Article

Light and electron microscopical observations of the dinoflagellate Actiniscus pentasterias (Dinophyceae)

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Abstract

ABSTRACTI examined the heterotrophic non-armored dinoflaget-late Actiniscus pentasterias (Ehrenberg) Ehrenberg by light and electron microscopy. Actiniscus pentasterias contains an internal skeleton consisting of two star-like siliceous elements. Special emphasis is given to the flagellar apparatus, the nucleus, and a new type of extrusome, named a docidosome. A three dimensional model of the flagerllar apparatus includes a fibrous nuclear connnective, a posterior striated root, and a dorsal striated component of the longitudinal microtabular root. The nucleus is surrounded by a conspicuous fibrous lamina, also visible in the light microscope. The nuclear pores are situated in annulated invaginations of the nuclear envelope, increasing the nuclear surface area by 15–25%. The docidosomes are rod-shaped membrane-bound structures that terminate in a distinct proximal head. They show very complex substructure, consisting of an inner medulla with highly ordered paired ribbons and an outer cortex.

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... However, G. smaydae does not possess the representative features such as the nematocysts in Gyrodiniellum, Nematodinium, Paragymnodinium , and Polykrikos, an ocelloid as in Warnowia and Proterythropsis, body scales as in Lepidodinium or a pseudocolonial organization as in Polykrikos and Pheopolykrikos (Greuet 1987; Hansen et al. 2007a ; Hoppenrath and Leander 2007a,b; Hoppenrath et al. 2009a,b; Kang et al. 2010 Kang et al. , 2011a). The genera Actiniscus, Biecheleriopsis, Lepidodinium, Nematodinium, and Polykrikos also have the NFC (Bradbury et al. 1983; Hansen 1993; Hansen and Moestrup 2005; Moestrup et al. 2009b; Roberts and Taylor 1995). However, unlike G. smaydae, Biecheleriopsis has a single elongate vesicle with knob-like structures as part of the apical furrow system, and Actiniscus has an internal skeleton (Hansen 1993; Moestrup et al. 2009b). ...
... The genera Actiniscus, Biecheleriopsis, Lepidodinium, Nematodinium, and Polykrikos also have the NFC (Bradbury et al. 1983; Hansen 1993; Hansen and Moestrup 2005; Moestrup et al. 2009b; Roberts and Taylor 1995). However, unlike G. smaydae, Biecheleriopsis has a single elongate vesicle with knob-like structures as part of the apical furrow system, and Actiniscus has an internal skeleton (Hansen 1993; Moestrup et al. 2009b). The genera Actiniscus, Barrufeta, Lepidodinium, Noctiluca , and Polykrikos possess NC, a vesicular structure built into the nuclear envelope (Afzelius 1963; Hansen 1993; Hansen et al. 2007a; Hoppenrath and Leander 2007a,b; Sampedro et al. 2011; Soyer 1969). ...
... However, unlike G. smaydae, Biecheleriopsis has a single elongate vesicle with knob-like structures as part of the apical furrow system, and Actiniscus has an internal skeleton (Hansen 1993; Moestrup et al. 2009b). The genera Actiniscus, Barrufeta, Lepidodinium, Noctiluca , and Polykrikos possess NC, a vesicular structure built into the nuclear envelope (Afzelius 1963; Hansen 1993; Hansen et al. 2007a; Hoppenrath and Leander 2007a,b; Sampedro et al. 2011; Soyer 1969). However, despite these similarities, G. smaydae differed in details of the AG system; Barrufeta has a smurf-cap shaped AG, and Noctiluca lacks AG system (Afzelius 1963; Sampedro et al. 2011; Soyer 1969; seeTable 1;Fig. ...
Article
The marine phototrophic dinoflagellate Gymnodinium smaydae n. sp. is described from cells prepared for light, scanning, and transmission electron microscopy. Also, sequences of the small (SSU) and large subunits (LSU) and the internal transcribed spacer region (ITS1–5.8S–ITS2) of ribosomal DNA were analyzed. This newly isolated dinoflagellate possessed nuclear chambers, nuclear fibrous connective, an apical groove running in a counterclockwise direction around the apex, and a major accessory pigment peridinin, which are four key features for the genus Gymnodinium. The epicone was conical with a round apex, while the hypocone was ellipsoid. Cells growing photosynthetically were 6.3–10.9 μm long and 5.1–10.0 μm wide, and therefore smaller than any other Gymnodinium species so far reported except Gymnodinium nanum. Cells were covered with polygonal amphiesmal vesicles arranged in 11 horizontal rows, and the vesicles were smaller than those of the other Gymnodinium species. This dinoflagellate had a sharp and elongated ventral ridge reaching half way down the hypocone, unlike other Gymnodinium species. Moreover, displacement of the cingulum was 0.4–0.6 × cell length while in other known Gymnodinium species it is less than 0.3 × cell length. In addition, the new species possessed a peduncle, permanent chloroplasts, pyrenoids, trichocysts, pusule systems, and small knobs along the apical furrow, but it lacked an eyespot, nematocysts, and body scales. The sequence of the SSU, ITS1–5.8S–ITS2, and LSU rDNA region differed by 1.5–3.8%, 6.0–17.4%, and 9.1–17.5%, respectively, from those of the most closely related species. The phylogenetic trees demonstrated that the new species belonged to the Gymnodinium clade at the base of a clade consisting of Gymnodinium acidotum, Gymnodinium dorsalisulcum, Gymnodinium eucyaneum, etc. Based on morphological and molecular data, we suggest that the taxon represents a new species, Gymnodinium smaydae n. sp.
... Vesicles and ribosomes were present in the space between the two layers (Greuet 1972). The nuclear envelope was associated with the inner layer and the nuclear pores appeared to be situated in invaginations very similar to those present in Polykrikos and Actiniscus (Bradbury, Westfall, and Townsend 1983;Hansen 1993), but very different from C. polykrikoides. This indicates that Cochlodinium as presently defined is polyphyletic. ...
... The vc has so far been reported from unarmored dinoflagellates, such as Actiniscus pentasterias (Ehrenberg) Ehrenberg, A. sanguinea, G. aureolum, G. fuscum, and Lepidodinium spp. (Hansen 1993, as PSR, 2001Hansen and Moestrup 2005;Hansen et al. 2000Hansen et al. , 2007Roberts and Roberts 1991). In Actiniscus, Gymnodinium, and Lepidodinium, the vc is considerably shorter, extending only to the proximal part of the LFC and terminating around the LSC (Hansen 1993(Hansen , 2001. ...
... (Hansen 1993, as PSR, 2001Hansen and Moestrup 2005;Hansen et al. 2000Hansen et al. , 2007Roberts and Roberts 1991). In Actiniscus, Gymnodinium, and Lepidodinium, the vc is considerably shorter, extending only to the proximal part of the LFC and terminating around the LSC (Hansen 1993(Hansen , 2001. On the other hand, the vc of A. sanguinea is very similar to that of C. polykrikoides as its proximal part is fibrous and flares out toward the R1, becoming striated and extending downwards (Roberts and Roberts 1991). ...
Article
The external and internal ultrastructure of the harmful unarmored dinoflagellate Cochlodinium polykrikoides Margalef has been examined with special reference to the apical groove and three-dimensional structure of the flagellar apparatus. The apical groove is U-shaped and connected to the anterior sulcal extension on the dorsal side of the epicone. The eyespot is located dorsally and composed of two layers of globules situated within the chloroplast. A narrow invagination of the plasma membrane is associated with the eyespot. The nuclear envelope has normal nuclear pores similar to other eukaryotes but different from the Gymnodinium group with diagnostic nuclear chambers. The longitudinal and transverse basal bodies are separated by approximately 0.5-1.0 microm and interconnected directly by a striated basal body connective and indirectly by microtubular and fibrous structures. Characteristic features of the flagellar apparatus are as follows: (1) a nuclear extension projects to the R1 (longitudinal microtubular root) and is connected to the root by thin fibrous material; (2) fibrillar structures are associated with the longitudinal and transverse flagellar canal; and (3) a striated ventral connective extends toward the posterior end of the cell along the longitudinal flagellar canal. We conclude, based on both morphological and molecular evidence, that Cochlodinium is only distantly related to Gymnodinium.
