bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of tributary debris on the longitudinal profile of the Colorado River in Grand Canyon
Authors: Hanks Thomas C. , Webb Robert H.
Published: June 2006

The Colorado River in Grand Canyon has long been known as a “rapids‐and‐pools” river, with the rapids owing their existence primarily to tributary debris flows. The debris flows deposit subaerial debris fans that constrict the channel laterally and, when they enter the river, raise the bed elevation. The rapids are short‐wavelength (∼0.1 to ∼1 km), small‐amplitude (≤ ∼5 m) convexities in the river's longitudinal profile, arising from the shallow gradient in the upstream pool and the steep gradient through the rapid itself. Analysis of the entire longitudinal profile through Grand Canyon reveals two long‐wavelength (∼100 km), large‐amplitude (15–30 m) river profile convexities: the eastern canyon convexity between river mile (RM) 30 and RM 80 and the western canyon convexity between RM 150 and RM 250. Convexities of intermediate scale are also identified in the longitudinal profile. These longer‐wavelength, larger‐amplitude convexities have strong spatial correlations with high rates of debris flow occurrence, high densities of Holocene debris fans, the largest debris fans along the river, and alluvial thicknesses of 10 m or more. River profile convexities are unstable and require an active and powerful geologic process to maintain them, in this case the abundant, frequent, and voluminous Holocene debris flow activity in Grand Canyon. At all wavelengths the most likely cause for these river profile convexities is Holocene aggradation of the riverbed beneath them, driven by the coarse particles of tributary debris flows. Large enough debris flows will slow river flow for kilometers upstream, causing it to drop much of its suspended load. Integrated over time and all of the tributary point source contributions, this process will build short‐wavelength convexities into long‐wavelength convexities. For most if not all of the Holocene the Colorado River has been dissipating most of its energy in the rapids and expending the remainder in transporting fine sediment through Grand Canyon, with little or no regional incision of bedrock.
Statistical characteristics of hydrogen and oxygen ENA emission from the storm‐time ring current
Authors: Ohtani S. , Brandt P. C. , Singer H. J. , Mitchell D. G. , Roelof E. C.
Published: June 2006

The present study statistically examines energetic neutral atom (ENA) emission from the storm‐time inner magnetosphere using measurements from the IMAGE/HENA instrument. It is found that the total image‐integrated ENA energy flux is well correlated (∣c.c.∣ ∼ 0.7) with the Sym‐H index. However, the increase is not linear but exponential with ∣Sym‐H∣, which can be attributed to the fact that the ring current moves closer to Earth as the storm becomes more intense. The oxygen (52–180 keV) energy flux increases more steeply with ∣Sym‐H∣ than the hydrogen (27–60 keV and 60–119 keV) energy flux, which is consistent with the results of in situ measurements reported previously. The relative contribution of near‐Earth emission to total energy flux is larger during the main phase than during the recovery phase presumably because during the main phase the ring current moves closer to Earth and ion precipitation is more intense. Interestingly, if Sym‐H is the same, the ring current emission of 60–119 keV hydrogen and 52–180 keV oxygen is systematically weaker during the main phase than during the recovery phase. This can be explained if the ring current is indeed weaker during the main phase than during the recovery phase (for a given Sym‐H), and its smaller contribution to Sym‐H is compensated by the contribution of a more intense tail current. This idea is confirmed by the finding that the geosynchronous magnetic field is more stretched during the main phase.
Temporal variations of elemental carbon in Tokyo
Authors: Kondo Y. , Komazaki Y. , Miyazaki Y. , Moteki N. , Takegawa N. , Kodama D. , Deguchi S. , Nogami M. , Fukuda M. , Miyakawa T. , Morino Y. , Koike M. , Sakurai H. , Ehara K.
Published: June 2006

Mass concentrations of elemental carbon (EC) in fine mode and mixing ratios of carbon monoxide (CO) were measured at the University of Tokyo campus in Tokyo in different seasons in 2003–2005. Measurements of EC were made using a semicontinuous thermal‐optical analyzer. The mass concentrations of nonvolatile aerosol measured by the calibrated scanning mobility particle sizer combined with a heated inlet agreed with the independent EC measurements with a systematic difference of about 4%, demonstrating that the mass concentrations of nonvolatile aerosol well represent those for EC. A majority of the nonvolatile aerosol and therefore EC mass concentration was in volume equivalent diameters between 50 and 200 nm, peaking at around 130 nm. The correlation of EC and CO was generally compact throughout the measurement period because of the similarity in sources. The slope of the EC‐CO correlation (ΔEC/ΔCO) is therefore a useful parameter in validating EC emission inventories. The EC concentration and ΔEC/ΔCO showed distinct diurnal variation. On weekdays, EC and ΔEC/ΔCO reached maximum values of about 3 μg m−3 and 9 ng m−3/parts per billion by volume, respectively, in the early morning (0400–0800 local time), when the traffic density of heavy‐duty trucks with diesel engines was highest. In addition, these values were lower by a factor of 2 on Sundays. The heavy truck traffic showed similar diurnal and weekday/weekend variations, indicating that exhaust from diesel engines is an important source of EC. Monthly mean ΔEC/ΔCO showed a seasonal variation, reaching broad maximum values in spring‐autumn and reaching minimum values in midwinter, following the seasonal variation in temperature, as observed in Maryland, United States (Chen et al., 2001). This temperature dependence is likely due to the temperature dependence of EC emissions from diesel engines on intake air temperature. More stringent regulation of emissions of particles from diesel cars started in the Tokyo Metropolitan Area in October 2003. The ΔEC/ΔCO values did not change, however, exceeding the natural variability (10%) after 1 year from the start of the new regulations, when the temperature dependence is taken into account. This indicates that the regulation of particle emissions in the Tokyo Metropolitan Area was not effective in reducing the EC concentrations after 1 year.
Aerosol size spectra and CCN activity spectra: Reconciling the lognormal, algebraic, and power laws
Authors: Khvorostyanov Vitaly I. , Curry Judith A.
Published: June 2006

