The effects of organic nitrogen sources on growth of cell cultures of Douglas-fir

In order to establish rapidly growing, friable cell cultures of Douglas-fir ( Pseudotsuga menziesii [Mirb. (Franco)], the effects of organic sources of nitrogen on growth were investigated. Of the nitrogen sources studied, including allantoin, allantoic acid, glutamine and glutamic acid, all were capable of increasing growth. Glutamine (50 m M ) produced the most marked increase in growth boosting dry weight production to a level of four times that of controls. Glutamine additions also eliminated the lag phase of growth and caused cells to become densely cytoplasmic. Results are discussed in relation to the pathway for assimilation of nitrogen.     

Effect of the cholesterol content of small unilamellar liposomes on their stability in vivo and in vitro

Small unilamellar neutral, negatively and positively charged liposomes composed of egg phosphatidylcholine, various amounts of cholesterol and, when appropriate, phosphatidic acid or stearylamine and containing 6-carboxyfluorescein were injected into mice, incubated with mouse whole blood, plasma or serum or stored at 4°C. Liposomal stability, i.e. the extent to which 6-carboxyfluorescein is retained by liposomes, was dependent on their cholesterol content. (1) Cholesterol-rich (egg phosphatidylcholine/cholesterol, 7:7 molar ratio) liposomes, regardless of surface charge, remained stable in the blood of intravenously injected animals for up to at least 400min. In addition, stability of cholesterol-rich liposomes was largely maintained in vitro in the presence of whole blood, plasma or serum for at least 90min. (2) Cholesterol-poor (egg phosphatidylcholine/cholesterol, 7:2 molar ratio) or cholesterol-free (egg phosphatidylcholine) liposomes lost very rapidly (at most within 2min) much of their stability after intravenous injection or upon contact with whole blood, plasma or serum. Whole blood and to some extent plasma were less detrimental to stability than was serum. (3) After intraperitoneal injection, neutral cholesterol-rich liposomes survived in the peritoneal cavity to enter the blood circulation in their intact form. Liposomes injected intramuscularly also entered the circulation, although with somewhat diminished stability. (4) Stability of neutral and negatively charged cholesterol-rich liposomes stored at 4°C was maintained for several days, and by 53 days it had declined only moderately. Stored liposomes retained their unilamellar structure and their ability to remain stable in the blood after intravenous injection. (5) Control of liposomal stability by adjusting their cholesterol content may help in the design of liposomes for effective use in biological systems in vivo and in vitro.     

A stochastic model of a temperature-dependent population

The theoretical basis is developed for a population model which allows the use of constant temperature experimental data in predicting the size of an insect population for any variable temperature environment. The model is based on a stochastic analysis of an insect's mortality, development, and reproduction response to temperature. The key concept in the model is the utilization of a physiological time scale. Different temperatures affect the population by increasing an individual's physiological age by differing rates. Conditions for the temperature response properties are given which establish the validity of the model for variable temperature regimes. These conditions refer to the relationship between chronological and physiological age. Reasonable agreement between the model and field populations demonstrates the practicality of this approach.     

Thapsigargin inhibits contraction and Ca2+ transient in cardiac cells by specific inhibition of the sarcoplasmic reticulum Ca2+ pump.

Regulation of the level of ionized calcium, [Ca2+]i, is critical for its use as an important intracellular signal. In cardiac and skeletal muscle the control of fluctuations of [Ca2+]i depend on sarcolemmal and sarcoplasmic reticulum ion channels and transporters. We have investigated the sesquiterpine lactone, thapsigargin (TG), because of its reported action to alter cellular calcium regulation in diverse cell types, including striated muscle cells. We have combined biochemical and physiological methods at the cellular level to determine the site of action of this agent, its specificity, and its cellular effects. Using a patch-clamp method in whole cell configuration while measuring [Ca2+]i with Indo-1 salt, we find that TG (100 nM) largely blocks the contraction and the [Ca2+]i transient in rat ventricular myocytes. Analysis of these data indicate that no sarcolemmal current or transport system is directly altered by TG, although indirect [Ca2+]i-dependent processes are affected. In permeabilized myocytes, TG blocked oxalate-stimulated calcium uptake (half-maximal effect at 10 nM) into the SR. However, TG (100 microM) had no effect on Ca(2+)-induced Ca(2+)-release in purified muscle (ryanodine-receptor enriched) vesicles while clearly blocking Ca(2+)-ATPase activity in purified (longitudinal SR) vesicles. We conclude that in striated muscle TG markedly alters calcium metabolism and thus alters contractile function only by its direct action on the Ca(2+)-ATPase.     

