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.     

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.     

Swimming behavior and ultrastructure of sperm of<Emphasis Type="Italic"> Lygodium japonicum</Emphasis> (Pteridophyta)

Swimming behavior of the sperm of Lygodium japonicum (Pteridophyta) and the associated ultrastructure of the flagellar apparatus were studied by video microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The sperm has approximately 70 flagella that emerge from a sinistrally-coiled flagellar apparatus, and swims forward by ciliary beat of these flagella. Backward swimming was not observed even after sperm collided with obstacles. Video microscopy showed that the flagella of the swimming sperm are oriented laterally and oblique-anteriorly. TEM and SEM observations revealed that the basal bodies of these flagella are arranged in at least two rows and oriented in the same directions as observed by video microscopy. These basal bodies (flagella) are categorized into two types according to their orientation: group I (laterally directed) and group II (oblique-anteriorly directed). The directionality of the basal bodies appears to be fixed by electron-dense material around their base. The outer dynein arms of the flagellar axoneme are entirely absent. These morphological characteristics of basal bodies (flagella) may relate to the lack of backward swimming behavior of the sperm. Based on these results, the evolution of swimming behavior in the archegoniates is discussed in connection with lack of backward swimming in a distantly related green alga, Mesostigma viride, and the Streptophyta.     

Flagellar elongation and shortening in Chlamydomonas. IV. Effects of flagellar detachment, regeneration, and resorption on the induction of flagellar protein synthesis

Synthesis of new proteins is required to regenerate full length Chlamydomonas flagella after deflagellation. Using gametes, which have a low basal level of protein synthesis, it has been possible to label and detect the synthesis of many flagellar proteins in whole cells. The deflagellation-induced synthesis of the tubulins, dyneins, the flagellar membrane protein, and at least 20 other proteins which co- migrate with proteins in isolated axonemes, can be detected in gamete cytoplasm, and the times of initiation and termination of synthesis for each of the proteins can be studied. The nature of the signal that stimulates the cell to initiate flagellar protein synthesis is unknown. Flagellar regeneration and accompanying pool depletion are not necessary for either the onset or termination of flagellar protein synthesis, because colchicine, which blocks flagellar regeneration, does not change the pattern of proteins synthesized in the cytoplasm after deflagellation or the timing of their synthesis. Moreover, flagellar protein synthesis is stimulated after cells are chemically induced to resorb their flagella, indicating that the act of deflagellation itself is not necessary to stimulate synthesis. Methods were defined for inducing the cells to resorb their flagella by removing Ca++ from the medium and raising the concentration of K+ or Na+. The resorption was reversible and the flagellar components that were resorbed could be re-utilized to assemble flagella in the absence of protein synthesis. This new technique is used in this report to study the control of synthesis and assembly of flagella.     

A complete set of flagellar genes acquired by horizontal transfer coexists with the endogenous flagellar system in Rhodobacter sphaeroides

Bacteria swim in liquid environments by means of a complex rotating structure known as the flagellum. Approximately 40 proteins are required for the assembly and functionality of this structure. Rhodobacter sphaeroides has two flagellar systems. One of these systems has been shown to be functional and is required for the synthesis of the well-characterized single subpolar flagellum, while the other was found only after the genome sequence of this bacterium was completed. In this work we found that the second flagellar system of R. sphaeroides can be expressed and produces a functional flagellum. In many bacteria with two flagellar systems, one is required for swimming, while the other allows movement in denser environments by producing a large number of flagella over the entire cell surface. In contrast, the second flagellar system of R. sphaeroides produces polar flagella that are required for swimming. Expression of the second set of flagellar genes seems to be positively regulated under anaerobic growth conditions. Phylogenic analysis suggests that the flagellar system that was initially characterized was in fact acquired by horizontal transfer from a gamma-proteobacterium, while the second flagellar system contains the native genes. Interestingly, other alpha-proteobacteria closely related to R. sphaeroides have also acquired a set of flagellar genes similar to the set found in R. sphaeroides, suggesting that a common ancestor received this gene cluster.     

