Chemical and Electron Microscopic Studies of Cattle (Bos taurus) With Four Types of Phenotypic Pigmentation

The biological behavior of the pigmentary phenotypes of four breeds of cattle has been analysed: the black pigmentation of Holstein Friesian; the red pigmentation of Limousin; the dilution in Charolais; and the postnatal disappearance of red pigmentation in Chianina. The analytic techniques included the characterization of melanins by high-performance liquid chromatography, the examination of follicular melanocytes by light microscopy, and the examination of melanosomes by electron microscopy. The black phenotype was very strongly eumelanogenic. The red phenotype in Limousin is polymorphic: individual follicular melanocytes contain both mature eumelanosomes and pheomelanosomes. Charolais and Chianina cattle exhibited a dramatic reduction in melanogenic activity, which was characterized by the almost exclusive presence of prephaoemelanosomes in Charolais and of immature premelanosomes in Chianina. In the dilute Charolais phenotype, the density of distribution of follicular melanocytes also seemed to be reduced. The genes that are responsible for these four phenotypes seem to act on the maturation, differentiation, and density of distribution of the melanosomes.     

Plasma Membrane Glycoproteins of Ciona intestinalis Spermatozoa that Interact with the Egg1

In the ascidian Ciona intestinalis the species-specific interaction between the spermatozoon and the egg occurs between the vitelline coat (VC) of the egg and the plasma membrane of the apical part of the head of the spermatozoa. Concanavalin A (Con A)-binding sites are present on this area of the sperm surface. We used Con A to identify and isolate the spermatozoon plasma membrane components that may be involved in the interaction with the VC. These glycoproteins have been identified on SDS-PAGE of a sperm membrane fraction (SMF) enriched with the extermal proteins, after incubation of the gel with ³H-Con A. Affinity chromatography on Con A-agarose has been used for the purification of sperm plasma membrane proteins with and affinity for the lectin. The biological activity of the Con A-retained fraction was determined with binding and fertilization assays.     

Physiological and Biochemical Aspects of Symbiotic Nitrogen Fixation in Cowpea (Vigna unguiculata (L.) Walp. var. Tuy) Plants Infected by Cowpea Mosaic Virus

Three-day-old cowpea seedlings were inoculated with the severestrain of Cowpea Mosaic Virus (CpMV) and 24 h later with Bradyrhizobiumsp. cowpea, strain I-125, when virus translocation to rootsstill had not taken place. Plants were harvested at 22, 30,45 and 59 d after germination. Active virus replication wasassociated with increased protein content, detected in the leavesof 22-d-old plants. CpMV infection reduced the total leaf area,dry weight of shoots and the chlorophyll content of the firsttrifoliolate leaf at all experimental times. Low sugar contentwas recorded in leaves of 22- and 30-d-old CpMV-infected plantsand in nodules and roots of 30- and 45-d-old CpMV-infected plants.Up to 45 d, the nodule mass of CpMV-infected plants was lowerthan in controls, but reached control values at the 4th harvest.In CpMV-infected nodules, massive agglomeration of virus particles,crystalline virus inclusions and the proliferation of the endoplasmicreticulum were observed only in those cells containing bacteroids.In 30- and 45-d-old plants, CpMV infection decreased the contentof ureides in nodules, roots, and petioles. Virus infectiondid not alter the -amino-N content of roots and nodules butinduced a transient 74% reduction in the level of -amino-N inpetioles of 45-d-old plants. At the 1st and 2nd harvests theactivity of uricase (EC 1.7.3.3 [EC] ) in the nodules and of pyruvatekinase (EC 2.7.1.40 [EC] ) in the nodules and leaves were decreasedseverely by virus infection. CpMV did not hinder the allantoinase(EC 3.5.2.5 [EC] ) activity in the leaves but caused a 9% transitorydecrease in the activity of this enzyme in nodules of 45-d-oldplants. Measurements of NAD-malic enzyme (EC 1.1.1.38 [EC] ) in nodulesalso showed the non-effect of CpMV on this enzyme, except fora temporary 16% reduction at the 2nd harvest. As compared tocontrols, the relative abundance of ureides in 30-d-old CpMV-infectedplants indicated a 15%, 10%, and 51% reduction in the nodules,roots, and petioles, respectively. Results indicate that atthe time of the 4th harvest the symbiotic process, measuredin terms of ureide content and enzymatic activities, was functioningat a near normal level despite nodule infection by CpMV. Key words: Cowpea Mosaic Virus, nitrogen fixation, cowpea, enzymes, ultrastructure     

The Potential for Nitrogen Fixation in a Lake Receiving Sewage Effluent (Grasmere, English Lake District)

The potential for nitrogen fixation in the water column and sediment of Grasmere (English Lake District) was investigated using the acetylene reduction technique, with reference to seasonal changes and concentrations of dissolved oxygen and inorganic nitrogen in the epilimnion and hypolimnion. Potential rates of nitrogen fixation and MPN counts of nitrogen-fixing bacteria correlated with each other and with decreases in dissolved oxygen concentration. The results suggested that selective changes in the nitrogen-fixing microflora took place during the period of thermal stratification. Neither light-dependent fixation, nor cyanobacteria could be detected in water column samples, and acetylene reduction was detected, for most of the season, only in samples of water and sediment to which a source of carbon and phosphorus had been added. The possible role of the sewage effluent in suppressing nitrogen fixation is discussed.     