... The shape of the apical groove of new genus Barrufeta also differs from that of other gymnodinioids. Furthermore, referring to the different kinds of apical-furrow apparatuses described in the literature (Hansen andDaugbjerg 2009, Moestrup et al. 2009a, b), we made a detailed structural comparison between the apical groove of Barrufeta and that of a species belonging to the genus Gymnodinium, G. impudicum. Although both contained three elongated vesicles, small knobs ornamented the central vesicle in B. bravensis, whereas in G. impudicum the lateral vesicles were ornamented. ...
... Table 2. A comparison of the major morphological features of similar and closest species to Barrufeta brevensis; based on Hulburt (1957) 1 , Watanabe et al. (1990) 6 , Fraga et al. (1995) 5 , Takayama (1998) (Hansen 1993), Nematodinium (Roberts and Taylor 1995), and Biecheleriopsis (Moestrup et al. 2009b). While nuclear chambers were observed in Barrufeta, they are not as numerous as in Gymnodinium fuscum (Hansen et al. 2000b) or L. viride (Hansen et al. 2007), and nuclear pores were not observed. ...
Article
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The present study describes a new dinoflagellate genus, Barrufeta N. Sampedro et S. Fraga gen. nov., with one new species, B. bravensis Sampedro et S. Fraga sp. nov., isolated from the Costa Brava (NW Mediterranean Sea). The dinoflagellate was characterized at the genus and species levels by LM and EM; LSU and internal transcribed spacer (ITS) rDNA sequences; and HPLC analyses of the pigments, fatty acids, and possible presence of toxins of several cultured strains. The new Barrufeta species is oval shaped (22–35 μm long and 16–25 μm wide) and dorsoventrally flattened. It possesses numerous small chloroplasts that radiate from two large equatorially located pyrenoids and is a typical peridinin-containing dinoflagellate. The nucleus is in the anterior part of the epicone. The apical groove has a characteristic “Smurf-cap” shape that runs counterclockwise on the epicone and terminates on its right posterior part. B. bravensis is similar to the previously described species Gyrodinium resplendens Hulburt in its external morphology, but the original report of the latter lacked a description of the complete shape of the apical groove. It is therefore likely that some of the G. resplendens species reported in the literature are Barrufeta since they possess a Barrufeta-type apical groove. Fatty acids of Barrufeta were more similar to those of Karenia brevis than those obtained from other unarmored analyzed species including three species of Gymnodinium and Akashiwo sanguinea.
... The shape of the apical groove of new genus Barrufeta also differs from that of other gymnodinioids. Furthermore, referring to the different kinds of apical-furrow apparatuses described in the literature (Hansen andDaugbjerg 2009, Moestrup et al. 2009a, b), we made a detailed structural comparison between the apical groove of Barrufeta and that of a species belonging to the genus Gymnodinium, G. impudicum. Although both contained three elongated vesicles, small knobs ornamented the central vesicle in B. bravensis, whereas in G. impudicum the lateral vesicles were ornamented. ...
... Table 2. A comparison of the major morphological features of similar and closest species to Barrufeta brevensis; based on Hulburt (1957) 1 , Watanabe et al. (1990) 6 , Fraga et al. (1995) 5 , Takayama (1998) (Hansen 1993), Nematodinium (Roberts and Taylor 1995), and Biecheleriopsis (Moestrup et al. 2009b). While nuclear chambers were observed in Barrufeta, they are not as numerous as in Gymnodinium fuscum (Hansen et al. 2000b) or L. viride (Hansen et al. 2007), and nuclear pores were not observed. ...
Article
The present study describes a new dinoflagellate genus, Barrufeta N. Sampedro et S. Fraga gen. nov., with one new species, B. bravensis Sampedro et S. Fraga sp. nov., isolated from the Costa Brava (NW Mediterranean Sea). The dinoflagellate was characterized at the genus and species levels by LM and EM; LSU and internal transcribed spacer (ITS) rDNA sequences; and HPLC analyses of the pigments, fatty acids, and possible presence of toxins of several cultured strains. The new Barrufeta species is oval shaped (22–35 lm long and 16–25 lm wide) and dorsoventrally flattened. It possesses numerous small chloroplasts that radiate from two large equatorially located pyrenoids and is a typical peridinin-containing dinoflagellate. The nucleus is in the anterior part of the epicone. The apical groove has a characteristic ‘‘Smurf-cap’’ shape that runs counterclockwise on the epicone and terminates on its right posterior part. B. bravensis is similar to the previously described species Gyrodinium resplendens Hulburt in its external morphology, but the original report of the latter lacked a description of the complete shape of the apical groove. It is therefore likely that some of the G. resplendens species reported in the literature are Barrufeta since they possess a Barrufeta-type apical groove. Fatty acids of Barrufeta were more similar to those of Karenia brevis than those obtained from other unarmored analyzed species including three species of Gymnodinium and Akashiwo sanguinea.
... The nucleus of the specimens observed with TEM was a typical dinokaryon with permanently condensed chromosomes and a nucleolus (Fig. 6A). However, the splits in the nuclear envelope (Fig. 6B) were unlike any other structures found in athecate dinoflagellates, such as Actiniscus pentasterias (Ehrenberg) Ehrenberg, Polykrikos, Gymnodinium and Gyrodinium (Bradbury et al. 1983; Hansen 1993 Hansen , 2001 Hansen and Daugbjerg 2004; Hansen et al. 2000; Hoppenrath and Leander 2007b). Interestingly, these dinoflagellates do possess vesicular or nuclear chambers in the nuclear envelope in which the nuclear pores are situated. ...
... Nuclear pores were not found within the split membranes, but only in the parts of the nuclear envelope where the two membranes were in close proximity to each other. Splits could also be found in varying sizes, unlike the nuclear chambers reported from other dinoflagellates (Bradbury et al., 1983; Hansen 1993 Hansen , 2001 Hansen and Daugbjerg 2004; Hansen et al. 2000; Hoppenrath and Leander 2007b). It cannot be completely ruled out, however, that the splits represent an artifact caused by a suboptimal fixation. ...
Article
The composition of the dinoflagellate genus Amphidinium is currently polyphyletic and includes several species in need of re-evaluation using modern morphological and phylogenetic methods. We investigated a broad range of uncultured morphotypes extracted from marine sediments in the Eastern Pacific Ocean that were similar in morphology to Amphidinium glabrum Hoppenrath and Okolodkov. To determine the number of distinct species associated with this phenotypic diversity, we collected LM, SEM, TEM and small subunit ribosomal DNA sequence information from different morphotypes, including the previously described A. glabrum. Both comparative morphological and molecular phylogenetic data supported the establishment of a new genus, Apicoporus n. gen., including at least two species, A. glaber n. comb., and A. parvidiaboli n. sp. Apicoporus is characterized by having amphiesmal pores and an apical pore covered by a hook-like protrusion; neither of these characters has been observed in other athecate dinoflagellates. The posterior end of Apicoporus parvidiaboli possessed varying degrees of "horn formation", ranging from slight to prominent. By contrast, the posterior end of Apicoporus glaber was distinctively rounded and lacked evidence of horn formation. Although these species were previously interpreted to be obligate heterotrophs, TEM and epifluorescence microscopy demonstrated that some cells of both species had unusually small but otherwise typical dinoflagellate plastids. The number and density of plastids in any particular cell varied significantly in the genus, but the plastids were almost always concentrated at the posterior end of the cells or around the nucleus. The presence of cryptic photosynthetic plastids in these benthic species suggests that photosynthesis might be much more widespread in dinoflagellates than is currently assumed.
