bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of transferrin receptor 1 transcription by a cell density response element
Authors: Wang Jian , Chen Guohua , Pantopoulos Kostas
Published: December 2005

TfR1 (transferrin receptor 1) mediates the uptake of transferrin-bound iron and thereby plays a critical role in cellular iron metabolism. Its expression is coupled to cell proliferation/differentiation and controlled in response to iron levels and other signals by transcriptional and post-transcriptional mechanisms. It is well established that TfR1 levels decline when cultured cells reach a high density and in the present study we have investigated the underlying mechanisms. Consistent with previous findings, we demonstrate that TfR1 expression is attenuated in a cell-density-dependent manner in human lung cancer H1299 cells and in murine B6 fibroblasts as the result of a marked decrease in mRNA content. This response is not associated with alterations in the RNA-binding activity of iron regulatory proteins that are indicative of a transcriptional mechanism. Reporter assays reveal that the human TfR1 promoters contains sequences mediating cell-density-dependent transcriptional inhibition. Mapping of the human and mouse TfR1 promoters identified a conserved hexa-nucleotide 5′-GAGGGC-3′ motif with notable sequence similarity to a previously described element within the IGF-2 (insulin-like growth factor-2) promoter. We show that this motif is necessary for the formation of specific complexes with nuclear extracts and for cell-density-dependent regulation in reporter gene assays. Thus the TfR1 promoter contains a functional ‘cell density response element’ (CDRE).
Agonist-induced regulation of mitochondrial and endoplasmic reticulum motility
Authors: Brough David , Schell Michael J. , Irvine Robin F.
Published: December 2005

Using fluorescently tagged markers for organelles in conjunction with confocal microscopy, we have studied the effects of agonist-induced Ca2+ signals on the motility of mitochondria and the ER (endoplasmic reticulum). We observed that the muscarinic agonist carbachol produced a rapid, simultaneous and reversible cessation of the movements of both organelles, which was dependent on a rise in cytosolic Ca2+. This rise in Ca2+ was shown to cause a fall in cellular ATP levels, and the effect of carbachol on organelle movement could be mimicked by depleting ATP with metabolic inhibitors in the absence of any such rise in Ca2+. However, a Ca2+-sensing process independent of ATP appears also to be involved, because we identified conditions where the ATP depletion was blocked (by inhibitors of the Ca2+ pumps), but the organelle movements still ceased following a rise in cytosolic Ca2+. We conclude that the co-ordinated cessation of mitochondria and ER motility is a process regulated by the cytosolic concentration of both Ca2+ and ATP, and that these two parameters are likely to synergize to regulate the localization of the two organelles, and to facilitate the transfer of Ca2+ between them.
A computational model of mitochondrial AZT metabolism
Authors: Bradshaw Patrick C. , Li Jiaxin , Samuels David C.
Published: December 2005

The mechanisms of the mitochondrial toxicity of AZT (azidothymidine; zidovudine) are not clear. The two main contenders are the incorporation of phosphorylated AZT into the mtDNA (mitochondrial DNA) and the competitive inhibition of natural deoxynucleotide metabolism. We have built a computational model of AZT metabolism in mitochondria in order to better understand these toxicity mechanisms. The model includes the transport of non-phosphorylated and phosphorylated forms of AZT into mitochondria, phosphorylation, and incorporation into mtDNA. The model also includes the mitochondrial metabolism of the natural deoxynucleotides. We define three simulated cell types, i.e. rapidly dividing, slowly dividing and postmitotic cells. Our standard simulation indicates that incorporation of AZT into mtDNA is highest in rapidly dividing cells because of the higher mitochondrial AZTTP (3′-azidothymidine-5′-triphosphate)/dTTP ratio in this cell type. However, under these standard conditions the rate of incorporation into mtDNA is too low to be a major cause of toxicity. These simulations relied on the assumption that phosphorylated AZT is transported with the same kinetics as phosphorylated thymidine. In simulations with mitochondria set to have a limited ability to transport phosphorylated AZT, AZTTP accumulates to toxic levels in the mitochondria of postmitotic cells, while low levels are maintained in mitochondria from rapidly dividing cells. This result is more consistent with the tissue toxicities observed in patients. Our model also predicts that inhibition by AZT of mitochondrial deoxycytidine phosphorylation by thymidine kinase 2 may contribute to the mitochondrial toxicity, since in simulations using a typical peak plasma AZT level the mtDNA replication rate is decreased by 30% in postmitotic cell simulations.
Comparison of the SUMO1 and ubiquitin conjugation pathways during the inhibition of proteasome activity with evidence of SUMO1 recycling
Authors: Bailey Daniel , O'Hare Peter
Published: December 2005

