Posterior Basal Body Research Articles

Ophirina amphinema n. gen., n. sp., a New Deeply Branching Discobid with Phylogenetic Affinity to Jakobids

We report a novel nanoflagellate, Ophirina amphinema n. gen. n. sp., isolated from a lagoon of the Solomon Islands. The flagellate displays ‘typical excavate’ morphological characteristics, such as the presence of a ventral feeding groove with vanes on the posterior flagellum. The cell is ca. 4 µm in length, bears two flagella, and has a single mitochondrion with flat to discoid cristae. The flagellate exists in two morphotypes: a suspension-feeder, which bears flagella that are about the length of the cell, and a swimmer, which has longer flagella. In a tree based on the analysis of 156 proteins, Ophirina is sister to jakobids, with moderate bootstrap support. Ophirina has some ultrastructural (e.g. B-fibre associated with the posterior basal body) and mtDNA (e.g. rpoA–D) features in common with jakobids. Yet, other morphological features, including the crista morphology and presence of two flagellar vanes, rather connect Ophirina to non-jakobid or non-discobid excavates. Ophirina amphinema has some unique features, such as an unusual segmented core structure within the basal bodies and a rightward-oriented dorsal fan. Thus, Ophirina represents a new deeply-branching member of Discoba, and its mosaic morphological characteristics may illuminate aspects of the ancestral eukaryotic cellular body plan.

Three‐dimensional organization of flagellar basal apparatus in Ectocarpus gametes

SummaryThe flagellar basal apparatus of the brown alga Ectocarpus siliculosus was re‐investigated in details using transmission electron microscopy and electron tomography. As a result, three‐dimensional structures with spatial arrangement of bands and microtubular flagellar rootlets were observed. Fibrous structures linking the anterior flagellar basal body to the major anterior rootlet (R3) or the bypassing rootlet was newly discovered in this study. A direct attachment from the minor anterior rootlet (R4) to the anterior and posterior basal bodies was also discovered, as were attachments from the minor posterior rootlet (R1) to the deltoid striated band and from the major posterior rootlet (R2) to the posterior fibrous band. The microtubular flagellar rootlets were connected to the bands and to the anterior or posterior basal body. These bands may have a role in maintaining the spatial arrangement of the anterior and posterior flagellar basal bodies and the microtubular flagellar rootlets. A numbering system of the basal body triplets was established by tracing axonemal doublets in the serial sections. From these observations, the precise position of two flagellar basal bodies, bands, and flagellar rootlets was determined.

Reduction of meckelin leads to general loss of cilia, ciliary microtubule misalignment and distorted cell surface organization

BackgroundMeckelin (MKS3), a conserved protein linked to Meckel Syndrome, assists in the migration of centrioles to the cell surface for ciliogenesis. We explored for additional functions of MKS3p using RNA interference (RNAi) and expression of FLAG epitope tagged protein in the ciliated protozoan Paramecium tetraurelia. This cell has a highly organized cell surface with thousands of cilia and basal bodies that are grouped into one or two basal body units delineated by ridges. The highly systematized nature of the P. tetraurelia cell surface provides a research model of MKS and other ciliopathies where changes in ciliary structure, subcellular organization and overall arrangement of the cell surface can be easily observed. We used cells reduced in IFT88 for comparison, as the involvement of this gene’s product with cilia maintenance and growth is well understood.ResultsFLAG-MKS3p was found above the plane of the distal basal body in the transition zone. Approximately 95% of those basal bodies observed had staining for FLAG-MKS3. The RNAi phenotype for MKS3 depleted cells included global shortening and loss of cilia. Basal body structure appeared unaffected. On the dorsal surface, the basal bodies and their associated rootlets appeared rotated out of alignment from the normal anterior-posterior rows. Likewise, cortical units were abnormal in shape and out of alignment from normal rows. A GST pull down using the MKS3 coiled-coil domain suggests previously unidentified interacting partners.ConclusionsReduction of MKS3p shows that this protein affects development and maintenance of cilia over the entire cell surface. Reduction of MKS3p is most visible on the dorsal surface. The anterior basal body is attached to and moves along the striated rootlet of the posterior basal body in preparation for duplication. We propose that with reduced MKS3p, this attachment and guidance of the basal body is lost. The basal body veers off course, causing basal body rows to be misaligned and units to be misshapen. Rootlets form normally on these misaligned basal bodies but are rotated out of their correct orientation. Our hypothesis is further supported by the identification of novel interacting partners of MKS3p including a kinetodesmal fiber protein, KdB2.

