30 research outputs found
Homogalacturonan Accumulation in Cell Walls of the Green Alga Zygnema sp. (Charophyta) Increases Desiccation Resistance
Land plants inherited several traits from their green algal ancestors (Zygnematophyceae), including a polysaccharide-rich cell wall, which is a prerequisite for terrestrial survival. A major component of both land plant and Zygnematophyceaen cell walls is the pectin homogalacturonan (HG), and its high water holding capacity may have helped algae to colonize terrestrial habitats, characterized by water scarcity. To test this, HG was removed from the cell walls of Zygnema filaments by pectate lyase (PL), and their effective quantum yield of photosystem II (YII) as a proxy for photosynthetic performance was measured in response to desiccation stress by pulse amplitude modulation (PAM). Old filaments were found to contain more HG and are more resistant against desiccation stress but relatively lose more desiccation resistance after HG removal than young filaments. After rehydration, the photosynthetic performance recovered less efficiently in filaments with a HG content reduced by PL, independently of filament age. Immunolabeling showed that partial or un-methylesterified HG occurs throughout the longitudinal cell walls of both young and old filaments, while no labeling signal occurred when filaments were treated with PL prior labeling. This confirmed that most HG can be removed from the cell walls by PL. The initial labeling pattern was restored after ~3 days. A different form of methylesterified HG was restricted to cell poles and cross cell walls. In conclusion, it was shown that the accumulation of HG in Zygnema filaments increases their resistance against desiccation stress. This trait might have played an important role during the colonization of land by Zygnematophyceae, which founded the evolution of all land plants
Spectroscopy and Reactivity Studies of Hydrated Electrons and Carbon Dioxide Radical Anions
Wassercluster mit einem Elektron (H2O)n- (n = 20200) und das hydratisierte Kohlendioxid Radikalanion CO2-(H2O)n (n = 261) wurden im infrarot und sichtbaren Bereich spektroskopisch untersucht. Für die Experimente wird ein Fourier Transformation Ion Zyklotron Resonanz Massenspektrometer mit einer auf T = 80 K gekühlten Messzelle verwendet. Außerdem wird die Reaktion von CO2-(H2O)n mit 3-butyn-1-ol bei Raumtemperatur studiert.
Bei den Maxima der optischen Absorptionsspektren der (H2O)n- Cluster wurde eine Blauverschiebung mit steigender Clustergröße beobachtet. Die Verschiebung stagniert ab n 100, leicht rotverschoben zum Maximum des Spektrums des hydratisierten Elektrons (1.72 eV) in flüssigem Wasser, bei etwa 1.6 eV. Ab n 50 ähneln die Spektren der Cluster der Form des Bulk Spektrums. Für n 40 werden zwei Isomere identifiziert, welche energetisch sehr nahe beisammen liegen (Isomer I, Isomer II). Isomer I kann in allen Spektren untersucht werden, Isomer II verschwindet in den Spektren mit n 50. Ersteres wird Elektronen zugeordnet welche sich größtenteils innerhalb des Clusters befinden, Isomer II Elektronen auf der Oberfläche des Clusters. Der Gyrationsradius des Elektrons zeigt einen ähnlichen Trend und erreicht den Wert 2.65 Å für n 100, welcher mit dem Literaturwert für das hydratisierte Elektron übereinstimmt. Unsere Resultate zeigen, dass Wassercluster mit einem Elektron ein gutes Modellsystem für das hydratisierte Elektron darstellen.
