Root and nodule respiration in relation to acetylene reduction in intact nodulated peas

Inoculated pea plants (Pisum sativum L.) were grown with N-free nutrients in a controlled environment room and rates of respiratory CO₂ evolution and C₂H₂ reduction by the intact nodulated roots were determined. Experiments followed changes related to diurnal cycles, light and dark treatments, partial defoliation, aging of plants and NH₄NO₃ addition. In all experiments, changes in C₂H₂ reduction were associated with parallel changes in the respiration rate, although in all but the defoliation experiment there was a basal level of respiration which was independent of the rate of C₂H₂ reduction. In conditions which affected growth or plant size as well as C₂H₂ reduction, respiration changed by an average of 0.42 mg CO₂ (μmol C₂H₂ reduced)⁻¹. However, some treatments decreased C₂H₂ reduction without greatly changing the growth and in these conditions respiration was decreased by an average of 0.27 mg CO₂ (μmol C₂H₂ reduced)⁻¹. While this value may also include some respiration associated with other processes, it is proposed that it more closely estimates respiration directly associated with energy utilization for acetylene reduction; whereas the higher value includes respiration related to maintenance and growth processes as well.     

Fish production in Lake Kariba,reconsidered

Synopsis Revised total and available production, yield and mean biomass per ha were calculated for each species in Lake Kariba, and for the whole lake. The revision was undertaken because (1) the original value 1 g for W₀ for each species was too high, (2) B_i+1 was occasionally used instead of B_i in the calculation of mean biomass for an interval i to i + 1, and (3) species' contributions to mean parameter values for the whole lake were not weighted according to their mean standing crop. Revised values are, A = 1224, P = 720, Y_A = 400, Y_{Pp, = 202 and B} = 827 kg ha^–1y–1. These correspond to 38.2%, 66.7%, 107.1% and 25.8% respectively of the values calculated initially.     

Approach to drug therapy for hypertension.

Prevention of complications of hypertension requires the lowering of blood pressure. The therapeutic goal is to achieve and maintain a diastolic pressure of less than 90 mm Hg with minimal adverse effects. The treatment of patients with established diastolic blood pressures between 90 and 104 mm Hg (determined from three separate readings) should be individualized; general measures such as weight loss and salt restriction should be tried first as an alternative to drug therapy. Patients with diastolic pressure in excess of 104 mm Hg should be treated with antihypertensive drugs; the first step should be the use of a thiazide diuretic in addition to general measures. Patients with diastolic pressures of 90 to 115 mm Hg may require the addition of a beta-adrenergic-receptor antagonist, methyldopa or clonidine if the therapeutic goal is not achieved; rarely they require the further addition of hydralazine or prazosin. Patients with diastolic pressures of 116 to 129 mm Hg usually require initially both a thiazide diuretic and a beta-blocker, methyldopa or clonidine; if the therapeutic goal is not achieved, hydralazine or prazosin is added, and if a further hypotensive effect is required guanethidine can be added. Patients with severe hypertension (diastolic pressures greater than 130 mm Hg) may require urgent treatment with combinations of drugs of all three levels. Emphasis should be placed on individualized therapy and patient compliance in the assessment of therapeutic failures. These "step-care" guidlines represent a framework for antihypertensive therapy devised from information available in 1977. It is not a rigid scheme and should be adjusted to the individual patient to ensure as normal a life as possible.     

Chromosome size-dependent control of meiotic reciprocal recombination in Saccharomyces cerevisiae: the role of crossover interference.

In the yeast Saccharomyces cerevisiae, small chromosomes undergo meiotic reciprocal recombination (crossing over) at rates (centimorgans per kilobases) greater than those of large chromosomes, and recombination rates respond directly to changes in the total size of a chromosomal DNA molecule. This phenomenon, termed chromosome size-dependent control of meiotic reciprocal recombination, has been suggested to be important for ensuring that homologous chromosomes cross over during meiosis. The mechanism of this regulation was investigated by analyzing recombination in identical genetic intervals present on different size chromosomes. The results indicate that chromosome size-dependent control is due to different amounts of crossover interference. Large chromosomes have high levels of interference while small chromosomes have much lower levels of interference. A model for how crossover interference directly responds to chromosome size is presented. In addition, chromosome size-dependent control was shown to lower the frequency of homologous chromosomes that failed to undergo crossovers, suggesting that this control is an integral part of the mechanism for ensuring meiotic crossing over between homologous chromosomes.     

Supramolecular structures of peptide assemblies in membranes by neutron off-plane scattering: method of analysis

In a previous paper (Yang et al., Biophys. J. 75:641-645, 1998), we showed a simple, efficient method of recording the diffraction patterns of supramolecular peptide assemblies in membranes where the samples were prepared in the form of oriented multilayers. Here we develop a method of analysis based on the diffraction theory of two-dimensional liquids. Gramicidin was used as a prototype model because its pore structure in membrane in known. At full hydration, the diffraction patterns of alamethicin and magainin are similar to gramicidin except in the scale of q (the momentum transfer of scattering), clearly indicating that both alamethicin and magainin form pores in membranes but of different sizes. When the hydration of the multilayer samples was decreased while the bilayers were still fluid, the in-plane positions of the membrane pores became correlated from one bilayer to the next. We believe that this is a new manifestation of the hydration force. The effect is most prominent in magainin patterns, which are used to demonstrate the method of analysis. When magainin samples were further dehydrated or cooled, the liquid-like diffraction turned into crystal-like patterns. This discovery points to the possibility of investigating the supramolecular structures with high-order diffraction.     

