bluuebunny/crossref_metadata_2025 huggingface dataset:
Oceanic phosphorus imbalance: Magnitude of the mid‐ocean ridge flank hydrothermal sink
Authors: Wheat C. Geoffrey , McManus James , Mottl Michael J. , Giambalvo Emily
Published: September 2003

We present a new estimate for the crustal phosphorous sink that results from reactions among seawater, basalt, and sediment blanketing low temperature mid‐ocean ridge flank hydrothermal systems. New estimates for global hydrothermal power output, sediment thickness, and the dissolved phosphate concentrations in basement formation fluids indicate that fluid flow through ridge flanks removes 2.8 × 1010 mol P yr−1. This value is larger (130%) than the riverine dissolved flux of inorganic phosphate and is as much as 35% of the sedimentary P sink. The concordant seawater flux (2.1 × 1016 kg yr−1) is 65% of the riverine fluid flux and circulates a fluid volume equivalent to the entire ocean in about 70,000 yr. Additional sampling of seafloor springs is required to further constrain the range of calculated phosphate fluxes; nevertheless the modern phosphorus budget is clearly unbalanced with total sinks outpacing sources.
A new climate regime in northeast pacific ecosystems
Authors: Peterson William T. , Schwing Franklin B.
Published: September 2003

Following a strong El Niño, the climate of the North Pacific underwent a rapid and striking transition in late 1998. Upwelling‐favorable winds strengthened over the California Current (CC), and winds weakened in the Gulf of Alaska (GOA). Coastal waters of the CC and GOA cooled by several degrees, and the Pacific Decadal Oscillation (PDO) reversed sign and remained negative through summer 2002. Zooplankton biomass in the northern CC doubled and switched from warm to cold water species dominance, coho and chinook salmon stocks rebounded, and anchovy and osmeriids increased. Persistent changes in atmosphere and upper ocean fields and ecosystem structure suggest a climate regime shift has occurred, similar (opposite) to shifts observed in 1947 (1925 and 1976). If the 1998 regime shift in the northern CC is completely analogous to earlier shifts, then ecosystem structure should have changed in the GOA. Recent surveys indicate this ecosystem has transformed as well.
Mapping b‐values in France using two different magnitude ranges: Possible non power‐law behavior
Authors: Beauval Céline , Scotti Oona
Published: September 2003

The first step in probabilistic seismic hazard assessment is the characterization of seismic sources. The fundamental assumption is that the Gutenberg‐Richter power law can be applied and is valid at all scales. In this study, we found that the power‐law model may not be verified in the southeastern regions of France. Frequency‐magnitude distributions are mapped using 2 different magnitude ranges: (1) [3.0–4.4] using only homogeneous instrumental data, (2) [3.5‐Mmax(observed)] using instrumental and historical data. b‐values estimated on these two magnitude ranges are similar in the Pyrenees and the Rhine Basin. However, they differ significantly in the Southern Alps: the slopes estimated on magnitude range [3.0–4.4] are much steeper (b > 1.4) than the slopes estimated on magnitudes above 3.5 (0.9 < b < 1.1). Until a clear identification of the underlying processes is made, a conservative option (i.e., lowest b‐values) should be considered for probabilistic estimation of hazard in the eastern part of France.
The sensitivity of the present‐day Atlantic meridional overturning circulation to freshwater forcing
Authors: Otterå O. H. , Drange H. , Bentsen M. , Kvamstø N. G. , Jiang D.
Published: September 2003

Mounting evidence indicates that the Atlantic Meridional Overturning Circulation (AMOC) was strongly reduced during cold climate episodes in the past, possible due to freshwater influx from glacial melting. It is also expected that the freshwater input to high northern latitudes will increase as human‐induced global warming continues, with potential impacts on the AMOC. Here we present results from a 150 years sensitivity experiment with the Bergen Climate Model (BCM) for the present‐day climate, but with enhanced runoff from the Arctic region throughout the integration. The AMOC drops by 30% over the first 50 years, followed by a gradual recovery. The simulated response indicates that the present‐day AMOC might be robust to the isolated effect of enhanced, high‐latitude freshwater forcing on a centennial time scale, and that the western tropical North Atlantic may provide key information about the long‐term variability, and by that monitoring, of the AMOC.
Field relations among coseismic ground motion, water level change and liquefaction for the 1999 Chi‐Chi (Mw = 7.5) earthquake, Taiwan
Authors: Wang Chi‐Yuen , Dreger Douglas S. , Wang Chung‐Ho , Mayeri Daniel , Berryman James G.
Published: September 2003

Field‐based, basin‐wide relations are discovered among coseismic ground motion, water‐level change and liquefaction induced by the 1999 (Mw = 7.5) Chi‐Chi earthquake, Taiwan. The relations imply thresholds of 4.4 m/s2 and 0.6 m/s in the spectral acceleration and velocity at 1 Hz, respectively, below which pore pressure does not change appreciably and above which pore pressure increases exponentially with increasing acceleration and velocity. Liquefaction occurs when the 1‐Hz spectral acceleration and velocity and the peak ground acceleration exceed ∼16 m/s2, ∼2.4 m/s, and ∼2.5 m/s2 (∼0.26 g), respectively. Broad consistency between the present and previous results suggests that the relations may be transferable to other areas and may provide fundamental constraints for modeling coseismic pore‐pressure increase and liquefaction.
A novel method to study the phase relationship between Antarctic and Greenland climate
Authors: Caillon N. , Jouzel J. , Severinghaus J. P. , Chappellaz J. , Blunier T.
Published: September 2003