... Cells of P. kofoidii were discerned as binucleate "pseudocolonies" with four girdle flagella, which lacked plastids and have nematocysts (Fig. 1A). Cells of A. pentasterias were identified by the pair of five-pointed silica stars around their nuclei and their apical "docidosome" extrusomes (30). Cells likely belonging to G. fasciculatum were identified by the presence of docidosomes, lack of plastids, and gymnodinoid shape (round, unarmored cells with equatorial girdle). ...
Article
Full-text available
We examine the origin of harpoon-like secretory organelles (nematocysts) in dinoflagellate protists. These ballistic organelles have been hypothesized to be homologous to similarly complex structures in animals (cnidarians); but we show, using structural, functional, and phylogenomic data, that nematocysts evolved independently in both lineages. We also recorded the first high-resolution videos of nematocyst discharge in dinoflagellates. Unexpectedly, our data suggest that different types of dinoflagellate nematocysts use two fundamentally different types of ballistic mechanisms: one type relies on a single pressurized capsule for propulsion, whereas the other type launches 11 to 15 projectiles from an arrangement similar to a Gatling gun. Despite their radical structural differences, these nematocysts share a single origin within dinoflagellates and both potentially use a contraction-based mechanism to generate ballistic force. The diversity of traits in dinoflagellate nematocysts demonstrates a stepwise route by which simple secretory structures diversified to yield elaborate subcellular weaponry.
... Testudodinium magnum possesses unique internal structures , the props, that were previously unknown from any other dinoflagellate. Internal siliceous skeletons were discovered in the dinoflagellates Actiniscus pentasterias (Ehernberg ) Ehrenberg (Hansen 1993) and Dicroerisma psilonereiella Taylor & Cattell (Gómez 2008), but their structures are very different from props of T. magnum. The props extend from the dorsum to the ventrum; they are fibrous in nature but the composition and function are currently unknown and under investigation. ...
Article
A new marine benthic dinoflagellate, Testudodinium magnum sp. nov., was described from a sand sample collected on the seafloor at a depth of 35 m off Mageshima Island, Kagoshima, Japan. The dinoflagellate possessed the characteristic features of the genus Testudodinium, but was distinguished by its extremely large size and pebbled dorsal surface of the hyposome, caused by the presence of numerous nodules. The cells of this dinoflagellate possessed a dominant sessile and a rare motile form that were morphologically distinct from each other: The sessile form was larger and the small rounded episome with longitudinal furrow was completely embedded in the hyposome; the motile form was smaller and the episome was only partly embedded in the hyposome. The ultrastructural investigations revealed the presence of a large, circular, starch-sheathed pyrenoid whose matrix was traversed by randomly arranged thylakoid lamellae. The chloroplasts formed a network radiating outward from the pyrenoid. Uniquely, this dinoflagellate possessed internal props - structures that spanned the thickness of the cell and were fibrous in nature. The props were numerous and passed through organelles and cell contents. Phylogenetic analyses based on the small-subunit ribosomal DNA gene sequences placed this dinoflagellate firmly within the Testudodinium clade with high support. On the basis of the morphological features and phylogenetic analyses, we concluded that this dinoflagellate was a new species in the genus Testudodinium.
... Moestrup 1982), occurs only sporadically in dinoflagellates. It was first discovered in Polykrikos by Bradbury et al. (1983), followed by reports in Actiniscus (Hansen 1993), Nematodinium (Roberts & Taylor 1995) and species of Gymnodinium (e.g. Roberts 1986;Hansen 2001). ...
... 50 microtubules) r1 root (labelled sc-pmr in Roberts 1985, figs 16, 17, 22). A similar structure was found by Hansen (1993) in another, very aberrant species, Actiniscus pentasterias, a species characterized by cells possessing an internal silicified skeleton (Hansen 1993). Its phylogenetic relationships remain unknown, but another similarity between this species and Levanderina is the presence of a distinct, muscle-like, striated fibre (vf), which from the ventral side of r1 proceeds along the Fig. 68, which also illustrates all four flagellar roots. ...
Article
Full-text available
Gymnodinium fissum was described by Levander (1894) from the Baltic Sea near Helsinki, and we argue, based on morphological and molecular studies of material from the type locality, and on cultures from the Åland islands, Puerto Rico, Portugal and USA identified as Gyrodinium instriatum, Gymnodinium instriatum, Gyrodinium uncatenum and Gyrodinium sp., that all these taxa are conspecific. They were morphologically and genetically distinct from Gymnodinium and were described here as Levanderina fissa gen. et comb. nov. This species also includes Gyrodinium pavillardii Biecheler (1952). Levander observed chloroplasts in the cell and on some occasions diatoms, probably the first report of mixotrophy in a dinoflagellate. Biecheler (1952) described the process of food uptake in G. pavillardii, feeding it with ciliates and other dinoflagellates. Prey was taken up through the posterior part of the sulcus, some prey items being almost as large as the host. Our observations showed that the longitudinal flagellum, in contrast to what was described in all other dinoflagellates possessing a longitudinal sulcal furrow, was not located in the furrow but in a separate, internal tube beneath the sulcal furrow. The tube opened to the exterior dorsally near the posterior end of the cell, and the sulcus appeared to be used for food uptake only. The cytoskeleton of L. fissa was complex and included a large number of muscle-like fibers. Food uptake using the sulcus involved major changes of cell shape, which required the presence of a highly flexible cytoskeleton. Levanderina fissa was not morphologically or genetically close to any other dinoflagellate for which molecular sequences were available. The detailed structure of the apical furrow or acrobase comprised three rows of elongate vesicles, one row forming the bottom of a furrow. The new term Apical Structure Complex (ASC) was introduced as a general term to replace apical furrow or acrobase, none of which adequately described all the many known types. The ASC in Levanderina may be characteristic of most if not all species of the Gymnodiniales (an apomorphy of the order?) and different from the types present in the Suessiales, the other order of mainly thin-walled dinoflagellates.
... Both characters were, however, reported in species of Lepidodinium (Hansen et al., 2007) and Polykrikos (Bradbury et al., 1983; Hoppenrath and Leander, 2007). Either the nuclear chamber, or NFC, was reported in Barrufeta (Sampedro et al., 2011), Actiniscus Ehrenberg (Hansen, 1993), Biecheleriopsis Moestrup, K. Lindberg & N. Daugbjerg (Moestrup et al., 2009) and Nematodinium (Roberts and Taylor, 1995), suggesting that these characters might not be genus-specific. Gymnodinium inusitatum differs from Gymnodinium aureolum (E.M. Hulburt) G. Hansen in terms of the cell shape, cell surface, nucleus configuration and pyrenoid type (Hansen, 2001; Tang et al., 2008). ...
