ULTRASTRUCTURE OF THE FLAGELLAR APPARATUS OF PYROBOTRYS (CHLOROPHYCEAE)1

The flagellar apparatus of Pyrobotrys has a number of features that are typical of the Chlorophyceae, but others that are unusual for this class. The two flagella are inserted at the apex, but they extend to the side of the cell toward the outside of the colony, here designated as the ventral side. Four basal bodies are present, two of which extend into flagella. Four microtubular rootlets alternate between the functional and accessory basal bodies. In each cell, the two ventral rootlets are nearly parallel, but the dorsal rootlets are more widely divergent. The rootlets alternate between two and four microtubules each. A striated distal fiber connects the two functional basal bodies in the plane of the flagella. Two additional, apparently nonstriated, fibers connect the basal bodies proximal to the distal fiber. Another striated fiber is associated with each four-membered rootlet near its insertion into the flagellar apparatus. A fine periodic component is associated with each two-membered rootlet. A rhizoplast-like structure extends into the cell from each of the functional basal bodies. The arrangement of these components does not reflect the 180° rotational symmetry that is usually present in the Chlorophyceae, but appears to be derived from a more symmetrical ancestor. It is suggested that the form of the flagellar apparatus is associated with the unusual colony structure of Pyrobotrys.     

COMPARATIVE ULTRASTRUCTURE OF ZOOSPORES WITH PARALLEL BASAL BODIES FROM THE GREEN ALGAE DICTYOCHLORIS FRAGRANS AND BRACTEACOCCUS SP.

The chlorococcalean algae Dictyochloris fragrans and Bracteacoccus sp. produce naked zoospores with two unequal flagella and parallel basal bodies. Ultrastructural features of the flagellar apparatus of these zoospores are basically identical and include a banded distal fiber, two proximal fibers, and four cruciately arranged microtubular rootlets with only one microtubule in each dexter rootlet. In D. fragrans, each proximal fiber is composed of two subfibers, one striated and one nonstriated, and each sinister rootlet is composed of five microtubules (4/1), decreasing to four away from the basal bodies. In Bracteacoccus sp., each proximal fiber is a single unit, the sinister rootlets are four (3/1) or rarely five (4/1) microtubules, and each basal body is associated with an unusual curved structure. The basic features of the flagellar apparatus of the zoospores of these two algae resemble those of Heterochlamydomonas rather than most other chlorococcalean algae that have equal length flagella, basal bodies in the V-shape arrangement, and clockwise absolute orientation. It is proposed that these algae with unequal flagella and parallel basal bodies have a shared common ancestry within the green algae.     

Microtubules and the flagellar apparatus in zoospores and cysts of the fungusPhytophthora cinnamomi

Summary A correlated immunofluorescence and ultrastructural study of the microtubular cytoskeleton has been made in zoospores and young cysts ofPhytophthora cinnamomi. Labelling of microtubules using antibodies directed towards tubulin has revealed new details of the arrangement of the flagellar rootlets in these cells, and of the variability that occurs from cell to cell. Most of the variation exists at the distal ends of the rootlets, and may be correlated with differences in cell shape in these regions. The rootlets have the same right and left configuration in all zoospores. The arrangement of the rootlet microtubules at the anterior end of the zoospores raises the possibility that the microtubules on the left hand side of the groove may not comprise an independent rootlet which arises at the basal bodies.The absolute configuration of the flagellar apparatus has been determined from ultrastructural observations of serial sections. In the vicinity of the basal bodies, there is little, if any, variation between individuals, and the structure of the flagellar apparatus is similar to that described for related species of fungi. Two ribbon-like coils surround the central pair of microtubules at the distal tip of the whiplash flagellum, and clusters of intramembranous particles, similar to ciliary plaques, have been found at the bases of both flagella. There are two arrays of microtubules associated with the nucleus in the zoospores. One array lies next to the outer surface of the nuclear envelope, and probably functions in the shaping and positioning of the apex of the nucleus. The nuclear pores in this region are aligned in rows alongside these microtubules. The second array is formed by kinetochore microtubules which extend into a collar-like arrangement of chromatin material around the narrow end of the (interphase) nucleus. During encystment, all flagellar rootlets are internalized when the flagella are detached at the terminal plate. The rootlets arrays are no longer recognizable 5–10 minutes after the commencement of encystment.     

