bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of observed and modeled deviations from the great circle direction for a 4490 km HF propagation path along the midlatitude ionospheric trough
Authors: Stocker A. J. , Warrington E. M. , Jones T. B.
Published: June 2003

Measurements of the direction‐of‐arrival of signals propagating on a long (4490 km) path along the midlatitude trough show that the azimuth can be deviated by up to 100° from the great circle bearing. In this paper an attempt has been made to model the shift in azimuth through a ray tracing simulation. Two possible mechanisms which lead to changes in azimuth have been investigated: (1) propagation along the density gradients which form the equatorward wall of the trough and (2) side scatter from regions of the sea well to the south of the trough. Of these two mechanisms, sea scatter gives results which are much closer to those observed.
HYCELL—A new hybrid model of the rain horizontal distribution for propagation studies: 1. Modeling of the rain cell
Authors: Féral Laurent , Sauvageot Henri , Castanet Laurent , Lemorton Joël
Published: June 2003

From radar observations of rain fields at midlatitudes, a new physical model of rain cells is proposed. It strives to describe optimally the rain rate horizontal distribution within rain cells down to 1 mm h−1. The approach is similar to that of the well‐known EXCELL model. The mathematical definition of the model lies in the combination of a gaussian function and an exponential one, the cells having an elliptic horizontal cross section. Due to its hybrid structure, the new model has been named HYCELL. From a conceptual point of view, the gaussian component describes the convective‐like high rain rate core of the cell, while the exponential component accounts for the surrounding stratiform‐like low rain rate spreading down to 1 mm h−1. The modeling of a rain cell with HYCELL then requires the determination of seven parameters. The latter is obtained, cell by cell, by solving a set of five fit‐forcing equations completed by two continuity equations. The fit‐forcing equations involve radar parameters of integral nature which refer not only to the rain cell geometry (area, ellipticity) but also to the rain rate R distribution inside the cell (mean and root mean square values of R and gradient of R). Their analytical expressions are derived from the model definition, while their values are forced to be those derived from radar measurements. Using this method, thousands of rain cells identified from radar observations in the regions of Bordeaux (southwestern France) and Karlsruhe (southwestern Germany) have been modeled. Though both sites are at midlatitude, the climatic contexts differ: oceanic for Bordeaux and continental for Karlsruhe. Results of rain rate horizontal distribution modeling within cells using HYCELL and EXCELL are compared. It is then suggested that the HYCELL model is a new tool which deserves to be considered by system designers to compute propagation parameters.
HYCELL—A new hybrid model of the rain horizontal distribution for propagation studies: 2. Statistical modeling of the rain rate field
Authors: Féral Laurent , Sauvageot Henri , Castanet Laurent , Lemorton Joël
Published: June 2003

A methodology to simulate typical two‐dimensional rain rate fields over an observation area Ao of a few tens up to a few hundreds of square kilometers (i.e., the scale of a satellite telecommunication beam or a terrestrial Broadband Wireless Access network) is proposed. The scenes generated account for the climatological characteristics intrinsic to the simulation area Ao. The methodology consists of the conglomeration of rain cells modeled by HYCELL and of two analytical expressions of the rain cell spatial density, both derived from the statistical distribution of the rain cell size. The scene generating requires, as an input parameter, the local Cumulative Distribution Function (CDF) of the rain rate, a meteorological data commonly available throughout the world. The rain rate field is then generated numerically, according to an iterative scheme, under the constraint of accurately reproducing the local CDF intrinsic to the simulation area Ao, and following rigorously the rain cell spatial density. All the potentialities of the HYCELL model are thus used in order to generate a two‐dimensional scene having a mixed composition of hybrid, gaussian, and exponential cells accounting for the local climatological characteristics. Various scenes are then simulated throughout the world, showing the ability of the method to reproduce the local CDF, with a mean error, with respect to the rain rate distribution, smaller than 1.86%, whatever the location, that is, whatever the climatology. It is suggested that this statistical modeling of the rain rate field horizontal structure be used as a tool by system designers to evaluate, at any location of the world, diversity gain, terrestrial path attenuation, or slant path attenuation for different azimuth and elevation angle directions.
Two‐medium description of dispersion in heterogeneous porous media: Calculation of macroscopic properties
Authors: Cherblanc F. , Ahmadi A. , Quintard M.
Published: June 2003

In this paper, a numerical procedure is proposed to calculate effective properties associated with the generalized two‐equation model developed by Ahmadi et al. [1998]. A transformation of the original closure problems was found that allowed the introduction of a finite volume formulation. Results are presented for a heterogeneous porous medium made up of nodules embedded in a continuous matrix. The properties of the effective parameters are discussed in terms of the influence of the Péclet number, the permeability ratio, and the local‐scale dispersivity. In addition, the problem of the asymptotic behavior of the two‐equation model is discussed in some details. Finally, a comparison is made with results available from the literature in simplified cases.
Solute dispersion in a variably saturated sand
Authors: Sato Takeshi , Tanahashi Hideyuki , Loáiciga Hugo A.
Published: June 2003

