TWO TYPES OF CYTOPLASMIC CLEAVAGE IN THE COENOCYTIC SOIL ALGA PROTOSIPHON BOTRYOIDES (CHLOROPHYCEAE)1

Cytokinesis in the coenocytic green alga Protosiphon botryoides (Kütz.) Klebs was studied with transmission electron microscopy. In vegetative cells, nuclei with associated basal bodies and dictyosomes are scattered throughout the cytoplasm. Mature cells may develop either multinucleate resting spores (coenocysts) or uninucleate zoospores. Cytokinesis may be preceded by contraction of the protoplast due to the disintegration of vacuoles that are present in larger, siphonous cells. The formation of coenocysts in ageing, siphonous cells, is signalled by cleavage of the chloroplast and the development of arrays of phycoplast microtubules in one or more transversely oriented planes through the cell. Nuclei with associated basal apparatuses stay dispersed throughout the cytoplasm; the basal bodies apparently are not involved in organization of the phycoplast. The plasma membrane invaginates, resulting in a centripetal cleavage of the protoplast into two or more multinucleate daughter protoplasts. Simultaneously, wall material is deposited along the outside of the daughter protoplasts by dictyosome-derived vesicles, and finally two or more thick-walled coenocysts are formed. The formation of zoospores, on the other hand, is signalled by clustering of the nuclei in one or more groups depending on the shape of the mother cell. The nuclei become arranged with the associated basal apparatuses facing toward the center of the cluster. Bundles of phycoplast microtubules develop between the nuclei, radiating from the center of a cluster toward the plasma membrane; basal apparatuses or associated structures apparently are involved in organization of the phycoplast. Cleavage furrows grow out centrifugally along these bundles of micro-tubules, fed by dictyosome-derived vesicles. No wall material is deposited. An additional mitotic division occurs during cleavage, and finally numerous uninucleate, wall-less, biflagellate zoospores are formed. The ultrastructural features of the two different types of cytoplasmic cleavage associated with two different types of daughter cells have not previously been reported for chlorophycean algae.     

Vicariance patterns in the Mediterranean Sea: east–west cleavage and low dispersal in the endemic seagrass Posidonia oceanica

Aim The seagrass, Posidonia oceanica is a clonal angiosperm endemic to the Mediterranean Sea. Previous studies have suggested that clonal growth is far greater than sexual recruitment and thus leads to low clonal diversity within meadows. However, recently developed microsatellite markers indicate that there are many different genotypes, and therefore many distinct clones present. The low resolution of markers used in the past limited our ability to estimate clonality and assess the individual level. New high‐resolution dinucleotide microsatellites now allow genetically distinct individuals to be identified, enabling more reliable estimation of population genetic parameters across the Mediterranean Basin. We investigated the biogeography and dispersal of P. oceanica at various spatial scales in order to assess the influence of different evolutionary factors shaping the distribution of genetic diversity in this species. Location The Mediterranean. Methods We used seven hypervariable microsatellite markers, in addition to the five previously existing markers, to describe the spatial distribution of genetic variability in 34 meadows spread throughout the Mediterranean, on the basis of an average of 35.6 (± 6.3) ramets sampled. Results At the scale of the Mediterranean Sea as a whole, a strong east–west cleavage was detected (amova) . These results are in line with those obtained using previous markers. The new results showed the presence of a putative secondary contact zone at the Siculo‐Tunisian Strait, which exhibited high allelic richness and shared alleles absent from the eastern and western basins. F statistics (pairwise θ ranges between 0.09 and 0.71) revealed high genetic structure between meadows, both at a small scale (about 2 to 200 km) and at a medium scale within the eastern and western basins, independent of geographical distance. At the intrameadow scale, significant spatial autocorrelation in six out of 15 locations revealed that dispersal can be restricted to the scale of a few metres. Main conclusions A stochastic pattern of effective migration due to low population size, turnover and seed survival is the most likely explanation for this pattern of highly restricted gene flow, despite the importance of an a priori seed dispersal potential. The east–west cleavage probably represents the outline of vicariance caused by the last Pleistocene ice age and maintained to this day by low gene flow. These results emphasize the diversity of evolutionary processes shaping the genetic structure at different spatial scales.     

