bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phosphorus sources and availability modify growth and distribution of root clusters and nodules of native Australian legumes
Authors: Adams M. A. , Bell T. L. , Pate J. S. 
Published: March 2003

AbstractA variety of native Western Australian legumes produced root clusters in sand culture confirming field and published observations. In general, these legumes grew equally well when supplied with organic or inorganic sources of phosphorus. The nitrogen content of shoots and roots varied little among treatments for all species, however, phosphorus content was always greater in plants supplied with inositol‐P. The plasticity of root growth in response to localized placement of organic and inorganic sources of phosphorus was demonstrated using a simple ‘split root’ technique. Total root dry weight was, on average, more than doubled in P‐amended sand when compared with non‐amended sand. Root clusters tended to be produced in areas of relatively high phosphorus concentration and nodules in areas of low phosphorus concentration. Levels of phosphorus in lateral roots grown in P‐amended sand were significantly different from lateral roots grown in the corresponding non‐amended sand. Growth increases averaging 70% for white sand to over 100% for yellow sand indicated a large degree of ‘plasticity’ in roots under conditions of heterogeneous supply of phosphorus. Spatially exclusive development of organs for the acquisition of nutrients is discussed in relation to requirements for carbon in organ production and maintenance.
Photosynthetic acclimation of Pinus taeda (loblolly pine) to long‐term growth in elevated pCO2 (FACE)
Authors: Rogers A. , Ellsworth D. S. 
Published: March 2003

AbstractGrowth in elevated pCO2 generally leads to a stimulation of net CO2 uptake rate. However, with long‐term growth the magnitude of this stimulation is often reduced. This phenomenon, termed acclimation, has been largely attributed to a loss of Rubisco (ribulose 1,5 bisphosphate carboxylase). The mechanism by which Rubisco content declines with long‐term growth is not certain. There is evidence for a sugar‐mediated, selective down‐regulation of Rubisco protein and also for a non‐selective loss of total leaf nitrogen, which impacts Rubisco levels indirectly. Over a season, and including needles at different developmental stages, we investigated these two potential mechanisms in well‐developed Pinus taeda grown for approximately 2·5 years in elevated (56 Pa) pCO2 using free air CO2 enrichment technology. Photosynthetic acclimation, as manifested by a decrease in the activity of Rubisco measured both in vivo (− 25%, via gas exchange) and in vitro (− 35%, via enzyme assays), was observed with growth in elevated pCO2. This acclimation was observed in one‐year‐old needles but not in current‐year needles. Needles exhibiting acclimation had reduced levels of Lsu Rubisco (− 25%) and an increased foliar carbohydrate content (+ 30%) but showed no evidence of a decrease in needle nitrogen or total protein content. These data support the concept that photosynthetic acclimation in elevated pCO2 is caused by a selective down‐regulation of Rubisco.
Desert dogma revisited: coupling of stomatal conductance and photosynthesis in the desert shrub, Larrea tridentata
Authors: Ogle K. , Reynolds J. F. 
Published: March 2003

AbstractThe success of the desert shrub Larrea tridentata (creosotebush) has been largely attributed to temperature acclimation and stomatal control of photosynthesis (A) under drought stress. However, there is a paucity of field data on these relationships. To address this void, we conducted a joint field and modelling study that encompassed a diverse set of environmental conditions. At a Larrea‐dominated site in southern New Mexico we manipulated soil moisture during the growing season over a 2‐year period and measured plant pre‐dawn water potential (Ψpd), stomatal conductance (g) and A of individual shrubs. We used these data to develop a semi‐mechanistic photosynthesis model (A–Season) that explicitly couples internal CO2 (Ci) and g. Vapour pressure deficit (VPD) and Ψpd affect instantaneous g in a manner that is consistent with a biophysical model of stomatal regulation of leaf water potential. Ci is modelled as a function of g, derived from a simplification of a typical A–Ci curve. After incorporating the effects of growing temperature on stomatal behaviour, the model was able to capture the large diurnal fluctuations in A, g and Ci and the observed hysteresis in g versus Ci dynamics. Our field data and application of the A–Season model suggest that dogma attributed to Larrea's success is supported with regard to stomatal responses to VPD and Ψpd, but not for mechanisms of temperature acclimation and CO2 demand.
Variation in economically and ecologically important traits in onion plant organs during reproductive development
Authors: Briggs W. H. , Goldman I. L. 
Published: March 2003

