Trebouxiophyceae, Chlorophyta - (S)FTP hesla na Botany

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1.1 Traditional morphology General introduction Traditionally, green algae were classified according to the morphological species concept based on the organisation level of the vegetative state (Brunnthaler 1915; Ettl & Gärtner 1988; Hindák 1977, 1980, 1984; Komárek & Fott 1983). The main morphological and structural characteristics used as taxonomic criteria in green microalgae were: form and dimensions of cells, cell wall characteristics, number of nuclei, chloroplast morphology, presence or absence of pyrenoid, number and size of autospores, and possibility to form zoospores (Ettl & Gärtner 1995; Komárek & Fott 1983). Morphological observations and species descriptions made by a number of phycologists considerably increased our knowledge of the biodiversity, morphological variability and systematics of green algae. Morphological studies of several prominent cytologists are still much accounted for their quality of observations, being sometimes at the limits of the laws of optics (Fott & Nováková 1969 1 ; Gärtner 1985; Tschermak- Woess 1989). However, recent molecular and physiological studies have demonstrated high plasticity of several morphological characters used for species delimitation and they evoked need for critical evaluation of observed morphological differences among the species. For example, presence of pyrenoid has been widely used to distinguish particular green algal species and genera, e.g. to differentiate flagellate species Chlamydomonas and Chloromonas (Ettl 1983, Fig. 2). However, phylogenetic analyses revealed that strains of both traditional genera could belong to the same clade and, in the case of Chloromonas reticulata, even to the same species (Buchheim et al. 1997, Pröschold et al. 2001). Nozaki et al. (1998) demonstrated that presence or absence of pyrenoids in Chlorogonium depends primarily on culture conditions (autotrophics vs. heterotrophics), instead on evolutionary differentiation. Similarly, production of mucilaginous envelopes around the cells, considered as discriminative character of green algal family Radiococcaceae (Komárek & Fott 1983), occurs in various unrelated algal lineages (Wolf et al. 2003). Moreover, it now appears that mucilaginous production often depends rather on the environmental conditions (Buzzelli et al. 1997, Reynolds 2007) than on phylogenetic position. Another example includes the genera Chlorella and Micractinium (Fig. 3), traditionally classified into different families of Chlorococcales (Chlorellaceae and Micractiniaceae). The 18S rDNA and ITS data revealed close relation- Fig. 2. Morphological distinction between genera Chlamydomonas (a) and Chloromonas (b) (modified after Ettl 1983). Fig. 3. Morphology of Chlorella vulgaris (a) and Micractinium pusillum (b) (modified after Komárek & Fott 1983). ship of these genera (Krienitz et al. 2004). Moreover, formation of colonies and cell wall bris- 1 cited paper has presently 114 citations in WOS (ISI Web of Science, http://portal.isiknowledge.com/portal.cgi) 2
General introduction tles that characterize the genus Monoraphidium was proven to represent phenotypic adaptation against grazer pressure of Brachionus calciflorus (Luo et al. 2006). Finally, morphology can be considerably influenced by the bacterial or fungal contamination. Common marine green alga Ulva is characterized by foliose morphology. However, by adding specific marine bacteria, strains of this genus are able to develop Fig. 4. Enteromorpha-like morphology of cultivated Ulva lactuca, induced by specific marine bacteria (after Provasoli & Pintner 1980). the Enteromorpha-like tubular thallus (Fig. 4, Provasoli & Pintner 1980). The phylogenetic analyses of ITS rDNA sequences later proved that green seaweeds Ulva and Enteromorpha are not distinct genera, and therefore, Enteromorpha was included into the genus Ulva (Hayden et al. 2003). The same effect of considerable variation in morphology occurs in green microalgae. Morphology of “Interfilum massjukiae” seems to vary from filamentous to packet-like in dependence to degree of bacterial contamination (own observations, Mikhailyuk et al. 2007). Similarly, massive contamination of Pseudococcomyxa simplex by unidentified ascomycote fungus probably causes significant changes of cell width (Fig. 5, Nemjová 2007). Fig. 5. Cell width variation in three Pseudococcomyxa simplex strains. Shaded box-plot indicates strain contamined by ascomycote fungus (modified after Nemjová 2007). 1.2 Confocal microscopy - an example of modern morphological approaches In late 1980s, advent of a new procedure for optical sectioning of plant tissues using the confocal laser scanning microscope (CLSM) provided an exciting new tool for the morphological observation of living and intact cells. Although the principle of CLSM has been patented in 1957, the commercial application of this method in general started three decades later. The main advantages of CLSM consist in the increasing of micrograph contrast and the possibility to reconstruct three-dimensional images of investigated structures. The special confocal pinhole eliminates out-of-focus information, so that just the light within the focal plane can be detected (Fig. 6, Pawley 2006). Resulting image quality is much better than that of wide-field images obtained by conven- Fig. 6. The mechanics of confocal microscopy (from http://www.microscopyu.com/). 3
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4 Conclusions Conclusions Tradition
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References GUNNING, B.E.S. & SCHWAR
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References VERSCHOOR, A.M.; VAN DER
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Trebouxiophyceae, Chlorophyta - (S)FTP hesla na Botany

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