Article
Four Gymnodinium species have previously been reported to produce microreticulate cysts. Worldwide, Gymnodinium catenatum strains are conservative in terms of larger subunit (LSU) rDNA and internal transcribed spacer region (ITS) sequences, but only limited information on the molecular sequences of other species is available. In the present study, we explored the diversity of Gymnodinium by incubating microreticulate cysts collected from the Yellow Sea off China. A total of 18 strains of Gymnodinium, from three species, were established. Two of these were identified as Gymnodinium catenatum and Gymnodinium microreticulatum, and the third was described as a new species, Gymnodinium inusitatum. Motile cells of G. inusitatum are similar to those of Gymnodinium trapeziforme, but they only share 82.52% similarity in LSU sequences. Cysts of G. inusitatum are polygonal in shape, with its microreticulate wall composed of approximately 14 concave sections. G. microreticulatum strains differ from each other at 69 positions (88.00% similarity) in terms of ITS sequences, whereas all G. catenatum strains share identical ITS sequences and belonged to the global populations. Phylogenetic analyses, based on LSU sequences, revealed that Gymnodinium species that produce microreticulate cysts are monophyletic. Nevertheless, the genus as a whole appears to be polyphyletic. Paralytic shellfish toxins (PSTs) were found in all G. catenatum strains tested (dominated by 11-hydroxysulfate benzoate analogs and N-sulfocarmaboyl analogs) but not in any of the G. microreticulatum and G. inusitatum strains. Our results support the premise that cyst morphology is taxonomically informative and is a potential feature for subdividing the genus Gymnodinium.
... Moestrup 1982), occurs only sporadically in dinoflagellates. It was first discovered in Polykrikos by Bradbury et al. (1983), followed by reports in Actiniscus (Hansen 1993), Nematodinium (Roberts & Taylor 1995) and species of Gymnodinium (e.g. Roberts 1986; Hansen 2001). ...
Article
An isolate of the very small marine dinoflagellate Biecheleriopsis adriatica gen. et sp. nov. (12–15 µm long) has been examined by light, scanning and transmission electron microscopy, combined with partial sequencing of nuclear-encoded large subunit rRNA. Biecheleriopsis is a genus of thin-walled dinoflagellates, related to Biecheleria and the taxonomic group of Polarella, Protodinium and Symbiodinium, the latter comprising mainly symbionts of marine invertebrates. The mixotrophic Biecheleriopsis adriatica is characterized by: (i) a special type of apical furrow apparatus; (ii) an eyespot of Type E sensu Moestrup and Daugbjerg; (iii) an unusual type of pyrenoid; and (iv) a spiny resting cyst. Thin sections showed the presence a fibrous connection between the flagellar apparatus and a finger-like extension of the nucleus (‘rhizoplast’). It forms a physical connection between the flagella and the nucleus. This unusual structure has previously been considered to characterize the ‘true’ gymnodinioids, represented by Gymnodinium sensu Daugbjerg et al. and related forms. However, the apical furrow apparatus and the nuclear envelope of Biecheleriopsis are woloszynskioid rather than gymnodinioid. The related genus Biecheleria lacks a rhizoplast, and it also lacks a 51-base pair fragment of domain D2 of the large subunit rRNA, which is present in other woloszynskioids. A physical connection between the flagellar apparatus and the nucleus mediated by a fibrous structure is known in other groups of protists, for example, the ‘rhizoplast’ of many heterokont flagellates, some green algal flagellates, etc. The phylogenetic significance of a rhizoplast in two groups of dinoflagellates that are only distantly related is presently difficult to assess.
... The ultrastructure of dinoflagellates is an active field of research, particularly the examination of the flagellar bases and associated components, believed to provide useful data for unravelling the phylogenetic history within the group. The flagellar apparatus has been described, with different degrees of detail, from about a dozen species of unarmored dinoflagellates (Hansen 1993, Roberts et al. 1995a, ...
Article
Amphidinium lacustre Stein, non sensu auctt. was identified by reference to original descriptions, which differ significantly from later interpretations. Mixed cultures containing A. lacustre, cryptomonads, Spermatozopsis exsultans Korshikov, and small chlorelloid cells were examined for feeding events. The dinoflagellate ingested the cytoplasm of cryptomonads, leaving the periplast, and completely ingested Spermatozopsis and chlorelloid cells. A peduncle was used in the initial stages of prey capture, although it was not visible during food uptake. The ultrastructure of A. lacustre was typical of unarmored dinoflagellates. A single pusule per cell, consisting of one long, convoluted tube, opened directly into one of the flagellar canals. An eyespot was present, composed of presumably crystalline, vesicle-contained units, similar to those of Gymnodinium natalense Horiguchi et Pienaar. The main components of the flagellar apparatus resembled those of other Amphidinium species, but differences were noted. The transverse basal body overlapped the proximal end of the longitudinal one at an angle of about 120°. Three connectives were distinguished between basal bodies, one of which consisted of radiating fibers linking individual triplets of the longitudinal basal body to one triplet of the transverse. Some flagellar apparatus components were closely associated to a vesicle and to a mitochondrion. A ventral ridge extended from the (incomplete) longitudinal striated collar to the peduncular striated collar. The peduncle was supported by a single strand of microtubules, which were surrounded by numerous vesicles with electron-opaque contents.
... Also, the TMRE, rather than bending to the left as in L. viride, seems to bend towards the right (Hansen & Moestrup 2005). A nuclear fibrous connective is a characteristic of the Gymnodinium group, but has also been observed in the heterotrophic species Actiniscus pentasterias (Ehrenberg) Ehrenberg and Polykrikos kofoidii Chatton (Bradbury et al. 1983;Hansen 1993), which are related to but not included in the Gymnodinium sensu stricto group, in particular because of their peculiar nuclear capsules. In all examined species the NFC is a dense non-striated fibrous structure, except in Gymnodinium cryophilum (Wedemayer, Wilcox et Graham) Gert Hansen et Moestrup, where the NFC (originally interpretated as a striated root) also appears to be striated (Wilcox et al. 1982). ...
Article
The ultrastructure of the green dinoflagellate Lepididodinium viride M. M. Watanabe, S. Suda, I. Inouye Sawaguchi et Chihara was studied in detail. The nuclear envelope possessed numerous chambers each furnished with a nuclear pore, a similar arrangement to that found in other gymnodinioids. The flagellar apparatus was essentially identical to Gymnodinium chlorophorum Elbrächter et Schnepf, a species also containing chloroplasts of chlorophyte origin. Of particular interest was the connection of the flagellar apparatus to the nuclear envelope by means of both a fiber and a microtubular extension of the R3 flagellar root. This feature has not been found in other dinoflagellates and suggests a close relationship between these two species. This was confirmed by phylogenetic analysis based on partial sequences of the large subunit (LSU) rDNA gene of L. viride, G. chlorophorum and 16 other unarmoured dinoflagellates, including both the ‘type’ culture and a new Tasmanian isolate of G. chlorophorum. These two isolates had identical sequences and differed from L. viride by only 3.75% of their partial LSU sequences, considerably less than the difference between other Gymnodinium species. Therefore, based on ultrastructure, pigments and partial LSU rDNA sequences, the genus Lepidodinium was emended to encompass L. chlorophorum comb. nov.
... These shared morphological characters are consistent with the close relationships between Polykrikos and Gymnodinium s.s. in our molecular phylogenetic analyses (Fig. 9). The so-called 'double-layered fibrous nuclear cortex (capsule)' directly beneath the nuclear envelope in P. kofoidii does not appear to be present in other species of Gymnodinium s.s., including P. lebourae (Fig. 6 F), and so far is shared only with Actiniscus pentasterias (Bradbury et al. 1983; Hansen 1993). Nonetheless, like other members of the Gymnodinium s.s. ...
Article
Both the photosynthetic and heterotrophic forms of the only known marine benthic (sand-dwelling) species of Polykrikos, namely P. lebourae, were investigated using light and electron microscopy and molecular phylogenetic analyses. The pseudocolonies usually contained eight integrated zooids and two nuclei. Pseudocolonies consisting of four or five zooids and one nucleus were observed for the first time for this species; some of these reduced pseudocolonies contained plastids, while others were heterotrophic and contained taeniocyst-nematocyst complexes. The ultrastructure of the plastids in P. lebourae did not conform to the organization of thylakoids and enveloping membranes present in the peridinin-containing plastids of other photosynthetic dinoflagellates (i.e. stacks of 3 thylakoids and 3 outer membranes). Instead, the plastids in P. lebourae had thylakoids arranged in pairs and appeared to be enveloped by only two membranes. Molecular phylogenetic data using small subunit rDNA demonstrated that the photosynthetic and heterotrophic forms of P. lebourae represent two distinct clades. The more inclusive clade containing both forms of P. lebourae was most closely related to heterotrophic polykrikoids, namely P. kofoidii. These results led us to conclude that the photosynthetic and heterotrophic forms of P. lebourae are in fact two distinct lineages, and the heterotrophic form is described here as Polykrikos herdmanae n. sp.