Gamma-tubulin in Chlamydomonas: characterization of the gene and localization of the gene product in cells

In addition to their role in nucleating the assembly of axonemal microtubules, basal bodies often are associated with a microtubule organizing center (MTOC) for cytoplasmic microtubules. In an effort to define molecular components of the basal body apparatus in Chlamydomonas reinhardtii, genomic and cDNA clones encoding gamma-tubulin were isolated and sequenced. The gene, present in a single copy in the Chlamydomonas genome, encodes a protein with a predicted molecular mass of 52,161 D and 73% and 65% conservation with gamma-tubulin from higher plants and humans, respectively. To examine the distribution of gamma-tubulin in cells, a polyclonal antibody was raised against two peptides contained within the protein. Immunoblots of Chlamydomonas proteins show a major cross-reaction with a protein of Mr 53,000. In Chlamydomonas cells, the antibody stains the basal body apparatus as two or four spots at the base of the flagella and proximal to the microtubule rootlets. During cell division, two groups of fluorescent dots separate and localize to opposite ends of the mitotic apparatus. They then migrate during cleavage to positions known to be occupied by basal bodies. Changes in gamma-tubulin localization during the cell cycle are consistent with a role for this protein in the nucleation of microtubules of both the interphase cytoplasmic array and the mitotic spindle. Immunogold labeling of cell sections showed that gamma-tubulin is closely associated with the basal bodies. The flagellar transition region was also labeled, possibly indicating a role for gamma-tubulin in assembly of the central pair microtubules of the axoneme.     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR POSITION IN THE COLONIAL GREEN ALGA PLATYDORINA CAUDATA (CHLOROPHYCEAE)1

The ultrastructure of the flagellar apparatus in pre-inversion and inversion stages of Platydorina resembles that of Chlamydomonas in having 180° rotational symmetry and clockwise absolute orientation. Basal bodies are in a “V” configuration and connected by one distal and two proximal fibers. Alternating two- and four-membered microtubular rootlets are cruciately arranged. During maturation, the basal bodies rotate and separate, and 180° rotational symmetry is lost. Simultaneously, each proximal fiber detaches from one of the functional basal bodies, and the distal fiber detaches from both. The mature apparatus has widely separated and nearly parallel basal bodies. Flagellar orientation in Platydorina is completed just after inversion and a flattening of the colony called intercalation, resulting in the pairs of flagella of neighboring cells extending from the colony in opposite directions in an alternating fashion. Flagellar orientation and separated basal bodies minimize the interference between the flagella of neighboring cells. Basal bodies and rootlets of the two intercalated halves of a colony rotate, resulting in the effective strokes of the flagella of every cell being towards the colonial posterior. The flagella of each cell beat with an effective stroke in the direction of the two inner rootlets. The flagella have an asymmetrical ciliary type beat. The rotated, separated, and parallel basal bodies, together with the nearly parallel rootlets probably are adaptations for movement of this colonial volvocalean alga. The flagellar apparatus in immature stages of Platydorina lends support to the suggestion that the alga has evolved from a Chlamydomonas-like ancestor.     

FLAGELLAR MOTION AND FINE STRUCTURE OF THE FLAGELLAR APPARATUS IN CHLAMYDOMONAS

The biflagellate alga Chlamydomonas reinhardi was studied with the light and electron microscopes to determine the behavior of flagella in the living cell and the structure of the basal apparatus of the flagella. During normal forward swimming the flagella beat synchronously in the same plane, as in the human swimmer's breast stroke. The form of beat is like that of cilia. Occasionally cells swim backward with the flagella undulating and trailing the cell. Thus the same flagellar apparatus produces two types of motion. The central pair of fibers of both flagella appear to lie in the same plane, which coincides with the plane of beat. The two basal bodies lie in a V configuration and are joined at the top by a striated fiber and at the bottom by two smaller fibers. From the area between the basal bodies four bands of microtubules, each containing four tubules, radiate in an X-shaped pattern, diverge, and pass under the cell membrane. Details of the complex arrangement of tubules near the basal bodies are described. It seems probable that the connecting fibers and the microtubules play structural roles and thereby maintain the alignment of the flagellar apparatus. The relation of striated fibers and microtubules to cilia and flagella is reviewed, particularly in phytoflagellates and protozoa. Structures observed in the transitional region between the basal body and flagellar shaft are described and their occurrence is reviewed. Details of structure of the flagellar shaft and flagellar tip are described, and the latter is reviewed in detail.     

