bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of hyperglycaemia on expression and re‐distribution of VE‐cadherin in human endothelial cells
Authors: Maillard M. , Leach L.
Published: March 2003

In vitro studies using animal vascular endothelial cells have shown that hyperglycaemia increases monolayer permeability. The mechanism underlying this increase is thought to involve disruption of adherens junctions by phosphorylation of the transmembrane molecule vascular‐endothelium cadherin (VE‐cadherin) and loss of its perijunctional actin anchorage. Recently an alternate mechanism of disruption, i.e. inflammation induced loss of actin independent VE‐cadherin, has been proposed (Lim et al. Microvas. Res. 2001 on IDEAL). The purpose of this study was to expose human endothelial cells to high glucose and follow the fate of VE‐cadherin. Human vein umbilical endothelial cells (HUVEC) were grown to confluence before being exposed to media containing different concentrations of glucose: 5 mm d‐glucose as euglycaemic control, 25 mm d‐glucose as hyperglycaemic medium, and 25 mm l‐glucose as osmotic control. VE‐cadherin localisation was studied using immunocytochemistry and systemic randomised count of junctional profiles which allowed classification of the VE‐cadherin immunoreactivity at cell‐cell borders as continuous or discontinuous. Immunoblot studies and selective protein extraction into Triton‐soluble and Triton‐insoluble fractions were performed in order to measure total protein levels of expression and actin association of VE‐cadherin under the different experimental conditions. Immunoprecipitation studies were used to investigate tyrosine phosphorylation status of VE‐cadherin. Hyperglycaemic exposure of HUVEC for 2 h resulted in a statistically significant (one‐way Anova, P < 0.01) increase in the percentage of discontinuous VE‐cadherin at cell‐cell contacts of HUVEC monolayers, this significance was lost after longer durations (4 d). After 2 h of glucose insult, the total VE‐cadherin expression was not altered, whilst the selective extraction studies showed VE‐cadherin had a greater association with the actin‐cytoskeleton. The tyrosine phosphorylation level of VE‐cadherin was not altered. Our studies reveal that hyperglycaemia does cause redistribution of VE‐cadherin. However the pattern of VE‐cadherin redistribution favours the hypothesis of a loss of VE‐cadherin from actin‐independent membrane microdomains. Furthermore we find this loss is not mediated by the tyrosine kinase signalling pathway.

Funded by the European Social Fund.
Endothelial barriers: from hypothetical pores to membrane proteins
Authors: Firth J. A.
Published: March 2003

The presence of small (4–6 nm diameter) pores in nonbrain capillary walls, permeable to water and small hydrophilic solutes but not most proteins, was established 50 y ago (Pappenheimer et al. Amer. J. Physiol. 167, 1951). This model provides a basis for long recognised features of hydraulic and oncotic pressure driven flows across capillary walls (Starling, J. Physiol. 19, 1896).

However the anatomical counterpart of the small pore system proved difficult to establish. Polarised preferences for the caveolar systems or for the paracellular pathway have now matured into a broad agreement that the main small pore pathway in continuous (nonfenestrated) capillaries is likely to be paracellular. The caveolar system is strongly associated with far rarer large pores and with opening‐up by inflammatory agents.

Analogy with epithelial paracellular pathways would suggest that tight junctions are likely to be the most restrictive elements. The repeated demonstration by electron microscopy of a gap 4–5 nm wide in the tight junction strands of nonbrain endothelia failed an important test. Such a slit pore occupying the total length of the paracellular cleft would make the total pore area of capillaries in tissues such as muscle about an order of magnitude larger than physiological estimates suggested. Recognition that the tight junctions are interrupted by discontinuities much larger than small pores suggested that the tight junction might function as a shutter limiting the available cleft area rather than as the filter.

