LIFE HISTORY OF COLPOMENIA SINUOSA (SYCTOSIPHONACEAE,PHAEOPHYCEAE) IN THE AZORES1

Colpomenia sinuosa (Mertens ex Roth) Derbès and Solier (Scytosiphonaceae, Phaeophyceae) is a common species on the rocky intertidal shores of the Azores, where reproductive gametophytes occur throughout the year. Life‐history studies of this species were carried out in culture, and both sexual and asexual reproduction were observed. Anisogamous gametes fused to form zygotes. The zygotes gave rise to a filamentous prostrate sporophyte generation bearing unilocular sporangia, under both short‐day and long‐day conditions at 15 and 22°C, and to both unilocular and plurilocular sporangia, under the lower temperature condition. Unispores developed into gametophytes, and plurispores gave rise to filamentous sporophytes. Asexual reproduction was carried out by unfused female gametes and asexual plurispores produced from the same gametophyte. Unfused gametes developed into filamentous prostrate sporophytes producing unilocular sporangia in both culture conditions, and unispores released from the sporangia gave rise to gametophytes. Asexual plurispores from field gametophytes, under both culture conditions, developed directly into new gametophytes. The species exhibited three types of life history: a heteromorphic, diplohaplontic; a heteromorphic, monophasic (both with alternation between the erect and filamentous prostrate thalli); and a monomorphic, monophasic.     

MORPHOLOGY AND LIFE HISTORY OF SCYTOSIPHON LOMENTARIA (SCYTOSIPHONACEAE,PHAEOPHYCEAE) FROM THE AZORES1

Morphological and culture studies of Scytosiphon lomentaria (Lyngbye) Link and Microspongium gelatinosum Reinke (Scytosiphonaceae, Phaeophyceae) were undertaken on material collected on the Island of São Miguel, Azores, where both species were commonly found. Erect thalli of S. lomentaria collected in the field were up to 33 cm long and 2.3 mm wide, tubular, hollow, and commonly constricted at intervals. The plurilocular sporangia were positioned in continuous sori on the thallus surface. Ascocysts were present. In the field, M. gelatinosum formed crustose to slightly pulvinate plants, were spongy in texture, and dark brown to black in color, which were circular or irregularly spreading over several centimeters and firmly attached to the substratum. Sessile unilocular sporangia were located in sori on the crust surface. In culture S. lomentaria plurispores developed into Microspongium‐like crustose prostrate thalli that formed unilocular sporangia. Unispores developed into new erect thalli that formed plurilocular sporangia. Sexual reproduction was not observed. In culture, M. gelatinosum unispores developed into erect thalli identical with S. lomentaria. These results are similar to those reported for other areas and suggest the occurrence in the Azorean plants of a monophasic and heteromorphic life history, involving both entities studied.     

MORPHOLOGY,LIFE HISTORY,AND MOLECULAR PHYLOGENY OF STSCHAPOVIA FLAGELLARIS (TILOPTERIDALES,PHAEOPHYCEAE) AND THE ERECTION OF THE STSCHAPOVIACEAE FAM. NOV.1

The phenology, life history, ultrastructure of reproductive structures, and molecular phylogeny using rbcL and rDNA (5.8S, internal transcribed spacer 2, and partial 26S) gene sequences of Stschapovia flagellaris, endemic to the northwestern Pacific Ocean, were studied. This species was first classified in the order Delamareales together with Delamarea, Coelocladia, and Cladothele. Those three genera, however, were later transferred to Dictyosiphonales, whereas the systematic position of Stschapovia remained unclear. At Abashiri, Hokkaido, Japan, the species regenerated by forming a new erect thallus from a perennial crustose holdfast or by presumably parthenogenetic development of eggs released from the erect thallus. There was no alternation of generations. In winter, the monoecious erect thallus formed reproductive structures (i.e. plurilocular antheridia and oogonia) in the thickened part of the thallus. Sperm had a chloroplast with an eyespot and a long anterior and short posterior flagellum. Eggs contained numerous disc‐shaped chloroplasts, physodes, and vacuoles. Neither sexual attraction of the presumptive sperm by eggs nor their sexual fusion was observed. Molecular phylogenetic analyses revealed the closest phylogenetic relationship between Stschapovia and Halosiphonaceae, and they grouped with Phyllariaceae and Tilopteridaceae (Tilopteridales s. s.). Stschapovia and Tilopteridaceae have several important morphological similarities: chloroplasts lacking pyrenoids, lack of sexual reproduction despite the release of obvious sperm, occurrence of monoecious gametophytes, and similarity in the early developmental pattern of the erect thallus. In conclusion, we propose the establishment of the new family Stschapoviaceae to accommodate Stschapovia and the placement of the family in the order Tilopteridales together with Tilopteridaceae, Halosiphonaceae, and Phyllariaceae.     

HYBRIDIZATION OF MACROCYSTIS (PHAEOPHYTA) WITH OTHER FLOAT-BEARING KELPS1,2

Sporophytes were produced in 22 out of 23 attempts to cross Macrocystia angustifolia Bory with Pelagophycus porra (Lemon) Setchell. Representative samples of these plants were raised in a surge-tank under greenhouse conditions to several meters in length. The plants resulting from this intergeneric cross were intermediate in morphology between the parental genera. The intermediate plants were similar to those found fry one of the authors (MN) in 1957, and by others since then, in California kelp beds where Macrocystis and Pelagophycus co-occur, A cross between M. angustifolia and Nereocystis luetkeana (Mertens) P. & R., also produced normal sporophytes. The taxonomic, evolutionary, morphogenetic and genetic implications of these hybridizations are discussed.     