A classical method for understanding the coupling between northern and southern hemispheres during millennial‐scale climate events is based on the correlation between Greenland and Antarctic ice core records of atmospheric composition. Here we present a new approach based on the use of a single Antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the North and of its Antarctic counterpart. We applied it to the Marine Isotope Stage (MIS) 5d/c transition early in the last glaciation ∼108 ky BP. Our results indicate that the Antarctic temperature increase occurred 2 ky before the methane increase, which is used as a time marker of the warming in the Northern Hemisphere. This result is in agreement with the “bipolar seesaw” mechanism used to explain the phase relationships documented between 23 and 90 ky BP [Blunier and Brook, 2001].
Mutual relationship between microseismicity and seismic reflectivity: Case study at the German Continental Deep Drilling Site (KTB)
Authors: Rothert E. , Shapiro S. A. , Buske S. , Bohnhoff M.
Published: September 2003

Two fluid injection experiments were conducted at the German Continental Deep Drilling Site (KTB) in 1994 and 2000. Microseismicity occurred at different depth intervals. Hypocenter locations were precisely localized. Here, microseismicity is analyzed in terms of its spatio‐temporal evolution characteristics. An approach is applied which assumes microseismicity to be triggered by a diffusive process of pore pressure relaxation. The method yields estimates of hydraulic parameters of rocks on large spatial scales. At the KTB site the method enables us to study hydraulic diffusivity at two different depth intervals. We observe significant variations in the evolution characteristics of the seismic activity at different depths. Estimates of hydraulic diffusivity for shallower parts of the crust seem to be much smaller than for deeper regions. To understand reasons for this, we have analyzed spatial relations of hypocenter locations to the distribution of intensities of seismic reflections. Low values of hydraulic diffusivity correlate with low reflection intensities and high diffusivities with large intensities, respectively. The analysis confirms the hypothesis that the process of pore pressure relaxation along pre‐existing and critically stressed natural fractures is an important triggering factor for induced microseismicity.
High resolution tropical climate record for the last 6,000 years
Authors: Tedesco Kathy , Thunell Robert
Published: September 2003

Planktonic foraminiferal oxygen isotope records from the Cariaco Basin, offshore Venezuela were used to construct high‐resolution tropical Atlantic climate records for the mid to late Holocene. Our results indicate that major increases in δ18O due both to increases in salinity and decreases in sea surface temperature occurred at least six times over the last 6,000 years (∼6,000–5,000, 4,500–4,200, 3,800–3,200, 3,000–2,800, 2,200–2,000, and 1200–800 cal yrs. B.P.). The initial δ18O increase centered at 5,500 years ago is coincident with the development of arid conditions in the Caribbean region and the end of the “African humid period” indicating a global drying of the northern tropics at this time. Synchronous with the aridification of the Caribbean region are the onset of wetter conditions in the South American Altiplano and the reoccupation of this region by humans. This combination of contrasting climate conditions is attributed to a southward displacement of the Inter‐Tropical Convergence Zone (ITCZ) that would have resulted in decreased precipitation and increased trade wind intensity in the Caribbean region and increased rainfall over the Altiplano.
Gale force winds over the Irminger Sea to the east of Cape Farewell, Greenland
Authors: Moore G. W. K.
Published: September 2003

High wind events that occur over the Irminger Sea to the east of Cape Farewell Greenland are of interest as a result of the significant hazard they represent to maritime activity as well as their potential role in forcing deep ocean convection in the region. In this paper, the NCEP reanalysis is used to develop a climatology of gale force wind events over the Irminger Sea. In addition to the previously identified ‘tip jet’ events that are characterized by strong westerly flow, we show that there also exist ‘reverse tip jet’ events that are characterized by strong easterly flow. Both types of events are associated with deep extra‐tropical cyclones that are undergoing an interaction with the high topography of southern Greenland. We also show that the frequency of both types of events is highest in the winter months and is modulated by the phase of the North Atlantic Oscillation (NAO).
Importance of land‐surface parameterization for latent heat simulation in global atmospheric models
Authors: Irannejad P. , Henderson‐Sellers A. , Sharmeen S.
Published: September 2003

Simulations of atmospheric general circulation models' (AGCMs') continental latent heat flux (LH) depend on the land‐surface schemes (LSSs), the atmospheric forcing and feedbacks between these. This paper introduces a novel method for evaluating the dependence of 19 Atmospheric Model Intercomparison Project AGCMs' LH on the LSS by excluding the impact of forcing from, and feedback to, the atmosphere. Pseudo LSSs (PLSSs) for LH in the form of multi‐variable linear models expressing mean monthly LH as a function of atmospheric forcing are developed. Analysis over three large and climatically diverse river basins shows estimates of mean annual LH from the PLSSs agreeing well with the AGCMs' simulations. Root mean square errors range from 0.4 to 2.2 Wm−2 depending on the region and the AGCM. When the PLSSs are driven by single realisations of atmospheric forcing, different LSSs interact differently with the atmosphere, exhibiting a range of climate sensitivities, and the variability of mean annual LH among AGCMs increases. We conclude that LSSs are important to AGCM predictions and new, or changed, land‐surface components will increase diversity among climate simulations.
Temporal variations of extreme precipitation events in the United States: 1895–2000
Authors: Kunkel Kenneth E. , Easterling David R. , Redmond Kelly , Hubbard Kenneth
Published: September 2003