Analysis of flagellar size control using a mutant of Chlamydomonas reinhardtii with a variable number of flagella

A mutant of Chlamydomonas reinhardtii with a variable number of flagella per cell has been used to investigate flagellar size control. The mutant and wild-type do not differ in cell size nor in flagellar length, yet the size of the intracellular pool of flagellar precursor protein can differ dramatically among individual mutant cells, with, for example, triflagellate cells having three times the pool of monoflagellate cells. Because cells of the same size, but with very different pool sizes, have flagella of identical length, it appears that the concentration of the unassembled flagellar precursor protein pool does not regulate flagellar length. The relation between cell size, pool size, and flagellar length has also been investigated for wild-type cells of different sizes and ploidies. Again, flagellar length appears to be maintained independent of pool size or concentration.     

The shape and dynamics of the Leptospiraceae

Most swimming bacteria produce thrust by rotating helical filaments called flagella. Typically, the flagella stick out into the external fluid environment; however, in the spirochetes, a unique group that includes some highly pathogenic species of bacteria, the flagella are internalized, being incased in the periplasmic space; i.e., between the outer membrane and the cell wall. This coupling between the periplasmic flagella and the cell wall allows the flagella to serve a skeletal, as well as a motile, function. In this article, we propose a mathematical model for spirochete morphology based on the elastic interaction between the cell body and the periplasmic flagella. This model describes the mechanics of the composite structure of the cell cylinder and periplasmic flagella and accounts for the morphology of Leptospiraceae. This model predicts that the cell cylinder should be roughly seven times stiffer than the flagellum. In addition, we explore how rotation of the periplasmic flagellum deforms the cell cylinder during motility. We show that the transition between hook-shaped and spiral-shaped ends is purely a consequence of the change in direction of the flagellar motor and does not require flagellar polymorphism.     

Attachment and structural features of flagella of certain bacilli

Abram, Dinah (Purdue University, Lafayette, Ind.), A. E. Vatter, and Henry Koffler. Attachment and structural features of flagella of certain bacilli. J. Bacteriol. 91:2045-2068. 1966.-The attachment of flagella to cells of various mesophilic and thermophilic strains of Bacillus was studied electron microscopically. Studies of ghost cells and membrane fragments indicate that flagella are connected to the cytoplasmic membrane. Flagella removed from cells mechanically, during autolysis, or by phage lysis, have attached to the base of their proximal hooks material that is heterogeneous in character. In part, this material consists of cytoplasmic membrane; its varied shape appears to be caused by the folding of the membrane around the proximal end of the flagellum at the site of attachment. It is uncertain whether this material represents a real structure or an artifact. Highresolution microscopy reveals differences in the fine structure of intact flagella of the various strains studied. The proximal hook and the flagellar filament are distinct in morphology and fine structure. A specialized structure is associated with the hook of flagella of B. brevis and B. circulans. The filament of flagella of B. stearothermophilus 2184 has two regions that show marked differences in the manner in which the subunits appear to be organized. No correlation was found between the site of origin of flagella and the location of reduced tellurite when the reduction of potassium tellurite was used to indicate the loci of enzymatic respiratory activities.     