To investigate potential interplay between the SUMO1 (small ubiquitin-related modifier-1) and ubiquitin pathways of post-translational protein modification, we examined aspects of their localization and conjugation status during proteasome inhibition. Our results indicate that these pathways converge upon the discrete sub-nuclear domains known as PML (promyelocytic leukaemia protein) NBs (nuclear bodies). Proteasome inhibition generated an increased number of PML bodies, without any obvious increase in size. Using a cell line that constitutively expresses an epitope-tagged version of SUMO1, which was incorporated into high-molecular-mass conjugates, we observed SUMO1 accumulating in clusters around a subset of the NBs. Nuclear ubiquitin was initially observed in numerous speckles and foci, which bore no relationship to PML NBs in the absence of proteasome inhibition. However, during proteasome inhibition, total ubiquitin-conjugated species increased in the cell, as judged by Western blotting. Concomitantly the number of nuclear ubiquitin clusters decreased, and were almost quantitatively associated with the PML NBs, co-localizing with the SUMO-conjugated pool. Proteasome inhibition depleted the pool of free SUMO1 in the cell. Reversal of proteasome inhibition in the presence or absence of protein synthesis demonstrated that free SUMO1 was regenerated from the conjugated pool. The results indicate that a significant fraction of the free SUMO1 pool could be accounted for by recycling from the conjugated pool and indeed it may be that, as for ubiquitin, SUMO1 needs to be removed from conjugated species prior to processing by the proteasome. Taken together with other recent reports on the proteasome and PML NBs, these results suggest that the PML NBs may play an important role in integrating these pathways.
The basal proton conductance of mitochondria depends on adenine nucleotide translocase content
Authors: Brand Martin D. , Pakay Julian L. , Ocloo Augustine , Kokoszka Jason , Wallace Douglas C. , Brookes Paul S. , Cornwall Emma J.
Published: December 2005

The basal proton conductance of mitochondria causes mild uncoupling and may be an important contributor to metabolic rate. The molecular nature of the proton-conductance pathway is unknown. We show that the proton conductance of muscle mitochondria from mice in which isoform 1 of the adenine nucleotide translocase has been ablated is half that of wild-type controls. Overexpression of the adenine nucleotide translocase encoded by the stress-sensitive B gene in Drosophila mitochondria increases proton conductance, and underexpression decreases it, even when the carrier is fully inhibited using carboxyatractylate. We conclude that half to two-thirds of the basal proton conductance of mitochondria is catalysed by the adenine nucleotide carrier, independently of its ATP/ADP exchange or fatty-acid-dependent proton-leak functions.
Refolding of Escherichia coli outer membrane protein F in detergent creates LPS-free trimers and asymmetric dimers
Authors: Visudtiphole Virak , Thomas Matthew B. , Chalton David A. , Lakey Jeremy H.
Published: December 2005

The Escherichia coli OmpF (outer-membrane protein F; matrix porin) is a homotrimeric β-barrel and a member of the bacterial porin superfamily. It is the best characterized porin protein, but has resisted attempts to refold it efficiently in vitro. In the present paper, we report the discovery of detergent-based folding conditions, including dodecylglucoside, which can create pure samples of trimeric OmpF. Whereas outer membrane LPS (lipopolysaccharide) is clearly required for in vivo folding, the artificially refolded and LPS-free trimer has properties identical with those of the outer-membrane-derived form. Thus LPS is not required either for in vitro folding or for structural integrity. Dimeric forms of OmpF have been observed in vivo and are proposed to be folding intermediates. In vitro, dimers occur transiently in refolding of trimeric OmpF and, in the presence of dodecylmaltoside, pure dimer can be prepared. This form has less β-structure by CD and shows lower thermal stability than the trimer. Study of these proteins at the single-molecule level is possible because each OmpF subunit forms a distinct ion channel. Whereas each trimer contains three channels of equal conductance, each dimer always contains two distinct channel sizes. This provides clear evidence that the two otherwise identical monomers adopt different structures in the dimer and indicates that the asymmetric interaction, characteristic of C3 symmetry, is formed at the dimer stage. This asymmetric dimer may be generally relevant to the folding of oligomeric proteins with odd numbers of subunits such as aspartate transcarbamoylase.
Augmentation of endothelial function following exercise training is associated with increased L-arginine transport in human heart failure
Authors: Parnell Melinda M. , Holst Diane P. , Kaye David M.
Published: December 2005

We have reported previously a decrease in the clearance of the NO (nitric oxide) precursor L-arginine in the forearm circulation of CHF (congestive heart failure) patients, suggesting a potential rate-limiting mechanism contributing to the common finding of endothelial dysfunction in CHF. Given data that show exercise training augments endothelial function in CHF, the aim of the present study was to investigate whether these improvements were due to an increase in L-arginine transport. Measures of L-arginine transport, endothelial function and exercise capacity were repeated before and after 8 weeks of ‘usual living’ or exercise training in 21 CHF patients [NYHA (New York Heart Association) class II/III]. Exercise capacity (6-min walk test) increased following exercise training (496±21 to 561±17 m; P=0.005), whereas the control group demonstrated no change [488±18 to 484±21 m; P=ns (not significant)]. Basal FBF (forearm blood flow) remained stable following exercise training (2.68±0.55 to 2.46±0.32 ml·min−1·100 ml−1 of tissue) and ‘usual living’ (2.16±0.37 to 2.91±0.55 min−1·100 ml−1 of tissue). FBF responses to ACh (acetylcholine) increased following exercise by 49.6±17.7% (area under curve; P=0.01) demonstrating augmented endothelial function. FBF responses to SNP (sodium nitroprusside) were also improved following exercise training (30.8±8.2%; P=0.02). There was no change in vascular function in the ‘usual living’ group. The clearance of L-arginine was significantly increased following involvement in the exercise programme (69.4±7.8 to 101.0±9.5 ml/min; P=0.04), whereas there was no change in the ‘usual living’ group (78.4±17.5 to 81.0±14.9 ml/min; P=ns). In conclusion, the augmentation in endothelial function observed following exercise may be due, in part, to an increase in the transport of L-arginine in CHF patients.
Photoinduced absorption and anomalous dichroism in NaCa2Mn2V3O12 garnet as evidence for the formation of oxygen hole dynamics
Authors: Eremenko V. V. , Gnatchenko S. L. , Kachur I. S. , Piryatinskaya V. G. , Ratner A. M. , Shapiro V. V. , Kosymna M. B. , Nazarenko B. P. , Puzikov V. M.
Published: November 2005