The understanding of solute dispersion in unsaturated porous media is still nascent. This work focuses on the measurement of solute dispersion in porous media at various levels of pore‐volume saturation and on the parameterization of longitudinal dispersivity in terms of the saturation ratio and a soil's textural characteristics. The dispersion coefficient was determined in partly saturated columns packed with Toyoura sand or glass beads under steady state flow. A 0.0282 N sodium chloride solution was used as a nonreactive tracer in a series of laboratory experiments in which, for a fixed water content, the average pore‐water velocity was varied. The column experiments showed that the dispersion coefficient increases linearly with increasing water velocity for a fixed water content and that the slope of the dispersion coefficient versus water velocity relationship diminishes as the water content is increased. The Peclet number (Pe) was fitted to the experimental tracer data by a nonlinear function Pe = aSrb, in which Sr is the saturation ratio and a and b are textured‐dependent parameters. The dispersivity (α, in centimeters) of the test columns' porous media was then estimated in terms of the saturation ratio and the median grain size (d50, in centimeters) by the power law α = d50/Pe = d50/aSrb, which provides a specific functional relationship among a porous medium's dispersion properties, the saturation ratio, and the medium's textural characteristics.
Aircraft observations of NO, NOy, CO, and O3 in the upper troposphere from 60°N to 60°S ‐ Interhemispheric differences at mitlatitudes
Authors: Baehr Janine , Schlager Hans , Ziereis Helmut , Stock Paul , van Velthoven Peter , Busen Reinhold , Ström Johan , Schumann Ulrich
Published: June 2003

Measurements of NO, NOy, CO, and O3 made in the middle and upper troposphere over Punta Arenas, Chile (53°S) and Prestwick, Scotland (55°N) during the INCA (Interhemispheric Differences in Cirrus Properties from Anthropogenic Emissions) experiment in 2000 are used to examine the interhemispheric differences in the abundance of these species during local autumn. Median mixing ratios of NO, NOy, O3, and CO in the upper troposphere (8 km‐tropopause) are 4.5, 3, 1.5 and 1.2 times higher over Prestwick compared to Punta Arenas, respectively. Corresponding enhancement factors for the middle troposphere are 5, 7.8, 1.5, and 1.4. The present data represent a considerable extension of the sparse NO and NOy data so far available for the middle and upper troposphere at southern midlatitudes.
Atmospheric observations of enhanced NO2‐HONO conversion on mineral dust particles
Authors: Wang Shuhui , Ackermann Ralf , Spicer Chester W. , Fast Jerome D. , Schmeling Martina , Stutz Jochen
Published: June 2003

Nitrous acid is an important precursor for OH radicals in the polluted troposphere. The heterogeneous conversion of NO2 to HONO, however, is currently not well understood. Measurements of HONO and NO2 in Phoenix in summer 2001 using long path DOAS show ratios of chemically formed secondary [HONO] to [NO2] that rarely exceeded 3%. During two nocturnal dust storm events, however, a significant increase of this ratio was observed. The unprecedented high ratios near 19% suggest a highly efficient NO2 to HONO conversion process on mineral dust particles. The particle composition in Phoenix is similar to other mineral dusts, implying that the enhanced NO2 conversion could be an important HONO, and therefore also OH, source in regions where pollution and dust storms coincide.
Crustal structure of the Peninsular Ranges batholith from magnetic data: Implications for Gulf of California rifting
Authors: Langenheim V. E. , Jachens R. C.
Published: June 2003

A 70‐km‐wide belt of magnetic highs extends ∼1200 km northwest from the southern tip of the Baja California peninsula into southern California. The anomalies are caused by the mafic western belt of the Peninsular Ranges batholith, which is exposed extensively along the northern 800 km length of the magnetic belt. Modeling indicates that the source of the anomalies extends to mid‐to lower crustal depths. The linearity and undisrupted nature of the magnetic belt support the hypothesis that the peninsula has behaved as a rigid block and has resisted significant (>50 km) strike‐slip deformation during the Tertiary. The absence of a corresponding magnetic belt along the coast of mainland Mexico to the south suggests that the location of rifting in the Gulf of California was influenced by the mafic Western Peninsular Ranges batholithic crust, perhaps because it is thermally and mechanically more resistant to deformation than the surrounding crust.
Oceanic thermal and biological responses to Santa Ana winds
Authors: Hu Hua , Timothy Liu W.
Published: June 2003

Ocean surface wind vectors with improved spatial resolutions were derived from the National Aeronautics and Space Administration's (NASA's) Quick Scatterometer (QuikSCAT) satellite. They allow us to examine the details and extent of oceanic influence of a Santa Ana event ‐ a strong offshore and downslope wind in southern California that may spread wide fires, damage properties, and endanger aviation. The oceanic thermal and biological responses to the surface wind jets were observed with other spaceborne sensors. It is found that surface wind jets reduce sea surface temperatures and increase biological productivities. Spacebased measurements demonstrate the inadequacy of current operational numerical weather prediction (NWP) models to accurately and consistently predict the characteristics of Santa Ana winds over the coastal ocean.
SS‐wave sensitivity to upper mantle structure: Implications for the mapping of transition zone discontinuity topographies
Authors: Zhao Li , Chevrot Sébastien
Published: June 2003

Studies of the depths of the upper mantle discontinuities have relied on the differential travel times between the SS wave and its precursors. We examine the effect of velocity heterogeneities on these differential travel time data. Ray‐theory, which is used to correct these data for the effect of velocity heterogeneities, is shown to be inaccurate if the characteristic heterogeneity length scales are similar to those seen in regional models or if the station is near the SS wave radiation nodal plane.
Laser spectroscopic measurement of helium isotope ratios
Authors: Wang L.‐B. , Mueller P. , Holt R. J. , Lu Z.‐T. , O'Connor T. P. , Sano Y. , Sturchio N. C.
Published: June 2003

