COMPARATIVE CYTOLOGY AND TAXONOMY OF THE ULVAPHYCEAE. I. THE ZOOSPORE OF ULOTHRIX ZONATA (CHLOROPHYTA)1

This fine structural study of the quadriflagellate zoospore of Ulothrix zonata (Weber & Mohr) Kützing, with special attention to the flagellar root system, demonstrates that it is very similar to the zoospore of Ulva lactuca L. in several aspects. Common features include the presence of a cruciate root system (4-2-4-2 type), a non-striated band that connects basal bodies, a so-called terminal cap, and system I and system II striated root components. Only slight differences exist, i.e. in the shape of the terminal cap, and in the number and position of the system II root components. It is concluded that the taxonomic affinities of U. zonata lie with the Ulvaphyceae sensu Stewart and Mattox rather than with the Chlorophyceae. Additional support for this conclusion is the discovery of tiny, flat body scales on the zoospore of U. zonata. A summary of the distinctive characteristics of the Chlorophyceae, Charophyceae and Ulvaphyceae reflecting the current state of knowledge is given.     

STRUCTURE OF THE ANISOGAMETES OF THE GREEN SIPHON PSEUDOBRYOPSIS SP. (CHLOROPHYTA)1

The fine structure of the male and female gametes of Pseudobryopsis, particularly that of the flagellar apparatus, is compared with that of swarmers of other green algae. There is general similarity, with differences in detail, to the Ulvales and other green siphons that have been studied. The similarities include overlapping basal bodies, the capping plate type of connective between basal bodies, terminal caps, and system II fibrous roots (rhizoplasts). The capping plate of the female gamete differs from that in other green siphons and the Ulvales in form and in the presence of a faint striation. A diagram illustrating the actual arrangement of the components of the flagellar apparatus is given, along with a discussion of the fact that the mirror image of the true arrangement has been given in some reports on ulvaphycean algae.     

A Phagomyxa-like Endoparasite of the Centric Marine Diatom Bellerochea malleus: A Phagotrophic Plasmodiophoromycete1

In September 1993 the marine centric diatom, Bellerochea malleus (Brightwell) Heurck, collected in the Wadden Sea near List/Sylt, was parasitized by a Phagomyxa algarum-like organism. Karling (1944) reported Phagomyxa algarum Karling in North Carolina as a parasite of the filamentous brown algae Ectocarpus and Pylaiella. The Bellerochea parasite develops an endocytoplasmic Plasmodium and incorporates host cytoplasm into a large, central digestion vacuole, by a form of phagocytosis. Later on, the Plasmodium cleaves to form a zoosporangiosorus. Each zoosporangium is surrounded by a thin wall. It releases zoospores (2.5 × 4 μm) with two unequal flagella, an anterior (4 μm long) and a posterior (8 μm long). Cystosori and cysts could not be detected. The ultrastructure of the zoosporangia and zoospores was investigated, with particular attention to the flagellar apparatus and its rearrangement during zoospore release. This process is very similar to that recorded for zoospores of the plasmodiophoromycete Polymyxa graminis Ledigham (Barr and Allan, 1982). The Bellerochea parasite is closely related to or identical with Phagomyxa algarum. The taxonomic position of Phagomyxa is discussed. In spite of its phagotrophic nutrition and the possible lack of cystosori and cysts, Phagomyxa should be regarded as a member of the Plasmodiophoromycota (or Plasmodiophorida) but not included in a separate order Phagomyxida as proposed by Cavalier-Smith (1993a).     

ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS OF BIFLAGELLATE ZOOSPORES OF ENTEROMORPHA FLEXUOSA SSP. PILIFERA (ULVOPHYCEAE,CHLOROPHYTA)1

The absolute configuration of the flagellar apparatus of biflagellate zoospores of Enteromorpha flexuosa (Wulfen ex Roth.) J. Agardh ssp. pilifera (Kütz.) Bliding was determined. Viewed from the anterior of the cell, the flagellar apparatus shows 180° rotational symmetry with a counter-clockwise absolute orientation of its components. In longitudinal sections, the posteriorly directed basal bodies form an angle of about 170°–180° to one another. A reduced striated distal fiber connects the two basal bodies. The cruciate microtubular rootlet system has a 4–2–4–2 alternation pattern. Striated microtubule-associated components (SMACs or system I-fibers) and rhizoplasts (or system II fibers) accompany the two-membered rootlets. Striated bands connect the proximal sheaths with the four-Membered rootlets. The bilobate terminal caps do not completely cover the proximal ends of the basal bodies. This is the first ultrastructural study of biflagellate zoospores in a member of the Ulvales.     