AbstractThe spatial distribution of organosulphur compounds throughout the onion (Allium cepa L.) plant body during reproduction is of ecological and horticultural interest. These secondary metabolites are associated with both pest resistance and many of the vegetable's culinary and medicinal properties, including the ability to inhibit platelet aggregation. Inhibition of platelet aggregation can be of benefit to human cardiovascular health. Organosulphur compound concentrations are associated with elemental sulphur, pungency, soluble solids and effect on human platelet aggregation. These parameters were evaluated in extracts collected separately from bulb scales, leaf blades, scapes and umbels biweekly throughout the reproductive phase of the life cycle of the onion. Significant variation in pungency, platelet inhibition, total sulphur content and soluble solids existed among samples of organs and within organs over time during reproductive growth. Furthermore, some extracts from leaf, scape and bulb induced rather than inhibited platelet aggregation.
Impact of waterlogging on the N‐metabolism of flood tolerant and non‐tolerant tree species
Authors: Kreuzwieser J. , Fürniss S. , Rennenberg H. 
Published: March 2003

AbstractThe present study was conducted to characterize the N‐metabolism of important European tree species with different degrees of flooding tolerance. The roots of Fagus sylvatica (sensitive to flooding), Quercus robur (moderately flood tolerant) and Populus tremula × P. alba (flood tolerant) saplings were exposed to different flooding regimes and N uptake, amino acid, protein and chlorophyll concentrations as well as gas exchange were measured. The effects of these treatments on the tree species varied distinctly. In general, the N metabolism of beech was severely affected whereas less impacts were observed on oaks and almost no effects on poplars. The concentrations of amino compounds, particularly of Asp, Asn, Glu and Gln, were lower in the roots of flooded trees than in controls. By contrast, γ‐amino butyric acid concentrations increased. Root protein concentrations remained unaffected in oak and poplar but decreased in beech in response to flooding. The concentrations of pigments remained unaffected by flooding in all tree species investigated. However, photosynthesis and transpiration were severely affected in beech but much less in oak and poplar. The data obtained show a clear correlation between the different flooding tolerances of the trees investigated and the impacts of flooding on N uptake and N metabolism.
Nuclear magnetic resonanceimaging of membrane permeability changes in plants during osmoticstress
Authors: Van Der Weerd L. , Claessens M. M. A. E. , Efdé C. , Van As H. 
Published: March 2003

AbstractThe cell water balance of maize (Zea mays L., cv LG 11) andpearl millet (Pennisetum americanum L., cv MH 179) duringosmotic stress was studied non‐invasively using 1H nuclearmagnetic resonance (NMR) microscopy. Single NMR parameter imagesof (i) the water content (ii) the transverse relaxation time (T2)and (iii) the apparent diffusion coefficient (Dapp)were used to follow the water status of the stem apical region duringosmotic stress. During stress there are hardly any changes in watercontent or T2 of the stem region of maize. Incontrast, the apical tissue of pearl millet showed a ∼ 30% decreaseof T2 within 48 h of stress, whereasthe water content and Dapp did not change. Thesechanges can be explained by an increase of the membrane permeabilityfor water. This conclusion is supported by results from scanningelectron microscopy, relaxation measurements of sugar solutionsand numerical simulations of the relaxation and (apparent) diffusionbehaviour of water in a plant cell.
Long‐distance transport of gases in plants: a perspective on internal aeration and radial oxygen loss from roots
Authors: COLMER T. D. 
Published: March 2003

