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.     

The Philodinavidae (Rotifera Bdelloidea): a special family

Here we focus on the fine morphology and present observations on the biology of representatives of family Philodinavidae. Philodinavus paradoxus and Henoceros falcatus were collected and cultured under laboratory conditions. Rotifers of both species are tiny, about 200 μm long, have protrudable trophi and creep with leech-like movements. A very specific feature of these rotifers is their corona; a V-shaped lower lip contours the mouth opening, bilaterally bordered by two arched cuticular structures (‘cheeks’). The presence of the cheeks is a feature shared by the third genus, Abrochtha. On the basis of the morphology and biology of the three genera, we advance the hypothesis that Philodinavus is a primitive bdelloid, and that it can have originated Henoceros and Abrochtha, from which the other bdelloids could have stemmed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Tsukubamonas globosa n. gen., n. sp., a novel excavate flagellate possibly holding a key for the early evolution in "Discoba"

We report the ultrastructure and phylogenetic position of a free-living heterotrophic flagellate, Tsukubamonas globosa n. gen., n. sp. This flagellate was isolated from a pond in the University of Tsukuba, Japan. Under light microscopy, the spherical vegetative cells were naked and highly vacuolated, and always swam with rotating motion. Electron microscopic observations revealed that T. globosa possessed a ventral feeding groove, which is one of the hallmark characteristics of the supergroup Excavata. The position of T. globosa was unresolved in the small subunit ribosomal RNA phylogeny. On the other hand, a multigene phylogeny using α-tubulin, β-tubulin, actin, heat shock protein 90, and translation elongation factor 2 robustly united T. globosa with members of the "Discoba" clade of Excavata, composed of jakobids, euglenozoans, and heteroloboseans, although the precise position of T. globosa in this clade remained unresolved. Our detailed morphological comparisons elucidated that T. globosa possessed a novel set of morphological features, and could not be classified into any taxa in the Discoba clade. Instead we classified T. globosa into Tsukubamonadidae n. fam. under Tsukubamonadida n. ord.     

Aurearenophyceae classis nova, a new class of Heterokontophyta based on a new marine unicellular alga Aurearena cruciata gen. et sp. nov. inhabiting sandy beaches

A new heterokontophyte alga, Aurearena cruciata gen. et sp. nov., was isolated from sandy beaches in Japan. Isolates were characterized by light and electron microscopy, spectroscopy of pigment composition, and molecular phylogenetic analyses using 18S rDNA and rbcL. The alga usually possessed a cell wall but also retained two heterokont flagella beneath the cell wall. Each walled cell first produced only a single flagellate cell that subsequently divided into two flagellate cells. Electron-opaque vesicles, possibly associated with cell wall formation, were observed beneath the cell membrane. The chloroplast consisted of two compartments, each enclosed by a chloroplast envelope and the inner membrane of the chloroplast endoplasmic reticulum; these two compartments were surrounded by a common outer membrane of chloroplast endoplasmic reticulum. Molecular phylogenetic trees suggested that this alga was a new and independent member of the clade that included the Phaeophyceae and Xanthophyceae (PX clade). A new class, Aurearenophyceae classis nova was proposed for A. cruciata.     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR ORIENTATION IN THE COLONIAL GREEN ALGA GONIUM PECTORALE (VOLVOCALES)1

Vegetative cells of Gonium pectorale have a fine structure similar to that of Chlamydomonas. In addition, three zones comprise an extracellular matrix; a fibrillar sheath and tripartite boundary surround individual cells, and a fragile capsule zone surrounds the entire colony. Cytokinesis is accomplished by a phycoplast and cleavage furrow. The flagellar apparatus of the immature vegetative cell of this colonial alga is similar to that of Chlamydomonas, but the basal bodies are slightly separated at their proximal ends. The four microtubular rootlets alternate between two and four members. During development, the basal bodies become further separated and nearly parallel. The distal fiber is stretched, but it remains attached to both basal bodies. At maturity, the basal bodies of peripheral cells of the colony have rotated in opposite directions on their longitudinal axes resulting in a displacement of the distal fiber to one side, an asymmetrical orientation of the rootlets and loss of 180° rotational symmetry. Central cells remain similar to Chlamydomonas in that basal bodies do not rotate, rootlets are cruciate, the distal fiber remains medially inserted and 180° rotational symmetry is conserved. A “pin-wheel” configuration of flagellar pairs and the orientation of parallel rootlets toward the colony perimeter probably accounts for the rotation of the colonies during forward swimming. In addition, these ultrastructural features support the traditional placement of G. pectorale as an intermediate between the unicellular Chlamydomonas and the more complex colonial volvocalean genera.     