THE FLAGELLAR DEVELOPMENT CYCLE OF THE UNIFLAGELLATE PELAGOMONAS CALCEOLATA (PELAGOPHYCEAE)1

Vegetative cells of Pelagomonas calceolata Andersen & Saunders were confirmed to possess a reduced flagellar apparatus, consisting of a single basal body/flagellum that is not accompanied by either flagellar roots or a barren basal body. Just prior to division, the parental flagellum retracts (or is abscised) as two new basal bodies/flagella arise de novo. During cytokinesis the parental basal body segregates with a new basal body/flagellum, briefly producing a progeny cell typical of other known uniflagellates (i.e. containing a basal body/flagellum and accompanying barren basal body). The parental basal body then disintegrates or "transforms" out of existence, leaving both progeny cells with a single basal body/flagellum (i.e. neither progeny cell possesses any vestige of a mature flagellum/basal body ). Pelagomonas calceolata belongs to a lineage of chromophyte algae characterized by having a reduced flagellar apparatus, but it is the only known species, not only in this lineage but among all eukaryotes, to have undergone the complete elimination of the mature flagellum /basal body .     

STRUCTURE AND SIGNIFICANCE OF THE CRYPTOMONAD FLAGELLAR APPARATUS. I. CRYPTOMONAS OVATA (CRYPTOPHYTA)1

The absolute configuration of the flagellar apparatus in Cryptomonas ovata has been elucidated and found to be similar to that reported for Chilomonas paramecium. Variations apparent in the flagellar apparatus of Cryptomonas ovata include the presence of striations in the mitochondrion associated lamella, a rhizostyle which does not bear wing-like extensions from the microtubules and does not lie close to the nucleus, and a striated fibrous anchoring structure associated with one basal body which has not hitherto been described. The flagellar apparatus also includes a four stranded microtubular root which traverses into the anterior dorsal lobe of the cell, a striated fibrous root which is associated with a five stranded microtubular root, and a two stranded Cr root. The homologous nature of these roots to those in the larger cryptomonads is discussed in relation to the apparent reduction in flagellar apparatus size and complexity among the smaller cryptomonads. A diagrammatic reconstruction of the flagellar apparatus of Cryptomonas ovata is also presented.     

ULTRASTRUCTURE OF THE GAMETE OF PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

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

The Jakobid Flagellates: Structural Features of Jakoba, Reclinomonas and Histiona and Implications for the Early Diversification of Eukaryotes

ABSTRACT. Jakobid flagellates are small, free-living, bacterivorous heterotrophs, with similar morphology, asexual reproduction, and nucleocytoplasmic ultrastructural features at interphase and during cell division. Jakoba is typified by aloricate trophic cells, each containing a branched mitochondrion with prominent nucleoids and flattened cristae. Reclinomonas and Histiona are characterized by loricate trophic cells, each with an unbranched mitochondrion without prominent nucleoids or otherwise differentiated regions and bearing tubular cristae. An undescribed genus is typified by aloricate cells, each with an unbranched mitochondrion bearing discoidal cristae. I propose, on the basis of cytoskeletal architecture and other structural and developmental features, that jakobids are ancestral mitochondrial protists, sister taxa to the amitochondnal retortamonads and ancestral to diverse lineages of mitochondrial eukaryotes. Application of different classification paradigms produces different family-level taxonomies for jakobids.     

Flagellar Photoresponses of Chlamydomonas Cells Held on Micropipettes: III. Shock Response

Using high-speed microcinematography flagellar shock responses of a great number of Chlamydomonas cells, free-swimming as well as immobilized on micropipettes, were investigated in this study. Responses were elicited by flashes, by blue, red or white light steps or occurred “spontaneously”. A large variety of shock responses has been found, in part due to various kinds of flagellar deactivations. Typical courses of flagellar responses are described in detail. The major part of the analyzed responses consists of a transition back from undulatory beats, characteristic for shock responses, to the normal breaststroke beats, probably as a result of a decreasing Ca⁺⁺ concentration at the axoneme. It is known that undulatory beats are triggered by a transient strong influx of Ca⁺⁺ ions into the flagella. Responses are initiated simultaneously in the two flagella but are finished independently. Differences in cis (= next to the stigma) and trans (= far from it) flagella were observed but were not consistent. The origin of the deactivations during the shock responses is discussed, as well as an involvement of basal body-associated structures in flagellar beating and in the change between the two beating modes. The comparison of the two fundamentally different types of beating and a close study of transitional beats may convey insight into the complexity of flagellar beating in Chlamydomonas.