A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of 3He/4He = 10−7 − 10−5. The resonant absorption of 1083 nm laser light by the metastable 3He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of 4He was measured by a direct absorption technique. The results on three different samples extracted from the atmosphere and commercial helium gas were in good agreement with values obtained with mass spectrometry. The achieved 3σ detection limit of 3He in helium is 4 × 10−9. This demonstration required a 200 μL STP sample of He. The sensitivity can be further improved, and the required sample size reduced, by several orders of magnitude with the addition of cavity enhanced spectroscopy.
From pro defensins to defensins: synthesis and characterization of human neutrophil pro α‐defensin‐1 and its mature domain
Authors: Wu Z. , Prahl A. , Powell R. , Ericksen B. , Lubkowski J. , Lu W.
Published: June 2003

Abstract: Human neutrophil α‐defensins (HNPs) are small, cationic, Cys‐rich antimicrobial proteins that play important roles in innate immunity against infectious microbes such as bacteria, fungi and enveloped viruses. Synthesized as inactive precursors in vivo (pre‐proHNPs), HNPs are activated through proteolytic removal of the inhibitory pro‐peptide required for subcellular sorting and correct folding. We seek to understand the molecular basis for the recognition between the 45‐residue pro‐peptide and the C‐terminal functional domain. Here we described, total chemical synthesis of the 75‐residue human neutrophil pro α‐defensin‐1 (proHNP1) via native chemical ligation. After oxidative folding, proHNP1 is cleaved by cyanogen bromide at the Met45–Ala46 peptide bond to release the mature form. The native disulfide connectivity in HNP1, i.e. Cys1–Cys6, Cys2–Cys4 and Cys3–Cys5, is verified by mass mapping of peptide fragments generated by proteolytic digestion and Edman degradation. Fluorescence spectroscopy studies and antimicrobial activity assays further support that synthetic proHNP1 and HNP1 are correctly folded. While largely unstructured in aqueous solution, the pro‐peptide binds to HNP1 intermolecularly with an apparent Kd value of 6.2 μm at pH 7.4, confirming the mode of intramolecular inactivation of human α‐defensin precursors.
Gravitropic response plays an important role in the nutational movements of the shoots of Pharbitis nil and Arabidopsis thaliana
Authors: Hatakeda Yasuko , Kamada Motoshi , Goto Nobuharu , Fukaki Hidehiro , Tasaka Masao , Suge Hiroshi , Takahashi Hideyuki
Published: June 2003

The shoots of a Japanese strain of morning glory (Pharbitis nil ) called ‘Shidare‐asagao’ display agravitropic and weeping growth. It has been shown that this shoot agravitropism may be due to the defective differentiation of endodermal cells that contain statoliths. Roots of the weeping morning glory show normal responsiveness to gravity and the shoots are positively phototropic. Shoots of the morning glory cultivar Violet used as a wild type exhibited distinct circumnutation with circular movements that increase as the plants grow. In weeping morning glory, however, nutation was limited to slight back and forth or side to side movements. To determine whether endodermal cells participate in circumnutation through a function that is independent of their role in gravitropism, the nutational movements of various gravitropic mutants of Arabidopsis thaliana were compared. The inflorescences of wild‐type Arabidopsis showed relatively large circular movements. Inflorescences of the pgm‐1 mutant, which is defective in starch synthesis, showed reduced nutation. Even more seriously affected were the sgr1‐1/scr‐3 and sgr7‐1/shr‐2 mutants, which are defective in endodermal cell differentiation, and the auxin‐resistant axr2‐1 mutant showed no significant nutational movements at all. 1‐N‐naphthylphthalamic acid (NPA) could inhibit Violet circumnutation, supporting the notion that auxin participates in circumnutation. Thus, the gravitropic response is an essential component in plant shoot circumnutation. Endodermal cells are involved in such circumnutation possibly because of their role in inducing the gravitropic response.
Differential expression and evolutionary analysis of the three ferritin genes in the legume plant Lupinus luteus
Authors: Strozycki Paweł M. , Skąpska Anna , Szcześniak Katarzyna , Sobieszczuk Ewa , Briat Jean‐François , Legocki Andrzej B.
Published: June 2003

We identified three genes coding for ferritins in the legume plant – yellow lupine (LlFer1, LlFer2, LlFer3). Proteins coded by these genes have a typical ‘plant’ structure, and precursors of their functional subunits are probably targeted to plastids. Despite very high amino acid sequence identity of mature polypeptides (86–90%), their genes are differentially induced by iron and the ‘stress‐related’ hormone abscisic acid (ABA). In tissues of lupine plants grown in hydroponics, the transcription of all three classes was induced by both iron and ABA with different kinetics. However, in homogenous lupine cell suspension, the accumulation of all classes of ferritin messages was also induced with iron, whereas only one gene (LlFer2 class) was transcribed in response to ABA. Moreover, the activity of LlFer3 gene was repressed by ABA, but up‐regulated by light. During the development of symbiotic interactions of lupine plants with the bacteria Bradyrhizobium lupini, only two out of three ferritin genes were active –LlFer2 and LlFer3. Increased accumulation of ferritin RNAs and polypeptide(s) correlated with late developmental stages of root nodules, suggesting the involvement of two types of ferritin subunits in the protection against senescence‐related iron release. The phylogenetic analysis of ferritin amino acid sequences is in agreement with classical systematics. However, because of clear grouping of some legume ferritins outside all other legume sequences, a possibility of a more diverse character of ferritins in this family should also be considered.
K+ATP channel opening prevents succinate‐dependent H2O2 generation by plant mitochondria
Authors: Casolo Valentino , Braidot Enrico , Chiandussi Elisa , Vianello Angelo , Macrì Francesco
Published: June 2003