Empirical power law expressions of the form NCCN = Csk have been used in cloud physics for over 4 decades to relate the number of cloud condensation nuclei (CCN) and droplets formed on them to cloud supersaturation, s. The deficiencies of this parameterization are that the parameters C and k are usually constants taken from the empirical data and not directly related to the CCN microphysical properties and this parameterization predicts unbounded droplet concentrations at high s. The activation power law was derived in several works from the power law Junge‐type aerosol size spectra and parameters C and k were related to the indices of the power law, but this still does not allow to describe observed decrease of the k‐indices with s and limited NCCN. Recently, new parameterizations for cloud drop activation have been developed based upon the lognormal aerosol size spectra that yield finite NCCN at large s, but does not explain the activation power law, which is still traditionally used in the interpretation of CCN observations, in many cloud models and some large‐scale models. Thus the relation between the lognormal and power law parameterizations is unclear, and it is desirable to establish a bridge between them. In this paper, algebraic and power law equivalents are found for the lognormal size spectra of partially soluble dry and wet interstitial aerosol, and for the differential and integral CCN activity spectra. This allows derivation of the power law expression for cloud drop activation from basic thermodynamic principles (Köhler theory). In the new power law formulation, the index k and coefficient C are obtained as continuous analytical functions of s and expressed directly via parameters of aerosol lognormal size spectra (modal radii, dispersions) and physicochemical properties. This approach allows reconciliation of this modified power law and the lognormal parameterizations and their equivalence is shown by the quantitative comparison of these models as applied to several examples. The advantages of this new power law relationship include bounded Nd at high s, quantitative explanation of the experimental data on the k‐index and possibility to express k(s) and C(s) directly via the aerosol microphysics. The modified power law provides a framework for using the wealth of data on the C, k parameters accumulated over the past decades, both in the framework of the power law and the lognormal parameterizations.
Role of climate change in global predictions of future tropospheric ozone and aerosols
Authors: Liao Hong , Chen Wei‐Ting , Seinfeld John H.
Published: June 2006

A unified tropospheric chemistry‐aerosol model within the Goddard Institute for Space Studies general circulation model II′ is applied to simulate an equilibrium CO2‐forced climate in the year 2100 to examine the effects of climate change on global distributions of tropospheric ozone and sulfate, nitrate, ammonium, black carbon, primary organic carbon, secondary organic carbon, sea salt, and mineral dust aerosols. The year 2100 CO2 concentration as well as the anthropogenic emissions of ozone precursors and aerosols/aerosol precursors are based on the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (SRES) A2. Year 2100 global O3 and aerosol burdens predicted with changes in both climate and emissions are generally 5–20% lower than those simulated with changes in emissions alone; as exceptions, the nitrate burden is 38% lower, and the secondary organic aerosol burden is 17% higher. Although the CO2‐driven climate change alone is predicted to reduce the global O3 burden as a result of faster removal of O3 in a warmer climate, it is predicted to increase surface layer O3 concentrations over or near populated and biomass burning areas because of slower transport, enhanced biogenic hydrocarbon emissions, decomposition of peroxyacetyl nitrate at higher temperatures, and the increase of O3 production by increased water vapor at high NOx levels. The warmer climate influences aerosol burdens by increasing aerosol wet deposition, altering climate‐sensitive emissions, and shifting aerosol thermodynamic equilibrium. Climate change affects the estimates of the year 2100 direct radiative forcing as a result of the climate‐induced changes in burdens and different climatological conditions; with full gas‐aerosol coupling and accounting for ozone and aerosols from both natural and anthropogenic sources, year 2100 global mean top of the atmosphere direct radiative forcings by O3, sulfate, nitrate, black carbon, and organic carbon are predicted to be +0.93, −0.72, −1.0, +1.26, and −0.56 W m−2, respectively, using present‐day climate and year 2100 emissions, while they are predicted to be +0.76, −0.72, −0.74, +0.97, and −0.58 W m−2, respectively, with year 2100 climate and emissions.
Measurement of atmospheric NO2 by pulsed cavity ring‐down spectroscopy
Authors: Osthoff Hans D. , Brown Steven S. , Ryerson Thomas B. , Fortin Tara J. , Lerner Brian M. , Williams Eric J. , Pettersson Anders , Baynard Tahllee , Dubé William P. , Ciciora Steven J. , Ravishankara A. R.
Published: June 2006

