Base Of Flagellum Research Articles

Transient flagellar waveforms in reactivated sea urchin sperm.

Flagellar waveforms have been studied during spontaneous stopping and starting transients of sperm of the sea urchin Tripneustes gratilla reactivated at pH 7.7 with 1 mM MgATP2- in the presence of 15 microM free Ca2+. A stopping transient begins abruptly when a reverse bend fails to be initiated at the proper time, and leaves the last-formed principal bend remaining stationary near the flagellar base while the more distal principal and reverse bends all propagate normally to the tip. After a brief quiescent interval lasting 0.5-4 beat periods, the starting transient begins with initiation of a new reverse bend that then propagates nearly normally to the tip. The total duration of stopping and starting transients is about 1.5 beat periods each, much shorter than the duration of the corresponding transients in the flagella of live sperm studied previously. The brief duration of reactivated transients is interpreted to indicate that the response time of the mechanochemical mechanisms regulating the tubule sliding associated with bend propagation is significantly faster than that of the mechanism responsible for Ca2+-induced asymmetry and quiescence.

Ultrastructural investigations on the spermatozoon and its genesis in Aeolosoma litorale with considerations on the phylogenetic implications for the aeolosomatidae (annelida)

The spermatozoa of Aeolosoma litorale are threadlike cells with a slight swelling in the midregion. The acrosome consists of a simple elongate vesicle without any accessory structures. The nucleus is a long, slightly conical cylinder. A column-shaped body derived from the proximal centriole underlies the nucleus and is united with the distal centriole forming a conventional basal body. The centriolar complex is surrounded by a mitochondriril derivative arising from two ring-shaped mitochondria that fuse to constitute a short tube. Lysosome-like vesicles are assembled on one side of the middle piece. The axoneme displays the common 9+2 pattern of microtubules. During spermiogenesis the acrosome protrudes in the distal region of the late spermatid while the flagellar base is shifted toward the cytophoral side. The absence of synapomorphies with the spermatozoa of the clitellate species corroborates the view that the Aeolosomatidae are not closely related to these taxa.

Ultrastructure and reconstruction of the flagellar apparatus in Chrysochromulina apheles sp. nov. (Prymnesiophyceae = Haptophyceae)

A new marine species of Chrysochromulina, C. apheles, is described from light and electron microscopy of a culture established from Danish coastal waters. The cells are among the smallest known in any species of Chrysochromulina, measuring ca. 4 μm in diameter. The general fine structure is illustrated and the structure of the haptonema and the flagellar apparatus is described in detail, based on serial sections. The flagellar root system, not previously examined in detail in any member of Chrysochromulina, is shown to consist of four microtubular roots, while cross-banded roots are lacking. Four cross-banded fibres were seen to interconnect the flagellar bases and the haptonema base. The haptonema belongs to the rather unusual six-stranded type. Two very similar looking types of small organic scales are present on the cell body. Unpublished data on the flagellar roots of the type species of Chrysochromulina, C. parva, are included. Chrysochromulina apheles is apparently cosmopolitan. It has presently been found in material from Denmark, Finland, England, Thailand, Australia, and New Zealand.

Ultrastructure in bryophyte systematics and evolution: an evaluation

AbstractWithin the bryophytes scanning electron microscopy has revealed an abundance of surface features useful in elucidating affinities at generic and specific levels. Appraisal of the broader systematic significance of such data requires transmission electron microscope (TEM) studies of the underlying developmental processes. TEM has made an incisive contribution to the understanding of interrelationships between bryophytes, charalian green algae and tracheophytes. New ultrastructural information should be incorporated into modern schemes of bryophytic classification. The presence of proximal triplet extensions to the two flagellar bases in the spermatids of bryophytes is the only attribute at the ultrastructural level which draws mosses, hepatics and Anthocerotae together. Although cellular organization is basically similar to that in tracheophytes, an increasing list of cytological features and developmental processes peculiar to each of these groups is strongly indicative of wide phyletic difference...