It is shown that long-lived photoinduced dichroism in garnets is caused by photoproduced charges with anisotropic structure, which retains a memory of the pumping light polarization for a long time, while photoinduced absorption is due to all photoproduced charges irrespective of their intrinsic structure. The charges with anisotropic structure are indentified as two-center oxygen holes. The formation of an oxygen hole is preceded by the excitation of a charge-transfer state with an electron partially transferred to a cation C (V5+ for NaCa2Mn2V3O12 garnet) from an adjacent oxygen anion. To turn this excited state into a free hole state requires a time τhole during which the hole axis can reorient, resulting in a diminution of dichroism. The time τhole decreases with increasing ionization potential of the cation C (very high for V5+). Such a mechanism explains qualitatively a number of unusual experimental facts, specifically, very strong dichroism observed only in NaCa2Mn2V3O12 garnet, where after the irradiation is switched off the photoinduced changes in all optical properties disappear much more quickly than in the other garnets studied.
Chemisorption and dissociation of single oxygen molecules on Ag(110)
Authors: Hahn J. R. , Ho W.
Published: December 2005

The chemisorption of single oxygen molecules on Ag(110) and the dissociation of the adsorbed molecules induced by tunneling electrons were studied at 13 K using a variable-low-temperature scanning tunneling microscope. Two predominant types of chemisorbed O2 molecules were identified, one with the O2 molecular axis aligned along the [001] direction of the substrate [O2(001)], and the other with the molecular axis aligned along the [11¯0] direction [O2(11¯0)]. Tunneling of electrons between the scanning tunneling microscope tip and O2(001) caused the molecule either to rotate or dissociate, depending on the direction of electron tunneling. In contrast, electron tunneling caused O2(11¯0) to dissociate regardless of tunneling direction. In addition to O2(001) and O2(11¯0), several other oxygen species and their dynamical behaviors were observed.
Electron-spin multiplicities and molecular structures of neutral and ionic scandium-benzene complexes
Authors: Sohnlein Bradford R. , Li Shenggang , Yang Dong-Sheng
Published: December 2005

Scandium-benzene complexes, Sc–(C6H6)1,2 are produced by interactions between the laser-vaporized scandium atoms and benzene vapor in pulsed molecular beams, and identified by photoionization time-of-flight mass spectrometry and photoionization efficiency spectroscopy. The electron-spin multiplicities and geometries of these complexes and their ions are determined by combining pulsed field-ionization zero electron kinetic-energy spectroscopy and density-functional theory calculations. For scandium-monobenzene, a short-range quartet ground state is determined for the neutral complex, and a low-energy triplet state is probed for the ion. For the dibenzene complex, the neutral ground state is a doublet, and two low-energy ion states are singlet and triplet. The quartet and triplet states of scandium-monobenzene and the triplet state of scandium-dibenzene possess sixfold symmetry, whereas the doublet and singlet of the dibenzene complex have twofold symmetry. Moreover, ionization energies and metal-ring stretching wavenumbers are measured for both complexes.
Diffusion and transport of spin pulses in an n-type semiconductor quantum well
Authors: Jiang L. , Weng M. Q. , Wu M. W. , Cheng J. L.
Published: November 2005

We perform a theoretical investigation on the time evolution of spin pulses in an n-type GaAs (001) quantum well with and without external electric field at high temperatures by constructing and numerically solving the kinetic spin Bloch equations and the Poisson equation, with the electron-phonon, electron-impurity, and electron-electron Coulomb scatterings explicitly included. The effect of the Coulomb scattering, especially the effect of the Coulomb drag on the spin diffusion/transport is investigated and it is shown that the spin oscillations and spin polarization reverse along the direction of spin diffusion in the absence of the applied magnetic field, which were originally predicted in the absence of the Coulomb scattering by Weng and Wu [J. Appl. Phys. 93, 410 (2003)], can sustain the Coulomb scattering at high temperatures (∼200K). The results obtained are consistent with a recent experiment in bulk GaAs but at a very low temperature (4 K) by Crooker and Smith [Phys. Rev. Lett. 94, 236601 (2005)].
Purcell effect for CdSe∕ZnSe quantum dots placed into hybrid micropillars
Authors: Robin I. C. , André R. , Balocchi A. , Carayon S. , Moehl S. , Gérard J. M. , Ferlazzo L.
Published: November 2005