Low Divergence in rDNA ITS Sequences Among Five Species of Fucus (Phaeophyceae) Suggests a Very Recent Radiation

Sequences from the two ribosomal DNA internal transcribed spacers (ITS1 and ITS2) were compared among five species of Fucus. Based on the present taxon sampling, parsimony analysis showed that Fucus serratus is the sister-group of the remaining Fucus species when Ascophyllum nodosum was used as an outgroup. The topology of the tree was (Fucus serratus (F. lutarius (F. vesiculosus (F. spiralis+F. ceranoides)))). The extremely low variation observed suggests a very recent radiation of the genus which supports the view widely accepted that the Fucales are among the most evolutionarily advanced of the brown algae. We further note that sequence differences between Fucus and Ascophyllum were 28%: this does not rule out the utility of ITS sequences within the Fucaceae. The very low number of informative positions allows to demonstrate empirically that distance matrix methods group on the basis of symplesiomorphies. Received: 17 February 1997 / Accepted: 17 April 1997     

Centrosome and microtubule dynamics in apical cells ofSphacelaria rigidula (Phaeophyceae) treated with nocodazole

Summary Treatment of young thalli ofSphacelaria rigidula with 0.04 g of nocodazole (Nz) per ml for up to 36 h affects microtubules (Mts) only slightly, but blocks a large number of mitotic cells in metaphase, without disruption of the metaphase plate. Higher concentrations of Nz (0.1 g/ml) depolymerize interphase Mts. Only a few perinuclear and some short Mts resist and remain associated with the centrosomes. Fragmented Mts or groups of Mts sometimes remain in the apical dome. After treatment with 0.1 g of Nz per ml, prometaphase cells are blocked at metaphase, while post-metaphase cells become binuclear, due to the failure of cytokinesis. With anticentrin immunofluorescence, a positive centrin signal is always observed in the centrosome area. Centrosome duplication is not affected by Nz, but separation is disturbed. After recovering for 2–4 h, most of the blocked metaphases proceed normally. In such cells duplicated centrosomes are seen in different stages of separation. In some cells independent aster-like microtubule configurations appear in the apical dome, occasionally displaying centrin at their centre. During recovery various configurations of bimitosis or multipolar mitosis were found. The multipolar spindles may share common centrosomes. Up to four centrosomes may accompany each nucleus. In some 24 h treated cells, as well as in cells recovering for 2 h, the centrin-positive structure is rod-like, extending in opposite directions from the usual position to the poles. Electron microscopical examination of thin sections revealed that the growth pattern of the apical cells is disrupted after Nz treatment. The observations show that: (a) the Mt cytoskeleton is involved in maintaining the polarity and growth pattern of apical cells, (b) mitosis is blocked by low concentrations of Nz without significant depolymerization of Mts, (c) the centrosome cycle is independent of the nuclear cycle, (d) centrosome separation and differentiation are disturbed by Nz treatment, (e) during recovery from Nz treatment, centrosomal material that may have separated from the centrosomes, as well as Mt fragments that resisted depolymerization, may operate as Mt nucleation centres.Abbreviations DIC differential interference contrast - EM electron microscope - Mt microtubule - MTOC microtubule-organizing center - Nz nocodazole - NBBC nucleus-basal body connector     

Life histories of Colpomenia sinuosa and Hydroclathrus clathratus (Scytosiphonaceae, Phaeophyceae) in culture

Life-history studies in culture were carried out on Colpomenia sinuosa (Mertens ex Roth) Derbès et Solier and Hydroclathrus clathratus (C. Agardh) Howe (Scytosiphonales, Phaeophyceae) from Japan. These species showed a heteromorphic life-history pattern with an alternation between erect thalli bearing plurilocular zoidangia and prostrate thalli bearing ectocarpoid plurilocular and unilocular zoidangia. Plurizoids released from erect and prostrate thalli developed into prostrate thalli. Unizoids, however, developed into erect thalli. Prostrate thalli produced plurilocular zoidangia in long-day conditions and unilocular zoidangia in short-day conditions at 10-20°C. Prostrate thalli of C. sinuosa formed ascocysts. Germlings of both species did not grow at 5°C.     

Sterols of the senegalese brown alga Padina vickersiae

Contrary to all the brown algae already studied for sterol content the Senegalese Padina vickersiae contains a great amount of cholesterol, chiefly in the later stages of growth. The seasonal variation of the sterols is studied and compared to other Phaeophyceae belonging to the genus Cystoseira.     

Carbohydrates of Padina tetrastromatica

Extraction with hydrochloric acid (pH 2.5) of the brown alga Padina tetrastromatica afforded water-soluble and water-insoluble polysaccharides. The water-soluble polysaccharide was fractionated using cetyltritmethyl ammonium bromide and chromatography on DEAE-cellulose and Sephadex G-100. A neutral laminaran like glucan and two new sulphated heteropolysaccharides comprising d-glucuronic acid, l-fucose, l-rhamnose, d-xylose, d-arabinose, d-galactose, d-glucose and half-ester sulphate were obtained. The alginic acid isolated from this brown seaweed was found to be predominantly of poly 1 → 4β-d-mannuronic acid type. The water-soluble sulphated polymer showed high anticoagulant activity.