Ozone-induced ultrastructural changes in the plasma membrane of Chlorella sorokiniana

Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm⁻³(140 p.p.m.) O₃ for 30 min. Sixty-eight per cent of the cells were plasmolysed after 15 min O₃ exposure with disruption of organelles similar to that previously described in higher plants. Freeze-fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O₃for short periods. After 20 min O₃ 90% of the cells cross-fracture, which indicates a change in molecular interactions in the membrane exposed to O₃ The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O₃ Changes in ⁸⁶Rb influx occur during a similar time. After more extended exposure to O³ the plasma membrane P face shows regions of lipid phase transition to the crystalline state.     

Serum Proteins Promoting [3H]Thymidine Uptake by Trypanosoma (Schizotrypanum) cruzi (Chagas) in vitro

SYNOPSIS. Five proteins capable of stimulating [³H]thymidine uptake by Trypanosoma cruzi in vitro were isolated from fetal calf serum by (NH₄)₂SO₄ precipitation and ion exchange column chromatography. The proteins were partially characterized by immunodiffusion, immunoelectrophoresis, polyacrylamide gel disc electrophoresis, and SDS electrophoresis. As estimated by SDS electrophoresis, using 4 standards, the molecular weight of protein 1 was 100,000, that of protein 2 was 76,000. and that of proteins 3–5 was 68,000 daltons.     

Lectin-Binding Sites Involved in Paramecium primaurelia Mating Pair Formation

ABSTRACT. Mating pair formation in Paramecium primaurelia was shown to be inhibited by incubating mating-competent mating type (mt) I and mt U cells with Limulus polyphemus agglutinin (LPA) or wheat germ agglutinin (WGA). Preincubation of LPA and WGA with their specific binding-monosaccharides, N-acetylneuraminic acid (NeuAc) and N-acetylglucosamine (GlcNAc), respectively, prevented the lectin effect on pair formation. Addition either of NeuAc or GlcNAc resulted in a reversal of cell pairing inhibition by LPA or WGA, respectively. Both NeuAc and GlcNAc monosaccharides inhibited pair formation when their concentration exceeded a threshold value. The pattern of the relative distribution of NeuAc and GlcNAc molecules on the cell surface was analyzed using fluorescence resonance energy transfer techniques combined with imaging systems. Mt I1 cells showed a high lectin-binding site density localized just on the surface region engaged in conjugation. The pattern of mt I cells, consisting of a quite homogeneous lectin-binding site density spread on the cell surface, was also common to nonmating-competent cells and to immature cells. These findings suggest that in P. primaurelia pair formation involves both NeuAc and GlcNAc residues and that the development of mating-competence is related to a modification in NeuAc and GlcNAc relative distribution on the cell surface of mt 11 cells.     

How river structure and biological traits influence gene flow: a population genetic study of two stream invertebrates with differing dispersal abilities

1. Determined by landscape structure as well as dispersal‐related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small‐scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal‐related traits: an amphipod (Gammarus fossarum) with a purely aquatic life cycle and a mayfly (Baetis rhodani) with a terrestrial adult stage. 2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre‐alpine catchment and compared these results to the broader‐scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in‐stream barrier effects. 3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in‐stream barriers. 4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal‐related traits when planning management and conservation strategies.     

Effects of different thermal treatments during embryonic development on the artificial incubation efficiency of crayfish (Austropotamobius pallipes Lereboullet) eggs. Control of the embryogenetic duration and implications for commercial production

Summary

The development and improvement of artificial incubation techniques for freshwater crayfish eggs and their incorporation into the working schedule of breeding centres is of great interest for commercial production. Factors such as the water circulation system, flow rate, thermal treatment, etc., could strongly influence the success of the process. The present study attempts to test the possible influence of one of these variables, the thermal regime, on both the duration of embryonic development and the efficiency rates obtained in the artificial incubation of white-clawed crayfish (Austropotamobius pallipes) eggs. Four different thermal treatments were tested (three of them included a period at low temperature: 4°-5°C). Survival rates to juvenile stage 2 were similar in the four cases, ranging between 66.7 and 72.7%. We conclude that water cooling (an expensive management procedure) is not necessary in astacid breeding centres provided that egg development takes place at moderately low temperatures (8°-10°C) with a subsequent increase of up to 15°C from the eyed stage. However, the inclusion of periods at low temperature (4°-5°C) allows the staggered production of juvenile batches throughout a 3-week period without adverse effects on efficiency rates. This could be useful to breeding centres in meeting seasonal market requirements. In our study, egg and juvenile losses (mortality rate: 15–20%) were concentrated during the last phases of embryogenesis, particularly from the eyed stage to juvenile stage 2, during which they amounted to more than 90% of the overall mortality which took place during the artificial incubation process.