Reinhard Schnetter

Lotharella polymorpha sp. nov. (Chlorarachniophyta) from the coast of Portugal

Abstract Lotharella polymorpha was isolated from a sample of marine sediment collected at São Rafael, Albufeira, Portugal, in July 1998. Typical characteristics of a chlorarachniophyte alga are: chloroplasts containing chlorophylls a and b and lutein, the presence of a nucleomorph between the outer and inner pair of membranes surrounding the chloroplasts, and uniflagellate zoospores. In L. polymorpha, the nucleomorph is located in a periplastidial compartment beside the base of the pyrenoid. The pyrenoid is divided into two halves by the inner pair of chloroplast membranes. The position of the nucleomorph and the structure of the pyrenoid indicate that the new isolate belongs to the genus Lotharella. Lotharella polymorpha differs from the other species L. amoeboformis and L. globosa in the shape of the sessile cells and at the subcellular level. While amoeboid stages and meroplasmodia are lacking in L. globosa, L. polymorpha forms a meroplasmodium with two differently shaped types of sessile walled amoebae. Coccoid cells, migrating amoebae, heliozoan-like cells and zoospores also occur. Stellate amoeboid cells, as described for L. amoeboformis, were not detected. The pyrenoids of L. polymorpha have no stalks and their capping vesicles are filled with an amorphous substance. Sessile amoebae have a thick, compact, and electron-dense cell wall with pores. Because of these specific characteristics, we describe the first isolate of Lotharella found in the Atlantic Ocean as a new species, L. polymorpha.

Taxonomy of some North Atlantic Dictyota species (Phaeophyta)

Dictyota Lamouroux is a troublesome marine algal genus, as there are few morphological and anatomical differences among species but considerable infraspecific variation. In some tropical areas inhabited by several Dictyota species it may be often difficult to distinguish them from each other. For example van den Hoek (1969), in a study on the algal vegetation of Curacao, considered Dictyota bartayresii Lamouroux and D. divaricata Lamouroux to be but “extremes” of D. dichotoma (Hudson) Lamouroux.

Nuclear behaviour during the life cycle of Derbesia (Chlorophyceae)

Changes of DNA content of nuclei during the life cycle of Derbesia tenuissima, D. marina and D. cf. novae-zelandiae have been studied under culture conditions. In D. tenuissima ranges of DNA contents in the nuclei of the sporophytic filaments, gametophytes and macrogametes are identical, and the nuclei are hence considered as haploid. Karyogamy is indicated by higher DNA contents of nuclei in young sporangia of heterokaryotic sporophytes. There are no indications of karyogamy in homokaryotic sporophytes raised from macrogametes by parthenogenesis. In D. marina and D. cf. novae-zelandiae both the sporophytic filaments and gametophytes have identical ranges of DNA contents of their nuclei. Furthermore, in young sporangia of D. marina DNA contents indicating diploid nuclei were found. It is presumed that meiotic divisions of diploid nuclei take place soon after karyogamy without prior mitotic divisions and the life cycle of all three species is considered to be haplo-heterokaryotic. In D. cf. novae-zelandiae...

Synchroma pusillum sp. nov. and other New Algal Isolates with Chloroplast Complexes Confirm the Synchromophyceae (Ochrophyta) as a Widely Distributed Group of Amoeboid Algae

Seven new isolates of the heterokont algal class Synchromophyceae are described from coastal habitats of the Atlantic Ocean, including the Caribbean and Mediterranean Seas. All of the new isolates contain chloroplast complexes, a key feature of this group of algae. Morphology, pigments and DNA sequences support a monophyletic grouping of the Synchromophyceae to the exclusion of other Ochrophyta (primarily photosynthetic stramenopiles). Within the Synchromophyceae, two phylogenetic clades based on rbcL and 18S rDNA data were discovered, which differ in cell size and also the number of plastid complexes per cell. Two isolates form a clade with the type species Synchroma grande, while all other isolates form a separate clade, including the newly described species S. pusillum. Further species delineation of the isolates is difficult due to the highly similar morphology and life cycle strategy. Phylogenetic relationships with other genera of the Ochrophyta, such as Leukarachnion and Chlamydomyxa, are apparent and shed light on a heterogeneous branch of heterokont evolution.

Interaction of two myosins with microfilaments causes locomotion inLabyrinthula sp.

SummaryCytoskeleton elements of aLabyrinthula isolate from the Falkland Islands were studied. The most important characteristic of the genusLabyrinthula is a colourless branched plasmatic network of pseudopodia-like tubes with sliding spindle-shaped uninuclear plasma portions (cell bodies). After fluorescent staining tubulin appears to be uniformly and diffusely distributed throughout the whole network and to form a reticulate structure in the cell bodies. The inhibitor colchicine has no influence on the sliding motility of the cell bodies nor on the movement of the network. Actin is frequently found in the network, partly in the form of microfilament bundles, which are longitudinally arranged. Actin is also present in the cortical region of cell bodies, or of cell body groups. It was difficult to distinguish single cell bodies within groups by fluorescence. The inhibitors cytochalasin B and D stop the movement of cell bodies and network. Myosin is present in the cortical region of each cell body, and the central portions of each individual cell body contain accumulations of this protein. We could not observe any fluorescence in the network after myosin staining with the antibodies we used. An actin-myosin complex is probably responsible for the sliding movement of cell bodies in the Labyrinthula network, because actin is found in the pseudopodia-like tubes, and the cortex of the cell bodies is rich in actin and myosin. This actin-myosin complex seems to differ from another actin-myosin complex that has been postulated to be responsible for the locomotion of pseudopodia-like tubes. We propose that two actin-myosin complexes exist. One of them is responsible for locomotory phenomena of the network, and the second for cell body sliding in the pseudopodia-like tubes. In each case the myosin is probably anchored in the inner matrix membrane of the pseudopodia-like tubes. A model for actin-myosin interaction inLabyrinthula spp. is presented.