Das hydratisierte Kohlendioxid Radikalanion CO2-(H2O)n (n = 261) wurde in der 11502220 cm-1 Region mittels IR-Spektroskopie untersucht. Die Positionen der symmetrischen CO Streckschwingungen blauverschieben sich mit steigender Clustergröße. Bereits bei n = 20 wird ein ähnliches Absorptionsverhalten wie bei CO2- in flüssigem Wasser beobachtet, welches auf eine starke Interaktion des Radikals mit den Wassermolekülen schließen lässt. Quantenchemische Rechnungen unterstreichen diese Observation. Für die asymmetrische Streckschwingung kann nur eine leichte Clustergrößenabhängigkeit festgestellt werden, da sie mit der Wasser Biegeschwingung überlappt. Für große Cluster kann ein zusätzliches Absorptionsband identifiziert werden, welches einer Kombination aus Wasser Biegeschwingungen und Librationen zugeordnet wird. Die Interaktion des Kohlenstoffatoms mit Wassermolekülen hat eine untergeordnete Auswirkung auf das Absorptionsverhalten des Anions.
Die Reaktivität von CO2-(H2O)n (n0 50) mit 3-butyn-1-ol wurde in der kollisionsfreien Umgebung des FT-ICR MS untersucht. Das Radikalanion attackiert die Dreifachbindung des Reaktanten und formt eine schwache kovalente Bindung. Die mit diesem Prozess verbundene Barriere kann mit 3-4 butynol Moleküle überwunden werden. Im späten Verlauf der Reaktion werden die Transfers der Reaktant Fragmente H, OH und CCH zu [C4H5OH,CO2](H2O)n, sowie Wasserstofftransfer und Elimination von HOCO untersucht.Hydrated electron clusters (H2O)n- (n = 20200) and the hydrated carbon dioxide radical anion CO2-(H2O)n (n = 261) have been investigated in the gas phase spectroscopically in the visible and infrared range respectively. The cell of the Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR MS) is cooled to T = 80 K. Furthermore, the reaction of CO2-(H2O)n with 3-butyn-1-ol has been studied in detail at room temperature.
The maxima of the optical absorption spectra of (H2O)n- blueshift with increasing cluster size until n 100, where they reach a plateau at 1.6 eV, slightly redshifted to the bulk hydrated electron (1.72 eV). The spectra resemble the shape of the bulk hydrated electron spectrum for n 50. For n 40 two almost isoenergetic isomers are observed, labelled as Isomer I and Isomer II. Isomer I is identified as a partially embedded state and is present for all investigated cluster sizes. Isomer II vanishes for n 50 and is assigned to a proper surface state. A similar trend as for the absorption maxima is observed for the electron radius of gyration, stagnating at 2.65 Å for n 100, in good agreement with the literature for the bulk hydrated electron. The results indicate, that hydrated electron clusters with n 100 are a reasonable model system for hydrated electrons near the liquid-vacuum interface.
The hydrated carbon dioxide radical anion CO2-(H2O)n (n = 261) has been investigated in the 11502220 cm-1 region via IR-spectroscopy. The position of the symmetric CO stretching vibration blueshifts with increasing cluster size and approaches the bulk limit already for n = 20. Comparison with quantum chemical calculations suggests that the anion strongly interacts with the water environment. The asymmetric CO stretching vibration overlaps with the water bending vibration. The position of this intense band is only mildly effected by cluster size, well within the linewidth. For larger clusters, an additional band appears in the 2100 cm-1 region and is assigned to a combination of water bending and libration modes. The interaction of the carbon atom with a water molecule does not strongly influence the absorption behavior of CO2-.
