An investigation of the fine structure, cell surface carbohydrates, and appeal of the diatom Extubocellulus sp. as prey for small flagellates

Summary. The fine structure and surface exopolymers of a coastal planktonic nanodiatom of the sparsely reported genus Extubocellulus were studied respectively by scanning electron microscopy and confocal microscopy in conjunction with fluorescent lectins. Monitoring the suitability of the species as prey food for other protists was also investigated by video microscopy coupled with digital film. Cells are rectangular in girdle view, with a pervalvar axis longer than the apical axis. Valves are almost circular with a diameter of 2.8 to 3.6 μm. The valve face bears randomly distributed areolae (ca. 50 in 10 μm), which may be either open or occluded. Two small raised ocelluli occur at the apices, with a rim devoid of perforations and about 6–7 porelli. Glucose and N-acetyl-glucosamine moieties present on the surface of the live diatom were labelled with fluorescent lectins, and a differential pattern of distribution for both carbohydrates was observed. The potential role of fluorescent lectins as cellular probes of taxonomic value in small diatoms is compared with that of nucleotide and antibody probes. We provide the first illustrative evidence of the presence of Extubocellulus sp. in the cytoplasm of the nanoflagellate Goniomonas amphinema and of the egestion of diatom frustules. Results obtained are discussed in the light of the present knowledge of the role of carbohydrate–protein interactions in phagocytosis of prey by free-living protozoa. Correspondence (present address): M. Martin-Cereceda, Department of Ecology and Evolutionary Biology, Haworth Hall, 1200 Sunnyside Avenue, University of Kansas, Lawrence, KS 66045, U.S.A.     

Diplodinium (Ostracodinium) minorum sp. n., Ciliate from the Rumen of Domestic Sheep*

SYNOPSIS. Diplodinium (Ostracodinium) minorum sp. n., observed in rumen contents from several domestic sheep, resembles Diplodinium (O.) ypsilon and Diplodinium (O.) magnum. It differs from the latter 2 species primarily in the size and proportions of the body, size of the rectum and anus, and in the presence of a short right caudal lobe in many individuals. In the samples studied, D. (O.) minorum constituted from 0.06 to 0.67% of the total rumen ciliate population.     

New Family,Genus, and Species of Microsporida (Protozoa: Microsporida) from the Tropical Fire Ant,Solenopsis geminata (Fabricius) (Insecta: Formicidae)*

SYNOPSIS. A new species of Microsporida, Burenella dimorpha sp. n., representing a new family, Burenellidae fam. n. and genus, is described on the basis of light- and electron-microscope observations. The family is characterized by 2 sequences of sporogony, each sequence having morphologically different sporonts and spores. The parasite infects the tropical fire ant, Solenopsis geminata (Fabricius), producing distinct pathologic manifestations (clearing of the cuticle and eye malformation) and death in the pupal stage of development. Transmission of the infection per os to healthy S. geminata, to the Southern fire ant, Solenopsis xyloni McCook, and to the red and black imported fire ants, Solenopsis invicta Buren and Solenopsis richteri Forel, is reported.     

Chloroplast changes and differentiation of callus cells in Eckloniopsis radicosa (Kjellman) Okamura (Phaeophyta, Laminariales)

Excised rectangular blade pieces of young sporophytes of Eckloniopsis radicosa (Kjellman) Okamura were cultured at four different temperatures (10, 15, 20, 25 °C) and light intensities (10, 20, 40, 80 μmol photon m⁻² s⁻¹) to observe callus cell propagation and differentiation. Although rapidly propagating callus cells were observed at a low temperature (15 °C) and low light intensities of (10–20 μmol photon m⁻² s⁻¹), differentiation to bladelets was only observed at higher temperatures and light intensities. In rapidly propagating callus cells, the chloroplasts decreased in both size and number. When callus cells with few chloroplasts were exposed to high temperature and light intensity, the chloroplasts gradually increased in number and size until they were the same size as found in cells from young blades. Finally, these cells differentiated and produced bladelets. This is the first report describing a relationship between differentiation and chloroplast size and number in the callus cells on E. radicosa. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effect of local heating and cooling on cambial activity and cell differentiation in the stem of Norway spruce (Picea abies)

