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.     

The flagellar apparatus ofMesostigma viride (Prasinophyceae): Multilayered structures in a scaly green flagellate

Mesostigma viride Lauterborn (Prasinophyceae) is the first green flagellate found to have multilayered structures (MLS) in its flagellar apparatus. MLS's were previously known from green algae only in charophycean swarmers, linking theCharophyceae to the origin of land plants, whose male gametes (when flagellated) also possess an MLS.M. viride is, therefore, probably more closely related to the origin of theCharophyceae than any other green flagellate that has been thoroughly studied so far. The occurrence of MLS's in green flagellates and apparently in other algae and protozoans suggests that an MLS occurred in an ancient group of flagellates and has survived in various protistan lines, including the line of green algae related to land plants. The occurrence of a synistosome inM. viride and other of its characteristics suggest that it is more closely related toPyramimonas than to other genera of scaly green flagellates.This work was supported by National Science Foundation Grant DEB-78-03554.     

Comparative cytology and taxonomy of theUlvaphyceae II. Ulvalean characteristics of the stephanokont flagellar apparatus ofDerbesia tenuissima

Summary The stephanokont flagellar apparatus of the zoospores ofDerbesia tenuissima (De Not.) Crouan is examined and compared to the flagellar apparatuses of other green algae. The flagella ofDerbesia are attached to two of three bands which lie at the junction of the body and papilla. Serial longitudinal and cross sections reveal that the basal bodies are attached to the bands along their sides and at their proximal ends. The bands are not striated in any plane. The lack of striation in the bands and the partial covering of the proximal end of the basal bodies by one of the bands closely resemble the type of flagellar connection system described as the Bryopsis-type byMelkonian (1980). Zoospores of ulvalean green algae also possess these features, suggesting that green siphons are phylogenetically related to theUlvales. It is proposed that green siphons be tentatively classified in theUlvaphyceae rather than in theChlorophyceae orCharophyceae.This work supported by NSF Grant DEB 78-03554.     

Fine structure of the flagellar apparatus of gametesin situ and motile zygotes of the green algaUlothrix flacca var.Roscoffensis (Ulotrichales) (Chlorophyta)

Summary This fine structural study ofUlothrix flacca (Dillw.) ThuretRoscoffensis variety (Berger-Perrot), a marineUlothrix, describes in detail the flagellar apparatus configuration of gametesin situ in the gametangia and in motile zygotes. The gametes's flagellar apparatus shows two basal bodies overlapping at their proximal end at a 30° angle, in an 11/5 o'clock configuration or with a counterclockwise absolute orientation. The basal bodies are interconnected by a non-striated band or capping plate. They are wrapped in their proximal part by an electron-dense sheath and obtured by a bilobed terminal cap. A cruciate microtubular root system having a 4-2-4-2 alternation pattern is present. A striated microtubule associated component (S.M.A.C.) or system I fibres accompany the two membered root R₂. The system II fibres or rhizoplasts along with striated bands associated to the microtubular roots, were not observed and are presumed to be absent.In the motile zygotes, the basal bodies are paired in a cruciate pattern. During the fusion process, two basal bodies, one of each pair, slide in a face to face position with a slight displacement into the 11/5 o'clock direction; the other two make a 30° counterclockwise rotation, thus making a 60° angle between the two basal bodies of each pair instead of 30° in the gamete.After comparison with the flagellar apparatus of other green alga gametes, it is concluded that the taxonomic affinities ofUlothrix flacca var.Roscoffensis, lie with theUlvophyceae sensuStewart andMattox 1978.Abbreviations CP capping plate - ER endoplasmic reticulum - G Golgi body - LG lipid globule - M mitochondria - MS presumed mating structure - N nucleus - R ₂,R ₄ microtubular roots - SH sheath - SMAC striated microtubule associated component - TC terminal cap - V vacuole - Ve vesicles in the anterior papilla - 1, 2, 1, 2 basal bodies numerotation     

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.     

