bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluating different soil and plant hydraulic constraints on tree function using a model and sap flow data from ponderosa pine
Authors: Williams M. , Bond B. J. , Ryan M. G. 
Published: March 2003

AbstractRelationships between tree size and physiological processes such as transpiration may have important implications for plant and ecosystem function, but as yet are poorly understood. We used a process‐based model of the soil–plant–atmosphere continuum to investigate patterns of whole‐tree sap flow in ponderosa pine trees of different size and age (36 m and ∼250 years versus 13 m and 10–50 years) over a developing summer drought. We examined three different hypothetical controls on hydraulic resistance, and found that size‐related differences in sap flow could be best explained by absolute differences in plant resistance related to path length (hypothesis 1) rather than through different dynamic relationships between plant resistance and leaf water potential (hypothesis 2), or alterations in rates of cumulative inducement and repair of cavitation (hypothesis 3). Reductions in sap flow over time could be best explained by rising soil–root resistance (hypothesis 1), rather than by a combination of rising plant and soil–root resistance (hypothesis 2), or by rising plant resistance alone (hypothesis 3). Comparing hourly predictions with observed sap flow, we found that a direct relationship between plant resistance and leaf water potential (hypothesis 2) led to unrealistic bimodal patterns of sap flow within a day. Explaining seasonal reduction in sap flow purely through rising plant resistance (hypothesis 3) was effective but failed to explain the observed decline in pre‐dawn leaf water potential for small trees. Thus, hypothesis 1 was best corroborated. A sensitivity analysis revealed a significant difference in the response to drought‐relieving rains; precipitation induced a strong recovery in sap flow in the hypothetical case of limiting soil–root resistance (hypothesis 1), and an insignificant response in the case of limiting plant resistance (hypothesis 3). Longer term monitoring and manipulation experiments are thus likely to resolve the uncertainties in hydraulic constraints on plant function.
Developmental and seasonal changes of stress responsiveness in beech leaves (Fagus sylvatica L.)
Authors: Polle A. , Schwanz P. , Rudolf C. 
Published: March 2003

AbstractThe development of beech leaves (Fagus sylvatica L.) was characterized by determination of the pigment and electrolyte concentrations as well as the accumulation of dry mass and specific leaf mass from bud break to senescence. To test the hypothesis that stress tolerance and responsiveness of defences show developmental and/or seasonal changes, leaf discs were either incubated in the absence (control) or presence of paraquat to induce oxidative stress. Controls displayed developmental changes in stress susceptibility ranging from less than 15% of maximum electrolyte leakage in mature leaves to more than 20% leakage in senescent and 36–46% in immature leaves. Paraquat concentrations were chosen to result in about 95% of maximum electrolyte conductivity within 24 h in all developmental stages. Paraquat accumulation was about two‐fold lower in senescent as compared with immature leaves, whereas stress susceptibility, as characterized by the kinetics of the increase in relative leakage, was similar in these developmental stages with 50% of maximum electrolyte conductivity (EC50) = 6·5 h in immature and 7·5 h in senescent leaves. In mature leaves with intermediate paraquat accumulation rates, two classes of stress‐sensitivity were distinguished, namely stress‐resistant and stress‐susceptible leaves with EC50= 9·5 and 5·2 h, respectively. Stress‐resistance of mature leaves was accompanied by a rapid, approximately two‐fold induction of superoxide dismutase activity. Stress‐sensitive mature leaves initially contained high superoxide dismutase activities but showed a rapid, more than six‐ fold loss in activity in 24 h. Correlation of meteorological data with leakage rates suggested that high air temperatures and low precipitation might have been predisposing for loss of resistance against oxidative stress in beech leaves.
Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplings
Authors: Usami T. , Lee J. , Oikawa T. 
Published: March 2003

