bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct measurement of atmospheric dry deposition to natural surfaces in a semiarid region of north central India
Authors: Kumar Ranjit , Rani Abha , Kumari K. Maharaj , Srivastava S. S.
Published: October 2003

Dry deposition flux of major ions (Na+, K+, Ca2+, Mg2+, NH4+, F−, Cl−, NO3− and SO42−) to natural surfaces e.g., leaf of Ashok (Polyalthia longifolia) and Cassia (Cassia siamea), were determined at Dayalbagh, a suburban site of semiarid region. Dry deposition flux was highest for Ca2+ on both Ashok and Cassia while lowest for Na+ on Ashok leaf and F− on Cassia leaf. Overall average dry deposition fluxes varied from 0.27 mg m−2 d−1 to 3.98 mg m−2 d−1. The deposition was comparatively higher to Cassia leaf than Ashok. The high deposition flux to Cassia leaf may be due to surface roughness as shown by scanning electron micrographs. The sum of major cations (Na+, K+, Ca2+, Mg2+) and NH4+ was higher than sum of major anions (F−, Cl−, NO3− and SO42−). It indicates that dry deposition at present site is alkaline in nature and difference in the sum of major cations and major anions might be due to unmeasured carbonate and bicarbonate ions as well as organic anions (formate and acetate). Deposition flux of SO42− and NO3− is relatively lower than Ca2+ and Mg2+. Seasonally dry deposition fluxes were higher in monsoon or summer for cationic species while for anionic species fluxes were higher in winter or monsoon. Average dry deposition velocity of major ions on Ashok and Cassia leaf varied from 0.41 to 2.36 cm s−1, while seasonally values varied from 0.32 to 4.04 cm s−1. The variation in deposition velocity may be due to meteorological conditions and surface characteristics.
Soil emissions of nitrous oxide in fire‐prone African savannas
Authors: Andersson Michael , Kjøller Annelise , Struwe Sten
Published: October 2003

Only few estimates of soil emissions of nitrous oxide (N2O) are available from African savanna ecosystems, which account for two thirds of the savannas worldwide. Field measurements of soil emissions of N2O were conducted in seasonally dry savannas in Ethiopia and Ghana in order to study temporal and spatial variation in emission rates and to examine the effects of fire on the N2O flux. Soil emissions of N2O were measured by an enclosure technique. Soil emission rates were lowest in the dry season averaging 0.5 μg N2O‐N m−2 h−1, and the mean flux increased from 1.7 in the beginning to 3.5 in the middle and 5.5 μg N2O‐N m−2 h−1 by the end of the rainy season. Minor spatial variation in emissions according to differences in drainage capacity, vegetation type, and fire severity was associated with high spatial variation at field scale. The variation in water‐filled pore space in soil explained only 44% of the variation in the N2O flux. In an experiment separating the effect of fire and ash, the N2O flux was not different across treatments 1 week after the low‐intensity burning. In another experiment, the flux at early and late burn sites did not differ and was not different from an unburned site. The study clearly demonstrates that more measurements are needed to fully understand the seasonal and spatial variability of soil emissions of N2O in savanna ecosystems.
Distortion of radar pulses by the Martian ionosphere
Authors: Armand N. A. , Smirnov V. M. , Hagfors T.
Published: October 2003

In spacecraft borne radar investigations of planets such as Venus and Mars the waves must penetrate an ionospheric layer which causes absorption and dispersive phase delay if the waves reach the surface at all. If the purpose of the radar system is to explore the planetary subsurface, the radar frequency should be as low as possible for maximum skin depth, yet high enough to reach the surface. In order to resolve subsurface discontinuities the radar must use short pulses and because of the low frequency the dispersive pulse distortion in the ionosphere becomes a problem. In this paper we discuss ways to avoid the pulse distortion and to recover the original pulse shape. As the ionosphere is unknown and changes with time and position, the necessary ionospheric data must be derived from the radar observations themselves. The scheme described is designed to do this. We also discuss the effect of additive noise on the accuracy of this observation scheme. The investigation was motivated by the MARSIS experiment on Mars Express and by a similar experiment on the Russian spacecraft Mars96. The implementation of the scheme in MARSIS will depend on the computational resources which can be allocated to the task. In future space missions with the proper planning it is thought that the scheme presented will be even more attractive.
Sample area of two‐ and three‐rod time domain reflectometry probes
Authors: Nissen Henrik H. , Ferré Ty P. A. , Moldrup Per
Published: October 2003

