Sperm Nuclear Transformation and Aster Formation Related to Metabolic Behaviour in Amphibian Eggs

Bufo arenarum oocyte maturation is related to important modifications in the metabolism of carbohydrates. Such changes involve a different relative participation of the main oxidative routes and are under the influence of seasonal variations of the pituitary activity.
Ovulated coelomic oocytes obtained during the winter period, were unable to initiate cleavage after injection of a sperm suspension. The extent of sperm head transformation and aster formation in the cytoplasm of oocytes with a different metabolic behaviour (obtained during the winter and summer periods) were studied.
Our results show that sperm nuclear transformation and DNA synthesis were quite similar in both types of oocytes. In contrast to summer oocytes, in which the pronucleus was sourranded by an aster, no aster structure was formed in winter ooctyes notwithstanding pronucleus formation occurred.
These results suggest that the failure to develop aster may explain the lack of cleaving in winter oocytes. It appears that the metabolic changes, aster formation and the capability to cleave are closely related and could be dissociated from oocyte nuclear maturation in this species.     

Preliminary Studies on the Photosynthetic Structures of Trifolium alpinum L. as Related to Productivity

Trifolium alpinum L. is a high-quality alpine forage plant growingspontaneously from 1900 to 2800 m above sea level and is widelydistributed in Piedmont and the Valle d'Aosta (Italy), whereit can reach population frequencies of 90 per cent. Yields weredetermined on forage harvested in the Valle dell'Orco (Piedmont)and were comparable to cultivated clovers from higher latitudes;yields decreased progressively as the elevation increased. Thechemical and nutritional characteristics of the forage, thoughcomparable to clovers cultivated in the Po valley (Italy), were,however, more constant. The structure of the leaf lamina asrelated to elevation was investigated using light microscopy,TEM and SEM. This is complemented by data on chlorophyll concentration,succulence, specific leaf weight and area. At all elevationsT. alpinum lacks, apart from bundle sheath cell chloroplastsin a centrifugal arrangement, the structural characteristicsof C₄ plants. The chlorophyll a:b ratio (less than four) istypical of a C₂ plant. Succulence indices (S and S_m) were verylow, making CAM pathway photosynthesis unlikely. Unusual anddifficult to interpret structures included: small functionalchloroplasts in both the epidermises, stomata present almostexclusively in the upper epidermis and mitochondria enveloped(or enclosed) by chloroplasts. It was observed that, as theelevation increases, populations are selected which are well-adaptedfor gas exchange (increase in specific leaf area, stomatal densityand intercellular spaces) and characterized by a decrease inthe grana thylacoid:integrana thylacoid ratio (consistent withthe increase in the chlorophyll a:b ratio), the per cent water,S_m and the specific leaf weight. Trifolium alpinum L., alpine trefoil, leaf structures, photosynthesis, yield, elevation, C₂, C₄     

Phylogenetic analysis of eleven species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae) based on comparisons of allozymes

Freshwater snails in the genus Biomphalaria transmit Schistosoma mansoni in Africa, South America and the Caribbean region. Although considerable attention has been given to the identification of species, little is known of evolutionary relationships among the species. A phylogenetic analysis of 25 populations representing 11 species was performed on 25 enzyme loci examined using starch gel electrophoresis. A phylogenetic analysis of the individual populations produced 60 trees of equal length. The 60 trees have a consistency index value of 75.9% and a retention index value of 76.5%. The phylogenetic analysis provided strong support for the monophyly of Biomphalaria with either 14 or 15 synapomorphies uniting all of the species included and separating them from the outgroup, two species of Helisoma. Four nominal species represented by multiple populations formed monophyletic groups. Populations of B. sudanica, B. choanomphala, and B. alexandrina were interspersed. Ten arrangements were obtained for the populations of these three species. A variety of ingroup taxa were used to root the trees, and all provided support for the use of Helisoma species as an outgroup. In all of the trees obtained, the African species together formed a monophyletic group. In none of the trees obtained did the neotropical species form a monophyletic group. A constrained analysis requiring the monophyly of the neotropical species as well as the African species resulted in 90 trees just two steps longer than the shortest trees. Analysis of the species from either hemisphere alone resulted in decreased resolution, as measured by an increase in the number of trees obtained. This finding suggests that further comparisons of species from the two hemispheres will be of considerable value. Finally, two species which are resistant to infection with S. mansoni were included among the eleven studied. Neither of these species formed the sister group to all of the other species included, indicating that susceptibility is the plesiomorphic state, and that resistance is derived. Similarly, in none of the trees obtained did the two resistant species fall out as sister taxa, indicating that resistance arose independently twice.     