AbstractThe interactive effects of increased temperature and CO2 enrichment on the growth of 2‐year‐old saplings of Quercus myrsinaefolia, an evergreen broad‐leaved oak, were studied throughout an entire year in the vicinity of their northernmost distribution. Saplings were grown under different conditions in two chambers: (1) a temperature gradient chamber at ambient temperature, 3 and 5 °C warmer conditions with an ambient CO2 concentration, and (2) in a CO2 temperature gradient chamber at 3 °C warmer conditions with 1·5 times the normal CO2 concentration, and 5 °C warmer conditions with doubled CO2 concentration. The 3 and 5 °C warmer conditions enhanced the relative growth rate during almost the entire year, producing 53 and 47% increases in annual biomass production, 27 and 44% enhancement of root growth during shoot dormancy and 3 and 5 week prolongation of the shoot growing period, respectively. However, a daily mean air temperature exceeding 30 °C under the 5 °C warmer condition caused a marked reduction in net assimilation rate (NAR) from July to September. The CO2 enrichment further enhanced the positive effects of warming in spring and the resulting increases in NAR almost completely compensated for the negative effect of warming during summer. From autumn to winter, attenuation of the effects of CO2 was compensated by the increased sink strength produced by the warming. The annual biomass production was more than doubled by the combination of temperature elevation and CO2 enrichment.
Signalling drought in guard cells
Authors: Luan S. 
Published: March 2003

AbstractA number of environmental conditions including drought, low humidity, cold and salinity subject plants to osmotic stress. A rapid plant response to such stress conditions is stomatal closure to reduce water loss from plants. From an external stress signal to stomatal closure, many molecular components constitute a signal transduction network that couples the stimulus to the response. Numerous studies have been directed to resolving the framework and molecular details of stress signalling pathways in plants. In guard cells, studies focus on the regulation of ion channels by abscisic acid (ABA), a chemical messenger for osmotic stress. Calcium, protein kinases and phosphatases, and membrane trafficking components have been shown to play a role in ABA signalling process in guard cells. Studies also implicate ABA‐independent regulation of ion channels by osmotic stress. In particular, a direct osmosensing pathway for ion channel regulation in guard cells has been identified. These pathways form a complex signalling web that monitors water status in the environment and initiates responses in stomatal movements.
Chromium ions inactivate electron transport and enhance superoxide generation in vivo in pea (Pisum sativum L. cv. Azad) root mitochondria
Authors: Dixit V. , Pandey V. , Shyam R. 
Published: March 2003

AbstractThe effect in vivo of hexavalent chromium (Cr6+) on the respiratory electron transport activity and production of superoxide (O2–) radicals, was studied in submitochondrial particles (SMPs) prepared from mitochondria isolated from roots of 15‐day‐old pea (Pisum sativum L. cv. Azad) plants exposed to environmentally relevant (20 µm) and acute (200 µm) concentrations of chromium for 7 d. A concentration ‐dependent inactivation of electron transport activity from both NADH to O2 (NADH oxidase) and succinate to O2 (succinate oxidase) was observed. The electron transport activity was more sensitive to Cr6+ with NADH as the substrate than with succinate as the substrate. Although NADH dehydrogenase and succinate dehydrogenase were less affected, NADH: cytochrome c oxidoreductase and succinate: cytochrome c oxidoreductase activities were prominently affected by Cr6+. Cytochrome oxidase was the most susceptible complex of mitochondrial membranes to Cr6+, exhibiting maximal inactivation of activity both at 20 and 200 µm chromium concentrations. Cr6+ increased the generation of O2– radicals. This effect was more evident at 200 than at 20 µm. A significant increase in lipid peroxidation of mitochondrial membranes at 200 µm Cr6+ was the physiological impact of the metal‐induced enhanced generation of O2– radicals. An increase in superoxide dismutase (SOD) activity at 20 µm Cr6+ towards enhanced production of O2– radicals appeared to be a defence response in pea root mitochondria that, however, could not be sustained at 200 µm Cr6+. The results obtained concerning inactivation of mitochondrial electron transport and subsequent enhancement in the generation of O2– radicals suggest that root mitochondria are an important target of Cr6+‐induced oxidative stress in pea.
Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast‐ and slow‐growing plant species
Authors: Loveys B. R. , Scheurwater I. , Pons T. L. , Fitter A. H. , Atkin O. K. 
Published: March 2003