Recent advances in the application of numerical analyses to the spatial sensitivity of conventional two‐ and three‐rod time domain reflectometry (TDR) probes allow for investigation of the response of TDR in spatially heterogeneous media. In this study, we present numerical analyses and laboratory measurements of the effects of steep gradients in relative dielectric permittivity (K) on the spatial sensitivity of TDR probes. Two‐ and three‐rod probes were placed horizontally through the walls of an experimental box. These horizontal probes were placed either within the same horizontal plane (horizontal probes) or within the same vertical plane (vertical probes). Then, an air/liquid interface was raised upward from below and past the probe. Three liquids (sunflower oil, ethanol, and water) with varying K values were used. The same system was analyzed using a numerical model of the spatial sensitivity of TDR probes to lateral variations in K. There was good agreement between measured and modeled K, demonstrating that the spatial sensitivity of TDR probes is biased toward the area of lowest K. The sample areas of all of the probe designs depend strongly on the relative dielectric permittivity distribution in the plane transverse to the direction of wave propagation. Two‐rod instead of three‐rod probes should be used if sharp changes in K are expected in the direction transverse to the plane containing the probe rods, owing to separation of the traveling electromagnetic (EM) waves in the three‐rod case. Generally, a horizontal probe orientation is more appropriate for monitoring across sharp vertical boundaries such as wetting fronts.
Diurnal variation of lightning activity over the Indian region
Authors: Kandalgaonkar S. S. , Tinmaker M. I. R. , Kulkarni J. R. , Nath Asha
Published: October 2003

Satellite (LIS) based lightning flash grid (0.5° × 0.5°) data for the Indian land mass region covering from 8°–33°N and 73°–86°E for a period of 4 years (1998–2001) were used to study the diurnal variation with one hour time resolution. The analysis revealed that there exists a strong diurnal cycle in the lightning activity with a prominent peak around 1000 UTC. An examination of seasonal diurnal variation suggests that the lightning activity was found highest in premonsoon and lowest in the postmonsoon season.
Stress change near the Kunlun fault before and after the Ms 8.1 Kunlun earthquake
Authors: Liao Chunting , Zhang Chunshan , Wu Manlu , Ma Yinsheng , Ou Mingyi
Published: October 2003

On 14 November, 2001, a great earthquake of Ms 8.1 occurred on the Kunlun fault in the Kusai Lake segment of the Kunlun Mountain, Qinghai Province in northwest China. The stresses measured at the sites near the Kunlun fault before and after the earthquake show a great drop after the earthquake. The values of the horizontal maximum principal stress at two sites are 12.9 Mpa and 6.8 Mpa before the earthquake. Measurement of the horizontal maximum principal stress at the same sites after the earthquake, showed values of 3.5 Mpa and 2.2 Mpa respectively. This is only about one‐third of that before the earthquake. Apparently stress that accumulated near the fault before the earthquake was released along with the rupturing of the surface. The direction of the maximum horizontal principal stress also varies before and after the earthquake. The direction is found to deviate from that of the regional structure stress field after the earthquake. Such stress changes offer a basis for predicting large earthquakes in the region.
Model‐based prediction of porosity and reservoir quality from P‐ and S‐wave data
Authors: Spikes Kyle T. , Dvorkin Jack P.
Published: October 2003

We present a deterministic methodology for mapping the lithology, pore fluid, and porosity from seismic data. The input is the P‐ and S‐wave data volumes that may come, e.g., from acoustic and elastic inversion or cross‐well measurements. The output is the pore fluid type (hydrocarbon versus water), total porosity, and clay content. The key element of this methodology is a site‐specific rock physics model that provides the needed transforms from the elastic rock properties to the reservoir properties. This model is established by comparing model‐based predictions, such as impedance versus porosity, to the relations present in well log data. Once selected, the model is used to identify the presence of hydrocarbons from a combination of the P‐wave impedance and Poisson's ratio. Then the P‐wave impedance is used to map porosity and clay content assuming that a deterministic relation exists between the latter two properties. All deterministic equations are calibrated at a well and then are applied to upscaled well log data to confirm their validity at the seismic scale. This methodology is applied to log data from a fluvial environment. The results indicate that the relative error in porosity determination is 14%, which is acceptable for reservoir characterization purposes.
In situ and ground‐based intercalibration measurements of plasma density at L = 2.5
Authors: Clilverd M. A. , Menk F. W. , Milinevski G. , Sandel B. R. , Goldstein J. , Reinisch B. W. , Wilford C. R. , Rose M. C. , Thomson N. R. , Yearby K. H. , Bailey G. J. , Mann I. R. , Carpenter D. L.
Published: October 2003