The role of a recently identified K+ATP channel in preventing H2O2 formation was examined in isolated pea stem mitochondria. The succinate‐dependent H2O2 formation was progressively inhibited, when mitochondria were resuspended in media containing increasing concentration of KCl (from 0.05 to 0.15 M). This inhibition was linked to a partial dissipation of the transmembrane electrical potential (ΔΨ) induced by KCl. Conversely, the malate plus glutamate‐dependent H2O2 formation was not influenced. The succinate‐sustained H2O2 generation was also unaffected by nigericin (a H+/K+ exchanger), but completely prevented by valinomycin (a K+ ionophore). In addition, cyclosporin A (a K+ATP channel opener) inhibited this H2O2 formation, while ATP (an inhibitor of the channel opening) slightly increased it. The inhibitory effect of ATP was strongly stimulated in the presence of atractylate (an inhibitor of the adenine nucleotide translocase), thus suggesting that the receptor for ATP on the K+ channel faces the intermembrane space. Finally, the succinate‐dependent H2O2 formation was partially prevented by phenylarsine oxide (a thiol oxidant).
Antifreeze proteins are secreted by winter rye cells in suspension culture
Authors: Pihakaski‐Maunsbach Kaarina , Tamminen Ilkka , Pietiäinen Milla , Griffith Marilyn
Published: June 2003

During cold‐acclimation, winter rye (Secale cereale L) leaves secrete antifreeze proteins (AFPs) into the apoplast. The AFPs bind to ice and modify its growth, which is easily observed in vitro. However, it is not yet known whether in planta AFPs interact with ice or whether they exert cryoprotective effects. These experiments are difficult to conduct with intact plants, so the aim of this work was to determine whether AFPs are produced in response to cold temperature in cell culture and to examine their function by using suspension cells. We showed that suspension cells secreted three of the six known winter rye AFPs into the culture medium during acclimation at 4°C. These AFPs were not present in washed suspension cells, thus indicating that they are not firmly bound to the cell walls. In order to examine the function of extracellular AFPs, non‐acclimated (NA) winter rye suspension cells and protoplasts isolated from NA winter rye leaves were then frozen and thawed in the presence of AFPs extracted from cold‐acclimated winter rye leaves. The AFPs had no effect on the survival of NA protoplasts after freezing; however, they lowered the lethal temperature at which 50% of the cells are killed by freezing (LT50) of NA suspension cells by 2.5°C. We conclude that low above‐zero temperatures induce winter rye suspension cells to secrete AFPs free in solution where they can protect intact suspension cells, but not protoplasts, from freezing injury, presumably by interacting with extracellular ice.
Sugar‐modulated gene expression of sucrose synthase in suspension‐cultured cells of rice
Authors: Liao Yi‐Chun , Wang Ai‐Yu
Published: June 2003

In suspension‐cultured cells of rice (Oryza sativa L. cv. Tainung 67), two sucrose synthase genes, RSus1 and RSus2, were found to be differentially regulated by sugars. Exogenously provided sugars triggered marked accumulation of the RSus1 transcripts and this required de novo synthesized proteins. In addition to being regulated at the transcriptional level, other regulatory mechanisms might be involved in the sugar‐modulated expression of RSus1 since the RSuS1 proteins were extremely stable in sucrose‐depleted cells. Glucose analogues, 3‐O‐methyl glucose, 6‐deoxyglucose and mannose, did not trigger the induction of RSus1 expression, suggesting that hexose uptake per se and hexokinase are not involved in the sugar‐sensing pathway controlling RSus1 expression. The accumulation of RSus2 mRNA was observed regardless of the presence or absence of sugars. However, newly synthesized proteins induced by sucrose and/or starvation were involved in the regulation of RSus2 expression at transcriptional and/or post‐transcriptional levels. The protein level of RSuS2 was elevated under prolonged starvation condition but a reciprocal change was observed in the sucrose‐fed cell. The constant presence of RSuS1 and RSuS2 proteins in both sucrose‐starved and sucrose‐provided cells may allow the cells to respond to sugar availability immediately.
Structural and physiological changes in the roots of tomato plants over‐expressing a basic peroxidase
Authors: Lucena Miguel A. , Romero‐Aranda Remedios , Mercado Jose A. , Cuartero Jesús , Valpuesta Victoriano , Quesada Miguel A.
Published: June 2003

