Veratridine triggers exocytosis in Paramecium cells by activating somatic Ca channels

Paramecium tetraurelia wild-type (7S) cells respond to 2.5 mm veratridine by immediate trichocyst exocytosis, provided [Ca²⁺] _o (extracellular Ca²⁺ concentration) is between about 10^–4 to 10^–3 m as in the culture medium. Exocytosis was analyzed by light scattering, light and electron microscopy following quenched-flow/ freeze-fracture analysis. Defined time-dependent stages occurred, i.e., from focal (10 nm) membrane fusion to resealing, all within 1 sec.Veratridine triggers exocytosis also with deciliated 7S cells and with pawn mutants (without functional ciliary Ca channels). Both chelation of Ca²⁺ _o or increasing [Ca²⁺] _o to 10^–2 m inhibit exocytotic membrane fusion. Veratridine does not release Ca²⁺ from isolated storage compartments and it is inefficient when microinjected. Substitution of Na⁺ _o for N-methylglucamine does not inhibit the trigger effect of veratridine which also cannot be mimicked by aconitine or batrachotoxin. We conclude that, in Paramecium cells, veratridine activates Ca channels (sensitive to high [Ca²⁺] _o ) in the somatic, i.e., nonciliary cell membrane and that a Ca²⁺ influx triggers exocytotic membrane fusion. The type of Ca channels involved remains to be established.We thank Dr. C. Kung (Madison, WI) for providing the pawn mutant, Drs. G. Lehle and R. Waldschütz-Schüppel (Konstanz, Germany) for their help with light scattering experiments, and Ms. E. Dassler and D. Bliestle for continuous help during the extensive photographic documentation. This work has been supported by Deutsche Forschungsgemeinschaft, Schwerpunkt Neue mikroskopische Techniken für Biologie und Medizin (grant P178/11) and SFB156/B4.     

Deep-water stromatolites andFrutexites Maslov from the early and Middle Jurassic of S-Germany and Austria

Summary Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine, aphotic origin of these stromatolites. Former interpretations of the Posidonien-Schiefer as a shallow-water deposit are mainly based on the occurrence of stromatolites. We favour the model of a temporarily stagnant, deep, aphotic basin for these planktonrich sediments. Particles resembling ooids, but lying within mudstones cannot be taken as evidence for shallow agitated water. They either formed within the mud or are allochthonous. The deep-water setting of the red limestone of the Alpine Early and Middle Jurassic is indicated by a lack of platform-typical components like coated grains and phototrophic benthos and by shells of plankton and nekton forming a major part of the sediment. Stromatolites occur on the steep slope of a drowned Rhaetian reef with an estimated relief of 50–100 m and immediately below and within radiolarian limestones, deposited below the aragonite compensation depth (ACD). The aphotic stromatolites show some morphological differences to their shallow water counterparts. In all of our sections they occurred during intervals of reduced sedimentation. They form only thin horizons and probably grew very slowly. Mineralizations by Fe−Mn oxides and phosphate are very common. The presence of a microbial film is evident from binding of sedimentary particles, but the nature of the microbes is not known. Growth habits within the very distinct environments of red limestone and black shales show some common features, but also clear differences. The microproblematicumFrutexites Maslov is a very common component in deep-water stromatolites, but may also itself form small crusts or dendrolites. It occurs in two different forms. Opaque, slender forms with indistinct outlines probably grew within the weakly lithified sediment. Thicker, transparent forms with well defined outlines are found in cavities and probably also grew on the seafloor. Well preserved specimens display an internal fabric of radially arranged fibres of Fe−Mn oxides and calcite. It is suggested that calcite or aragonite were one original mineralogy ofFrutexites, which was later replaced by Fe−Mn oxides or phosphate. It is not certain whetherFrutexites is an organic, biomineralized structure or an inorganic mineralization, but the variable mineralogy and growth forms in different environments point to an organic origin. But even if organic, the occurrence in cryptic habitats and negative phototactic growth-directions make it clear thatFrutexites was not phototrophic.     