A newly available data set of daily precipitation observations was used to study the temporal variability of the frequency of short‐duration extreme precipitation events for 1895–2000 in the conterminous United States. Event durations of 1, 5, 10, and 30 day and return periods of 1, 5, and 20 year were analyzed. For all combinations of duration and return period, heavy precipitation frequencies were relatively high during the late 19th/early 20th Centuries, decreasing to a minimum in the 1920s and 30s, followed by a general increase into the 1990s. The frequencies at the beginning of the 20th Century were nearly as high as during the late 20th Century for some combinations of duration and return period, suggesting that natural variability cannot be discounted as an important contributor to the recent high values. Extensive quality control of data and Monte Carlo testing was performed to provide confidence in the reality of the early period high frequencies.
Can friction coefficient be estimated from cross stream flow structure in tidal channels?
Authors: Li C.
Published: September 2003

Bottom drag coefficient is usually estimated from vertical structures of horizontal flows. Analytic models have demonstrated that bottom friction causes cross channel variations of velocity such that the amplitude of the along channel velocity increases with depth, and the velocity in shallow water has a phase lead, i.e. flood and ebb occur earlier in shallow water along the same cross channel transect. Based on these facts, we have developed a simple method to estimate the drag coefficient using lateral flow structure. The method is verified by data from a vessel‐towed acoustic Doppler current profiler (ADCP) in unstratified tidal channels of Georgia, US. The cross channel average of the drag coefficient is 4.55 × 10−3 (1 ± 18.6%), a reasonable value compared to previous results.
Vertical distribution of ozone at Marambio, Antarctic Peninsula, during 1987–1999
Authors: Karhu Juha A. , Taalas Petteri , Damski Juhani , Kaurola Jussi , Ginzburg Máximo , Villanueva Carlos A. , Piacentini Eduardo , Garcia Mario
Published: September 2003

The vertical distribution of ozone at Marambio (64°S, 56°W) has been studied using ozonesonde measurements for 1990–1999. Total ozone has been studied using Dobson spectrophotometer measurements for 1987–1999. Marambio is well placed to study the Antarctic ozone depletion mechanism because it is frequently located inside, outside, and in the edge region of the polar vortex and sees the early return of sunshine in late winter. The ozone data have been classified according to the location of the polar vortex with respect to Marambio. The vortex edge definition based on potential vorticity (PV) and its gradient has been compared to two other methods. The method used here gives better results than the use of predetermined PV limits or the use of maximum PV gradient only. The Marambio total ozone records have been compared to the 11‐year (1957–1967) record of the nearby Argentine Islands (65°S, 64°W) to estimate long‐term ozone changes over the Antarctic Peninsula. The largest decreases of ozone during 1987–1999 were observed in the lower stratosphere in July–August in the polar vortex edge region, as well as inside the vortex in September–October. Our analysis does not give indications of an ozone recovery so far. The Marambio data show that since the mid‐1990s the magnitude of the seasonal ozone decline inside and in the edge region of the vortex has remained at roughly a constant level. Outside the vortex in September–December, as well as from midsummer to midwinter (January–June), ozone levels have remained practically unchanged during the whole period from 1987 until 1999.
Application of the antenna theory model to a tall tower struck by lightning
Authors: Kordi Behzad , Moini Rouzbeh , Janischewskyj Wasyl , Hussein Ali M. , Shostak Volodymyr O. , Rakov Vladimir A.
Published: September 2003

The interaction of lightning with the 553‐m high CN Tower in Toronto is modeled using the antenna theory model. A simple lossless wire structure is used to represent the tower. The return‐stroke channel is modeled as a lossy vertical antenna attached to the tower top. The lossy antenna and the wire structure representing the tower are assumed to be fed at their junction point by a voltage source. The voltage waveform of this source is selected so that the source current resembles a typical lightning current waveform not influenced by the presence of the tall strike object. An electric field integral equation in the time domain is employed to calculate the lightning return stroke current distribution along the CN Tower and along the lightning channel. The equation is solved numerically using the method of moments. The lightning current flowing in the tower at the 474‐m level above ground, predicted by the antenna theory (AT) model, compares favorably with the measurements conducted at the CN Tower. Once the temporal and spatial distributions of the current along the tower and along the lightning channel are determined, the corresponding remote electromagnetic fields are computed. Waveshapes of model‐predicted electric and magnetic fields at a distance of 2 km from the tower are in good agreement with measurements. The contribution of the tower to the electric and magnetic fields at 2 km is about four to five times the contribution of the lightning channel.
Interpretation of aerosol particle fluxes over a pine forest: Dry deposition and random errors
Authors: Rannik Ü. , Aalto P. , Keronen P. , Vesala T. , Kulmala M.
Published: September 2003

Aerosol particle fluxes were measured above a Scots pine forest in southern Finland by the eddy covariance (EC) technique. Condensational particle counter (CPC) was used in the EC system to detect the total particle number concentration in the size interval from about 10 nm to 500 nm. Turbulent records of velocity components and concentrations as well as fluxes were analysed for non‐stationary behaviour by using quality tests. Aerosol particle concentration revealed often non‐stationary behaviour, more frequently than other scalars like temperature, water vapour and carbon dioxide. During stationary episodes most of the flux estimates indicated deposition of particles into forest. Size‐dependent deposition velocities were estimated by using auxiliary measurements of particle size distribution. A semi‐empirical deposition model explained most of the variance observed in particle fluxes when size spectrum was dominated by below 100 nm particles. However, deposition velocity estimates for above 100 nm particles remained very uncertain.
Deriving flow directions for coarse‐resolution (1–4 km) gridded hydrologic modeling
Authors: Reed Seann M.
Published: September 2003

