Effect of the Polydispersity of RBCs on the Recovery Rate of RBCs during the Removal of CPAs

In the process of removing cryoprotectants from cryopreserved blood, the theoretically optimal operating condition, which is based on the assumption that the distribution of red blood cells is uniform, is often used to reduce or even avoid the hypotonic damage to cells. However, due to the polydispersity of cells, the optimal condition is actually not reliable. In this study, based on the discrete concept developed in our previous work, the effect of the polydispersity on the recovery rate of cells in the dilution-filtration system was statistically investigated by assigning three random parameters, isotonic cell volume, cell surface area, and osmotically inactive cell volume, to cells in small units of blood. The results show that, due to the polydispersity, the real recovery rate deviates from the ideal value that is based on uniform distribution. The deviation significantly increases with the standard errors of cell parameters, and it can be also magnified by high cryoprotectant concentrations. Under the effect of polydispersity, the uniform distribution-based optimized blood or diluent flow rate is not perfect. In practice, one should adopt a more conservative blood or diluent flow rate so that the hypotonic damage to cells can be further reduced.

Comparative Freezing Response of Ejaculated and Epididymal Rhesus Monkey Sperm

In the present study, we report the effects of cooling ejaculated and epididymal rhesus monkey (Macaca mulatta) sperm in the presence of extracellular. Water transport data during freezing of ejaculated and epididymal sperm cell suspensions were obtained at a cooling rate of 20 °C/min in the absence of any cryoprotective agents. Additional water transport data was obtained from ejaculated sperm at a cooling of 5 °C/min without CPAs and at 20 °C/min in the presence of 0.7M of glycerol, as well. Using previously published values, the bovine sperm cell was modeled as a cylinder of length 73.83 μm and a radius of 0.32 μm with an osmotically inactive cell volume, Vb, of 0.772Vo, where Vo is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, Lpg and activation energy, ELp). The predicted best-fit permeability parameters ranged from, Lpg = 0.0023 to 0.0029 μm/min-atm and ELp = 10.6 to 45.5 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal macaque spermatozoa under corresponding cooling conditions.

Paraquat Resistance of Weeds - the Case of Conyza canadensis (L.) Cronq

The paper gives an overview of literature on paraquat resistance of weeds and the proposed mechanism of resistance. New results we achieved on horseweed ( Conyza canadensis /L./, Cronq.) are discussed in detail. It was demonstrated that there is no significant constitutive difference related to the paraquat resistance between untreated susceptible and paraquat-resistant horseweed plants. The lower sensitivity of flowering resistant plants may be due to the fact that paraquat content in treated leaves of flowering resistant plants was only 25% as compared to those measured at rosette stage. Our results confirm that paraquat resistance is not based on elevated level and activity of antioxidant enzyme system. The hypothesized role of polyamines in the resistance mechanisms can be excluded. The higher putrescine and total polyamine content of paraquat treated resistant leaves can rather be regarded as a general stress response, than as a symptom of paraquat resistance. A paraquat-inducible protein is supposed to play a role in the resistance, which presumably functions by binding paraquat to an inactivating site and/ or by carrying paraquat to metabolically inactive cell compartment (vacuole, cell wall). From model experiments it is concluded that paraquat and diquat preferentially form hydrophylic interactions with proteins containing a higher amount of lysine and glutamic acid. Consequently, the reason for paraquat resistance in horseweed is probably a hydrophylic interaction of paraquat with a protein, leading to inactivation of paraquat through forming a conjugate and/or sequestration into the vacuole or the cell wall.

Mathematical modeling of trichloroethylene (TCE) degradation in membrane-attached biofilms

A mathematical model for the counter-diffusional membrane-attached methanotrophic biofilm reactor was developed. The model included competitive inhibition between trichloroethylene (TCE) and methane, production of inactive cells by TCE byproduct toxicity, and biomass detachment as a function of inactive cell concentration. Simulation results indicated that the optimum oxygen to methane ratio was dependent on the biofilm and the membrane thickness. Furthermore, the model confirmed experimental observations that the efficiency of the process is not limited by competitive inhibition or substrates mass transfer, but by the back-diffusion of TCE through the membrane and the consequent TCE accumulation in the gas phase.

