Flagellar regeneration and associated scale deposition inPyramimonas gelidicola (Prasinophyceae,Chlorophyta)

Summary During regeneration of mechanically amputated flagella, flagellar scales and the subtending membrane accumulate in a villiform scale reservoir in which the scales interact to form patterns on the villi reminiscent of the arrangement they later assume on the flagellum. The reservoir membrane is continuous with the plasmalemma, and the scales, attached directly and indirectly to the membrane, leave the reservoir and migrate toward the developing flagella where they assemble into highly ordered layers. It is proposed that scale-scale interactions induce a process of auto-assembly initiating the complex arrangement of scale tiers on the flagellum and cell body.     

Flagellar adhesion ofCrithidia fasciculata to Millipore filters

Summary Millipore filters composed of mixed cellulose esters have been used to investigate the adhesion of flagella ofCrithidia fasciculata to a non-living substrate. After 4 days on the surface of a culture of the flagellate, one side of the filter was covered with a monolayer of cells. In most cases the flagella penetrated the pores of the filter and at one or more points along their length presumed sites of adhesion were marked by the presence of hemidesmosomes, characterized by a thickened inner leaflet of the flagellar membrane and the presence of large numbers of fine filaments. If the interstitial space of the filter was sufficiently large, the hemidesmosomes occurred at the apex of an evagination of the flagellar membrane. These evaginations are believed to arise by movement of the flagellum relative to the point of adhesion. The addition of distilled water causes de-adhesion of the flagellum and its withdrawal from the filter. The hypothesis that cells adhere to one another and to non-living substrates by different mechanisms is discussed in the light of the results obtained here.     

The Mode of Attachment of Trypanosoma vivax in the Proboscis of the Tsetse Fly Glossina fuscipes: an Ultrastructural Study of the Epimastigote Stage of the Trypanosome*

SYNOPSIS. The ultrastructure of attached Trypanosoma vivax epimastigote clusters in the proboscis of the tsetse fly Glossina fuscipes is described from electron micrographs of thin sections. Some flagellates are attached directly to the lining of the insect's labrum by their flagella, most of which are aligned along the long axis of the proboscis. Other trypanosomes are attached indirectly, their flagella adhering to those of flagellates which are directly attached. Junctional complexes similar to those described from metazoan epithelia are found on the flagellar membrane. A long zonular hemidesmosome attaches the flagellum to the proboscis wall and a series of closely set macular desmosomes link the flagellar membranes of adjacent flagellates. Unlike the trypomastigote stages of T. vivax, more than one row of macular desmosomes may be present along the flagellum-body junction of the trypanosome. It is suggested that all these Junctional complexes serve to buttress the flagellate's attachment to its insect host and so maintain anchorage of the parasite during the fly's blood meals. The ability of the flagellum of trypanosomatids to form Junctional complexes may be a factor contributing to their success as parasites, this adaptation enabling them to multiply while attached to host surfaces.     

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

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

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.     

The main cell morphology of the freshwater colorless chrysomonad Spumella sp. (Ochromonadales, Chrysophyceae)

The cell structure of the freshwater chrysomonad Spumella sp. has been studied. The cell contains a vesicular nucleus, mitochondria with tubular cristae, Golgi apparatus, flagellar roots, and wide dorsal microtubular band. The flagella bear the spiral of four to five coils in the transitional zone. The rudiments of mastigonemes have been found in the perinuclear space. The compact leucoplast has an amorphous core surrounded by the membrane. No stigma has been detected. The leucosin vacuole, rhizoplast, and swelling of the short flagellum are absent. One to three osmiophilic granules lie near the leucoplast. The contractile vacuole is surrounded by tubules. The resemblance and difference of investigated flagellate with other chrysomonads are discussed.     

Flagellar transformation in the heterokontEpipyxis pulchra (Chrysophyceae): Direct observations using image enhanced light microscopy

Summary Cells ofEpipyxis pulchra possess two heteromorphic flagella that differ markedly in function, particularly during motility and prey capture. Flagellar heterogeneity is achieved during the course of at least three cell cycles. Prior to cell division, cells produce two new long, hairy flagella while the parental long flagellum is transformed into a new short, smooth flagellum. The parental short flagellum remains a short flagellum for this and subsequent cell division cycles. Although flagellar transformation requires only two cell cycles, developmental differences exist between daughter cells and the maturation of a flagellum/basal body requires at least three cycles.     

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.     

The flagellar developmental cycle in algae: flagellar transformation inCyanophora paradoxa (Glaucocystophyceae)

Summary Flagellar development during cell division was studied inCyanophora paradoxa using agarose-embedded cells, Nomarski optics and electronic flash photography. The cells bear two heterodynamic and differently oriented (anterior and posterior) flagella. Prior to cell division, cells produce two new anterior flagella while the parental anterior flagellum transforms into a posterior flagellum. The parental posterior flagellum remains a posterior flagellum throughout this and subsequent cell divisions. The development of a single flagellum thus extends through at least two cell cycles and flagellar heterogeneity is achieved by semiconservative distribution of the flagella during cell division. Based on these principles a universal numbering system for basal bodies and flagella of eukaryotic cells is proposed.     