The National Weather Service Hydrology Laboratory (NWS‐HL) is currently testing a grid‐based distributed hydrologic model at a resolution (4 km) commensurate with operational, radar‐based precipitation products. To implement distributed routing algorithms in this framework, a flow direction must be assigned to each model cell. A new algorithm, referred to as cell outlet tracing with an area threshold (COTAT) has been developed to automatically, accurately, and efficiently assign flow directions to any coarse‐resolution grid cells using information from any higher‐resolution digital elevation model. Although similar to previously published algorithms, this approach offers some advantages. Use of an area threshold allows more control over the tendency for producing diagonal flow directions. Analyses of results at different output resolutions ranging from 300 m to 4000 m indicate that it is possible to choose an area threshold that will produce minimal differences in average network flow lengths across this range of scales. Flow direction grids at a 4 km resolution have been produced for the conterminous United States.
Plasmodium falciparum EBA‐140 kDa protein peptides that bind to human red blood cells
Authors: Rodriguez L.E. , Ocampo M. , Vera R. , Puentes A. , Lopez R. , Garcia J. , Curtidor H. , Valbuena J. , Suarez J. , Rosas J. , Rivera Z. , Urquiza M. , Patarroyo M.E.
Published: September 2003

Abstract:  The erythrocyte‐binding antigen 140 (EBA140) sequence was chemically synthesized in 61 20‐mer sequential peptides covering the entire 3D7 protein strain, each of which was tested in erythrocyte‐binding assays. Peptides 26135, 26144, 26147, 26160, 26170 and 26177 presented high erythrocyte‐binding activity, with affinity constants ranging from 350 to 750 nm. Critical erythrocyte‐binding residues were determined by competition‐binding assays with glycine analogous peptides. Cross‐linking assays with SDS‐PAGE from high erythrocyte membrane protein binding peptides showed that all these peptides bound specifically to 25, 52 and 75 kDa erythrocyte membrane proteins. The nature of these receptor sites was studied in peptide‐binding assays using enzyme‐treated erythrocytes, showing that these protein receptors are susceptible to structural changes provoked by enzyme treatment (neuraminidase, trypsin or chymotrypsin). Inhibition invasion assays in ‘in vitro’ cultures showed that all specific high binding sequences were able to inhibit invasion by 11–69% at 200 μm concentration.
Conformational analysis of endomorphin‐1 by molecular dynamics methods
Authors: Leitgeb B. , Szekeres A. , Tóth G.
Published: September 2003

Abstract: Endomorphin‐1 (EM1, H‐Tyr‐Pro‐Trp‐Phe‐NH2) is a highly potent and selective agonist for the μ‐opioid receptor. A conformational analysis of this tetrapeptide was carried out by simulated annealing and molecular dynamics methods. EM1 was modeled in the neutral (NH2‐) and cationic (NH‐) forms of the N‐terminal amino group. The results of NMR measurements were utilized to perform simulations with restrained cis and trans Tyr1‐Pro2 peptide bonds. Preferred conformational regions in the Φ2–Ψ2, Φ3–Ψ3 and Φ4–Ψ4 Ramachandran plots were identified. The g(+), g(−) and trans rotamer populations of the side‐chains of the Tyr1, Trp3 and Phe4 residues were determined in χ1 space. The distances between the N‐terminal N atom and the other backbone N and O atoms, and the distances between the centers of the aromatic side‐chain rings and the Pro2 ring were measured. The preferred secondary structures were determined as different types of β‐turns and γ‐turns. In the conformers of trans‐EM1, an inverse γ‐turn can be formed in the N‐terminal region, but in the conformers of cis‐EM1 the N‐terminal inverse γ‐turn is absent. Regular and inverse γ‐turns were observed in the C‐terminal region in both isomers. These β‐ and γ‐turns were stabilized by intramolecular H‐bonds and bifurcated H‐bonds.
Bifunctional indole‐3‐acetyl transferase catalyses synthesis and hydrolysis of indole‐3‐acetyl‐myo‐inositol in immature endosperm of Zea mays
Authors: Kowalczyk Stanislaw , Jakubowska Anna , Zielińska Elżbieta , Bandurski Robert S.
Published: September 2003

1‐O‐(indole‐3‐acetyl)‐β‐d‐glucose: myo‐inositol indoleacetyl transferase (IA‐myo‐inositol synthase) is an important enzyme in IAA metabolism. This enzyme catalyses the transfer of the indole acetyl (IA) moiety from 1‐O‐(indole‐3‐acetyl)‐β‐d‐glucose to myo‐inositol to form IA‐myo‐inositol and glucose. IA‐myo‐inositol synthase was purified to an electrophoretically homogenous state from maize liquid endosperm by fractionation with ammonium sulphate, anion‐exchange, adsorption on hydroxylapatite, affinity chromatography on ConA‐Sepharose, preparative PAGE and isoelectric focusing. We thus obtained two enzyme preparations which differ in their Rf on 8% polyacrylamide gel. The preparation of Rf 0.36 contained a single 56.4 kDa polypeptide, whereas the preparation of Rf 0.39 consisted of two polypeptides of 56.4 and 53.5 kDa. Both purified preparations of IAInos synthase also exhibited the activity of an IAInos hydrolase, showing that the dual activity was associated with a single protein. Results of gel filtration and analytical SDS‐PAGE suggest that the native enzyme exists as both a monomeric (65 kDa) and homo‐ or heterodimeric form (110–130 kDa). Analysis of peptide maps and amino acid sequences of two 21 amino‐acid peptides showed that polypeptides of 56.4 and 53.5 kDa have the same primary structure and that the 3 kDa difference in molecular mass is probably caused by different glycosylation levels. Comparison of this partial and internal amino acid sequence with sequences of other plant acyltransferases indicated similarity to several proteins which belonged to the serine carboxypeptidase‐like (SCPL) acyltransferase family.
Exogenous ethylene stimulates the long‐term expression of genes related to anthocyanin biosynthesis in grape berries
Authors: El‐Kereamy Ashraf , Chervin Christian , Roustan Jean‐Paul , Cheynier Veronique , Souquet Jean‐Marc , Moutounet Michel , Raynal José , Ford Christopher , Latché Alain , Pech Jean‐Claude , Bouzayen Mondher
Published: September 2003

