bluuebunny/crossref_metadata_2025_split huggingface dataset:
BEHAVIOR OF CHLOROPLAST NUCLEOIDS DURING THE CELL CYCLE OFCHLAMYDOMONAS REINHARDTII(CHLOROPHYTA) IN SYNCHRONIZED CULTURE1
Authors: Ehara Tomoko , Ogasawara Yutaka , Osafune Tetsuaki , Hase Eiji 
Published: October 2004

ABSTRACTCells ofChlamydomonas reinhardtiiDangeard were synchronized under a 12:12 h light: dark regimen. They increased in size during the light period, while nuclear division, chloroplast division and cytokinesis occurred during the dark period. Zoospores were liberated toward the end of the dark period. Changes in profile and distribution of chloroplast nucleoids were followed with a fluorescence Microscope after fixation with 0.1%(w/v) glutaraldehyde followed by staining with 4′.6‐diamidino‐2‐phenylidole (DAPI), a DNA fluorochrome. About ten granular nucleoids were dispersed in the chloroplast at the beginning of the light period (0 h). Within 4 h the nucleoids aggregated around the pyrenoid giving a compact profile. The formation of the compact aggregate of cp‐nucleoids around the pyrenoid occurred with maximal frequency twice during the light period. Toward the end of the light period the nucleoids were transformed into the form of threads interconnected with fine fibrils spreading throughout the chloroplast. Initially the thread‐like nucleoids fluoresced only faintly. The fluorescence of some parts of the threadlike form became brighter over a period of 6 h; these nucleoids were divided into daughter chloroplasts during chloroplast division. Soon after chloroplast division, these thread‐like nucleoids were transformed into about 20 granular forms, which were gradually combined to form about ten larger granular bodies in zoospores immediately prior to liberation from mother cells. Fixation of cells with glutaraldehyde at high concentrations or treatment of cells with protease significantly modified the profiles of DAPI‐stained nucleoids. The different morphologies of chloroplast nucleoids are discussed in relation to changes in configuration of their protein components.
ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS OF PTEROSPERMA CRISTATUM (PRASINOPHYCEAE) AND CONSIDERATION OF ITS PHYLOGENETIC POSITION1
Authors: Inouye Isao , Hori Terumitsu , Chihara Mitsuo 
Published: October 2004

ABSTRACTPterosperma cristatum Schiller, a member of the Pra‐sinophyceae, was examined with light and electron microscopy with special attention on the absolute configuration of flagellar apparatus components and associated structures. This alga is characterized by asymmetrically arranged basal bodies, connecting fibers and microtubular roots. The microtubular root system is homologous with the cruciate root system, the so‐called X‐2‐X‐2 root system typical of non‐charophycean green algae. Two ducts are associated with microtubular roots. A similar flagellar apparatus and duct system was found in two other prasinophyte genera, Pyramimonas and Halosphaera. The close phylogenetic affinity of these three genera is discussed.
THE FINE STRUCTURE OF TWO PHOTOSYNTHETIC SPECIES OF DINOPHYSIS (DINOPHYSIALES, DINOPHYCEAE)1
Authors: Lucas Ian A. N. , Vesk Maret 
Published: October 2004

ABSTRACTTwo closely related, photosynthetic species belonging to the genus Dinophysis were examined, D. acuminata Claparède et Lachmann and D. fortii Pavillard. Typical dinoflagellate features include the amphiesmal covering enclosing the cells and the structure of the nucleus and mitochondria. Many other characteristics seem to be specific to the order Dinophysiales. Many rhabdosomes are present, and complex mucocysts are found beneath the amphiesma. The thecal pores are unusual with the base of the pore occluded by a thin disc that is continuous with the main amphiesmal plate. The structure of the apical pore is also distinctive. Chloroplasts are grouped together in chromatospheres, enclosed by a double membrane, and contain paired thylakoids with electron dense contents in the lumen. The two pusules are extensive, each branching off the flagellar canal, and consisting of a large antechamber and a number of convoluted sacs. The entrance of each antechamber, and site of an emerging flagellum, is surrounded by a striated fibrous collar. Near the flagellar pore is a prominent microtubular/microbody complex which penetrates deep into the cell cytoplasm. Consideration is given to taxonomic position of the Dinophysiales and also to the nature and origins of the chloroplasts.
PHENOTYPIC PLASTICITY IN SCENEDESMUS COMMUNIS (CHLOROPHYCEAE). I. RELATIONSHIP OF S. COMMUNIS TO S. KOMAREKII1
Authors: Egan Patrick F. , Trainor Francis R. 
Published: October 2004

