bluuebunny/crossref_metadata_2025 huggingface dataset:
Shallow velocity–depth model imaging by refraction tomography1
Authors: Belfer Igor , Landa Evgeny
Published: April 2006

A tomographic imaging technique combined with coherence inversion is proposed for constructing a near‐surface model from refraction events. A model obtained from coherence inversion serves as a good background model for the tomographic reconstruction. A simultaneous iterative reconstruction technique (SIRT) algorithm was used for this purpose. This is a simple algorithm and can be easily adapted to irregular acquisition geometry and limited angular aperture. Using synthetic data it was shown that the proposed procedure can be used for determination of local velocity anomalies in a shallow subsurface. The technique was also tested on a real data set.
A case example of near‐surface correction for multicomponent VSPS
Authors: Zeng Xinwu , MacBeth Colin
Published: April 2006

A deterministic near‐surface correction procedure is developed for multicomponent VSP data, shot using directional sources and recorded using three‐component receivers. The method is capable of removing unwanted effects of acquisition such as unequal source strengths or misorientations, but may also remove near‐surface multiples and anisotropy. This is of considerable benefit for obtaining accurate and consistent estimates of subsurface anisotropy from different source combinations. Application of the technique is illustrated using a dataset from the Romashkino reservoir in Russia, where three or four different directional sources are used at the same source locations. The technique corrects for the large discrepancies which exist between the estimates obtained using different source combinations. Application of the technique to three wells in the survey region reveals a nearly isotropic subsurface, except for a few isolated zones of moderate to high (2 to 8%) anisotropy which lie close to the expected depth for the reservoir. Although there is no significant correlation with the production figures for each well, the qS1 polarization azimuth within the reservoir does vary at each well location, suggesting that this may be a more sensitive indicator of reservoir Drocess.
A few case histories of subsurface imaging with EMAP as an aid to seismic processing and interpretation1
Authors: Warren Roy K.
Published: April 2006

The electromagnetic array profiling (EMAP) exploration method can be combined with a direct one‐dimensional inversion process for conversion to depth to produce a subsurface resistivity cross‐section. This cross‐section may then be interpreted in parallel with a seismic cross‐section to enhance the prediction of rock type and structure. In complex thrust environments and areas of shallow carbonate rocks, the EMAP method is often used to provide additional data either to help the seismic processor and/or to aid the seismic interpretation. In particular, the electromagnetic (EM) data can be used to build an independent seismic velocity file for depth migration.

Three EMAP test areas in the western United States are used to demonstrate such a use of EMAP as an expioration tool. The first shows how a velocity file is estimated from resistivity data for seismic depth migration processing in a complex thrust environment. In the second example, the method is applied in layer‐cake geology with high seismic velocity rocks at the earth's surface. The third example is another complex thrust environment, but in this case the velocity file derived from the resistivity data is used for stacking the seismic data.
Electromagnetic mapping of electrical conductivity beneath the Columbia basalts1
Authors: Morrison H. Frank , Shoham Yoram , Hoversten G. Michael , Torres‐Verdín Carlos
Published: April 2006

Sedimentary rocks beneath the Columbia River Basalt Group are recognized as having potential for oil and gas production, but the overlying layered basalts effectively mask seismic reflections from the underlying sediments. Four electromagnetic (EM) methods have been applied on profiles crossing Boylston Ridge, a typical east–west trending anticline of the Yakima Fold Belt, in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments. The EM surveys detected strong variations in resistivity within the basalts, and in particular the continuous magnetotelluric array profiling (EMAP) revealed resistivity lows beneath the surface anticlines. These low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile.

The controlled‐source EM surveys (in‐loop transient, long‐offset transient, and variable‐offset frequency‐domain) were designed in anticipation of relatively uniform high resistivity basalts, and were found to have been seriously distorted by the intrabasalt conductors discovered in the field. In particular, the resistivity sections derived from 1D inversions were found to be inconsistent and misleading. The EMAP survey provided the most information about the subsurface resistivity distribution, and was certainly the most cost‐effective. However, both controlled‐source and EMAP surveys call for accurate 2D or 3D inversion to accommodate the geological objectives of this project.
Transient electromagnetic vs. seismic prospecting—a correspondence principle1
Authors: de Hoop Adrianus T.
Published: April 2006

A correspondence principle is derived that relates the Green's functions (point‐receiver responses to point‐source excitations) for 2D transient diffusive electro‐magnetic fields with electric field in the vertical plane to 2D seismic waves (in the acoustic approximation) with particle velocity in the vertical plane in arbitrarily inhomogeneous media. The constituent medium parameters in the two cases are related via two global proportionality constants. The kernels in the integral operators that express the diffusion phenomenon in terms of the wave phenomenon are of a smoothing nature. The fact that they are explicitly known can be of importance to the inverse operation. The correspondence principle is the fundamental tool in comparing the spatial resolving powers in the two methods of geophysical prospecting.
Integrating long‐offset transient electromagnetics (LOTEM) with seismics in an exploration environment1
Authors: Strack K.‐M. , Vozoff K.
Published: April 2006

The applications of electromagnetics have increased in the past two decades because of an improved understanding of the methods, improved service availability, and the increased focus of exploration in the more complex reservoir characterization issues. For electromagnetic methods surface applications for hydrocarbon Exploration and Production are still a special case, while applications in borehole and airborne research and for engineering and environmental objectives are routine.