ABSTRACTInternal transport of gases is crucial for vascular plants inhabiting aquatic, wetland or flood‐prone environments. Diffusivity of gases in water is approximately 10 000 times slower than in air; thus direct exchange of gases between submerged tissues and the environment is strongly impeded. Aerenchyma provides a low‐resistance internal pathway for gas transport between shoot and root extremities. By this pathway, O2is supplied to the roots and rhizosphere, while CO2, ethylene, and methane move from the soil to the shoots and atmosphere. Diffusion is the mechanism by which gases move within roots of all plant species, but significant pressurized through‐flow occurs in stems and rhizomes of several emergent and floating‐leaved wetland plants. Through‐flows can raise O2concentrations in the rhizomes close to ambient levels. In general, rates of flow are determined by plant characteristics such as capacity to generate positive pressures in shoot tissues, and resistance to flow in the aerenchyma, as well as environmental conditions affecting leaf‐to‐air gradients in humidity and temperature. O2diffusion in roots is influenced by anatomical, morphological and physiological characteristics, and environmental conditions. Roots of many (but not all) wetland species contain large volumes of aerenchyma (e.g. root porosity can reach 55%), while a barrier impermeable to radial O2loss (ROL) often occurs in basal zones. These traits act synergistically to enhance the amount of O2diffusing to the root apex and enable the development of an aerobic rhizosphere around the root tip, which enhances root penetration into anaerobic substrates. The barrier to ROL in roots of some species is induced by growth in stagnant conditions, whereas it is constitutive in others. An inducible change in the resistance to O2across the hypodermis/exodermis is hypothesized to be of adaptive significance to plants inhabiting transiently waterlogged soils. Knowledge on the anatomical basis of the barrier to ROL in various species is scant. Nevertheless, it has been suggested that the barrier may also impede influx of: (i) soil‐derived gases, such as CO2, methane, and ethylene; (ii) potentially toxic substances (e.g. reduced metal ions) often present in waterlogged soils; and (iii) nutrients and water. Lateral roots, that remain permeable to O2, may be the main surface for exchange of substances between the roots and rhizosphere in wetland species. Further work is required to determine whether diversity in structure and function in roots of wetland species can be related to various niche habitats.
Logistics of water and salt transport through the plant: structure and functioning of the xylem
Authors: DE BOER A. H. , VOLKOV V. 
Published: March 2003

ABSTRACTThe xylem is a long‐distance transport system that is unique to higher plants. It evolved into a very sophisticated plumbing system ensuring controlled loading/unloading of ions and water and their effective translocation to the required sinks. The focus of this overview will be the intrinsic inter‐relations between structural and functional features of the xylem. Taken together the xylem is designed to prevent cavitation (entry of air bubbles), induced by negative pressures under transpiration and to repair the cavitated vessels. Half‐bordered pits between xylem parenchyma cells and xylem vessels are on the one hand the gates to the vessels but on the other hand a serious ‘bottle‐neck’ for transport. Hence it becomes evident that special transport systems exist at the interface between the cells and vessels, which allow intensive fluxes of ions and water to and out of the xylem. The molecular identification and biophysical/biochemical characterization of these transporters has just started. Paradigms for the sophisticated mechanism of controlled xylem transport under changing environmental conditions are SKOR, a Shaker‐like channel involved in K+‐loading and SOS1, a Na+/H+ antiporter with a proposed dual function in Na+ transport. In view of the importance of plant water relations it is not surprising to find that water channels dominate the gate of access to xylem. Future studies will focus on the mechanism(s) that regulate water channels and ion transporters and on their physiological role in, for example, the repair of embolism. Clearly, progress in this specific field of research will greatly benefit from an integration of molecular and biophysical techniques aimed to understand ‘whole‐plant’ behaviour under the ever‐changing environmental conditions in the daily life of all plants.
Cadmium loading into potato tubers: the roles of the periderm, xylem and phloem
Authors: REID R. J. , DUNBAR K. R. , MCLAUGHLIN M. J. 
Published: March 2003

ABSTRACTThe mobility of Cd in potato plants (Solanum tuberosum) was examined using both short‐term radioisotopic labelling with 109Cd and long‐term growth experiments in soil supplemented with Cd, with an emphasis on the pathways through which Cd is taken up by tubers. Split‐pot experiments showed that tubers and their associated stolons and stolon roots contribute only a minor fraction to the overall Cd absorption by the plant. Most of the Cd was absorbed by the basal roots. 109Cd absorbed from the soil was rapidly exported to other parts of the plant, especially the stem, with significant amounts appearing in the tubers within 30 h. Application of 109Cd to leaves showed that Cd can be rapidly distributed via the phloem to all tissues. The results suggest that unlike Ca, Cd has high mobility in plants in both xylem and phloem, and that stems may have an important role in transfer between these two pathways.
Evolution and distribution of virulence in the German population of Bremia lactucae
Authors: Lebeda A. , Zinkernagel V. 
Published: March 2003