Reconstruction of the flagellar apparatus and microtubular cytoskeleton inPyramimonas gelidicola (Prasinophyceae,Chlorophyta)

Summary The absolute configuration of the flagellar apparatus inPyramimonas gelidicola McFadden et al. has been determined and shows identity withP. obovata, indicating that they are closely related. Comparison with the flagellar apparatus of quadriflagellate zoospores from the more advancedChlorophyceae suggest thatPyramimonas may be a primitive ancestral form. The microtubular cytoskeleton has been examined in detail and is shown to be unusual in that it does not attach to the flagellar apparatus. Cytoskeletal microtubules are nucleated individually, and this is interpreted as an adaptation to the methods of mitosis and scale deployment. In view of the primitive nature of these processes, it is proposed that this type of cytoskeletal organization may represent a less advanced condition than that of the flagellar root MTOCs (microtubule organizing centers) observed in theChlorophyceae.     

The flagellar root system in the gamete ofAcetabularia mediterranea

Summary 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.     

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.     

Vischeria stellata (Eustigmatophyceae): ultrastructure of the zoospores,with special reference to the flagellar apparatus

Summary Ultrastructure of the zoospores ofVischeria stellata (R. Chodat ex Poulton) Pascher is investigated, with particular reference to the system of flagellar roots. Microtubular roots and a rhizoplast are present and a model showing their distribution is proposed. Four microtubular roots attach to the basal bodies in a system basically similar to that displayed by the heterokont algae and fungi. The rhizoplast is also similar to that of other heterokont algae. We conclude from these observations that the class Eustigmatophyceae should be placed within the division Heterokontophyta.Abbreviations C chloroplast - B basal body of the emergent flagellum - B' second basal body - E eyespot - F emergent flagellum - FS flagellar swelling - LV lamellate vesicle - M mastigonemes - MTs microtubules - N nucleus - R 1–R 4 microtubular roots - Rh rhizoplast - SB striated band - SV spiral vesicle     

An ultrastructural comparison betweenSpermatozopsis andDunaliella (Chlorophyceae)

The ultrastructure of the type species of the genusDunaliella, D. salina, has been reinvestigated in an attempt to clarify the relationships betweenDunaliella andSpermatozopsis. Dunaliella salina differs in the following ultrastructural characters fromSpermatozopsis (as exemplified byS. similis Preisig etMelkonian): presence of a distinctive surface coat covering the plasmalemma; presence of a prominent pyrenoid (with pairs of thylakoids partially entering the pyrenoid matrix); dictyosomes parabasal; endoplasmic reticulum closely underlying the plasmalemma around most of the cell; contractile vacuoles absent; cell form ovoid to elongated and not spirally twisted; mitochondrial profiles near the flagellar apparatus. Differences in the ultrastructure of the flagellar apparatus: basal body angle more or less fixed; distal connecting fibre cross-striated; system II fibre (rhizoplast) present, associated with mitochondrial profile; system I fibre underlying two-stranded microtubular root; mating structure present. These ultrastructural differences justify distinction between the two taxa at generic level. The problematical status of freshwater species ofDunaliella is briefly discussed.     

The flagellar root system inHeterosigma akashiwo (Raphidophyceae)

Summary The flagellar apparatus of 3 isolates ofHeterosigma akashiwo (Hada) Hada has been studied by serial sectioning. The two basal bodies lie at almost right angles to one another, but in a different plane, and are interconnected by an extensive root system. This consists of three roots (i) a massive cross-banded fibrous root (= rhizoplast) which extends from near the proximal ends of both basal bodies to the anterior surface of the nucleus, (ii) a compound microtubular root with a layered structure, associated with the hairy anterior flagellum and extending to the anterior surface and (iii) the rhizostyle which passes between the two basal bodies leading anteriorly to a vesicle in the flagellar groove region and following the nucleus posteriorly terminating deep in the cytoplasm. Both the characteristic arrangement of the basal bodies and the presence of the complex layered structure are characteristic of theRaphidophyceae. The broad microtubular root, however, to which the layered structure is attached, appears to be characteristic of nearly all heterokont algae, fungi and protozoa so far examined. Thus, our findings have important implications on phylogenetic relationships within the heterokonts and lead us to question whether some of the present classes such as theChrysophyceae andXanthophyceae are indeed natural groups.     