We have constructed a pulsed cavity ring‐down spectrometer (CARDS) for simultaneous measurements of nitrogen dioxide (NO2), the nitrate radical (NO3), and dinitrogen pentoxide (N2O5) in the atmosphere. In this paper, we describe the development of the instrument to measure NO2 via its absorption at 532 nm. The NO2 detection channel was calibrated against a NIST traceable calibration standard as well as a photolysis‐chemiluminescence (P‐CL) NO2 detector. The absorption cross section of NO2 at 532 nm was determined to be (1.45 ± 0.06) × 10−19 cm2. The NO2 detection limit (1σ) for 1 s data is 40 pptv, and the instrument response is accurate within ±4% (1σ) under laboratory conditions. The linear dynamic range of the instrument has been verified from the detection limit to above 200 ppbv (r2 > 99.99%). For field measurements it is necessary to correct the CARDS NO2 signal for absorption by ozone. Under ambient conditions we report 1 s NO2 CARDS data with total uncertainty ±(4%, 60 pptv + 0.4 × (pptv/ppbv) × O3) (1σ). The instrument was deployed in the field during the New England Air Quality Study–International Transport and Chemical Transformation on board the NOAA research vessel Ronald H. Brown in the summer of 2004 and in Boulder, Colorado, in the winter of 2005. In both campaigns, CARDS and P‐CL NO2 measurements were highly correlated (r2 > 98%), indicating the absence of interfering gas phase absorbers at 532 nm other than ozone and the suitability of CARDS to measure NO2 in the troposphere.
Modeling the Martian dust cycle and surface dust reservoirs with the NASA Ames general circulation model
Authors: Kahre Melinda A. , Murphy James R. , Haberle Robert M.
Published: June 2006

We employ the NASA Ames Mars general circulation model (GCM) to investigate the dust lifting mechanisms responsible for the observed Martian dust cycle and the net surface response to the combined influence of dust lifting and deposition. This GCM includes lifting, transport, and deposition of radiatively active dust. Two dust lifting mechanisms are accounted for: wind stress lifting and dust devil lifting. A “baseline” simulation is presented and shown to compare well to available spatial and temporal observations of atmospheric opacity, wind stress dust lifting events, and atmospheric temperatures recorded during a nonglobal dust storm year. Multiple simulations were conducted to explore the model's sensitivity to a wide range of dust lifting parameters (the functional dependence of surface dust flux on wind stress, the wind stress threshold for lifting, etc.) Model results robustly suggest that wind stress lifting produces the peak in atmospheric dust load during southern spring and summer and that dust devils maintain the background haze of atmospheric dust during northern spring and summer. These results are consistent with previously published conclusions. Dust devil and wind stress lifting contribute equally to the simulated total amount of dust lifted annually during nonglobal dust storm years. The simulated spatial pattern of annual net deflation/deposition suggests that the low thermal inertia regions (Tharsis, Arabia, and Elysium) are not currently net dust accumulation regions. This net deflation is the result of dust devil dust lifting, suggesting that dust devils could play an important role in the present‐day pattern of surface dust reservoirs.
Formation of refrozen snowpack layers and their role in slab avalanche release
Authors: Jamieson Bruce
Published: June 2006

In a variety of snow climates, numerous slab avalanches release over crusts consisting of refrozen snow. Slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts, often within a day. Weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients. These processes create interfaces where differences in grain radii can contribute to weak bonding. In western Canada, layers of faceted crystals (facet layers) on crusts are most common in early and late winter when thaws and rain are more frequent. Also, thin facet layers occur in spring when surface melting by solar radiation is common. Shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase. The spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer.
NABP1, a novel RORγ-regulated gene encoding a single-stranded nucleic-acid-binding protein
Authors: Kang Hong Soon , Beak Ju Youn , Kim Yong-Sik , Petrovich Robert M. , Collins Jennifer B. , Grissom Sherry F. , Jetten Anton M.
Published: June 2006

RORγ2 (retinoid-related orphan receptor γ2) plays a critical role in the regulation of thymopoiesis. Microarray analysis was performed in order to uncover differences in gene expression between thymocytes of wild-type and RORγ−/− mice. This analysis identified a novel gene encoding a 22 kDa protein, referred to as NABP1 (nucleic-acid-binding protein 1). This subsequently led to the identification of an additional protein, closely related to NABP1, designated NABP2. Both proteins contain an OB (oligonucleotide/oligosaccharide binding) motif at their N-terminus. This motif is highly conserved between the two proteins. NABP1 is highly expressed in the thymus of wild-type mice and is greatly suppressed in RORγ−/− mice. During thymopoiesis, NABP1 mRNA expression is restricted to CD4+CD8+ thymocytes, an expression pattern similar to that observed for RORγ2. These observations appear to suggest that NABP1 expression is regulated either directly or indirectly by RORγ2. Confocal microscopic analysis showed that the NABP1 protein localizes to the nucleus. Analysis of nuclear proteins by size-exclusion chromatography indicated that NABP1 is part of a high molecular-mass protein complex. Since the OB-fold is frequently involved in the recognition of nucleic acids, the interaction of NABP1 with various nucleic acids was examined. Our results demonstrate that NABP1 binds single-stranded nucleic acids, but not double-stranded DNA, suggesting that it functions as a single-stranded nucleic acid binding protein.
The gap junction cellular internet: connexin hemichannels enter the signalling limelight
Authors: Evans W. Howard , De Vuyst Elke , Leybaert Luc
Published: June 2006