The significance of partial migration for food web and ecosystem dynamics

Migration is ubiquitous and can strongly shape food webs and ecosystems. Less familiar, however, is that the majority of life cycle, seasonal and diel migrations in nature are partial migrations: only a fraction of the population migrates while the other individuals remain in their resident ecosystem. Here, we demonstrate different impacts of partial migration rendering it fundamental to our understanding of the significance of migration for food web and ecosystem dynamics. First, partial migration affects the spatiotemporal distribution of individuals and the food web and ecosystem-level processes they drive differently than expected under full migration. Second, whether an individual migrates or not is regularly correlated with morphological, physiological, and/or behavioural traits that shape its food-web and ecosystem-level impacts. Third, food web and ecosystem dynamics can drive the fraction of the population migrating, enabling the potential for feedbacks between the causes and consequences of migration within and across ecosystems. These impacts, individually and in combination, can yield unintuitive effects of migration and drive the dynamics, diversity and functions of ecosystems. By presenting the first full integration of partial migration and trophic (meta-)community and (meta-)ecosystem ecology, we provide a roadmap for studying how migration affects and is affected by ecosystem dynamics in a changing world.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

A secoisolariciresinol branched fatty diester from Salvia plebeia seed

The structure of a second new lignan diester from Salvia plebeia seed has been determined. Hydrolysis of this diester yields two compounds, 12-methyltetradecanoic acid and secoisolariciresinol.     

A heme-nonapeptide tracer for electron microscopy

Summary A heme-nonapeptide (H-9-P)¹, applicable to electron microscopic cytochemistry via peroxidase-like activity, was prepared by passing horse heart cytochrome c through a column with Sepharose and covalently attached trypsin. After purification by column chromatography (Sephadex G50 Superfine, Biogel P-2) a maximal yield of 50% and purity of >99% was achieved. A concise schedule allows for inexpensive preparation of H-9-P with standard laboratory equipment. H-9-P has the following properties: Its structure is (14) Cys-Ala-Gln-Cys-His-Thr-Val-Glu-Lys (22) with heme attached to Cys (14) and (17). MW=1630, pI=4.95, _E(max) ^{pH 7} = 397.5 nm, _{22 °C, pH 7} ^{397.5 nm} = 1.11 × 10⁵ [Liter/Mole x cm]. With the use of a diaminobenzidine-H₂O₂-medium — as applied for cytochemistry — we determined spectrophotometrically a pH_opt=12.5 and an apparent K₅ = 3.14 × 10^{– 3} [M]. Glutardialdehyde leads to considerable de-activation and, according to SDS-polyacrylamide-gel-electrophoresis, to diffuse crosslinking accompanied by a shift of the active pH-region towards neutral pH values. An attempt was made to optimize the cytochemical assay. The peroxidase-like activity of H-9-P is well comparable to that of other heme-tracers; only horseradish peroxidase has a higher turnover number. When injected to mice or added to cell suspensions, even high concentrations of H-9-P did not entail any signs of toxicity.Abbreviations AAA amino acid analysis - AHC ammoniumhydrogencarbonate - BSA bovine serum albumin - Cyt c cytochrome c - DAB 5,3-diaminobenzidine - GA glutardialdehyde - H-8-P heme-octapeptide - H-9-P heme-nonapeptide - H-11-P heme-undecapeptide - HR-POX horseradish peroxidase - MW molecular weight - PAGE polyacrylamid-gel-electrophoresis - pI isoelectric point - SDS sodiumdodecylsulphate - SG-TLC silicagel-thin-layer-chromatography This work was supported by the Österreichische Forschungsfonds     

Decoupling of exocytotic membrane fusion from protein discharge in Paramecium cells

Under certain conditions it is possible in Paramecium cells to induce selectively the fusion of the secretory organelle membrane with the cell membrane without the involvement of any further steps (release of secretory contents, etc.). A Ca2+-mobilizing fusogen was used in the presence of components which inhibit the discharge of the secretory contents (Mg2+ and EGTA, mainly). One can thus produce many exocytotic openings with the secretory contents (which are normally vigorously discharged) still retained.