Arrangement of F-actin and microtubules in the pseudopodia ofCryptochlora perforans (Chlorarachniophyta)

SummaryThe distribution of actin and the arrangement of microtubules within the filopodia of amoeboid stages of Chlorarachniophyta were studied inCryptochlora perforans by indirect immunofluorescence. Actin is located along the whole pseudopodium, but at different concentrations. Microtubules run like coiled cables throughout the length of the pseudopodium. At the leading edges the pseudopodium frequently appears fan-shaped and the microtubules then show a spread-out arrangement, but they do not reach the cytoplasm front. Colchicine inhibited particle motility in the filopodia. The particle transport seems to be insensitive to cytochalasin D, but cells contracted their filopodia.

Possible significance of different DNA content ranges of gametophytic and tetrasporophytic nuclei in two species of Laurencia (Rhodomelaceae, Rhodophyta)

In species of the red algal genus Laurencia the life cycle is isomorphic, with haploid gametophytic and diploid tetrasporophytic thalli similar or identical in shape. Identical total nuclear DNA contents are postulated in the literature for homologous somatic thallus cells of both generations. However, in the closely related genus Osmundea differences in DNA content were observed between some homologous somatic cells of the isomorphic gametophytes and tetrasporophytes. To find out if differences between nuclear gametophytic and tetrasporophytic DNA contents also exist in Laurencia, comparative studies were carried out in two species of this genus. Microfluorometric measurements of nuclear DNA contents in the uninucleate cells of the central filaments in distal portions of thalli of Laurencia majuscula and Laurencia sp. were up to 64C for tetrasporophytes and up to 32C for gametophytes. Most probably nuclei of apical cells in G2 phase were 128C in tetrasporophytes and 64C in gametophytes. Nuclei of the multinucleate medullary, cortical and epidermal cells were mostly 8C and 4C in tetrasporophytes and gametophytes. Flow charts for nuclear DNA contents starting with apical cells are presented. Average C-levels of gametophytic nuclei were lower than those of homologous tetrasporophytic nuclei, reflecting the respective haploid and diploid states in these isomorphic generations. Because homologous gametophytic and tetrasporophytic cells had identical numbers of nuclei, total nuclear DNA contents per cell were also different. Nuclear DNA content ranges in multinucleate cells were 1C – 16C in gametophytes and 2C – 32C in tetrasporophytes. So, some tetrasporophytic nuclei had C-values identical to those of some gametophytic nuclei. Tetrasporophytic and gametophytic nuclei with identical C-levels are considered to be responsible for isomorphy of the two generations. We suggest that low C-levels in trichoblasts of gametophytes and high C-levels in cortical and epidermal cells of tetrasporophytes control the development of gametangia and tetrasporangia, respectively. Previous reports that nuclear DNA contents in homologous gametophytic and tetrasporophytic cells are identical in Laurencia are not confirmed.

Guanchochroma wildpretii gen. et spec. nov. (Ochrophyta) Provides New Insights into the Diversification and Evolution of the Algal Class Synchromophyceae.

A new relative of the chrysophyte genus Chrysopodocystis was found in Tenerife and termed Guanchochroma wildpretii. This unicellular alga was most noticeably discernible from Chrysopodocystis socialis (the only species of this genus) by the presence of a cyst-like stage with a multilayered lorica, which also functions as a dispersal unit and shows secondary wall growth. Secondary expansion of loricae (cell casings not involved in cell division, usually with a more or less pronounced opening) has never been observed previously and marks a unique feature of the new taxon. Plastids are non-randomly distributed within cells of G. wildpretii. 18S rRNA gene analyses identified the two species as sister lineages and placed them in a monophyletic group with the Synchromophyceae, a heterokont algal (Ochrophyta) class characterized by the presence of chloroplast complexes. Yet, neither Chrysopodocystis nor Guanchochroma showed this feature in ultrastructure analyses. Additionally, their 18S rRNA genes possessed distinct inserts, the highest GC-content known for Ochrophyta and exceptionally long branches on the Ochrophyta 18S rDNA phylogenetic tree, suggesting substantially increased substitution rates along their branch compared to Synchromophyceae. Plastid marker data (rbcL) recovered a monophyletic clade of Chrysopodocystis, Guanchochroma and Synchromophyceae as well, yet with lower supports for internal split order due to limited resolution of the marker. Evidence for the sequence of events leading to the formation of the plastid complex of Synchromophyceae still remains ambiguous because of the apparently short timeframe in which they occurred.