A reactivity study of CO2-(H2O)n (n0 50) with 3-butyn-1-ol (C4H5OH) has been conducted in the collision free environment of the FT-ICR MS. The radical anion attacks the triple bond of the reactant and forms a weak covalent bond. The process is associated with a barrier and 34 butynol molecules are required for the reaction. Once almost all water molecules are evaporated, the transfer of the reactant fragments H, OH and CCH to [C4H5OH,CO2](H2O)n is investigated. In the late stage of the experiment hydrogen transfer and the release of HOCO are observed.Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersArbeit an der Bibliothek noch nicht eingelangt - Daten nicht geprüftInnsbruck, Univ., Diss., 2019(VLID)450404
Photodissociation spectroscopy of protonated leucine enkephalin
Protonated leucine enkephalin (YGGFL) was studied by ultraviolet photodissociation (UVPD) from 225 to 300 nm utilizing an optical parametric oscillator tunable wavelength laser system (OPO). Fragments were identified by absolute mass measurement in a 9.4 T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Bond cleavage was preferred in the vicinity of the two aromatic residues, resulting in high ion abundances for a4, a1, b3, y2 and y1 fragments. a, b and y ions dominated the mass spectrum, and full sequence coverage was achieved for those types. Photodissociation was most effective at the short wavelength end of the studied range, which is assigned to the onset of the La -* transition of the tyrosine chromophore, but worked well also at the Lb -* chromophore absorption maxima in the 35000-39000 cm-1 region. Several side-chain and internal fragments were observed. H atom loss is observed only above 41000 cm-1, consistent with the requirement of a curve crossing to a repulsive 1* state. It is suggested that the photochemically generated mobile H atom plays a role in further backbone cleavages, similar to the mechanism for electron capture dissociation. The b4 fragment is most intense at the Lb chromophore absorptions, undergoing additional fragmentation at higher photon energies. The high resolution of the FT-ICR MS revealed that out of all x and z-type fragments only x3 and x4 were formed, with low intensity. Other previously reported x- and z-fragments were re-assigned to internal fragments, based on exact mass measurement.(VLID)4795227Version of recor
Localisation and substrate specificities of transglycanases in charophyte algae relate to development and morphology
Cell wall-modifying enzymes have been previously investigated in charophyte green algae (CGA) in cultures of uniform age, giving limited insight into their roles. Therefore, we investigated the in situ localisation and specificity of enzymes acting on hemicelluloses in CGA genera of different morphologies and developmental stages. In vivo transglycosylation between xyloglucan and an endogenous donor in filamentous Klebsormidium and Zygnema was observed in longitudinal cell walls of young (1 month) but not old cells (1 year), suggesting that it has a role in cell growth. By contrast, in parenchymatous Chara, transglycanase action occurred in all cell planes. In Klebsormidium and Zygnema, the location of enzyme action mainly occurred in regions where xyloglucans and mannans, and to a lesser extent mixed-linkage beta-glucan (MLG), were present, indicating predominantly xyloglucan: xyloglucan endotransglucosylase (XET) activity. Novel transglycosylation activities between xyloglucan and xylan, and xyloglucan and galactomannan were identified in vitro in both genera. Our results show that several cell wall-modifying enzymes are present in CGA, and that differences in morphology and cell age are related to enzyme localisation and specificity. This indicates an evolutionary significance of cell wall modifications, as similar changes are known in their immediate descendants, the land plants.
This article has an associated First Person interview with the first author of the paper
Induction of Conjugation and Zygospore Cell Wall Characteristics in the Alpine Spirogyra mirabilis (Zygnematophyceae, Charophyta): Advantage under Climate Change Scenarios?
Extreme environments, such as alpine habitats at high elevation, are increasingly exposed to man-made climate change. Zygnematophyceae thriving in these regions possess a special means of sexual reproduction, termed conjugation, leading to the formation of resistant zygospores. A field sample of Spirogyra with numerous conjugating stages was isolated and characterized by molecular phylogeny. We successfully induced sexual reproduction under laboratory conditions by a transfer to artificial pond water and increasing the light intensity to 184 µmol photons m−2 s−1. This, however was only possible in early spring, suggesting that the isolated cultures had an internal rhythm. The reproductive morphology was characterized by light- and transmission electron microscopy, and the latter allowed the detection of distinctly oriented microfibrils in the exo- and endospore, and an electron-dense mesospore. Glycan microarray profiling showed that Spirogyra cell walls are rich in major pectic and hemicellulosic polysaccharides, and immuno-fluorescence allowed the detection of arabinogalactan proteins (AGPs) and xyloglucan in the zygospore cell walls. Confocal RAMAN spectroscopy detected complex aromatic compounds, similar in their spectral signature to that of Lycopodium spores. These data support the idea that sexual reproduction in Zygnematophyceae, the sister lineage to land plants, might have played an important role in the process of terrestrialization