The treatment of grape berries (Vitis vinifera L. cv. Cabernet Sauvignon) with the ethylene‐releasing compound, 2‐chloroethylphosphonic acid (2‐CEPA), at veraison is a method known to enhance grape skin colour. We observed that it produced a 6‐fold increase, up to 30 pmol g−1 FW, of the cluster internal ethylene compared to untreated controls within the 24 h following treatment. This ethylene upsurge was associated with increased levels of chalcone synthase (CHS) and flavanone 3‐hydroxylase (F3H) transcripts, which persisted over the following 20 days. Transcript levels of leucoanthocyanidin dioxygenase (LDOX) and UDP glucose‐flavonoid 3‐O‐glucosyl transferase (UFGT) were similarly enhanced by 2‐CEPA, although to a lesser extent. The effect on UFGT was confirmed at the protein level by an immunoblot analysis. The transcript accumulation of dihydroflavonol 4‐reductase (DFR) was unaffected by 2‐CEPA treatment. Examination of the levels of CHS, F3H and UFGT mRNAs in berries during bunch exposure to ethylene, revealed elevated levels of each transcript within the first 6 h of treatment when compared to nonethylene‐treated controls. HPLC analyses of berry skin extracts showed that levels of each of the anthocyanins analysed (delphinidin, cyanidin, petunidin, peonidin and malvidin) increased over the 10 days following the ethylene burst, and decreased thereafter. However, anthocyanin levels at harvest were still higher in ethylene treated grapes than in controls. This data is the first evidence that ethylene triggers gene expression related to anthocyanin synthesis in grapes, and in addition, our results also confirm the existence of other regulatory modes in the anthocyanin biosynthetic pathway.
Survey of wound‐induced ethylene production by excised root segments
Authors: Cabrera Roberto M. , Saltveit Mikal E.
Published: September 2003

Ethylene production was measured from excised 10‐mm apical and subapical root segments from 50 cultivars in 19 species of 7 families. Monocotyledonous species tended to have much lower rates of ethylene production than dicotyledonous species. Ethylene production was generally higher in apical root segments than in subapical segments within 1 h of wounding. However, cultivars of Cucumis melo, C. sativus, Helianthus annuus, Hibiscus esculentus, and Zea mays had higher rates of ethylene production from subapical segments. In apical root segments, Phaseolus aureus cv. Berken had the highest ethylene production rate (76.7 ηl g−1 h−1), while Zea mays cv. Silver Queen had the lowest rate (0.6 ηl g−1 h−1). In subapical root segments, Cucumis sativus cv. Armenian had the highest rate (55.7 ηl g−1 h−1), while Zea mays cv. Silver Queen again had the lowest rate (0.6 ηl g−1 h−1). The many different responses in magnitude and kinetics of wound‐induced ethylene production among the species, cultivars and tissues should provide interesting and useful systems with which to study wound responses and induced ethylene production.
SAG2 and SAG12 protein expression in senescing Arabidopsis plants
Authors: Grbić Vojislava
Published: September 2003

During leaf senescence, nutrients are remobilized from the senescing tissues to the growing parts of the plant. Many senescence‐associated genes (SAGs) were identified based on the induction of their transcripts. However, little is known about the protein expression of the corresponding genes. We have raised antibodies against two Arabidopsis SAGs, SAG2 and SAG12, which encode putative cysteine proteases. The SAG2 antibodies recognized a 29‐kDa protein that was abundant in senescing leaves, but was also present at low levels in green tissues. SAG12 antibodies labelled a 38‐kDa protein present only in senescent leaves. The protein expression of these SAGs parallels their mRNA expression patterns, indicating that control of SAG2 and SAG12 is at the level of transcription or transcript stability. In addition, we found that SAGs are induced during stem senescence with delayed kinetics of their expression relative to leaf expression, suggesting that age‐dependent factor(s) regulating the onset of senescence in Arabidopsis may act in tissue‐dependent manner.
Low irradiance modifies the effect of water stress on survival and growth‐related parameters during the early developmental stages of buckwheat (Fagopyrum esculentum)
Authors: Delpérée C. , Kinet J. M. , Lutts S.
Published: September 2003