Previous studies on the tomato (Lycopersicon esculentum Mill.) peroxidase TPX1, including the development of transgenic tomato over‐expressing this gene, supported an involvement of this peroxidase in the synthesis of lignin and suberin. The transgenic plants showed a wilty phenotype at flowering, but the relationship between this role in ligno‐suberization and this phenotype was not clear. In the present study a histological approach and the measurement of water‐related parameters have been performed in order to obtain an insight into the origin of this phenotype. Clear differences between transgenic and non‐transgenic roots were observed in the cross‐sections of the basal root zones where secondary growth was evident. The diameter of the xylem vessel was diminished in the transgenic plants. Total area corresponding to xylem in the basal cross‐sections decreased 3.9 fold in the transgenic roots. In addition, the radial and outer tangential walls of the exodermis cells were more ligno‐suberized in transgenic than in non‐transgenic plants. After fruit set, predawn and midday water potentials were lower in transgenic than in‐non‐transgenic plants. At midday, the stomatal conductance was also lower in the transgenic plants, 494±69 versus 594±60 mmol m−2 s−1. Root hydraulic conductances of the transgenic and non‐transgenic plants were 1.4±0.38 and 3.47±0.19 g water min−1 MPa−1, respectively. The results obtained support that the phenotype is caused by the anatomical differences found in the transgenic roots. These differences would be the cause of a increased resistance to water flow in the roots that would negatively affect the water supply to the shoot and, as a consequence, resulted in a decreased water potential in the leaves.
Formation and vacuolar localization of salicylic acid glucose conjugates in soybean cell suspension cultures
Authors: Dean John V. , Shah Reena P. , Mohammed Leila A.
Published: June 2003

The metabolism and intracellular localization of salicylic acid (SA) was investigated in soybean (Glycine max[L.] cv Williams 82) cell suspension cultures. [7–14C]SA was added to the cell cultures, the metabolites were extracted from the cells at various time points and analysed by TLC and HPLC. The [7–14C]SA was taken up rapidly from the culture media and converted primarily to SA 2‐O‐β‐d‐glucose (SAG). Lower levels of glucosylated 2,5‐dihydroxbenzoic acid (gentisic acid) and methyl salicylate 2‐O‐β‐d‐glucose were also formed. Examination of the intracellular localization of the glucose conjugates revealed that all of the conjugates associated with the protoplasts were found in the vacuoles. An SA glucosyltransferase (SAGT) that could catalyse the formation of SAG from SA and UDP‐glucose could be extracted from soybean cells and assayed in vitro. Increasing concentrations of SA added to the culture media induced the SAGT activity. The highest levels of SAGT activity were observed in cells treated with 0.5 mM SA. The SAGT activity in these cells was 88‐fold greater than the SAGT activity in the untreated cells. The intracellular localization of the SAGT activity was also examined and it was determined that the majority of the SAGT activity in the protoplasts was located outside the vacuole. Therefore, it appears as if SAG is formed from SA outside the vacuole, presumably in the cytoplasm, and then subsequently transported into the vacuole where it accumulates.
Plant response to destruxins visualized by imaging of chlorophyll fluorescence
Authors: Soukupová Julie , Smatanová Silvia , Nedbal Ladislav , Jegorov Alexandr
Published: June 2003

Kinetic fluorescence imaging was used to set a new detection limit for plant exposure to low levels of destruxins – phytotoxins of Alternaria brassicae. A general experimental algorithm is presented that can be used to identify the combination of fluorescence parameters providing the highest contrast between the affected and unaffected plants or plant segments. Leaves of canola (Brassica napus) and white mustard (Sinapis alba) were exposed to various concentrations of destruxins and images of key fluorescence signals (F0, FM, FP, and of FS) were captured in a single kinetic experiment. Contrast was quantified within these images between the leaf areas exposed to destruxins and the untreated areas. The highest contrast was found in the image constructed by pixel‐to‐pixel division of images F0 by FP and F0 by FM. Using the F0/FM ratio image, we were able to detect exposure to destruxin concentration as low as approximately 0.05 mg l−1 applied to canola leaf and approximately 10 mg l−1 when applied to mustard. The detection limits were significantly lower than those obtained by optical microscopy indicating that kinetic chlorophyll fluorescence imaging can be used as a diagnostic tool in screening for varieties with an enhanced resistance to destruxins of Alternaria brassicae.
Higher electron transport rate observed at low intercellular CO2 concentration in long‐term drought‐acclimated leaves of Japanese mountain birch (Betula ermanii)
Authors: Kitao Mitsutoshi , Lei Thomas T. , Koike Takayoshi , Tobita Hiroyuki , Maruyama Yutaka
Published: June 2003

The influence of long‐term drought stress on photosynthesis of Japanese mountain birch (Betula ermanii Cham.) was examined using chlorophyll fluorescence and gas exchange measurements. Drought stress was imposed in potted plants by reducing irrigation frequency from daily (control) to twice‐weekly and once‐weekly. Thirty‐day‐old leaves, which had developed under fully stressed conditions, were used for the measurements. The decline in net CO2 assimilation rate (A) observed in situ in drought‐stressed plants resulted from a lower intercellular CO2 concentration (Ci) due to stomatal closure but the carboxylation efficiency was not affected as there was no difference in the initial slope of the A/Ci response after watering. Although there were no treatment differences in A at Ci below 270 μmol mol−1 (with ambient air at 360 μmol mol−1 CO2), higher electron transport rate (ETR), photochemical quenching (qP) and the efficiency of energy conversion of open PSII (Fv′/Fm′), and similar or even lower non‐photochemical quenching (NPQ) were observed at a given Ci in drought‐stressed plants (of both twice‐ and once‐weekly irrigation), suggesting a higher fraction of open PSII resulting from energy dissipation achieved through higher electron flow rather than through thermal dissipation in PSII antennae. The once‐weekly watered plants showed a lower ratio of gross carbon assimilation rate to ETR (A*/ETR), suggesting an enhanced alternative pathway of electron flow probably involving the Mehler‐peroxidase (MP) reaction as indicated by a higher ΦPSII at a given ΦCO2 under non‐photorespiratory conditions. On the other hand, plants of twice‐weekly watering exhibited almost the same A*/ETR and ΦPSII–ΦCO2 relationship as control plants, indicating no enhanced alternative pathways under mild drought stress.
A polarized cell: the root statocyte
Authors: Driss‐Ecole Dominique , Lefranc Agnès , Perbal Gérald
Published: June 2003