The 3D structure of the apical complex and association with the flagellar apparatus revealed by serial TEM tomography in Psammosa pacifica, a distant relative of the Apicomplexa.

The apical complex is one of the defining features of apicomplexan parasites, including the malaria parasite Plasmodium, where it mediates host penetration and invasion. The apical complex is also known in a few related lineages, including several non-parasitic heterotrophs, where it mediates feeding behaviour. The origin of the apical complex is unclear, and one reason for this is that in apicomplexans it exists in only part of the life cycle, and never simultaneously with other major cytoskeletal structures like flagella and basal bodies. Here, we used conventional TEM and serial TEM tomography to reconstruct the three dimensional structure of the apical complex in Psammosa pacifica, a predatory relative of apicomplexans and dinoflagellates that retains the archetype apical complex and the flagellar apparatus simultaneously. The P. pacifica apical complex is associated with the gullet and consists of the pseudoconoid, micronemes, and electron dense vesicles. The pseudoconoid is a convex sheet consisting of eight short microtubules, plus a band made up of microtubules that originate from the flagellar apparatus. The flagellar apparatus consists of three microtubular roots. One of the microtubular roots attached to the posterior basal body is connected to bypassing microtubular strands, which are themselves connected to the extension of the pseudoconoid. These complex connections where the apical complex is an extension of the flagellar apparatus, reflect the ancestral state of both, dating back to the common ancestor of apicaomplexans and dinoflagellates.

The Microtubular Cytoskeleton of the Apusomonad Thecamonas, a Sister Lineage to the Opisthokonts

Apusomonads are of evolutionary interest because they are close relatives to the supergroup Opisthokonta, which contains both animals and fungi. There are no detailed morphological studies of 'amastigomonad' type apusomonads, such as Thecamonas trahens, despite this species having a sequenced genome. We use serial-section transmission electron microscopy and 3D reconstruction to examine the cell architecture and complete microtubular cytoskeleton of Thecamonas. Thecamonas has two flagella and an anteriorly projecting 'tusk'. The anterior basal body associates with one microtubular root, which travels leftward, and a non-root 'ribbon' of six microtubules that travels down the right side of the cell. The posterior basal body associates with three roots: an eight-membered right root, a doublet left root, and an intermediate singlet root. These rearrange into two bands, both on the left side of the cell. One comprises the left and singlet roots plus one right root microtubule. The other comprises the remaining right root microtubules. A splitting right root and supernumerary singlet root are also present in breviates, ancyromonads, and 'typical excavates', suggesting that these characters are ancestral for much of eukaryote diversity. If so, opisthokonts, and most or all living eukaryotes, probably arose from cells with complex microtubular cytoskeletons.

The flagellar apparatus of Breviata anathema, a eukaryote without a clear supergroup affinity

Breviata anathema is an anaerobic amoeboid flagellate that does not branch within any established ‘supergroup’. Molecular phylogenies suggest affinities to Amoebozoa, Opisthokonta, or apusomonads. Here we describe its flagellar apparatus ultrastructure. Breviata has two basal bodies. The flagellated anterior basal body (AB) is associated with a fan of ∼18 microtubules and a short singlet microtubular root. Three microtubular roots associate with the posterior basal body. One, the right root (RR), is initially a triplet that splits into two parts. The other two are singlets: the left root (LR), and the middle root (MR), which arises on the posterior side of the basal body. The MR, LR and smaller part of RR support the left ventral side of the cell, while the larger part of RR runs down the right. Outer dynein arms were not observed on the flagellar axoneme. The mitochondrion-like organelle sometimes contains some tubular cristae. The posterior flagellar apparatus resembles that of several eukaryotic lineages, particularly apusomonads, ancyromonads, excavates, and myxogastrid amoebozoans. This comparison suggests that the complex flagellar apparatus of myxogastrids is actually plesiomorphic within Amoebozoa. The widely distributed splitting right root and posterior singlet (MR in Breviata) may be plesiomorphies in many eukaryotic lineages, and thus could be features of the last eukaryotic common ancestor.