Cyclin F disruption compromises placental development and affects normal cell cycle execution

Human cyclin F was originally isolated as a cDNA capable of suppressing the temperature sensitivity of a Saccharomyces cerevisiae cdc4-1 mutant. Its tightly regulated expression and high conservation in the evolutionary progression from amphibians to mammals suggest that it coordinates the timing of a critical cell cycle event. The fact that it contains an F box and can form an SCF (Skp1-Cul1/Cdc53-F-box) complex in vivo further suggests that it may also function in proteolysis. To investigate the role of cyclin F in vivo, we generated mice deficient for cyclin F and conditionally deficient mice as well as mouse embryonic fibroblasts (MEFs) conditionally deficient for cyclin F. Heterozygous animals are normal and fertile, but CycF(-/-) animals, with a myriad of developmental anomalies due in large part to failures in yolk sac and chorioallantoic placentation, die around embryonic day 10.5. Tissue-specific deletion of cyclin F revealed that it was not required for the development and function of a number of different embryonic and adult tissues. In contrast, MEFs lacking cyclin F, while viable, do exhibit cell cycle defects, including reduced population-doubling time and a delay in cell cycle reentry from quiescence, indicating that cyclin F plays a role in cell cycle regulation.     

Vitamin D receptor-deficient mice fail to develop experimental allergic asthma

The active metabolite of vitamin D (1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))) is known to modulate the immune response in Th1 cell-directed diseases. To investigate the role of vitamin D in Th2 cell-directed diseases, experimental allergic asthma was induced in vitamin D receptor (VDR) knockout and in wild-type (WT) mice. As expected, WT mice developed symptoms of airway inflammation with an influx of eosinophils, elevated Th2 cytokine levels, mucous production, and airway hyperresponsiveness. The administration of 1,25(OH)(2)D(3) had no effect on asthma severity. The only discernable effect of 1,25(OH)(2)D(3) on experimental allergic asthma in WT mice was an increased expression of two Th2-related genes (soluble CD23 and GATA-3) in lungs of BALB/c mice exposed to Ag through the nasal route only. By contrast, asthma-induced VDR knockout mice failed to develop airway inflammation, eosinophilia, or airway hyperresponsiveness, despite high IgE concentrations and elevated Th2 cytokines. The data suggest that although 1,25(OH)(2)D(3) induced these Th2-type genes, the treatment failed to have any affect on experimental asthma severity. However, VDR-deficient mice failed to develop experimental allergic asthma, suggesting an important role for the vitamin D endocrine system in the generation of Th2-driven inflammation in the lung.     

Cloning and characterization of SK2 channel from chicken short hair cells

In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74±0.17 M. The expressed channels were blocked by apamin (IC₅₀=73.3±5.0 pM) and d-tubocurarine (IC₅₀=7.6±1.0 M), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates.     

A-Raf associates with and regulates platelet-derived growth factor receptor signalling

Raf kinases are important intermediates in epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) mediated activation of the mitogen-activated protein kinase (MAPK) pathway. In this report, we show that the A-Raf kinase is associated with activated EGF receptor complexes and with PDGF receptor (PDGFR) complexes independent of prior PDGF treatment. The ability of A-Raf to associate with receptor tyrosine kinases could provide a Ras-GTP-independent mechanism for the membrane localization of A-Raf. Expression of a partially activated A-Raf mutant resulted in decreased tyrosine phosphorylation of the PDGFR, specifically on Y857 (autophosphorylation site) and Y1021 (phospholipase Cgamma1 (PLCgamma1) binding site), but not the binding sites for other signalling proteins (Nck, phosphatidylinositol 3'-kinase (PI3K), RasGAP, Grb2, SHP). Activated A-Raf expression also altered the activation of PLCgamma1, and p85-associated PI3K. Thus, A-Raf can regulate PLCgamma1 signalling via a PDGFR-dependent mechanism and may also regulate PI3K signalling via a PDGFR-independent mechanism.     

Bordetella pertussis adenylate cyclase toxin modulates innate and adaptive immune responses: distinct roles for acylation and enzymatic activity in immunomodulation and cell death

Adenylate cyclase toxin (CyaA) of Bordetella pertussis belongs to the repeat in toxin family of pore-forming toxins, which require posttranslational acylation to lyse eukaryotic cells. CyaA modulates dendritic cell (DC) and macrophage function upon stimulation with LPS. In this study, we examined the roles of acylation and enzymatic activity in the immunomodulatory and lytic effects of CyaA. The adenylate cyclase activity of CyaA was necessary for its modulatory effects on murine innate immune cells. In contrast, acylation was not essential for the immunomodulatory function of CyaA, but was required for maximal caspase-3 activation and cytotoxic activity. The wild-type acylated toxin (A-CyaA) and nonacylated CyaA (NA-CyaA), but not CyaA with an inactive adenylate cyclase domain (iAC-CyaA), enhanced TLR-ligand-induced IL-10 and inhibited IL-12, TNF-alpha, and CCL3 production by macrophages and DC. In addition, both A-CyaA and NA-CyaA, but not iAC-CyaA, enhanced surface expression of CD80 and decreased CpG-stimulated CD40 and ICAM-1 expression on immature DC. Furthermore, both A-CyaA and NA-CyaA promoted the induction of murine IgG1 Abs, Th2, and regulatory T cells against coadministered Ags in vivo, whereas iAC-CyaA had more limited adjuvant activity. In contrast, A-CyaA and iAC-CyaA induced caspase-3 activation and cell death in macrophages, but these effects were considerably reduced or absent with NA-CyaA. Our findings demonstrate that the enzymatic activity plays a critical role in the immunomodulatory effects of CyaA, whereas acylation facilitates the induction of apoptosis and cell lysis, and as such, NA-CyaA has considerable potential as a nontoxic therapeutic molecule with potent anti-inflammatory properties.