Ribosomal RNA sequence comparisons demonstrate an evolutionary relationship betweenZygnematales and charophytes

The nuclear-encoded small subunit ribosomal RNA (rRNA) sequences were determined forGenicularia spirotaenia, Mesotaenium caldariorum, andStaurastrum spec. (Zygnematales) to elucidate the evolutionary position of these green algae. Results of neighbour-joining and maximum parsimony phylogenetic analyses support a monophyletic origin of theZygnematales within the evolutionary assemblage defined by theCharophyceae (sensuMattox & Stewart) and land plants. TheZygnematales/Charophyceae/land plants are evolutionarily distinct from the monophyletic lineage defined by theChlorodendrales, Pseudoscourfieldiales, and theMicrothamniales/Chlorophyceae. In memoriamRobert W. Hoshaw.     

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.     

The architecture of the flagellar apparatus ofPrymnesium patellifera (Prymnesiophyta)

The flagellar apparatus of the small prymnesiophytePrymnesium patellifera has been analysed and a reconstruction is presented. Externally, the cell carries two sub-equal flagella and a short non-coiling haptonema. Within the cell, there are four microtubular roots and a number of fibrous bands, the latter interconnecting the two basal bodies and the haptonema base. One of the roots (r1) consists of a sheet of up to 25 microtubules originating close to the proximal extremity of the haptonema base, but the other three roots are composed of between 1 and 4 microtubules only. Distally, a large striated fibrous auxiliary connecting root extends across the anterior part of the cell linking root r1 and a mitochondrial profile on the opposite side of the cell. The arrangement of the components of the flagellar apparatus ofP. patellifera is commensurate with the general pattern found in many prymnesiophytes other than members of the Pavlovales, but there are a number of differences in detail from the other species described hitherto.     

Changes in the absolute configuration of the basal/flagellar apparatus and evidence of centrin during male gametogenesis in Chara contraria var. nitelloides (Charales, Charophyta)

The absolute configurations of the basal/flagellar apparatus during male gametogenesis of Chara contraria var. nitelloides (Charales, Charophyta) were carefully analysed. Emphasis was placed on the changes in the angles and lengths of the basal bodies, the microtubular root angles and the development of the distal as well the proximal connecting fibers. Six principal stages were recognized: a) parallel, non-axonemal, developing basal bodies connected by a non-striated, proximal fiber; b) non-parallel, non-axonemal, mature basal bodies connected by a developing, striated, distal fiber; c) non-parallel, axonemal basal bodies connected by a fully developed, striated, distal fiber; d) opposite, axonemal basal bodies not connected by fibers, e) axonemal basal bodies not connected by fibers and directed backwards and f) parallel, axonemal basal bodies not connected by fibers. A headpiece, a 3-membered root and a reduced multilayered structure developed during ontogeny. The initial parallel disposition of the basal bodies, the initial lack of MLS and the presence of only two microtubular roots from the very inception of the basal apparatus development, suggest a Mamiella-like ancestor for Charales. Ontogenetic evidence supports previous ideas in the sense that similarities of sperm morphology of charalean and bryophytan gametes are likely due to convergent evolution. In addition, the present study clearly reveals the presence of centrin in Charales.     

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 structure inMicrospora (Chlorophyceae) confirms a close evolutionary relationship with unicellular green algae