In the past, electromagnetic techniques, in particular deep transient electromagnetics, made up a completely different discipline in geophysics, although many of the principles are similar to the seismic one. With an understanding of the specific problems related to data processing initially and then acquisition, the inclusion of principles learned from seismics happened almost naturally. Initially, the data processing was very similar to seismic full‐waveform processing. The hardware was also changed to include multichannel acquisition systems, and the field procedures became very similar to seismic surveying. As a consequence, the integration and synergism of the interpretation process is becoming almost automatic.

The long‐offset transient electromagnetic (LOTEM) technique will be summarized from the viewpoint of its similarity to seismics. The complete concept of the method will also be reviewed. An interpretation case history that integrates seismic and LOTEM from a hydrocarbon area in China clearly demonstrates the limitations and benefits of the method.
Structural mapping in basin‐and‐range‐like geology by electromagnetic methods: a powerful aid to seismic
Authors: Galibert Pierre‐Yves , Guerin Roger , Andrieux Pierre
Published: April 2006

A case history is presented where electromagnetic (EM) methods were applied as a complement to seismic, for structural mapping in basin‐and‐range‐like geology: 366 five‐component magnetotelluric (MT) soundings were carried out together with 331 transient soundings (TDEM) along seismic lines.

Due to high structural complexity, seismic shows a number of limitations. For the same reasons, MT is highly perturbed and three specific interpretation techniques were comprehensively applied:

1. a classical correction of static effect using TDEM sounding, to determine the high‐frequency nondistorted apparent resistivities and thus the corrected tensor;

2. a so‐called regional correction based upon the same concept as the static effect, to transform distorted resistivity curves due to the horst/graben situation into plausible 1D curves, through the use of nomograms built for 2D H‐polarization situations;

3. a stripping technique which made it possible to map areas where a deep conductive Mesozoic shale was present below carbonates, at a depth of 3 km.

After the best MT interpretation was obtained along each line, it was integrated with seismic and with the results from two boreholes. A crude empirical law relating resistivity and acoustic velocity was established and the MT horizons were plotted on the two‐way traveltime seismic sections.

The final integrated cross‐sections obtained are undoubtedly of greater use to the explorationist than the initial seismic sections alone and two wells were accurately predicted.
Advances in the combined interpretation of seismics with magnetotellurics1
Authors: Nagy Zoltán
Published: April 2006

Five examples, obtained during exploration for hydrocarbons in the Pannonian Basin of Hungary, are used to show how the interpretation of seismic sections can be usefully complemented by results from MT surveys.

Selection of the most appropriate MT quantities, considered to be proper ‘MT attributes’ for the purpose of visualization as well as recognition of the subsurface structures and the different inversions of MT data is essential for practical integration of seismic and MT surveys.

A new technique providing a semiquantitive MT‐attribute pseudosection for the purpose of visualization of the subsurface structures is proposed. The procedure utilizes derivative functions of the phase of MT impedance for visualization and derives estimated depths from the Bostick transformation of Cagniard apparent resistivities.

On the basis of the MT‐attribute pseudosections, constructed from the phase derivatives and transformed resistivity data, depths are estimated for interfaces between geological formations with significant resistivity contrast. In particular examples, the interface between the Tertiary sediments and the older basement rocks as well as tectonic fracture zones with decreased resistivity can be resolved.
Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas
Authors: Sarasola José Hernán , Negro Juan José
Published: April 2006

Aim  The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting.

Location  Pampas grasslands, Argentina.

Methods  We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers.

Results  Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks).

Main conclusions  The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.
Improving generalized regression analysis for the spatial prediction of forest communities
Authors: Maggini Ramona , Lehmann Anthony , Zimmermann Niklaus E. , Guisan Antoine
Published: April 2006

Aim This study used data from temperate forest communities to assess: (1) five different stepwise selection methods with generalized additive models, (2) the effect of weighting absences to ensure a prevalence of 0.5, (3) the effect of limiting absences beyond the environmental envelope defined by presences, (4) four different methods for incorporating spatial autocorrelation, and (5) the effect of integrating an interaction factor defined by a regression tree on the residuals of an initial environmental model.

Location State of Vaud, western Switzerland.

Methods Generalized additive models (GAMs) were fitted using thegrasppackage (generalized regression analysis and spatial predictions,http://www.cscf.ch/grasp).

