Ultrastructure of the flagellar apparatus inPleurochrysis (classPrymnesiophyceae)

Summary The ultrastructure of the flagellar apparatus of aPleurochrysis, a coccolithophorid was studied in detail. Three major fibrous connecting bands and several accessory fibrous bands link the basal bodies, haptonema and microtubular flagellar roots. The asymmetrical flagellar root system is composed of three different microtubular roots (referred to here as roots 1,2, and 3) and a fibrous root. Root 1, associated with one of the basal bodies, is of the compound type, constructed of two sets of microtubules,viz. a broad sheet consisting of up to twenty closely aligned microtubules, and a secondary bundle made up of 100–200 microtubules which arises at right angles to the former. A thin electron-dense plate occurs on the surface of the microtubular sheet opposite the secondary bundle. The fibrous root arises from the same basal body and passes along the plasmalemma together with the microtubular sheet of root 1. Root 2 is also of the compound type and arises from one of the major connecting bands (called a distal band) as a four-stranded microtubular root and extends in the opposite direction to the haptonema. From this stranded root a secondary bundle of microtubules arises at approximately right angle. Root 3 is a more simple type, composed of at least six microtubules which are associated with the basal body. The flagellar transition region was found to be unusual for the classPrymnesiophyceae. The phylogenetic significance of the flagellar apparatus in thePrymnesiophyceae is discussed.     

STRUCTURE AND PHYSIOLOGY OF THE HAPTONEMA IN CHRYSOCHROMULINA (PRYMNESIOPHYCEAE). I. FINE STRUCTURE OF THE FLAGELLAR/HAPTONEMATAL ROOT SYSTEM IN C. ACANTHA AND C. SIMPLEX1

The intracellular structural relationships between the flagella and haptonema in Chrysochromulina acantha Leadbeater & Manton (Prymnesiophyceae) were studied in detail and a reconstruction is presented. Three micro-tubular roots are associated with the flagellar apparatus. The largest, consisting of a sheet of approximately 20 microtubules, has its origins at the base of the left basal body. The main body of microtubules passes over the surface of a mitochondrion toward the left chloroplast and apparently terminates at a pair of microtubules oriented perpendicularly to it. Four microtubules diverge from the sheet and pass behind the left basal body. Two other roots–one consisting of a 2 + 2 + 1 arrangement of microtubules, the other of a single microtubule only—are associated with the right basal body. The two basal bodies are connected by distal and proximal fibers, and they are linked also to the base of the haptonema, three fibers extending from the haptonemal base to the right basal body, one only to the left. An additional fiber extending from the right basal body passes between the left basal body and the base of the haptonema, terminating at the largest microtubular root. Lateral extensions link this fiber to both the left basal body and the haptonematal base. Negative staining of isolated root systems of C. simplex Estep et al. shows that the arrangement of microtubules and fibrous connections is similar to that in C. acantha. The root system of C. acantha is compared to those of other members of the Prymnesiophyceae.     

Transformation of the flagella and associated flagellar components during cell division in the coccolithophoridPleurochrysis carterae

Summary Immunofluorescence microscopy, conventional and high voltage transmission electron microscopy were used to describe changes in the flagellar apparatus during cell division in the motile, coccolithbearing cells ofPleurochrysis carterae (Braarud and Fagerlund) Christensen. New basal bodies appear alongside the parental basal bodies before mitosis and at prophase the large microtubular (crystalline) roots disassemble as their component microtubules migrate to the future spindle poles. By prometaphase the crystalline roots have disappeared; the flagellar axonemes shorten and the two pairs of basal bodies (each consisting of one parental and one daughter basal body) separate so that each pair is distal to a spindle pole. By late prometaphase the pairs of basal bodies bear diminutive flagellar roots for the future daughter cells. The long flagellum of each daughter cell is derived from the parental basal bodies; thus, the basal body that produces a short flagellum in the parent produces a long flagellum in the daughter cell. We conclude that each basal body in these cells is inherently identical but that a first generation basal body generates a short flagellum and in succeeding generations it produces a long flagellum. At metaphase a fibrous band connecting the basal bodies appears and the roots and basal bodies reorient to their interphase configuration. By telophase the crystalline roots have begun to reform and the rootlet microtubules have assumed their interphase appearance by early cytokinesis.Abbreviations CR1, CR2 crystalline roots 1 and 2 - CT cytoplasmic tongue microtubules - DIC differential interference contrast light microscopy - H haptonema - HVEM high voltage transmission electron microscopy - IMF immunofluorescence microscopy - L left flagellum/basal body - M metaphase plate - MT microtubule - N nucleus - R right flagellum/basal body - R1, R2, R3 roots 1, 2, and 3 - TEM transmission electron microscopy     

