Micrasterias

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Ursula Lütz-meindl - One of the best experts on this subject based on the ideXlab platform.

  • Biomineralization of strontium and barium contributes to detoxification in the freshwater alga Micrasterias.
    Journal of plant physiology, 2018
    Co-Authors: Martin Niedermeier, Notburga Gierlinger, Ursula Lütz-meindl
    Abstract:

    Abstract The unicellular model alga Micrasterias denticulata inhabits acid peat bogs that are highly endangered by pollutants due to their high humidity. As it was known from earlier studies that algae like Micrasterias are capable of storing barium naturally in form of BaSO4 crystals, it was interesting to experimentally investigate distribution and sequestration of barium and the chemically similar alkaline earth metal strontium. Additionally, we intended to analyze whether biomineralization by crystal formation contributes to diminution of the generally toxic effects of these minerals to physiology and structure of this alga which is closely related to higher plants. The results show that depending on the treatment differently shaped crystals are formed in BaCl2 and Cl2Sr exposed Micrasterias cells. Modern microscopic techniques such as analytical TEM by electron energy loss spectroscopy and Raman microscopy provide evidence for the chemical composition of these crystals. It is shown that barium treatment results in the formation of insoluble BaSO4 crystals that develop within distinct compartments. During strontium exposure long rod-like crystals are formed and are surrounded by membranes. Based on the Raman signature of these crystals their composition is attributed to strontium citrate. These crystals are instable and are dissolved during cell death. During strontium as well as barium treatment cell division rates and photosynthetic oxygen production decreased in dependence of the concentration, whereas cell vitality was reduced only slightly. Together with the fact that TEM analyses revealed only minor ultrastructural alterations as consequence of relatively high concentrated BaCl2 and Cl2Sr exposure, this indicates that biomineralization of Sr and Ba protects the cells from severe damage or cell death at least within a particular concentration range and time period. In the case of Sr treatment where ROS levels were found to be elevated, hallmarks for autophagy of single organelles were observed by TEM, indicating beginning degradation processes.

  • Carbon starvation induces lipid degradation via autophagy in the model alga Micrasterias.
    Journal of Plant Physiology, 2017
    Co-Authors: Viola Schwarz, Ancuela Andosch, Anja Geretschläger, Matthias Affenzeller, Ursula Lütz-meindl
    Abstract:

    Abstract Autophagy is regarded as crucial intracellular process in plant development but also in intracellular stress response. It is known to be controlled by the energy level of the cell and consequently can be triggered by energy deprivation. In this study carbon starvation evoked in different ways was investigated in the freshwater algae model system Micrasterias denticulata (Streptophyta) which is closely related to higher plants. Cells exposed to the photosynthesis inhibiting herbicide DCMU, to the glycolysis inhibitor 2-Deoxy- d -glucose and to complete darkness over up to 9 weeks for preventing metabolism downstream of glucose supply, were investigated by means of Nile red staining and analyses in CLSM, and TEM after cryo-preparation. Our results show that lipid bodies containing both neutral and polar lipids are evenly distributed inside the chloroplast in control cells. During carbon starvation they are displaced into the cytoplasm and are either degraded via autophagy and/or excreted from the cell. Upon discharge from the chloroplast lipid bodies become engulfed by double membranes probably deriving from the ER, thus forming autophagosomes which later fuse with vacuoles. Coincidently indications for autophagy of other organelles and cytoplasmic portions were found during starvation and particularly in DCMU treated cells the number of starch grains decreased and pyrenoids disintegrated. Additionally our molecular data provide first evidence for the existence of a single ATG8 isoform in Micrasterias. ATG8 is known as main regulator of both bulk and selective autophagy in eucaryotes. Our study indicates that lipid degradation during carbon starvation is achieved via “classical” autophagy in the alga Micrasterias. This process has so far only been very rarely observed in plant cells and seems to allow recruitment of lipids for energy supply on the one hand and elimination of unusable or toxicated lipids on the other hand.

