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Nuclear events during conjugation in the poorly studied model ciliate Paramecium jenningsi
Get PDFCiliated protists are highly differentiated unicellular eukaryotes that possess special sexual processes (conjugation and autogamy) that rely on their unique nuclear dimorphism, i.e., the presence of both a germline micronucleus (MIC) and a somatic macronucleus (MAC) in a single cell. The sexual processes show a high diversity in different ciliates. To better understand the differentiation and evolution of sexual processes in closely related species, we investigated the nuclear events during conjugation in Paramecium jenningsi strain GZ, a poorly studied close relative of the well-known P. aurelia complex. The main results include: (1) the conjugation process takes about 48 h, including three prezygotic divisions (meiosis I, II, and mitosis) and three postzygotic divisions; (2) the MICs are dominated by the “parachute” phase at the prophase of meiosis I; (3) after meiosis II, a variable number of nuclei undergo the third prezygotic division, and the two products near the paroral cone become the genetically identical migratory and stationary pronuclei; (4) the synkaryon divides three times to form the MIC and the MAC anlagen, but only one nuclear product of the first postzygotic division completes the next two divisions; and (5) an extra cell division is required to complete the last step of conjugation, during which two MIC anlagen undergo mitotic division while two MAC anlagen are distributed between the daughter cells without division. The comparison of the nuclear events during conjugation in representatives of the class Oligohymenophorea reveals that usually there are three prezygotic divisions and a variable number of postzygotic divisions. However, the number of selected and differentiated nuclei after each division differs among species. This study provided a new model ciliate for further investigations of nuclear selection and differentiation as well as nuclear morphology during meiosis
A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap.
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Venus flytrap's leaves can catch an insect in a fraction of a second. Since the time of Charles Darwin, scientists have struggled to understand the sensory biology and biomechanics of this plant,
Dionaea muscipula
. Here we show that insect-capture of
Dionaea
traps is modulated by the phytohormone abscisic acid (ABA) and jasmonates. Water-stressed
Dionaea
, as well as those exposed to the drought-stress hormone ABA, are less sensitive to mechanical stimulation. In contrast, application of 12-oxo-phytodienoic acid (OPDA), a precursor of the phytohormone jasmonic acid (JA), the methyl ester of JA (Me-JA), and coronatine (COR), the molecular mimic of the isoleucine conjugate of JA (JA-Ile), triggers secretion of digestive enzymes without any preceding mechanical stimulus. Such secretion is accompanied by slow trap closure. Under physiological conditions, insect-capture is associated with Ca
2+
signaling and a rise in OPDA, Apparently, jasmonates bypass hapto-electric processes associated with trap closure. However, ABA does not affect OPDA-dependent gland activity. Therefore, signals for trap movement and secretion seem to involve separate pathways. Jasmonates are systemically active because application to a single trap induces secretion and slow closure not only in the given trap but also in all others. Furthermore, formerly touch-insensitive trap sectors are converted into mechanosensitive ones. These findings demonstrate that prey-catching
Dionaea
combines plant-specific signaling pathways, involving OPDA and ABA with a rapidly acting trigger, which uses ion channels, action potentials, and Ca
2+
signals.
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Morphogenesis and morphological redescription of a poorly known Ciliate Apokeronopsis ovalis (Kahl, 1932) nov. comb. (Ciliophora: Urostylida).
No full textThree marine interstitial scuticociliates, including two new species (Schizocalyptra similis sp. n., S. sinica sp. n.) and one insufficiently described form (Hippocomos salinus Small and Lynn, 1985) collected from sandy beaches in China, were morphologicallyinvestigated. The small subunit rRNA gene of the two new Schizocalyptra species was sequenced in order to compare with that of the onlyother sequenced congener, S. aeschtae. Both forms investigated in the present paper are demonstrated to be distinctive members of thisrelatively poorly known genus. Hippocomos salinus was observed in vivo for the first time. A redescription and improved diagnosis are heresupplied based on the China-population
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A unified organization of the Stichotrichine oral apparatus, including a description of the Buccal Seal (Ciliophora: Spirotrichea).