BACKGROUND AND AIMS The effect of heating and cooling on cambial activity and cell differentiation in part of the stem of Norway spruce (Picea abies) was investigated. METHODS: A heating experiment (23-25 degrees C) was carried out in spring, before normal reactivation of the cambium, and cooling (9-11 degrees C) at the height of cambial activity in summer. The cambium, xylem and phloem were investigated by means of light- and transmission electron microscopy and UV-microspectrophotometry in tissues sampled from living trees. KEY RESULTS: Localized heating for 10 d initiated cambial divisions on the phloem side and after 20 d also on the xylem side. In a control tree, regular cambial activity started after 30 d. In the heat-treated sample, up to 15 earlywood cells undergoing differentiation were found to be present. The response of the cambium to stem cooling was less pronounced, and no anatomical differences were detected between the control and cool-treated samples after 10 or 20 d. After 30 d, latewood started to form in the sample exposed to cooling. In addition, almost no radially expanding tracheids were observed and the cambium consisted of only five layers of cells. Low temperatures reduced cambial activity, as indicated by the decreased proportion of latewood. On the phloem side, no alterations were observed among cool-treated and non-treated samples. CONCLUSIONS: Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.     

Sphaeromyxa maiyai sp. n. (Protozoa: Myxosporidea), Coelozoic Parasite of the Pacific Tomcod,Microgadus proxiimus*

SYNOPSIS. Sphaeromyxa maiyai sp. n. (Myxosporidea: Myxiidae) is described from the gall bladder of the Pacific tomcod Microgadus proximus Girard, from Newport, Oregon. The plasmodial stage is discoid averaging between 1 and 2 cm. The spore averages 27.6 × 5.6 μm in breadth, with pyriform polar capsules measuring 9.3 × 3.7 μm. Scanning electron microscopy reveals the presence of numerous longitudinal striations.     

A comparison of methods for callus culture and plant regeneration of RD25 rice (Oryza sativa L.) in two laboratories

While methodology is transferable from one laboratory to another, an exact transfer does not usually occur and even a nearly exact transfer of methods does not always result in repeatable data. Researchers should not expect that an effort to duplicate a published procedure will necessarily lead to identical results.In attempting to transfer rice tissue culture methods between laboratories in Fort Collins, Colorado, USA and Bangkok, Thailand, we discovered that a combination of the methods of each laboratory produced the best results in term of callus productions and plant regeneration. In the experiments reported here, the type of culture vessel used and the geographical location were also important variables.Supported by the USAID/Cooperative Agreement No DAN-4137-A-00-4053-00.     

Exogenous Stages of Isospora serini (Aragão) and Isospora canaria sp. n. in the canary (serinus canarius Linnaeus)*

Exogenous stages of Isospora serini (Aragão) and Isospora canaria sp. n. from the canary (Serinus canarius Linnaeus) are described. Oocysts of I. serini are spheroid and average 19.2 × 20.1 μ m, while those of I. canaria are larger, more ellipsoid, and average 21.8 × 24.6 μ m. No oocyst residuum is present and the oocyst walls of both species are colorless, transparent, and single layered. Sporocysts average 9.4 × 15.2 μ m for I. serini and 11.5 × 18.1 μ m for I. canaria. The I. canaria sporocyst has a substiedal body, but none was found in I. serini sporocysts. Both species have a spherical sporocyst residuum; this was obscured in the I. serini sporocyst by scattered granules. Living sporozoites of I. canaria average 3.6 × 16.9 μ m and have 1 to 3 refractile globules; those of I. serini have 2 globules and average 2.8 × 12.6 μ m. A disseminated infection of the mononuclear phagocytes results from administration of I. serini while I. canaria oocysts give rise to a typical coccidian infection restricted to the intestinal epithelium. Asexual stages of I. serini in macrophages are indistinguishable from parasites previously called avian Toxoplasma, Atoxoplasma, and Lankesterella.     

A morphological and quantitative characterization of early floral development in apple (Malus x domestica Borkh.)

Apple is an important crop and a focus of research worldwide. However, some aspects of floral commitment and morphogenesis remain unclear. A detailed characterization of bourse shoot apex development was undertaken to provide a framework for future genetic, molecular and physiological studies. Eight morphologically distinct stages of shoot apex development, prior to winter dormancy, were defined. Based on measurements of meristem diameter, two stages of vegetative development were recognized. Vegetative meristems were flat, and either narrow (stage 0) or broad (stage 1). Pronounced doming of the apex marked stage 2. During stage 3, the domed meristem initiated four to six lateral floral meristems and subtending bracts before converting to a terminal floral meristem (stage 4). The terminal floral meristem proceeded directly with bractlet and sepal initiation, while lateral floral meristems initiated bractlets (stage 5). Sepal initiation began on the basal lateral flower (stage 6) and continued in an acropetal direction until all floral meristems had completed sepal initiation (stage 7). In this study, only stage 0 and stage 7 apices were observed in dormant buds, indicating that stages 1-6 are transient. The results suggest that broadening of the apex (stage 1) is the first morphological sign of commitment to flowering.