Results Model selection based on cross‐validation appeared to be the best compromise between model stability and performance (parsimony) among the five methods tested. Weighting absences returned models that perform better than models fitted with the original sample prevalence. This appeared to be mainly due to the impact of very low prevalence values on evaluation statistics. Removing zeroes beyond the range of presences on main environmental gradients changed the set of selected predictors, and potentially their response curve shape. Moreover, removing zeroes slightly improved model performance and stability when compared with the baseline model on the same data set. Incorporating a spatial trend predictor improved model performance and stability significantly. Even better models were obtained when including local spatial autocorrelation. A novel approach to include interactions proved to be an efficient way to account for interactions between all predictors at once.

Main conclusions Models and spatial predictions of 18 forest communities were significantly improved by using either: (1) cross‐validation as a model selection method, (2) weighted absences, (3) limited absences, (4) predictors accounting for spatial autocorrelation, or (5) a factor variable accounting for interactions between all predictors. The final choice of model strategy should depend on the nature of the available data and the specific study aims. Statistical evaluation is useful in searching for the best modelling practice. However, one should not neglect to consider the shapes and interpretability of response curves, as well as the resulting spatial predictions in the final assessment.
No relationship between microsatellite variation and neonatal fitness in Antarctic fur seals, Arctocephalus gazella
Authors: HOFFMAN J. I. , FORCADA J. , AMOS W.
Published: April 2006

Published studies of wild vertebrate populations have almost universally reported positive associations between genetic variation measured at microsatellite loci and fitness, creating the impression of ubiquity both in terms of the species and the traits involved. However, there is concern that this picture may be misleading because negative results frequently go unpublished. Here, we analyse the relationship between genotypic variation at nine highly variable microsatellite loci and neonatal fitness in 1070 Antarctic fur seal pups born at Bird Island, South Georgia. Despite our relatively large sample size, we find no significant association between three different measures of heterozygosity and two fitness traits, birth weight and survival. Furthermore, increasing genetic resolution by calculating parental relatedness also yields no association between genetic variation and fitness. Our findings are consistent with necropsy data showing that most pups die from starvation or trauma, conditions that are unlikely to be influenced strongly by genetic factors, particularly if the benefits of high heterozygosity are linked to immune‐related genes.
Chloroplast diversity in the genus Malus: new insights into the relationship between the European wild apple (Malus sylvestris (L.) Mill.) and the domesticated apple (Malus domestica Borkh.)
Authors: COART E. , VAN GLABEKE S. , DE LOOSE M. , LARSEN A. S. , ROLDÁN‐RUIZ I.
Published: April 2006

To unravel the relationship between the European wild apple, Malus sylvestris (L.) Mill., and its domesticated relative M. domestica Borkh., we studied chloroplast DNA variation in 634 wild and 422 domesticated accessions originating from different regions. Hybridization between M. sylvestris and M. domestica was checked using 10 nuclear microsatellites and a Bayesian assignment approach. This allowed us to identify hybrids and feral plants escaped from cultivation. Sixty‐eight genotypes belonging to 12 other wild Malus species, including 20 M. sieversii (Ledeb.) Roem. accessions were also included in the analysis of chloroplast diversity. Marker techniques were developed to type a formerly described duplication and a newly detected transversion in the matK gene. Chloroplast DNA variation was further investigated using PCR‐RFLP (Polymerase Chain Reaction‐Random Fragment Length Polymorphism), and haplotypes were constructed based on all mutational combinations. A closer relationship than presently accepted between M. sylvestris and M. domestica was established at the cytoplasmic level, with the detection of eight chloroplast haplotypes shared by both species. Hybridization between M. sylvestris and M. domestica was also apparent at the local level with sharing of rare haplotypes among local cultivars and sympatric wild trees. Indications of the use of wild Malus genotypes in the (local) cultivation process of M. domestica and cytoplasmic introgression of chloroplast haplotypes into M. sylvestris from the domesticated apple were found. Only one of the M. sieversii trees studied displayed one of the three main chloroplast haplotypes shared by M. sylvestris and M. domestica. This is surprising as M. sieversii has formerly been described as the main maternal progenitor of the domesticated apple. This study hereby reopens the exciting discussion on the origin of M. domestica.
MHC class IIB alleles contribute to both additive and nonadditive genetic effects on survival in Chinook salmon
Authors: PITCHER TREVOR E. , NEFF BRYAN D.
Published: April 2006