Cxs (connexins), the protein subunits forming gap junction intercellular communication channels, are transported to the plasma membrane after oligomerizing into hexameric assemblies called connexin hemichannels (CxHcs) or connexons, which dock head-to-head with partner hexameric channels positioned on neighbouring cells. The double membrane channel or gap junction generated directly couples the cytoplasms of interacting cells and underpins the integration and co-ordination of cellular metabolism, signalling and functions, such as secretion or contraction in cell assemblies. In contrast, CxHcs prior to forming gap junctions provide a pathway for the release from cells of ATP, glutamate, NAD+ and prostaglandin E2, which act as paracrine messengers. ATP activates purinergic receptors on neighbouring cells and forms the basis of intercellular Ca2+ signal propagation, complementing that occuring more directly via gap junctions. CxHcs open in response to various types of external changes, including mechanical, shear, ionic and ischaemic stress. In addition, CxHcs are influenced by intracellular signals, such as membrane potential, phosphorylation and redox status, which translate external stresses to CxHc responses. Also, recent studies demonstrate that cytoplasmic Ca2+ changes in the physiological range act to trigger CxHc opening, indicating their involvement under normal non-pathological conditions. CxHcs not only respond to cytoplasmic Ca2+, but also determine cytoplasmic Ca2+, as they are large conductance channels, suggesting a prominent role in cellular Ca2+ homoeostasis and signalling. The functions of gap-junction channels and CxHcs have been difficult to separate, but synthetic peptides that mimic short sequences in the Cx subunit are emerging as promising tools to determine the role of CxHcs in physiology and pathology.
The life-extending gene Indy encodes an exchanger for Krebs-cycle intermediates
Authors: Knauf Felix , Mohebbi Nilufar , Teichert Carsten , Herold Diana , Rogina Blanka , Helfand Stephen , Gollasch Maik , Luft Friedrich C. , Aronson Peter S.
Published: June 2006

A longevity gene called Indy (for ‘I'm not dead yet’), with similarity to mammalian genes encoding sodium–dicarboxylate cotransporters, was identified in Drosophila melanogaster. Functional studies in Xenopus oocytes showed that INDY mediates the flux of dicarboxylates and citrate across the plasma membrane, but the specific transport mechanism mediated by INDY was not identified. To test whether INDY functions as an anion exchanger, we examined whether substrate efflux is stimulated by transportable substrates added to the external medium. Efflux of [14C]citrate from INDY-expressing oocytes was greatly accelerated by the addition of succinate to the external medium, indicating citrate–succinate exchange. The succinate-stimulated [14C]citrate efflux was sensitive to inhibition by DIDS (4,4′-di-isothiocyano-2,2′-disulphonic stilbene), as demonstrated previously for INDY-mediated succinate uptake. INDY-mediated efflux of [14C]citrate was also stimulated by external citrate and oxaloacetate, indicating citrate–citrate and citrate–oxaloacetate exchange. Similarly, efflux of [14C]succinate from INDY-expressing oocytes was stimulated by external citrate, α-oxoglutarate and fumarate, indicating succinate–citrate, succinate–α-oxoglutarate and succinate–fumarate exchange respectively. Conversely, when INDY-expressing Xenopus oocytes were loaded with succinate and citrate, [14C]succinate uptake was markedly stimulated, confirming succinate–succinate and succinate–citrate exchange. Exchange of internal anion for external citrate was markedly pHo-dependent, consistent with the concept that citrate is co-transported with a proton. Anion exchange was sodium-independent. We conclude that INDY functions as an exchanger of dicarboxylate and tricarboxylate Krebs-cycle intermediates. The effect of decreasing INDY activity, as in the long-lived Indy mutants, may be to alter energy metabolism in a manner that favours lifespan extension.
Two-dimensional optical three-pulse photon echo spectroscopy. II. Signatures of coherent electronic motion and exciton population transfer in dimer two-dimensional spectra
Authors: Pisliakov Andrei V. , Mančal Tomáš , Fleming Graham R.
Published: June 2006

Using the nonperturbative approach to the calculation of nonlinear optical spectra developed in a foregoing paper [Mančal et al., J. Chem. Phys. 124, 234504 (2006), preceding paper], calculations of two-dimensional electronic spectra of an excitonically coupled dimer model system are presented. The dissipative exciton transfer dynamics is treated within the Redfield theory and energetic disorder within the molecular ensemble is taken into account. The manner in which the two-dimensional spectra reveal electronic couplings in the aggregate system and the evolution of the spectra in time is studied in detail. Changes in the intensity and shape of the peaks in the two-dimensional relaxation spectra are related to the coherent and dissipative dynamics of the system. It is shown that coherent electronic motion, an electronic analog of a vibrational wave packet, can manifest itself in two-dimensional optical spectra of molecular aggregate systems as a periodic modulation of both the diagonal and off-diagonal peaks.
The Hofmeister series and protein-salt interactions
Authors: Shimizu Seishi , McLaren William M. , Matubayasi Nobuyuki
Published: June 2006