THE FLAGELLAR APPARATUS OF HYMENOMONAS CORONATA (PRYMNESIOPHYTA)1

The ultrastructure of Hymenomonas coronata Mills was reinvestigated to determine the microarchitecture of the flagellar apparatus. Cell morphology and flagellar apparatus structure are very similar to those of Pleurochrysis. Some important variations occur. First, a crystalline root (= compound root) is absent on microtubular root 1. Second, a two-stranded microtubular root emanates at a right angle from microtubular root 2. Third, a fibrous root emanates from the dorsal region between the basal bodies and extends to the cell's right, paralleling microtubular root 3. These similarities and variations in flagellar apparatus characters are discussed in reference to known variations in the Prymnesiophyta.     

Evolution of the Toxoglossa venom apparatus as inferred by molecular phylogeny of the Terebridae

Toxoglossate marine gastropods, traditionally assigned to thefamilies Conidae, Terebridae, and Turridae, are one of the mostpopulous animal groups that use venom to capture their prey.These marine animals are generally characterized by a venomapparatus that consists of a muscular venom bulb and a tubularvenom gland. The toxoglossan radula, often compared with a hypodermicneedle for its use as a conduit to inject toxins into prey,is considered a major anatomical breakthrough that assistedin the successful initial radiation of these animals in theCretaceous and early Tertiary. The pharmacological success oftoxins from cone snails has made this group a star among biochemistsand neuroscientists, but very little is known about toxins fromthe other Toxoglossa, and the phylogeny of these families islargely in doubt. Here we report the first molecular phylogenyfor the Terebridae and use the results to infer the evolutionof the venom apparatus for this group. Our findings indicatethat most of the genera of terebrids are polyphyletic, and onespecies ("Terebra" (s.l.) jungi) is the sister group to allother terebrids. Molecular analyses combined with mapping ofvenom apparatus morphology indicate that the Terebridae havelost the venom apparatus at least twice during their evolution.Species in the genera Terebra and Hastula have the typical venomapparatus found in most toxoglossate gastropods, but all otherterebrid species do not. For venomous organisms, the dual analysisof molecular phylogeny and toxin function is an instructivecombination for unraveling the larger questions of phylogenyand speciation. The results presented here suggest a paradigmshift in the current understanding of terebrid evolution, whilepresenting a road map for discovering novel terebrid toxins,a largely unexplored resource for biomedical research and potentialtherapeutic drug development.     

Ultrastructure of Gyrodinium spirale, the type species of Gyrodinium (Dinophyceae), including a phylogeny of G. dominans, G. rubrum and G. spirale deduced from partial LSU rDNA sequences

A detailed ultrastructural analysis of the type species of Gyrodinium, G. spirale, was made based on cells collected from Skagerrak and southern Kattegat (Denmark). This material is considered very similar to the type material studied by Bergh from southern Kattegat. The analysis revealed many characters typical for dinoflagellates as well as a number of previously undescribed features. Here, emphasis was given to a three-dimensional configuration of the flagellar apparatus, the surface ridges, and the nuclear capsule. The latter had a rather complex ultrastructure consisting of two wall-like layers surrounded by membranes, with nuclear pores restricted to globular invaginations of these layers. To overcome difficulties with culturing of many auto- and heterotrophic dinoflagellates, we designed a specific reverse primer to amplify ca. 1800 base pairs of nuclear-encoded LSU rDNA. Using this approach, LSU rDNA sequences were determined from three heterotrophic species of Gyrodinium, including the type species. Using other alveolates (i.e. ciliates and Apicomplexa) as outgroup species, phylogenetic analyses based on Maximum Likelihood, Maximum Parsimony, and Neighbor-Joining supported Gyrodinium as a separate lineage. Unfortunately, the nearest sister group to Gyrodinium could not be established due to low bootstraps support for the deep branching pattern.     

Fractionation of suspension cultures of wild carrot and kinetics of membrane labeling

Summary Wild carrot (Daucus carota L.) cells, grown in suspension culture, were labeled with radioactive precursors and fractionated into constituent membranes to be analyzed for specific radioactivity. Results show rapid incorporation of [³H] leucine into endoplasmic reticulum (ER)-, Golgi apparatus-, and plasma membrane/tonoplast-enriched fractions. The time lag between incorporation into ER and its appearance in Golgi apparatus or plasma membrane/tonoplast were less than 5 minutes. With an average time of 3–4 minutes for cisternal formation estimated from studies with monensin, and an average of 5 cisternae per dictyosome (total transit time of 15–20 minutes), it was not possible to account for early incorporation of radioactivity into plasma membranes by passage of proteins from ER to plasma membrane via the Golgi apparatus. To account for the findings, it would appear that at least some proteins were delivered to the plasma membrane via the first membranes that exited (i.e., mature face vesicles) from the Golgi apparatus post-pulse and that some of these proteins had been translated and inserted into membranes at or near the mature face of the Golgi apparatus.