Two independent ground‐based experiments and two satellite‐borne experiments are used to interpret the changes in plasmaspheric composition at the same point in space during moderate geomagnetic activity on 22 January and 14 February 2001. Mass density at L = 2.5 was determined from an array of magnetometers on the Antarctic Peninsula, while the electron number density along the same flux tube was determined from analysis of the group delay of man‐made VLF transmissions from north‐east America. The IMAGE satellite RPI experiment provided in situ measurements of the electron number density in passing the equatorial region of the same field line, while the EUV Imager experiment was able to resolve the He+ abundance by looking back toward the same place a few hours later. On 22 January 2001 all measurements were consistent with a moderately disturbed plasmasphere. On 14 February 2001 there appeared to be a significant response of the plasmasphere to the moderate (Kp = 5) activity levels. Both the electron number density and the mass density determined from the ground‐based experiments were markedly higher than on 22 January 2001. Also, the IMAGE RPI gave a markedly lower electron number density than did the ground‐based data; this is explained by differences in the longitude at which the measurements were made and the presence of localized plasmaspheric structures. At Antarctic Peninsula longitudes a He+ column abundance value of 6 × 1010 cm−2 is found to be equivalent to plasmaspheric electron density levels of 3000 cm−3 at L = 2.5. For these conditions the He+ mass abundance was about 12–16% compared with H+. Both decreases and increases in the He+ column abundance measured by the EUV Imager appear to be linearly correlated to changes in the percentage occurrence of He+ as determined from a combination of ground‐based VLF and ULF observations.
Predictability in the Epidemic‐Type Aftershock Sequence model of interacting triggered seismicity
Authors: Helmstetter Agnès , Sornette Didier
Published: October 2003

As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of seismicity on the basis of interacting events which may trigger a cascade of earthquakes, known as the Epidemic‐Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg‐Richter law, and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large‐magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitudeM≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered seismicity models. Quantitatively, the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes.
Are aftershocks of large Californian earthquakes diffusing?
Authors: Helmstetter Agnès , Ouillon Guy , Sornette Didier
Published: October 2003

We analyze 21 aftershock sequences of California to test for evidence of space‐time diffusion. Aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening. Here we test an alternative mechanism to explain aftershock diffusion, based on multiple cascades of triggering. In order to characterize aftershock diffusion, we develop two methods, one based on a suitable time and space windowing, and the other using a wavelet transform adapted to the removal of background seismicity. Both methods confirm that diffusion of seismic activity is very weak, much weaker than reported in previous studies. A possible mechanism explaining the weakness of observed diffusion is the effect of geometry, including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes.
Analysis of columnar joint patterns from three‐dimensional stress modeling
Authors: Saliba R. , Jagla E. A.
Published: October 2003

We consider a crack pattern penetrating into a solid material, forming a columnar structure as observed in basalts, tuffs, and also in starches. Using the finite element method, we calculate the strain field ahead of the crack front, in the presence of a uniform lateral expansion simulating the strain induced by cooling (in rocks) or drying (in starches). We observe the tendency of the cracks to adapt dynamically in order to reach a stable polygonal pattern. The polygons have different numbers of sides and different areas, with slightly curved borders. We find that the tendency of the cracks to shift laterally upon penetration depends on the geometry of the neighbor cracks, but it is independent of the global scale of the pattern. We suggest that the mean width of the columns is determined by two different effects: the typical size of the (irregular) crack pattern at the free surface, from which the polygonal pattern develops upon penetration, and the further possibility of terminate some cracks during advance, which leads to a thickening of the columns as a function of depth.
Analysis of year‐to‐year ozone variation over the subtropical western Pacific region using EP_TOMS data and CCSR/NIES nudging CTM
Authors: Zhou L. B. , Akiyoshi H. , Kawahira K.
Published: October 2003

The year‐to‐year ozone variation over the subtropical western Pacific region is studied, especially the ozone lows in the 1996/1997, 1998/1999, and 2001/2002 winters, using the Earth Probe Total Ozone Mapping Spectrometer (EP_TOMS) ozone data from August 1996 to July 2002. Regression analyses show that dynamical signals, such as the quasi‐biennial oscillation, play an important role in determining total ozone variation. A nudging chemical transport model (CTM) is used to simulate the year‐to‐year ozone variation and explain the mechanism for producing ozone lows in a three‐dimensional distribution of ozone. The CTM was developed using the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) atmospheric general circulation model and introducing a nudging process for temperature and horizontal wind velocity. The year‐to‐year ozone variation, especially the winter ozone low, is well simulated by the model excluding heterogeneous reaction processes between 45°S and 45°N latitude. Results show that the year‐to‐year ozone variation is mainly controlled by dynamical transport processes.
Asian aerosols in North America: Extracting the chemical composition and mass concentration of the Asian continental aerosol plume from long‐term aerosol records in the western United States
Authors: VanCuren Richard A.
Published: October 2003

Empirical assessment of the frequency and intensity of dust transport from Asia to North America has found that the dust regularly impacts elevated sites in the western United States, revealing a pattern of consistent, frequent transport above the marine boundary layer. Using the dust as a marker for Asian transport, a subset of Asian‐influenced samples was identified within a decade of routine aerosol samples from two sites in the western cordillera of North America: Crater Lake, Oregon, and Mount Lassen, California. This subset was used to guide a statistical analysis to isolate Asian aerosol against the “background” of local contaminants. The analysis was then generalized to all samples during the transport season (March–October) for 1989–1999. A mixture of dust and combustion products dominates the Asian aerosol with typical concentration around 5 μg/m3 and mass median diameter between 2 and 3 μm. Major fine particle (<2.5 μm diameter) constituent fractions are ∼30% mineral, 28% organic compounds, 4% elemental carbon, 10% sulfate, <5% nitrate, and <1% sea salt. A second, possibly Asian, component of aged biomass smoke and sea salt is also present, with typical concentration (when present) around 1.5 μg/m3. Averaged over the transport season the dusty Asian aerosol and the smoky aerosol comprise 60 and 6%, respectively, of total particle mass (<10 μm diameter) and 72 and 13% of fine particle mass at these sites. These data indicate that the Asian continental plume is a significant contributor to aerosol loading at remote high‐altitude sites across western North America. This implies a significant influence for Asian emissions on free troposphere aerosols over North America and suggests that they need to be explicitly accounted for in aerosol analyses ranging from climate studies to aerosol regulatory programs.
On the verification of the quality of SABER temperature, geopotential height, and wind fields by comparison with Met Office assimilated analyses
Authors: Remsberg E. , Lingenfelser G. , Harvey V. L. , Grose W. , Russell J. , Mlynczak M. , Gordley L. , Marshall B. T.
Published: October 2003