Chapter
Silicon (Si) is incorporated in species from most of the biological kingdoms. In this review we focus on what is known about: Si accumulation and the formation of siliceous structures in microalgae and some related non-photosynthetic groups, molecular and genetic mechanisms controlling silicification in the microalgae, and the potential costs and benefits associated with silicification in the microalgae.
Article
The syndinean dinoflagellates are a diverse assemblage of alveolate endoparasites that branch basal to the core dinoflagellates. Because of their phylogenetic position, the syndineans are considered key model microorganisms in understanding early evolution in the dinoflagellates. Closed mitosis with an extranuclear spindle that traverses the nucleus in cytoplasmic grooves or tunnels is viewed as one of the morphological features shared by syndinean and core dinoflagellates. Here we describe nuclear morphology and mitosis in the syndinean dinoflagellate Amoebophrya sp. from Akashiwo sanguinea, a member of the A. ceratii complex, as revealed by protargol silver impregnation, DNA specific fluorochromes, and transmission electron microscopy. Our observations show that not all species classified as dinoflagellates have an extranuclear spindle. In Amoebophrya sp. from A. sanguinea, an extranuclear microtubule cylinder located in a depression in the nuclear surface during interphase moves into the nucleoplasm via sequential membrane fusion events and develops into an entirely intranuclear spindle. Results suggest that the intranuclear spindle of Amoebophrya spp. may have evolved from an ancestral extranuclear spindle and indicate the need for taxonomic revision of the Amoebophryidae.
Article
Full-text available
Ebridian flagellates have a long geological history, but only two extant species: Ebria tripartita and Hermesinum adriaticum. The former species feeds extensively on diatoms and has a widespread distribution in coastal oceans; the latter species is mixotrophic and possibly autotrophic, with numerous Synechococcus-like endosymbiotic cyanobacteria, and is restricted to warmer waters associated with hypoxic or anoxic conditions. Ebridians were previously classified erroneously with dinoflagellates, but their nuclear structure is similar to that of euglenoid flagellates. These relict flagellates exhibit a distinct dichotomy in their structure, distribution, and trophic status. Their role in coastal ecosystems and their proper taxonomic classification is unclear since they have yet to be grown in vitro, but their occasional abundance suggests they may have an impact on nanoplankton and picoplankton biodiversity and microbial loop processes.
Article
Full-text available
Phytoplankton samples were taken during several oceanographic cruises in the Mexican Pacific Ocean (1998–2000), following three different protocols of collection and analysis, and from the material we report six new records of planktonic dinoflagellates in the region. Two species, Asterodinium spinosum and Brachydinium capitatum, are unarmored, another species, Actiniscus pentasterias, has internal siliceous skeletons, whereas Thoracosphaera heimii usually develops a calcareous coccoid vegetative stage. Calciodinellum operosum produces calcareous cysts that were also found in this study, and Achradina pulchra has an internal skeleton of organic material. Three species, A. spinosum, B. capitatum and C. operosum, were represented by very few specimens, whereas all others were more frequent. Brief descriptions and illustrations of these species by light and scanning electron microscopy are provided. The methods and techniques to study this group have been diverse and useful in finding a greater diversity. The world distribution of the species recorded here is revised.
Article
Examination of the ultrastucture of the unarmored dinoflagellate Gymnodinium aureolum (Hulburt) G. Hansen (syn: Gyrodinium aureolum Hulburt) revealed the presence of nuclear chambers, which are specialized differentiations of the nuclear envelope, similar to those described in the type species of Gymnodinium, G. fuscum (Ehrenberg) Stein and certain other Gymnodinium species. The nuclear pores were restricted to these chambers. In the flagellar apparatus a nuclear fibrous connective linked the longitudinal microtubular root and the nucleus. This structure had so far been observed only in Gymnodinium spp. and in the heterotrophic species Actiniscus pentasterias (Ehrenberg) Ehrenberg, Nematodinium armatum (Dogiel) Kofoid et Swezy and Polykrikos kofoidii Chatton. Another unusual feature of G. aureolum was the presence of a striated fiber in the longitudinal flagellum, a feature previously only found in Ceratium furca (Ehrenberg) Claparède et Lachmann and C. tripos (O.F. Müller) Nitzsch. Gymnodinium aureolum also possessed a prominent ventral protrusion associated with the peduncle and containing electron opaque material. It is concluded that G. aureolum belongs to the Gymnodinium sensu stricto group. This may be a temporary classification, however, because G. aureolum and its allies differ from the type species G. fuscum by the presence of a transverse striated root, striated collars, trichocysts, and a peduncle.
Article
Ebria tripartita is a phagotrophic flagellate present in marine coastal plankton communities worldwide. This is one of two (possibly four) described extant species in the Ebridea, an enigmatic group of eukaryotes with an unclear phylogenetic position. Ebriids have never been cultured, are usually encountered in low abundance and have a peculiar combination of ultrastructural characters including a large nucleus with permanently condensed chromosomes and an internal skeleton composed of siliceous rods. Consequently, the taxonomic history of the group has been tumultuous and has included a variety of affiliations, such as silicoflagellates, dinoflagellates, 'radiolarians' and 'neomonads'. Today, the Ebridea is treated as a eukaryotic taxon incertae sedis because no morphological or molecular features have been recognized that definitively relate ebriids with any other eukaryotic lineage. We conducted phylogenetic analyses of small subunit rDNA sequences from two multi-specimen isolations of Ebria tripartita. The closest relatives to the sequences from Ebria tripartita are environmental sequences from a submarine caldera floor. This newly recognized Ebria clade was most closely related to sequences from described species of Cryothecomonas and Protaspis. These molecular phylogenetic relationships were consistent with current ultrastructural data from all three genera, leading to a robust placement of ebriids within the Cercozoa.
Article
Full-text available
The nuclear lamina, a protein meshwork lining the nucleoplasmic surface of the inner nuclear membrane, is thought to provide a framework for organizing nuclear envelope structure and an anchoring site at the nuclear periphery for interphase chromatin. In several higher eukaryotic cells, the lamina appears to be a polymer comprised mainly of one to three immunologically related polypeptides of relative molecular mass (Mr) 60,000-75,000 (60-70K) termed lamins. Three lamins (A, B, and C) are typically present in mammalian somatic cells. Previous studies on nuclear envelopes of rat liver and Xenopus oocytes suggested that the lamina has a fibrillar or filamentous substructure. Interestingly, protein sequences recently deduced for human lamins A and C from complementary DNA clones indicate that both of these polypeptides contain a region of approximately 350 amino acids very similar in sequence to the coiled-coil alpha-helical rod domain that characterizes all intermediate-type filament (IF) proteins. Here we analyse the supramolecular organization of the native nuclear lamina and the structure and assembly properties of purified lamins, and show that the lamins constitute a previously unrecognized class of IF polypeptides.
Article
The general ultrastructure of A. poecilochroum is typical of dinoflagellates. The proximal part of the longitudinal flagellum possesses a previously undescribed structure consisting of three dense rods running alongside, and attached to, the axoneme. Hexagonal vesicles containing crystalline rods are found regularly in the cell.