Structure of the cell of the amoeboid flagellate <Emphasis Type="Italic">Thaumatomonas coloniensis</Emphasis> Wylezich et al., 2007 (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of the amoeboid flagellate Thaumatomonas coloniensis Wylezich et al. has been studied. The cell is surrounded by somatic scales forming on the surface of the mitochondria. The heterodynamic flagella emerge from the small flagellar pocket. Both flagella are covered by pineal scales and thin twisted mastigonemes. The kinetosomes lie parallel to each other. The transitional zone of the flagella carries the thin-walled cylinder. The transversal plate of the flagella is above the cell surface. The flagellar root system consists of three microtubular bands and a fibrillar rhizoplast. The vesicular nucleus and Golgi apparatus are of the usual structure. The mitochondria contain tubular cristae. The extrusive organelles (kinetocysts) contain amorphous material and a capsule; they are located in cytoplasm. The capsule consists of a muff and cylinder. Osmiophilic bodies of various shapes contain crystalloid inclusions. The pseudopodia capturing the bacteria emerge from the ventral groove. The groove is armored by the two longitudinal groups of the close situated microtubules. Microbodies and symbiotic bacteria have not been discovered. The resemblance of Th. coloniensis with other thaumatomonads is discussed.     

Existence of an additional structural component in the basal bodies of Escherichia coli and Vibrio alginolyticus flagellae

The structure of Escherichia coli and Vibrio alginolyticus flagella was studied using electron microscopy. An additional protein structure was shown to exist in the basal bodies of intact flagella in these organisms. It is possible that this structure involves three proteins important for the assembly of flagella, energy transduction, and a change-over in the direction of flagellar rotation.     

Swimming with protists: perception, motility and flagellum assembly

In unicellular and multicellular eukaryotes, fast cell motility and rapid movement of material over cell surfaces are often mediated by ciliary or flagellar beating. The conserved defining structure in most motile cilia and flagella is the '9+2' microtubule axoneme. Our general understanding of flagellum assembly and the regulation of flagellar motility has been led by results from seminal studies of flagellate protozoa and algae. Here we review recent work relating to various aspects of protist physiology and cell biology. In particular, we discuss energy metabolism in eukaryotic flagella, modifications to the canonical assembly pathway and flagellum function in parasite virulence.     

FLAGELLAR DEVELOPMENT AND REGENERATION IN VOLVOX CARTERI (CHLOROPHYTA)1

The biflagellate somatic cells of Volvox carteri f. nagariensis lyengar exhibit an asymmetric pattern of flagellar development. Initiallt each somatic cell has two short (4 μm) flagella but after several hours one flagellum on each cell elongates unitl it reaches a length of 12 μm. Due to the regular arrangement of somatic cells in the Volvox spheroid it is apparent that the same flagellum on each somatic is the first to elongale. The asymmetric flagellar length is maintained for about 8 h after which the second flagellum on each somatic cell elongates. When the second flagellum attains the same length (12 μm) as the first flagellum, both flagella elongale at the same rate until reaching a final length of 22 μm. Experimental removal of somatic cell flagella results in their regeneration. Somatis cells regenerate both flagella simultaneously and full length flagella are produced in about 2 h. The intial rate of flagellar regeneration is about ten times faster than the intial rate of flagllar growth in development. Cycloheximide, an inhibitor of protein synthesis, has no effect on the initial rate of flagellar regeneration but the flagella produced in the presence of the drug are half the length of flagella produced in its absence. Somatic cells are able to regenerate flagella up to the time of α and β tubulin, the major structural proteins of the flagellar axoneme, and other cellular proteins.     

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.     

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.     

Ultrastructure and development of the amoebo-flagellate cells of the protostelidProtosporangium articulatum

Summary Amoebo-flagellate cells develop upon spore germination in the protostelidProtosporangium articulatum. The germling may emerge flagellate or as an amoeba. In either case the cell undergoes mitosis within an hour of germination. The spindle is open and centric, and typically has several pairs of kinetosomes at the poles. During telophase, the kinetosomes are found at the surface of the cell and flagella and flagellar rootlets begin to develop. Some flagella remain in close association with the nucleus, the nucleus-associated flagella; others are located away from the nucleus, the supernumerary flagella. The flagellar apparatus is identical for both nucleus-associated flagella and supernumerary flagella. However, only the nucleus-associated flagella are able to generate the jerking, helical swim typical of amoebo-flagellates with a swarm cell-like morphology.     