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     

Ultrastructural analysis of flagellar development in plurilocular sporangia of Ectocarpus siliculosus (Phaeophyceae)

Flagellar development in the plurilocular zoidangia of sporophytes of the brown alga Ectocarpus siliculosus was analyzed in detail using transmission electron microscopy and electron tomography. A series of cell divisions in the plurilocular zoidangia produced the spore-mother cells. In these cells, the centrioles differentiated into flagellar basal bodies with basal plates at their distal ends and attached to the plasma membrane. The plasma membrane formed a depression (flagellar pocket) into where the flagella elongated and in which variously sized vesicles and cytoplasmic fragments accumulated. The anterior and posterior flagella started elongating simultaneously, and the vesicles and cytoplasmic fragments in the flagellar pocket fused to the flagellar membranes. The two flagella (anterior and posterior) could be clearly distinguished from each other at the initial stage of their development by differences in length, diameter and the appendage flagellar rootlets. Flagella continued to elongate in the flagellar pocket and maintained their mutually parallel arrangement as the flagellar pocket gradually changed position. In mature zoids, the basal part of the posterior flagellum (paraflagellar body) characteristically became swollen and faced the eyespot region. Electron dense materials accumulated between the axoneme and the flagellar membrane, and crystallized materials could also be observed in the swollen region. Before liberation of the zoospores from the plurilocular zoidangia, mastigoneme attachment was restricted to the distal region of the anterior flagellum. Structures just below the flagellar membrane that connected to the mastigonemes were clearly visible by electron tomography.     

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 absolute configuration of the flagellar apparatus in zoospores from two species ofLaminariales (Phaeophyceae

Summary We examined the zoospores produced by the unilocular sporangia ofLaminaria digitata (L.) Lamour. andNereocystis luetkeana Post. & Rupr. by serial sectioning to determine the absolute configuration of their flagellar apparatuses. The basal bodies, which are interconnected by three striated bands, lie parallel to the ventral face of the zoospore, and the posterior basal body always is found to the right of the anterior basal body when the cell is viewed from the ventral face, anterior end up. The four rootlets associated with the basal bodies include a major anterior rootlet of about seven microtubules extending from the anterior basal body along the ventral face towards the apex, a five-membered bypassing rootlet that passes ventral to the basal bodies and is connected to the posterior basal body by a posterior fibrous band, and two short rootlets having a single member each, the minor anterior and posterior rootlets. We consider the configuration observed here to be typical of most phaeophycean motile cells. The flagellar apparatus features suggest a considerable phylogenetic difference between thePhaeophyceae and other classes of chlorophyll c-containing organisms.     

The restructuring of the flagellar base and the flagellar necklace during spermatogenesis of Ephestia kuehniella Z. (Pyralidae,Lepidoptera)

Summary Transmission electron microscopy was used to study the development of the flagellar base and the flagellar necklace during spermatogenesis in a moth (Ephestia kuehniella Z.). Until mid-pachytene, two basal body pairs without flagella occur per cell. The basal bodies, which contain a cartwheel complex, give rise to four flagella in late prophase I. The cartwheel complex appears to be involved in the nucleation of the central pair of axonemal microtubules. In spermatids, there is one basal body; this is attached to a flagellum. At this stage, the nine microtubular triplets of the basal body do not terminate at the same proximal level. The juxtanuclear triplets are shifted distally relative to the triplets distant from the nuclear envelope. Transition fibrils and a flagellar necklace are formed at the onset of axoneme elongation. The flagellar necklace includes Y-shaped elements that connect the flagellar membrane and the axonemal doublets. In spindle-containing spermatocytes, the flagellar necklace is no longer detectable. During spermatid differentiation, the transition fibrils move distally along the axoneme and a prominent middle piece appears. Our observations and those in the literature indicate certain trends in sperm structure. In sperms with a short middle piece, we expect the presence of a flagellar necklace. The distal movement of the transition fibrils or equivalent structures is prevented by the presence of radial linkers between the flagellar membrane and the axonemal doublets. On the other hand, the absence of a flagellar necklace at the initiation of spermiogenesis enables the formation of a long middle piece. Thus, in spermatozoa possessing an extended middle piece, a flagellar necklace may be missing.     