Subsequent attention has focussed on other regions of the cleft and on the presence of 3 dimensional molecular meshes. Proposed sieve elements range from the glycocalyx to the adhesion molecule complexes of the adherens junctions. The molecular architecture of tight junctions and adherens junctions is moderately well defined in terms of molecular species, and there are differences at both sites between the endothelial and epithelial spectrum of protein expression. However, definition of the size‐restricting pore remains elusive and may require structural biology approaches to the spatial arrangements and interactions of the membrane molecular complexes surrounding the endothelial paracellular clefts.
A quantitative analysis of perineurial cell basement membrane collagen IV, laminin and fibronectin in diabetic and non‐diabetic human sural nerve
Authors: Hill R. E. , Williams P. E.
Published: March 2003

The thickness of the perineurial cell basement membrane was examined in diabetic and non‐diabetic human sural nerve. A significant increase in thickness was found in the diabetic group. The nature of this thickening was investigated using immunohistochemistry and image analysis in order to semi‐quantify three of the major intrinsic components of the perineurial cell basement membrane: collagen IV, laminin and fibronectin. Amounts of all three components were shown to be increased in the diabetic group, but not significantly so. However, significant linear correlations between fascicle size and perineurial collagen IV, laminin and fibronectin were identified in both diabetic and non‐diabetic nerve.
An analysis of the balance between root and shoot activity in Lolium perenne cv. Melvina. Effects of CO2 concentration and air temperature
Authors: NIJS IVAN , IMPENS IVAN
Published: March 2003

This study investigated the mechanisms which control the partitioning between roots and shoots in plants subjected to changes in environment. Two types of analyses were used: firstly, an examination of the cost and revenue associated with investment in different plant parts, and secondly, a test of the principle of functional equilibrium between roots and shoots, i.e. whether root dry matter × root specific activity balances shoot dry matter × shoot specific activity. Measurements were made on individual plants of Lolium perenne in sunlit controlled environments, grown from germination to canopy closure under optimal nitrogen supply. At the final harvest, increased air temperature (+ 4 °C above ambient) reduced whole‐plant dry matter by 12% relative to the control, whereas elevated CO., mole fraction (700 μmol mol −1) led to a 38 % gain. The combined treatment yielded an intermediate result (+ 19%). Plants grown at + 4°C maintained balanced activity between roots and shoots throughout the experimental period, irrespective of CO2 concentration. This required enhanced allocation to roots in young plants to compensate for a strong negative effect of higher temperature on root specific activity, which suggests that plants conserve balanced activity by adjusting dry matter partitioning. The extra cost involved with the adjustment at +4°C significantly enhanced the cost:revenue ratio of plant investment. In ambient temperature, the balance between roots and shoots departed from equilibrium, slightly at ambient but substantially at elevated CO2: the plants accumulated excess carbon relative to nitrogen, and this imbalance increased with plant age. At elevated CO2, the cost: revenue ratio increased in young plants but this was later reversed owing to loss of root specific activity, which explains the gradually declining CO2, stimulation with time. The strategies in equilibrating root and shoot functioning observed in the different treatments are discussed in the light of whole plant performance.
Environmental factors and genotypic changes in lipids contribute to the winter hardiness of Norway spruce (Picea abies)
Authors: WELLBURN ALAN R.
Published: March 2003

Lipids were extracted from needles of Norway spruce plants of different provenances. The plants, seeds of which were originally collected from all over Europe, were grown at two sites in England at the same longitude but one 350 km north of the other. Significant correlations were observed between monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) ratios on the one hand and, on the other, the lowest extreme winter temperature at the original site of seed collection (EWTS).

In the case of lipid changes, however, environmental differences due to site were more important than the inherent genotypic characteristics of the planted trees while provenances with the lowest EWTS values had more MGDG than DGDG. This implies that existing winter hardiness under mild climatic conditions does not come from changes in this ratio although DGDG formation from MGDG is known to be an important feature of winter hardening in Norway spruce elsewhere in Europe. However, closer analysis of the fatty acids in lipids from provenances at individual sites did reveal significant correlations between those provenances with low EWTS values and certain molar amounts or ratios of fatty acids in DGDG, some of which could be traced to genotypic expression. These partly involved the unusual Δ5 desaturations which are mainly confined to the fatty acids of those conifers like Norway spruce that harden to very low temperatures.
The influence of nitrogen fertilization on the carbon economy of Paxillus involutus in ectomycorrhizal association with Betula pendula
Authors: EK H.
Published: March 2003