This letter reports the observation of the Purcell effect for CdSe∕ZnSe quantum dots located in a hybrid micropillar. The sample consist of a λ∕2-ZnSe cavity sandwiched between two SiO2∕TiO2 Bragg reflectors. Time-resolved photoluminescence (PL) measurements on a series of single-quantum dots were used to probe the Purcell effect in a 1.1μm diameter pillar. A three-fold enhancement of quantum-dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar. The variation of the PL decay shortening from dot to dot is interpreted calculating the theoretical maximal Purcell factor for the different modes resonant with the dots.
The microrheology of polystyrene sulfonate combs in aqueous solution
Authors: Papagiannopoulos A. , Fernyhough C. M. , Waigh T. A.
Published: December 2005

Video particle tracking (VPT) and diffusing wave spectroscopy were used to characterize the microrheology of polystyrene sulfonate combs in aqueous solutions. At low frequencies VPT demonstrated predominantly viscous behavior. The manner in which the viscosity scaled as a function of monomer concentration was a sensitive function of the comb architecture. Densely branched combs or combs with long side chains demonstrated entangled polyelectrolyte scaling above the overlap concentration, whereas sparsely branched combs had unentangled polyelectrolyte scaling. A dynamic scaling model was developed for the viscosity of unentangled semidilute solutions of comb polyelectrolytes. Diffusing wave spectroscopy demonstrated Rouse modes (G′∼G″∼ω1∕2) for the high-frequency dynamics of the semidilute comb solutions. The form of the high-frequency viscoelasticity was independent of the chain architecture and the modulus scaled as expected for linear flexible polyelectrolytes.
A new method to reconstruct three-dimensional spatial distribution function from radial distribution function in solvation structure
Authors: Yokogawa Daisuke , Sato Hirofumi , Sakaki Shigeyoshi
Published: December 2005

Three-dimensional spatial distribution function (SDF) of solvent is a fundamental quantity for analysis of solvation. However, its calculation has been very limited because long computational time is required. We here developed a novel and robust method to construct approximated SDFs of solvent sites from radial distribution functions. In this method, the expansion of SDFs in real solid harmonics around atoms of solute leads to a linear equation, from which SDFs are evaluated with reasonable computational time. This method is applied to the analysis of the solvation structure of liquid water, as an example. The successful results clearly show that this method is very powerful to investigate solvation structure.
Frequency shift imaging of quantum dots with single-electron resolution
Authors: Zhu J. , Brink M. , McEuen P. L.
Published: December 2005

We employ atomic force microscope-based frequency shift microscopy to study the electronic properties of quantum dots formed in carbon nanotubes. The nontransport detection scheme of frequency shift allows us to probe nearly isolated quantum dots in a few electron regime. At 4K, we observe Coulomb oscillations of quantum dots with single-electron resolution and extract the charging energy of a quantum dot.
Tuning porosity of YBa2Cu3O7−δ vicinal films by insertion of Y2BaCuO5 nanoparticles
Authors: Emergo R. L. S. , Wu J. Z. , Haugan T. J. , Barnes P. N.
Published: November 2005

High critical current density (Jc) is the most critical specification for high-temperature-superconductor-coated conductors as required by numerous electric power-related applications. This has motivated an intensive research effort on the effects of microstructure on Jc. By growing YBa2Cu3O7−δ (YBCO) films at a small vicinal angle [R. L. S. Emergo, J. Z. Wu, T. Aytug, and D. K. Christen, Appl. Phys. Lett. 85, 618 (2004)] we have recently obtained a highly porous structure in these films accompanied with a significantly enhanced Jc. This result raises a challenging question on whether the porosity can be tailored in YBCO films to allow a higher Jc. In this study, we have explored the insertion of Y2BaCuO5 (211) nanoparticles in vicinal YBCO thick films to alter the strain at the nanometer scale; a nearly doubled pore density was obtained. A further improved Jc as the consequence of the enhanced pore density in these films suggests a direct correlation between microstructure and Jc and projects an even higher Jc in YBCO films with microstructure engineered optimally at a nanometer scale.
Anisotropy in periodic mesoporous silica and organosilica films studied by generalized ellipsometry
Authors: Peiris F. C. , Hatton B. D. , Ozin G. A. , Perovic D. D.
Published: December 2005

The dielectric functions of a series of periodic mesoporous silica as well as periodic mesoporous organosilica thin films were measured using generalized variable angle spectroscopic ellipsometry over the spectral range 300–1400nm. Ellipsometry results indicate that following template removal, both types of films possess uniaxial anisotropy, with the optic axis perpendicular to the plane of the film. This anisotropy is apparently caused by the structural distortion of the channels, oriented primarily parallel to the substrate plane. We also find that the birefringence increases as a function of porosity.
Reduction of damage threshold in dielectric materials induced by negatively chirped laser pulses
Authors: Louzon E. , Henis Z. , Pecker S. , Ehrlich Y. , Fisher D. , Fraenkel M. , Zigler A.
Published: December 2005