Flagellar apparatus ultrastructure inMesostigma viride (Prasinophyceae)

The ultrastructure of the flagellar apparatus ofMesostigma viride Lauterborn (Prasinophyceae) has been studied in detail with particular reference to absolute configurations, numbering of basal bodies, basal body triplets and flagellar roots. The two basal bodies are interconnected by three connecting fibers (one distal fiber = synistosome, and two proximal fibers). The flagellar apparatus shows 180° rotational symmetry; four microtubular flagellar roots and two system II fibers are present. The microtubular roots represent a 4-6-4-6-system. The left roots (1s, 2s) consist of 4 microtubules, each with the usual 3 over 1 root tubule pattern. Each right root (1d, 2d) is proximally associated with a small, but typical multi-layered structure (MLS). The latter displays several layers corresponding to the S₁ (the spline microtubules: 5–7), and presumably the S₂—S₄ (the lamellate layers) of the MLS of theCharophyceae. At its proximal origin (near the basal bodies) each right root originates with only two microtubules, the other spline microtubules being added more distally. The structural and positional information obtained in this study strongly suggest that one of the right roots (1d) ofMesostigma is homologous to the MLS-root of theCharophyceae and sperm cells of archegoniate land plants. Thus the typical cruciate flagellar root system of the green algae and the unilateral flagellar root system of theCharophyceae and archegoniates share a common ancestry. Some functional and phylogenetic aspects of MLS-roots are discussed.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.     

Transformation and development of the flagellar apparatus ofCryptomonas ovata (Cryptophyceae) during cell division

Summary InCryptomonas ovata, long, dorsal flagella are produced which transform during the following cell division into short, ventral flagella. At division there is a reorientation in cell polarity, and the parental basal apparatus, which comprises the basal bodies and associated roots, is distributed to the daughter cells via a complex sequence of events. Flagellar apparatus development includes the transformation of a four-stranded microtubular root into a mature root of different structure and function. Each newly formed basal body nucleates new microtubular roots, but receives a striated fibrous root from a parental basal body. The striated roots are originally produced on the transforming basal body and are transferred to the new basal bodies at each successive division. The development of the asymmetric flagellar apparatus throughout the cell cycle is described.     

The flagellar apparatus ofDunaliella: Isolation of basal body-flagellar root complex

Summary InDunaliella bioculata, a biflagellate wall-less unicellular alga, the cytoskeleton is organized around the two basal bodies. Each basal body is associated with two dissymetric flagellar roots and numerous micro tubules which constitue a regular frame around the cell. We isolated the basal body-flagellar-root apparatus and studied its ultrastructure after negative staining. The two different flagellar roots are formed of microtubules and bundles of twisted filaments 3,5–4 nm in diameter. The proximal end of each root fans out and envelopes the basal body. We have shown preliminary results on the protein composition of basal body-flagellar roots fraction.     

STRUCTURE AND SIGNIFICANCE OF THE CRYPTOMONAD FLAGELLAR APPARATUS. I. CRYPTOMONAS OVATA (CRYPTOPHYTA)1

The absolute configuration of the flagellar apparatus in Cryptomonas ovata has been elucidated and found to be similar to that reported for Chilomonas paramecium. Variations apparent in the flagellar apparatus of Cryptomonas ovata include the presence of striations in the mitochondrion associated lamella, a rhizostyle which does not bear wing-like extensions from the microtubules and does not lie close to the nucleus, and a striated fibrous anchoring structure associated with one basal body which has not hitherto been described. The flagellar apparatus also includes a four stranded microtubular root which traverses into the anterior dorsal lobe of the cell, a striated fibrous root which is associated with a five stranded microtubular root, and a two stranded Cr root. The homologous nature of these roots to those in the larger cryptomonads is discussed in relation to the apparent reduction in flagellar apparatus size and complexity among the smaller cryptomonads. A diagrammatic reconstruction of the flagellar apparatus of Cryptomonas ovata is also presented.     