In the gravity‐perceiving cells (statocytes), located in the centre of the root cap, polarity is expressed in the arrangement of the organelles since, in most genera, the nucleus and the endoplasmic reticulum are maintained at the opposite ends of each cell by actin. Polarity is also evident in the distribution of plasmodesmata, which are more numerous in the transverse walls than in the longitudinal walls. The centre of each statocyte is depleted of microtubules (they are only located at the periphery) but is occupied by numerous amyloplasts (statoliths), denser than the cytoplasm. The amyloplasts do not contribute to the inherent structural polarity since their position is dependent upon the gravity vector. This article focuses on new microscopic analyses and on data obtained from experiments performed in microgravity, which have contributed to our better understanding of the architecture of the actin web implicated in the perception of gravity. Depending upon the plant, the actin network seems to be formed of single filaments arranged in various ways, or, of thin bundles of actin filaments. The amyloplasts are enmeshed in this web of actin and their envelopes are associated with it, but they can have autonomous movement via myosin in the absence of gravity. From calculations of the value of the force necessary to move one amyloplast in the lentil root, and from videomicroscopy performed with living statocytes of maize roots, it is hypothesized that actin microfilaments could be orientated in an overall diagonal direction in the statocyte. These observations could help in understanding how slight amyloplast movements may trigger and transmit the gravitropic signal.
Transformation efficiencies and expression patterns of a series of truncated GS1‐2 promoter/GUS transgenes in maize
Authors: Muhitch Michael J. , Liang Hua , Sollenberger Kurtis G.
Published: June 2003

One isoform of maize glutamine synthetase, encoded by GS1‐2, is localized exclusively in the maternal tissues of the developing kernel. Previously, we have demonstrated the ability of the proximal 664 base pair 5′ upstream portion of GS1‐2 to drive maternal tissue‐specific GUS expression in transgenic maize kernels (Muhitch et al. Plant Sci. 163: 865–872). In this report, a series of GS1‐2 promoter/GUS reporter transgenes, progressively truncated from the 5′ end of the full length 664 base pair promoter, were evaluated for transformation efficiency and their ability to drive tissue‐specific gene expression in transgenic maize. Analysis of transgene integration and expression suggests that GS1‐2/GUS transgenes were incorporated efficiently into the maize genome, but were not expressed efficiently in maize cells. Truncation of the promoter from −664 to −394, −206 or −72, relative to the putative transcription start site, resulted in the loss of tissue specific expression within the kernels of transformed plants. Among the truncated series, moderate staining was exhibited by the −394 promoter/GUS gene transformants, stronger staining was found in −206 promoter/GUS gene transformants, but relatively weak and variable staining occurred in plants transformed with the −72/GUS gene. Likely explanations for these observations are considered.
Involvement of cytokinin in the stimulation of nodulation by low concentrations of ammonium inPisum sativum
Authors: Fei Houman , Vessey J. Kevin
Published: June 2003

Nodulation in pea (Pisum sativumL.) grown in hydroponic and sand culture systems is stimulated by low concentrations (<1.0 mM) of ammonium, but the physiological mechanisms underlying this stimulation are unknown. The current study involves a series of experiments, which investigate if the ammonium‐induced stimulation of nodulation involves changes in endogenous hormone (auxin and cytokinin) levels.P. sativumL. cv. Express was grown in growth pouches for 1 week with mineral N (0.5 and 2.0 mMNH4+or NO3–) or for 3 weeks exposed to exogenous indole‐3‐acetic acid (IAA) or 6‐benzylaminopurine (BAP) at a range of concentrations (10‐9−10‐5 M). Ammonium enhanced nodulation on the basis of both early whole plant (nodules plant−1) and specific nodulation (nodules g−1root DW), especially in 0.5 mMtreatment in which nodulation was approximately 4‐fold of the mineral‐N‐free control 1 week after inoculation. Correspondingly, the roots treated with ammonium contained much higher levels oft‐zeatin (Z) and lowert‐zeatin riboside (ZR) than that the control or nitrate‐treated plants. There was no significant difference in IAA levels between the control and ammonium treatments. Exogenous application of BAP for 3 weeks at concentrations of 10‐7−10‐5 Mstrongly inhibited nodulation. However, 10−9 MBAP, but not IAA, significantly enhanced nodulation. These data support the theory that a relatively high ratio of cytokinin:auxin in roots is favourable for nodule initiation, but that an excessively high level of cytokinin inhibits nodulation. Based on these results we propose that stimulation of nodulation by low concentrations of ammonium may be mediated through increasing Z level in roots, which alters the balance of cytokinin and auxin, which in turn induces cortical cell divisions leading to nodule initiation.
Hydrogen peroxide and jasmonic acid mediate oligogalacturonic acid‐induced saponin accumulation in suspension‐cultured cells ofPanax ginseng
Authors: Hu Xiangyang , Neill Steven , Cai Weiming , Tang Zhangcheng
Published: June 2003