In order to understand the origin of the Hofmeister series, a statistical-mechanical analysis, based upon the Kirkwood-Buff (KB) theory, has been performed to extract information regarding protein hydration and water-mediated protein-salt interactions from published experimental data—preferential hydration and volumetric data for bovine serum albumin in the presence of a wide range of salts. The analysis showed a linear correlation between the preferential hydration parameter and the protein-cosolvent KB parameter. The same linear correlation holds even when nonelectrolyte cosolvents, such as polyethelene glycol, have been incorporated. These results suggest that the Hofmeister series is due to a wide variation of the water-mediated protein-cosolvent interaction (but not the change of protein hydration) and that this mechanism is a special case of a more general scenario common even to the macromolecular crowding.
Novel genes derived from noncoding DNA in
Drosophila melanogaster
are frequently X-linked and exhibit testis-biased expression
Authors: Levine Mia T. , Jones Corbin D. , Kern Andrew D. , Lindfors Heather A. , Begun David J.
Published: June 2006

Descriptions of recently evolved genes suggest several mechanisms of origin including exon shuffling, gene fission/fusion, retrotransposition, duplication-divergence, and lateral gene transfer, all of which involve recruitment of preexisting genes or genetic elements into new function. The importance of noncoding DNA in the origin of novel genes remains an open question. We used the well annotated genome of the genetic model system
Drosophila melanogaster
and genome sequences of related species to carry out a whole-genome search for new
D. melanogaster
genes that are derived from noncoding DNA. Here, we describe five such genes, four of which are X-linked. Our RT-PCR experiments show that all five putative novel genes are expressed predominantly in testes. These data support the idea that these novel genes are derived from ancestral noncoding sequence and that new, favored genes are likely to invade populations under selective pressures relating to male reproduction.
The Dam1 kinetochore complex harnesses microtubule dynamics to produce force and movement
Authors: Asbury Charles L. , Gestaut Daniel R. , Powers Andrew F. , Franck Andrew D. , Davis Trisha N.
Published: June 2006

Kinetochores remain attached to microtubule (MT) tips during mitosis even as the tips assemble and disassemble under their grip, allowing filament dynamics to produce force and move chromosomes. The specific proteins that mediate tip attachment are uncertain, and the mechanism of MT-dependent force production is unknown. Recent work suggests that the Dam1 complex, an essential component of kinetochores in yeast, may contribute directly to kinetochore–MT attachment and force production, perhaps by forming a sliding ring encircling the MT. To test these hypotheses, we developed an
in vitro
motility assay where beads coated with pure recombinant Dam1 complex were bound to the tips of individual dynamic MTs. The Dam1-coated beads remained tip-bound and underwent assembly- and disassembly-driven movement over ≈3 μm, comparable to chromosome displacements
in vivo
. Dam1-based attachments to assembling tips were robust, supporting 0.5–3 pN of tension applied with a feedback-controlled optical trap as the MTs lengthened ≈1 μm. The attachments also harnessed energy from MT disassembly to generate movement against tension. Reversing the direction of force (i.e., switching to compressive force) caused the attachments to disengage the tip and slide over the filament, but sliding was blocked by areas where the MT was anchored to a coverslip, consistent with a coupling structure encircling the filament. Our findings demonstrate how the Dam1 complex may contribute directly to MT-driven chromosome movement.
An inorganic carbon transport system responsible for acclimation specific to air levels of CO
2
in
Chlamydomonas reinhardtii
Authors: Wang Yingjun , Spalding Martin H.
Published: June 2006

Many photosynthetic microorganisms acclimate to CO
2
limited environments by induction and operation of CO
2
-concentrating mechanisms (CCMs). Despite their central role in CCM function, inorganic carbon (Ci) transport systems never have been identified in eukaryotic photosynthetic organisms. In the green alga
Chlamydomonas reinhardtii
, a mutant,
pmp1
, was described in 1983 with deficiencies in Ci transport, and a Pmp1 protein-associated Ci uptake system has been proposed to be responsible for Ci uptake in low CO
2
(air level)-acclimated cells. However, even though
pmp1
represents the only clear genetic link to Ci transport in microalgae and is one of only a very few mutants directly affecting the CCM itself, the identity of Pmp1 has remained unknown. Physiological analyses indicate that
C. reinhardtii
possesses multiple Ci transport systems responsible for acclimation to different levels of limiting CO
2
and that the Pmp1-associated transport system is required specifically for low (air level) CO
2
acclimation. In the current study, we identified and characterized a
pmp1
allelic mutant,
air dier 1
(
ad1
) that, like
pmp1
, cannot grow in low CO
2
(350 ppm) but can grow either in high CO
2
(5% CO
2
) or in very low CO
2
(<200 ppm). Molecular analyses revealed that the Ad1/Pmp1 protein is encoded by
LciB
, a gene previously identified as a CO
2
-responsive gene.
LciB
and three related genes in
C. reinhardtii
compose a unique gene family that encode four closely related, apparently soluble plastid proteins with no clearly identifiable conserved motifs.
Activation of the nonreceptor protein tyrosine kinase Ack by multiple extracellular stimuli
Authors: Galisteo Maria L. , Yang Yan , Ureña Jesus , Schlessinger Joseph
Published: June 2006

