ARAGONITE CRYSTALS IN SPIROGYRA SP. (CHLOROPHYTA)

Intracellular crystals of aragonite have been identified by selected area electron diffraction (SAED) in a species of the freshwater filamentous alga Spirogyra from the Thames River, Ontario, Canada. The crystals are 2 to 24 μm in diameter, and characterized by a unique cross-shaped morphology, in which needle-like, or prismatic outgrowths develop from a common axis. Crystals may be dispersed throughout filaments, but tend to cluster as aggregates towards the centre .     

A generalised transducing bacteriophage for Rhodococcus erythropolis

Summary Q4, a bacteriophage isolated from soil, mediated the transduction of a number of unlinked markers in Rhodococcus erythropolis. Highest numbers of transductants were obtained at multiplicities of infection of over 100, transductants only being obtained because of the temperate nature of the phage. Under optimal conditions, transduction to prototrophy of auxotrophic markers was over 50 times the spontaneous reversion rate and transduction of some antibitic resistance markers was over 10 times the spontaneous mutation rate. Segregation of unselected, but linked, markers was observed and the phage was used to order loci in a three factor cross. The virus required magnesium ions. Highest phage titres and greatest transduction frequency were obtained with stationary phase cultures.     

Nutrient concentrations in litterfall from some western conifers with special reference to calcium

Foliar litterfall nutrient concentrations were analysed for selected members of Taxodiaceae and Cupressaceae families andPseudotsuga menziesii for two arboreta in western Oregon and Washington. Nutrient results between arboreta show similar concentrations with the exception of magnesium, which may be the result of historical land use. Nutrient concentrations between species vary considerably.Pseudotsuga menziesii is particularly distinctive from the Cupressaceae and Taxodiaceae by retaining large amounts of phosphorus and potassium. Taxodiaceae is distinctive by high concentration of Mg while Cupressaceae retains calcium, especiallyChamaecyparis nootkatensis. Results suggest that all members of Taxodiaceae and Cupressaceae retain considerably more Ca than Pinaceae in foliar litter.     

Distribution of calcium ATPase in the sarcoplasmic reticulum of fast- and slow-twitch muscles determined with monoclonal antibodies

Summary Four monoclonal antibodies against the calcium ATPase in sarcoplasmic reticulum (SR) of rabbit fast-twitch skeletal muscle were characterized using SDS-PAGE, Western blots and immunofluorescence. The ultrastructural distribution of the antigens was determined using post-embedding immunolabeling. The antibodies recognized the calcium ATPase in the SR but not in transverse (T-) tubule or plasma membranes. The antibody, D12, had the same binding affinity for the calcium ATPase from fast-twitch (rabbit sternomastoid) and slow-twitch (rabbit soleus) fibers and the affinity fell by 30% after fixation for electron microscopy in both types of muscle fiber. Ultrastructural studies revealed that the density of D12 antibody binding to the terminal cisternae membrane of extensor digitorum longus (edl) and sternomastoid fibers was on average seven times greater than in the slow-twitch soleus and semimembranosus fibers. Since the affinity of the ATPase for the antibody was the same in SR from fast- and slow-twitch muscles, the concentration of calcium ATPase in the terminal cisternae membrane of fast-twitch fibers was seven times greater than in slow-twitch fibers. This conclusion was supported by the fact that the concentration of calcium ATPase in light SR membranes was six times greater in SR from fast-twitch fibers than in SR from slow-twitch fibers. The results provide strong evidence that the different calcium accumulation rates in mammalian fast- and slow-twitch muscles are due to different concentrations of calcium ATPase molecules in the SR membrane.     

Bacteriophage P22 as a vehicle for transducing cosmid gene banks between smooth strains of Salmonella typhimurium: use in identifying a role for aroD in attenuating virulent Salmonella strains

Summary A cosmid gene bank of the virulent Salmonella typhimurium C5 was constructed in Escherichia coli K12. The bank was repackaged into bacteriophage heads and transduced into the semi-rough S. typhimurium strain AS68 which expresses the LamB receptor protein. Approximately 6000 ampicillin-resistant transductants were pooled and used as host for the propagation of bacteriophage P22. The P22 lysate was able to transduce cosmid recombinants to smooth strains of S. typhimurium and individual transductants were selected which complemented various S. typhimurium auxotrophic mutations. A stable mutation was introduced into the aroD gene of S. typhimurium C5. The resulting aroD ^- mutant, named CU038, was highly attenuated compared with the wild-type parent strain and BALB/c mice immunised orally with CU038 were well protected against challenge with the virulent C5 parental strain. Using the cosmid bank repackaged into bacteriophage P22 heads it was possible to isolate cosmid recombinants that could complement the aroD mutation of CU038 either by in vitro selection using minimal medium or in vivo selection for restoration of virulence in BALB/c mice. Repackaged P22 cosmid banks could provide a simple system for selecting in vivo for Salmonella virulence determinants. A Salmonella typhi strain harbouring mutations in aroA and aroD was constructed for potential use as a live oral typhoid vaccine in humans.     

The response of stomata to CO2 relates to its effect on respiration and ATP level

External ATP enhanced stomatal opening of Commelina communis L. differently from EDTA. ATP was more effective in opening stomata than EDTA, when both were applied in amounts yielding equivalent free Ca²⁺ concentration. The stimulation by ATP depended upon its de-phosphorylation and was not due to the P₁ released. Hence an energetical contribution of external ATP appears possible. Increase in CO₂ concentration increased the stimulation of stomatal opening by ATP and diminished the internal ATP level, ATP/(ADP+AMP) ratio and respiration rate.     

