The microtubule cytoskeleton in developing cysts of the green algaAcetabularia: Involvement in cell wall differentiation

Summary Cysts of the green algaAcetabularia develop a unique lid structure to enable the release of gametes. This lid is separated from the rest of the thick cellulose cell wall by a circular fault line formed within the fibrillar texture of the wall. By immunofluorescence microscopy, we show that, prior to the first division of the single cyst nucleus, the radially symmetrical, perinuclear microtubule system which is a remnant carried over from previous developmental stages of cyst morphogenesis transforms into a circular microtubule band (CMB) around the nucleus. This band consisting of only a few bundled microtubules beneath the plasma membrane encircles the cyst nucleus at a distance of 75 to 100m. In a previous fine structural study, a lid-forming apparatus (LFA) was described as a circular band of rod-like structures in the plane of the plasma membrane, demarcating the contour of the future lid. Both the CMB and the LFA are superimposed on the rim of the lid. We therefore propose that the microtubule band is a component of the LFA identical with the rod-like structures. Formation of the CMB and, hence, lid formation are blocked by the microtubule-specific herbicide Oryzalin but not by the actin filament-disrupting inhibitor cytochalasin D. Upon recovery from Oryzalin treatment, the nuclei but not the prospective sites of the CMBs serve as nucleation centers, indicating that the CMB is not formed by a pre-existing template in the plasma membrane. This suggests that the dynamic behavior of the microtubules within the perinuclear microtubule cytoskeleton gives rise to the CMB. Since the stage of CMB assembly marks the beginning of cell wall formation, it is proposed that the CMB determines the position of the lid by spatially controlling cell wall deposition. On the basis of current hypotheses, two scenarios for the role of the LFA/CMB in lid formation are discussed.Abbreviations CMB circular microtubule band - EGTA ethylene glycol bis-(-aminoethyl ether) N,N,N,N-tetraacetic acid - FITC fluorescein isothiocyanate - LFA lid-forming-apparatus - MAP microtubule-associated protein - MT microtubule - MTOC microtubuleorganizing center Dedicated to the memory of Professor Oswald Kiermayer     

TIMING AND LIGHT REGULATION OF APICAL MORPHOGENESIS DURING REPRODUCTIVE DEVELOPMENT IN WILD-TYPE POPULATIONS OF ACETABULARIA ACETABULUM (CHLOROPHYCEAE)

In the giant unicellular green alga, Acetabularia acetabulum (L.) Silva, development is altered by light. For example, blue light induces the vegetative apex to produce whorls of hairs that encircle the stalk and, later, blue light may trigger reproductive onset. The two goals of this study were to determine when changes in apical shape occur during formation of the reproductive structure, or "cap," and to determine which of these differentiation events require light. The first visible indication of cap initiation was a rounded swelling of the apex, which we call a knob-shaped apex (time = 0 hours). Subsequent changes in shape were a hyaline, knob-shaped apex, reached by 50% of the population 3 h later, and the formation of a whorl of unilobed chambers at 16 h. These chambers became bilobed at 33 h and trilobed at 34 h. Successive sets of cap hairs grew from protuberances found on the surface of the uppermost lobes of the chambers (superior corona). After knob, the remainder of cap formation was largely independent of light. However, the initiation of each set of cap hairs required light. If a recently initiated cap was amputated, the individual recapitulated development, repeating a portion of vegetative morphogenesis (i.e. it made whorls of sterile hairs) before initiating a new cap. The developmental sequence between amputation and initiation of a new cap required light. A model for light-regulated changes in shape at the apex of Acetabularia acetabulum, which integrates whorl and cap formation and encompasses both vegetative and reproductive development of this organism, is presented.     

Analyse biostratigraphique et paléontologique de l'Albien marin d'Estremadura (Portugal)

The marine Albain from Estremadura is splited up into four Orbitolinidae zones, adjusted to biostratigraphic scales from mesogean province: zone with Orbitolina (Mesorbitolina) minuta (lower to middle Albian); zone with Neorbitolinopsis conulus (base of upper Albian); zone with Orbitolina (Orbitolina) concava (top of upper Albian) and zone with Orbitolina (Orbitolina) duranddelgai (Vraconian). The vertical extension of the main fossils is replaced in the framework of these zones. The most interesting species for biostratigraphy, paleoecology or taxinomy are summarily described.     