Mycorrhizal mycelium was allowed to grow into a compartment from which roots were excluded. Ammonium or nitrate was supplied exclusively to the fungus and the respiration rate before and after nitrogen addition was measured. Mycelial respiration in the fungal compartment represented 11–29%, of total fungal and root respiration. The mycelium in the fungal compartment received 20–29% of shoot net assimilation, and 43–64%, of the carbon allocated to the mycelium was respired. The nitrogen‐induced respiration increase ranged, in the fungal compartment, from 54 to 180%.
Responses to water stress in an ABA‐unresponsive hybrid poplar (Populus koreana×trichocarpa cv. Peace) III. Consequences for photosynthetic carbon assimilation
Authors: RIDOLFI MICHÉLE , DREYER ERWIN
Published: March 2003

Net CO2 assimilation rates and chlorophyll a fluorescence were measured on leaves of an ABA‐unresponsive poplar (Populus trichocarpa×koreana cv. Peace) during a period of drought. Stomata of fully expanded leaves of ‘Peace’ partly closed during drought, while those of Populus euramericana cv. Robusta closed almost completely. The measured data were used to calculate total light‐driven electron flows and to derive an estimate of a CO., mole fraction in the chloroplasts. Two major results were obtained, (i) In well watered plants, photosynthesis operated at lower CO2 mole fractions in the chloroplasts of cv. Peace than in those of cv. Robusta, whereas CO2 mole fractions in the sub stomatal spaces were of the same order of magnitude. We concluded that a higher resistance to CO2 influx in the mesophyll contributed to the lower net assimilation rates in ‘Peace’, (ii) Drought induced an important decrease in CO2 availability in ‘Robusta’ but not in ‘Peace’. This suggested that reduced CO2 influx was a major cause of the limitation of net CO2 assimilation during drought in ‘Robusta’, but not in ‘Peace’, where drought probably reversibly reduced the apparent carboxylation efficiency of Rubisco. Measurements of O2evolution under saturating CO2 supported this view, as photosynthesis decreased in draughted plants of ‘Peace’ but not of ‘Robusta’. Moreover, estimates of the 13C/12C isotope ratio in the leaves of both cultivars showed drought‐related decreases in discrimination, which, in the case of ‘Peace’, could only be explained by changes in activity of the photosynthetic carbon reduction cycle.
Xerophytic implications of increased sclerophylly: interactions with water and light in Hakea psilorrhyncha seedlings
Authors: GROOM PHILIP. K. , LAMONT BYRON B.
Published: March 2003

Hakea psilorrhyncha R. M. Barker seedlings were subjected to a two‐way interaction experiment with two levels of water availability and two levels of light. Physiological drought was imposed by adding 6000 MW polyethylene glycol (PEG), at an osmotic potential of − 0.56 MPa, in a continuous‐flow drip irrigation system. Unstressed plants (‐PEG) were watered with distilled water (osmotic potential of −0.01 MPa). Seedlings were grown under natural light (120–500 μmol m−2 s−1 sunlight at midday + L) or shaded (< 150 μMmol m−2 s−1 sunlight at midday; – L. Plant morphology tissue water relations and carbon isotope composition ($13C) were measured after 12 wk growth. The smallest leaves had the highest mass per unit area (LMA, an index of sclerophylly) and were present in the + PEG+ L treatment, whereas the largest, thickest leaves had the lowest density and were produced in the – PEG + L treatment. Plants in shade were smaller and less sclerophyllous. There was a linear decrease in osmotic potential at full turgor and turgor loss point, and an increase in elastic modulus and $13PC, as level of sclerophylly increased, with ‐PEG‐L leaves at one extreme and +PEG + L at the other. We conclude that high levels of sclerophylly induced by low water availability and high light intensity are associated with substantial drought tolerance in H. psilorrhyncha.
Spontaneous hybridization of the putative ancestors of the allotetraploid Poa annua
Authors: DARMENCY H. , GASQUEZ J.
Published: March 2003