Comprehensive Ultrastructure of Kipferlia bialata Provides Evidence for Character Evolution within the Fornicata (Excavata)

Carpediemonas-like organisms (CLOs) are important for understanding the evolutionary history of anaerobic excavates (e.g. diplomonads and parabasalids), especially their cytoskeletal traits and the functions of their modified mitochondria (e.g., hydrogenosomes and mitosomes). Kipferlia bialata is probably the most commonly encountered CLO and has an intriguing molecular phylogenetic position within the Fornicata; however, this species has yet to be described at the ultrastructural level. This study provides a comprehensive account of the ultrastructure of this excavate using light microscopy, SEM, and serial TEM sectioning. The pattern of flagellar transformation observed with SEM confirms that the posterior basal body is the 'eldest', enabling us to emend the numbering system and associated terminology of the flagellar apparatus in excavates. This revised terminology is fundamental for comparing the cytoskeletons of the Excavata supergroup with other eukaryotes. Moreover, K. bialata had several unusal features, such as a hood, a distinct gutter within the ventral groove, and hairs along a single flagellar vane. The ultrastractural data reported here significantly improve our understanding of fornicate morphology, and when placed within a molecular phylogenetic context, these data shed light onto patterns of character evolution within the Excavata.

The Ultrastructure of Ancyromonas; a Eukaryote without Supergroup Affinities

The small heterotrophic flagellate Ancyromonas (=Planomonas) lacks close relatives in most molecular phylogenies, and it is suspected that it does not belong to any of the recognized eukaryote 'supergroups', making it an organism of great evolutionary interest. Proposed relatives include apusomonads and excavates, but limited understanding of the ancyromonad cytoskeleton has precluded identification of candidate structural homologies. We present a detailed analysis of the ultrastructure of Ancyromonas through computer-based reconstruction of serial sections. We confirm or extend previous observations of its major organelles (mitochondria, Golgi body, extrusomes, etc.) and pellicle, and distinguish a system of stacked endomembranes that may be developmentally connected to the glycocalyx. Ancyromonas has two basal bodies, each with its own flagellar pocket. The anterior basal body associates with two microtubular elements: a doublet root that runs from between the basal bodies to support the cell's rostrum, and a short singlet root. The posterior basal body is associated with two multi-microtubular structures and a singlet root. One multi-microtubular structure, L1, is a conventional microtubular root. The other structure appears as a curved ribbon of ∼8 microtubules near the basal body, but then flares out into two multi-microtubular elements, L2 and L3, plus two single microtubules. The posterior singlet root originates independently near this second complex. L1, the singlet, L2, and L3 all support the posterior flagellar pocket and channel. We also identified several groups of peripheral microtubules. Possible homologies with the flagellar apparatus of both apusomonads and excavates include a splitting root on the right side of the posterior basal body and a singlet root, both supporting a longitudinal channel or groove associated with the posterior flagellum. The anterior flagellar apparatus in each includes a root supporting structures to the left of the anterior flagellum. Given the probable deep divergences of Ancyromonas, apusomonads and excavates within eukaryotes, it is possible that the eukaryotic cenancestor also possessed these features.

Ultrastructure and Ribosomal RNA Phylogeny of the Free‐Living Heterotrophic Flagellate Dysnectes brevis n. gen., n. sp., a New Member of the Fornicata

Dysnectes brevis n. gen., n. sp., a free-living heterotrophic flagellate that grows under microaerophilic conditions possesses two flagella. The posterior one lies in a ventral feeding groove, suggesting that this flagellate is an excavate. Our detailed electron microscopic observations revealed that D. brevis possesses all the key ultrastructural characters considered typical of Excavata. Among the 10 excavate groups previously recognized, D. brevis displays an evolutionary affinity to members of the Fornicata (i.e. Carpediemonas, retortamonads, and diplomonads). Firstly, a strong D. brevis-Fornicata affinity was recovered in the phylogenetic analyses of small subunit ribosomal RNA (SSU rRNA) sequences, albeit the internal branching pattern of the D. brevis+Fornicata clade was not resolved with confidence. Corresponding to the SSU rRNA phylogeny, D. brevis and the Fornicata shared the following components of the flagellar apparatus: the arched B fiber bridging the right root; a posterior basal body; and a left root. Combining both morphological and molecular phylogenetic analyses, D. brevis is classified as a new free-living excavate in the Fornicata incertae sedis.

The flagellar apparatus of heteroloboseans.