AbstractWe examined the effect of growth temperature on the underlying components of growth in a range of inherently fast‐ and slow‐growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 °C. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter‐specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 °C but were not related to variations in RGR at 18 °C. When grown at 18 °C, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 °C used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 °C‐grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.
Interactions between atmospheric CO2 concentration and phosphorus nutrition on the formation of proteoid roots in white lupin (Lupinus albus L.)
Authors: Campbell C. D. , Sage R. F. 
Published: March 2003

AbstractAtmospheric [CO2] affects photosynthesis and therefore should affect the supply of carbon to roots. To evaluate interactions between carbon supply and nutrient acquisition, the [CO2] effects on root growth, proteoid root formation and phosphorus (P) uptake capacity were studied in white lupin (Lupinus albus L.) grown hydroponically at 200, 410 and 750 µmol mol−1 CO2, under sufficient (0·25 mm P) and deficient (0·69 µm P) phosphorus. Plant size increased with increasing [CO2] only at high P. Both P deficiency and increasing [CO2] increased the production of proteoid clusters; the increase in response to increased [CO2] was proportionally greater from low to ambient [CO2] than from ambient to high. The activity of phosphoenol pyruvate carboxylase in the proteoid root, the exudation of organic acids from the roots, and the specific uptake of P increased with P deficiency, but were unaffected by [CO2]. Increasing [CO2] from Pleistocene levels to those predicted for the next century increased plant size and allocation to proteoid roots, but did not change the specific P uptake capacity per unit root mass. Hence, rising [CO2] should promote nutrient uptake by allowing lupins to mine greater volumes of soil.
Time lags for xylem and stem diameter variations in a Scots pine tree
Authors: Sevanto S. , Vesala T. , Perämäki M. , Nikinmaa E. 
Published: March 2003

AbstractDiameter variations in the xylem and whole stem (i.e. over bark) stem of a Scots pine (Pinus sylvestris L.) tree were measured at four heights over a 23 d period at 5 min intervals. Cross‐correlation analysis was used to calculate time lags between the measurements. Xylem diameter measurements at the different heights had time lags varying from 10 to 50 min, measurements at the lower heights lagging behind the most. This result was in good agreement with the cohesion theory of transpiration. For the whole stem diameter measurements, the treetop lagged behind all other heights and the shortest lags were midway along the stem. Changes in whole stem diameter always lagged behind those of xylem stem diameter (30–110 min), and at all heights. The considerable differences in the behaviour of xylem and whole stem diameter support the Münch hypothesis of phloem flow. Time lags calculated separately for the shrinkage (morning) and swelling (afternoon) periods indicated shorter time lags during the swelling periods. The non‐destructive methods used show promise in the simultaneous study of flow dynamics of xylem and phloem in trees.
Carbon dioxide transport inxylem causes errors in estimation of rates of respiration in stemsand branches of trees
Authors: Teskey R. O. , Mcguire M. A. 
Published: March 2003

AbstractComplementary laboratory and field experiments showed that theinternal transport of carbon dioxide (CO2) in the xylemof trees is an important pathway for carbon movement. Carbon dioxidereleased by respiration dissolves in sap and moves upward in thetranspirational stream. The concentration of CO2 in xylemsap can be up to three orders of magnitude greater than that foundin the atmosphere. In the present experiments, diffusion outwardof a portion of xylem‐transported CO2 caused a substantialoverestimation of the apparent rate of stem and branch respiration.Rates of CO2 efflux were linearly related to sap CO2 concentration.Direct manipulations of xylem sap CO2 concentration producedrapid and reversible changes in CO2 efflux from stemsand branches, in some cases quadrupling the rate of efflux. Theseresults demonstrated that apparent rates of stem and branch respirationof trees are in large part a by‐product of the rate of CO2 diffusionfrom xylem sap.
A general model of plant‐virus disease infection incorporating vector aggregation
Authors: Zhang X.‐S. , Holt J. , Colvin J. 
Published: March 2003