The genes of the major histocompatibility complex (MHC) are found in all vertebrates and are an important component of individual fitness through their role in disease and pathogen resistance. These genes are among the most polymorphic in genomes and the mechanism that maintains the diversity has been actively debated with arguments for natural selection centering on either additive or nonadditive genetic effects. Here, we use a quantitative genetics breeding design to examine the genetic effects of MHC class IIB alleles on offspring survivorship in Chinook salmon (Oncorhynchus tshawytscha). We develop a novel genetic algorithm that can be used to assign values to specific alleles or genotypes. We use this genetic algorithm to show simultaneous additive and nonadditive effects of specific MHC class IIB alleles and genotypes on offspring survivorship. The additive effect supports the rare‐allele hypothesis as a potential mechanism for maintaining genetic diversity at the MHC. However, contrary to the overdominance hypothesis, the nonadditive effect led to underdominance at one heterozygous genotype, which could instead reduce variability at the MHC. Our algorithm is an advancement over traditional animal models that only partition variance in fitness to additive and nonadditive genetic effects, but do not allocate these effects to specific alleles and genotypes. Additionally, we found evidence of nonrandom segregation during meiosis in females that promotes an MHC allele that is associated with higher survivorship. Such nonrandom segregation could further reduce variability at the MHC and may explain why Chinook salmon has one of the lowest levels of MHC diversity of all vertebrates.
Major histocompatibility complex class II variation in the giant panda (Ailuropoda melanoleuca)
Authors: WAN QIU‐HONG , ZHU LIANG , WU HUA , FANG SHENG‐GUO
Published: April 2006

Habitat destruction and human activity have greatly impacted the natural history of the giant panda (Ailuropoda melanoleuca). Although the genetic diversity of neutral markers has been examined in this endangered species, no previous work has examined adaptive molecular polymorphisms in the giant panda. Here, the major histocompatibility complex (MHC) class IIDRBlocus was investigated in the giant panda, using single‐strand conformation polymorphism (SSCP) and sequence analysis. Comparisons of DNA samples extracted from faecal and blood samples from the same individual revealed that the two materials yielded similar quantities and qualities of DNA, as well as identical SSCP patterns and allelic sequences, demonstrating the reliability of DNA isolation from panda faeces. Analysis of faecal samples from 60 giant pandas revealed relatively low number of alleles: seven alleles. However, the alleles were quite divergent, varying from each other by a range of 7–47 nucleotide substitutions (4–25 amino acid substitutions). Construction of a neighbour‐joining tree and comparisons amongDRBalleles from other species revealed that both similar and highly divergent alleles survived in the bottlenecked panda populations. Despite species‐specific primers used and excellent faecal DNA isolated, a lower level of heterozygosity than expected was still observed due to inbreeding. There were three types of evidence supporting the presence of balancing selection in the giant panda: (i) an obvious excess of nonsynonymous substitutions over synonymous at the antigen‐binding positions; (ii)trans‐species evolution of two alleles between the giant panda and other felids; and (iii) a more even distribution of alleles than expected from neutrality.
Sieve‐plate pores, open or occluded? A critical review
Authors: SPANNER D. C.
Published: April 2006

Abstract It is widely believed that there is a growing body of evidence that sieve plate pores in functioning phloem are open and quite free from obstruction. The arguments used to establish this idea are critically examined one by one and the conclusion is reached that it has very little foundation in published work. On the contrary, the view that sieve plate pores are delicately‐occluded with P‐protein in the angiosperms has much more evidence to substantiate it. Since ‘open’ and ‘occluded’ are physiologically defined this means that the pressure‐flow hypothesis must be regarded as seriously in doubt.
An apparatus for measuring photosynthetic quantum yields and quanta absorption spectra of intact plants
Authors: ÖQUIST G. , HÄLLGREN J.‐E. , BRUNES L.
Published: April 2006

Abstract An apparatus is described which consists of an assimilation chamber mounted in the centre of a light‐integrating Ulbricht sphere, irradiated through two fibreoptic light pipes. This arrangement provides totally diffuse radiation in the sphere. The quantum flux density in die sphere is measured by an integrating quantaspectrometer connected to the sphere by eight fibreoptic light pipes. The quantaspectrometer gives the spectral and the total quantum flux density in the sphere. By measuring the quantum flux density in the sphere before and after the insertion of a plant the number of absorbed quanta per unit time and plant area can be determined. In addition, the spectral distribution of the absorbed quantum flux density is obtained.

CO2‐assimilation per unit time and plant area is determined in the same apparatus. The totally diffuse radiation within the sphere minimizes mutual shading between branches and leaves. Hence, well‐defined light‐responsecurves of photosynthesis can be obtained by plotting the flux density of C02‐assimilation as a function of the absorbed quantum flux density, and the quantum yields of intact plants can be calculated.

