Responses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form

Responses in stomatal conductance (g _st ) and leaf xylem pressure potential ( _leaf ) to elevated CO₂ (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO₂ concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, _leaf was usually higher in all species at elevated CO₂ and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO₂ resulted in decreased g _st in 10 of the 12 species measured. Greatest decreases in g _st (ca. 50%) occurred in growth forms with the highest potential growth rates (C₃ and C₄ grasses, and C₃ ruderals). In contrast, no significant decrease in g _st was measured in the two C₃ shrubs. During a dry period in September, reductions in g _st at elevated CO₂ were measured in only two species (a C₃ ruderal and a C₄ grass) whereas increased g _st at elevated CO₂ was measured in the shrubs and a C₃ forb. These increases in g _st were attributed to enhanced _leaf in the elevated CO₂ plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g _st were measured in response to elevated CO₂. Thus, there was significant interspecific variability in stomatal responses to CO₂ that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g _st and was greatest (>30%) when water availability was low, but only 6–12% when _leaf was high.The results of this study confirm the importance of considering interactions between indirect effects of high CO₂ of plant water relations and direct effects of elevated CO₂ on g _st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g _st to be measured at elevated levels of CO₂.     

A transgenic class I antigen is recognized as self and functions as a restriction element

The function of a transgenic Dd class I molecule in the induction of immunologic tolerance to major histocompatibility complex antigens and in directing major histocompatibility complex restriction in C57BL/6 mice were investigated. All of the transgenic Dd mouse strains were found to be tolerant for the Dd antigen. Spleen cells from transgenic mice were immunocompetent but consistently failed to generate an anti-Dd cytotoxic T lymphocyte response in vitro, and skin grafts between transgenic Dd mice were not rejected. These data suggests that the Dd antigen was recognized as a self molecule. In addition, the transgenic Dd mice generated antigen-specific Dd-restricted cytotoxic T lymphocyte, indicating that the Dd antigen also functioned as a restriction element for antigen recognition. These observations demonstrate the usefulness of the transgenic mouse system for studying class I antigen expression and function.     

Core temperature measurement by microwave radiometry

A ‘double-container model’ was used for core temperature (T_c) measurement by microwave emission radiometry (MR) of warm fluid inside a tube, placed in a container with a cooler fluid. The intensity of microwaves emitted from the warmer fluid inside the tube were measured using a MR metering device, consisting of an antenna linked to a low-noise radio frequency amplifier (bandwidth 500 MHz, centered at 4.0 GHz). Based on the MR measurements, a T_c prediction model was developed for measuring the temperature of fluid inside a tube, achieving a sensitivity of ±0.5 °C at environmental temperature of 33–37 °C.     

Biaxial incremental homeostatic elastic moduli of coronary artery: two-layer model

The detailed mechanical properties of various layers of the coronary artery are important for understanding the function of the vessel. The present article is focused on the determination of the incremental modulus in different layers and directions in the neighborhood of the in vivo state. The incremental modulus can be defined for any material subjected to a large deformation if small perturbations in strain lead to small perturbations of stresses in a linear fashion. This analysis was applied to the porcine coronary artery, which was treated as a two-layered structure consisting of an inner intima-media layer and an outer adventitia layer. We adopted a theory based on small-perturbation experiments at homeostatic conditions for determination of incremental moduli in circumferential, axial, and cross directions in the two layers. The experiments were based on inflation and axial stretch. We demonstrate that under homeostatic conditions the incremental moduli are layer- and direction dependent. The incremental modulus is highest in the circumferential direction. Furthermore, in the circumferential direction, the media is stiffer than the whole wall, which is stiffer than the adventitia. In the axial direction, the adventitia is stiffer than the intact wall, which is stiffer than the media. Hence, the coronary artery must be treated as a composite, nonisotropic body. The data acquire physiological relevance in relation to coronary artery health and disease.     

Mouse embryos stressed by physiological levels of osmolarity become arrested in the late 2-cell stage before entry into M phase