The threshold fluence for laser induced damage in wide band gap dielectric materials, fused silica and MgF2, is observed to be lower by up to 20% for negatively (down) chirped pulses than for positively (up) chirped, at pulse durations ranging from 60 fs to 1 ps. This behavior of the threshold fluence for damage on the chirp direction was not observed in semiconductors (silicon and GaAs). Based on a model including electron generation in the conduction band and Joule heating, it is suggested that the decrease in the damage threshold for negatively chirped pulse is related to the dominant role of multiphoton ionization in wide gap materials.
Evidence for hot electron magnetocurrent in a double barrier tunnel junction device
Authors: Ladak S. , Hicken R. J.
Published: November 2005

Hot electron transport has been studied in three terminal Ta∕TaOx∕Co∕AlOx∕Ni81Fe19 structures fabricated by magnetron sputtering through shadow masks. With the Co base and Ta collector connected together via a small resistor, the collector current contains contributions first from hot electrons injected from the Ni81Fe19 emitter, and second from a geometrical artifact that leads to tunneling from the Fermi level in the base. Both sources of collector current lead to a room temperature magnetocurrent effect. The hot electron contribution begins to dominate as the emitter-base voltage −Veb exceeds 0.3 V.
Equations of coupled radial and translational motions of a bubble in a weakly compressible liquid
Authors: Doinikov Alexander A.
Published: November 2005

Coupled equations of radial and translational motions of a spherical bubble, accounting to the first order for the compressibility of the surrounding liquid, are derived using an energy approach. It is shown that the compressibility corrections appear only in the radial equation, while the translational equation keeps the same form as in an incompressible liquid. However, if the radial equation is recast to the Keller-Miksis form, the translational term in this equation acquires a correction that is of importance in high-intensity fields.
Short-term response of the nitrogen nutrition status of tall fescue and Italian ryegrass swards under water deficit
Authors: Gonzalez-Dugo Victoria , Durand Jean-Louis , Gastal François , Picon-Cochard Catherine
Published: November 2005

Grasslands are rarely irrigated, thus water deficits often induce a reduction of the nitrogen nutrition index (NNI) during summer. This is measured using the ratio between the actual N concentration and the minimum N concentration required to achieve the maximum growth rate. NNI is derived from the standing biomass by a simple relationship. This paper details the results of a field experiment, combining 2 levels of irrigation with 2 levels of nitrogen fertilisation during the summer, on 2 commonly cultivated grass species in pure swards (tall fescue, Festuca arundinacea L., and Italian ryegrass, Lolium multiflorum). Plant water status, NNI, root length density (RLD), soil volumetric water content (θv), and mineral nitrogen concentration [N] were followed under water deficit and recovery. In both species, RLD was high (>6 cm/cm3) in the 0–0.25 m soil layer. Whereas the NNI of tall fescue responded strongly to its water status, Italian ryegrass was most often above optimal nitrogen nutrition because of its slow growth in that particular season and its higher superficial RLD. However, its NNI generally followed the θv closely, whereas tall fescue exhibited a delay in response of NNI upon rewatering, suggesting lasting effects of water deficits on the absorption capacity of roots in that species.
A quantitative top-down view of interactions between stresses: theory and analysis of nitrogen - water co-limitation in Mediterranean agro-ecosystems
Authors: Sadras Victor O.
Published: November 2005

The multiple factors constraining the growth, reproduction, and survival of diverse organisms are often non-additive. Research of interacting factors generally involves conceptual models that are specific for target organism, type of stress, and process. As a complement to this reductionist, bottom-up view, in this review I discuss a quantitative top-down approach to interacting stresses based on co-limitation theory. Firstly, co-limitation theory is revised. Co-limitation is operationally identified when the output response of a biological system (e.g. plant or population growth) to two or more inputs is greater than its response to each factor in isolation. The hypothesis of Bloom, Chapin, and Mooney, that plant growth is maximised when it is equally limited by all resources, is reworded in terms of co-limitation and formulated in quantitative terms, i.e. for a given intensity of aggregate stress, plant growth is proportional to degree of resource co-limitation. Emphasis is placed on the problems associated with the quantification of co-limitation. It is proposed that seasonal indices of nitrogen and water stress calculated with crop simulation models can be integrated in indices accounting for the aggregated intensity of water and nitrogen stress (SWN), the degree of water and nitrogen co-limitation (CWN), and the integrated effect of stress and co-limitation (SCWN = CWN/SWN). The expectation is that plant growth and yield should be an inverse function of stress intensity and a direct function of co-limitation, thus proportional to SCWN. Secondly, the constraints imposed by water and nitrogen availability on yield and water use efficiency of wheat crops are highlighted in case studies of low-input farming systems of south-eastern Australia. Thirdly, the concept of co-limitation is applied to the analysis of (i) grain yield responses to water–nitrogen interactions, and (ii) trade-offs between nitrogen- and water-use efficiency. In agreement with theoretical expectations, measured grain yield is found to be proportional to modelled SCWN. Productivity gains associated with intensification of cropping practices are interpreted in terms of a trade-off, whereby water-use efficiency is improved at the expense of nitrogen-use efficiency, thus leading to a higher degree of resource co-limitation.
Drought resistance of native and introduced perennial grasses of south-eastern Australia
Authors: Bolger T. P. , Rivelli A. R. , Garden D. L.
Published: November 2005