Changes in the genetic structure of the lettuce crop (Lactuca sativa) and populations of the lettuce downy mildew pathogen (Bremia lactucae) in Germany from 1974 to 1997 were studied and the genetic and population genetic results of race surveys of B. lactucae were reinterpreted. Data on 176 B. lactucae isolates collected from L. sativa cultivars at 48 sites in 11 German federal states were analysed. The host population contained 12 well‐defined race‐specific resistance genes (Dm1, Dm2, Dm3, Dm4, Dm5/8, Dm6, Dm7, Dm11, R12, Dm13, Dm16 and R18). However, only some of these genes (e.g. Dm3, Dm7, Dm11, Dm16 and R18) played an important role in management of resistance in the host crop. Substantial changes in the frequencies of these R‐genes were recorded over the period as a reaction to the occurrence of new virulent phenotypes in the pathogen population. Generally, the durability of resistance was very short. However, distinct regional patterns were observed for the frequencies of different virulence (v) factors. The data on changes in the virulence of B. lactucae population exemplified well the process of host–pathogen coevolution. During the period studied, there was a considerable increase in the frequency of some v‐factors (v2, v3, v5/8, v6, v7, v11 and v16) and in the complexity of v‐phenotypes, while the diversity in the pathogen population in general decreased. In 1996/97, 12 of the 14 v‐factors evaluated reached frequencies higher than 0·90 in the pathogen population. Relatively low frequencies were observed only for factors v14 (0·17) and v18 (0·24). The presence of 23 v‐factors was studied in six German isolates virulent on lettuce cultivar Titan, possessing the resistance gene R36 derived from Lactuca saligna and introduced in German lettuce crops during the mid‐1990s. Isolate DEG2 showed the highest complexity of v‐phenotype; it overcame the resistance in cv. Mariska (R18) and line CS‐RL (R18+?), but some sporulation occurred also on cv. Titan (Dm6 + R36). Conversely, the isolates SR2 and SAW1 overcame resistance based on R36, but were avirulent to R18. Future utilization of R‐genes in commercial lettuce cultivars is proposed; R‐genes R18 and R36 could be considered most efficient for this purpose. However, they may be effective only in certain regions.
Isolation of Human Anti‐idiotypes Broadly Cross Reactive with Anti‐dsDNA Antibodies from Patients with Systemic Lupus Erythematosus
Authors: Zhang W. , Winkler T. , Kalden J. R. , Reichlin M. 
Published: March 2003

Antibodies to double stranded (ds)DNA play a central role in clinical diagnosis and disease expression in Systemic lupus erythematosus (SLE). This paper describes the isolation of anti‐idiotype reagents (anti/antidsDNA) from four SLE sera and the demonstration of broad and quantitatively similar cross reactivity to both polyclonal and monoclonal anti‐dsDNA antibodies isolated from SLE patients. Seven affinity‐purified polyclonal and three monoclonal human anti‐dsDNA preparations reacted preferentially with anti‐idiotype F(ab′)2 coated plates compared to normal immunoglobulin (Ig)G F(ab′)2 coated plates in elisa. In contrast, autoantibodies of other specificities (anti‐Ro/SSA, anti‐La/SSB, and anti‐U1RNP) reacted equally with anti/anti‐dsDNA F(ab′)2 and normal IgG F(ab′)2 coated plates. Such anti‐idiotypic antibodies could play a significant role in the regulation of anti‐dsDNA antibody levels in SLE.
Maturation of Dendritic Cells by Recombinant Human CD40L‐Trimer Leads to a Homogeneous Cell Population with Enhanced Surface Marker Expression and Increased Cytokine Production
Authors: Würtzen P. A. , Nissen M. H. , Claesson M. H. 
Published: March 2003