The signalling pathways mediating defence responses induced in suspension cultures of ginseng,Panax ginsengC. A. Meyer, by the plant cell wall‐derived elicitor oligogalacturonic acid (OGA), were investigated. OGA induced the rapid generation and release of hydrogen peroxide, H2O2, potentially via an NADPH oxidase‐like enzyme. In addition, OGA elicited the accumulation of jasmonic acid (JA) and the defence compound saponin, and expression of genes encoding squalene synthase (SQS; EC 2.5.1.21) and squalene epoxidase (SQE; EC 1.14.99.7), key enzymes of saponin biosynthesis. H2O2and JA also induced saponin accumulation and transcription ofsqsandsqe. The accumulation of JA, but not that of H2O2, was inhibited by an inhibitor of JA biosynthesis, whereas the accumulation of both H2O2and JA were inhibited by treatments that removed H2O2or inhibited its production. Moreover, H2O2stimulated JA accumulation, but JA treatment had no effect on H2O2generation. These data place H2O2and JA as early signalling intermediaries in the cellular responses mediating saponin biosynthesis in response to OGA, and position H2O2upstream of JA. Inhibitors of calcium fluxes and protein phosphorylation inhibited all responses to some extent, indicating the requirements for a protein kinase and calcium in at least one step in the signal cascade leading to saponin accumulation.
Chloroplast biogenesis by Arabidopsis seedlings is impaired in the presence of exogenous glucose
Authors: To Jennifer P. C. , Reiter Wolf‐Dieter , Gibson Susan I.
Published: June 2003

Seedlings of Arabidopsis thaliana (L.) Heynh. fail to become green when germinated and grown on media containing high concentrations of glucose (Glc). Although previous studies have shown that sugar concentration affects chlorophyll levels and photosynthetic gene expression, the possibility that sugar concentration might affect actual chloroplast biogenesis has received little attention. Therefore, experiments were conducted to determine whether germination and growth on Glc impairs development of mature chloroplasts from the proplastids found in plant embryos. To monitor chloroplast biogenesis, the levels of a chloroplast‐specific fatty acid, hexadecatrienoic (16:3) fatty acid, were measured in Arabidopsis seedlings grown on media containing different concentrations of Glc. These experiments indicate that moderate concentrations of Glc delay accumulation of 16:3. The effects of Glc on 16:3 levels are not solely due to osmotic stress, as equi‐molar and even twice equi‐molar concentrations of sorbitol do not exert comparable effects. Seedlings grown on concentrations of Glc high enough to prevent greening accumulate almost no 16:3, even after 22 days of growth under continuous light conditions. The lack of 16:3, a major structural component of chloroplast membranes, suggests that seedlings do not develop mature chloroplasts when grown in the presence of high concentrations of exogenous Glc. Further support for this hypothesis is provided by electron microscopy studies revealing that seedlings grown on high concentrations of Glc lack identifiable chloroplasts. Although Glc has been reported to inhibit chloroplast development in unicellular organisms, similar studies on intact higher plants have been lacking.
Synthesis and proof‐of‐function of a [14C]‐labelled form of the plant iron chelator nicotianamine using recombinant nicotianamine synthase from barley
Authors: Schmiedeberg Lars , Krüger Claudia , Stephan Udo W. , Bäumlein Helmut , Hell Rüdiger
Published: June 2003

The amino acid nicotianamine (NA) is essential for micronutrient metabolism in plants. Lack of NA results in a chlorotic phenotype and oxidative stress, since NA is a chelator of iron and other metal nutrients. To investigate the precise cellular function of NA in micronutrient transport and homeostasis, a protocol for the production of [14C]‐labelled NA was developed. Recombinant NA synthase was used to generate [14C]‐NA from [14C]‐S‐adenosylmethionine. After purification by solid‐phase ion exchange about 66% yield was achieved. The identity of the [14C]‐NA with chemically synthesized NA was demonstrated by several independent methods, including two TLC systems, two HPLC systems and immuno‐detection. Moreover, biological function was shown by complementation of the Lycopersicon esculentum mutant chloronerva that is free of NA due to a defect in NA synthase. Proof‐of‐function for the produced [14C]‐NA as a suitable tool for transport studies was provided monitoring the distribution of [14C]‐NA after feeding to tomato and Ricinus communis seedlings.
Cloning, characterization and expression analysis of a sucrose synthase gene from tropical epiphytic orchid Oncidium Goldiana
Authors: Li Chang Run , Zhang Xiao Bo , Hew Choy Sin
Published: June 2003

A full‐length cDNA encoding sucrose synthase was isolated from the tropical epiphytic orchid Oncidium Goldiana. The cDNA is 2829 bp in length containing an open reading frame of 2447 bp encoding 816 amino acids with a predicted molecular mass of 93.1 kDa. The deduced amino acid sequence of O. Goldiana sucrose synthase (Osus) shares more than 80% identity with those from other monocotyledonous plants. The sucrose synthase gene was demonstrated to encode a functional sucrose synthase protein by expression as recombinant protein in Escherichia coli. The Osus mRNA is present in all the tissues analysed, with the highest levels in strong sinks such as developing inflorescence and root tips. Incubation with sucrose or glucose resulted in a significant increase in the steady‐state Osus mRNA levels in root tips and mature leaves in a similar pattern to maize Sus1. Expression of the Osus mRNA in mature leaves was markedly enhanced by anaerobic conditions and elevated CO2. The expression pattern and regulation of the gene suggest that the sucrose synthase plays an important role in the growth and development of the tropical epiphytic orchid O. Goldiana.
Water‐ and temperature‐dependence of DNA damage and repair in the fruticose lichen Cladonia arbuscula ssp. mitis exposed to UV‐B radiation
Authors: Buffoni Hall Roberta S. , Paulsson Markus , Duncan Kirsty , Tobin Alyson K. , Widell Susanne , Bornman Janet F.
Published: June 2003