Examples of photosynthetic quantum yield determinations and quanta absorption spectra are given for some plant species.
Sucrose transport by seedlings of Ricinus communis L: the export of sucrose from the cotyledons to the hypocotyl as a function of sucrose concentration in the cotyledons
Authors: WALDHAUSER J. , KOMOR E.
Published: April 2006

Abstract Using seedlings of Ricinus communis L. sucrose export from the cotyledons to the hypocotyl and roots was measured at different levels of sucrose concentration in the cotyledons. Sucrose export followed Michaelis‐Menten kinetics with a half‐saturation of export at 35 mM sucrose in the cotyledons. A maximal export flux of 90 μmol h−l g−1 fresh weight of the cotyledons was obtained. Both these figures coincide with those obtained for sucrose uptake into the cotyledons. It is postulated that sucrose uptake and sucrose export occurs by the same mechanism and possibly by the same cells which then would have to be part of the phloem. Since sucrose uptake has been shown to proceed as proton‐sucrose co‐transport, phloem loading might also be energized by the protonmotive potential difference. The data, furthermore, are difficult to reconcile with the symplastic route of phloem loading.
Photosynthetic characteristics of the leaves of ‘Golden Delicious’ appletrees
Authors: WATSON R. L. , LANDSBERG J. J. , THORPE M. R.
Published: April 2006

Abstract Using an open‐system leaf chamber, gas exchange measurements on attached leaves of 3‐4‐year‐old Golden Delicious apple trees, made through two seasons, provided data from which the parameters of a leaf photosynthesis model could be derived. The equation is:
image

where C1 is internal CO2 concentration and Qp is the incident quantum flux. There was considerable leaf to leaf variation in the values of the parameters but no clear seasonal trends were established. The initial slope (a) had an average value of about 2.5 × 10−3 mg μmol−1† (i.e. quantum yield ∼ 0.057); the mesophyll conductance (gm) was about 3.5 mm s−1 in extension leaves of trees carrying fruit and 2.5 mm s−1 in extension leaves of defruited trees. Differences between the values of gm for spur leaves with and without subtending fruits were not significant; 2.5 mm s−1 may be used. Dark respiration (Rd, mg m−2 s−1) increased exponentially with temperature (T°C); Rd∼ 0.006 exp (0.09 T). At saturating photon flux density Pn was linearly related to Ci, up to Ci∼ 250 mg m−3. Optimum temperatures for Pn were slightly different in the two years and were in the range 16‐26°C.
Correction of infra‐red gas analyser readings for changes in reference tube CO2 concentration
Authors: THORPE M. R.
Published: April 2006

Abstract The theoretical basis for correcting infra‐red gas analyser readings for changes in reference tube CO2 concentration is developed, but in practice the corrections made are empirical. Analyser gain (GA) is related to reference tube concentration (A) in hyperbolic manner. The constants in the equation are determined by plotting 1/GA against A. Calibration and operating procedure for a particular type of analyser are described and a numerical example given.
Mechanism of iron uptake by plants
Authors: BROWN JOHN C.
Published: April 2006

Abstract. Green plants require a continuous supply of Fe as they grow, because Fe does not not move from the older to the newer leaves. Soils do not lack Fe per se, but it may not be available to plants grown in alkaline soils. Plants are classed ‘Fe‐efficient’ if they respond to Fe‐deficiency stress by inducing biochemical reactions that make Fe available in a useful form, and ‘Fe‐inefficienT’ if they do not. Iron uptake induced in response to Fe stress involves release of hydrogen ions and reductants by the root. The lowered pH and presence of reductant at the root zone, along with reduction of Fe3+ to Fe2+ at the root surface, enables Fe2+ to be taken up primarily through the young lateral roots. Ferrous iron is present throughout the protozylem and may or may not have entered the root by a carrier. The root‐absorbed Fe2+ is oxidized to Fe3+ at the junction of the protoxylem and the metaxylem, chelated by citrate, and then transported in the metaxylem to the plant top. In the plant, the chemical reactions injuced by Fe‐deficiency stress may affect nitrate reductase activity, use of Fe from Fe3+ phosphate and chelating agents, and tolerance to heavy metals. An efficient mechanism for Fe uptake in roots appears to be important for the efficient use of Fe in plant tops.
Stomatal mechanics: volume changes during opening
Authors: SHARPE PETER J. H. , WU HSIN‐I
Published: April 2006

Abstract. The determination of guard cell lumen volume in relation to its geometric characteristic dimensions is presented. Stomatal movements can be divided into two stages: Spannungsphase and motorphase, with a transition point between them. During the Spannungsphase movement, the lumen volume increases as a result of the change in its geometric shape. At transition, the lumen volume is approximated by a portion of a circular tube with a rounded cross‐section. The volume increase during the motorphase comes from three different sources: expansion by wall stretching, increasing inner cross‐section of a guard cell by wall thinning, and polar expansion. The relationship between the aperture and the lumen volume is also established. The results set forth in this geometric model are essential to studies of the pressure interaction between a guard cell and its surrounding epidermal cells.
Photosynthesis and transpiration of an isolated tree: model and validation
Authors: THORPE M. R. , SAUGIER B. , AUGER S. , BERGER A. , METHY M.
Published: April 2006