Perennial grasses are the key to the economic and environmental sustainability of pastures for livestock grazing in south-eastern Australia. Mortality of perennial grasses can occur during drought periods and there is anecdotal evidence of differences in drought resistance among species, but information on the basic ecophysiological responses of these species to drought is lacking. An experiment was conducted to determine the responses of 7 native and 3 introduced perennial grass species to continuous drought. Leaf survival during severe drought varied among the species nearly 4-fold, from 11 to 40 days, and was considered a measure of their overall drought resistance. All of the species had good dehydration tolerance, so the differences in drought resistance were related more to their dehydration avoidance traits, specifically to the amount of water available to the plant at the point where plant transpiration became minimal. The native species had both the longest and shortest leaf survival periods, with the introduced species ranking intermediate. Species exhibited various morphological traits that contributed to dehydration avoidance during severe drought, including leaf folding or rolling, rapid leaf shedding, and large amounts of cuticular wax. The results are discussed in terms of their implications for perennial grass persistence in south-eastern and in south-western Australia.
The role of management in yield improvement of the wheat crop—a review with special emphasis on Western Australia
Authors: Anderson W. K. , Hamza M. A. , Sharma D. L. , D'Antuono M. F. , Hoyle F. C. , Hill N. , Shackley B. J , Amjad M. , Zaicou-Kunesch C.
Published: November 2005

Modern bread wheat (Triticum aestivum) has been well adapted for survival and production in water-limited environments since it was first domesticated in the Mediterranean basin at least 8000 years ago. Adaptation to various environments has been assisted through selection and cross-breeding for traits that contribute to high and stable yield since that time. Improvements in crop management aimed at improving yield and grain quality probably developed more slowly but the rate of change has accelerated in recent decades. Many studies have shown that the contribution to increased yield from improved management has been about double that from breeding. Both processes have proceeded in parallel, although possibly at different rates in some periods, and positive interactions between breeding and management have been responsible for greater improvements than by either process alone.
In southern Australia, management of the wheat crop has focused on improvement of yield and grain quality over the last century. Adaptation has come to be equated with profitability and, recently, with long-term economic and biological viability of the production system. Early emphases on water conservation through the use of bare fallow, crop nutrition through the use of fertilisers, crop rotation with legumes, and mechanisation, have been replaced by, or supplemented with, extensive use of herbicides for weed management, reduced tillage, earlier sowing, retention of crop residues, and the use of ‘break’ crops, largely for management of root diseases.
Yields from rainfed wheat crops in Western Australia have doubled since the late 1980s and water-use efficiency has also doubled. The percentage of the crop in Western Australia that qualifies for premium payments for quality has increased 3–4 fold since 1990. Both these trends have been underpinned by the gradual elimination or management of the factors that have been identified as limiting grain yield, grain quality, or long-term viability of the cropping system.
Changes in soil carbon and soil nitrogen after tree clearing in the semi-arid rangelands of Queensland
Authors: Harms B. P. , Dalal R. C. , Cramp A. P.
Published: November 2005

Changes in soil carbon (C) and nitrogen (N) stocks following tree clearing were estimated at 32 rangeland sites in central and southern Queensland by using paired-site sampling. When corrected for soil bulk-density differences at each site, average soil C across all sites decreased after tree clearing by 8.0% for 0–0.3-m soil depth, and by 5.4% for 0–1.0-m depth; there were corresponding declines in soil C of 2.5 and 3.5tha–1, respectively. Mean soil C stocks (excluding surface litter, extractable roots and coarse charcoal) at uncleared sites were 29.5tha–1 for 0–0.3-m soil depth, and 62.5tha–1 for 0–1.0-m depth. Mean soil C stocks (0–0.3m) were 41% of the mean total C for the soil–plant system (soil + litter/woody debris + stand biomass) at uncleared sites. Soil C decline (0–0.3m) accounted for approximately 7% of the average total C lost because of land clearing across all sites. Soil C stocks at uncleared sites were correlated with tree basal area, clay content and soil phosphorus (P) content. Changes in soil C after tree clearing were strongly correlated to initial soil C contents at the uncleared sites, and were associated with particular vegetation groups and soil types. Changes in soil N were strongly correlated with changes in soil C; however, the average change in soil N across all sites was not significant. Given the size of the C and N pools in rangeland soils, the factors that influence soil C and soil N dynamics in rangeland systems need to be better understood for the effective management of C stocks in these soils.
Efficient growth inhibition of
Bacillus anthracis
by knocking out the ribonucleotide reductase tyrosyl radical
Authors: Torrents Eduard , Sahlin Margareta , Biglino Daniele , Gräslund Astrid , Sjöberg Britt-Marie
Published: December 2005

