彼得森黄群藻孢囊的形成及形态

利用光镜及扫描电镜对彼得森黄群藻的形态结构、孢囊形成进行详细观察和描述.结果显示,彼得森黄群藻分布广泛,营养体形态变化也大,可以分为不同的变种和变型,其孢囊形态也有多种形态.根据鳞片结构,鉴定出其中的2个变型,并对其所产生的孢囊形态进行了对应.     

ENVIRONMENTAL FACTORS CORRELATED WITH CHRYSOPHYTE CYST ASSEMBLAGES IN LOW ARCTIC LAKES OF SOUTHWEST GREENLAND1

We analyzed the relationship between chrysophyte cyst assemblages in surface sediment samples and limnological and geographical variables for 70 lakes located along Søndre Strømfjord in southwest Greenland. Over 247 stomatocysts were identified and of these, 153 were sufficiently abundant for use in statistical analyses. Eight stomatocysts were considered to be new and are described formally. Canonical correspondence analysis indicated that conductivity was the dominant variable explaining cyst distribution, reflecting the large conductivity gradient in lake water chemistry in this area. High conductivity lakes had distinctive cyst assemblages with lower diversity than low alkalinity lakes, where assemblages were similar to alpine soft‐water lakes elsewhere. The high conductivity lakes, however, had similar cysts to other saline lakes elsewhere in the arctic. Additionally, pH, calcium, maximum depth, longitude, sulfate, total phosphorus, and altitude all explained significant amounts of variability of cyst assemblages. Longitude was the only geographical variable that explained cyst variability independently of other variables (i.e. had a unique effect), which suggests that the climatic gradient from the coast to the head of the fjord has a structuring effect on cyst assemblages. Conductivity (weighted‐averaging partial least squares, r²=0.917; root mean square error=0.142; r²_jack=0.861, root mean square error of prediction=0.191) and pH inference models (weighted averaging, r²=0.924; root mean square error=0.158; r²_jack=0.826, root mean square error of prediction=0.240) were developed. For the pH model, high conductivity lakes (>800 μ S₂₀·cm^?1) were removed. Both models are statistically robust and could be applied to lakes in west Greenland to reconstruct conductivity and/or pH. Such paleolimnological reconstructions provide the means of acquiring long‐term data for use in the evaluation of, for example, regional paleoclimatic models.     

Localization of plastid DNA replication on a nucleoid structure

Plastids contain multiple copies of the plastid genome that are arranged into discrete aggregates, termed nucleoids. Nucleoid molecular organization and its possible role in ensuring genome continuity have not yet been carefully explored. We examined the relationship between plastid DNA synthesis and nucleoid cytology in the unicellular chrysophyte Ochromonas danica, which is useful for such work because the genomes in each plastid are arranged in a single ring-shaped nucleoid. Immunocytochemical detection of thymidine analog incorporation into replicating DNA revealed that plastid DNA synthesis occurs at several sites along the ring nucleoid simultaneously, and that all plastids of a single cell display similar replication patterns. Plastid DNA replication was observed in G1, S, and G2 phase cells. Pulse-chase-pulse labelling with two different thymidine analogs revealed that new sites are activated as cells progress through the cell cycle while some old sites continue. The double labelling patterns suggest that the individual genomes are arranged consecutively, either singly or in clusters, along the nucleoid perimeter and that the selection of which genome replicates when is a matter of chance. These observations eliminate a number of alternative hypotheses concerning plastid DNA organization, and suggest how cells might maintain a constancy of plastid DNA amount and why plastid genome variants segregate so rapidly during mitosis.     

Isolation and characterization of dinoflagellate and chrysophyte cytochrome-f (553–4)

Cytochrome-f (553–4) was isolated from mass cultures of the six dinoflagellates, Amphidinium carterae (2 strains), Cachonina niei, Glenodinium sp., Peridinium foliaceum, Gonyaulax polyedra, and one chrysophyte, Cricospherae carterae. Sonication of whole cell suspensions released the water-soluble protein, which was then purified by vacuum dialysis, salt fractionation and column chromatography. Reduced forms of isolated cytochromes had absorption maxima at 270–6, 316–8, 415–6, 522–3 and 553–4 rim. The α-absorption peak was asymmetrical. MW's, as determined by SDS polyacrylamide gel electrophoresis, ranged from 10 700 to 13 500. Amino acid analysis of C. niei cytochrome-f revealed 102 residues, with a composite MW of 10836. Purified cytochromes had isoelectric points ranging from 3·45 to 4·25 and oxidation-reduction potentials ranging from +0·374 to +0·351 V.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF DINOBRYON CYLINDRICUM (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Dinobryon cylindrioum Imhof. (UTEX no. LB 2266) was determined using serial section reconstruction. Four microtubular rootlet systems (R₁, R₂, R₃, and R₄)and a rhizoplast are present, following the general pattern found in other chrysophytes. The R₁ rootlet, containing seven microtubules, originates at the basal body of the long flagellum that bears mastigonemes (F₁). The R₁ rootlet forms an arc which curves in clockwise direction (when viewed from the anterior end of the cell) approximately halfway around the pit from which the short smooth flagellum (F₂) emerges. Numerous microtubules cascade from the exterior-facing side of this rootlet to the tail of the cell. The R₂ rootlet originates between the F₁ and F₂ basal bodies, is attached to the F₁ basal body by a fibrous connection, and forms a clockwise arc above the R₁ rootlet. This rootlet extends approximately one quarter of the way around the pit. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts, designated R₃ and R₃. Both parts circle the pit in counter-clockwise direction, pass beneath the F₂ basal body, and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material, passes diagonally over the top of the F₂ basal body, forms a clockwise loop at least three quarters of the way around the pit to the interior of the R₃ and R₃ rootlets, and ends in the cytoplasm. Similarities of rootlet origins and other details of the flagellar apparatus of D. cylindricum with those of other heterokont organisms reinforce the idea that these organisms are phylogenetically related.     