Food uptake and the fine structure of the dinophytePaulsenella sp. an ectoparasite of marine diatoms

Motile dinospores ofPaulsenella attach to a host diatom frustule, form a feeding tube, drive it between epi- and hypocingulum, pierce the host plasmalemma and suck up host cytoplasm gradually. This mode of endocytosis (“myzocytosis”) implies that the host plasmalemma is not ingested and that the host cytoplasm within the food vacuole is bounded only by the vacuolar membrane. The feeding tube is formed by the emergence of a preformed “microtubular basket” consisting of plates of microtubules. At its entrance into the cell body the feeding tube channel is surrounded by an electron-dense ring. Similar “sphincters” enclose the two exits through which the two flagella emerge. These sphincters are composed of microfibrils which reveal a cross striation when the fixative does not contain calcium ions. The flagellar bases as well as the internal part of the feeding tube are surrounded by a common cavity which is in open connection also with the ampullae of the pusule. The light and electron microscopical observations do not support the assumption that food uptake is driven by a flow of the membrane of the feeding tube channel caused by an interaction with the microtubular basket (as postulated for food uptake inSuctoria) but rather by an hydrostatic gradient which might be caused by rhythmical ion pumping and be based on the existence of the common cavity and the sphincters. Myzocytosis is inhibited by cytochalasin B.—The fine structure of dinospores and trophonts, especially with respect to the cell covering, the amphiesma, and the en- and excystment, is described.

Electron microscopic observations of structures associated with the flagella of Spirillum volutans.

Electron microscopy of thin-sectioned Spirillum volutans (ATCC 19554) showed that at the insertion site of the flagellum there was a cylindrical structure with a diameter of ca. 36 nm which extended ca. 19 nm into the cytoplasm. This structure, termed a cytoplasmic flagellar base, enclosed a central rod which was continuous with the hook. There was a continuation of the flagellar base into the peptidoglycan layer, enclosing ringlike structures and the central rod. The flagellar hook and proximal part of the flagellar filament contained a central channel which was large enough to accommodate the flagellin subunit. The flagella of fixed cells may project perpendicularly from the outer membrane in a position corresponding to a trailing, swimming orientation or may bend almost parallel to the membrane in a leading orientation. Maximum bending occurred in the hook region, which may be the structure responsible for executing changes in swimming direction.

Mitosis and cytokinesis in Chroomonas africana Meyer & Pienaar (Cryptophyceae)

Mitosis and cytokinesis have been examined in a recently described species of Chroomonas , viz. Chroomonas africana Meyer & Pienaar. A comparison between this species and the three other species in which cell division has been studied ( Chroomonas salina and two Cryptomonas spp.) has revealed certain common characteristics such as an open spindle, a chromosomal plate at metaphase and similar types of spindle microtubules with indistinct kinetochores. However, the cell division process in C. africana differs from that in the above mentioned species in that (i) the spindle microtubules maintain their association with the flagellar bases throughout mitosis, (ii) the movement of the chromatin masses at anaphase is synchronous but unequal, i.e. parts of the chromatin masses move at different rates, (iii) in late anaphase and early telophase the chromatin masses arch around the flagellar bases forming cup-shaped structures and (iv) cytokinesis is accomplished by an extension of the anterior vestibular region forming a cleavage furrow which extends posteriorly. The formation of the branched vestibular region is also described.

SEXUAL PROCESSES IN THE LIFE CYCLE OFGYRODINIUM UNCATENUM(DINOPHYCEAE): A MORPHOGENETIC OVERVIEW1

ABSTRACTSexual processes in the life cycle of the dinoflagellateGyrodinium uncatenumHulburt were investigated in isolated field populations. Morphological and morphogenetic aspects of gamete production, planozygote formation, encystment, excystment, and planomeiocyte division are described from observations of living specimens, Protargol silver impregnated material and scanning electron microscope preparations. The sexual cycle was initiated by gamete formation which involved two asexual divisions of the vegetative organism. Gametes were fully differentiated following the second division and immediately capable of forming pairs. Either isogamous or anisogamous pairs were formed by the mid‐ventral union of gametes. Gametes invariably joined with flagellar bases in close juxtaposition. Complete fusion of gametes required ca. 1 h, involved plasmogamy followed by karyogamy and resulted in a quadriflagellated planozygote. Planozygotes encysted in 24–48 h to yield a hypnozygote capable of overwintering in estuarine sediments. Hypnozygotes collected from sediment in late winter readily excysted upon exposure to temperatures above 15°C. A single quadriflagellated planomeiocyte emerged from the cyst and under culture conditions divided one to two days later. The four flagella were not evenly distributed at the first division and both bi‐ and tri‐flagellated daughter cells were formed.