Bacillus anthracis
, the causative agent of anthrax, is a worldwide problem because of the need for effective treatment of respiratory infections shortly after exposure. One potential key enzyme of
B. anthracis
to be targeted by antiproliferative drugs is ribonucleotide reductase. It provides deoxyribonucleotides for DNA synthesis needed for spore germination and growth of the pathogen. We have cloned, purified, and characterized the tyrosyl radical-carrying NrdF component of
B. anthracis
class Ib ribonucleotide reductase. Its EPR spectrum points to a hitherto unknown three-dimensional geometry of the radical side chain with a 60° rotational angle of C
α
-(C
β
-C
1
)-plane of the aromatic ring. The unusual relaxation behavior of the radical signal and its apparent lack of line broadening at room temperature suggest a weak interaction with the nearby diiron site and the presence of a water molecule plausibly bridging the phenolic oxygen of the radical to a ligand of the diiron site. We show that
B. anthracis
cells are surprisingly resistant to the radical scavenger hydroxyurea in current use as an antiproliferative drug, even though its NrdF radical is efficiently scavenged
in vitro
. Importantly, the antioxidants hydroxylamine and
N
-methyl hydroxylamine scavenge the radical several orders of magnitude faster and prevent
B. anthracis
growth at several hundred-fold lower concentrations compared with hydroxyurea. Phylogenetically, the
B. anthracis
NrdF protein clusters together with NrdFs from the pathogens
Bacillus cereus
,
Bacillus thuringiensis
,
Staphylococcus aureus
, and
Staphylococcus epidermidis
. We suggest the potential use of N-hydroxylamines in combination therapies against infections by
B. anthracis
and closely related pathogens.
Endocrine self and gut non-self intersect in the pancreatic lymph nodes
Authors: Turley Shannon J. , Lee Je-Wook , Dutton-Swain Nick , Mathis Diane , Benoist Christophe
Published: November 2005

The autoimmune cascade that culminates in diabetes initiates within pancreatic lymph nodes (PLNs). Here, we show that developmentally controlled lymphogenesis establishes a preferential trafficking route from the gut to the PLN, where T cells can be activated by antigens drained from the peritoneum and the gastrointestinal tract. Furthermore, intestinal stress modifies the presentation of pancreatic self-antigens in PLNs. The convergence of endocrine and intestinal contents within PLNs has significant implications for type 1 diabetes and may help to explain the link between autoimmune pathogenesis and environmental provocation.
Oxidizing potential of endosomes and lysosomes limits intracellular cleavage of disulfide-based antibody–drug conjugates
Authors: Austin Cary D. , Wen Xiaohui , Gazzard Lewis , Nelson Christopher , Scheller Richard H. , Scales Suzie J.
Published: December 2005

Antibody–drug conjugate therapy entails targeted killing of cancer cells with cytotoxic compounds covalently linked to tumor-specific antibodies and shows promise in the treatment of several human cancers. Current antibody–drug conjugate designs that incorporate a disulfide linker between the antibody and cytotoxic drug are inspired by indirect evidence suggesting that the redox potential within the endosomal system is reducing. It is presumed that antigen-dependent endocytosis leads to disulfide linker reduction and intracellular release of free drug, but direct demonstration of such a mechanism is lacking. To determine whether the disulfideN-succinimidyl 4-(2-pyridyldithio)pentanoate (SPP) linker would be reduced during endocytic recycling of the anti-HER2 antibody trastuzumab (Herceptin, Genentech), we synthesized a trastuzumab-SPP-Rhodamine red conjugate and developed a linker cleavage assay by using the self-quenching property of this fluorophore. In breast carcinoma SKBr3 cells, no SPP linker cleavage was observed, as detected by fluorescence dequenching upon internalization. By contrast, the conjugate did display fluorescence dequenching when diverted to the lysosomal pathway by geldanamycin, an effect partly due to proteolytic degradation rather than disulfide reduction. To understand why linker reduction was inefficient, we measured redox potentials of endocytic compartments by expressing a redox-sensitive variant of GFP fused to various endocytic proteins. Unexpectedly, we found that recycling endosomes, late endosomes, and lysosomes are not reducing, but oxidizing and comparable with conditions in the endoplasmic reticulum. These results suggest that intracellular reduction is unlikely to account for the potency of disulfide-linked antibody–drug conjugates.
Exercise With Lack of Motor Control: Lessons From Studies on Spinal Cord Patients
Authors: Kjær Michael
Published: December 2005

Study of cardiovascular and metabolic regulation can be performed using electrical stimulation on paralyzed muscle. Simultaneously, electrical induced training of spinal cord injured individuals can beneficially improve their aerobic capacity and thus lower risk for inactivity associated diseases. The normal correlation between oxygen uptake and cardiac output is maintained during electrical involuntary exercise, and venous blood return is most likely a candidate for this relation during exercise. With regards to metabolism, substrate mobilization of glucose and fatty acids is impaired in the absence of motor control and neural feedback from muscle, during electrical exercise in spinal cord injured muscle glycogenolysis dominates. Electrical stimulation ergometer training in spinal cord injured rapidly increases glycolytic and oxidative enzymes, and with a more delayed response results in a fiber‐type transformation from dominating myosin heavy chain isoform IIx to IIa and ultimately towards type I. Intramuscular connective tissue, collagen type IV content did not change in response to training, whereas degradation rate rose, indicating an increased turnover rate in connective tissue with training.
Molecular regulation of the training response: New techniques to study old questions
Authors: Ordway George
Published: December 2005