The role of mixotrophic protists in the population dynamics of the microbial food web in a small artificial pond

• 1 The seasonal variations of protist and rotifer populations were monitored over 1 year in a small artificial pond. Grazing rates on fluorescently labelled bacteria were also determined.
• 2 The data showed population dynamics similar to other small freshwater bodies; diatoms were numerous during the spring, chlorophytes dominated during the summer months, and mixotrophs, in particular Gymnodinium, dominated during the autumn and winter.
• 3 The mixotrophic dinoflagellates were responsible for a high chlorophyll concentration during the autumn and winter. Mixotrophs were important consumers of bacteria, particularly during the autumn when population densities of pure heterotrophs were low. Mixotrophs were an important component of the microbial food web in this pond.

     

FURTHER EVIDENCE FOR A MEMBRANE-BOUND ENDOSYMBIONT WITHIN THE DINOFLAGELLATE PERIDINIUM FOLIACEUM1

The fine structure of the binucleate, fucoxanthin-containing dinoflagellate Peridinium foliaceum (Stein) Biechler was re-examined for evidence of an endosymbiout. The eucaryotic nucleus, chloroplasts and associated ribosome-dense cytoplasm were separated by a single invaginating membrane from the rest of the dinoflagellate cell. The triple membrane-enclosed eyespot, mesocaryotic nucleus, trichocysts and accumulation bodies resided in the dinoflagellate cytoplasm. These observations suggest that P. foliaceum contains a membrane-bound endosymbiont, similar to that already described for the closely related species. P. balticum (Levander) Lemmermann.     

PIGMENTS OF THE DINOFLAGELLATE PERIDINIUM BALTICUM AND ITS PHOTOSYNTHETIC ENDOSYMBIONT1

An examination of the pigments of the binucleate dinoflagellate Peridinium balticum (Levander) Lemmerman revealed the presence of chlorophylls a, c₁ and c₂ and the carotenoids: fucoxanthin (most abundant), diadinoxanthin, diatoxanthin, an unidentified fucoxanthin-like xanthophyll, β-carotene, γ-carotene and astaxanthin. A comparison of the pigments of P. balticum and P. foliaceum (Stein) Biecheler, also a binucleate dinoflagellate, demonstrated similar compositions. However P. balticum lacked the β-carotene precursors (e.g. phytoene) which accumulated outside the chloroplast in P. foliaceum. This study indicates that P. balticum and P. foliaceum are closely related; each species is a heterotrophic dinoflagellate with a photosynthetic endosymbiont taxonomically affiliated with the Chrysophyta (Chrysophyceae or Bacillariophyceae).     

PHOTOSYNTHETIC ELECTRON TRANSPORT IN CELL-FREE EXTRACTS OF DIVERSE PHYTOPLANKTON1,2

A simple and rapid procedure for preparing thylakoid membranes that are active in photosynthetic electron transport from diverse phytoplankton species is described. The method requires disruption of algal cells with glass beads, exposure to mild hypotonic stress, and subsequent enrichment of the thylakoid membranes by differential centrifugation. Isolated thylakoid membranes were assayed for photosynthetic electron transport activity by measuring rates of oxygen consumption and oxygen production, using a variety of electron donors and acceptors. In the dinoflagellate Gonyaulax polyedra Stein, a relatively broad pH optimum between 7.0 and 8.0 was determined for the whole chain electron transport from water to methyl viologen. The preparation maintained maximum activity for 45 min following the preparation. The assay for photosystem I activity in G. polyedra, determined as electron flow from ascorbate/2,6-dichlorophenolindophenol to methyl viologen, had a somewhat narrower pH optimum around 8.0. Rates of whole chain photosynthetic electron transport on a per cell and on a per chlorophyll a basis were shown to decrease dramatically with cell age in batch cultures of G. polyedra. Using the procedures optimized for G. polyedra, reproducible rates of electron transport on a per cell chlorophyll a basis were also measured in cultures of the dinoflagellate Glenodinium sp., the diatom Nitzschia closterium (Ehrenberg 1839) Wm. Smith 1853 and the chrysophyte Monochrysis lutheri Droop {= Pavlova lutheri (Droop) Green}. Other electron transport assays applied to G. polyedra, and that resulted in comparable rates to those found in other algal groups, include the photosystem II assay from water to diaminodurene/ferricyanide and the photosystem I assay from durohydroquinone to methyl viologen.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF UROGLENA AMERICANA (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Uroglena americana Calkins (Uroglenopsis americana [Calkins] Lemmerman) was determined using serial section reconstruction. The three microtubular rootlet systems (R₂, R₃, and R₄) follow the general pattern found in other chrysophytes. The R₂ rootlet originates between the basal bodies of the mastigoneme-bearing long flagellum (F₁) and the short smooth flagellum (F₂) and is attached to the former by a fibrous connection. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts (designated R₃ and R₃) which circle the depression from which the F₂ flagellum emerges in counter-clockwise direction. These two rootlets pass beneath the F₂ basal body and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material which passes diagonally over the F₂ basal body, forms a clockwise loop about three-quarters of the way around the depression, and ends in the cytoplasm. In place of a typical chrysophyte R₁ rootlet, U. americana has a different array of microtubules attached to the F₁ basal body which we have designated the descending rootlet (DR). This rootlet is a hairpin-shaped structure lying just below the surface of the cell; its longitudinal axis is predominantly parallel to the longitudinal axis of the cell. The DR resembles the bypassing rootlet which occurs in phaeophyte zoospores. Other chrysophytes may possess rootlets which are similar to the DR found in Uroglena.