Winter survival of the unicellular green alga Micrasterias denticulata: insights from field monitoring and simulation experiments

Peat bog pools around Tamsweg (Lungau, Austria) are typical habitats of the unicellular green alga Micrasterias denticulata. By measurement of water temperature and irradiation throughout a 1-year period (2018/2019), it was intended to assess the natural environmental strain in winter. Freezing resistance of Micrasterias cells and their ability to frost harden and become tolerant to ice encasement were determined after natural hardening and exposure to a cold acclimation treatment that simulated the natural temperature decrease in autumn. Transmission electron microscopy (TEM) was performed in laboratory-cultivated cells, after artificial cold acclimation treatment and in cells collected from field. Throughout winter, the peat bog pools inhabited by Micrasterias remained unfrozen. Despite air temperature minima down to −17.3 °C, the water temperature was mostly close to +0.8 °C. The alga was unable to frost harden, and upon ice encasement, the cells showed successive frost damage. Despite an unchanged freezing stress tolerance, significant ultrastructural changes were observed in field-sampled cells and in response to the artificial cold acclimation treatment: organelles such as the endoplasmic reticulum and thylakoids of the chloroplast showed distinct membrane bloating. Still, in the field samples, the Golgi apparatus appeared in an impeccable condition, and multivesicular bodies were less frequently observed suggesting a lower overall stress strain. The observed ultrastructural changes in winter and after cold acclimation are interpreted as cytological adjustments to winter or a resting state but are not related to frost hardening as Micrasterias cells were unable to improve their freezing stress tolerance.

Structural studies on cell wall biogenesis-I: A method to produce high-quality protoplasts from alga Micrasterias denticulata, an emerging model in plant biology

Micrasterias denticulate is a freshwater unicellular green alga emerging as a model system in plant cell biology. This is an algae that has been examined in the context of cell wall research from early 1970s. Protoplast production from such a model system is important for many downstream physiological and cell biological studies. The algae produce intact protoplast in a straight two-step protocol involving 5% mannitol, 2% cellulysin, 4mM calcium chloride under a temperature ramping strategy. The process of protoplast induction and behavior of protoplast was examined by light microscopy and reported in this study.

Fusion of Mitochondria to 3-D Networks, Autophagy and Increased Organelle Contacts are Important Subcellular Hallmarks during Cold Stress in Plants

Low temperature stress has a severe impact on the distribution, physiology, and survival of plants in their natural habitats. While numerous studies have focused on the physiological and molecular adjustments to low temperatures, this study provides evidence that cold induced physiological responses coincide with distinct ultrastructural alterations. Three plants from different evolutionary levels and habitats were investigated: The freshwater alga Micrasterias denticulata, the aquatic plant Lemna sp., and the nival plant Ranunculus glacialis. Ultrastructural alterations during low temperature stress were determined by the employment of 2-D transmission electron microscopy and 3-D reconstructions from focused ion beam–scanning electron microscopic series. With decreasing temperatures, increasing numbers of organelle contacts and particularly the fusion of mitochondria to 3-dimensional networks were observed. We assume that the increase or at least maintenance of respiration during low temperature stress is likely to be based on these mitochondrial interconnections. Moreover, it is shown that autophagy and degeneration processes accompany freezing stress in Lemna and R. glacialis. This might be an essential mechanism to recycle damaged cytoplasmic constituents to maintain the cellular metabolism during freezing stress.

On the new desmids parasite - Legenidium podbielkowskii sp.nov.

Below is a description of the new fungus parasitizing on <i>Micrasterias denticulata</i> Bréb. The fungus has been named <i>Lagenidium podbielkowskii</i> sp. nov. and the taxonomic relationships with the most closely allied species, namely - <i>L. closterii</i> de Wildeman are discussed.

Variação temporal do fitoplâncton de um lago pertencente à Área de Proteção Permanente no estado de Alagoas, nordeste do Brasil

Este trabalho teve como objetivo determinar a variação espaço-temporal do microfitoplâncton e variáveis ambientais no Lago Azul, Área de Proteção Permanente do município de Marechal Deodoro, Alagoas. As coletas ocorreram no período de abril a setembro de 2008. As amostras do fitoplâncton foram obtidas através de arrastos horizontais superficiais, com rede de abertura de malha de 45 µm e, concomitantemente, coletadas amostras de água utilizando garrafa de Van Dorn, para a determinação dos parâmetros físico-químicos. Foram identificados 27 táxons predominando as Chlorophyta (63%), destacando-se como espécies "dominantes" Desmidium swartzii var. quadrangulatum (Ralfs) A. Roy (62,3%) e D. cylindricum Greville (55,1%), seguidos das Bacillariophyta (26%) e Cyanobacteria (11%). O pH levemente ácido e a baixa disponibilidade de nutrientes ofereceram condições favoráveis para o desenvolvimento das Desmidiaceae: Closterium sp., Cosmarium goniodes West & West, C. margaritiferum Meneghini ex Ralfs, C. vogeciacum Gutwinski, Desmidium cylindricum Greville, D. pseudotreplonema West & West, D. swartzii var. quadrangulatum (Ralfs) A. Roy, Euastrum brasiliense Borge var. minus G.S.West, Gymnozyga moniliformis Ehrenberg, Micrasterias denticulata Brébisson ex Ralfs, M. (Kützing) Ralfs, M. radians Turner e Tetmemorus laevis (Kuetzing) Ralfs.