The flagellar apparatus of four heterolobosean species Percolomonas descissus, Percolomonas sulcatus, Tetramitus rostratus, and Naegleria gruberi were examined. P. descissus lives in oxygen-poor water. It is a quadriflagellated cell with a ventral groove. The two pairs of basal bodies are connected to an apical structure from which the peripheral dorso-lateral microtubules and a short striated rhizoplast originate. There is one major microtubular root, R1, which originates from the posterior basal body pair and splits into left and right portions that support the sides of the ventral groove. The anterior pair of basal bodies is associated with a root of four to five microtubules that runs to the left of the groove. This organisation is similar to that previously reported for Psalteriomonas, Lyromonas, and Percolomonas cosmopolitus. Percolomonas sulcatus has two parallel pairs of basal bodies, each of which is associated with a well-developed R1 root. These roots divide to give two distinct left portions and one merged right portion that support the margins of the slit-like ventral groove. Tetramitus rostratus has two pairs of basal bodies, several rhizoplast fibres, and two R1 roots. Each R1 root supports one wall of the ventral groove. Naegleria gruberi may have two pairs of basal bodies, each associated with a microtubular root and one long rhizoplast fibre. From available data, a 'double bikont'-like organisation of the heterolobosean flagellar apparatus is inferred, where both of the eldest basal bodies have largely 'mature' complements of microtubular roots. The cytoskeletal organisation of heteroloboseans is compared to those of (other) excavates. Our structural data and existing molecular phylogenies weaken the case that Percolomonas, Psalteriomonas, and Lyromonas are phylogenetically separable from other heteroloboseans, undermining many of the highest-level taxa proposed for these organisms, including Percolozoa, Striatorhiza, Percolomonada, Percolomonadea, and Lyromonadea.

An ultrastructural and molecular study of Hyperamoeba dachnaya, n. sp., and its relationship to the mycetozoan slime moulds

Hyperamoeba dachnaya, a new taxon affiliated with Hyperamoeba flagellata, is described from freshwater anaerobic sediments. Organisms exist as amoeboid flagellates, amoebae and cysts. The flagellates of H. dachnaya are distinguished from those of H. flagellata by larger size and a longer anteriorly-directed finger-shaped pseudopodium. H. dachnaya cysts have bilaminar walls with connectives between the outer and inner layers appearing to be T-shaped spines, while cyst walls of H. flagellata are smooth. H. dachnaya has two basal bodies and a single anteriorly-directed flagellum emerging from the anterior one (BB1). A fibrillar rootlet with a microtubule organising centre (MTOC; ‘R1’) arises from a diaphragm-shaped basal plate at the base of BB1; a short striated fibre (SSF) covers the dorsal side of BB1 and initiates microtubular rootlets ‘R2’ and ‘R3’ and the fibrillar bridge leading to microtubular rootlet ‘R4’. ‘R5’ is composed of 2 microtubules splitting from R4 and 2 others initiating by BB1. The posterior basal body is associated with a fibrillar posterior parakinetosomal structure. A long striated fibre arises in association with the right end of the SSF. A Golgi apparatus is associated with the flagellar apparatus. The flagellar apparatus is present internally in amoebae. All three stages have mitochondria with tubular cristae and an electron-dense central body. Analysis of small subunit ribosomal RNA sequences shows H. dachnaya branching with the myxogastrids within the mycetozoa, but polyphyletic with a nominal Hyperamoeba sp. isolate that is morphologically similar to H. flagellata. We reject the suggestion that H. flagellata and this Hyperamoeba sp. isolate of Zaman et al. (1999) are conspecific. The study reveals extensive similarities between Hyperamoeba and the flagellated stages of myxogastrids.

Glossomastix chrysoplasta n. gen., n. sp. (Pinguiophyceae), a new coccoidal, colony-forming golden alga from southern Australia