Abstract. A model for the distribution of radiation incident on leaves in an isolated apple tree is presented. The simulated area of shadow cast by a tree compared well with measured values. The radiation model is combined with leaf models of photosynthesis and stomatal behaviour to simulate diurnal variations in the exchanges of carbon dioxide and water by the tree. Satisfactory correspondence was obtained when observed rates of transpiration and photosynthesis were compared with simulations. Further simulations indicated the diurnal patterns of transpiration and photosynthesis to be expected for trees with various shapes and leaf areas.
The carbon gain benefits of solar tracking in a desert annual
Authors: MOONEY H. A. , EHLERINGER J. R.
Published: April 2006

Abstract. A comparison between two sympatric winter desert annuals, Camissonia claviformis and Malvastrum rotundi folium showed that both gained similar amounts of carbon during a spring day, although by very different means. Camissonia has horizontally fixed leaves which have a very high photosynthetic capacity. The temperature optimum of photosynthesis for this species is near 20°C. Malvastrum has leaves with a lower photosynthetic capacity and a photosynthetic temperature optimum near 30°C. Leaves of the latter species remain normal to the sun throughout the course of the day. The tracking response and high temperature optimum for photosynthesis of Malvastrum result in a high daily carbon gain and also a high water‐use efficiency.
Recent advances in the insertion of DNA into higher plant cells
Authors: LURQUIN PAUL F. , KADO CLARENCE I.
Published: April 2006

Abstract Recent advances in the insertion, uptake and expression of exocellular DNA in plant protoplasts are reviewed. A comparison is made between plant and mammalian cell systems, in which exogenous DNA is processed during metabolism.
A storage role for albumins in pea cotyledons
Authors: MURRAY DAVID R.
Published: April 2006

Abstract It is widely held that the albumins of pea seeds are mainly enzyme proteins. In the present study of Pisum sativum cv. Greenfeast, certain major polypeptides confined to the albumin fraction from the cotyledons were shown to be degraded in vivo following germination, thus functioning as a reserve of amino nitrogen and carbon skeletons. A general definition of seed storage proteins is proposed, to encompass any protein present in major quantity in the seed which is degraded following imbibition, and for which no other function may be demonstrated.
Stomatal mechanics II*: material properties of guard cell walls
Authors: WU HSIN‐I , SHARPE PETER J. H.
Published: April 2006

Abstract In this revised formulation of guard cell mechanics, the material properties of the walls are re‐examined. The observed elastic anisotropy of guard cell walls can be explained by non‐random orientation of the cellulose micellae in the unstrained state. This micellar network is assumed to be loosely embedded in the wall matrix causing a two phase elongation process. In the first phase, the micellar network is ‘loose’ resulting in the walls behaving as an isotropic polymer when stretched. As the volume of the cell expands beyond some threshold, the network becomes ‘tightened’ and a second phase of elongation is initiated. During this anisotropic phase of cell expansion, wall elasticity reflectes changes in the orientation of the network to reduce its load.

Using the above theoretical analysis, a turgor‐pressure versus lumen volume relationship is simulated for Vicia faba. The relationship between aperture and water potential for this species is also established. The simulated results agree with the experimental evidence reported for Vicia faba. The estimated shear modulus of elasticity for guard cell walls is 2 MPa (20 bars) which is well within the limits of reported values for other biological tissues.
Acid‐base regulation during nitrate assimilation in Hydrodictyon africanum
Authors: RAVEN J. A. , DE MICHELIS M. I.
Published: April 2006

Abstract The acid‐base balance during NO3− assimilation in Hydrodictyon africanum has been investigated during growth from (1) an analysis of the elemental composition of the cells, (2) the alkalinity of the ash and (3) the net H+ changes in the medium during growth. These investigations agree in showing that some 0.25 excess organic negative charges are generated per N assimilation from No3− as N‐source and C02 as C‐source; the excess OH− (0.75 OH− per NO3− assimilated) appears in the medium. Approximately half of the excess organic negative charge is attributable to cell wall uronates; the remainder is intracellular. All of the excess OH− appearing in the medium must have crossed the plasmalemma (as net downhill H+ influx or OH− efflux).

Previous work has shown that the value of ψco is more negative than ψK+ during NO3− assimilation, suggesting that the active electrogenic H+ extrusion pump is still operative despite the net downhill H+ influx. The interpretation of this in terms of H+−NO3− symport which causes the entry of more H+ than is consumed in NO3− metabolism, with extrusion of the excess H+via the active, electrogenic H+ pump, was tested by measuring short‐term H+ influx upon addition of NO−3. A net H+ influx occurs before NOa assimilation (as indicated by additional O2 evolution in the light) has commenced, suggesting a mechanistic relation of H+ and NO3− influxes. This is consistent with the interpretation suggested above. Determinations of cytoplasmic pH showed no significant effect of NO3− assimilation, suggesting that cytoplasmic pH changes sufficient to change the ‘pH‐regulating’ H+ fluxes are smaller than the errors in the determination of cytoplasmic pH.
A scheme to account quantitatively for the action of phytochrome in etiolated and light‐grown plants
Authors: JOHNSON C. B. , TASKER R.
Published: April 2006