In plant‐virus disease epidemiology, dynamical models have invariably incorporated a bilinear inoculation rate that is directly proportional to both the abundance of healthy (susceptible) hosts and the abundance of infective vectors. Similarly, the acquisition rate is usually assumed to be directly proportional to the abundance of nonviruliferous vectors and that of infectious hosts. These bilinear assumptions have been questioned for certain human diseases, and infection rates that incorporate power parameters of the variables have been proposed. Here, infection rates for plant‐virus diseases that are of a more general form than the familiar bilinear terms are examined. For such diseases, the power parameter can be regarded as a measure of the spatial aggregation of the vectors or as a coefficient of interference between them, depending on the context.Field data of cassava mosaic virus disease (CMD) incidence were examined. When vector population density and disease incidence were high, disease progress curves over the first 6 months from planting could not be explained using models with bilinear infection rates. Incorporation of the new infection terms allowed the range of observed disease progress curve types to be described. New evidence of a mutually beneficial interaction between the viruses causing CMD and the whitefly vector, Bemisia tabaci, has shown that spatial aggregation of the vectors is an inevitable consequence of infection, particularly with a severe virus strain or a sensitive host. Virus infection increases both vector fecundity and the density of vectors on diseased plants. It is postulated that this enhances disease spread by causing an increased emigration rate of infective vectors to other crops. Paradoxically, within the infected crop, vector aggregation reduces the effective contact rate between vector and host and therefore the predicted disease incidence is less than when a bilinear contact rate is used.
Development of phoma lesions on oilseed rape leaves inoculated with ascospores of A‐group or B‐groupLeptosphaeria maculans(stem canker) at different temperatures and wetness durations
Authors: Toscano‐Underwood C. , West J. S. , Fitt B. D. L. , Todd A. D. , Jedryczka M. 
Published: March 2003

In controlled‐environment experiments, ascospores of both A‐group and B‐groupLeptosphaeria maculanswere able to infect leaves of oilseed rape and produce phoma leaf spot lesions at temperatures from 5 to 20°C and wetness durations from 8 to 72 h after inoculation. Lesions formed on leaves inoculated with B‐group ascospores had few pycnidia and were darker, smaller and less noticable than the larger, pale grey lesions with many pycnidia produced by A‐group ascospores. Lesions formed by A‐group or B‐groupL. maculanson naturally infected winter oilseed rape experimental crops were similar to lesions produced by the two groups on inoculated plants. The greatest numbers of lesions were produced with a leaf wetness duration of 48 h and at temperatures of 15–20°C for both A‐group and B‐group ascospores. As leaf wetness duration and temperature decreased below the optimal values, the number of lesions decreased. The incubation period, estimated as the time from inoculation to the appearance of the first lesions (t1), or the time to the appearance of 50% of the lesions (t50), of B‐group was often shorter than that of A‐groupL. maculans. As temperature decreased below 20°C, the length of the incubation period of both A‐group and B‐groupL. maculansincreased.
Symptom severity of cassava mosaic disease in relation to concentration of African cassava mosaic virus in different cassava genotypes
Authors: Ogbe F. O. , Atiri G. I. , Dixon A. G. O. , Thottappilly G. 
Published: March 2003