The Ultrastructure of the Freshwater, Colorless Dinoflagellate Peridiniopsis berolinense (Lemm.) Bourrelly (Mastigophora, Dinoflagellida)1,2

ABSTRACTThe 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.

CYTOLOGY AND ULTRASTRUCTURE OF CHLORARACHNION REPTANS (CHLORARACHNIOPHYTA DIVISIO NOVA, CHLORARACHNIOPHYCEAE CLASSIS NOVA)1

ABSTRACTThe green amoeboid cells of Chlorarachnion reptans Geitler are completely naked and each contains a central nucleus, several bilobed chloroplasts each with a central projecting pyrenoid enveloped by a capping vesicle, several Golgi bodies, mitochondria with tubular cristae, extensive rough ER, and a distinct layer of peripheral vesicles. Complex extrusome‐like organelles occur rarely in both the amoeboid and flagellate stages. The only organelles entering the reticulopodia are mitochondria, but microtubules are also present. The chloroplasts contain chlorophylls a and b, but histochemical tests suggest that the carbohydrate storage product probably is not a starch. The chloroplast lamellae are composed of one to three thylakoids or form deep stacks. A girdle lamella and interlamellar partitions are absent. Each chloroplast is bounded by either four separate membranes, a pair of membranes with vesicular profiles between them, or three membranes; all three arrangements may occur in the same chloroplast. A periplastidal compartment occurs near the base of the pyrenoid where there are always four surrounding membranes. The compartment has a relatively dense matrix and contains ribosome‐like particles and small dense spheres; it extends over and into a deep invagination in the pyrenoid where its contents are enclosed in a double‐membraned envelope which is penetrated by wide pores. The zoospores are ovoid and each bears a single laterally inserted flagellum which appears to be wrapped helically around the cell body during swimming. The flagellum lies in a groove in the cell surface and bears fine lateral hairs. Neither a second flagellum or vestige of one, nor an eyespot, is present. A single microtubular root and a larger homogeneous root run from the flagellar base parallel to the emerging flagellum, between the nuclear envelope and the plasmalemma. In the simple flagellar transition region, fine filaments connect adjacent axonemal doublets. A detailed comparison of C. reptans with all other algal taxa results in the conclusion that it must be segregated in the new class Chlorarachniophyceae, the only class in the new division Chlorarachniophyta. The possibility that C. reptans evolved from a symbiosis between a colorless amoeboid cell and a chlorophyll b‐ containing eukaryote is considered, but the possible affinities of the symbiont remain enigmatic. The implications of the unique chloroplast structure of C. reptans for current hypotheses concerning the origin of chloroplasts are discussed.

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). IV. ABSOLUTE CONFIGURATION ANALYSIS OF THE CRUCIATE FLAGELLAR APPARATUS AND MULTILAYERED STRUCTURES IN THE PRE‐ AND POST‐RELEASE GAMETES

Transmission electron microscopy of pre‐release and post‐release biflagellate gametes ofCephaleuros virescenshas produced comparative data on these cells and on the detailed absolute arrangement of the flagellar apparatus. In all major respects including the presence of two multilayered structures (MLS's) the closely compacted, non‐motile but mature pre‐release gametes are similar to the mature, free swimming post‐release gametes. The elongated shape of the free‐swimming gametes differs from the more compact form of the pre‐release gametes, but does not reflect a major difference in the arrangement of internal components. The flagella are bilaterally keeled and each keel contains a cylindrical element. Each flagellar base is encircled by a densely staining collar of modified plasmalemma at the point of entry into the apical papilla. The equal anterior flagella enter the papilla from opposite sides; their basal bodies are parallel and overlapping. Each terminates in a densely staining terminal cap. No capping plate is present. Each basal body is associated both with a three‐layered MLS, the anterior layer of which becomes a lateral microtubular spline of 2 to 8 microtubules, and with an additional medial compound root of two layers of microtubules (2 over 4 or 5). Both the compound microtubule root and the spline may acquire additional microtubules as they extend distally in close proximity to mitochondria and the plasmalemma. No striated roots, or rhizoplasts, have been observed. Two densely staining plaques are associated with the plasma membrane at specific anterior sites and may be comparable to the presumptive mating structures seen in other green algal motile cells. The reversed bilateral symmetry of the cells produces two possible arrangements of the flagellar apparatus, namely, a 11/5 (or left‐handed) arrangement or a 1/7 (or right‐handed) arrangement. Only 11/5 cells have been found. Despite the presence of distinct multilayered structures, some aspects of the gametes ofCephaleurosquite closely resemble the cruciate motile cells of algae now regarded by some authors as typical of Ulvophyceae, sensu Stewart and Mattox.