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite has delivered over 1 year of radiance profile data from which middle atmosphere temperature profiles have been retrieved. Version 1.01 temperatures are precise and sufficiently accurate, such that one can obtain estimates of their synoptic distributions on pressure surfaces. A sequential estimation algorithm was used to generate daily, zonal Fourier coefficients of temperature (through zonal wave number 6), and maps on constant pressure surfaces were generated using those coefficients. Maps of temperature, geopotential height, and geostrophic winds are compared with products from the Met Office analyses. Stratospheric differences are within about 2 K for temperature and 160 m for geopotential height. The respective wind fields indicate flow patterns that are similar. Examples of the fields are shown for a period in February 2002 during a sudden stratospheric warming event that occurred in the Northern Hemisphere. A cooling of the middle mesosphere accompanies the warming. It is anticipated that large‐scale, middle atmospheric dynamics and transport studies can be undertaken and that data assimilation products can be extended to near the mesopause using the SABER profiles.
Transient pumping well flow in weakly heterogeneous formations
Authors: Indelman Peter
Published: October 2003

The solution of pumping well flow serves for identifying aquifer's properties. Most results available in the literature assume homogeneous aquifers or at most stratified structures. This study investigates the unsteady well flow in heterogeneous aquifers by modeling the hydraulic conductivity as a three‐dimensional stationary random function of axisymmetric anisotropy and Gaussian correlations. The main result of the investigation is the mean drawdown in a transient flow toward a fully penetrating well pumping at a constant rate. The solution is obtained in terms of one quadrature over time and is easily calculated. Closed form approximations of the mean head are developed for moderate and large times. The mean drawdowns derived in the study generalize the Theis and Copper and Jacob distributions for aquifers of constant transmissivity. It is shown that the transmissivity, which is identified by using the Cooper and Jacob asymptotic, is precisely the effective conductivity for uniform horizontal flow Khefu. This is compared with the finding that the equivalent conductivity for the steady state flow approaches Khefu with distance from the well [Indelman et al., 1996].
Effect of spreading coefficient on three‐phase relative permeability of nonaqueous phase liquids
Authors: Keller Arturo A. , Chen Mingjie
Published: October 2003

Three‐phase flow conditions are encountered regularly, for example, during migration of released NAPL through the vadose zone, certain stages of soil vapor extraction, bioslurping, or generation of gases by microbes. To model three‐phase flow, a common approach is to construct three‐phase relative permeabilities based on a combination of two‐phase relative permeabilities. Although this circumvents a lack of experimental data, it can lead to serious underprediction or overprediction of residual NAPL saturation. This can mislead decision makers that need to predict whether a particular spill will reach the water table or predict the speed of a NAPL front or conduct an assessment of the performance of remediation actions. Experimental data to estimate three‐phase relative permeabilities is sparse. A study by DiCarlo et al. [2000a] generated significant experimental information. Their analysis focused on the high NAPL saturation region, given their emphasis on oil reservoir engineering. For environmental applications the low saturation region is of more interest. Using this data set, we derived a set of empirical relations that relate NAPL three‐phase relative permeability krn to NAPL saturation Sn and spreading coefficient Cs for Sn less than about 0.1, such that krn = where A1 = 0.012 exp (−1.3Cs) and A2 = 2.1 − 0.60Cs + 0.036Cs2. At higher Sn, krn ≈ Sn4, independent of Cs. We present a pore‐scale conceptual model that provides a phenomenological basis for the use of Cs as a predictor of krn at low Sn. We then present a number of simulated case studies that highlight the effect of these three‐phase relative permeabilities on risk assessment or remediation design.
N‐terminal modifications leading to peptide ORL1 partial agonists and antagonists
Authors: Judd A. K. , Kaushanskaya A. , Tuttle D. J. , Sanchez A. , Khroyan T. , Polgar W. , Toll L.
Published: October 2003