Unusual swimming mechanism in Calycopsis borchgrevinki (Hydrozoa)

Calycopsis borchgrevinki (Browne, 1910) from Antarctic waterswas studied histologically. The entire bell is enclosed in achitin-like skin, supported by chitin-like rods in the radialmesogleal fibres. In the tentacles a thick mesogloea is presentwithout chitinous structures. The gonads are embedded in thestomach folds. It is postulated that these characters are adaptationsto ecological conditions in Antarctic waters.     

Comparative radionuclide and thermodilution determinations of cardiac output and stroke volume in the baboon (Papio ursinus)

Thermodilution cardiac output determinations and multigated equilibrium blood-pool scintigraphy were performed in ten healthy chacma baboons (Papio ursinus). The correlation was moderately good between both the radionuclide and thermodilution stroke volume (r = 0.58, SEE = 3 ml; SVth = 0.78SVr + 15.6 ml) as well as the cardiac output (r = 0.72, SEE = 0.2 liter/min; COth = 0.56 Cor + 2.1 liter/min). The attenuation depth dr as determined by radionuclide techniques was found to correlate well with the radiologically determined values dx (r = 0.8, SEE = 0.4 cm; dx = 0.87dr + 0.72 cm) which validated the depth values used in the calculations.     

The role of bacterial cell wall hydrophobicity in adhesion

In this study, the adhesion of bacteria differing in surface hydrophobicity was investigated. Cell wall hydrophobicity was measured as the contact angle of water on a bacterial layer collected on a microfilter. The contact angles ranged from 15 to 70 degrees. This method was compared with procedures based upon adhesion to hexadecane and with the partition of cells in a polyethylene glycol-dextran two-phase system. The results obtained with these three methods agreed reasonably well. The adhesion of 16 bacterial strains was measured on sulfated polystyrene as the solid phase. These experiments showed that hydrophobic cells adhered to a greater extent than hydrophilic cells. The extent of adhesion correlated well with the measured contact angles (linear regression coefficient, 0.8).     

Reductive dechlorination of 2,4-dichlorobenzoate to 4-chlorobenzoate and hydrolytic dehalogenation of 4-chloro-, 4-bromo-, and 4-iodobenzoate by Alcaligenes denitrificans NTB-1

Alcaligenes denitrificans NTB-1, previously isolated on 4-chlorobenzoate, also utilized 4-bromo-, 4-iodo-, and 2,4-dichlorobenzoate but not 4-fluorobenzoate as a sole carbon and energy source. During growth, stoichiometric amounts of halide were released. Experiments with whole cells and cell extracts revealed that 4-bromo- and 4-iodobenzoate were metabolized like 4-chlorobenzoate, involving an initial hydrolytic dehalogenation yielding 4-hydroxybenzoate, which in turn was hydroxylated to 3,4-dihydroxybenzoate. The initial step in the metabolism of 2,4-dichlorobenzoate was catalyzed by a novel type of reaction for aerobic organisms, involving inducible reductive dechlorination to 4-chlorobenzoate. Under conditions of low and controlled oxygen concentrations, A. denitrificans NTB-1 converted all 4-halobenzoates and 2,4-dichlorobenzoate almost quantitatively to 4-hydroxybenzoate.     

Plasmids in Leuconostoc oenos

A new procedure was used to isolate 11 plasmids from eight Leuconostoc oenos strains. Plasmid DNA was not detected in 34 other strains of this species. Plasmid sizes ranged from 2.47 to 4.61 kilobase pairs. This is the first report of extrachromosomal elements in L. oenos.     

The oxidation product of molybdenum cofactor from milk xanthine oxidase

In extracts of acid treated molybdenum cofactor containing xanthine oxidase, fluorescence is maximally developed upon a three hours incubation. Analysis by means of reversed phase HPLC revealed the presence of several fluorescent compounds, the main one being a blue fluorescent compound with an emission maximum of 465 nm when maximal excited at 395 nm at a neutral pH. Definite proof is presented that this compound is the oxidation product of the molybdenum cofactor. The remaining fluorescent products are shown to be pterin-derivatives, yielding predominantly pterin-6-carboxylic acid upon permanganate oxidation. Purified oxidation product of molybdenum cofactor however, didn's yield a fluorescent derivative at all upon treatment with permanganate.