Ack/Ack1 is a nonreceptor protein tyrosine kinase that comprises a tyrosine kinase core, an SH3 domain, a Cdc42-binding region, a Ralt homology region, and a proline-rich region. Here we describe a detailed characterization of the Ack protein as well as the chromosomal localization of human Ack (chromosome 3q29) and the primary structure of murine Ack. We demonstrate that Ack is ubiquitously expressed, with highest expression seen in thymus, spleen, and brain. Activation of integrins by cell adhesion on fibronectin leads to strong tyrosine phosphorylation and activation of Ack. Upon cell stimulation with EGF or PDGF, Ack is tyrosine-phosphorylated and recruited to activated EGF or PDGF receptors, respectively. A pool of endogenous Ack molecules is constitutively tyrosine-phosphorylated, even in starved cells. Moreover, tyrosine-phosphorylated Ack forms a stable complex with the adapter protein Nck via its SH2 domain. Finally, we have characterized a membrane-targeting sterile α motif-like domain in the amino terminus of Ack. Using several Ack mutants, we show that the amino-terminal and CRIB domains are necessary for Ack autophosphorylation, whereas the SH3 domain appears to have an autoinhibitory role. These experiments suggest a functional role for Ack as an early transducer of multiple extracellular stimuli.
The origin of modern crocodyliforms: new evidence from the Cretaceous of Australia
Authors: Salisbury Steven W , Molnar Ralph E , Frey Eberhard , Willis Paul M.A
Published: June 2006

While the crocodyliform lineage extends back over 200 million years (Myr) to the Late Triassic, modern forms—members of Eusuchia—do not appear until the Cretaceous. Eusuchia includes the crown group Crocodylia, which comprises Crocodyloidea, Alligatoroidea and Gavialoidea. Fossils of non-crocodylian eusuchians are currently rare and, in most instances, fragmentary. Consequently, the transition from Neosuchia to Crocodylia has been one of the most poorly understood areas of crocodyliform evolution. Here we describe a new crocodyliform from the mid-Cretaceous (98–95 Myr ago; Albian–Cenomanian) Winton Formation of Queensland, Australia, as the most primitive member of Eusuchia. The anatomical changes associated with the emergence of this taxon indicate a pivotal shift in the feeding and locomotor behaviour of crocodyliforms—a shift that may be linked to the subsequent rapid diversification of Eusuchia 20 Myr later during the Late Cretaceous and Early Tertiary. While Laurasia (in particular North America) is the most likely ancestral area for Crocodylia, the biogeographic events associated with the origin of Eusuchia are more complex. Although the fossil evidence is limited, it now seems likely that at least part of the early history of Eusuchia transpired in Gondwana.
Metabolic imprinting: critical impact of the perinatal environment on the regulation of energy homeostasis
Authors: Levin Barry E
Published: June 2006

Epidemiological studies in humans suggest that maternal undernutrition, obesity and diabetes during gestation and lactation can all produce obesity in offspring. Animal models have allowed us to investigate the independent consequences of altering the pre- versus post-natal environments on a variety of metabolic, physiological and neuroendocrine functions as they effect the development in the offspring of obesity, diabetes, hypertension and hyperlipidemia (the ‘metabolic syndrome’). During gestation, maternal malnutrition, obesity, type 1 and type 2 diabetes and psychological, immunological and pharmacological stressors can all promote offspring obesity. Normal post-natal nutrition can reduce the adverse impact of some of these pre-natal factors but maternal high-fat diets, diabetes and increased neonatal access to food all enhance the development of obesity and the metabolic syndrome in offspring. The outcome of these perturbations of the perinatal environmental is also highly dependent upon the genetic background of the individual. Those with an obesity-prone genotype are more likely to be affected by factors such as maternal obesity and high-fat diets than are obesity-resistant individuals. Many perinatal manipulations appear to promote offspring obesity by permanently altering the development of central neural pathways, which regulate food intake, energy expenditure and storage. Given their strong neurotrophic properties, either excess or an absence of insulin and leptin during the perinatal period are likely to be effectors of these developmental changes. Because obesity is associated with an increased morbidity and mortality and because of its resistance to treatment, prevention is likely to be the best strategy for stemming the tide of the obesity epidemic. Such prevention should begin in the perinatal period with the identification and avoidance of factors which produce permanent, adverse alterations in neural pathways which control energy homeostasis.
Brain mechanisms underlying flavour and appetite
Authors: Rolls Edmund T
Published: June 2006

Complementary neurophysiological recordings in macaques and functional neuroimaging in humans show that the primary taste cortex in the rostral insula and adjoining frontal operculum provides separate and combined representations of the taste, temperature and texture (including viscosity and fat texture) of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by learning with olfactory and visual inputs. Different neurons respond to different combinations, providing a rich representation of the sensory properties of food. In the orbitofrontal cortex, feeding to satiety with one food decreases the responses of these neurons to that food, but not to other foods, showing that sensory-specific satiety is computed in the primate (including human) orbitofrontal cortex. Consistently, activation of parts of the human orbitofrontal cortex correlates with subjective ratings of the pleasantness of the taste and smell of food. Cognitive factors, such as a word label presented with an odour, influence the pleasantness of the odour and the activation produced by the odour in the orbitofrontal cortex. These findings provide a basis for understanding how what is in the mouth is represented by independent information channels in the brain; how the information from these channels is combined; and how and where the reward and subjective affective value of food is represented and is influenced by satiety signals. Activation of these representations in the orbitofrontal cortex may provide the goal for eating, and understanding them helps to provide a basis for understanding appetite and its disorders.
Role of brain dopamine in food reward and reinforcement
Authors: Wise Roy A
Published: June 2006