Abstract:  Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide that is the endogenous ligand for the G protein‐coupled receptor (opioid receptor like 1, ORL1), a member of the opioid receptor family. Although it is clear that this receptor system is involved in a variety of physiological functions, including analgesia, the precise actions of N/OFQ remain largely uncharacterized. One reason for this has been limited high affinity ligands to ORL1, and particularly the lack of availability of useful specific antagonists. Herein we describe the pharmacological activity of a series of N‐terminally modified hexapeptides with high affinity for ORL1. These compounds were tested for binding affinity using [3H]N/OFQ binding to human ORL1 in CHO cells, and functional activity by measuring stimulation of [35S]GTPγS binding in CHO cell membranes. The N‐terminal modifications have produced compounds that maintained very high receptor affinity, but led to significant changes in intrinsic activity. One compound, pentanoyl‐RYYRWR‐NH2, with barely measurable agonist activity was tested in vivo. It was found to possess modest analgesic activity, but it was unable to block the morphine modulatory activity of N/OFQ.
Using protein‐based motifs to stabilize peptides
Authors: Walker J. R. , Altman R. K. , Warren J. W. , Altman E.
Published: October 2003

Abstract: While the use of synthetically derived novel inhibitor peptides as a source of new therapeutics for medicine remains incredibly promising, there is a major problem with implementing this technology, as many synthetic peptides have proven to be unstable and are degraded by peptidases in the host cell. In this study, we have investigated methods by which peptides can be stabilized using protein‐based motifs in order to prevent the action of peptidases. Using anin vivoapproach our laboratory developed to screen for synthetic peptides which can inhibit the growth ofEscherichia coli, we found that protecting the amino or carboxyl terminus of the peptides via fusion to the very stable Rop protein, or the incorporation of two proline residues, increased the frequency at which potent inhibitor peptides could be isolated. Using anin vitrodegradation assay in which extracts from several different cell types were tested, we demonstrated that peptides stabilized with multiple proline residues were more resistant to degradation than peptides stabilized by amidation or acetylation, two approaches that are routinely utilized to improve the stability of peptide drugs.
Vein cavitation and stomatal behaviour of sunflower (Helianthus annuus) leaves under water limitation
Authors: Trifilò Patrizia , Nardini Andrea , Lo Gullo Maria A. , Salleo Sebastiano
Published: October 2003

The impact of leaf vein cavitation and embolism on stomatal response and leaf hydraulic conductance was studied in potted plants of sunflower subjected to water limitation. Plant dehydration was achieved either by cutting well‐watered plants near their base and leaving them dehydrating in air or by depriving intact plants of irrigation. The vein cavitation threshold (ΨCAV) was estimated in terms of ultrasound acoustic emissions (UAE) from the leaf blade versus leaf water potential (ΨL). This was found to be the same (ΨCAV ≈ −0.6 MPa) for leaves of both cut and intact plants where stomata began to close in coincidence with starting vein cavitation. Vein embolism was detected by infiltrating leaves at different ΨL with 0.7 mM fluorescein and measuring the percentage fluorescent area as percentage of total leaf surface area. A distinct loss of vein functionality (up to 50%) was found to occur in leaves at progressively decreasing ΨL, starting when leaves reached ΨCAV. A linear positive relationship with high statistical significance was found to exist between gL and percentage leaf fluorescent area, thus indicating that stomata were sensitive to vein embolism. The hydraulic conductance (KL) of the leaf was affected by leaf dehydration less than expected (KL decreased by about 20% between near full turgor and ΨL = −1.3 MPa). When the extravascular leaf compartment was excluded either by killing cells by immersing leaves in 70% ethanol or by cutting the main leaf venous system through to allow flow to bypass it, KL turned out to increase 5.5 times, thus suggesting that the high dominance of the hydraulic resistance of the extravascular leaf compartment over the total leaf resistance might buffer or mask possibly large local changes in KL inducing stomatal closure.
Molecular dissection of photosystem I in higher plants: topology, structure and function
Authors: Jensen Poul Erik , Haldrup Anna , Rosgaard Lisa , Scheller Henrik Vibe
Published: October 2003

Photosystem I catalyses the light driven electron transfer from plastocyanin/cytochrome c6 on the lumenal side of the thylakoid membrane to ferredoxin/flavodoxin at the stromal side. Photosystem I of higher plants consists of 18 different protein subunits. Fourteen of these make up the chlorophyll a‐containing core, which also contains the cofactors involved in the electron transfer reactions, and four make up the peripheral chlorophyll a/b‐containing antenna. Arabidopsis plants devoid of the nuclear‐encoded photosystem I subunits have been obtained either by different suppression techniques or by insertional knock‐out of the genes. This has allowed a detailed analysis of the role and function of the individual subunits. This review is focused on recent developments in the role of the individual subunit in the structure and function of photosystem I of higher plants.
The 70‐kDa protein bound to hsp90 in wheat germ lysate is a plant homologue of animal Hop
Authors: Krishna Priti , Kanelakis Kimon C.
Published: October 2003