Basal bodies and associated structures are not required for normal flagellar motion or phototaxis in the green alga Chlorogonium elongatum

The interphase flagellar apparatus of the green alga Chlorogonium elongatum resembles that of Chlamydomonas reinhardtii in the possession of microtubular rootlets and striated fibers. However, Chlorogonium, unlike Chlamydomonas, retains functional flagella during cell division. In dividing cells, the basal bodies and associated structures are no longer present at the flagellar bases, but have apparently detached and migrated towards the cell equator before the first mitosis. The transition regions remain with the flagella, which are now attached to a large apical mitochondrion by cross-striated filamentous components. Both dividing and nondividing cells of Chlorogonium propagate asymmetrical ciliary-type waveforms during forward swimming and symmetrical flagellar-type waveforms during reverse swimming. High-speed cinephotomicrographic analysis indicates that waveforms, beat frequency, and flagellar coordination are similar in both cell types. This indicates that basal bodies, striated fibers, and microtubular rootlets are not required for the initiation of flagellar beat, coordination of the two flagella, or determination of flagellar waveform. Dividing cells display a strong net negative phototaxis comparable to that of nondividing cells; hence, none of these structures are required for the transmission or processing of the signals involved in phototaxis, or for the changes in flagellar beat that lead to phototactic turning. Therefore, all of the machinery directly involved in the control of flagellar motion is contained within the axoneme and/or transition region. The timing of formation and the positioning of the newly formed basal structures in each of the daughter cells suggests that they play a significant role in cellular morphogenesis.     

Ultrastructure of the quadriflagellate zoospores of the filamentous green algaeChaetophora incrassata andPseudoschizomeris caudata (Chaetophorales,chlorophyceae) with emphasis on the flagellar apparatus

Quadriflagellate zoospores ofChaetophora incrassata andPseudoschizomeris caudata have similar features including an appressed membrane between the pyrenoid matrix and the starch sheath, and identical flagellar apparatuses. Components of the flagellar apparatus include: directly opposed upper basal bodies, lower basal bodies in the clockwise absolute orientation, a grooved distal fiber, peripheral and terminal fibers between adjacent basal bodies, proximal fibers connecting the lower basal bodies to the X-membered rootlets two- and X-membered rootlets associated with electron-dense components, and at least one rhizoplast. The X-membered rootlets, are comprised of five microtubules inC. incrassata and four or five inP. caudata. These features of the flagellar apparatus suggest that the two algae are closely related, and together withStigeoclonium, Uronema, Draparnaldia andFritschiella, form a natural group, the Chaetophoraceae, Chaetophorales (sensu Mattox and Stewart).     

The Fine Structure of the Colonial Kinetoplastid Flagellate Cephalothamnium cyclopum Stein

Cell structure, cell adhesion, and stalk formation have been examined by electron microscopy in the colonial flagellate, Cephalothamnium cyclopum. Each cell is obconical or spindle-shaped, pointed posteriorly and truncated anteriorly. The cell membrane is underlain by epiplasm 0.1 μm thick in the posterior region, but bands of microtubules support the anterior region which is differentiated into a flagellar pocket, oral apparatus and contractile vacuole. Each of 2 flagella, joined a short way above their bases by an interflagellar connective, has a paraxial rod and mastigonemes. One flagellum is free and is important in food gathering while the other is recurrent and lies in a shallow groove on the ventral cell surface but projects posteriorly into the stalk. The basal bodies of these flagella are bipartite structures connected by a pair of striated rootlets with accessory microtubular fibers. The oral apparatus consists of a funnel-shaped buccal cavity and cytostome. It is supported by helical and longitudinal microtubules and also has nearby striated and microtubular fibers. Possible roles of associated oral vesicles in relation to ingestion are discussed. A reticulate mitochondrion houses a massive kinetoplast which has a fibrillar substructure resembling that of dinoflagellate chromosomes. Adjacent flagellates adhere by laminate extensions of their posterior regions and attach by their recurrent flagella to a communally secreted stalk composed of finely fibrillar material. This study indicates that Cephalothamnium belongs in the order Kinetoplastida, and has many features in common with members of the family Bodonidae.     