Norian calcareous Algae from the Matese Mountains (northern Campania,Italy)

The Norian portion of the Costa dei Frascari succession (Matese Mountains, northern Campania) provides an example of a calcareous algae association dominated by the family Pseudoudoteaceae; subordinately, Gymnocodiaceae and Dasycladaceae also occur. The present study deals with the record of Garwoodia maxima Dragastan, Garwoodia toomeyi Dragastan, Pseudoudotea magna Dragastan et al., Jabrianella sp., and Asterocalculus heraki Sokac and Grgasovic, from the open-lagoon carbonate deposits which were referred to the portion of the Norian below the Triasina hantkeni Zone.Riassunto. Vengono presentati i risultati di uno studio sistematico condotto sulle alghe calcaree del Norico dei Monti del Matese (Campania settentrionale), per la prima volta segnalate in Italia. La ricca associazione è composta da prevalenti pseudoudoteacee e precisamente: Garwoodia maxima, Garwoodia toomeji, Pseudoudotea magna, Jabrianella sp., oltre a Asterocalculus heraki, Heteroporella zankli e Probolocuspis espakhensis, recentemente attribuito alle Dasycladales da Senowbari-Daryan and Majidifard. I campioni analizzati provengono dalla porzione inferiore della successione della Costa dei Frascari (versante meridionale dei Monti del Matese) i cui 160 m basali sono costituiti da prevalenti calcari granulo-sostenuti e da rare intercalazioni di calcari fango-sostenuti, talora loferitici, spesso dolomitizzati e stromatolitici. Labbondanza di antozoi, chetetidi, gasteropodi di grandi dimensioni e, in particolare, di resti di echinodermi indica che tali sedimenti si sono deposti in un ambiente di open-lagoon caratterizzato da continui scambi con il mare aperto che garantivano condizioni di salinità e ossigenazione delle acque idonee a questo tipo di organismi. In base allassociazione micropaleontologica e considerata lassenza di Triasina hantkeni e di Griphoporella curvata, la cui comparsa avviene a circa 160 m dalla base della successione, questi sedimenti sono stati riferiti alla porzione di Norico sottostante la Zona a Triasina hantkeni (sensu Marcoux et al. 1993).     

Le genre Petrascula Gümbel 1873, algue dasycladacée: Émendation,révision des espèces du genre,création de nouvelles espèces

The genus Petrascula has not been reviewed since J. Pia in 1920. At present, seven species are attributed to this genus. Different characteris have been used to define it by the authors. After abundant sampling in the Upper Kimmeridgian or the Southern Jura Mountains, the species-type has been reviewed and divided in two species, the second one named: Petrascula guembeli nov. sp.An other level of Portlandian age, in the same azea, is very rich in Petrascula piaiBachmayer, 1944. This species which has not been observed since that time is here reviewed. Associated with this species, a new one was found and described Petrascula? bugesiaca nov. sp., in spite a doubtful genus attribution.So many different species allow the review and emendation of the genus Petrascula. Then, the other species of the genus: P. globosa (Alth) P. herakiSokac & Nikler, P. illyricaSokac & Nikler, are discussed using the new definition.     

Poly(a)+ rna during vegetative development ofacetabularia peniculus

Summary In the juvenile stage, the diploid giant-celled green algae Acetabularia spp. are differentiated into an upright stalk and an irregularly branched rhizoid. Early amputation and grafting experiments as well as biochemical and molecular analyses have shown that mRNA (as poly(A)⁺ RNA) is continuously supplied from the primary nucleus in the rhizoid and accumulates in the stalk apex. In the present study, localization of poly(A)⁺ RNA in the juvenile stage of theAcetabularia peniculus was investigated by fluorescent in situ hybridization using oligo(dT) as a probe. The signal was localized in the apical cytoplasm and, in addition, multiple longitudinal striations throughout the stalk and rhizoid cytoplasm. A large portion of the poly(A)⁺ RNA striations exhibited structural polarity, broadened at one end and gradually thinned toward the other end. Some of the striations in the rhizoid cytoplasm were continuous with a zone of signal in the area of the perinuclear rim. The poly(A)⁺ RNA striations were associated with thick bands of longitudinal actin bundles which run through the entire length of the stalk. Cytochalasin D caused fragmentation of the actin bundles and irregular distribution of the fluorescent signal. We suggest that the poly(A)⁺ RNA striations constitute a hitherto unknown form of packaged mRNA that is transported over large distances along the actin cytoskeleton to be stored and expressed in the growing apex.     