Effect of pod zone moisture content on reproductive growth in three cultivars of peanut (Arachis hypogaea)

Very little research has been done to investigate the effect of a dry podding zone on reproductive development in peanut plants that are otherwise well hydrated via subsoil moisture extraction. The influence of podding zone moisture content on reproductive development and growth of three peanut cultivars (McCubbin, Gajah and Robut 33-1) was investigated in pots grown in the glasshouse. In two cultivars (McCubbin and Gajah) seed yield was reduced in a dry (air-dry) compared to a wet (field capacity) podding zone. Seed yield of Robut 33-1 was unaffected by podding zone moisture content, indicating that cultivar variation in reproductive performance in response to podding zone moisture may exist.     

Dietary fat influences electric membrane properties of neurons in cell culture

1. SJL/J mice were maintained on semipurified diets which differed in the ratio of polyunsaturated/saturated fatty acid content (P/S). Exposure was from conception and was maintained for periods ranging from 6 to 34 weeks. 2. Neural cell cultures were prepared from dorsal root ganglia (DRG). After 6 and 20 days of culture, neuronal electric membrane properties were determined quantitatively by intracellular recording. 3. A number of significant differences were observed for the two dietary conditions. DRG from mice on the low-P/s diet had an increase in the rate of fall of both phases of repolarization which, in conjunction with the reduced action potential overshoot, led to a reduced action potential duration. This shift to shorter-duration action potentials was accompanied by a shift to more monophasic falling phases. The low-P/S neurons also exhibited a decreased afterhyperpolarization, decreased specific membrane resistance, and decreased membrane electrical time constant compared to high-P/S neurons. 4. It was concluded that the P/S ratio in the diet can have a significant effect on the electric properties of neurons. The high-P/S neurons tended to have action potentials with biphasic repolarizations and longer durations. In contrast, the low-P/S neurons tended to have action potentials with monophasic repolarizations and shorter durations. Moreover, the known ionic dependence of these two types of action potentials suggested that the low-P/S diet resulted in action potentials with a more exclusive Na dependence, while the high-P/S diet resulted in action potentials with both Na and Ca dependence.     

Effect of calcium overload on the phosphoinositide breakdown in the rat left ventricular papillary muscle

We investigated the effect of Ca²⁺ overload on the phospholipase C-catalyzed hydrolysis of phosphoinositides in the rat left ventricular papillary muscle. Ca²⁺ overload on the papillary muscle was induced by treatment with 0.3 mM ouabain in Ca²⁺-containing medium following either Ca²⁺-containing or Ca²⁺-free superfusion. The phosphoinositide breakdown was evaluated by determining accumulations of [³H]inositol phosphates ([³H]IPs) in the tissues prelabeled with [³H]inositol. Ca²⁺ repletion following Ca²⁺-free superfusion resulted in a rapid but small increase in resting tension that was not followed by contracture, nor was it associated with a significant increase in [³H]IPs accumulations. Treatment with ouabain following Ca²⁺-containing superfusion increased resting tension after a lag period of several minutes and produced contracture associated with an increase in [³H]IPs accumulations. The ouabain induced increases in resting tension, and accumulations of [³H]IPs were significantly potentiated by prior Ca²⁺-free superfusion instead of Ca²⁺-containing superfusion. There was a significant positive correlation between increases in resting tension and the phosphoinositide breakdown. The increased resting tension and the accumulations of [³H]IPs were not antagonized by treatments with prazosin plus atropine or indomethacin, but were abolished by superfusion with Ca²⁺-free buffer solution. Although the enhanced phospholipase C-catalyzed hydrolysis of phosphoinositides appears to be a consequence rather than a cause of increased intracellular Ca²⁺, such a biochemical change may provoke a positive feedback mechanism to develop the muscle contracture through the putative intracellular messenger action of inositol triphosphate and diacylglycerol.Abbreviations [³H]IPs [³H]Inositol Phosphates - IP Inositol Phosphate - IP₂ Inositol Bisphosphate - IP₃ Inositol Trisphosphate - PI Phosphatidylinositol - PI-4-P Phosphatidylinositol-4-phosphate - PI-4,5-P₂ Phosphatidylinositol 4,5-bisphosphate - PRZ Prazosin - ATR Atropine - INDO Indomethacin - min Minutes     

Mechanisms of transmembrane signalling in human T cell activation

Several monoclonal antibodies directed against a number of T cell surface molecules are used to elucidate the role of these molecules (cell surface molecules) in T cell activation. The activation of T cells via these molecules are both antigen-dependent (CD3/TcR complex) and antigen-independent. Irrespective of their antigen-dependency, these monoclonal antibodies activate T cells by a classical signal transduction pathway, in which the binding of monoclonal antibodies to their cell surface receptors leads to activation of phospholipase C resulting in the the depolarization of plasma membrane, hydrolysis of IP2 and IP3 and DAG, the second messengers. IP3 leads to mobilization of intracellular calcium to contribute to an increase in [Ca⁺⁺]_i, whereas DAG causes activation and translocation of PKC and an increasing apparent affinity for Ca⁺⁺. The role of IN in the mobilization of intracellular calcium is emerging. In addition, influx of extracellular calcium also contributes to increase in [Ca^–+];. The increase in [Ca⁺⁺]; following activation via some T cell surface antigen is predominantly due to intracellular mobilization of Ca^–+ (e.g. CD3/TcR complex), whereas activation via other T cell surface antigen, the increase in [Ca^+–]_i is almost entirely due to an influx of extracellular calcium (e.g. CD5 antigen). All these molecules activate autocrine system of T cell growth, namely IL-2 production, IL-2 receptor expression and T cell proliferation.