SUMMARY Glossomastix chrysoplasta gen. et sp. nov. is described from cultures isolated from sandstone rubble, Sorrento Back Beach, Mornington Peninsula, Victoria, Australia. The alga forms wall-less, coccoidal vegetative cells that congregate in mucilaginous colonies and reproduce by successive bipartition. Plastids have girdle lamellae and partially embedded pyrenoids that are traversed by cytoplasmic channels. Zoospores are uniflagellate and swim poorly; a narrow lingulate pseudopod provides their primary form of motion. The single flagellum, which lacks hairs, a flagellar swelling, and autofluorescence, is the equivalent of the posterior flagellum in other golden algae. The anterior flagellum is absent; the basal body with which it would normally be associated is blind. The flagellar apparatus has two basal bodies, three microtubular roots, and a rhizoplast. The posterior (elder) basal body has a transitional helix that is proximal to the basal plate. Glossomastix chrysoplasta, placed in the Pinguiophyceae on the basis of molecular sequence and biochemical data, shares some ultrastructural features with other members of the class, especially Polypodochrysis teissieri, which has similar zoospores, but it also differs from other pinguiophytes in many respects. Glossomastix chrysoplasta is the pinguiophyte with, on average, the largest cells (exclusive of external materials), and it is the only one with a colonial habit.

On core jakobids and excavate taxa: the ultrastructure of Jakoba incarcerata.

The cellular organisation of the 'excavate' flagellate Jakoba incarcerata Bernard, Simpson and Patterson 2000 is described. Cells have one nucleus and dictyosome. The putative mitochondria lack cristae. Two flagella (anterior and posterior) insert anterior to the feeding groove. The posterior flagellum bears a dorsal vane. An 'anterior' microtubular root arises against the anterior basal body. Two main microtubular roots, left and right, and a singlet 'root' arise around the posterior basal body and support the groove. Non-microtubular fibres termed 'A', 'B', 'I', and 'composite' associate with the right root. A multilaminar 'C' fibre associates with the left root. The cytoskeleton of J. incarcerata indicates a common ancestry with other excavate taxa (i.e. diplomonads, retortamonads, heteroloboseids, 'core jakobids', Malawimonas, Carpediemonas, and Trimastix). Overall, J. incarcerata is most similar to (other) core jakobids, namely Jakoba libera, Reclinomonas, and Histiona. We regard J. incarcerata as a core jakobid and identify the group by the synapomorphy 'vanes restricted to dorsal side of the posterior flagellum'. The anterior root and position of the B fibre (and presence of dense inclusions in the cartwheels and a conscpicuous singlet root-associated fibre) in J. incarcerata are novel for core jakobids and argue for close relationships with Trimastix and/or Heterolobosea. The C fibre is similar in substructure to the costal fibre of parabasalids and it is possible that the structures are homologous.

The ultrastructure of Trimastix marina Kent 1880 (Eukaryota), an excavate flagellate

Summary The ultrastructure of Trimastix marina is documented for the first time. This protist has four flagella which insert at the head of a longitudinal feeding groove. The basal bodies are elongate and arranged in a cruciate pattern. The anterior and posterior basal bodies lack cartwheels. The posterior flagellum bears two vanes. The anterior flagellum is thickened. The cell has a poorly organised Golgi-like region and small hydrogenosome-like organelles. The flagellar apparatus includes left and right major microtubular roots which support the margins of the groove, and a third, major anterior root associated with a fan of microtubules which supports the dorsal side of the cell. There is also a singlet ‘root’ associated with the groove, a minor anterior root and a suite of non-microtubular structures (including the A, B, C and I fibres). Arrays of microtubules diverge from both left and right roots to support the floor of the groove. Some microtubules from the right array converge to form an inner right root. Halfway down the cell the left root ends, while the right root reduces and associates with a sheet-like striated/dense composite fibre. The groove ends as a cytopharynx, with a ‘tongue’ structure associated with its opening. Trimastix marina is most similar to T. pyriformis, the only previously studied member of Trimastix. Among the other ‘excavate taxa’, Trimastix is most similar to ‘core jakobids’, Malawimonas, Carpediemonas and retortamonads but also shares several unusual features with some heteroloboseids. The complexities and detail of structural similarities amongst various excavate taxa support the ‘excavate hypothesis’ (i.e. that the excavate taxa have a common excavate ancestor) but suggest that understanding the relationships amongst the excavate taxa through morphological data will be a complex task.

