Article

Aurearenophyceae classis nova, a New Class of Heterokontophyta Based on a New Marine Unicellular Alga Aurearenacruciata gen. et sp. nov. Inhabiting Sandy Beaches

Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8572, Japan.
Protist (Impact Factor: 3.05). 08/2008; 159(3):435-57. DOI: 10.1016/j.protis.2007.12.003
Source: PubMed

ABSTRACT

A new heterokontophyte alga, Aurearena cruciata gen. et sp. nov., was isolated from sandy beaches in Japan. Isolates were characterized by light and electron microscopy, spectroscopy of pigment composition, and molecular phylogenetic analyses using 18S rDNA and rbcL. The alga usually possessed a cell wall but also retained two heterokont flagella beneath the cell wall. Each walled cell first produced only a single flagellate cell that subsequently divided into two flagellate cells. Electron-opaque vesicles, possibly associated with cell wall formation, were observed beneath the cell membrane. The chloroplast consisted of two compartments, each enclosed by a chloroplast envelope and the inner membrane of the chloroplast endoplasmic reticulum; these two compartments were surrounded by a common outer membrane of chloroplast endoplasmic reticulum. Molecular phylogenetic trees suggested that this alga was a new and independent member of the clade that included the Phaeophyceae and Xanthophyceae (PX clade). A new class, Aurearenophyceae classis nova was proposed for A. cruciata.

    • "There is no chlorophyll c present as in all other Stramenopile algae. Accessory pigment (carotenoid) composition is similar to Xanthophytes except for the absence of heteroxanthin (Andersen, 2004; Kai et al., 2008). "
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    ABSTRACT: The Xanthophyceae, Eustigmatophyceae, and Raphidophyceae are three independent classes of stramenopile algae (Heterokontophyta or Ochrophyta); they are not closer related with each other. Most Xanthophytes are unicellular or colonial coccoid algae, others from multicellular filaments and or exhibit thalli composed of multinucleate siphons. The Eustigmatophyceae comprises only coccoid members which are very difficult to distinguish from the coccoid Xanthophytes. Freshwater Raphidophytes are rather distinct, because they form flagellated vegetative stages. The color of Xanthophytes and Eustigmatophytes is yellowish green due to the absence of the brown fucoxanthin, present in Raphidophytes and other stramenopile algae. Only the Eustigmatophytes lack chlorophyll c. Many Xanthophytes and Eustigmatophytes share that they predominately occur in terrestrial habitats, e.g. soil, representing a small group of terrestrial algae with their plastids obtained from an ancestral red alga by secondary symbiosis. For Raphidophytes only three genera are recognized in freshwater yet and they are observed within the plankton.
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    • "Our ML analysis strongly supports including Schizocladia in Phaeophyceae, but confirms that Phaeothamnion and Stichogloea (here treated together with Phaeoschizochlamys as Phaeothamniales sensu stricto) are much more closely related to the unicellular brownish alga Aurearena than to multicellular Phaeophyceae, as Kai et al. (2008) first showed. We therefore establish this new class for the robust clade (BS 81%) comprising Aurearenales (Kai et al. 2008) and Phaeothamniales sensu stricto (Fig. 15). Several differences between Aurearena and Phaeothamniales are simply differential losses of ancestral characters for Fucistia (e.g. "
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    • "Two transitional plates have been reported in Coscinodiscus and Chaetoceros (Jensen et al. 2003) and are evident in electron micrographs of Lithodesmium (Manton and von Stosch 1966, fig. 12), but their absence in the two diatoms studied here, together with the much more diffuse appearance of the upper plate in the three diatoms in which it has been reported, compared to Bolidomonas (Guillou et al. 1999), Pelagomonas (Andersen et al. 1993) or other heterokonts (Kawai et al. 2003; Kai et al. 2008; Kim et al. 2010) leads us to suggest that homology should not be assumed. "
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    ABSTRACT: The most complete account to date of the ultrastructure of flagellate cells in diatoms is given for the sperm of Thalassiosira lacustris and Melosira moniliformis var. octogona, based on serial sections. The sperm are uniflagellate, with no trace of a second basal body, and possess a 9 + 0 axoneme. The significance of the 9 + 0 configuration is discussed: lack of the central pair microtubules and radial spokes does not compromise the mastigoneme-bearing flagellum's capacity to perform planar beats and thrust reversal and may perhaps be related to sensory/secretory function of the sperm flagellum during plasmogamy. The basal bodies of diatoms are confirmed to contain doublets rather than triplets, which may correlate with the absence of some centriolar proteins found in most cells producing active flagella. Whereas Melosira possesses a normal cartwheel structure in the long basal body, no such structure is present in Thalassiosira, which instead possesses 'intercalary fibres' linking the basal body doublets. No transitional helices or transitional plates are present in either species studied. Cones of microtubules are associated with the basal body and partially enclose the nucleus in M. moniliformis and T. lacustris. They do not appear to be true microtubular roots and may arise through transformation of the meiosis II spindle. A close association between cone microtubules and tubules containing mastigonemes may indicate a function in intracellular mastigoneme transport. No correlation can yet be detected between methods of spermatogenesis and phylogeny in diatoms, contrary to previous suggestions.
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