No full textWe investigated the oral apparatus of several stichotrichine spirotrichs, such as Stylonychia, Saudithrix, and Holosticha. Scanning electron microscopy reveals the oral opening into the buccal cavity covered by a membranous sheet, the “buccal seal”, which is very fragile and thus probably restored after each feeding process. Depending on the depth of the buccal cavity, there is an upper or an upper and a lower seal, for example, in Cyrtohymena and Saudithrix, where the buccal cavity extends near to the dorsal side of the cell. Scanning electron microscopy further reveals special cilia at the right end of the ventral membranelles. These “lateral membranellar cilia” originate mainly from the short fourth row at the anterior side of each membranelle. The lateral membranellar cilia, which are usually covered by the (upper) buccal seal, may be numerous and long (Cyrtohymena) or sparse and short (Holosticha). Live observations reveal that they are involved in feeding, while the long paroral and endoral cilia remain almost motionless. Based on these and other new observations, especially on the buccal lip and the membranellar bolsters, we propose an improved model for the organization of the stichotrichine oral apparatus. The distribution of buccal seal-like structures throughout the ciliate phylum, the nature and possible functions of the buccal seal and the lateral membranellar cilia, and the alpha-taxonomic significance of the new features are discussed
Notes on the poorly-known marine peritrichous ciliate, Zoothamnium plumula Kahl, 1933 (Protozoa, Ciliophora), an ectocommensal organism from cultured scallops in Qingdao, China.
No full textThe living morphology and the infraciliature of a poorly-known marine ectocommensal peritrich ciliate, Zoothamnium plumula Kahl, 1933 (pro Zoothamnium plumosum Perejaslawzewa, 1886) have been investigated based on specimens collected from within the mantle cavity and the shell surface of the cultured scallop, Chlamys farreri, off the coast of Qingdao, China. The Qingdao-population measures about 50-100 x 30-50 µm in vivo and is characterized by having one apically located contractile vacuole, one-layer peristomial collar, slender body shape and alternatively arranged colony branches. The C-shaped macronucleus is horizontally oriented. Number of silverlines between oral area and aboral ciliary wreath, ca 70; between aboral ciliary wreath and scopula, 24-28. Unlike most other congeners, zooids of this species are often enlarged at the distal end of branches
The morphology, morphogenesis and SSrRNA gene sequence of a new marine ciliate, Diophrys apoligothrix spec. nov. (Ciliophora; Euplotida).
No full textThe morphology,morphogenesisandsmallsubunitrRNA(SSrRNA)genesequenceofanewmarineeuplotid ciliate, Diophrys apoligothrix spec. nov.,isolatedfromasandybeachnearQingdao,northChina,wereinvestigated. This organismischaracterizedasfollows:rigidbodywithasculpturedsurface;size in vivo about 60–110_40–70 mm;adoralzonecomprisingabout28membranelles;fivefrontal,twoventral,fivetransverse,oneleftmarginalandthree caudalcirri;fivedorsalkinetieswithsparselydistributeddikinetids;twoellipsoidmacronuclearnodules;marine habitat.Althoughthemainmorphogeneticeventsaresimilartothosereportedinothercongeners,threefeaturesare noteworthy:(1)theparentaladoralzoneisretainedalmostunchangedbytheproterexceptfortheoutermarginof membranellesintheproximalportion,wherethede-differentiationandthenreorganizationtakeplaceinsituinthe mid-to-latephasesofdivision;(2)thedorsalkinetyanlagenareformedviaatwo-stepmode;(3)themarginalcirrus anlage isformeddenovoneartheoldstructureanddoesnotdivide.Basedonthemorphological,morphogeneticand SSrRNAgenesequencedata,itwasconcludedthat D. apoligothrix is awell-outlinedanddistinctivememberofthe genus Diophry
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