summary

Spontaneous hybrids between the two diploids Poa infirma Kunth and P. supina Schrader were obtained at the rate of 0.2%. No reciprocal maternal effect was observed. Almost all hybrids survived, grew normally but were sterile. Hybrids were diploid, and resembled in morphology the tetraploid P. annua L. (annual meadow grass). In their isozymes, they showed additivity of the parental patterns, and were very similar to those found in P. annua populations. The ease with which hybrids were obtained and the similarity of their morphological and isozyme pattern to P. annua suggest that the two diploid species are closely related to the allotetraploid species, and are perhaps its parent species.
Root production and turnover and carbon budgets of two contrasting grasslands under ambient and elevated atmospheric carbon dioxide concentrations
Authors: FITTER A. H. , GRAVES J. D. , WOLFENDEN J. , SELF G. K. , BROWN T. K. , BOGIE D. , MANSFIELD T. A.
Published: March 2003

summary

Monoliths of two contrasting vegetation types, a species‐rich grassland on a brown earth soil over limestone and species‐poor community on a peaty gley, were transferred to solardomes and grown under ambient (350 μ 1−1) and elevated (600 μ11−1) CO2 for 2 yr. Shoot biomass was unaltered but root biomass increased by 40–50% under elevated CO2. Root production was increased by elevated CO2 in the peat soil, measured both as instantaneous and cumulative rates, but only the latter measure was increased in the limestone soil. Root growth was stimulated more at 6 cm depth than at 10 cm in the limestone soil. Turnover was faster under elevated CO2in the peat soil, but there was only a small effect on turnover in the limestone soil. Elevated CO2 reduced nitrogen concentration in roots and might have increased mycorrhizal colonization. Respiration rate was correlated with N concentration, and was therefore lower in roots grown at elevated CO2. Estimates of the C budget of the two communities, based upon root production and on net C uptake, suggest that C sequestration in the peat soil increases by c. 0.2 kg C m −2yr−1(= 2 t ha yr−1) under elevated CO2.
Phosphorus allocation and utilization in three grass species with contrasting response to N and P supply
Authors: RYSER PETER , VERDUYN BETTY , LAMBERS HANS
Published: March 2003

summary

The growth of the grass Brachypodium pinnatum (L.) Beauv. in Dutch nutrient‐poor chalk grasslands increases with enhanced nitrogen supply, whereas other grass species also require an enhanced phosphorus supply for a similar response (e.g. Dactylis glomerata L.), or are competitively suppressed at any increase in nutrient supply (e.g. Briza media L.). We investigated whether this interspecific variation in response to N and P supply is caused by differences in P productivity (PP), i.e. the instantaneous rate of biomass production per unit of P present in the plant. We hypothesized that PP is highest in Brachypodium pinnatum, in contrast to N productivity which is known to be the highest in Dactylis glomerata. Phosphorus productivity and its components were studied using a growth analysis with four exponential P addition rates of 0.03, 0.06, 009 and 0.11/0.15 mg P mg−1P d−1.

Although Brachypodium pinnatum allocated more P to its leaf blades, it had a lower P productivity at high N and low P supply than did Dactylis glomerata. This was associated with a higher productivity per unit leaf P in Dactylis glomerata. Across all species and treatments, leaf PP showed a distinct negative correlation with P concentration per leaf area, regardless whether the variation in area‐based leaf P concentration was caused by variation in leaf thickness, leaf tissue mass density or mass‐based P concentration. A possible explanation for this would be a positive correlation between leaf chlorophyll concentration and P concentration, leading at high concentrations to shading within the leaf and to a low photosynthetic rate per unit leaf P. We conclude that a high pp is determined by the ability of a plant to distribute its P over a large leaf area, rather than by greater allocation of P to the leaves. Interspecific relationships for P productivity are similar to those known for N productivity.
Performance of the thistle gall fly, Urophora cardui, in relation to host plant nitrogen and mycorrhizal colonization
Authors: GANGE ALAN C , NICE HELEN E.
Published: March 2003

summary

Many hypotheses have been developed to explain the adaptive nature of insect galls. One of these, the nutrition hypothesis, states that gall formers have advantages over other insects because gall tissue provides a better (higher quality) food source than unmodified tissue. However, this has rarely been experimentally tested. In a test of this hypothesis, we grew plants of Cirsium arvense (L.) Scop. in a factorial design with two main treatments: the addition of nitrogen (to enhance foliar N levels) and of fungicide (to reduce colonization of roots by arbuscular mycorrhizal fungi). Mycorrhizal fungi have been shown previously to reduce the N concentration of host plants. Plants were exposed to adult gall flies, Urophora cardui L., and maintained through one season to allow maturation of galls.

