Tissue elastic properties of eight Hawaiian Dubautia species that differ in habitat and diploid chromosome number

Summary Eight Hawaiian Dubautia species grow in habitats as varied as exposed lava, dry scrub, mesic forest, wet forest, and bog. These species also differ in diploid chromosome number, with four species having 13 pairs of chromosomes and four species having 14 pairs. This ecological and chromosomal variation is paralleled by significant interspecific variation in tissue elastic properties. The four 13-paired species from dry habitats exhibit significantly lower tissue elastic moduli near full hydration (E _i) than the four 14-paired species from mesic to wet habitats. Values of E _i range from 2 to 4 MPa among the former species and from 9 to 18 MPa among the latter species. The turgor dependence of the elastic modulus also differs markedly between the two groups of species. As a result of these differences in tissue elastic properties, the capacity for maintaining high turgor pressures as tissue water content decreases is much greater in the 13-paired species from dry habitats than in the 14-paired species from mesic to wet habitats. These results indicate that the evolutionary diversification of the Dubautia species has been accompanied by a significant degree of change at the physiological level.     

An innovative lattice Boltzmann model for simulating Michaelis–Menten-based diffusion–advection kinetics and its application within a cartilage cell bioreactor

Lattice Boltzmann models (LBM) are rapidly showing their ability to simulate a lot of fluid dynamics problems that previously required very complex approaches. This study presents a LBM for simulating diffusion–advection transport of substrate in a 2-D laminar flow. The model considers the substrate influx into a set of active cells placed inside the flow field. A new innovative method was used to simulate the cells activity using the LBM by means of Michaelis–Menten kinetics. The model is validated with some numerical benchmark problems and proved highly accurate results. After validation the model was used to simulate the transport of oxygen substrates that diffuse in water to feed a set of active cartilage cells inside a new designed bioreactor.     

DnaB proteolysis in vivo regulates oligomerization and its localization at oriC in Bacillus subtilis

Initiation of bacterial DNA replication at oriC is mediated by primosomal proteins that act cooperatively to melt an AT-rich region where the replicative helicase is loaded prior to the assembly of the replication fork. In Bacillus subtilis, the dnaD, dnaB and dnaI genes are essential for initiation of DNA replication. We established that their mRNAs are maintained in fast growing asynchronous cultures. DnaB is truncated at its C-terminus in a growth phase-dependent manner. Proteolysis is confined to cytosolic, not to membrane-associated DnaB, and affects oligomerization. Truncated DnaB is depleted at the oriC relative to the native protein. We propose that DNA-induced oligomerization is essential for its action at oriC and proteolysis regulates its localization at oriC. We show that DnaB has two separate ssDNA-binding sites one located within residues 1–300 and another between residues 365–428, and a dsDNA-binding site within residues 365–428. Tetramerization of DnaB is mediated within residues 1–300, and DNA-dependent oligomerization within residues 365–428. Finally, we show that association of DnaB with the oriC is asymmetric and extensive. It encompasses an area from the middle of dnaA to the end of yaaA that includes the AT-rich region melted during the initiation stage of DNA replication.     

Transnational Migration in Rural Oaxaca, Mexico: Dependency, Development, and the Household

Contradictory models of dependency and development have dominated the discussion of migration between Mexico and the United States. Transnational models of migration resolve these contradictions by defining a series of interdependencies (economy and society, for example). Using data collected in a rural Zapotec community in Oaxaca, Mexico, this article focuses on three areas: the stage-specific development of transnational movement; the domestic cycle, household decision making, and migration/remittance outcomes; and the changing nature of community participation. Rooting the discussion in household decision making captures the important role local social variability and economic dynamism play in understanding transnational processes and advancing migration studies. [ households, migration, transnationalism, dependency and development, Oaxaca, Mexico ]     

Stereospecificity and requirements for activity of the respiratory NADH dehydrogenase of Escherichia coli

The respiratory NADH dehydrogenase of Escherichia coli has been further amplified in vivo by genetic methods. The enzyme, a single polypeptide of Mr 47 200 of known amino acid sequence [Young, I. G., Rogers, B. L., Campbell, H. D., Jaworowski, A., & Shaw, D. C. (1981) Eur. J. Biochem. 116, 165-170], constitutes 10-15% of the total protein in the amplified membranes. In situ in the membrane, the enzyme contains 1 mol of FAD/mol of subunit and has a specific NADH:ubiquinone-1 oxidoreductase activity of approximately 1100-1200 units mg-1 at 30 degrees C, pH 7.5. The purified enzyme contains phospholipid, which remains closely associated with it during gel filtration on Sephacryl S-300 in the presence of 0.1% (w/v) cholate at low ionic strength. Under these conditions the enzyme is extensively aggregated (apparent Mr greater than 10(6]. This procedure yielded enzyme with a specific activity of 980 units mg-1, similar to the value observed in the membrane. This preparation contained less than 0.1 mol of Fe/mol of enzyme, confirming that Fe is not involved in reduction of ubiquinone 1 catalyzed by the enzyme. Neutron activation analysis of purified enzyme has demonstrated the absence of 35 trace elements including Se, Zn, Mn, Co, W, Cu, and Fe. The enzyme polypeptide, prepared completely free of phospholipid, FAD, and ubiquinone by gel filtration in the presence of sodium dodecyl sulfate, has been reactivated. The results show that the only components necessary for catalysis of ubiquinone-1 reduction by NADH in this system are the enzyme polypeptide, FAD, and phospholipid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intracellular and Extracellular Uptake of Cadmium by the Moss Rhytidiadelphus squarrosus

Intra- and extracellular Cd uptake were investigated in themoss Rhytidiadelphus squarrosus. Intracellular Cd uptake displayedMichaelis–Menten kinetics and showed that the moss hada high uptake rate and high affinity for Cd. Extracellular Cdbinding capacity was also high. The anion used had little effecton Cd uptake to either location but both intra- and extracellularCd uptake were reduced by equimolar concentrations of Ca, Mgor Zn, although inhibition was not wholly competitive. IntracellularCd uptake was not significantly affected by the supply of energygenerating reserves but, like extracellular Cd uptake, showedaltered characteristics following growth under controlled laboratoryconditions. The results are compared with data on Cd uptakeby the lichen genus Peltigera. Rhytidiadelphus squarrosus, moss, cadmium, intra- and extracellular uptake characteristics, kinetics