ABSTRACTWhen scenedesmus communis Hegew. (UTEX 76) was transferred daily in dilute media and a low cell density was maintained (ca. 1000 cells · mL−1), up to 30% unicells were produced in that population. Unlike previously described uncell‐coenobium‐unicell transformation with other species, these unicells never produced S. communis coenobia (large coenobium type, LCT) but rather small coenobium type (SCT) resembling S. komarekii Hegew. Growth and morphological development of the paratype strain of S. komarekii (UTEX 1236) was compared with an isolated SCT strain (SCT 76–8). SCT 76–8 never produced LCTs and grew significantly faster than UTEX 1236. Both SCT 76–8 and UTEX 1236 produced uncells at low cell densities. Coenobia formed when cell densities increased over time in batch cultures. SCT 76–8 and UTEX 1236 did not differ morphologically when viewed with the light microscope. Under scanning electron microscopy, an outer opaque layer covered an inner warty layer on unicells. The outer layer was reduced or absent in coenobia from batch cultures in stationary growth. In addition, long spikelets, not present on the walls of unicells, were prominent on coenobial walls. The spikelets of UTEX 1236 appeared smaller and more uniformly distributed than in strain 76–8. In contrast, the surface wall morphology of LCT S. communis was composed of an outer reticulate layer supported by spikelets and appeared as a pentagonal meshwork covering the cell walls. This phenotypic plasticity, as demonstrated by SEM and light microscopy, provides further evidence needed for an understanding of Scenedesmus evolution.
PHOTOADAPTATION, GROWTH AND PRODUCTION OF BOTTOM ICE ALGAE IN THE ANTARCTIC1
Authors: Cota Glenn F. , Sullivan Cornelius W. 
Published: October 2004

ABSTRACTBiomass, chemical composition, growth rates and the photosynthetic response of natural populations of sea ice algae in McMurdo Sound, Antarctica were followed over most of the spring bloom to examine temporal variability under a relatively constant incident irradiance (ca. 1500–1700 μE · m‐2· s‐1 at solar noon). Collection were restricted to bottom 20 cm of the ice sheet in an area with little or no snow (0–5 cm). At low temperature and irradiance these algae normally exhibited low assimilation numbers (ca. 0.1–0.4 mg C · mg Chl‐1· h‐1). Average growth rates (0.02–0.45 d‐1), based on changes in standing stocks, were also low. Biomass, biochemical composition, growth rates, assimilation numbers and photosynthetic efficiencies (mg C · mg Chl‐1· h‐1 (μE · m‐2· s‐1)‐1) displayed large fluctuations over periods of several days during the growth season. On the other hand, Ik which is an index of photoadaptation, and Im, the optimal irradiance for photosynthesis, were relatively constant with less than twofold variation throughout our study.Substantial nutrient fluxes (3.3–8.0 mmol Si or N · m‐2· d‐1) were necessary to satisfy the minimum nutrient demand for the observed biomass levels and population growth rates; over the 41 days of our study, integrated nutrient demand represented 69–150 mmol N or Si · m‐2, Only 5–25% of this total demand could be met by all of the nutrients in the ice sheet, if they were readily available. However, adequate amounts were present in the top few meters of the water column. With small nutrient gradients in surface waters below the sea ice, vertical eddy diffusivities on the order of 3.8–9.3 cm2· s‐ should supply sufficient nutrients to meet algal demand.
LIPID SYNTHESIS AND FATTY ACID COMPOSITION IN NANNOCHLOROPSIS SP. (EUSTIGMATOPHYCEAE) GROWN IN A LIGHT‐DARK CYCLE1
Authors: Sukenik Assaf , Carmeli Yael 
Published: October 2004

