Effects of asexual reproduction on the neighborhood area of cyclical parthenogens

The habitat occupied by a subpopulation and withinwhich there is random mating is known as itsneighborhood area. Neighborhood area is dependenton dispersal rates and organisms with low rates ofdispersal are expected to have small neighborhoodareas. In the absence of evolutionary forces,neighborhood areas under sexual reproduction will beconstant in size as long as dispersal patterns do notchange. This scenario differs when reproduction is bycyclical parthenogenesis since recombination anddispersal may occur in different generations. Ingeneral, dispersal distances increase with the numberof parthenogenetic generations. We show that cyclicalparthenogenesis increases neighborhood area which,concomitantly, decreases the potential for geneticsubdivision. It is noteworthy, however, that theincrease in neighborhood area is a decreasing functionof the number of parthenogenetic generations.This mechanism may have important implications for thepopulation structure of planktonic rotifers living ina horizontally undifferentiated habitat. In suchhabitats organisms are effectively unrestricted intheir lateral movements. Because rotifers typicallyhave low dispersal rates spatial geneticdiscontinuities may develop that divide the populationinto genetically distinct subpopulations. Counteringthis tendency is the increased neighborhood areaproduced by dispersal during the parthenogeneticphase. Thus cyclical parthenogenesis in organismslike rotifers may have important and previouslyunreported effects on the population's geneticstructure.     

Effects of intracerebroventricular administration of aminophylline on hyperbaric-induced increase in carotid blood flow

Carotid blood flow was measured in rats by implanted transit-time ultrasonic flowprobes during hyperbaric experiments at up to 70 bar (7 MPa) using an helium-oxygen hyperoxic (partial pressure of O₂ = 400 mbar) mixture. Before the hyperbaric experiment, an intracerebroventricular injection of phosphate saline buffered solution (PBS) or aminophylline, an adenosine receptor blocker, in PBS was given. Throughout the hyperbaric experiment carotid blood flow increased with ambient pressure in both PBS, i.e. control, and aminophylline treated rats. The increase in carotid blood flow was significantly attenuated in aminophylline treated rats. Additional experiments showed that the increased carotid blood flow was independent of hyperoxia as well as of temperature. The hypothesis that the hyperbaric dependent increase in carotid blood flow was mediated by brain adenosine receptors and its implication regarding a cerebral vasodilatation are discussed.     

Analysis of viability and cell types of macroalgal protoplasts using flow cytometry

The ability to rapidly distinguish viable sub-populations of cells within populations of macroalgal protoplast isolations was demonstrated using flow cytometry. Viable protoplasts from Ulva sp. and Porphyra perforata J. Ag. were distinguished from non-viable protoplasts based on differential fluorescein accumulation. The identities of cortical and epidermal protoplasts from Macrocystis pyrifera (L.) C. Ag. were inferred based on light-scattering and chlorophyll a autofluorescence. Three cell types could be distinguished among protoplasts released from thalli of P. perforata based on chlorophyll a and phycoerythrin autofluorescence. Mixed protoplast populations of Ulva sp. and P. perforata were also discernable based on relative chlorophyll a and phycoerythrin autofluorescence. The ability to screen heterogenous protoplast populations rapidly, combined with the cell sorting capabilities of many flow cytometers, should prove valuable for seaweed biotechnology.     

Morphological and ultrastructural characterization of mammalian spermatozoa processed for flow cytometric DNA analyses

The morphological and ultrastructural changes that occur during preparation of porcine, bovine, and murine spermatozoa for flow cytometric quantification of the relative DNA content of the X- and Y-chromosome-bearing sperm populations were examined. Ejaculated spermatozoa from the boar and bull were washed using a series of dimethyl sulfoxide (DMSO) solutions prior to fixation, whereas the epididymal mouse spermatozoa were washed only in phosphate-buffered saline (PBS). Spermatozoa from all three species were then fixed in ethanol and processed for fluorochrome staining by a treatment regimen consisting of sulfhydryl reduction and proteolysis. The processed sperm nuclei were stained for DNA with the fluorochrome, 4′-6-diamidino-2-phenylindole (DAPI) before quantification by flow cytometry. Scanning and transmission electron micrographs of sperm heads taken at various steps of the preparation and staining procedures show 1) that the rigorous washing procedure disrupted the plasma and outer acrosomal membranes, 2) that ethanol fixation resulted in removal of the outer membranes and disintegration of the nuclear envelope, and 3) that thiol and proteolysis treatment removed the remaining cellular organelles including the tail and rapidly induced partial decondensation of the tightly packed chromatin. Sequential micrographs showed that the nuclear matrix of all three species increased in thickness about twofold during the preparation and staining. Consequently, the harsh procedures currently used for quantitative staining of DNA for high-resolution flow cytometric analyses destroy most cellular organelles and thereby prevent simultaneous characterization of DNA content and other sperm cell constituents.     

An analysis of proton fluxes coupled to electron transport and ATP synthesis in chloroplast thylakoids

Electron transport, phosphorylation and internal proton concentration were measured in illuminated spinach chloroplast thylakoid membranes under a number of conditions. Regardless of the procedure used to vary these parameters, the data fit a simple chemiosmotic model. Protons from Photosystem II did not appear to be utilized differently from those derived from Photosystem I. The maximal phosphorylation efficiency ($\text{P}\text{e}{}_2$) for photophosphorylation in washed thylakoids under oxidizing conditions is likely to be $\text{4}\text{3}$. This value is consistent with a proton-to-electron-pair ratio of 4 for electron flow through both photosystems and a proton-to-ATP ratio of 3 for the chloroplast proton-ATPase.     

Effect of monensin on osmotic water flow across the toad bladder and its stimulation by vasopressin and cyclic AMP

Summary The effects of the sodium ionophore monensin on osmotic water flow across the urinary bladder of the toadBufo marinus were studied. Monensin alone did not alter osmotic water flow; however, the ionophore inhibited the hydrosmotic response to vasopressin and cyclic AMP in a dose-dependent manner. The inhibitory effects of monensin were apparent when the ionophore was added to the serosal bathing solution but not when it was added to the mucosal bathing solution. The inhibitory effect of serosal monensin required the presence of sodium in the serosal bathing solution but not the presence of calcium in the bathing solutions. Thus, it appears that intracellular sodium concentration is a regulator of the magnitude of the hydrosmotic response to vasopressin and cyclic AMP.     

Effect of inoculation withGlomus mosseae on nitrogen fixation by field grown soybeans

Summary This field study was undertaken to determine the effect of inoculation withGlomus mosseae on N₂ fixation and P uptake by soybean. The inoculation withGlomus mosseae was achieved using a new type of inoculant, alginate-entrapped (AE) endomycorrhizal fungus. N₂ fixation was assessed using the A value method. In P-fertilized plots, inoculation with AEGlomus mosseae increased the harvest index based on dry weight (+20%) and N content of seeds (+17%), the A value (+31%) and %N derived from fixation (+75%). Inoculation with AEGlomus mosseae decreased the coefficient of variation for the A value and for the dry weights of the different plant parts.