COMPARATIVE ANALYSES OF THE DINOFLAGELLATE FLAGELLAR APPARATUS. III. FREEZE SUBSTITUTION OF AMPHIDINIUM RHYNCHOCEPHALUM1

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.     

THE FLAGELLAR APPARATUS OF OXYRRHIS MARINA (PYRROPHYTA)1

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.     

The flagellar apparatus of the golden algaSynura uvella: Four absolute orientations

Summary Flagellated vegetative cells of the colonial golden algaSynura uvella Ehr, were examined using serial sections. The two flagella are nearly parallel as they emerge from a flagellar pit near the apex of the cell. The photoreceptor is restricted to swellings on the flagella in the region where they pass through the apical pore in the scale case and the swellings are not associated with the cell membrane or an eyespot. A unique ring-like structure surrounds the axonemes of both flagella at a level just above the transitional helix. The basal bodies are interconnected by three striated, fibrous bands. Four short (<100 nm) microtubules lie between the basal bodies at their proximal ends. Two rhizoplasts extend down from the basal bodies and separate into numerous fine striated bands which lie over the nucleus. Three- and four-membered microtubular roots arise from the rhizoplasts and extend apically together. As the roots reach the cell anterior, the three-membered root bends and curves clockwise to form a large loop around the flagella; the four-membered root bends anticlockwise and terminates under the distal end of the three-membered root as it completes the loop. There are four absolute orientations, termed Types 1–4, in which the flagellar apparatus can occur. With each orientation type the positions of the Golgi body, nucleus, rhizoplasts, chloroplasts and microtubular roots change with respect to the flagella, basal bodies and photoreceptor. Two new basal bodies appear in pre-division cells, and three short microtubules appear in a dense substance adjacent to each new basal body. Based upon the positions of new pre-division basal bodies, a hypothesis is proposed to explain why there are four orientations and how they are maintained through successive cell divisions.     

The flagellar root system of zoospores of the green algaChlorosarcinopsis (Chlorosarcinales) as compared withChlamydomonas (Volvocales)

The flagellar root system of zoospores in two species ofChlorosarcinopsis (C. minuta andC. spec.) has been studied in detail. The biflagellate zoospores show a cruciate root system, two of the four microtubular roots containing two microtubules, the other two four microtubules. The flagellar apparatus is otherwise identical with that ofChlamydomonas reinhardi as described byRingo (1967). Evidence is presented that the genusChlamydomonas is characterized by a bilateral symmetric root system (4-2-4-2) rather than a system with four equally numbered roots (i.e. 4-4-4-4). It is suggested that a root system with four identical cruciate roots is not present in any biflagellate algal cell. The taxonomic significance of cruciate root systems in green algae is discussed refering to the identical root systems ofChlorosarcinopsis andChlamydomonas.     

Flagellar systems in the euglenoid flagellates

The flagellar apparatus of euglenoids consists of two functional basal bodies, three unequal microtubular roots subtending the reservoir, and a fourth band of microtubules nucleated from one of the flagellar roots and subtending the reservoir membrane. The flagellar apparatus of some euglenoids may contain additional basal bodies, striated roots ("rhizoplasts"), fibrous roots, striated connecting fibers between basal bodies, layered structures, or various electron-dense connective substances. With the possible exception of Petalomonas cantuscygni, nearly all euglenoids are biflagellate although the length of one flagellum may be highly reduced. The flagellar transition zone and number of basal bodies are highly variable among species. In recent years a cytoplasmic pocket that branches off from the reservoir has been discovered. The microtubules of the ventral flagellar root are continuous with the microtubules which line this pocket. Based on positional and structural similarities, this structure is believed to be homologous with the MTR/cytostome of bodonids. Coupled with other ultrastructural and biochemical data, the fine structure of the flagellar apparatus supports the belief that the euglenoid flagellates are descendant from bodonid ancestors.     