In order to characterize physiological modifications encountered by buckwheat plants exposed to both drought and low‐light stresses, seedlings (cv. La Harpe) were exposed under controlled environmental conditions, to a progressive decline in soil volumetric water content under two light regimes: low irradiance (80 µmol m−2 s−1) or moderate irradiance (160 µmol m−2 s−1). Phenological evolution of the whole plant until the macroscopic appearance of the reproductive structure and physiological properties of leaves in relation to their position on the main axis were quantified. Water stress reduced net assimilation rate (NAR) before specific leaf area (SLA) and induced a decrease in stomatal conductance (gl) and carbon isotope discrimination (Δ). Water consumption by stressed plants was similar under both light treatments. Water‐stressed plants under moderate irradiance exhibited higher growth, NAR, osmotic adjustment, and lower SLA than plants maintained under low irradiance. However, the former died after 27 days of treatment while the latter still remained alive until the experiment was discontinued (40 days). We concluded that the physiological strategy adopted by the water‐stressed plants maintained under moderate irradiance did not afford a long‐term advantage in terms of survival. The effects of a combination of low‐light and water stress on chlorophyll concentration and carbon isotope discrimination (Δ) are discussed in relation to growth parameters.
Changes in phosphatidylinositol and phosphatidylinositol monophosphate kinase activities during the induction of somatic embryogenesis in Coffea arabica
Authors: Ek‐Ramos María Julissa , Racagni‐Di Palma Graciela , Hernández‐Sotomayor S. M. Teresa
Published: September 2003

Evidence was obtained for the presence of phosphatidylinositol (PIK) and phosphatidylinositol monophosphate kinase (PIPK) at different developmental stages during somatic embryogenesis in Coffea arabica L. by in vitro phosphorylation of endogenous lipids in the presence of [γ‐32P]ATP followed by thin‐layer chromatography. The results indicate the existence of a relationship between the development stages that were analysed and the kinases found. In cells without differentiated structures (EC, embryogenic calli) phosphatidylinositol kinase and phosphatidylinositol monophosphate 5‐kinase (EC 2.7.1.68) activities were present. These activities increased significantly in the first differentiated stage (PREG, preglobular structures) and decreased as the development stages advanced. Phosphatidylinositol monophosphate (PIP) formation decreased from the globular (GLO) to the cotyledonary (COT) stage. The PIP fraction contained both isomers, PI 3‐P and PI 4‐P. This demonstrates PI3K (EC 2.7.1.137) and PI4K (EC 2.7.1.67) activity during somatic embryogenesis in Coffea arabica L. When wortmannin, an inhibitor of PI3K and PI4K activities, was included in an in vitro assay, a dose‐dependent inhibition of the formation of both isomers was observed. The addition of wortmannin to the induction medium during the PREG stage reduced the number of normal embryos. Our results suggest that PI and PIP kinases and the formation of certain phosphoinositides may play roles in the regulation of somatic embryo development in Coffea arabica L.
Dark chilling increases glucose‐6‐phosphate dehydrogenase activity in soybean leaves
Authors: Van Heerden Philippus D. R. , De Villiers Magdaleen F. , Van Staden Johannes , Krüger Gert H. J.
Published: September 2003

Available evidence suggests that the stress‐induced increase in the activity of glucose‐6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49), the key regulatory enzyme of the oxidative pentose phosphate pathway, might often be related to the presence of plant water deficit. The response of G6PDH to dark chilling in chilling sensitive plant species is still unknown. In this communication we report on this response and its dependence on the presence of chill‐induced drought stress. A chilling sensitive soybean (Glycine max L. Merr.) genotype was exposed to dark chilling of the entire plant (whole‐chilled) or only the shoots and leaves (shoot‐chilled). The development of chill‐induced drought stress upon illumination was quantified by measurement of proline and relative water content (RWC). Chill‐induced drought stress (decrease in RWC and increase in proline content) developed with time in whole‐chilled plants, but not in shoot‐chilled plants. The response of the above‐mentioned treatments on G6PDH activity in fully expanded leaves was assessed. In parallel, the effects on CO2 assimilation, PSII activity and chloroplast fructose‐1,6‐bisphosphatase (FBPase EC 3.1.3.11) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco EC 4.1.1.39) activity were quantified. A decrease in CO2 assimilation rate, FBPase activity and ribulose‐1,5‐bisphosphate (RuBP) content was observed in whole‐chilled but not in shoot‐chilled plants. However, in shoot‐chilled plants regulation of diurnal PSII activity was altered. The increase in the activation state of NADP‐dependent malate dehydrogenase (NADP‐MDH EC 1.1.1.82) in shoot‐chilled plants suggests an increase in stromal redox state. Although the two different dark chilling treatments resulted in distinct physiological and biochemical effects, both induced an increase in foliar G6PDH activity, suggesting an important role of this enzyme during and following dark chilling stress, irrespective of the presence of chill‐induced drought stress.
Ecophysiological responses of two Mediterranean shrubs, Erica multiflora and Globularia alypum, to experimentally drier and warmer conditions
Authors: Llorens Laura , Peñuelas Josep , Estiarte Marc
Published: September 2003

