations in the membrane potential. [ABSTRACT FROM AUTHOR]

Effects of amphiphilic derivatives of glycine esters of the general formula (CH3)3N+CH2COOnH2n+1C1- (n = 10, 12, 14, 16) on membrane potential and conductance in internodal cells of the alga Nitellopsis obtusa were studied. The compounds decreased the potential difference between vacuole and external medium and increased the electric conductance. The effects depended on the length of the alkyl chain (n) and the concentration of these quaternary ammonium salts. Light induced hyperpolarization was suppressed by the salts. We suggest that the ammonium salts inhibit the electrogenic proton pump in the plasmalemma and enhance the passive efflux of Cl- from the algal cell. [ABSTRACT FROM AUTHOR]