THE FLAGELLAR APPARATUS OF GYMNODINIUM SP. (DINOPHYCEAE)1

The detailed structure of the flagellar apparatus has been determined in a small dinoflagellate of the genus Gymnodinium. Although diminutive, this dinoflagellate possesses a complex flagellar apparatus consisting of a posteriorly directed microtubular root, a transverse striated fibrous root, several striated fibrous connectives that attach the basal bodies to one another as well as to the different roots, and a conspicuous non-striated fibrous connective that directly links the posteriorly directded microtubular root with the extended lobe of the nucleus. This represents the second discovery of a nuclear connective linked to the flagellar apparatus in the Dinophyceae but is the first report to elucidate the spatial relationships of the connective with the flagellar apparatus and the cell. A detailed diagrammatic reconstruction is provided and the similarities between these flagellar apparatus features are compared with those known for other dinoflagellates. Additionally, the structure and displacement of the nuclear connective are compared with nuclear connectives described in other protists.     

THE FLAGELLAR APPARATUS OF CHRYSOCHROMULINA SP. (PRYMNESIOPHYCEAE)1

The flagellar apparatus of an undescribed species of Chrysochromulina Lackey that bears “eyelash” scales is reconstructed. The transitional region consists of two transitional plates each with an axosome, with no stellate pattern between them. Fine osmiophilic rings lie between the flagellar membrane and the outer doublets in the transitional region. The two jagella and the haptonema are inserted in a subapical depression that is lined ventrally by a spine-like projection formed by one of the parietal chloroplasts. The angles of insertion are similar to those of some other Chrysochromulina species in that both the haptonema and the right basal body lie at an extreme angle to the left basal body. The connectives of the apparatus consist of a striated distal band with a dorsal extension to the R1 and a ventral extension overlying the R2, a striated distal accessory band, an auxiliary connective from the right basal body to the adjacent ventral chloroplast, a well-developed intermediate band, two striated proximal bands, and a striated proximal accessory band. Of the microtubular roots in this Chrysochromulina species, three are associated with the left side of the cell (an R1 of 8+3; a small crystalline compound root, the R1C, associated with the R1; an R2 of three micro-tubules), and two are associated with the right basal body (an R3 of 2/2 microtubules with which the single-stranded R4 converges to form a 2/2+1 and then a 2/3 tiered arrangement). Comparisons are drawn with other species in the genus and related genera, particularly Prymne-sium.     

Observations on the flagellar apparatus of a coccolithophorid,Cruciplacolithus neohelis (Prymnesiophyceae)

The flagellar apparatus ofCruciplacolithus neohelis (McIntyre and Bé) Reinhardt including its transition region is described. The transition region contains a hat-shaped structure, which is suggested to be one of the common features of the Prymnesiophyceae. Its flagellar root system resembles that of most coccolithophorids examined so far, except that only one vestigial crystalline root is present associated with root 1. Two well-developed crystalline roots associated with roots 1 and 2, respectively, appear in the preprophase of nuclear division, suggesting conversion to a mitotic spindle. The taxonomic and evolutionary significance of the flagellar apparatus is discussed.     

The flagellar apparatus of the scaly green flagellatePyramimonas obovata: Absolute configuration

Summary The flagellar apparatus of the quadriflagellate scaly green algaPyramimonas obovata has been studied in detail and the absolute configuration of the flagellar apparatus has been determined. The flagellar root system is cruciate (4-2-4-2-system). 18 major basal body associated fibrous structures connect the four basal bodies with each other. Each basal body is linked to an adjacent basal body by a unique set of connecting fibres, i.e., the flagellar apparatus does not exhibit 180° rotational symmetry. The flagellar apparatus ofPyramimonas obovata is compared with that of quadriflagellate motile cells of theChlorophyceae sensu Stewart andMattox and the phylogenetic relationships are discussed.     