  • RESEARCH ARTICLE Open Access
    2016
    Co-Authors: Ursula Lütz-meindl, Jeroen Gillard, Lieven De Veylder, Alain Goossens, Dirk Inzé, Wim Vyverman
    Abstract:

    Transcriptional analysis of cell growth and morphogenesis in the unicellular green alga Micrasterias (Streptophyta), with emphasis on the role of expansi

  • 3-D analysis of dictyosomes and multivesicular bodies in the green alga Micrasterias denticulata by FIB/SEM tomography.
    Journal of structural biology, 2013
    Co-Authors: Gerhard Wanner, Tillman Schäfer, Ursula Lütz-meindl
    Abstract:

    In the present study we employ FIB/SEM tomography for analyzing 3-D architecture of dictyosomes and formation of multivesicular bodies (MVB) in high pressure frozen and cryo-substituted interphase cells of the green algal model system Micrasterias denticulata. The ability of FIB/SEM of milling very thin ‘slices’ (5–10 nm), viewing the block face and of capturing cytoplasmic volumes of several hundred μm3 provides new insight into the close spatial connection of the ER–Golgi machinery in an algal cell particularly in z-direction, complementary to informations obtained by TEM serial sectioning or electron tomography. Our FIB/SEM series and 3-D reconstructions show that interphase dictyosomes of Micrasterias are not only closely associated to an ER system at their cis-side which is common in various plant cells, but are surrounded by a huge “trans-ER” sheath leading to an almost complete enwrapping of dictyosomes by the ER. This is particularly interesting as the presence of a trans-dictyosomal ER system is well known from mammalian secretory cells but not from cells of higher plants to which the alga Micrasterias is closely related. In contrast to findings in plant storage tissue indicating that MVBs originate from the trans-Golgi network or its derivatives our investigations show that MVBs in Micrasterias are in direct spatial contact with both, trans-Golgi cisternae and the trans-ER sheath which provides evidence that both endomembrane compartments are involved in their formation.

  • A freshwater green alga under cadmium stress: ameliorating calcium effects on ultrastructure and photosynthesis in the unicellular model Micrasterias.
    Journal of plant physiology, 2012
    Co-Authors: Ancuela Andosch, Matthias Affenzeller, Cornelius Lutz, Ursula Lütz-meindl
    Abstract:

    Abstract Cadmium is a highly toxic heavy metal pollutant arising mainly from increasing industrial disposal of electronic components. Due to its high solubility it easily enters soil and aquatic environments. Via its similarity to calcium it may interfere with different kinds of Ca dependent metabolic or developmental processes in biological systems. In the present study we investigate primary cell physiological, morphological and ultrastructural responses of Cd on the unicellular freshwater green alga Micrasterias which has served as a cell biological model system since many years and has proved to be highly sensitive to any kind of abiotic stress. Our results provide evidence that the severe Cd effects in Micrasterias such as unidirectional disintegration of dictyosomes, occurrence of autophagy, decline in photosystem II activity and oxygen production as well as marked structural damage of the chloroplast are based on a disturbance of Ca homeostasis probably by displacement of Ca by Cd. This is indicated by the fact that physiological and structural cadmium effects could be prevented in Micrasterias by pre-treatment with Ca. Additionally, thapsigargin an inhibitor of animal and plant Ca2+-ATPase mimicked the adverse Cd induced morphological and functional effects on dictyosomes. Recovery experiments indicated rapid repair mechanisms after Cd stress.

Jiří Neustupa - One of the best experts on this subject based on the ideXlab platform.

  • Asymmetry and integration of cellular morphology in Micrasterias compereana
    BMC evolutionary biology, 2017
    Co-Authors: Jiří Neustupa
    Abstract:

    Unicellular green algae of the genus Micrasterias (Desmidiales) have complex cells with multiple lobes and indentations, and therefore, they are considered model organisms for research on plant cell morphogenesis and variation. Micrasterias cells have a typical biradial symmetric arrangement and multiple terminal lobules. They are composed of two semicells that can be further differentiated into three structural components: the polar lobe and two lateral lobes. Experimental studies suggested that these cellular parts have specific evolutionary patterns and develop independently. In this study, different geometric morphometric methods were used to address whether the semicells of Micrasterias compereana are truly not integrated with regard to the covariation of their shape data. In addition, morphological integration within the semicells was studied to ascertain whether individual lobes constitute distinct units that may be considered as separate modules. In parallel, I sought to determine whether the main components of morphological asymmetry could highlight underlying cytomorphogenetic processes that could indicate preferred directions of variation, canalizing evolutionary changes in cellular morphology. Differentiation between opposite semicells constituted the most prominent subset of cellular asymmetry. The second important asymmetric pattern, recovered by the Procrustes ANOVA models, described differentiation between the adjacent lobules within the quadrants. Other asymmetric components proved to be relatively unimportant. Opposite semicells were shown to be completely independent of each other on the basis of the partial least squares analysis analyses. In addition, polar lobes were weakly integrated with adjacent lateral lobes. Conversely, higher covariance levels between the two lateral lobes of the same semicell indicated mutual interconnection and significant integration between these parts. Micrasterias cells are composed of several successively disintegrated parts. These integration patterns concurred with presumed scenarios of morphological evolution within the lineage. In addition, asymmetric differentiation in the shape of the lobules involves two major patterns: asymmetry across the isthmus axis and among the adjacent lobules. Notably, asymmetry among the adjacent lobules may be related to evolutionary differentiation among species, but it may also point out developmental instability related to environmental factors.

  • Asymmetry and integration of cellular morphology in Micrasterias compereana
    BMC Evolutionary Biology, 2017
    Co-Authors: Jiří Neustupa
    Abstract:

    Background Unicellular green algae of the genus Micrasterias (Desmidiales) have complex cells with multiple lobes and indentations, and therefore, they are considered model organisms for research on plant cell morphogenesis and variation. Micrasterias cells have a typical biradial symmetric arrangement and multiple terminal lobules. They are composed of two semicells that can be further differentiated into three structural components: the polar lobe and two lateral lobes. Experimental studies suggested that these cellular parts have specific evolutionary patterns and develop independently. In this study, different geometric morphometric methods were used to address whether the semicells of Micrasterias compereana are truly not integrated with regard to the covariation of their shape data. In addition, morphological integration within the semicells was studied to ascertain whether individual lobes constitute distinct units that may be considered as separate modules. In parallel, I sought to determine whether the main components of morphological asymmetry could highlight underlying cytomorphogenetic processes that could indicate preferred directions of variation, canalizing evolutionary changes in cellular morphology. Results Differentiation between opposite semicells constituted the most prominent subset of cellular asymmetry. The second important asymmetric pattern, recovered by the Procrustes ANOVA models, described differentiation between the adjacent lobules within the quadrants. Other asymmetric components proved to be relatively unimportant. Opposite semicells were shown to be completely independent of each other on the basis of the partial least squares analysis analyses. In addition, polar lobes were weakly integrated with adjacent lateral lobes. Conversely, higher covariance levels between the two lateral lobes of the same semicell indicated mutual interconnection and significant integration between these parts. Conclusions Micrasterias cells are composed of several successively disintegrated parts. These integration patterns concurred with presumed scenarios of morphological evolution within the lineage. In addition, asymmetric differentiation in the shape of the lobules involves two major patterns: asymmetry across the isthmus axis and among the adjacent lobules. Notably, asymmetry among the adjacent lobules may be related to evolutionary differentiation among species, but it may also point out developmental instability related to environmental factors.

  • Additional file 1: of Asymmetry and integration of cellular morphology in Micrasterias compereana
    2017
    Co-Authors: Jiří Neustupa
    Abstract:

    Coordinates of 208 landmarks depicted on cells of Micrasterias compereana. (TXT 231 kb

  • Patterns of symmetric and asymmetric morphological variation in unicellular green microalgae of the genus Micrasterias (Desmidiales, Viridiplantae). Fottea 2013
    2016
    Co-Authors: Jiří Neustupa
    Abstract:

    Abstract: Morphological symmetry and asymmetry in three clonal populations of Micrasterias cells was decomposed using a new geometric morphometric method specifically developed for shape analysis of complex symmetric structures. Micrasterias cells are symmetric relative to two perpendicular axes of symmetry: a left–right axis and a juvenile–adult axis. Shape variation is decomposed into a component of symmetric variation and other components of asymmetry. Principal component analysis suggested that symmetric variation and juvenile–adult asymmetry were dominant in describing morphological differences among objects in all three datasets. The left– right asymmetric variation among adjacent quadrants of the same semicells was consistently more pronounced than the asymmetric variation with respect to the transversal axis. The strains of Micrasterias radians var. bogoriensis (SVCK 389) and M. radians var. evoluta (SVCK 518) were consistently more variable than the population of M. semiradiata (CAUP K606), with respect to both symmetric and different aspects of asymmetric variation. The shape differences among cell quadrants from opposite semicells were statistically not different from shape differences among cell quadrants from different cells of clonal populations