Article
SYNOPSIS The fine structure of Amoeba discoides, Amoeba dubia, and Amoeba amazonas was studied and compared with that of Amoeba proteus. The different kinds of amebas showed general similarities but differed in the ultrastructural details of their organelles. With respect to fine structure, A. discoides was indistinguishable from A. proteus, while both A. dubia and A. amazonas had distinctive features. The nuclei of all had a prominent honeycomb-like fibrous lamina, but A. dubia differed from the others in the distribution of nucleoli within the nucleus. The mitochondria of A. amazonas were unusual in having a variable pattern of cristae, some being plate-like and others tubular. Golgi bodies in A. amazonas had a greater proportion of vesicles and a smaller number of cisternae than those of the others, while Golgi bodies in A. dubia had highly flattened cisternae without a lining of filamentous material such as is found in the other types. The plasma membrane of A. dubia also lacked the prominent filamentous cell coat common to A. proteus and other amebas. The relation between the Golgi apparatus and the cell coat and the significance of the degree of development of the cell coat for pinocytosis and other phenomena is considered. The experimental use of these cells, including the formation of hybrids by nuclear transplantation is discussed.
Article
The flagellar apparatus of the marine dinoflagellate Amphidinium rhynchocephalum Anissimowa was examined using the techniques of rapid freezing/freeze substitution and serial thin section three dimensional reconstruction. The flagellar apparatus is composed of two basal bodies that are offset from one another and lie at an angle of approximately 150° The transverse basal body is associated with two individual microtubules that extend from the proximal end of the basal body toward the flagellar opening. One of these microtubules is closely appressed to a striated fibrous root that also extends from the proximal base of the transverse basal body. The longitudinal basal body is associated with a nine member microtubular root that extends from the proximal end of the basal body toward the posterior of the cell. The longitudinal microtubular root and the transverse striated fiber are connected by a striated connective fiber. In addition to the microtubules associated with the transverse and longitudinal basal bodies, a group of microtubules originates adjacent to one of the transverse flagellar roots and extends into the cytoplasm. Vesicular channels extend from the flagellar openings to the region of the basal bodies where they expand to encompass the various connective structures of the flagellar apparatus. The possible function and evolutionary importance of these structures is discussed.
Article
The multilayered structure (MLS), best-known from the flagellar apparatus of charophycean green algae and land plant motile cells, is reported for the first time in members of the Dinophyceae. The MLSs in two dinoflagellates, Katodinium campylops (Harris) Fott and Woloszynskia pascheri (Suchlandt) von Stosch, are similar to other MLSs in possessing the microtubular spline and lamellar strip. Also, as in the majority of MLS-containing organisms, 1) the MLS of each dinoflagellate is closely associated with basal bodies; 2) the spline microtubules possess “keel-like” extensions and 3) extend beyond the MLS, forming a microtubular rootlet that runs beneath the cell surface in a posterior direction; and 4) a mitochondrion is associated with the MLS (K. campylops only) The size, location, and general construction of the MLSs of K. campylops and W. pascheri suggest that they may be homologous to previously described MLSs.
Article
The ultrastructure of the cell covering (amphiesma) of vegetative cells ofNoctiluca miliaris (Dinophyceae) was studied in detail using thin sections. The amphiesma is typically amphidinoid and contains the following components (starting from the outside): (a) a continuous outer membrane (plasmamembrane) surrounding the cell; (b) a layer of contiguous vesicles (amphiesmal vesicles) that contain a thin “honeycomb-patterned” layer of material appressed mainly to the outer portion of the vesicle membrane; (c) a finely granular pellicular layer that lies beneath the amphiesmal vesicles and (d) groups of cortical microtubules (only present in certain regions of the cell). The pellicular layer is always present but its thickness is highly variable (20–800 nm) depending on regional specializations of the amphiesma. Trichocysts and mucocysts project through the pellicular layer and amphiesmal vesicles, the apical portion of their limiting membrane docks at the plasmamembrane. Small vesicles that presumably contain material for the “honeycomb-patterned” layer traverse the pellicular layer through discontinuities and presumably fuse with the amphiesmal vesicles. We conclude thatNoctiluca has a typical dinophycean (i.e. amphidinoid) cell covering, and that the most recent proposal for the developmental origin of the dinoflagellate pellicle should be revised.
Article
Summary The surface coat of the dinoflagellateAmphidinium carterae Hulburt was examined by fluorescence and transmission electron microscopy, using various fluorochromes and cationic dyes. The overall results showed cell-surface reactions typical of acid mucopolysaccharides. The cationic dye staining revealed an outer fine fibrillar layer (15–70 nm thick) overlying a dense anionic coat (40–60 nm thick) which appeared to thicken progressively with age. In general, the structure of the amphiesmal vesicles was similar to that previously described by other investigators. However, an acidic mucopolysaccharide layer was observed on the inner surface of these vesicles. Each of these structures is traversed by 1–3 pores and at least 2 types of extrusomes are formed, the spindle trichocysts and the mucocysts. Cell to cell adhesion through the surface coat was frequently observed. Evidence was also obtained for internalization of all the surface-coat markers used.
Article
The nuclear lamina is a polymeric protein meshwork that lines the nucleoplasmic surface of the nuclear envelope. Recent work demonstrates that the lamina is composed of intermediate-type filaments, one of the major classes of structural filaments in cells. The lamina may be an important determinant of higher order chromatin architecture during interphase, and is implicated in regulation of nuclear envelope structure during the cell cycle.
Article
In 1908 Lohmann described a small dinoflagellate which appeared to lack a sulcus and was therefore placed in a new genus – Protodinium. The type species, P. simplex (Text-fig, IA) was broadly ellipsoidal with broad rounded apices, circular in cross-section and about 1–5 times as long as broad. The girdle was poorly defined, but was more or less median in position. The nucleus was relatively large and centrally located and yellow leaf-life chloroplasts, four to many in number, were arranged in the periphery of the cell.
Article
The dinoflagellate Amphidinium cryophilum sp. nov. is one of the few gymnodinians to be studied at the ultrastructural level. It resembles other dinoflagellates in the structure of the nucleus, trichocysts, storage materials, flagella, mitochondria, and microbodies. Other features of A. cryophilum less commonly observed in related organisms include a network of small interconnected vesicles, a system of large, peripheral vacuoles, chloroplasts bound by two rather than three membranes, an accumulation body, thylakoid-associated plastoglobuli, a vesiculated nuclear envelope, a complex tubular pusule, striated flagellar collars, collared pits, and a peduncle. The occurrence of a peduncle, a structure implicated in phagotrophy, in this autotrophic organism is noteworthy. The ultrastructure of the peduncle of A. cryophilum differs significantly from that reported in another dinoflagellate.
Article
SYNOPSIS. The family Actiniscaceae Kützing, 1845, (generally placed in the dinoflagellates) includes species derived from Actiniscus pentasterias Schütt, some of which became lacustrine relicts. A. pentasterias v. arcticus. living in Arctic and Altantic waters, differs from the Mediterranean species in having a greater number of siliceous skeletons (pentasters). Advanced atrophy of pentasters in lacustrine A. canadensis, and absence of such structures in Pseudoactiniscus apentasterias, probably results from decreased salinity and an undetermined ecologic factor. Morphogenesis and physiologic transformation of past euryhaline Actiniscaceae into contemporary limnobionts began, presumably, during the prelimnic phase of Great Bear Lake and Keyhole Lake. Arctic Actiniscus which exist under subzero temperatures and endure 10-month-long winters, appear to satisfy their energy requirements by heterotrophy and frequent phagocytosis. Survival of lacustrine Actiniscus species in both Arctic lakes seems possible because of lack of competition from co-existing phytoplankton organisms which can endure extreme dystrophic conditions.