Unusual distribution of a glycolipid antigen in the flagella ofChlamydomonas

Summary Mouse hybridomas were obtained that secrete monoclonal antibodies recognizing glycolipid antigens located in the flagellar membrane of the biflagellate alga,Chlamydomonas reinhardtii. The antigen is an acidic lipid that migrates slightly slower than a GM1 ganglioside on thin layer chromotography. The binding of the antibodies to the thin layer plate was inhibited by periodate oxidation suggesting that the antibodies are recognizing a carbohydrate epitope. In a variety ofChlamydomonas strains, these antibodies were found to stain the flagella of only a sub-set of the cells in the population, generally varying from 50% to 75% of the cells. Even after cloning, the population of cells continued to express this variability in staining, and presumably, expression of the glycolipid epitope. Although most cells showed either strong staining of both flagella or no detectable staining of both flagella, a subset of the cells in the culture exhibited differential antibody labeling of the two flagella, suggesting that an individualChlamydomonas can exhibit a different glycolipid composition in each of its two flagellar membranes and even differential expression along the length of an individual flagellum.     

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 LSU RDNA‐BASED PHYLOGENY OF ESOPTRODINIUM GEMMA (DINOPHYCEAE), WITH NOTES ON FEEDING BEHAVIOR AND THE DESCRIPTION OF THE FLAGELLAR BASE AREA OF A PLANOZYGOTE1

A small, freshwater dinoflagellate with an incomplete cingulum, identified as Esoptrodinium gemma Javornický (=Bernardinium bernardinense sensu auctt. non sensu Chodat), was maintained in mixed culture and examined using light and serial section TEM. Vegetative flagellate cells, large cells with two longitudinal flagella (planozygotes), and cysts were examined. The cells displayed a red eyespot near the base of the longitudinal flagellum, made of two or three layers of pigment globules not bounded by a membrane. Yellow‐green, band‐shaped chloroplasts, bounded by three membranes and containing lamella with three thylakoids, were present in both flagellate cells and cysts. Most cells had food vacuoles, containing phagotrophically ingested chlamydomonads or chlorelloid green algae; ingestion occurred through the ventral area, involving a thin pseudopod apparently driven by the peduncle. The pusule was tubular, with numerous diverticula in its distal portion, and opened into the longitudinal flagellar canal. Three roots were associated with each pair of flagellar bases, both in vegetative cells and in a planozygote. The longitudinal microtubular root bifurcated around the longitudinal basal body. The planozygote contained a single peduncle and associated structures, and a single transverse flagellar canal with the two converging transverse flagella. Using two ciliates as outgroup species, phylogenetic analyses based on maximum parsimony, neighbor‐joining and posterior probability (Bayesian analysis) supported a clade comprising Esoptrodinium, Tovellia, and Jadwigia.     

A FLAVIN-LIKE AUTOFLUORESCENT SUBSTANCE IN THE POSTERIOR FLAGELLUM OF GOLDEN AND BROWN ALGAE1

An autofluorescent substance occurs in the flagella of flagellate cells of the golden and brown algae. It is localized only in the posterior (short) flagellum and could not be detected in the anterior (long) one. It showed maximum fluorescence emission at 515–520 nm upon excitation of 440 nm; therefore, it is considered to be a flavin. This substance is distributed widely among flagellate cells of golden and brown algae irrespective of their nature (vegetative cells, zoospores, gametes, or sperm). It is absent, however, in some brown algal zoospores and sperm which lack an eyespot and flagellar swelling and are considered to lack phototaxis. Because the flagellar swelling in the posterior flagellum is a presumptive photoreceptor for phototaxis in these groups, it is suggested that the flavin located in the posterior flagellum acts as a photoreceptor pigment in phototaxis.     

The ultrathin structure of amoeboid flagellate <Emphasis Type="Italic">Thaumatomastix</Emphasis> sp. (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. is considered. The cell is surrounded by two-layered triangular scales. They are formed on the surface of mitochondria. Pseudopodia grabbing bacteria run from ventricular furrow, which is armored with two longitudinal bands of microtubules. Heterodynamic flagella run from small flagellar pocket. Long back flagellum has thin mastigonemes. Proximal area of short flagellum is covered with flat oval scales. Transitional flagellant zone has no spiral or other additional elements. Transverse plate is localized above cell surface. Kinetosomes are parallel to each other. Vesicular nucleus and Golgi apparatus have typical structure. Oval mitochondria contain tubular cristae. Within cytoplasm, extrusive organelles (kinetocysts) containing amorphous material and capsule were found. The latter consists of muff and cylinder. Plasmodial and cystic phases of development have not been discovered. Contractile vacuole is absent. The resemblance between Thaumatomastix sp. and other thaumatomonads has been discussed.     

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.     