Malawimonas jakobiformis n. gen., n. sp. (Malawimonadidae n. fam.): A Jakoba‐like Heterotrophic Nanoflagellate with Discoidal Mitochondrial Cristae

ABSTRACT Malawimonas jakobiformis n. gen., n. sp., is established for a bacterivorous heterotrophic nanoflagellate isolated from the Malawi shore of Lake Nyasa (eastern Africa). Trophic stages observed were anteriorly biflagellate and naked. The posterior flagellum of a trophic cell resided in a conspicuous groove on the ventral surface, and bore a prominent vane. A Golgi stack and a mitochondrion with discoidal cristae were present anterior to the nucleus. The kinetid consisted of two short, slightly separated basal bodies, four microtubular roots, and associated fibers and bands. The three microtubular roots associated with the posterior basal body were associated with the ventral groove, while the single root associated with the anterior basal body gave rise to secondary cytoskeletal microtubules. Dividing cells became rounded, with persistent flagella. Cysts were uninucleate, and had thin organic walls without clearly differentiated apertures or ornamentation but with conspicuous attachment pads. Kinetid elements were present within cysts. On the basis of microscopical features, especially those of the kinetid, the nearest relatives of M. jakobiformis are the mitochondriate “jakobid” protists (families Histionidae and Jakobidae) and the amitochondriate retortamonads. Malawimonadidae n. fam. is established to accommodate this species.

Architecture of the Spermatozoid of Selaginella australiensis

Architecture of the Spermatozoid of Selaginella australiensis

Cercomonads and their relationship to the myxomycetes

Summary The typical cercomonad structure (based on original investigations of Heteromita sp., Cercomonas agilis and literature data) is as follows: the amoeboflagellate cell is covered by only a distinct glycocalyx; there are two flagella, extrusomes, microbodies, mitochondria with vesicular cristae, and the nucleus has a sharp end directed towards the basal bodies. Absolute orientation of the flagellar apparatus reveals an anterior basal body directed in a forward or ventral direction, and the posterior basal body is located on the ventral side and is directed to the right. There are 2–4 lateral microtubular rootlets, a layered structure and a nuclear fibrillar rootlet. A dictyosome occupies the dorsal position. The life-cycle of cercomonads includes a plasmodial stage. Comparison of cercomonad morphology and life-cycles with those of myxomycetes (predominantly with zoospores of protostelids) and Hyperamoeba flagellata (a fresh-water protist of uncertain taxonomic position) reveals the homology of structures in the flagellar rootlet system; the same absolute orientation of the flagellar apparatus and dictyosome; and mitochondria with vesicular cristae. Homology of the main stages in the life-cycles of all three groups has been also proposed. The relationship of cercomonads and protostelids has been confirmed by new ultrastructural data, and H. flagellata is considered as a bridge between these two groups. This view contradicts molecular data which usually demonstrates a long distance between cercomonads and myxomycetes.

The fine structure of the male gamete of Ectocarpus siliculosus (Ectocarpales, Phaeophyceae). II. The flagellar apparatus

The fine structure of the flagellar apparatus of male gametes of Ectocarpus siliculosus has been studied in negatively stained whole-mount preparations of isolated flagellar apparatuses and by transmission electron microscopy of embedded whole cells and flagellar apparatuses. Reconstructions from serial sections revealed a single absolute configuration and new structural details of the flagellar apparatus. A set of 5 microtubular roots is associated with the 2 flagellar basal bodies: the major anterior root consisting of 9 microtubules originates at the anterior basal body and loops through the anterior part of the cell. Cytoplasmic microtubules originate from this root at the apex of the cell and splay out in a posterior direction through the cell, thus determining cell shape. A broad microtubular band composed of a 9-membered bypassing root and a 3-membered major posterior root runs across the basal bodies. Two additional flagellar roots, the minor anterior and minor posterior rootlets, consist of a single microtubule each. The proximal end of the posterior basal body is laterally connected to the anterior basal body by a cross-striated connective (deltoid band). The basal bodies are connected to the nucleus by a small rhizoplast, and several other fibrous structures are associated with the basal bodies. The results are discussed in relation to earlier observations on flagellar apparatus organization in brown algae.

The fine structure of the male gamete of Ectocarpus siliculosus (Ectocarpales, Phaeophyceae). II. The flagellar apparatus

The fine structure of the flagellar apparatus of male gametes of Ectocarpus siliculosus has been studied in negatively stained whole-mount preparations of isolated flagellar apparatuses and by transmission electron microscopy of embedded whole cells and flagellar apparatuses. Reconstructions from serial sections revealed a single absolute configuration and new structural details of the flagellar apparatus. A set of 5 microtubular roots is associated with the 2 flagellar basal bodies: the major anterior root consisting of 9 microtubules originates at the anterior basal body and loops through the anterior part of the cell. Cytoplasmic microtubules originate from this root at the apex of the cell and splay out in a posterior direction through the cell, thus determining cell shape. A broad microtubular band composed of a 9-membered bypassing root and a 3-membered major posterior root runs across the basal bodies. Two additional flagellar roots, the minor anterior and minor posterior rootlets, consist of a single microtubule each. The proximal end of the posterior basal body is laterally connected to the anterior basal body by a cross-striated connective (deltoid band). The basal bodies are connected to the nucleus by a small rhizoplast, and several other fibrous structures are associated with the basal bodies. The results are discussed in relation to earlier observations on flagellar apparatus organization in brown algae.