  • Splitting of Micrasterias fimbriata (Desmidiales, Viridiplantae) into two monophyletic species and description of Micrasterias compereana sp. nov.
    2016
    Co-Authors: Jiří Neustupa, Jan Šťastný, Pavel Škaloud
    Abstract:

    The freshwater microalgal genus Micrasterias C.Agardh ex Ralfs represents a monophyletic lineage of the Desmi-diaceae (Škaloud et al. 2011). Besides the species tradition-ally included in this genus on the basis of the morphologi

Klaus Von Schwartzenberg - One of the best experts on this subject based on the ideXlab platform.

Hong Zhou - One of the best experts on this subject based on the ideXlab platform.

Jiri Neustupa - One of the best experts on this subject based on the ideXlab platform.

  • Symmetry Breaking of the Cellular Lobes Closely Relates to Phylogenetic Structure Within Green Microalgae of the Micrasterias Lineage (Zygnematophyceae)
    PeerJ, 2018
    Co-Authors: Jiri Neustupa, Jan Stastny
    Abstract:

    Green microalgae of the Micrasterias lineage are unicellular microorganisms with modular morphology consisting of successively differentiated lobes. Due to their morphological diversity and peculiar morphogenesis, these species are important model systems for studies of cytomorphogenesis and cellular plasticity. Interestingly, the phylogenetic structure of the Micrasterias lineage and most other Desmidiales is poorly related to the traditional morphological characters used for delimitation of taxa. In this study, we focused on symmetry breaking between adjacent cellular lobes in relation to phylogeny of the studied species. While pronounced morphological asymmetry between the adjacent lobes is typical for some species, others have been characterized by the almost identical morphologies of these structures. We asked whether there is any detectable average shape asymmetry between the pairs of lobes and terminal lobules in 19 Micrasterias species representing all major clades of this desmidiacean lineage. Then, we evaluated whether the asymmetric patterns among species are phylogenetically structured. The analyses showed that the phylogeny was in fact strongly related to the patterns of morphological asymmetry between the adjacent cellular lobes. Thus, evolution of the asymmetric development between the adjacent lobes proved to be the key event differentiating cellular shape patterns of Micrasterias. Conversely, the phylogeny was only weakly related to asymmetry between the pairs of terminal lobules. The subsequent analyses of the phylogenetic morphological integration showed that individual hierarchical levels of cellular morphology were only weakly coordinated with regard to asymmetric variation among species. This finding indicates that evolutionary differentiation of morphogenetic processes leading to symmetry breaking may be relatively independent at different branching levels. Such modularity is probably the key to the evolvability of cellular shapes, leading to the extraordinary morphological diversity of these intriguing microalgae.

  • Surfaces, volumes and landmark data of cells
    2016
    Co-Authors: Jiri Neustupa
    Abstract:

    Estimated surfaces and volumes of Micrasterias cells (sheet 1) and the landmark data of the semicells (sheet 2). The first column of both tables depicts the population affiliation of cells

  • Temperature-related phenotypic plasticity in the green microalga Micrasterias rotata
    Aquatic Microbial Ecology, 2008
    Co-Authors: Jiri Neustupa, Jan Stastny, Ladislav Hodac
    Abstract:

    Temperature-related morphological variation of Micrasterias rotata (Desmidiales) strain CAUP K604 was investigated using landmark-based geometric morphometrics. Cultured morpho- types were compared with natural populations of M. rotata collected in different seasons at a central European lowland peat bog. In addition, we compared temperature-related variation with morpho- metric differentiation among other species within the genus Micrasterias. As temperatures increased, the population size of cultured M. rotata generally decreased and shape of the individual tempera- ture groups differed significantly. The high temperature (30°C) population contained the vegetative diploid cells. The shape variation related to temperature was similar to the size-related change in shape. Natural populations of M. rotata were consistently similar to the low temperature cultured populations throughout the season, while the high temperature morphotypes seen in culture were not present in natural samples.

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