Turnover and transport of agglutinins in conjugatingChlamydomonas gametes

Summary During gamete-gamete adhesion in the unicellular green algaChlamydomonas eugametos, the sexual adhesion molecules or agglutinins that are located on the flagella are subject to tip-oriented migration and rapid inactivation. It is demonstrated that sexual adhesiveness is maintained by incorporation of additional agglutinins, recruited from a cellular pool. The location of this reservoir is unknown but, as indicated by its insensitivity to the chaotropic agent guanidine thiocyanate, it appears to be distinct from the large amount of agglutinins on the plasma membrane of the cell body. By viewing flagella of conjugating gametes in a confocal scanning laser microscope after immuno-labelling of the agglutinins, evidence was obtained for a linear arrangement of the agglutinins in two rows on the flagellar surface. This suggests that after insertion at the base of the flagellum, the agglutinins follow linear tracks to the tip and that the transport system is confined to two longitudinal domains. It is estimated that the half-life of flagellar agglutinins drops from 1–2 h in nonconjugating gametes to 1 min during conjugation, which suggests that after incorporation at the flagellar base, the agglutinins migrate to the tip with a velocity of 100 nm/s. Presumably after arrival at the tip, the molecules are inactivated. It is postulated that rapid turnover and transport of agglutinins are required for optimal signalling between partner gametes.Abbreviations BSA bovine serum albumine - CHI cycloheximide - CSLM confocal scanning laser microscope - GA glutaraldehyde - GTC guanidine thiocyanate - GAM-IgG goat-anti-mouse immuno-globuline - mAb monoclonal antibody - mt mating type - PBS phosphate-buffered saline - SDS sodiumdodecyl sulphate - TRIS tris-(hydroxymethyl)-aminomethane     

Flagella-dependent gliding motility inChlamydomonas

Summary Flagella are generally recognized as organelles of motility responsible for the ability ofChlamydomonas to swim through its environment. However, the same flagella are also responsible for an alternative form of whole cell locomotion, termed gliding. Use of paralyzed flagella mutants demonstrates that gliding is independent of axonemal bend propagation. Gliding motility results from an interaction of the flagellar surface with a solid substrate. Gliding is characterized by bidirectional movements at 1.6±0.3 m/second and occurs when the cell is in a characteristic gliding configuration, where the two flagella are oriented at 180° to one another. A variety of observations suggest that the leading flagellum is responsible for the force transduction resulting in cell locomotion, although both flagella have the capacity to function as the active flagellum. The characteristics of gliding motility have been compared with theChlamydomonas flagellar surface motility phenomenon defined as surface translocation of polystyrene microspheres.     

Ultrastructure of the flagellar apparatus inPyramimonas octopus (Prasinophyceae)

Summary While green algae usually lack one of the outer dynein arms in the axoneme, flagella of the octoflagellated prasinophytePyramimonas octopus possess dynein arms on all peripheral doublets. The outer dynein arm on doublet no. 1 is modified, and additional structures are associated with doublets no. 2 and 6. The flagellar scales are asymmetrically arranged. Thus the two rows of thick flagellar hairscales are displaced towards doublet no. 6,i.e., in the direction of the effective stroke of each flagellum. The underlayer of small scales includes two nearly opposite double rows scales, arranged in the longitudinal direction of the flagellum. The hairscales emerge from these rows. The double rows are separated on one side by 9, on the other by 11 rows of helically arranged scales. The central pair of microtubules twists, but the axoneme itself (represented by the 9 peripheral doublets), does not seem to rotate. The flagella are arranged in two groups, showing modified 180° rotational symmetry. The effective strokes of the two central flagella are exactly opposite, while the other flagella beat in six intermediate directions.     

A STUDY OF CELL WALL AND FLAGELLA FORMATION DURING CELL DIVISION IN THE SCALY GREEN ALGA,SCHERFFELIA DUBIA (CHLOROPHYTA)1

The thecate green flagellate Scherffelia dubia (Perty) Pascher divides within the parental cell wall into two progeny cells. It sheds all four flagella before cell division, and the maturing progeny cells regenerate new walls and flagella. By synchronizing cell division, we observed mitosis, cytokinesis, cell maturation, flagella extension, and cell wall formation via differential interference contrast microscopy of live cells and serial thin‐section EM. Synthesis of thecal and flagellar scales is spatially and temporally strictly separated. Flagellar scales are collected in a pool during late interphase. Before prophase, Golgi stacks divide, flagella are shed, the parental theca separates from the plasma membrane, and flagellar scales are deposited on the plasma membrane near the flagellar bases. At prophase, Golgi bodies start to synthesize thecal scales, continuing into interphase after cytokinesis. During cytokinesis, vesicles containing thecal scales coalesce near the cell posterior, forming a cleavage furrow that is initially oriented slightly diagonal to the longitudinal cell axis but later becomes transverse. After the progeny nuclei have moved into opposite directions, resulting in a “head to tail” orientation of the progeny cells, theca biogenesis is completed and flagellar scale synthesis resumes. Progeny cells emerge through a hole near the posterior end of the parental theca with four flagella of about 8 μm long. The precise timing of flagellar and thecal scale synthesis appears to be an evolutionary adaptation in a scaly green flagellate for the thecal condition, necessary for the evolution of the phycoplast and thus multicellularity in the Chlorophyta.