ABSTRACTChemical composition and lipid biosynthesis were studied in the marine eustigmatophyte Nannochloropsis sp. Grown under a 12:12 h light‐dark regime. Cellular division occurred in the dark and was associated with a reduction in cell volume. The cellular content of chlorophyll a and carotenoids increased during the light period and decreased during the dark period. Other cellular components, such as proteins, carbohydrates and lipids, followed a similar pattern. Nannochloropsis sp. Incorporated acetate, mostly into lipids during the light period, whereas a low rate of acetate incorporation was observed during the dark period, mostly into nonlipid compounds. Neutral lipids such as triacylglycerol were synthesized and accumulated in the light and showed a rapid turnover in the dark. Polar structural lipids such as monogalactosyl diacylglycerol were synthesized during the light period and hardly turned over during the dark period. Changes in lipid content were associated with variations in cellular fatty acid composition. The light period was characterized by an increase in the percentage of C16:0 and 16:1 fatty acids associated with triacylglycerols. However, in the dark period, as triglycerides were consumed for cellular maintenance, the relative distribution of the C20:5 fatty acid associated with the galactolipids increased.
ROLE OF LIGHT AND THE CELL CYCLE ON THE INDUCTION OF SPERMATOGENESIS IN A CENTRIC DIATOM1
Authors: Armbrust E. Virginia , Chisholm Sallie W. , Olson Robert J. 
Published: October 2004

ABSTRACTThe centric diatom, Thalassiosira weissflogii Grun., can be induced to undergo spermatogenesis by exposing cells maintained at saturating levels of continuous light to either dim light or darkness. Using flow cytometry to determine the relative DNA and chlorophyll content per cell, the number of cells within a population that responded to and induction signal was measured. From 0 to over 90% of a population differentiated into male gametes depending upon both the induction trigger and the population examined, regardless of the average cell size of the population. Through the use of synchromized cultures, we demonstrated that responsiveness to an induction trigger was a function of cell cycle stage; cells in early G1 were not yet committed to complete mitosis and were induced to form male gametes, whereas cells further along in their cell cycle were unresponsive to these same cues. A simple model combining the influence of light on the mitotic cell cycle and on the induction of spermatogenesis is proposed to explain the observed diversity in population responses to changes in light conditions.
THE FOSSIL GREEN ALGA MIZZIA (DASYCLADACEAE): A TOOL FOR INTERPRETATION OF PALEOENVIRONMENT IN THE UPPER PERMIAN CAPITAN REEF COMPLEX SOUTHEASTERN NEW MEXICO1
Authors: Kirkland Brenda L. , Chapman Russel L. 
Published: October 2004

ABSTRACTA 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.
DNA POLYMORPHISM WITHIN THE WH7803 SEROGROUP OF MARINE SYNECHOCOCCUS SPP. (CYANOBACTERIA)1,2
Authors: Wood A. Michelle , Townsend David 
Published: October 2004

ABSTRACTGenetic differences among ten strains of chroococcoid cyanobacteria (Synechococcus spp.) were identified by Southern blot hybridization. Data on shared number of restriction fragment length polymorphisms were used to identify the pattern and degree of genetic relatedness among the strains by two different methods of phylogenetic analysis. All the marine strains in the study contained phycoerythrin (PE) and cross‐reacted with antisera directed against strain WH7803. Five contained a PE composed of phycourobilin (PUB) and phycoerythrobilin (PEB) Chromophores, and three contained a PE composed of only PEB chromophores. Two freshwater strains which do not contain PE and do not cross‐react with the anti‐WH7803 serum were included in the study for comparison. Dollo Parsimony analysis and cluster analysis showed that the WH7803 serogroup includes at least four widely separated genetic lineages. Strains within each lineages were closely related but the differences between lineages were as great as those between any of the marine lineages and the freshwater lineage. Strains cultured simultaneously from the same water mass were associated with different lineages. Thus, we conclude that natural assemblages of marine. Synechococcus are, at least occasionally, composed of individuals as genetically distinct from each other as members of different species or genera in other taxa.
SEASONAL SUCCESSION OF ALGAL PERIPHYTON FROM A WASTEWATER TREATMENT FACILITY1
Authors: Davis Laurie S. , Hoffmann James P. , Cook Philip W. 
Published: October 2004