Dendritic cells (DC) have been shown to be potent inducers of specific cytotoxic T‐cell responses both in vivo and in vitro. Furthermore, exposure to cytokines such as tumour necrosis factor (TNF)‐α or CD40 triggering changes DC phenotype and cytokine production and may enhance the T‐cell activating capacity of the DC. We studied DC phenotype and cytokine production as well as the T‐cell proliferation and cytotoxic T lympocyte (CTL) activation induced by DC generated in vitro. In addition, the effect of exposure to recombinant human CD40L‐trimer (huCD40LT) on these parameters was investigated. Effective differentiation of monocytes derived from freshly isolated peripheral blood mononuclear cells (PBMC) was obtained with granulocyte macrophage‐colony stimulating factor (GM‐CSF) and interleukin (IL)‐4. The DC expression of human leucocyte antigen (HLA) molecules, CD80, CD83, and CD86 was markedly enhanced by exposure to huCD40LT even compared to TNF‐α exposure. Only a moderate cytokine production was observed initially, while TNF‐α addition or CD40 triggering, especially, induced enhanced production of IL‐6 and IL‐12 p40. Surprisingly, comparable induction of T‐cell proliferation by a DC allostimulus or through the presentation of PPD, and influenza M1‐peptide specific CTL activity was obtained with nonmaturated (CD83−) and maturated (CD83+) DC. In conclusion, a final maturation of monocyte‐derived DC through huCD40LT resulted in a highly homogeneous cell population with enhanced surface marker expression and high production of pro‐inflammatory cytokines. In addition, the induction of responses to allo or recall antigens presented by huCD40LT maturated DC was comparable to the responses obtained with the DC maturated through TNF‐α exposure.
T‐ and B‐Cell Epitopes in the Secreted Mycobacterium bovis Antigen MPB70 in Mice
Authors: Tollefsen S. , Pollock J. M. , Lea T. , Harboe M. , Wiker H. G. 
Published: March 2003

AbstractMPB70 is a soluble secreted protein highly expressed in Mycobacterium bovis and strains of bacille Calmette–Guérin (BCG); as such, it is a candidate for subunit and DNA vaccines against tuberculosis. MPB70 was screened for T‐cell epitopes in four different inbred mouse strains. Major histocompatibility complex (MHC) H‐2b‐expressing mice (C57BL/6) secreted interferon‐γ (IFN‐γ) after stimulation with peptides from the regions 1–20, 41–50, 81–110, 121–150 and 161–193 of the MPB70 sequence. H‐2db mouse (B6D2) splenocytes secreted IFN‐γ after stimulation with some of the same peptides, whereas H‐2d mice (BALB/c and DBA/2) did not secrete IFN‐γ upon stimulation with the peptides. Sera from H‐2db mice immunized with native MPB70 in incomplete Freund's adjuvant (IFA), mpb70 DNA or live BCG Moreau were found to contain antibodies against the native MPB70 antigen. H‐2db mice immunized with native MPB70 in IFA exhibited high titres of peptide‐reactive immunoglobulin G1 (IgG1) antibodies, whereas DNA‐immunized mice reacted with IgG2a antibodies against some of the same peptides. As some of the epitopes recognized by mouse T and B cells have previously been found to stimulate immune responses in humans, cattle and rabbits, we conclude that these epitopes may be good general epitopes for the stimulation of T‐ and B‐cell responses and candidates for a DNA vaccine with a broad applicability.
Estimating the windward slope profile of a barchan dune
Authors: Momiji Hiroshi , Bishop Steven R. 
Published: March 2003

AbstractA new theoretical scheme is presented to model the shape of a sand dune at equilibrium that does not require iterative calculations of the interaction between the wind flow and topography. The model is constructed by incorporating theory based on aerodynamics into a grain‐scale model that estimates the shear velocity at the dune crest through the calculation of the sand trapping efficiency of the slipface in the lee of the dune. Published field data, collected in southern Peru, California and southern Morocco, show that as a dune becomes higher the windward slope becomes steeper. For the model proposed, the wind flow over a dune was first assumed to be similar to that over a Gaussian hill. By further assuming a fixed shear velocity on the level surface, the windward slope angle and migration speed of dunes in southern Peru can be explained. To comply with all available data, some aspects are still open to further investigation. However the theoretical insight presented herein implies that the upper limit of dune height may be greater in windier environments.