Article
The ultrastructure of the amphiesma during pellicle formation was investigated in two species of Dinophyceae, Amphidinium rhynchocephalum Anissimowa and Heterocapsa niei (Loeblich) Morrill & Loeblich using thin sections. In both species the amphiesma consists of an outermost membrane (i.e. the plasma membrane) underlain by amphiesmal vesicles. In A. rhynchocephalum the latter appear empty whereas each amphiesmal vesicle in H. niei contains a thecal plate and a thin, amorphous layer (dark-staining layer) located between, the thecal plate and the inner amphiesmal vesicle membrane. When cells of both taxa are carefully fixed, amphiesmal vesicles are always separate entities (i.e. the sutures are undisrupted). During ecdysis the following amphiesmal components are shed: the plasma membrane, the outer amphiesmal vesicle membrane, and in H. niei the thecal plates. The inner membranes of the amphiesmal vesicles then fuse with each other and form a continuous membrane (termed pellicle membrane) that remains tightly oppressed to an underlying amorphous layer (pellicular layer). In A. rhynchocephalum the pellicular layer is already present in vegetative non-ecdysed cells, whereas in H. niei it forms during ecdysis beneath the pellicle membrane. During ecdysis in H. niei, material from the dark-staining layer precipitates on the outer surface of the pellicle membrane, where it forms a characteristic honeycomb pattern. The new observations are incorporated into a revised model of pellicle formation in dinoflagellates and contrasted with earlier proposals.
Article
Gymnodinium acidotum Nygaard is a freshwater dinoflagellate that is known to harbor a cryptomonad endosymbiont whose chloroplasls give the organism an overall blue-green color. The ultrastructure of G. acidotum was examined with particular attention being given to the three dimensional nature of the flagellar apparatus. The fiagellar apparatus is composed of two functional basal bodies that are slightly offset and lie at an angle of approximately 90° to one another. As in other dinoflagellates the transverse basal body is associated with a striated, fibrous root that extends from the proximal end of the basal body to the transverse flagellar opening. At least one microtubular root extends from the proximal end of the transverse basal body, and a multi-membered longitudinal microtubular root is associated with the longitudinal basal body. The most striking feature of the flagellar apparatus of G. acidotum is the large fibrous connective that extends from the region of the proximal ends of the basal bodies to the cingulum on the dorsal side of the cell. A similar structure has been reported from only one other dinoflagellate, Amphidinium cryophilum Wedemayer, Wilcox, and Graham. The presence of this structure as well as similarities in external morphology suggest thai these two species may be more closely related to each other than either is to other gymnodinioid taxa. The taxonomic importance of dinoflagellate flagellar apparatus components is discussed.
Article
The ultrastructure of the freshwater, heterotrophic dinoflagellate Peridiniopsis berolinense (Lemm.) Bourrelly resembles other dinoflagellates in the structure of its nucleus, theca, flagella, and mitochondria. Other features less frequently reported in related organisms include fine sub-sulcal fibers, collared pits in the flagellar base region, and unusual structures herein termed fibrillar lamellae. Numerous vesicles are present, some of whose contents are distinctly crystalline, while others contain what appears to be membranous material arranged in either whorls or parallel stacks; still other vesicles contain electron-dense, granular spheres. Of particular interest is the transitional helix present in the longitudinal flagellum, this being the first report of such a structure among the dinoflagellates. Plastids of any kind are lacking, and a peduncle is present and is used during phagotrophy.
Article
The three-dimensional structure of the flagellar apparatus in the dinoflagellate Oxyrrhis marina has been reinvestigated and found to consist of several previously unknown components and component combinations that appear strikingly similar to those of some gymnodinoid taxa.The flagellar apparatus of this dinoflagellate is asymmetric and extremely complex consisting of a longitudinal and a transverse basal body that gives rise to eight structurally different components. The only posteriorly directed component is the large microtubular root that consists of 45–50 microtubules at its origin and is attached proximally to a perpendicularly oriented striated fibrous component. Arising from each basal body, two striated fibrous roots with different periodicities extend to the cell's left. A single stranded microtubular root with associated electron dense material emanates from the transverse basal body and also extends to the cell's left. A striated fibrous connective arises from the longitudinal basal body and extends toward the cell's right ventral surface and terminates near the sub-thecal microtubular system. A compound root consisting of microtubules and electron dense material also originates from the longitudinal basal body and extends ventrally into the anterior region of the tentacle.Structural similarities between the parallel striated fibrous roots of Oxyrrhis and Polykrikos are discussed as are flagellar apparatus similarities among other gymnodinoid dinoflagellates. A diagrammatic reconstruction of the Oxyrrhis flagellar apparatus is also presented.
Article
Ultrastructural examination of the freshwater, blue-green dinoflagellate Gymnodinium acidotum Nygaard revealed the presence of an endosymbiotic cryptomonad. Features of the endosymbiont allying it with the Cryptophyceae include mitochondria with flattened cristae, paired thylakoids with electron-dense contents, and nucleomorphs, bodies unique to the Cryptophyceae. This report is the first conclusive documentation of a symbiosis involving these two groups.
Article
The fine structure of the fibrous lamina on the inner aspect of the nuclear envelope in cells of various invertebrates is reviewed, and attention is drawn to the common occurrence of a similar but thinner layer in nuclei of cells in vertebrates. Certain superficial similarities are pointed out in the relations of fibrous lamina to the nuclear pores and of the basement lamina to the endothelial capillary pores. It is suggested that in future considerations of the physiological exchange of materials between nucleoplasm and cytoplasm the properties of the fibrous lamina must be taken into account.
Article
Modern microscopical approaches have allowed more accurate investigations of the three-dimensional nature of the dinoflagellate flagellar apparatus (FA) and several other cytoskeletal protein complexes. Our presentation overviews the nature of the dinoflagellate FA and cytoskeleton in a number of taxa and compares them with those of other protists. As with other protists, the FA of the dinoflagellates can be characterized by the presence of fibrous and microtubular components. Our studies and others indicate that the dinoflagellate FA can be expected to possess a striated fibrous root on the basal body of the transverse flagellum and a multimembered microtubular root on the basal body of the longitudinal flagellum. Two other features that appear widespread in the group are the transverse striated root associated microtubule (tsrm) and the transverse microtubular root (tmr). The tsrm extends at least half the length of the transverse striated root while the tmr extends from the transverse basal body toward the exit aperture of the transverse flagellum. In most cases, the tmr gives rise to several cytoplasmic microtubules at a right angle. The apparent conserved nature of these roots leads us to the conclusion that the dinoflagellate FA can be compared to the FA of the cryptomonads, chrysophytes, and the ciliates for phylogenetic purposes. Of these groups, the chrysophytes possess an FA with the most structures in common with the dinoflagellates. Our immunomicroscopical investigations of the microtubular, actin and centrin components of the dinoflagellate cytoskeleton point to the comparative usefulness of these cytological features.
Article
In flagellate green algae two types of fibrous flagellar roots can be distinguished: system I fibres, cross-striated bundles of 2nm filaments (striation periodicity about 30 nm), which are associated with flagellar root microtubules, and system II fibres, contractile bundles of 4–8 nm filaments which are often cross-striated (striation periodicity variable but greater than 80 nm). The major protein of system II fibres is centrin, a Ca2+-modulated phosphoprotein, which is a member of the EF-hand protein family. The major protein of system I fibres (of severalChlamydomonas-type green algae) is a 34 kDa phosphoprotein, named assemblin. Because of the solubility characteristics of system I fibres and the properties of their major protein (paracrystal-formation in vitro, several isoelectric variants, heptad motifs in parts of the amino acid sequence), assemblin is presumably related to the k-m-e-f class of -helical fibrous proteins.