The hsp90‐based chaperone machinery is implicated in numerous cellular processes including signal transduction, genomic silencing, and protein degradation. Hop is a component of the animal hsp90 multichaperone complex, whose function is to link the two chaperones, hsp90 and hsp70. Currently there exists little information on a plant Hop homologue. Herein it is reported that a 70‐kDa protein in wheat germ lysate is associated with hsp90 and hsp70 and that this protein is a wheat homologue of Hop. It is also shown that, in addition to being detected in complexes, the wheat Hop as well as the previously identified immunophilin FKBP73, can bind directly to purified plant hsp90. In the steroid receptor folding assay, the wheat Hop was not detected in receptor complexes, but the wheat immunophilin FKBP73 could be detected when mammalian p23 was added to the plant lysate. The present results identify two hsp90‐binding proteins and provide a useful framework on which to further investigate their functions.
Transcripts of sunflower antioxidant scavengers of the SOD and GPX families accumulate differentially in response to downy mildew infection, phytohormones, reactive oxygen species, nitric oxide, protein kinase and phosphatase inhibitors
Authors: Herbette Stéphane , Lenne Catherine , De Labrouhe Denis Tourvieille , Drevet Joël R. , Roeckel‐Drevet Patricia
Published: October 2003

Messenger RNA accumulation of two previously characterized sunflower glutathione peroxidases (GPXha‐1 and GPXha‐2) was monitored in response to pathogen attack. The accumulation of GPXha‐1 and GPXha‐2 mRNAs was also followed after stimulation with various signalling molecules including stress related phytohormones, reactive oxygen species, nitric oxide and protein phosphatase or kinase inhibitors. To have a more complete view of the response of the plant enzymatic antioxidant system when challenged by these various stimuli, the accumulation of superoxide dismutase (SOD) mRNAs was monitored too. To do so, partial sunflower SOD cDNAs (SODha‐1 and SODha‐2) were cloned in the course of the study. We show here that sunflower GPX mRNA accumulated differently in leaves of plants infected with either a virulent or an avirulent race of pathogen (Plasmopara halstedii). We also observed that any of the stimuli used translated in a stronger accumulation of both GPX mRNAs. These data suggest that GPX enzymes are involved in the hypersensitive and stress responses in sunflower. When compared to each other, GPX and SOD messenger steady state levels behaved differently following biotic stress or treatments with stress signalling factors. This suggests that the antioxidant enzymes GPX and SOD are likely to play different functions in stress responses.
Effect of herbicide diclofop‐methyl on proton extrusion from Lolium multiflorum seedlings differing in resistance and in fungal endophyte (Neotyphodium sp.) infection
Authors: Vila‐Aiub Martin M. , Ghersa Claudio M. , Carceller Marta
Published: October 2003

Lolium multiflorum (Italian ryegrass), an annual weed invading wheat and barley cropping systems, has evolved resistance to diclofop‐methyl (DM) herbicide. Earlier studies on the mode of action of DM in susceptible L. multiflorum and L. rigidum populations have shown that herbicide promotes oxidative stress leading to senescence, a process reversible through the action of auxins. The disruption of cell membrane potential (Em) appears to be correlated with DM phytotoxicity in susceptible populations, suggesting that the continuous H+ extrusion from plasmalemma to extracellular space is inhibited. L. multiflorum usually establishes a symbiotic relationship with fungal endophytes of the Neotyphodium genus. This fungus confers to host plants higher survival at sublethal dosages of DM, probably due to the production of auxinic compounds. Our goal was to characterize DM‐resistant and DM‐susceptible L. multiflorum populations infected (E+) and non‐infected (E−) with endophytes, by studying the capacity of H+ bumping of plasmalemma of intact roots under DM selection. We correlated the effects of DM on H+ disruption with plant survival. DM inhibited acidification markedly more in susceptible than in resistant populations. Continued extrusion of H+ by DM‐resistant cell membranes was positively related to plant survival and growth. There was no detectable difference in the capacity of bumping H+ between DM‐susceptible E+ and E− seedlings, even though survival was higher in E+ plants. The basis for the differential response in H+ extrusion between resistant and susceptible populations of L. multiflorum is discussed.
The effect of potassium deficiency on growth and N2‐fixation in Trifolium repens
Authors: Høgh‐Jensen Henning
Published: October 2003