Abstract A scheme to account for the phytochrome responses of dark grown and green plants is presented. In contrast to some other models (e.g. Smith, 1970; Schäfer, 1975) it is proposed that both Pfr and the photoconversions of phytochrome are effectors of phytochrome action and interact to promote the observed responses. Under conditions where Ptot is not strongly wavelength dependent (e.g. with short pulses of light and in plants grown for prolonged periods in the light), responses will be predominantly related to Pfr concentration. Where Ptot is the major wavelength dependent variable (e.g. in the ‘high irradiance reaction’ of etiolated seedlings) it is proposed that the photoconversion process itself predominates in controlling the ultimate response. Some responses predicted by the scheme are compared with relevant published data.
The contribution of stored water to transpiration in Scots pine
Authors: WARING R. H. , WHITEHEAD D. , JARVIS P. G.
Published: April 2006

Abstract. The amount of water available diurnally and annually from the storage tissues was measured in plots of Scots pine trees with four different population densities (608–3281 trees per ha) in a 40‐year‐old plantation in north eastern Scotland. The water storage capacity of stems, branches, and foliage was estimated from equations derived from harvested trees and measurements of relative water content. On average 64% of the water considered to be available for transpiration was in the stem sapwood and less than 5% in the phloem, cambium and foliage. Trees on the plot with the highest population density had a water storage capacity of 212 m3 ha−1 (21.2 mm), whereas those on the plot with the lowest population density had a water storage capacity of 124 m3 ha−1 (12.4 mm). The utilization of stored water in transpiration was estimated from seasonal and diurnal measurements of the relative water content of foliage and stem sapwood. The largest change in sapwood relative water content over a 2‐week period was a reduction of 27% corresponding to extraction from the sapwood of 2.5 and 5.1 mm of water on the plots with the lowest and highest population densities, respectively. In rapidly changing weather conditions 1–1.5 mm day−1 could be removed from the stem sapwood alone. Since transpiration rarely exceeded 3 mm day−1, 30–50% of the transpired water was extracted from water stored in the stem sapwood over short periods. Trees on the plot with the lowest population density occasionally had slightly higher relative water contents and exhibited larger diurnal fluctuations than those on the plot with the highest population density, possibly because of differences in wood density. Sapwood water content was generally lower at times of high transpiration rate and in winter during freezing conditions. Resaturation took several months to complete during the winter.
The effect of benzo‐18‐crown‐6, a synthetic ionophore, on stomatal opening and its interaction with abscisic acid
Authors: RICHARDSON C. H. , TRUTER M. R. , WINGFIELD J. N. , TRAVIS A. J. , MANSFIELD T. A. , JARVIS R. G.
Published: April 2006

Abstract. Treatment of tomato seedlings with 5 mM benzo‐18‐crown‐6, a potassium ionophore, produced a reduction in transpiration of 40%. Treatments of epidermal strips of Commelina communis with ben‐zo‐18‐crown‐6 (1‐l0mM) inhibited stomatal opening, and this effect was shown to be reversible. An antagonistic interaction between abscisic acid (10−7M) and benzo‐18‐crown‐6 (4 × 10−3 M) was also observed.
Relationships between alkaloids in reed canarygrass (Phalaris arundinacea), soil moisture and nitrogen fertility
Authors: MAJAK WALTER , McDIARMID RUTH E. , POWELL THOMAS W. , VAN RYSWYK ALBERT L. , STOUT DARRYL G. , WILLIAMS RICHARD J. , TUCKER RICHARD E.
Published: April 2006

Abstract. The alkaloids of reed canarygrass respond to changes in soil moisture and nitrogen fertility. Gramine and hordenine levels increased under field conditions of moisture deprivation and this effect was enchanced when nitrogen fertilizer was applied. The level of 5‐methoxy‐N‐methyltryptamine was affected mainly by the nitrogen amendment. Exceptional alkaloid levels in reed canarygrass are interpreted in relation to climatic and plant osmotic parameters. Improved TLC fluorescence scanning procedures are presented for quantifying reed canarygrass alkaloids.
Carbon and nitrogen nutrition of nodulated roots of grain legumes
Authors: MINCHIN F. R. , SUMMERFIELD R. J. , HADLEY P. , ROBERTS E. H. , RAWSTHORNE S.
Published: April 2006

Abstract The spatial and temporal relationships between carbon (C) metabolism and nitrogen (N) nutrition in grain legumes are of great academic interest with the added bonus that any data for economically important species may ultimately prove useful to breeders and growers. So far there are no data which can be used to relate differences in carbon usage by any symbiotic association with differences in economic yield. Much research has focussed on the dependence of dinitrogen fixation on photosynthate supply, on the C–N relationships of nodulated roots and nodules and on diurnal and seasonal profiles of dinitrogen fixation. In all these aspects a plethora of responses have been described, often based on insufficiently proven measurement techniques; consequently unequivocal conclusions cannot be drawn. We know little about within‐species differences due to cultivar, strain of Rhi‐zobium or environment, or about the proportions of any heritable variations which might be sufficiently large to merit inclusion among the selection criteria of grain legume breeders.
Compartmental modelling of photorespiration and carbon metabolism of water stressed leaves
Authors: LAWLOR D. W. , PEARLMAN J. G.
Published: April 2006