A polyclonal antibody (anticentrin) distinguishes between two types of fibrous flagellar roots in green algae

Summary The two main types of fibrous flagellar roots present in the flagellar apparatus of green algae (system I and system II fibers) are immunologically distinct as indicated by the localization of a Ca²⁺-modulated contractile protein (centrin) exclusively in one type (system II fibers) but not in the other type (system I fibers). A polyclonal antibody generated against the major protein of the striated flagellar roots (system II fibers) of the quadriflagellate green algaTetraselmis striata was used to localize centrin by immunofluorescence and pre- and postembedding immunogold electron microscopy in the flagellar apparatus ofSpermatozopsis similis, S. exsultans, Chlamydomonas reinhardtii, Dunaliella bioculata, Polytomella parva and gametes ofMonostroma grevillei andEnteromorpha sp. Whereas the antibody recognizes centrin in connecting fibers and system II fibers, no labeling occurs in system I fibers in all taxa investigated. This study presents the first evidence that system I fibers lack centrin and indicates that the two main types of fibrous flagellar roots in green algae are biochemically distinct.     

Structure and significance of cruciate flagellar root systems in green algae: Female gametes ofBryopsis lyngbyei (Bryopsidales)

The ultrastructure of the flagellar apparatus in the biflagellate female gametes of the green algaBryopsis lyngbyei has been studied in detail. In the flagellum and basal body, microtubule septations occur in some of the B-tubules. The transition region of the flagellum is extremely long (260–290 nm), exhibits a stellate pattern in cross section but lacks the transverse diaphragm. The two basal bodies form an angle of 180° and overlap at their proximal ends. They are connected by a compound non-striated capping plate. Terminal caps associated with the capping plate partially close the proximal end of each basal body. A cruciate flagellar root system with three different types of microtubular roots is present, i. e. the flagellar apparatus does not show 180° rotational symmetry. One root type contains 2 microtubules which are connected to an elaborate cylindrical structure, presumably a mating structure. The opposite root exhibits 3 microtubules over its entire length and is not associated with a cylindrical structure. In their proximal parts both roots are linked to an underlying crescent body. The other two microtubular roots are probably identical and consist of 4 (or 5) microtubules which show configurational changes. These two identical roots insert into the capping plate and link to the inner side (i. e. the side adjacent to the other basal body) of each basal body, whereas the other two roots attach to the outer sides of each basal body. System I striated fibres are probably associated with each of the four roots, while system II fibres have not been observed. The flagellar apparatus of female gametes ofB. lyngbyei shows many unique features but in some aspects resembles that of ulvalean algae. Functional and phylogenetic aspects of cruciate flagellar root systems in green algae are discussed.     

Ultrastructure of the flagellar apparatus of the green algaTetraselmis subcordiformis

Summary The ultrastructure of the flagellar apparatus of the marine quadriflagellate green algaTetraselmis subcordiformis is described in detail. Special consideration is given to the functional significance of the contractile rhizoplast and also to a complex structure which anchors the flagellar apparatus to the cell membrane and theca. The flagellar apparatus lies at the base of a deep apical depression. Four basal bodies lie in a zigzag row with their long axes nearly parallel. Outer adjacent pairs of basal bodies are structurally linked by a Z-shaped, ribbon-like structure. A striated fiber (transfiber) connects each outer basal body with the inner basal body of the opposite, mirror image pair. A complex system of four laminated oval discs (rhizanchora), microtubule rootlets and fibrous material anchor the flagellar apparatus and rhizoplasts to the plasma membrane and theca. A 4-2-4-2 arrangement of microtubule rootlets is present. Rhizoplasts, which are contractile organelles, branch into five distinct arms and associate with the near outer basal body and each of the four rhizanchora. Rhizoplast contraction is thought to be linked to flagellar activity and may act to alter the direction of motion of the cell.     

The flagellar apparatus and cytoskeleton of the dinoflagellates

Summary 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.Abbreviations aptb apical transverse microtubular band - FA flagellar apparatus - Imr longitudinal microtubular root - mls multilayered structure - tmr transverse microtubular root - tmre transverse microtubular root extension - tsr transverse striated fibrous root - tsrm transverse striated root associated microtubule