Sugar Composition of Pectin and Hemicellulose Extracts of Peach Fruit during Softening over Two Harvest Seasons

Changes in cell wall polysaccharides associated with peach fruit softening were characterized over two harvest seasons. Enzymically inactive cell walls were prepared from mesocarp tissues of peach fruit harvested at three stages of softening. Pectin-associated and hemicellulose-associated polysaccharides were extracted from the cell walls sequentially, and glycosyl residue compositions were determined by GLC. Pectin extracts from both years were richest in galacturonosyl, arabinosyl, and rhamnosyl residues. Hemicellulose extracted with 1 m potassium hydroxide contained a high mole percentage of xylosyl, glucosyl, and fucosyl residues. Hemicellulose extracted with 4 m potassium hydroxide contained a substantial amount of pectin-associated sugar residues in addition to hemicellulose-associated sugar residues. During softening in both years, sugar compositions for cell walls, aqueous phenol-soluble polysaccharides, and imidazole extracts reflected a decrease in galacturonosyl residues and a concomitant increase in arabinosyl residues on a mole percent basis. The degree of change for galacturonosyl residues in these fractions depended on season, with greater variation exhibited from fruit at earlier stages of softening. With the notable exception of the seasonal variation exhibited for galacturonosyl residues in cell walls, the relative stability of other glycosyl compositional changes over seasons indicates conserved changes for pectins and hemicelluloses occur during peach fruit softening.

Determination of the Osmotic Characteristics of Hamster Pancreatic Islets and Isolated Pancreatic Islet Cells

The ability to store pancreatic islets using cryopreservation methodology would greatly assist the application of clinical islet transplantation to Type 1 (insulin-dependent) diabetics. It is our working thesis that the illumination of fundamental biophysical characteristics of these cells will lead to increased cryosurvival rates through theoretically predicted and experimental testing of optimal freezing protocol; as has been found for cells and tissues such as mammalian and Drosophila embryos. Pancreatic islets were isolated from Golden hamsters and their osmometric behavior, including inactive cell volume (Vb), was determined for either whole islets or isolated individual islet cells. When islets or islet cells were exposed to various concentrations of NaCl, they were found to exhibit a “classic” “Boyle-Van't Hoff” osmometric response. The Boyle-Van't Hoff representation of the volume curve (relative cell volume vs. 1/osmolality) yields a linear response with r values of .99 for each curve. Extrapolations to the normalized osmotically inactive volumes (Vb) were .43 and .22 for whole islets and individual islet cells, respectively. These data regarding the fundamental cryobiological characteristics of islets and islet cells should provide the foundation upon which to further the investigation of osmotic parameters of these cells and eventually lead to the determination of optimal freezing protocols.

CHANGES IN PECTIN AND HEMICELLULOSE IN `BELLE OF GEORGIA' PEACHES DURING SOFTENING.

The mechanism of softening was studied in a rapidly softening peach cultivar `Belle of Georgia' by assessing changes in pectins and hemicellulose from enzymically inactive cell walls. Cell wall preparations were sequentially extracted with imidazole and sodium carbonate (pectin extracts), and potassium hydroxide (hemicellulose extracts). The pectin extracts were particularly enriched in galacturonic acid, arabiiose and rhamnose, and contained only small amounts of hemicellulose associated sugars. Hemicellulose extracts were enriched in xylose, glucose, mannose, and fucose. More tightly bound hemicellulose fractions contained considerable amounts of pectin associated sugars. The proportion of pectin associated sugars in hemicellulose extracts was greater for cell wall extracts of softened fruit. Some possible relationships between pectin/hemicellulose solubility and fruit softening will be presented. Work was supported by USDA grant 90-34150-5022 and the Oklahoma Agricultural Experiment Station.

OSMOTIC PROPERTIES OF THE EGG CELLS OF THE OYSTER (OSTREA VIRGINICA)

Investigations of the osmotic properties of oyster eggs by a diffraction method for measuring volumes have led to the following conclusions: 1. The product of cell volume and osmotic pressure is approximately constant, if allowance is made for osmotically inactive cell contents (law of Boyle-van't Hoff). The space occupied by osmotically inactive averages 44 per cent of cell volume. 2. Volume changes over a wide range of pressures are reversible, indicating that the semipermeability of the cell during such changes remains intact. 3. The kinetics of endosmosis and of exosmosis are described by the equation, See PDF for Equation, where dV is rate of volume change; S, surface area of cell, (P-Pe), the difference in osmotic pressure between cell interior and medium, and K, the permeability of the cell to water. 4. Permeability to water during endosmosis is 0.6µ3 of water per minute, per square micron of cell surface, per atmosphere of pressure. The value of permeability for exosmosis is closely the same; in this respect the egg cell of the oyster appears to be a more perfect osmometer than the other marine cells which have been studied. Permeability to water computed by the equation given above is in good agreement with computations by the entirely different method devised by Jacobs. 5. Permeability to diethylene glycol averages 27.2, and to glycerol 20.7. These values express the number of mols x 10–15 which enter per minute through each square micron of cell surface at a concentration difference of 1 mol per liter and a temperature of 22.5°C. 6. Values for permeability to water and to the solutes tested are considerably higher for the oyster egg than for other forms of marine eggs previously examined. 7. The oyster egg because of its high degree of permeability is a natural osmometer particularly suitable for the study of the less readily penetrating solutes.