The effects of potassium (K) deficiency on growth, N2‐fixation and photosynthesis in white clover (Trifolium repens L.) were investigated using natural occurring gas fluxes on the nodules in real time of plants under three contrasting relative addition rates of K causing mild K deficiency, or following abrupt withdrawal of the K supply causing strong K deficiency of less than 0.65% in dry matter. A steady‐state below‐optimum K supply rate led to an increase in CO2‐fixation per unit leaf surface area as well as per plant leaf surface. However, nitrogenase activity per unit root weight and per unit nodule weight was maintained, as was the efficiency with which electrons were allocated to the reduction of N2 in the nodules. Abrupt K removals stimulated nodule growth strongly without delay, but as K concentrations decreased in the plant tissue a significant decline in nitrogenase activity per unit root weight as well as per unit nodule mass occurred. Further, the rate of photosynthesis per unit leaf area was unaffected, while the CO2 acquisition for the plant as a whole increased due to an expansion of total leaf area whereas the leaf area per unit leaf weight was unaffected. The ratio between CO2‐fixation and N2‐fixation increased, although not statistically significant, under short‐term K deprivation as well as under long‐term low K supply indicating a downregulation of nodule activity following morphological and growth adjustments. This downregulation took place despite a partly substitution of the K by Na. It is concluded that N2‐fixation does not limit the growth of K‐deprived clover plants. K deprivation induces changes in the relative growth of roots, nodules, and shoots rather than changes in N and/or carbon uptake rates per unit mass or area of these organs.
Copper treatment activates mitogen‐activated protein kinase signalling in rice
Authors: Yeh Chuan‐Ming , Hung Wan‐Chi , Huang Hao‐Jen
Published: October 2003

It is well known that mitogen‐activated protein kinase (MAPK) pathways are modules involved in the transduction of extracellular signals to intracellular targets in all eukaryotes. In plants, it has been shown that MAPKs play a role in the signalling of biotic and abiotic stresses. To characterize signalling pathways involved in heavy metal‐induced stress responses, we examine whether plant MAPKs are also involved in this process. The analyses of mRNA levels of OsMAPK genes have shown that only OsMAPK2 mRNA transcripts increased within 12 h upon CuCl2 treatment in suspension cells and roots. An in‐gel kinase assay revealed that three protein kinases, approximate 42, 50, and 64‐kDa, were activated by CuCl2 treatments. The approximate 42‐kDa protein kinase displayed MAPK properties. Antioxidant, GSH, prevented copper‐induced kinase activity. Furthermore, we found that rice roots underwent a rapid cell death upon this copper treatment. The copper‐induced cell death of rice roots was partially blocked by MAPK kinase inhibitor, PD98059. These results suggest that the MAPK cascades may function in the plant heavy metal induced‐signalling pathway.
The family of Deg/HtrA proteases: from Escherichia coli to Arabidopsis
Authors: Kieselbach Thomas , Funk Christiane
Published: October 2003

In the genomic era, an increasing number of protease genes have been identified in various organisms. During the last few years, many of these proteases have been characterized using biochemical as well as molecular biological techniques. However, neither the precise location nor the physiological substrates of these enzymes has been identified in many cases, including the Deg/HtrA proteases, a family of serine‐type ATP‐independent proteases. This family has become especially interesting for many researchers following the determination of the crystal structures of an Escherichia coli and a human Deg/HtrA protease. A breakthrough in photosynthesis research has revealed that a Deg/HtrA protease of Arabidopsis thaliana is involved in the degradation of the D1 protein of photosystem II following photoinhibition. In this review, the available data on Deg/HtrAs of different organisms are compared with those from the photoautotroph cyanobacterium Synechocystis sp. PCC 6803 and the plant Arabidopsis thaliana.
Mechanistic aspects of the xanthophyll dynamics in higher plant thylakoids
Authors: Morosinotto Tomas , Caffarri Stefano , Dall'Osto Luca , Bassi Roberto
Published: October 2003

Plant thylakoids have a highly conserved xanthophyll composition, consisting of β‐carotene, lutein, neoxanthin and a pool of violaxanthin that can be converted to antheraxanthin and zeaxanthin in excess light conditions. Recent work has shown that xanthophylls undergo dynamic changes, not only in their composition but also in their distribution among Lhc proteins. Xanthophylls are released from specific binding site in the major trimeric LHCII complex of photosystem II and are subsequently bound to different sites into monomeric Lhcb proteins and dimeric Lhca proteins. In this work we review available evidence from in vivo and in vitro studies on the structural determinants that control xanthophyll exchange in Lhc proteins. We conclude that the xanthophyll exchange rate is determined by the structure of individual Lhc gene products and it is specifically controlled by the lumenal pH independently from the activation state of the violaxanthin de‐epoxidase enzyme. The xanthophyll exchange induces important modifications in the organization of the antenna system of Photosystem II and, possibly of Photosystem I. Major changes consist into a modulation of the light harvesting efficiency and an increase of the protection from lipid peroxidation. The xanthophyll cycle thus appears to be a signal transduction system for co‐ordinated regulation of the photoprotection mechanisms under persistent stress from excess light.
Low‐temperature modulation of the redox properties of the acceptor side of photosystem II: photoprotection through reaction centre quenching of excess energy
Authors: Ivanov Alexander G. , Sane Prafullachandra , Hurry Vaughan , Król Marianna , Sveshnikov Dimitry , Huner Norman P. A. , Öquist Gunnar
Published: October 2003