The induction of cyclobutane pyrimidine dimers (CPDs) by ultraviolet‐B radiation (UV‐B, 280–315 nm) and repair mechanisms were studied in the lichen Cladonia arbuscula ssp. mitis exposed to different temperatures and water status conditions. In addition, the development and repair of CPDs were studied in relation to the different developmental stages of the lichen thallus podetial branches. Air‐dried lichen thalli exposed to UV‐B radiation combined with relatively high visible light (HL, 800 μmol m−2 s−1; 400–700 nm) for 7 days showed a progressive increase of CPDs with no substantial repair, although HL was present during and after irradiation with UV‐B. Fully hydrated lichen thalli, that had not been previously exposed to UV‐B radiation for 7 days, were given short‐term UV‐B radiation treatment at 25°C, and accumulated DNA lesions in the form of CPDs, with repair occurring when they were exposed to photoreactivating conditions (2 h of 300 μmol m−2 s−1, 400–700 nm). A different pattern was observed when fully hydrated thalli were exposed to short‐term UV‐B radiation at 2°C, in comparison with exposure at 25°C. High levels of CPDs were induced at 2°C under UV‐B irradiation, without significant repair under subsequent photoreactivating light. Likewise, when PAR (300 μmol m−2 s−1) and UV‐B radiation were given simultaneously, the CPD levels were not lowered. Throughout all experiments the youngest, less differentiated parts of the lichen thallus – namely ‘tips’, according to our arbitrary subdivision – were the parts showing the highest levels of CPD accumulation and the lowest levels of repair in comparison with the older thallus tissue (‘stems’). Thus the experiments showed that Cladonia arbuscula ssp. mitis is sensitive to UV‐B irradiation in the air‐dried state and is not able to completely repair the damage caused by the radiation. Furthermore, temperature plays a role in the DNA damage repairing capacity of this lichen, since even when fully hydrated, C. arbuscula ssp. mitis did not repair DNA damage at the low temperatures.
Activation of phospholipases by N‐acetylchitooligosaccharide elicitor in suspension‐cultured rice cells mediates reactive oxygen generation
Authors: Yamaguchi Takeshi , Minami Eiichi , Shibuya Naoto
Published: June 2003

The generation of reactive oxygen species (ROS) is a central component of the elicitor‐induced defence reactions in cultured cells as well as the resistance responses of plants to pathogen challenge. We show that N‐acetylchitooligosaccharide elicitor induces rapid and transient activation of phosphatidylinositol‐specific phospholipase C (PI‐PLC) and that phosphatidylcholine‐specific phospholipase D (PC‐PLD) in suspension‐cultured rice cells and their products, phosphatidic acid (PA) and diacylglycerol (DG), especially the former, play an important role in the elicitor‐induced ROS generation based on the following observations: (1) the amount of PA and DG in rice cells was rapidly increased by the elicitor treatment. (2) Elicitor‐induced activation of PI‐PLC and PC‐PLD in the membrane fraction was confirmed by the analysis of enzymatic products from radio‐labelled phospholipids as well as by 1‐butanol (1‐ButOH)‐specific formation of phosphatidylbutanol (PtdBut) (for PC‐PLD). Inhibitors of these phospholipases at least partly inhibited the elicitor‐induced ROS generation. (3) Exogenously applied PA and DG could induce ROS generation in the rice cells in the absence of the elicitor. (4) PA phosphohydrolase (PAPH) and diacylglycerol kinase (DGK) activities, which catalyse the conversion of PA and DG with each other, are present in the rice cells and the inhibitors of these enzymes inhibited/stimulated the elicitor‐induced ROS generation depending on the direction of the PA accumulation. These results indicate the important role of PI‐PLC/PC‐PLD and their products, especially PA, in the signal transduction cascade downstream of the N‐acetylchitooligosaccharide receptor.
Mammalian skin evolution: a reevaluation
Authors: Maderson P. F. A.
Published: June 2003

Abstract:  A 1972 model for the evolutionary origin of hair suggested a primary mechanoreceptor role improving behavioral thermoregulation contributed to the success of late Paleozoic mammal‐like reptiles. An insulatory role appeared secondarily subsequent to protohair multiplication. That model is updated in light of new data on (a) palaeoecology of mammalian ancestors; (b) involvement of HRPs in keratinization; (c) lipogenic lamellar bodies that form the barrier to cutaneous water loss; and (d) growth factors involved in hair follicle embryogenesis and turnover. It is now proposed that multiplication of sensory protohairs caused by mutations in patterning genes initially protected the delicate barrier tissues and eventually produced the minimal morphology necessary for an insulatory pelage. The latter permitted Mesozoic mammals to occupy the nocturnal niche ‘in the shadow of dinosaurs’. When the giant reptiles became extinct, mammals underwent rapid radiation and reemerged as the dominant terrestrial vertebrates.