The spatial configuration of the flagellar apparatus of the biflagellate zoospores of the green algal genusMicrospora is reconstructed by serial sectioning analysis using transmission electron microscopy. Along with the unequal length of the flagella, the most remarkable characteristics of the flagellar apparatus are: (1) the subapical emergence of the flagella (especially apparent with scanning electron microscopy); (2) the parallel orientation of the two basal bodies which are interconnected by a prominent one-piece distal connecting fiber; (3) the unique ultrastructure of the distal connecting fiber composed of a central tubular region which is bordered on both sides by a striated zone; (4) the different origin of the d-rootlets from their relative basal bodies; (5) the asymmetry of the papillar region which together with the subapical position of the basal bodies apparently cause the different paths of corresponding rootlets in the zoospore anterior; (6) the presence of single-membered d-rootlets and multi-membered s-rootlets resulting in a 7-1-7-1 cruciate microtubular root system which, through the different rootlet origin, does not exhibit a strict 180° rotational symmetry. It is speculated that the different basal body origin of the d-rootlets is correlated with the subapical implant of flagella. It is further hypothesized that in the course of evolution the ancestors ofMicrospora had a flagellar papilla that has migrated from a strictly apical position towards a subapical position. Simultaneously, ancestral shift of flagella along the apical cell body periphery has taken place as can be concluded from the presence of an upper flagellum overlying a lower flagellum in the flagellar apparatus ofMicrospora. The basic features of the flagellar apparatus of theMicrospora zoospore resemble those of the coccoid green algal generaDictyochloris andBracteacoccus and also those of the flagellate green algal genusHeterochlamydomonas. This strengthens the general supposition thatMicrospora is evolutionarily closely related to taxa which were formerly classified in the traditionalChlorococcales.     

ENTOSIPHON SULCATUM (EUGLENOPHYCEAE): FLAGELLAR ROOTS OF THE BASAL BODY COMPLEX AND RESERVOIR REGION1,2

The flagellar root system of Entosiphon sulcatum (Dujardin) Stein (Euglenophyceae) is described and compared with kinetoplastid and other euglenoid systems. An asymmetric pattern of three microtubular roots, one between the two flagellar basal bodies and one on either side (here called the intermediate, dorsal, and ventral roots), is consistent within the euglenoid flagellates studied thus far. The dorsal root is associated with the basal body of the anterior flagellum (F₁) and lies on the left dorsal side of the basal body complex. Originating between the two flagellar basal bodies, and associated with the basal body of the trailing flagellum (F₂), the intermediate root is morphologically distinguished by fibrils interconnecting the individual microtubules to one another and to the overlying reservoir membrane. The intermediate root is often borne on a ridge projecting into the reservoir. The ventral root originates near the F₂ basal body and lies on the right ventral side of the cell. Fibrillar connections link the membrane of F₂ with the reservoir membrane at the reservoir-canal transition level. A large cross-banded fiber joins the two flagellar basal bodies, and a series of smaller striated fibers links the anterior accessory and flagellar basal bodies. Large nonstriated fibers extend from the basal body complex posteriorly into the cytoplasm.     

THE FLAGELLAR APPARATUS OF CHRYSOLEPIDOMONAS DENDROLEPIDOTA (CHRYSOPHYCEAE), A SINGLE-CELLED MONAD COVED WITH ORGANIC SCALES1

The flagellar apparatus of Chrysolepidomonas dedrolepidota Peters et Andersen is similar to that of other members of the Ochromonadales, Chrysophyceae. there are four microtubular roots (R_1-4) and a system II fiber (= rhizoplast). the R₁ root consists of three microtubules that nucleate many cytoplasmic microtubules. One compressed band of 10 or more cytoplasmic microtubules is directed black along the R1 root in an anti-parallel direction. The R₂ root consists of one to two microtubules, and it extends toward the distal end of the R₁ root. The R₃ root consists of six (?seven) microtubules near its proximal end. The “a” and “f” microtubules of the R₃ root are under the short flagellum, and the “f” microtubule loops back and under the basal body, extending down to the nucleus. The R₄ root consists of one to two microtubules extending along the left side of the shot flagellum and curving under the short flagellum where it terminates near the “a” microtubule of R₃ Both flagella have a transitional plate and a transitional helix with five gyres. There is a thin, second plate in the basal body at the level of the distal end of the “c” tubules of the basal body triplets. The tripartite flagellar hairs have long lateral filaments but lack short lateral filaments. We compare the flagellar apparatus with that of other members of the Ochromonadales and members of the Hydrurales and Hibberdiales.     

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