Preimplantation mouse embryos of many strains become arrested at the 2-cell stage if the osmolarity of culture medium that normally supports development to blastocysts is raised to approximately that of their normal physiological environment in the oviduct. Arrest can be prevented if molecules that serve as "organic osmolytes" are present in the medium, because organic osmolytes, principally glycine, are accumulated by embryos to provide intracellular osmotic support and regulate cell volume. Medium with an osmolarity of 310 mOsM induced arrest of approximately 80% of CF1 mouse embryos at the 2-cell stage, in contrast to the approximately 100% that progressed beyond the 2-cell stage at 250 or 301 mOsM with glycine. The nature of this arrest induced by physiological levels of osmolarity is unknown. Arrest was reversible by transfer to lower-osmolarity medium at any point during the 2-cell stage, but not after embryos would normally have progressed to the 4-cell stage. Cessation of development likely was not due to apoptosis, as shown by lack of external annexin V binding, detectable cytochrome c release from mitochondria, or nuclear DNA fragmentation. Two-cell embryos cultured at 310 mOsM progressed through the S phase, and zygotic genome activation markers were expressed. However, most embryos failed to initiate the M phase, as evidenced by intact nuclei with decondensed chromosomes, low M-phase promoting factor activity, and an inactive form of CDK1, although a few blastomeres were arrested in metaphase. Thus, embryos become arrested late in the G(2) stage of the second embryonic cell cycle when stressed by physiological osmolarity in the absence of organic osmolytes.     

Diabetes induces sex-dependent changes in neuronal nitric oxide synthase dimerization and function in the rat gastric antrum

Diabetic gastroparesis is a disorder that predominantly affects women. However, the biological basis of this sex bias remains completely unknown. In this study we tested the hypothesis that a component of this effect may be mediated by the nitrergic inhibitory system of the enteric nervous system. Age-matched male and female Sprague-Dawley rats were studied 8 or 12 wk after streptozotocin (55 mg/kg body wt ip)-induced sustained hyperglycemia and compared with controls. Solid gastric emptying (GE) studies were performed in all the groups. Changes in gastric antrum neuronal nitric oxide synthase (nNOS) mRNA and protein levels were analyzed by real-time PCR and Western immunoblotting, respectively. nNOS dimerization studies were performed using low-temperature SDS-PAGE. In vitro nitrergic relaxation (area under curve/mg tissue wt) was studied after the application of electric field stimulation in an organ bath. Changes in intragastric pressure (mmHg.s) in freely moving rats in the presence or absence of N(G)-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor) were examined by an ambulatory telemetric method. After diabetes induction, GE is delayed in both male and female rats. However, diabetic females exhibited significant delayed GE than in diabetic males. Compared with male controls, gastric nNOS expression and nitrergic relaxation were substantially elevated in healthy female control rats, accompanied by significantly reduced intragastric pressure. The active dimeric form and dimer-to-monomer ratio of nNOSalpha were also higher in healthy females compared with male rats (P < 0.05). Diabetic females, but not males, showed significant (P < 0.05) impairment in both gastric nNOSalpha dimerization and nitrergic relaxation, accompanied by an increase in intragastric pressure. Our data provide evidence that females may have a greater dependency on the nitrergic mechanisms in health. Furthermore, diabetes seems to affect the nitrergic system to a greater extent in females than in males. Together, these changes may account for the greater vulnerability of females to diabetic gastric dysfunction.     

Evaluation of a high-density oligonucleotide array for characterization of grlA, grlB, gyrA and gyrB mutations in fluoroquinolone resistant Staphylococcus aureus isolates

Using high-density oligonucleotide array technology, 30 Staphylococcus aureus strains were studied for the presence of mutations in genes involved in fluoroquinolone resistance: grlA, gyrA, grlB and gyrB. For the two most important genes, gyrA and grlA, correlation with sequencing reached 95.1%. If all genes were considered, correlation was 88.8%.     

Expression screen by enzyme-linked immunofiltration assay designed for high-throughput purification of affinity-tagged proteins

High-throughput purification of affinity-tagged fusion proteins is currently one of the fastest developing areas of molecular proteomics. A prerequisite for success in protein purification is sufficient soluble protein expression of the target protein in a heterologous host. Hence, a fast and quantitative evaluation of the soluble-protein levels in an expression system is one of the key steps in the entire process. Here we describe a high-throughput expression screen for affinity-tagged fusion proteins based on an enzyme linked immunofiltration assay (ELIFA). An aliquot of a crude Escherichia coli extract containing the analyte, an affinity-tagged protein, is adsorbed onto the membrane. Subsequent binding of specific antibodies followed by binding of a secondary antibody horseradish peroxidase (HRP) complex then allows quantitative evaluation of the analyte using tetramethylbenzidine as the substrate for HRP. The method is accurate and quantitative, as shown by comparison with results from western blotting and an enzymatic glutathione S-transferase (GST) assay. Furthermore, it is a far more rapid assay and less cumbersome than western blotting, lending itself more readily to high-throughput analysis. It can be used at the expression level (cell lysates) or during the subsequent purification steps to monitor yield of specific protein.