Although it has been well established that acclimation to low growth temperatures is strongly correlated with an increased proportion of reduced QA in all photosynthetic groups, the precise mechanism controlling the redox state of QA and its physiological significance in developing cold tolerance in photoautotrophs has not been fully elucidated. Our recent thermoluminescence (TL) measurements of the acceptor site of PSII have revealed that short‐term exposure of the cyanobacterium Synechococcus sp. PCC 7942 to cold stress, overwintering of Scots pine (Pinus sylvestris L.), and acclimation of Arabidopsis plants to low growth temperatures, all caused a substantial shift in the characteristic TM of S2QB– recombination to lower temperatures. These changes were accompanied by much lower overall TL emission, restricted electron transfer between QA and QB, and in Arabidopsis by a shift of the S2QA–‐related peak to higher temperatures. The shifts in recombination temperatures are indicative of a lower activation energy for the S2QB– redox pair and a higher activation energy for the S2QA– redox pair. This results in an increase in the free‐energy gap between P680+QA– and P680+Pheo– and a narrowing of the free energy gap between QA and QB electron acceptors. We propose that these effects result in an increased population of reduced QA (QA–), facilitating non‐radiative P680+QA– radical pair recombination within the PSII reaction centre. The proposed reaction centre quenching could be an important protective mechanism in cyanobacteria in which antenna and zeaxanthin cycle‐dependent quenching are not present. In herbaceous plants, the enhanced capacity for dissipation of excess light energy via PSII reaction centre quenching following cold acclimation may complement their capacity for increased utilization of absorbed light through CO2 assimilation and carbon metabolism. During overwintering of evergreens, when photosynthesis is inhibited, PSII reaction centre quenching may complement non‐photochemical quenching within the light‐harvesting antenna when zeaxanthin cycle‐dependent energy quenching is thermodynamically restricted by low temperatures. We suggest that PSII reaction centre quenching is a significant mechanism enabling cold‐acclimated organisms to acquire increased resistance to high light.
Women's experiences of the gynecologic examination: factors associated with discomfort
Authors: Hilden Malene , Sidenius Katrine , Langhoff‐Roos Jens , Wijma Barbro , Schei Berit
Published: October 2003

Background.  The aim of this study was to evaluate how women experience the gynecologic examination and to assess possible factors associated with experiencing discomfort during the gynecologic examination.

Methods.  Consecutive patients visiting the Department of Obstetrics and Gynecology at Glostrup County Hospital, Denmark, were invited to participate in the study, and received a postal questionnaire that included questions about the index visit, obstetric and gynecologic history and sexual abuse history. The response rate was 80% (n = 798). The degree of discomfort during the gynecologic examination was indicated on a scale from 0 to 10. Experiencing discomfort was defined as a score of 6 or more, based on the 75th percentile.

Results.  Discomfort during the gynecologic examination was strongly associated with a negative emotional contact with the examiner and young age. Additionally, dissatisfaction with present sexual life, a history of sexual abuse and mental health problems such as depression, anxiety and insomnia were significantly associated with discomfort.

Conclusion.  The emotional contact between patient and examiner seemed to have great importance when focusing on discomfort during the gynecologic examination. Furthermore, we found that discomfort was associated with a number of factors that are seldom known to the gynecologists, such as sexual abuse history, mental health problems and patients' sexual life. Gynecologists need to focus on the emotional contact and to reevaluate issues for communication before the examination.
Comparison between bisection/morcellation and myometrial coring for reducing large uteri during vaginal hysterectomy or laparoscopically assisted vaginal hysterectomy: results of a randomized prospective study
Authors: Nazah Intissar , Robin François , Philippe Jais Jean , Jeffry Louis , Lelievre Loic , Camatte Sophie , Taurelle Roland , Lecuru Fabrice
Published: October 2003

Background.  Vaginal hysterectomy (VH) is being performed increasingly by gynecologic surgeons. Thus, enlarged uteri are more frequently removed vaginally, requiring reducing techniques to allow vaginal extraction.

Material and methods.  We designed a randomized prospective study to compare bisection–morcellation and myometrial coring. Patients scheduled for VH or laparoscopically assisted vaginal hysterectomy (LAVH) were offered entry into the study. Endometrial cancer was an exclusion criterion. Uterine size was not a contraindication for vaginal surgery. We compared data from preoperative workup as well as from the operative and the postoperative course. Data were recorded prospectively. Results were analyzed with nonparametric tests and logistic regression models.

Results.  Thirty patients were included in the study. Patients were similar in both groups. No severe peroperative complication occurred in this series. Operating time was comparable in both groups. Uteri weighed more than 280 g in more than 70% of patients in both groups. Myometrial coring failed more often than bisection–morcellation (25% vs. 0%, p = 0.06). Patients and uteri characteristics had no influence on the risk of failure, except for narrow uteri, which were associated with an increased risk of failure in the myometrial coring group only (68.3 vs. 83.9 mm, p = 0.01). Postoperative courses were similar for the two techniques, except for an increased rate of fever in the myometrial coring group (28%, p = 0.03).

Conclusion.  Both techniques appeared safe in this trial. Myometrial coring failed more frequently than bisection–morcellation, especially in the case of a narrow uterus. Postoperative fever was significantly more common after myometrial coring. Both techniques should be taught to resident surgeons.