A new approach was used to experimentally dry and warm a Mediterranean shrubland. By means of automatically sliding curtains, the drought period was extended by excluding rain over the two growing seasons (spring and autumn), and passive warming was created by avoiding infra‐red dissipation at night over the whole year. The aim of the study was to test how a future extended drought period and an increase in temperatures could affect the photosynthetic and water use strategies of two co‐occurring Mediterranean shrubs, Erica multiflora and Globularia alypum, which are common species of the dry coastal shrublands. The shoot water potential, leaf gas exchange rates and chlorophyll a fluorescence of plants was monitored seasonally during two years (1999–2001). In addition we measured the photosynthetic response curves to light and CO2 in autumn 2001 and the foliar N concentration and leaf C and N stable isotopes in summer 1999 and 2000. Droughted plants of both shrub species showed lower shoot water potentials, transpiration rates and stomatal conductances than control plants, although there was a high seasonal variability. Drought treatment reduced significantly the overall leaf net photosynthetic rates of E. multiflora, but not of G. alypum. Droughted plants of E. multiflora also showed lower leaf net photosynthetic rates in response to light and CO2 and lower carboxylation efficiency than controls, but there was no significant effect of drought on its overall photosystem II (PSII) photochemical efficiency. Although warming treatment did not affect the leaf net photosynthetic rates of the two species overall the study, it increased significantly the carboxylation efficiency and leaf net photosynthetic rates of G. alypum plants in response to CO2 levels in autumn 2001. In addition, warming treatment increased the potential photochemical efficiency of PSII (Fv/Fm) of both species (but especially of G. alypum) at predawn or midday and mainly in autumn and winter. Thus, the results suggest that drier conditions might decrease the annual productivity of these Mediterranean shrubs, particularly of E. multiflora, and that future warming could alleviate the present low temperature constraints of the photosynthetic performance of the two studied species, but especially of G. alypum, during the colder seasons. Ultimately, drier and warmer conditions in the near future may change the competitive relationship among these species in such Mediterranean ecosystems.
Metabolism of gibberellin A19 is under photoperiodic control in Populus, Salix and Betula, but not in daylength‐insensitive Populus overexpressing phytochrome A
Authors: Mølmann Jørgen A. , Berhanu A. T. , Stormo Svein K. , Ernstsen Arild , Junttila Olavi , Olsen Jorunn E.
Published: September 2003

Application experiments have suggested that short‐day‐induced cessation of elongation growth in trees is caused by photoperiodic regulation of the conversion of gibberellin GA19 to GA20. In the present study we examined further the photoperiodic control of GA metabolism in trees with focus on the conversion of GA19 in Salix pentandra, hybrid aspen (Populus tremula × tremuloides) and silver birch (Betula pendula) using [17,17‐2H2]‐GA19 or unlabelled GAs in application studies. GA20 and GA1 were able to restore growth also in hybrid aspen and silver birch under short days (SD), whereas GA19 had no or only a very small activity. Contrary to hybrid aspen and S. pentandra, the activity of GA20 in silver birch was significantly lower than that of GA1. Gas chromatography‐mass spectrometry (GC‐MS) analysis revealed a smaller turnover of [2H2]‐GA19 in SD than in long days (LD) in hybrid aspen. No such difference in turnover of [2H2]‐GA19 was observed in photoperiod‐insensitive hybrid aspen overexpressing PHYA. Application of unlabelled GAs to seedlings of S. pentandra, hybrid aspen and silver birch under SD followed by quantification of metabolites by GC‐MS analysis, showed that applied GA19 was not readily converted to GA20 and GA1. Although the sensitivity to GAs is also known to decrease under SD, the present data are in favour of a photoperiodic regulation of the metabolism of GA19in vivo in the woody species S. pentandra, hybrid aspen and silver birch. The data might also suggest that silver birch differs from S. pentandra and hybrid aspen by exhibiting a possible photoperiodic control also of the conversion of GA20 to GA1.
Nitrogenase activity and root nodule metabolism in response to O2 and short‐term N2 deprivation in dark‐treated Frankia‐Alnus incana plants
Authors: Lundquist Per‐Olof , Näsholm Torgny , Huss‐Danell Kerstin
Published: September 2003

Inhibition of nitrogenase (EC 1.18.6.1) activity by O2 has been suggested to be an early response to disturbance in carbon supply to root nodules in the Frankia‐Alnus incana symbiosis. Intact nodulated root systems of plants kept in prolonged darkness of 22 h were used to test responses to O2 and short‐term N2 deprivation (1 h in Ar:O2). By using a Frankia lacking uptake hydrogenase it was possible to follow nitrogenase activity over time as H2 evolution in a gas exchange system. Respiration was simultaneously recorded as CO2 evolution. Dark‐treated plants had lower initial nitrogenase activity in N2:O2 (68% of controls), which declined further during a 1‐h period in the assay system in N2:O2 at 21 and 17% O2, but not at 13% O2. When dark‐treated plants were deprived of N2 at 21 and 17% O2 nitrogenase activity declined rapidly to 61 and 74%, respectively, after 20 min, compared with control plants continuously kept in their normal light regime. In contrast, there was no decline in dark‐treated plants at 13% O2, and only a smaller and temporary decline in control plants at 21% O2. When dark‐treated plants were kept at 21% O2 during 45 min prior to N2 deprivation at 17% O2 the decline was abolished. This supports the idea that the decline in nitrogenase activity observed in N2:O2 at 21% O2 and during N2 deprivation was caused by O2, which affected a sensitive nodule fraction. Nodule contents of the amino acids Gln and Cit decreased during N2 deprivation, suggesting decreased assimilation of NH4+. Contents of ATP and ADP in nodules were not affected by short‐term N2 deprivation. ATP/ADP ratios were about 5 indicating a highly aerobic metabolism in the root nodule. We conclude that nitrogenase activity of Alnus plants exposed to prolonged darkness becomes more sensitive to inactivation by O2. It seemed that dark‐treated plants could not adjust their nodule metabolism at higher perceived pO2 and during cessation of NH4+ production.
Study of pectin esterase and changes in pectin methylation during normal and abnormal peach ripening
Authors: Lurie Susan , Zhou Hong‐Wei , Lers Amnon , Sonego Lilian , Alexandrov Svetlana , Shomer Ilan
Published: September 2003