The ability of food to establish and maintain response habits and conditioned preferences depends largely on the function of brain dopamine systems. While dopaminergic transmission in the nucleus accumbens appears sufficient for some forms of reward, the role of dopamine in food reward does not appear to be restricted to this region. Dopamine plays an important role in both the ability to energize feeding and to reinforce food-seeking behaviour; the role in energizing feeding is secondary to the prerequisite role in reinforcement. Dopaminergic activation is triggered by the auditory and visual as well as the tactile, olfactory, and gustatory stimuli of foods. While dopamine plays a central role in the feeding and food-seeking of normal animals, some food rewarded learning can be seen in genetically engineered dopamine-deficient mice.
Gastrointestinal hormones regulating appetite
Authors: Chaudhri Owais , Small Caroline , Bloom Steve
Published: June 2006

The role of gastrointestinal hormones in the regulation of appetite is reviewed. The gastrointestinal tract is the largest endocrine organ in the body. Gut hormones function to optimize the process of digestion and absorption of nutrients by the gut. In this capacity, their local effects on gastrointestinal motility and secretion have been well characterized. By altering the rate at which nutrients are delivered to compartments of the alimentary canal, the control of food intake arguably constitutes another point at which intervention may promote efficient digestion and nutrient uptake. In recent decades, gut hormones have come to occupy a central place in the complex neuroendocrine interactions that underlie the regulation of energy balance.

Many gut peptides have been shown to influence energy intake. The most well studied in this regard are cholecystokinin (CCK), pancreatic polypeptide, peptide YY, glucagon-like peptide-1 (GLP-1), oxyntomodulin and ghrelin. With the exception of ghrelin, these hormones act to increase satiety and decrease food intake. The mechanisms by which gut hormones modify feeding are the subject of ongoing investigation.

Local effects such as the inhibition of gastric emptying might contribute to the decrease in energy intake. Activation of mechanoreceptors as a result of gastric distension may inhibit further food intake via neural reflex arcs. Circulating gut hormones have also been shown to act directly on neurons in hypothalamic and brainstem centres of appetite control. The median eminence and area postrema are characterized by a deficiency of the blood–brain barrier. Some investigators argue that this renders neighbouring structures, such as the arcuate nucleus of the hypothalamus and the nucleus of the tractus solitarius in the brainstem, susceptible to influence by circulating factors. Extensive reciprocal connections exist between these areas and the hypothalamic paraventricular nucleus and other energy-regulating centres of the central nervous system. In this way, hormonal signals from the gut may be translated into the subjective sensation of satiety. Moreover, the importance of the brain–gut axis in the control of food intake is reflected in the dual role exhibited by many gut peptides as both hormones and neurotransmitters. Peptides such as CCK and GLP-1 are expressed in neurons projecting both into and out of areas of the central nervous system critical to energy balance.

The global increase in the incidence of obesity and the associated burden of morbidity has imparted greater urgency to understanding the processes of appetite control. Appetite regulation offers an integrated model of a brain–gut axis comprising both endocrine and neurological systems. As physiological mediators of satiety, gut hormones offer an attractive therapeutic target in the treatment of obesity.
Molecular Changes Occurring during Acquisition of Abscission Competence following Auxin Depletion in Mirabilis jalapa
Authors: Meir Shimon , Hunter Donald A. , Chen Jen-Chih , Halaly Vita , Reid Michael S.
Published: June 2006

To understand how auxin regulates sensitivity of abscission zone (AZ) tissues to ethylene, we used a polymerase chain reaction-based subtractive approach to identify gene transcripts in Mirabilis jalapa AZs that changed in abundance during the time the zones became competent to abscise in response to exogenous ethylene. Transcript expression was then examined in leaf and stem AZs over the period they became ethylene competent following indole-3-acetic acid (IAA) depletion either by leaf deblading, treatment with the IAA transport inhibitor naphthylphthalamic acid, or cutting the stem above a node (decapitation). Transcripts down-regulated by deblading/decapitation included Mj-Aux/IAA1 and Mj-Aux/IAA2, encoding Aux/IAA proteins, and three other transcripts showing highest identity to a polygalacturonase inhibitor protein, a β-expansin, and a β-tubulin. Application of IAA to the cut end of petioles or stumps inhibited abscission, and prevented the decline in the levels of transcripts in both AZs. Transcripts up-regulated in the AZ following deblading/decapitation or treatment with naphthylphthalamic acid were isolated from plants pretreated with 1-methylcyclopropene before deblading to help select against ethylene-induced genes. Some of the up-regulated transcripts showed identity to proteins associated with ethylene or stress responses, while others did not show homology to known sequences. Sucrose infiltration of stem stumps enhanced abscission following ethylene treatment and also enhanced the induction of some of the up-regulated genes. Our results demonstrate a correlation between acquisition of competence to respond to ethylene in both leaf and stem AZs, and decline in abundance of auxin regulatory gene transcripts.
Plastid Movement Impaired 2, a New Gene Involved in Normal Blue-Light-Induced Chloroplast Movements in Arabidopsis
Authors: Luesse Darron R. , DeBlasio Stacy L. , Hangarter Roger P.
Published: June 2006