Influence of root diameter on the penetration of seminal roots into a compacted subsoil

A field experiment was conducted to evaluate the influence of root diameter on the ability of roots of eight plant species to penetrate a compacted subsoil below a tilled layer. The soil was a fine sandy loam red-brown earth with a soil strength of about 3.0 MPa (at water content of 0.13 kg kg^-1, corresponding to 0.81 plastic limit) at the base of a tilled layer. Relative root diameter (RRD), which was calculated as the ratio of the mean diameters of roots of plants grown in compacted soil to the mean diameters of those from uncompacted soil, was used to compare the sensitivity of roots to thicken under mechanical stress.Diameters of root tips of plants grown in soil with a compacted layer were consistently larger than those from uncompacted soil. Tap-rooted species generally had bigger diameters and RRDs than fibrous-rooted species. A higher proportion of thicker roots penetrated the strong layer at the interface than thinner roots. There were differences between plant species in the extent to which root diameter increased in response to the compaction. The roots which had larger RRD also tended to have higher penetration percentage.The results suggest that the size of a root has a significant influence on its ability to penetrate strong soil layers. It is suggested that this could be related to the effects which root diameter may have on root growth pressure and on the mode of soil deformation during penetration.     

Decreased spermatozoal survivability associated with aberrant morphology of the ductuli efferentes proximales of the chicken (Gallus domesticus)

The objective of this research were twofold: 1) to determine if decreased spermatozoal longevity, a previously reported heritable trait in chickens, was attributable to spermatozoal passage through the excurrent ducts, and 2) to document the morphology of the testicular excurrent ducts from affected roosters. Though spermatozoa were viable at ejaculation, as evidenced by their exclusion of ethidium bromide, fertility after intravaginal insemination of spermatozoa from affected roosters was less (p less than 0.001) than that observed with spermatozoa from nonaffected controls, 37 +/- 2.3 versus 58 +/- 1.5%, respectively, over a 21-day egg-collection interval. In contrast, fertility after intramagnal insemination of testicular spermatozoa from affected roosters was equivalent (p greater than 0.05) to that of nonaffected controls, 47 +/- 2.2 versus 41 +/- 3.6%, respectively. After intravaginal insemination, neither type of testicular spermatozoa fertilized oocytes. The ductuli efferentes proximales from affected roosters were characterized by a greater luminal cross-sectional area as well as a diminished height and number of longitudinal epithelial folds (p less than 0.005). It was concluded that heritable decreased spermatozoal longevity in the chicken is not attributable to an inherent spermatozoal defect. Rather, the defect is acquired during passage of spermatozoa through the extragonadal ducts of the rooster.     

Syndecans promote integrin-mediated adhesion of mesenchymal cells in two distinct pathways

Syndecans are transmembrane proteoglycans that support integrin-mediated adhesion. Well documented is the contribution of syndecan-4 that interacts through its heparan sulphate chains to promote focal adhesion formation in response to fibronectin domains. This process has requirements for integrin and signaling through the cytoplasmic domain of syndecan-4. Here an alternate pathway mediated by the extracellular domains of syndecans-2 and -4 is characterized that is independent of both heparan sulphate and syndecan signaling. This pathway is restricted to mesenchymal cells and was not seen in any epithelial cell line tested, apart from vascular endothelia. The syndecan ectodomains coated as substrates promoted integrin-dependent attachment, spreading and focal adhesion formation. Syndecan-4 null cells were competent, as were fibroblasts compromised in heparan sulphate synthesis that were unable to form focal adhesions in response to fibronectin. Consistent with actin cytoskeleton organization, the process required Rho-GTP and Rho kinase. While syndecan-2 and -4 ectodomains could both promote integrin-mediated adhesion, their pathways were distinct, as shown by competition assays. Evidence for an indirect interaction of beta1 integrin with both syndecan ectodomains was obtained, all of which suggests a distinct mechanism of integrin-mediated adhesion.     

Pathogenicity of mouse hepatitis virus for preimplantation mouse embryos

Mouse embryos which were hatched from the zona pellucida in vitro in the presence of mouse hepatitis virus (MHV) or outgrown on coverslips and then exposed to MHV were shown by immunohistochemical staining to have virally infected trophoblast cells. Zona-intact embryos incubated with MHV for 48 h (2-cell embryos) or 1.5 h (blastocysts) were resistant to infection. Morulae and early blastocysts collected from donor mice experimentally infected with MHV were not infected, but the medium in which they were flushed from the uterine horns was contaminated with virus. No virus was detected after embryos were washed through three changes of uncontaminated medium. MHV was transmitted to foster mothers when embryos were transferred in medium contaminated with the virus. Fetal and decidual tissues were not infected. We suggest that embryo transfer is an effective and simple alternative to Caesarian rederivation of MHV-contaminated mice.