Peach fruit (Prunus persica cv. Hermosa) were allowed to ripen immediately after harvest or after 30 days of 0°C storage. The fruits lost 75–80% of their firmness after 5 days at 20°C. During ripening after harvest there was a loss of both uronic acid and methyl groups from the cell wall. Cell wall labelling with JIM 7, a monoclonal antibody which recognized pectins with a high degree of methylation, was lower in ripe fruits than in freshly harvested fruits. However, ripe fruit cell walls did not cross‐react with JIM 5, which recognizes pectins with low methylation. During storage, de‐methylation occurred and in fruit ripened after storage there was little further change in pectin methylation or pectin content in the cell walls. The labelling of stored or stored plus ripened cell walls with JIM 7 was similar, but the cell walls of fruit ripened after storage showed some low cross‐reactivity with JIM 5. The in vitro activity and mRNA abundance of pectin esterase (EC 3.1.1.11) was not correlated with the amount of de‐esterification as measured chemically or by immuno‐labelling in the cell walls. Eighty percent of the fruits which ripened after storage developed a woolly texture. It is suggested that woolliness is due to de‐esterification of pectins, not accompanied by depolymerization, which leads to the formation of a gel‐like structure in the cell wall.
Spatial and temporal changes in multiple hormone groups during lateral bud release shortly following apex decapitation of chickpea (Cicer arietinum) seedlings
Authors: Mader Johanna C. , Emery R. J. Neil , Turnbull Colin G N.
Published: September 2003

Although the co‐ordination of promotive root‐sourced cytokinin (CK) and inhibitory shoot apex‐sourced auxin (IAA) is central to all current models on lateral bud dormancy release, control by those hormones alone has appeared inadequate in many studies. Thus it was hypothesized that the IAA : CK model is the central control but that it must be considered within the relevant timeframe leading to lateral bud release and against a backdrop of interactions with other hormone groups. Therefore, IAA and a wide survey of cytokinins (CKs), were examined along with abscisic acid (ABA) and polyamines (PAs) in released buds, tissue surrounding buds and xylem sap at 1 and 4 h after apex removal, when lateral buds of chickpea are known to break dormancy. Three potential lateral bud growth inhibitors, IAA, ABA and cis‐zeatin 9‐riboside (ZR), declined sharply in the released buds and xylem following decapitation. This is in contrast to potential dormancy breaking CKs like trans‐ZR and trans‐zeantin 9‐riboside 5′phosphate (ZRMP), which represented the strongest correlative changes by increasing 3.5‐fold in xylem sap and 22‐fold in buds. PAs had not changed significantly in buds or other tissues after 4 h, so they were not directly involved in the breaking of bud dormancy. Results from the xylem and surrounding tissues indicated that bud CK increases resulted from a combination synthesis in the bud and selective loading of CK nucleotides into the xylem from the root.
Phenylpropanoid deficiency affects the course of plant acclimation to cold
Authors: Solecka Danuta , Kacperska Alina
Published: September 2003

The effects of phenylpropanoid deficiency on plant growth, photosynthetic efficiency of the photosystem II and freezing tolerance of leaves were studied during acclimation of winter oilseed rape plants (Brassica napus L. var. oleifera L. cv Jantar) at low temperature. Application of 2‐amino‐2‐indanophosphonic acid inhibited phenylalanine ammonia‐lyase (E.C. 4.3.1.5) activity by about 90%. This was followed by a marked reduction of soluble phenolics (in particular hydroxycinnamic acids) and anthocyanins in leaves. Inhibition of the cold‐promoted incorporation of ferulic acid into cell walls was also observed. The reduction of phenylpropanoid contents was associated with: (1) partial abrogation of the cold‐induced growth effects, such as inhibition of leaf fresh weight increments and accumulation of dry matter, proteins and cell walls; (2) decreased photochemical efficiency of photosystem II in low temperature‐affected leaves; and (3) decreased ability of leaves to develop tolerance to the extracellular formation of ice. These findings are discussed in terms of phenylpropanoids' role in plant responses to cold (> 0°C) and freezing temperatures.
Over‐reduction of cultured tobacco cells mediates changes in respiratory activities
Authors: Zhang Qisen , Moore Catherine S. , Soole Kathleen L. , Wiskich Joseph T.
Published: September 2003

Regulation of respiration in Nicotiana tabacum suspension cultures was studied using the respiratory inhibitor myxothiazol and the oxidative phosphorylation uncoupler carbonylcyanide p‐(trifluoromethoxy)phenylhydrazone (FCCP). Myxothiazol (2 μM) or FCCP (2 μM) almost completely inhibited cell growth for about 24 h, after which the cultures could resume a growth rate similar to that of the untreated culture. During the first 18 h of myxothiazol treatment, rates of cellular respiration were similar to control cultures. The capacity of the alternative pathway was significantly higher than control 2–3 h after myxothiazol treatment and increased further after 18 h. The capacity of the alternative pathway in FCCP‐treated tobacco cells also increased but to a lesser extent. ATP/ADP ratios decreased for at least 9 h after either myxothiazol or FCCP treatments, which triggered an increase in glycolytic flux and an over‐reduction of cultured tobacco cells, as demonstrated by increases in levels of reactive oxygen species and cellular ethanol. The generation of reactive oxygen species served as a signal for an induction of alternative oxidase, which in turn relieved the aerobic fermentation and over‐reduction of the cells.