Chloroplasts move in a light-dependent manner that can modulate the photosynthetic potential of plant cells. Identification of genes required for light-induced chloroplast movement is beginning to define the molecular machinery that controls these movements. In this work, we describe plastid movement impaired 2 (pmi2), a mutant in Arabidopsis (Arabidopsis thaliana) that displays attenuated chloroplast movements under intermediate and high light intensities while maintaining a normal movement response under low light intensities. In wild-type plants, fluence rates below 20 μmol m−2 s−1 of blue light lead to chloroplast accumulation on the periclinal cell walls, whereas light intensities over 20 μmol m−2 s−1 caused chloroplasts to move toward the anticlinal cell walls (avoidance response). However, at light intensities below 75 μmol m−2 s−1, chloroplasts in pmi2 leaves move to the periclinal walls; 100 μmol m−2 s−1 of blue light is required for chloroplasts in pmi2 to move to the anticlinal cell walls, indicating a shift in the light threshold for the avoidance response in the mutant. The pmi2 mutation has been mapped to a gene that encodes a protein of unknown function with a large coiled-coil domain in the N terminus and a putative P loop. PMI2 shares sequence and structural similarity with PMI15, another unknown protein in Arabidopsis that, when mutated, causes a defect in chloroplast avoidance under high-light intensities.
The Arabidopsis Flavin-Dependent Monooxygenase FMO1 Is an Essential Component of Biologically Induced Systemic Acquired Resistance
Authors: Mishina Tatiana E. , Zeier Jürgen
Published: June 2006

Upon localized attack by necrotizing pathogens, plants gradually develop increased resistance against subsequent infections at the whole-plant level, a phenomenon known as systemic acquired resistance (SAR). To identify genes involved in the establishment of SAR, we pursued a strategy that combined gene expression information from microarray data with pathological characterization of selected Arabidopsis (Arabidopsis thaliana) T-DNA insertion lines. A gene that is up-regulated in Arabidopsis leaves inoculated with avirulent or virulent strains of the bacterial pathogen Pseudomonas syringae pv maculicola (Psm) showed homology to flavin-dependent monooxygenases (FMO) and was designated as FMO1. An Arabidopsis knockout line of FMO1 proved to be fully impaired in the establishment of SAR triggered by avirulent (Psm avrRpm1) or virulent (Psm) bacteria. Loss of SAR in the fmo1 mutants was accompanied by the inability to initiate systemic accumulation of salicylic acid (SA) and systemic expression of diverse defense-related genes. In contrast, responses at the site of pathogen attack, including increases in the levels of the defense signals SA and jasmonic acid, camalexin accumulation, and expression of various defense genes, were induced in a similar manner in both fmo1 mutant and wild-type plants. Consistently, the fmo1 mutation did not significantly affect local disease resistance toward virulent or avirulent bacteria in naive plants. Induction of FMO1 expression at the site of pathogen inoculation is independent of SA signaling, but attenuated in the Arabidopsis eds1 and pad4 defense mutants. Importantly, FMO1 expression is also systemically induced upon localized P. syringae infection. This systemic up-regulation is missing in the SAR-defective SA pathway mutants sid2 and npr1, as well as in the defense mutant ndr1, indicating a close correlation between systemic FMO1 expression and SAR establishment. Our findings suggest that the presence of the FMO1 gene product in systemic tissue is critical for the development of SAR, possibly by synthesis of a metabolite required for the transduction or amplification of a signal during the early phases of SAR establishment in systemic leaves.
Beyond the Technocrat? The Professional Expert in Development Practice
Authors: Wilson Gordon
Published: June 2006

This article traces the use of the term ‘technocratic’ to describe development practice, and the concomitant use of ‘technocrat’ to describe professional experts who engage in development work. It locates the use of these terms as pejorative labels within understandings of professional experts as part of an apparatus of governmentality that depoliticizes development intervention. It argues, however, that such understandings miss the crucial point of engagement in development practice between these agents and other actors which opens ‘learning spaces’ that have the potential for a range of outcomes.
Contingency knowledge is necessary for learned motivated behaviour in humans: relevance for addictive behaviour
Authors: Hogarth Lee , Dickinson Anthony , Hutton Sam B. , Bamborough Helen , Duka Theodora
Published: June 2006

Aims  Many forms of human conditioned behaviour depend upon explicit knowledge of the predictive contingency between stimuli, responses and the reinforcer. However, it remains uncertain whether the conditioning of three key behaviours in drug addiction—selective attention, instrumental drug‐seeking behaviour and emotional state—are dependent upon contingency knowledge. To test this possibility, we employed an avoidance procedure to generate rapidly these three forms of conditioned behaviour without incurring the methodological problems of drug conditioning.

Design  In two experiments, participants (16 students) were trained on a schedule in which one stimulus (S +) predicted the occurrence of a startling noise, which could be cancelled by performing an instrumental avoidance response.

Measurements  The allocation of attention to the S + and the rate and probability of the avoidance response in the presence of S + were measured. Following training, participants were tested for their knowledge of the stimulus–noise contingencies arranged in the study and rated the emotional qualities of the stimuli. 

Findings  Both experiments showed that S + gained control of selective attention, instrumental avoidance behaviour and subjective anxiety, but only in participants who reported explicit knowledge of the Pavlovian contingency between the S + and the startling noise.

Conclusions  The implication of the present findings is that the control of selective attention, instrumental drug‐seeking behaviour and emotional state by drug‐paired stimuli is mediated by cognitive knowledge of the predictive contingency between the stimulus and the drug.