THE OCCURRENCE OF FLAGELLATED EGGS IN LAMINARIA ANGUSTATA (PHAEOPHYTA,LAMINARIALES)1

Eggs of laminaria angustata Kjellman were shown to have two flagella. Compared with flagella of other phaeophycean swarmers, those of Laminaria eggs have several unique characters such as lack of mastigonemes, widely spaced basal bodies and no flagellar rootlets. The flagella abscise during egg liberation.     

ULTRASTRUCTURE OF THE GAMETE OF PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

Gametes of Pediastrum duplex Meyen were investigated ultrastructurally, with emphasis on the flagellar apparatus. The cells are naked, biflagellate, and measure approximately 2.5 × 8 μm. Distinguishing them from zoospores is their possession of an eyespot and mating structure (the apical cap), and their lack of the peripheral band of cytoplasmic microtubules involved in colony formation. Four featurs of the flagellar apparatus are especially noteworthy: (1) the basal bodies are directly opposed and (2) are interconnected via their cores, (3) the central portion of the distal fiber is elaborated into an unusual ribbed structure which overlies the striated microtubule-associated component (SMAC) of the two-membered rootlets, and (4) the X-rootlets are dissimilar in microtubular number. The smaller X-rootlet consists of four microtubules in a three over one (3/1) configuration, whereas the larger has been found to be either 5 / 1, 6 / 1 or 7 / 1. The former rootlet extends past the nucleus whereas the latter extends down the opposite side of the cell, passing near the eyespot. The first two of these flagellar apparatus features have been previously noted in other motile cells of the Hydrodictyaceae. Although not specifically mentioned, published micrographs suggest the presence of the latter two as well, which may indicate that all four flagellar apparatus features are characteristics of all motile cells in the Hydrodictyaceae.     

ULTRASTRUCTURE OF THE ZOOSPORES AND VEGETATIVE CELLS OF TETRAEDRON AND CHLOROTETRAEDRON (CHLOROPHYCEAE)1

The flagellar apparatus of the zoospores of Tetraedron bitridens Beck-Mannagetta and Chlorotetraedron polymorphum MacEntee, Bold et Archibald includes directly opposed basal bodies, a distal fiber that is elaborated into a ribbed structure to which the continuous striated microtubule-associated component (SMAC) is connected, and partial caps over the proximal end of each basal body. The angle between basal bodies ranges from approximately 25° to 150°. Basal bodies at wider angles are interconnected via their cores. A septum is present in the B-tubule of one basal body triplet in C. polymorphum. Both organisms have four microtubular rootlets arranged in a cruciate pattern. The two X-membered rootlets in a single cell have dissimilar numbers of microtubules. In C. polymorphum there are 5 and 6 microtubules in a 4/1 and 5/1 arrangement. 3/1 and 4/1 rootlets are present in T. bitridens. Zoospores of T. bitridens have a fuzzy coat whereas those of C. polymorphum are naked. Pyrenoids in both species are covered by a continuous starch sheath. Vegetative, interphase cells of C. polymorphum have two centrioles connected by a fiber that are located in depressions in the nuclear envelope. We propose that these two genera may be closely related to Neochloris, and that the coenobial genera Hydrodictyon, Pediastrum and Sorastrum are derived from a Tetraedron-like alga.     

ELECTRON MICROSCOPE OBSERVATIONS ON THE FLAGELLAR APPARATUS OF BRYOPSIS MAXIMA (CHLOROPHYCEAE)1

The flagellar apparatus in male gametes of the siphonaceous green alga, Bryopsis maxima Okamura, was studied and compared with that of other green biflagellate cells. The proximal portions of two basal bodies are connected by a single striated proximal band, unique among the biflagellate reproductive cells of green algae studied. Anterior to the flagellar bases is a pair of distal bands different from the single structure in other biflagellate cells. These bands which arise from the distal portion of each basal body, extend upward in the papilla and curve down toward the lower edges of the basal bodies. They seem to have no direct association with each other. Two pairs of distinct flagellar roots, one consisting of 3–5 microtubules and the other of a partially striated fiber of undetermined numbers of microtubules, diverge from the basal body region and extend towards the cell posterior. Their component microtubules are disorganized into single or smaller groups midway over the cell length. The uniqueness of the flagellar apparatus is briefly discussed.