ABSTRACTAttached algal populations were sampled at weekly or biweekly to characterize successional changes in the secondary clarifiers of a wastewater treatment plant. Three communities were compared from areas of slow, medium and rapid current velocities. In general, the algae resembled those reported for other hypereutrophic flowing water. Of the twenty‐three algae recorded, Stigeoclonium, Oedogonium, Oscillatoria, Lyngbya, and Pleurocapsa were dominant at some point in the 15 month sampling period. Nutrient concentrations were consistently high (N = 1.1–21.4 mg·L−1; P = 0.1–10.4 mg·L−1); therefore, changes in temporal distribution of algae were probably dependent on seasonal changes in light and temperature. Colonization of artificial substrates was also observed. Small unicellular algae were the first autotrophs to attach and these were followed by larger filamentous forms.
EFFECTS OF ARSENATE ON GROWTH OF NITROGEN‐AND PHOSPHORUS‐LIMITED CHLORELLA VULGARIS (CHLOROPHYCEAE) ISOLATES1
Authors: Creed Irena F. , Havas Magda , Trick Charles G. 
Published: October 2004

ABSTRACTThe effects of arsenate on the growth characteristics of five isolates of the freshwater alga, Chlorella vulgaris Beij., were examined. Two field isolates originated from arsenic‐contaminated sites in Yukon, Canada and Kyushi, Japan; two reference isolates were obtained from the University of Texas Culture Collection. One isolate was selected for arsenic‐tolerance in the laboratory. All five strains survived in culture solutions containing high arsenate concentrations. Arsenate (1–25 mM As) reduced photosynthesis and cell growth, as reflected by induced lag periods, slower growth rates, and lower stationary cell yields. Field isolates had shorter lag periods, higher growth rates, and enhanced cell yields compared to lab isolates when exposed to the same arsenic concentrations. Growth of the phosphorus‐limited field strains was stimulated by the addition of arsenic. The cell yield of phosphorus‐limited C. vulgaris Yukon, when treated with arsenic, was two times that of the phosphorus‐limited control. This pattern was not evident when photosynthesis was used as a measure of cell response.
DEVELOPMENTAL STUDIES IN PORPHYRA (RHODOPHYCEAE). III. EFFECT OF CULTURE CONDITIONS ON WALL REGENERATION AND DIFFERENTIATION OF PROTOPLASTS1
Authors: Polne‐Fuller Miriam , Gibor Aharon 
Published: October 2004

ABSTRACTProtoplasts isolated from thalli of four Porphyra species regenerated successfully into differentiated plantlets. The efficiency of protoplast isolation and the developmental patterns of the regenerating protoplasts depended on the type of tissues from which they were isolated. However, culture conditions greatly influenced the patterns of development at the cellular and organismal levels. Sorbitol, nitrogen, and agar concentration in the medium controlled rates of cell division, thickening of cell walls, development of rhizoids, and formation of calluses or differentiated blades. Agitation disturbed the attachment of the protoplasts to a substrate. Cells in agitated cultures produced suspensions of single cells and non‐polarized small calluses. Calluses which developed from protoplasts survived in storage for over two years. The stored calluses, and cells and protoplasts that were isolated from them, were subcultured successfully. We forsee extensive use of Porphyra cell suspensions for strain selection and vegetative propagation of cultivars. This technology, which makes vegetative cloning of selected Porphyra plants possible, may eliminate the need for cultivation and storage of the conchocelis phase. Protoplasts are also being used as tools for studies in genetic engineering of these commercial species.
PHYLOGENY OF CHLAMYDOMONAS (CHLOROPHYTA) BASED ON CLADISTIC ANALYSIS OF NUCLEAR 18S rRNA SEQUENCE DATA1
Authors: Buchheim Mark A. , Turmel Monique , Zimmer Elizabeth A. , Chapman Russell L. 
Published: October 2004