Ultrastructure of the dinoflagellate Polykrikos. I. Development of the nematocyst-taeniocyst complex and morphology of the site for extrusion.

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.

Sexual reproduction inEudorina elegans (chlorophyta, volvocales)

Sexual reproduction inEudorina elegans Ehr. was studied in detail in laboratory cultures, with particular regard to conjugation between gametes and gone colony formation. Male and female gametes fused after being induced by changing the medium. The anterior end, including the flagellar base, of the male gamete entered the anterior region of the female gamete. Fusion of the two protoplasts proceeded laterally and posteriorly. The male gamete bore a slender cytoplasmic protrusion at the base of the flagella. This structure has not been previously described in the male gamete ofEudorina, and may participate in plasmogamy. A biflagellate gone cell swam from the germinating zygote and secreted a gelatinous envelope. It then divided to form a gone colony within the gelatious envelope, which moved during colony formation by means of the two flagella which were retained intact from the original gone cell.

Taxol effects cytoskeletal microtubules, flagella and spindle structure of the chrysoflagellate algaPoterioochromonas

Thein vivo-effects of the antitumor-drug taxol on the chrysoflagellate algaPoterioochromonas malhamensis were investigated with light-and electron microscopy. The effects depend on the concentration applied. Low concentrations up to 10−6M stabilize cytoplasmic tails and prolong cytokinesis, but microtubule number and arrangement seem normal. 1.2×10−6M taxol still stabilizes the cytoplasmic tail in some cells and inhibits cytokinesis, inducing large multinucleated cells. Mitosis is slowed down, but spindle structure is not disturbed. These effects are attributed to the microtubule stabilizing effects of taxol. 2.4−4.8×10−6 M taxol then induces numerous additional microtubules with a tendency to lateral association, leads to rounding up of most of the cells and induces irregular microtubules and microtubule bundles in the spindle. The most drastic effects are seen in stationary phase cells ofPoterioochromonas treated with 6×10−6M taxol for 72 hours: all cells get round, with a hoop of marginal microtubules consisting of up to several hundred microtubule profiles in cross section stabilizing this abnormal cell shape. Then the flagella are reduced to stumps with additional microtubules between the axoneme and the flagellai membrane, and additional microtubules are also found in the lumen of the flagellar base and surrounding the bases irregularly. It is concluded that taxol at lower concentrations mainly seems to stabilize microtubules, at higher concentrations it seems to promote assembly of numerous microtubules, with a tendency to lateral association and independence from the cellular MTOCs.

Twist of central pair microtubules in the flagellum of the green flagellate [formula omitted

The central pair microtubules in the two flagella of the green flagellate Scourfieldia caeca are twisted along their length. Twist of central pair microtubules occurs along straight regions of the flagellar shaft and in the elongated (2–3 μm length) flagellar tip region. In cross sections through flagella the orientation of the central pair microtubules with respect to axonemal doublets (one doublet lacks the outer dynein arm) and with respect to the flagellar base is variable.

Twist (and rotation?) of central-pair microtubules in flagella ofPoterioochromonas

The chrysoflagellate algaPoterioochromonas bears two unequal flagella. There is a short naked one and a long flagellum with mastigonemes. Ultrastructural investigation reveals that the centralpair microtubules in both flagella have no fixed position with respect to the flagellar base and root system, or the mastigoneme rows in the long flagellum. The central-pair microtubules are twisted several times along the length of the flagellum. This might indicate active or passive rotation of the central-pair microtubules during flagellar beat.