Abstract Carbon fluxes in photosynthesis and photorespiration of water stressed leaves have been analysed in a steady state model based on the ribulose diphosphate carboxylase (RuDP carboxylase) and RuDP oxygenase enzyme activities and the CO2 and O2 concentrations in the leaf. Agreement between predicted and observed photorespiration (Lawlor & Fock, 1975) and C flux in the glycollate pathway is good over much of the range of water stress, but not at severe stress. An alternative source of respiratory CO2 is suggested to explain the discrepancy. The model suggests that resistance to CO2 fixation is mainly in the carboxylation reactions, not in CO2 transport.

Using the steady state model, the kinetics of 14C incorporation into photosynthetic and photorespiratory intermediates are simulated. The predicted rate of 14C incorporation is faster than observed and delay terms in the model are used to simulate the slow rates of mixing and metabolic reactions. Inactive pools of glycine and serine are suggested to explain the observed specific activities of glycine and serine. Three models of carbon flux between the glycollate pathway, the photosynthetic carbon reduction cycle and sucrose synthesis are considered. The most satisfactory simulation is for glycollate pathway carbon feeding into the PCR cycle pool of 3‐phosphoglyceric acid which provides the carbon for sucrose synthesis. Simulation of the specific activity of CO2 released in photorespiration suggests that a source of unlabelled carbon may contribute to photorespiration.
Temporal separation of two components of phytochrome action
Authors: WHITELAM G. C. , JOHNSON C. B.
Published: April 2006

Abstract In germinating seedlings of Sinapis alba nitrate reductase activity as assayed in vivo becomes accessible to phytochrome control between 15 and 17 h after sowing. Phytochrome operates via the high irradiance reaction to control nitrate reductase activity in the period 15 to 20 h after sowing. Both continuous red light and far‐red light elicit this response with a strong fluence rate dependency being apparent in each case. The induction of nitrate reductase activity by light pulses at 20 h after sowing is greatly influenced by red light pre‐treatments (operating through phytochrome) given between 0 and 15 h after sowing. Low fluence rate pre‐treatments reduce the effectiveness of a subsequent pulse to below the level of a dark control whilst high fluence rate pre‐treatments greatly increase the effectiveness of a subsequent pulse.
The use of immunological methods to study the activity of cellulase isozymes (B 1:4 glucan 4‐glucan hydrolase) in bean leaf abscission
Authors: DURBIN M. L. , SEXTON R. , LEWIS L. N.
Published: April 2006

Abstract The changes in the levels of two different isozymes of cellulase (EC 3.2.1.4) have been followed during the abscission of the primary leaves of bean (Phaseolus vulgaris c.v. Red Kidney), using antibodies raised against the 9.5 form of the enzyme. Data from both radioimmune and direct assay show that the 9.5 form of cellulase is undetectable prior to the induction of abscission. After a 12 h lag this isozyme increases in activity, the increase preceding a decrease in integrity of the abscission zone cell walls. The results are consistent not only with the view that this specific isozyme is involved in wall hydrolysis but also with previous data which showed that cellulase is synthesized ‘de novo’.

The 4.5 isozyme of cellulase is more widely spread throughout the plant, being most active in young tissues. During abscission the activity of this isozyme in the abscission layer falls and consequently it is not thought to be involved directly in the abscission process.
Ontogenetic variation in response to temperature change in the control of seed dormancy of Rumex obtusifolius L. and Rumex crispus L.
Authors: TOTTERDELL SUSAN , ROBERTS E. H.
Published: April 2006

Abstract After the onset of imbibition, the dormant seeds of Rumex obtusifolius and R. crispus are stimulated to germinate by a change from an initial low temperature to a warmer temperature for a relatively brief period: the warmer that temperature the shorter is the optimum period spent at it, and this optimum value is unaffected by the initial temperature. The optimum period is more critical in R. crispus than in R. obtusifolius (about 1 h and 2.5 to 4 h, respectively, for a warmer temperature of 35°C in the dark); in the light the length of the period at the warmer temperature is less critical in both species. The sensitivity of the seeds to the change to the warmer temperature increases with time from the start of imbibition at a rate which is positively related to the initial temperature. In R. obtusifolius maximum sensitivity was typically reached after 3 to 5 d when the initial temperature was 20°C and then remained constant, or declined only slightly, over the period investigated (10 d). At the same initial temperature, however, R. crispus showed a cyclical pattern of sensitivity with peaks occurring at 3–4 d intervals from the start of imbibition.