ABSTRACTThe genus Chlamydomonas Ehrenberg may contain as many as 450 described species. Morphological, physiological and molecular data show that variation among some Chlamydomonas species can he great, leading to speculation that multiple, generic‐level lineages exist within this genus. The most recent systematic studies of Chlamydomonas have led to proposals of nine distinct morphological and 15 distinct sporangial autolysin groups. Partial sequences from the nuclear small subunit rRNAs from 14 Chlamydomonas species representing 12 autolysin and four morphological groups, and from three flagellates thought to he related to Chlamydomonas were determined in a phylogenetic study of relationships among these algae. Sequence comparisons among some Chlamydomonas species revealed differences comparable to the sequence divergence between soybeans and cycads. Cladistic analysis of the sequence data suggests that multiple lineages exist among species of Chlamydomonas. Some of these lineages represent alliances of both Chlamydomonas and non‐Chlamydomonas taxa; thus, the current taxonomy does not reflect natural, or monophyletic, groups. Collectively, these lineages may represent distinct families or even orders.
THE PLEURASTROPHYCEAE AND MICROMONADOPHYCEAE: A CLADISTIC ANALYSIS OF NUCLEAR rRNA SEQUENCE DATA1
Authors: Kantz Thomas S. , Theriot Edward C. , Zimmer Elizabeth A. , Chapman Russell L. 
Published: October 2004

ABSTRACTPartial sequences from the nuclear‐encoded 18S and 26S ribosomal RNA molecules from representatives of the five classes of Chlorophyta sensu Mattox and Stewart (1984) were analyzed cladistically in a study of the phylogenetic relationships among the Micromonadophyceae, Pleurastrophyceae, and other green algae. The sequence data indicate that the Micromonadophyceae (= Prasinophyceae) is not monophyletic but comprises at least three lineages occupying a basal position among the green algae. Though the Pleurastrophyceae and the Ulvophyceae both possess counter‐clockwise basal body orientations, the sequence data indicate that the Pleurastrophyceae is the sister group to the Chlorophyceae. The molecular data alone do not resolve the monophyly of the Pleurastrophyceae or the Ulvophyceae; however, a combined data set of molecular and non‐molecular characters support a monophyletic Pleurastrophyceae. Analyses with user‐defined tree topologies and the bootstrap method of character resampling indicate that the relationships shown in the most parasimonious cladograms are well supported by the character data.
We Can Work It Out: The Impact of Technological Change on the Demand for Low‐Skill Workers
Authors: Manning Alan 
Published: October 2004

AbstractThere is little doubt that technology has had the most profound effect on altering the tasks that we humans do in our jobs. Economists have long speculated on how technical change affects both the absolute demand for labour as a whole and the relative demands for different types of labour. In recent years, the idea of skill‐biased technical change has become the consensus view about the current impact of technology on labour demand, namely that technical change leads to an increase in the demand for skilled relative to unskilled labour painting a bleak future for the employment prospects of less‐skilled workers. But, drawing on a recent paper by Autor, Levy and Murnane (2003) about the impact of technology on the demand for different types of skills, this paper argues that the demand in the least‐skilled jobs may be growing. But, it is argued that employment of the less‐skilled is increasingly dependent on physical proximity to the more‐skilled and may also be vulnerable in the long‐run to further technological developments.
Understanding Mexican‐American Marriage Patterns Using a Life‐Course Approach*
Authors: Kelly Raley R. , Elizabeth Durden T. , Wildsmith Elizabeth 
Published: October 2004

Objective. Guided by a life‐course framework that incorporates the interconnection between marriage, migration, and other transitions, we critically examine the familism explanation for the earlier age at marriage among Mexican Americans.Methods. We compare the marriage patterns of Mexican immigrants derived from the National Survey of Family Growth (NSFG) to those of women living in Mexico derived from the Mexican Census. We then use data from the NSFG to estimate proportional hazard models of marriage using fixed variables such as parent's education and time‐varying variables such as school enrollment.Results. Analyses show that the Mexican immigrant population marries earlier than Mexicans who do not migrate to the United States. In addition, the U.S.‐born Mexican population has lower marriage rates than whites once family background characteristics associated with early marriage are controlled and Anglos are no less likely than Mexican Americans to marry in response to a pregnancy.Conclusion. We find reason to doubt that ethnic differentials are driven by a strong attachment to marriage, female chastity, and the “traditional” family. Although cultural factors may play an important role, researchers need to more carefully specify the aspects of Mexican culture that might encourage marriage and how these factors interrelate with economic and demographic constraints.