Article
The unicellular organism, Noctiluca, has been examined with the electron microscope. The nucleus is small compared to the very large size of the cell, but the nuclear border has an organization which indicates an active nucleocytoplasmic exchange. Whereas annuli are missing over most parts of the nuclear membrane proper, there are "annulated vesicles" in a layer inside the nuclear membrane. The hypothesis is put forth that nuclear substances move through the annuli into these vesicles, and that the annulated vesicles themselves are transported through the nuclear membrane. The various forms of the annulated vesicles are consistent with this hypothesis. An implication of this postulate is the synthesis of annulated membranes inside a closed nucleus which are physically separate from the endoplasmic reticulum. The chromosomes are in a state resembling prophase chromosomes and are surrounded by granular masses. Only a small portion of the entire nuclear volume is occupied by the chromosomes. There are many nucleolus-like bodies.
Article
This chapter discusses the extrusive organelles in protists. Extrusive organelles are membrane-bounded structures of protists, usually located in the cortical cytoplasm of these cells. Although they have different type-specific structures and functions, they all exhibit one general characteristic: they are readily discharged when subjected to a wide range of stimuli. This chapter describes the structural and functional diversity of extrusomes in protozoa. Some have a wide distribution in flagellates as well as in ciliates; others are restricted to small systematic groups, for example, the discobolocysts of the flagellate order Chrysophyceae or the cnidocysts of a few species of dinoflagellates. Some enigmatic similarity exists between extrusomes and organelles of systematically widely differing organisms such as ejectisomes of algae and the R bodies of the bacterial symbionts of Paramecium or the toxicysts of ciliates and the nematocysts of cnidarians.
Article
This study extends previous work on the nuclear envelope and associated structures. It illustrates that the cylindrical structures of the honeycomb lattice are not attached to the nuclear envelope, although generally perpendicular and closely apposed to it, and that there is a complex arrangement of fibrillar material between the cylinders of the lattice. The relationship of nuclear helices to these structures is described and the possible mode of their transfer from nucleus to cytoplasm is discussed.
Article
We have used enzymic digestion as a structural probe to investigate components of the nuclear envelope of germinal vesicles from Xenopus oocytes. Previous studies have shown that these envelopes are composed of a double membrane in which nuclear pore complexes are embedded. The nuclear pore complexes are linked to a fibrous lamina that underlies the nucleoplasmic face of the envelope. The pores are also linked by pore-connecting fibrils that attach near their cytoplasmic face. Xenopus oocyte nuclear envelopes were remarkably resistant to extraction with salt solutions and, even after treatment with 1 M NaCl or 3 M MgCl2, pores, lamina and pore-connecting fibrils remained intact. However, mild proteolysis with trypsin selectively removed the lamina fibres from Triton-extracted nuclear envelopes to leave only the pore complexes and connecting fibrils. This observation confirmed that the pore-connecting fibrils were different from the lamina fibres and were probably constructed from different proteins. Trypsin digestion followed by Triton treatment resulted in the complete disintegration of the nuclear envelope, providing direct evidence for a structural role for the lamina in maintaining envelope integrity. Digestion with ribonuclease did not produce any marked change in the structure of Triton-extracted nuclear envelopes, indicating that probably neither the pore-connecting fibrils nor the cytoplasmic granules on the pore complexes contained a substantial proportion of RNA that was vital for their structural integrity.
Article
Development of the nematocyst-taeniocyst complex in the four-zooid stage of a dinoflagellate, Polykrikos kofoidi, was studied by electron microscopy. We observed the following stages: formation of large spherical bodies in islets of cytoplasm containing extensive rough endoplasmic reticulum and Golgi complexes; differentiation of an anlage of first the nematocyst and then the taeniocyst into a tandem pair; and, maturation of the complex into a nematocyst with operculum and capsule, and a taeniocyst with head, neck and body. In the intermediate stages of dinoflagellate cnidogenesis the structurally elaborate pattern of development differed from that of coelenterate nematocysts but in certain features the mature organelles of both groups were similar. Nematocyst-taeniocyst complexes migrated into chutes on zooids and four near the junction of the annulus and sulcus at the flagellar bases. The specialized chute was partially lined by thimble-shaped organelles of unknown function. The taeniocyst protruded from the surface in association with a striated fibre whose structure and position were those of a trigger to discharge the two organelles. We found no cytostome in this holozoic colony; the structure of the chute suggested that it might also function as a cytostome.
Article
This chapter discusses the ultrastructure of dinoflagellate amphiesma. Amphiesma is a complete cell covering of a dinoflagellate. The chapter examines a number of amphiesmal structures and discusses the ontogeny of various components of amphiesma. The components of amphiesmal structure are thecal plates, pellicles, discontinuous layers, microtubules, and body scales. Because of the constraints imposed by the preparation of cells for electron microscopy (cells must be killed and fixed prior to examination), the ultrastructural studies of developmental processes must rely on circumstantial evidence. Comparative studies of the ultrastructure of the cell coverings of cryptomonads, dinoflagellates, and euglenids reemphasize the uniqueness of these three algal divisions. Although there are huge differences in construction among these three divisions, the intracellular nature of and the articulation of numerous subunits in the cell covering may imply a common ancestry in the distant past.
Article
Electron microscopy of the colonial dinoflagellate Polykrikos kofoidi revealed a nuclear cortex formed of two electron-dense cortical layers directly beneath the nuclear envelope. Nuclear pores were confined to vesicular outpocketings of the nuclear envelope over circular discontinuities in the cortical layers. A conspicuous fibrous ribbon extended from the nucleus to the flagellar apparatus of each zooid. The ribbons resembled in their structure and position the attractophores of termite flagellates. Each flagellar apparatus consisted of two flagella, two elongate axial kinetosomes, an oblique kinetosome, and two roots of markedly different periodicities.
T h e ultrastructure of the freshwater, colorless dinoflagellate Prricli,ziopsis brroli-) I P )
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  • L W Wilcox
Wedemayer, G. J. & Wilcox L. W. 1984. T h e ultrastructure of the freshwater, colorless dinoflagellate Prricli,ziopsis brroli-) I P ) I S C (Lemm.) Bourrelly (Mastigophora, Dinoflagellida). J. Protozool. 3 1 :444-53.
The Pnleobiologj ofPlntit Profists
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Algnr ns Exprrifnrnlal Sjstrms
  • A V Coleman
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  • Stein-Taylor
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T h e flagellar apparatus of Oxjrrhis inariiio Pyrrophyta) T h e flagellar apparatus of Gj/tttw/zniuw sp. (Di-nophyceae) Comparative analysis of the dinoflagellate flagellate apparatus. 11. Crrntium hirundi~irlln
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Roberts, K. R. 1985. T h e flagellar apparatus of Oxjrrhis inariiio Pyrrophyta). J. Phjcol. 21:641-55. -1986. T h e flagellar apparatus of Gj/tttw/zniuw sp. (Di-nophyceae). J. Phjcol. 22:456-66. 1989. Comparative analysis of the dinoflagellate flagellate apparatus. 11. Crrntium hirundi~irlln. J. Phjcol. 25:270-80.
L'envelope nuclkaire chez Nociiluca miliarzs Suriray (Dinoflagellata). I.-Quelques donnCes sur son ul-trastructure et son
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perinuclear structural elements formed in the dinoflagellate Gonyaulax pacifica Kofoid
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Ainphi-dilziuui rrjophiluvr sp. nov. (Dinophyceae) a new freshwater dinoflagellate
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Algal centrin: calcium-sensitive contractile Cjtd
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Dinoflagellatae (Peridineae) in Monogra-phischer Behandlung Rnbriihorst's Krjp/ogninr,i-Florn i'oii Drutschlniid, Osierrrick uiid drr Schuviz
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T h e fine structure of ,\Pitinlo-ditiiujn nrttinfum, a naked dinoflagel1ate
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Sulla formazione scheletrica intracellulare diun dinoflagellato
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