The golgi-mediated scale production in the marine haptophycean alga Ochrosphaera neapolitana Schussnig

Abstract Some ultrastructural features of cells of the marine haptophycean alga, Ochrosphaera neapolitana Schussnig in the palmelloid stage were examined. Chloroplasts which are contained in a compartment isolated from the cytoplasm by ER profiles and nuclear envelope, display trilamellated thylakoids running along the major axis. The stalked pyrenoid with inner bilamellated thylakoids, protrudes in a large membrane-bounded vacuole. Other structures, as the haptonematic and flagellar bases, autophagic vacuoles and mitochondria, are typical of the chrysophycean and haptophycean genera so far investigated. The Golgi apparatus is represented by a single dictyosome composed of stacked cisternae fonctioning in a way that they form organic scales which constitute the main part of the cell covering. The scales, build up of microfibrils disposed parallel each to other, lie in cisternal lumina of the dictyosomal maturing face; scaly cisternae are numerous in the peripheral cytoplasm and are observed merging in the plasma membrane and discharging the content outside the protoplast. Dictyosomal activity is evidenced morphologically by massive vesicle production. Three kinds of membrane-bounded vesicles were identified in the present material: i) inner-granulated vesicles, arising from the maturation face; ii) coated vesicles, scattered in the cytoplasm or at the periphery of the golgi body, and iii) dense-cored vesicles, present in the proximity of the maturation face. The possible functional relationships related to scale production and assembly outside the protoplast, and between the nucleus and dictyosome are discussed.

The flagellar root system in the gamete ofAcetabularia mediterranea

Ultrastructural investigation of the flagellar root system ofAcetabularia gametes reveals one type of organization for both male and female gametes. There is a modified cruciate system with four microtubular bands X-2-X-2, with X=4. A prominent distal striated fiber and a small proximal striated fiber connect the flagellar bases. A striated root fiber type I underlies the microtubular root type II, and a short striated root fiber type I underlies the microtubular root type I (terminology ofMelkonian 1980 b). This specific root system has some details in common with theChlamydomonas type, and others with theUlvaphyceae and the siphonalean algaeDerbesia andBryopsis. This might indicate the phylogenetic relationships.

Cell division inHymenomonas carterae(Braarud et Fagerland) Braarud (Prymnesiophyceae)

The cell division cycle of Hymenomonas carterae (Braarud et Fagerland) Braarud was investigated at the ultrastructural level. DNA synthesis and cytokinesis occurred during the 8-hour dark period. All organelles, including the flagellar bases were replicated prior to nuclear division. Prophase consisted of a clustering of the chromosomes into distinct groups and the disappearance of the nucleolus. During metaphase there was complete dissociation of the nuclear envelope resulting in the formation of an open spindle containing no major organelles. The metaphase plate formed at right angles to an imaginary line joining the two pairs of flagellar bases. Elongation of the cell and separation of the chromosomes occurred at anaphase. During early telophase the nuclear envelope veformed and was closely associated with the chromosome masses, resulting in the nuclear possessing convoluted profiles. Telophase was characterized by complete break down of spindle fibres, rounding off of the nuclear profiles, reappearanc...

Development of sperm cells of Volvox carteri f. weismannia (Chlorophyceae)

Abstract A high yield of male colonies of Volvox carteri f. weismannia can be attained in culture within 70–90 hr after inoculation of fresh Volvox medium to a concentration of 15–20 colonies/ml. The development and morphology of the sperm bundles in the male colonies were studied by light and electron microscopy. The nuclei of the mature sperm cells are characterized by osmiophilic material along the inner membrane and within the nucleus. Discrete spherical areas of fine fibrillar nuclear material are also observed. A tripartite layer of sheath material surrounds each sperm cell and the whole sperm bundle at maturity. Prominent eyespots are present in the reduced chloroplast; the cells contain rough endoplasmic reticulum, Golgi bodies, two contractile vacuoles, a microbody and a complex mitochondrial system near the flagellar bases. When the sperm cell is freed from the sheath and swims independently, the flagella are directed posteriorly from the apex. It is able to change its shape rapidly and can form...