Exercise training provides a powerful tool with which to study the adaptive capacity of tissues, organ systems, and organisms. A rich literature from a number of disciplines gives strong evidence that exercise training is perhaps the best chronic physiological stress for the study of human or animal function. It is a stress the allows one to look not only at how individual systems respond but also how they interact in providing an overall response. Although much is known about the adaptations to exercise training, we are only beginning to understand molecular mechanisms that regulate the responses to training. This summary paper will present some basic concepts regarding these molecular mechanisms and their role in the training response in skeletal muscle, followed by some examples of how these new techniques are being used to study old questions.
Polymorphism and exercise performance
Authors: Wolfarth Bernd
Published: December 2005

The fields of molecular genetics and molecular biology are of increasing interest in medicine and science. The aim of this article is to describe the current status of genetics in sports, with a special focus on genetic polymorphisms and endurance performance. Results from twin studies suggested a high percentage of heritability for endurance performance and maximal oxygen uptake (VO2max). Data from large sample sizes of monozygotic and dizygotic twins showed heritability values up to 40% for adjusted VO2max values. Today we are able to use molecular markers to look for specific genes and their implications for phenotypes of interest. The first results for endurance‐related phenotypes are available now. Till now we have evidence for association between different types of endurance measures and polymorphisms in the genes encoding the Angiotensin‐Converting‐Enzyme (ACE), the muscle type Creatine‐Kinase (CKMM), and the alpha‐2a‐adrenoceptor (ADRA2A) gene. The scientific focus in the next years will mainly involve case‐control studies and genome analysis with informative markers in known and unknown genes (regions) of interest.
The nature of force depression and force enhancement in skeletal muscle contraction
Authors: Herzog Walter
Published: December 2005

Here, we review the history‐dependent phenomena associated with muscle force production. Specifically, the depression of the steady‐state isometric force following muscle shortening, and the enhancement of the steady‐state isometric force following muscle stretching are discussed. First, we describe the observations that have been made experimentally, then we introduce the primary proposed mechanisms for force depression and force enhancement. Next, in view of the available results, we critically evaluate specific hypotheses based on these mechanisms. Finally, we recommend further discussion about some of the proposed mechanisms.
Assessment of sports performance with particular reference to field games
Authors: Reilly Thomas
Published: December 2005

Objective data on performance of game players provide a useful basis for monitoring the contributions of individuals towards the team's collective efforts. Notation analysis and motion analysis are different methods of recording patterns of play‐ and work‐rate of players, respectively. These types of observations yield profiles from which sport‐specific tests may be designed. Examples are given from soccer, rugby football, and field hockey. The observations are also useful in the design of laboratory‐based sports‐specific protocols for the design of experimental work. With the rapidly evolving technologies of performance analysis, this area of work is likely to increase in future.
Bone mineral density in top level male athletes of different sports
Authors: Platen Petra , Chae Eun‐heui , Antz Roswita , Lehmann Reiner , Kühlmorgen Jens , Allolio Bruno
Published: December 2005

The purpose of this study was to determine the influence of muscle strength, trainingspecific and anthropometric parameters on bone mineral density (BMD) in male top athletes of different sports in comparison to untrained controls. BMD was measured by dual energy X‐ray absorptiometry in 173 males, aged 18 to 31 years. Of these, 104 were athletes (runners, n = 21; cyclists, n = 12; triathletes, n = 18), heavy athletes (HA, judo and wrestling, n = 28), and team sport athletes (TS, handball, soccer, basketball, volleyball, n = 25); 44 were unspecifically trained sport students (STU); and 25 were untrained controls (UT). Sport‐ and group‐specific differences were found in anthropometric but not strength parameters. Marked sport‐ and group‐specific differences were found for BMD at lumbar spine (LSP) and the femoral sites (FEM). Group‐specific effects on BMD were clearest when calculating percentual differences between BMD of athletes and UT: In group I (HA, TS, and STU), BMD at LSP and FEM were significantly (p <. 01) higher compared to UT; in group II (R and TRI), BMD at FEM but not at LSP was higher compared to UT (p <.01); and in group III (C), no BMD value was significantly different from UT. Multiple regression analysis revealed lean body mass to be the strongest predictor for BMD at LSP and FEM. We conclude that mechanical loads have strong effects on bone adaptation. Sport‐specific and body region‐specific effects have to be taken into account for evaluation of osteogenic effects of exercise. Particularly dynamic sports with short, high, and multidimensional loads have the strongest effects on bone formation, independent of training quantity.
Analysis of the long jump technique in the transition from approach to takeoff based on time‐continuous kinematic data
Authors: Jaitner Thomas , Mendoza Luis , Schöllhorn Wolfgang
Published: December 2005

There are many studies on the biomechanics of the long jump, but few researchers have investigated how the athlete has to perform the last strides in order to prepare for takeoff. In this investigation, a pattern recognition approach was applied to analyze the movement structure during the last strides of the approach run and the jump. Time‐continuous kinematic data of 57 trials (4.45‐6.84 m) was analyzed. Cluster analysis identified at coarse level different movement patterns for each flight and support phase. Above these structural differences, individual movement patterns were diagnosed, especially for the jump. Further, the contribution of single variables on the differences of the complex movement patterns was determined by discriminant analysis. Based on the results, conclusions were drawn concerning the long jump and individuality in training. Overall, the applied pattern recognition method allows for the identification of structural changes of movement patterns as well as individual movement styles. This offers a wide range of application in various areas like sports training and rehabilitation.