The Blepharoplast of the Midstage Spermatid of Andreaeobryum macrosporum (Bryophyta: Andreaeopsida)

The blepharoplast of the midstage spermatid of Andreaeobryum macrosporum has a four-layered multilayered structure (MLS) and two superposed, slightly staggered, and overlapping basal bodies. The spline is composed of 30 parallel microtubules at its maximum width. Subtending the spline anteriorly, the lamellar strip (LS) is 1.83 pm long and 0.92 pm wide and has an elongated, wedge-shape with a pointed right anterior tip. Viewing the blepharoplast dorsally from anterior to posterior, the anterior basal body (ABB), approximately 0.95 pm in length, is situated over the right side of the MLS and is inserted at a level 0.42 pCm behind the spline's anterior apex. The posterior basal body (PBB), 2.75 pcm long, is positioned over the left side of the MLS and inserted 0.75 pm behind the spline's anterior apex. The ABB is essentially parallel with the spline microtubules over its entire length, while the anterior portion of the PBB curves outward gradually and becomes parallel with the spline in its posterior region. The combination of features that distinguish the midstage spermatid of Andreaeobryum from other mosses are its wide spline, wedge-shaped lamellar strip, comparatively short basal bodies, small length of stagger between basal bodies, and the PBB that curves gradually outward from its anterior tip. The data available for Andreaea suggest that its midstage spermatid resembles that of Andreaeobryum, although reconstructions and additional micrographic data are needed for both Andreaea and Takakia before generalizations for the class Andreaeopsida can be made. Andreaeobryum belongs to an unusual line of bryophyte evolution that also includes Andreaea and Takakia (Murray 1988; Renzaglia et al. 1991). While Andreaea is an old and well-established genus, Andreaeobryum is relatively new, having been described in 1976 by Steere and Murray (1976) and further defined by Murray (1988). Andreaea and Andreaeobryum have been grouped together in either the class Andreaeopsida (Crum & Anderson 1981; Murray 1988) or subclass Andreaeidae (Schofield 1985; Vitt 1984). According to Murray (1988), Andreaea and Andreaeobryum belong to separate orders, Andreaeales and Andreaeobryales, within the primitive class Andreaeopsida. The two genera are united by sporeling features and mode SAuthor for correspondence. e-mail: AnnRushing@ baylor.edu FIGUREs 1-6. Blepharoplast anatomy of Andreaeobryum macrosporum. -1-3. Tangential sections. -1. The spline anterior with its acutely curved left margin and closed aperture. Above, the extended triplet is part of the posterior basal body (cf. Fig. 18). -2. Slightly oblique section showing the left-marginal curvature of the subtending lamellar strip and the spline aperture (between arrows). -3. The spline aperture extends posteriorly beyond the lamellar strip where it closes by convergence of the microtubules on its right side with those on the left. -4. Near-median longitudinal section through the anterior basal body and the distal transition zone with its stellate pattern. The anterior mitochondrion is just becoming positioned beneath the lamellar strip. -5. Oblique-tangential section showing the full longitudinal extent of the anterior stellate pattern. -6. Oblique-tangential section section through the posterior basal body and the subtending spline and nucleus. Key to labeling: ABB, anterior basal body; AF, anterior flagellum; AM, anterior mitochondrion; ASP, anterior stellate pattern; EH, extended hub of basal body; ET, extended triplet; LS, lamellar strip; N, nucleus; PBB, posterior basal body; PSP, posterior stellate pattern; S, spline; S1-S4, specific strata of the multilayered structure; SA, spline aperture; bracket ([), lamellar strip. All micrographs are printed at a magnification of X67,500 except Fig. 6 where the magnification is X47,500. Except as otherwise noted for Figure 18, each scale bar represents