Defective temporal and spatial control of flagellar assembly in a mutant of Chlamydomonas reinhardtii with variable flagellar number

Wild-type Chlamydomonas reinhardtii carry two flagella per cell that are used for both motility and mating. We describe a mutant, vfl-1, in which the biflagellate state is disrupted such that the number of flagella per cell ranges from 0 to as many as 10. vfl-1 cells possess the novel ability to assemble new flagella throughout the G1 portion of the cell cycle, resulting in an average increase of about 0.05 flagella per cell per hour. Such uncoupling of the flagellar assembly cycle from the cell cycle is not observed in other mutants with abnormal flagellar number. Rather than being located in an exclusively apical position characteristic of the wild type, vfl-1 flagella can be at virtually any location on the cell surface. vfl-1 cells display abnormally wide variations in cell size, probably owing to extremely unequal cell divisions. Various ultrastructural abnormalities in the flagellar apparatus are also present, including missing or defective striated fibers and reduced numbers of rootlet microtubules. The pleiotropic defects observed in vfl-1 result from a recessive Mendelian mutation mapped to Chromosome VIII.     

Probing the role of IFT particle complex A and B in flagellar entry and exit of IFT-dynein in Chlamydomonas

Mediating the transport of flagellar precursors and removal of turnover products, intraflagellar transport (IFT) is required for flagella assembly and maintenance. The IFT apparatus is composed of the anterograde IFT motor kinesin II, the retrograde IFT motor IFT-dynein, and IFT particles containing two complexes, A and B. In order to have a balanced two-way transportation, IFT-dynein has to be carried into flagella and transported to the flagellar tip by kinesin II, where it is activated to drive the retrograde IFT back to the flagellar base. In this study, we investigated the role of complex A and complex B in the flagellar entry and exit of IFT-dynein. We showed that regardless of the amount of complex A, IFT-dynein accumulated proportionally to the amount of complex B in the flagella of fla15/ift144 and fla17-1/ift139, two complex A temperature-sensitive mutants. Complex A was depleted from both cellular and flagellar compartments in fla15/ift144 mutant. However, in fla17-1/ift139 mutant, the flagellar level of complex A was at the wild-type level, which was in radical contrast to the significantly reduced cellular amount of complex A. These results support that complex A is not required for the flagellar entry of IFT-dynein, but might be essential for the lagellar exit of IFT-dynein. Additionally, we confirmed the essential role of IFT172, a complex B subunit, in the flagellar entry of IFT-dynein. These results indicate that complexes A and B play complementary but distinct roles for IFT-dynein, with complex B carrying IFT-dynein into the flagella while complex A mediates the flagellar exit of IFT-dynein.     

Bacterial flagella rotate and do not contract

Summary When squeezed between slides which restrict the rotation of the flagella, the cell body ofSpirillum volutans can be seen to rotate, while the flagellar bundle is motionless. This proves that the flagella rotate with respect to the cell body. The appearance of helical waves on the flagella is not a result of flagellar contractility or bending, but results from a simple rotation of the rigid, helical flagella.     

Evidence for a sliding-resistance at the tip of the trypanosome flagellum

Motility in trypanosomes is achieved through the undulating behaviour of a single "9 + 2" flagellum; normally the flagellar waves begin at the flagellar tip and propagate towards the base. For flagella in general, however, propagation is from base-to-tip and it is believed that bend formation, and sustained regular oscillation, depend upon a localised resistance to inter-doublet sliding - which is normally conferred by structures at the flagellar base, typically the basal body. We therefore predicted that in trypanosomes there must be a resistive structure at the flagellar tip. Electron micrographs of Crithidia deanei, Herpetomonas megaseliae, Trypanosoma brucei and Leishmania major have confirmed that such attachments are present. Thus, it can be assumed that in trypanosomes microtubule sliding at the flagellar tip is resisted sufficiently to permit bend formation.     

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.