THE FOSSIL GREEN ALGA MIZZIA (DASYCLADACEAE): A TOOL FOR INTERPRETATION OF PALEOENVIRONMENT IN THE UPPER PERMIAN CAPITAN REEF COMPLEX SOUTHEASTERN NEW MEXICO1

A paleoenvironmental study of the dasyclad Mizzia Schubert, 1907 is potentially important because, unlike most of the other fossil reef-dwelling organisms found in the Guadalupe Mountains, the fossil Mizzia (restricted to the Permian) has a modern analog, Cymopolia Lamouroux, 1916 (Cretaceous to Holocene). The overall morphology of the two genera is similar: both are articulated, and observations on our specimens suggest that both were branched. The transition from the remarkably high-diversity sponge and algal assemblage in the reef into the remarkably low-diversity dasyclad-dominated assemblage in the back reef is abrupt, occurring over distances as short as 10 m. Mizzia is the dominant and usually the only component in grainstones, packstones, and wackestones found; immediately shelfward of the Capitan reef. The low percentage of broken segments (average 10%) and the discovery of several intact sections of thallus are evidence against wave action as a possible limiting factor. Because the climate in the Guadalupe Mountains was extremely arid and because dasyclads are euryhaline, hypersalinity is considered the most likely limiting factor in this case. Our conclusion that prolific stands of dasyclads formed in shallow protected lagoons immediately behind an emergent barrier reef is not compatible with the currently accepted marginal mound hypothesis for deposition of the Capitan reef complex. We suggest that the marginal mound model must either be modified or abandoned in favor of the originally proposed barrier reef model of deposition.     

Differences in amino acid sequence of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from two species of Dasycladaceae

In contrast to other plants the plastid genome of Acetabularia is larger in size and shows a high degree of variability. This study on the chloroplast-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase demonstrates that strongly conserved areas also exist in the plastid genome of the Dasycladaceae. Searching for differences in the amino acid sequence of the large subunit from Acetabularia mediterranea and Acicularia schenckii, proteolytic peptides which differ in their elution behaviour in reverse-phase high-performance liquid chromatography were sequenced. Only six amino acids were found to be exchanged in the large subunit from these two species. Since these two species diverged approx. 150 million years ago, these results imply that 0.84 amino-acid exchanges per 100 amino acids have occurred in 10⁸ years, underlining the strong conservatism of the large subunit.Abbreviations A Acetabularia mediterranea - Ac. Acicularia schenckii - HPLC high-performance liquid chromatography - LSU large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase - PAGE polyacrylamide gel electrophoresis - RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase - SDS sodium dodecyl sulfate     

A NEW,ARTIFICIAL SEA WATER THAT FACILITATES GROWTH OF LARGE NUMBERS OF CELLS OF ACETABULARIA ACETABULUM (CHLOROPHYTA) AND REDUCES THE LABOR INHERENT IN CELL CULTURE1

We designed a new, artificial seawater (Ace 25) in order to grow bulk cultures of Acetabularia acetabulum (L.) Silva with a minimum of labor. To this end, we modified the traditional recipe for cell growth (Müller's medium as modified by Schweiger et al.) We eliminated five of the inorganic chemicals and determined the optimum concentration for 16 of the remaining 18 inorganic chemicals from modified Müller's seawater. Ace 25 enables growth of A. acetabulum from the beginning of the juvenile phase through gametangial formation in 11 weeks at high cell densities without medium replenishment. This represents a 98% reduction in the seawater volume required to mature each cell, a 30–40% reduction of the duration of the life cycle, an estimated 80% reduction in labor, and a 50–95% reduction in the space required for culturing A. acetabulum as compared with traditional procedures. These improvements may facilitate studies that require large numbers of cells such as population studies, genetics, and biochemistry, contribute to understanding the nutritional requirements of marine algae, and extend the use of this cell to those who lack the space or manpower to grow the cells in the traditional manner.