The concentration of African cassava mosaic virus (ACMV) was assessed by enzyme‐linked immunosorbent assay in relation to symptom severity among resistant, moderately resistant and susceptible cassava genotypes. Resistant genotype NR 8083 had significantly lower symptom severity scores (P < 0·05) than the susceptible genotype TMS 91934, but the two genotypes contained similar levels of virus concentration. The moderately resistant genotypes TMS 30572 and NR 8082 expressed significantly lower symptom severities (P < 0·05) than the susceptible genotypes TMS 91934 and TME 117, but they contained significantly higher virus concentrations (P < 0·05) than TMS 91934 and similar virus concentration as in TME 117. However, two other resistant genotypes, TME 1 and TME 8, had low symptom severity scores and virus concentrations. There was significant interaction (P ≤ 0·05) between cropping season and virus concentration in all the genotypes except TMS 30572. The resistant and moderately resistant genotypes that had high virus concentrations sustained storage root yield losses. The severity of symptoms expressed was not necessarily a reflection of the virus concentration in some of the genotypes. In addition to the use of symptom severity scores to group genotypes into resistant classes, it is recommended that virus concentration should also be considered. Genotypes displaying mild symptoms, but with high levels of virus accumulation, could be an important source of inoculum in the spread of ACMV by the whitefly vectors. This suggests that each genotype should be tested for virus accumulation prior to its release to the farmers.
Intranasal Administration of One Alpha Gliadin Can Downregulate the Immune Response to Whole Gliadin in Mice
Authors: Maurano F. , Siciliano R. A. , De Giulio B. , Luongo D. , Mazzeo M. F. , Troncone R. , Auricchio S. , Rossi M. 
Published: March 2003

The mucosal lesion present in coeliac disease is an immune‐mediated injury triggered by gliadin and restricted by a particular assortment of major histocompatibility complex genes. In view of this, an immunomodulatory approach that induces tolerance to this antigen appears to be a possible alternative to a strict gluten‐free diet in treating coeliac disease. We have shown that intranasal administration of multiple doses of whole gliadin is required to specifically inhibit T helper 1‐like T‐cell reactivity in BALB/c mice immunized parenterally with whole gliadin. However, T‐cell activation to multiple antigens, as a consequence of the chemical complexity shown by the antigen gliadin, could hamper efforts to identify single component(s) useful for tolerance induction. In this study, gliadin fractions were purified and administered intranasally to study their ability to induce tolerance to whole gliadin in our animal model. We found that the alpha fraction was particularly effective in downregulating both the in vitro gliadin‐specific T‐cell proliferation and interferon‐γ production to whole gliadin. In particular, a purified α‐gliadin was able to suppress the immune response to the entire gliadin mixture. These results demonstrate how an immune response to a complex antigen may be controlled by treatment with a purified component and specifically indicate α‐gliadin to be a good candidate for further identification of short peptides to be used as tolerogens in this model.
Effect of Flavone Derivatives on Interleukin‐1β (IL‐1β) mRNA Expression and IL‐1β Protein Synthesis in Stimulated RAW 264.7 Macrophages
Authors: Blonska M. , Czuba Z. P. , Krol W. 
Published: March 2003

AbstractIt is known that the redox status of cells affects gene expression. Flavones, as natural antioxidants, efficiently modulate this status and may play a role in the regulation of inducible gene expression of inflammatory mediators. This study was designed to investigate the effect of five flavone derivatives variously substituted with hydroxyl groups (chrysin, galangin, kaempferol, quercetin and myricetin) on interleukin‐1β (IL‐1β) gene expression in stimulated RAW 264.7 macrophages. The cells were incubated with tested hydroxyflavones and stimulated with lipopolysaccharide (LPS) and interferon‐γ (IFN‐γ). Then, the following were estimated: the level of IL‐1β mRNA in these cells and the concentration of IL‐1β protein in cell‐culture supernatants and cell lysates.Each of the tested compounds significantly decreased IL‐1β mRNA expression. The most potent inhibitor was chrysin (hydroxyflavone with two hydroxyl groups and a weak antioxidant activity). The effects of galangin and kaempferol were similar. Myricetin (hydroxyflavone with a strong antioxidant activity) significantly decreased the level of IL‐1β mRNA, but it had no effect on the IL‐1β protein synthesis.The results indicated that hydroxyflavones could modulate the IL‐1β gene expression in activated RAW 264.7 macrophages via inhibiting gene transcription. This action seems unlikely to be the result of antioxidant properties of tested compounds.