Cryomicroscope investigation and thermodynamic modeling of the freezing of unfertilized hamster ova

Thermodynamic computer modeling was used to predict the freezing response of single-celled unfertilized hamster ova. The cell membrane transport characteristics were investigated, using a microscope diffusion chamber system. The mean osmotically inactive cell volume was determined to be 21.6% of the initial cell volume. An overall mean value of 0.8 +/- 0.1 micron3/micron2.min.atm (= 18 +/- 2.5 micron/sec) was determined for the membrane hydraulic coefficient, Lp. The effect of the extracellular solute concentration on Lp was determined at room temperature (approximately 23 degrees C). A thermodynamic computer model was used to predict the cell response to freezing. The predicted response was compared to the actual volumetric response observed during freezing on a temperature-controlled cryomicroscope conduction stage. The effect of the cooling rate on the nucleation temperature of unprotected ova and protected ova suspended in a 1.5 M DMSO solution was investigated. Overall mean nucleation temperatures of -13 and -57.1 degrees C were observed for unprotected and protected ova, respectively, where the mean nucleation temperature for protected ova was strongly cooling rate dependent.     

A plate assay for the detection of organophosphonate mineralization by environmental bacteria,and its modification as an activity stain for identification of the carbon — phosphorus bond cleavage enzyme phosphonoacetate hydrolase

Summary A replica plate screening technique,based on the acid molybdate assay for detection of phosphate,has been developed to permit the detection of microorganisms capable of mineralizing organophosphonates. The method was further adapted as the basis of an activity stain for the detection of the carbon - phosphorus bond cleavage enzyme phosphonoacetate hydrolase in PAGE gels.     

Photobleaching. A novel fluorescence method for diffusion studies in lipid system.

(1) The fluorescent molecular 12(9-anthroyloxy)-stearic acid dimerises on irradiation with light of 366 nm wavelength. (2) The dimer is nonfluorescent and can be reconverted to the parent compound by irradiation at 254 nm. (3) Kinetic analysis suggests that the dimerisation proceeds by a diffusion-limited second order mechanism in many solvents. (4) Anomalously high rates seen in other systems can be attributed to localised high concentration regions (clusters) of the fluorescent molecule. (5) The analysis has been extended to oriented lipid bilayers and the results suggest that below the gel-liquid crystalline transition temperature the 12(9-anthroyloxy)-stearic acid is excluded by the lipid matrix and forms regions of localised high concentration. (6) In fluid lipid the results suggest an isotropic distribution of the probe. Calculated diffusion coefficients correspond to those found by other techniques.     

Guidance of Cytophaga sp. strain U67 gliding on the sheaths of Oscillatoria princeps.

Individual cells of Cytophaga sp. strain U67 glided in helical patterns on the surface of sheaths deposited by the cyanobacterium Oscillatoria princeps. Possible bases for the helical substructure of the sheath are discussed.     

Genetic diversity in selected, historical US sugarbeet germplasm and Beta vulgaris ssp. maritima

 Diversity among sugar beet accessions released over the first 50 years of public breeding in the United States was examined to ascertain a baseline of genetic diversity and to gauge the effect of breeding on the loss or gain of diversity over this time period. Accessions were chosen as released germplasm from the major breeding stations contributing to the US germplasm pool and their presumed ancestors from Europe, including representatives for the wild forms Beta vulgaris ssp. maritima. Sixty nine polymorphic RAPD fragments were used for gene frequency analysis, and heterozygosity was determined within and among groups of accessions related either by breeding station or simply inherited agronomic characters for monogerm seed and restoration of fertility in a cytoplasmic male-sterile background. In general, heterozygosity within releases declined with time, but total genetic diversity in the US germplasm pool remained constant. Breeding for the agronomic characters had a marked influence in reducing diversity. Received: 20 October 1998 / Accepted: 28 October 1998