Cell Surface Saccharides in Three Phytomonas Species Differing in Host Specificity

ABSTRACT. Cell surface carbohydrates of three phytoflagellates, Phytomonas francai. Phytomonas serpens and Phytomonas sp. from different hosts including cassava, coreid insect Phthia picta and the milkweed plant Euphorbia hyssopifolia, respectively, were analysed by agglutination assays employing a battery of highly purified lectins with affinity for receptor molecules containing N-acetylglucosamine (d-GlcNAc), N-acetylgalactosamine (D-GalNAc), galactose, mannose-like (D-Man-like) residues and fucose, and by binding assay using radiolabeled [¹²⁵I]-wheat germ agglutinin (WGA) and fluorescent WGA lectin, as well as glycosidases of known sugar specificity, Escherichia coli K with mannose-affinity fimbrial lectin was also used as an agglutination probe. In general, the presence of D-GlcNAc. D-GalNAc and D-Man-like residues was detected in the phytomonads' plasma membrane. These sugar moieties were confirmed in whole cell hydrolysates as assessed by gas-liquid chromatography (GLC) which in addition, also showed the presence of galactose and xylose. However, marked differences in cell surface carbohydrate structures were observed. Wheat germ agglutinin, which binds to sialic acid and/or d-GlcNAc-containing residues, shows selective agglutinin activities for P. francai and Phytomonas sp., while Bandeiraea simplicifolia II agglutinin (which recognizes d-GlcNAc units) specifically bound to Phytomonas sp. Helix pomatia agglutinin which binds to D-GalNAc-containing residues reacted preferentially with Phytomonas sp. and P. serpens. Con A, which recognizes D-Man-like receptors, agglutinates all the phytomonads; however, the higher interaction was observed with Phytomonas sp. P. francai was selectively agglutinated in the presence of E. coli fimbrial lectin. Fluorescence WGA binding was significantly decreased by N-acetylglucosaminidase activities and the cell agglutination was not altered by neuraminidase treatment, suggesting the presence of an exposed D-GlcNAc moiety on the P. francai and Phytomonas sp. surfaces. Binding studies with [¹²⁵I]-WGA essentially confirmed the fluorescence WGA binding and agglutination assays.     

Content and Aggregation of Ribosomes during Formation, Dormancy and Sprouting of Tubers of Helianthus tuberosus

The ribosomes and their qualitative (monosomes-polysomes) and quantitative variations over a whole vegetative period of the tuber of Helianthus tuberosus L. (cv. OB 1) were examined. Tubers in different phases of growth, dormancy and sprouting or slices of dormant tubers activated with 2 x 10^-6M indol-3-acetic acid were used. The ribosomes were analyzed by a linear sucrose gradient. During flowering, polysomes of tuber disappeared almost completely and rRNA decreased in comparison with the level present at the beginning of tuber formation. After flowering, there was a new synthesis of monosomes and polysomes until the onset of dormancy; this last period was characterized by a marked increase in polysomes and a proportional increase in monosomes. The level remained almost constant till the break of dormancy. When the tubers sprouted, ribosomes, present almost exclusively as monosomes, decreased considerably; on the contrary the non-photosynthetic sprouts contained many monosomes and polysomes. The first phases of activation (3 h) of tuber slices were characterized by a RNA synthesis, which occurred during one hour, in the subunit region of the gradient. Successively (10 h of activation) the ³²P incorporation was seen also in the polysome region and increased with time. Some possible interpretations of these last results are discussed.     

On an undescribed, pleomorphic hyphomycete from litter

Pseudoyima prolifica is described from litter of Scirpus microcarpus Presl. The species produces dark hyphal colonies with few or no conidia, and pallid conidial colonies in which hyphae are sparse or absent. Conidial colonies, macroscopically yeast-like, consist of proliferating scolecoconidia, stauroconidia, and arthroconidia.     

Cell Surface Carbohydrate Differences in Wild and Mutant Strains of Crithidia fasciculata1

Wild type Crithidia fasciculata and three drug-resistant mutant strains that have shown “flagellar adherence” were studied as to their ability to agglutinate with lectins specific for receptor molecules containing N-acetyl glucosamine, N-acetyl galactosamine, galactose, mannose-like residues, fucose, and sialic acid. Escherichia coli with mannose-sensitive fimbriae was also used as an agglutination probe. The presence of D-GalNAc, D-Gal, and mannose-like residues was detected in the wild strain. Generally, in the mutants, residues of these sugar units were present in greater concentrations when compared to the wild type strain. β-Galactosidase treatment showed that β-D-Galp units are exposed on the cell membrane. All types of cell agglutination including flagellum-flagellum (F-F), flagellum-soma (F-S), and soma-soma (S-S) were observed when lectins were used; however, with E. coli only the F-F type of cell agglutination was observed with the wild type strain and the TFR^R1 mutant. All types of agglutination were observed with the other two mutants.     

Population structure and taxonomic discrimination among three species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae) from Kenya

The genetic basis for species designations for African species of Biomphalaria has received little attention. Populations of B. choanomphala, B. sudanica and B. pfeifferi from Kenya were examined using starch gel electrophoresis. Analysis of population structure as measured using Wright's F -statistics for B. sudanica and B. choanomphala revealed that both species show substantial departures from expectations under random mating. Populations of B. choanomphala show the least evidence of inbreeding, and populations of A sudanica are intermediate between B. choanomphala and previously reported levels of inbreeding for B. pfeifferi. Syn topic populations of B. pfeifferi and B. sudanica were genetically distinct. Syntopic populations of B. choanomphala and B. sudanica also showed evidence of separate gene pools, although the evidence is not as conclusive as for B. pfeifferi and B. sudanica. Possible explanations for the failure to find clear differences between B. sudanica and B. choanomphala are considered.