Reduction of the percentage mycorrhizal colonization by fungicide resulted in an elevation of total stem N comparable to that achieved by N addition, but gall N concentration remained unchanged in all treatments. Nitrogen application elevated stem N levels when mycorrhizal fungi were present, but application of both compounds together did not result in any increase over either single treatment. Fungicide application resulted in larger galls, which contained more larval chambers, with more live, and heavier, larvae. However, the main effects of N were not significant, as N addition only increased fly performance on plants where mycorrhizas were not reduced.

It is suggested that U. cardui gall inhabitants can manipulate N at an optimal level and thus might conform to a modified version of the nutrition hypothesis. Mycorrhizal colonization might reduce gall fly performance by delaying the appearance, or impairing the quality, of secondary nutritive tissue in the gall. Future tests of the nutrition hypothesis should include a consideration of the plant's mycorrhizal status.
Genetic structure of a natural population of the ectomycorrhizal fungus Suillus pungens
Authors: BONELLO PIERLUIGI , BRUNS THOMAS D. , GARDES MONIQUE
Published: March 2003

Sequence‐based markers were developed to study the genetic structure and reproductive biology of the ectomycorrhizal fungus Suillus pungens Thiers & Smith in a Bishop pine (Pinus muricata D. Don) forest. Six different basidiome genotypes were found in a 1200 m2 area. Five of the six genotypes were represented by single basidiomes. The remaining genotype comprised 13 basidiomes and covered an area of at least 300 m2, with maximum measured dimensions of 40 m and 14 m. This is the largest genet of an ectomycorrhizal fungus described to date, and is likely the result of vegetative growth, because analysis of single spore isolates eliminates the possibility of genetic identity resulting from either apomixis or fortuitously indistinguishable recombinant genotypes. Genetic analysis also shows that although out‐crossing appears to predominate in the population, at least a low percentage (1·4%) of spores are secondarily homothallic.

The combination of extensive vegetative growth and abundant fruiting suggests S. pungens utilizes more carbon than might be expected for a species which accounts for <3% of the total ectomycorrhizal abundance at the site. Additional carbon might come from either more efficient host–fungus transfer, pooling of carbon from the roots of different host plants, or saprophytism.
The response of Norway spruce seedlings to simulated acid mist
Authors: SHEPPARD LUCY J. , LEITH IAN D. , MURRAY MAUREEN B. , CAPE J. NEIL , KENNEDY VALERIE H.
Published: March 2003

Four pot experiments are reported in which Norway spruce (Picea abies (L.) Karst) seedlings, of different nutrient status, were treated with acid mist for one growing season in open‐top chambers (OTCs). Combinations of H+, SO42−, NH4+ and NO3− were applied at different frequencies of application and supplying different doses of S and N kg ha−1. Plant growth, visible injury, frost hardiness and nutrient status were observed. These experiments were undertaken to improve our understanding of the interaction of environmental factors such as nutrition and mist‐exposure frequency on seedling response to N and S deposition.

Both acidity (pH 2·7) and SO42− ions were necessary to induce visible injury. Mist containing SO42−, H+ and to a lesser extent NH4+ significantly reduced winter frost hardiness. Increasing the misting frequency, and to a lesser extent the overall dose, increased the likelihood of acid mist causing visible injury and reducing frost hardiness. Post‐planting stress, low N status and needle juvenility increased the likelihood of acid mist causing visible injury. Increased plant vitality, adequate N status and growth rate reduced the likelihood of acid‐mist‐induced reductions in frost hardiness.

Principles underlying the responses of spruce seedlings treated in controlled conditions to acid mist are discussed.
Interspecific differences in the response of arbuscular mycorrhizal fungi to Artemisia tridentata grown under elevated atmospheric CO2
Authors: KLIRONOMOS JOHN N. , URSIC MARGOT , RILLIG MATTHIAS , ALLEN MICHAEL F.
Published: March 2003

Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with the root systems of most plant species. These mutualisms regulate nutrient exchange in the plant–soil interface and might influence the way in which plants respond to increasing atmospheric CO2. In other experiments, mycorrhizal responses to elevated CO2 have been variable, so in this study we test the hypothesis that different genera of AM fungi differ in their response, and in turn alter the plant's response, to elevated CO2. Four species from three genera of AM fungi were tested. Artemisia tridentata Nutt. seedlings were inoculated with either Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, Acaulospora sp. or Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders and grown at either ambient CO2 (350 ppm) or elevated CO2 (700 ppm). Several significant inter‐specific responses were detected. Elevated CO2 caused percent arbuscular and hyphal colonization to increase for the two Glomus species, but not for Acaulospora sp. or S. calospora. Vesicular colonization was not affected by elevated CO2 for any fungal species. In the extra‐radical phase, the two Glomus species produced a significantly higher number of spores in response to elevated CO2, whereas Acaulospora sp. and S. calospora developed significantly higher hyphal lengths. These data show that AM fungal taxa differ in their growth allocation strategies and in their responses to elevated CO2, and that mycorrhizal diversity should not be overlooked in global change research.
Ecological effects of atmospheric reactive nitrogen deposition on semi‐natural terrestrial ecosystems
Authors: LEE J. A. , CAPORN S. J. M.
Published: March 2003

Evidence that enhanced reactive nitrogen deposition is affecting semi‐natural terrestrial ecosystems comes from historic increases in plant tissue N concentrations, correlations between tissue N concentrations and present‐day total atmospheric N deposition, changes in plant amino‐acid composition and effects on N assimilation. The ecological significance of such changes in biomarkers is uncertain. This paper explores the ecological significance of reactive atmospheric N deposition through a review of previous experimental findings and new experimental evidence from an acidic and a calcareous grassland, both showing phosphorus limitation, and a N‐limited Calluna vulgaris (L.) Hull heathland in upland Britain. Nitrogen addition in the range 0–20 g N m−2 yr−1 initially (years 0–4) increased the growth of Calluna and a decline in some subordinate species. In subsequent years, shoot extension was not stimulated, but winter injury was observed from 1993 onwards, suggesting a strong interaction between N supply and climatic conditions. By contrast, the grasslands showed a small decrease in the cover of higher plants in later years (6–7) of the experimental treatments (0–14 g N m−2 yr−1) and no growth stimulation. All N treatments reduced the bryophyte cover in the acidic grassland. There were marked effects on below‐ground processes, including a sustained stimulation of N mineralization in the grassland soils, and an increase in the bacterial utilization of organic substrates in the heathland, as measured in BIOLOG plates. The results strongly suggest the importance of atmospheric N deposition on microbially driven processes in soils, and are discussed in relation to the scale of potential ecosystem changes and their reversibility by pollution abatement.
Ozone and forest trees
Authors: BROADMEADOW MARK
Published: March 2003

Current estimates of forest yield losses attributable to ozone pollution amount to c. 10% over Europe as a whole. This figure is derived from a synthesis of all European studies using trees for which AOT40 exposure values are available. However, the choice of 40 nl l−1 as the threshold concentration for demonstrable effects has led to debate, and this value might not be low enough to predict ozone effects in Scandinavia, where concentrations are lower than in southern Europe, and chronic injury resulting from cumulative exposure is observed. This ‘level I’ approach provides a useful means for mapping physiologically effective concentrations but has significant shortcomings in that it is unable to take environmental conditions into account. In order to produce a mechanism capable of predicting yield losses resulting from ozone pollution at specific sites and for individual species, the effective ozone dose, a product of conductance and concentration, must be calculated. Process‐based models relating the environment (temperature, humidity/saturation deficit, incident light and soil moisture content) to conductance are available for a number of species (oak, Scots pine, Norway spruce, Sitka spruce, beech and poplar). Effective ozone doses could therefore be calculated, and the relationships between effective dose and yield loss could be determined by revisiting existing data for which only concentrations or AOT40 values are available at present. Yield loss must be the growth parameter with which ozone damage is expressed, since visible injury does not necessarily represent severe injury to the plant, whilst visibly unaffected plants may be significantly compromised in terms of biomass accumulation. For conifers, premature needle drop, although indicative of ozone pollution, might not represent a significant reduction in growth since older needles are, functionally, relatively unimportant.

When revisiting old experiments the question should also be asked ‘what is an appropriate control treatment’. It is unrealistic to expect ambient O3 concentrations on a global scale to return to pre‐industrialization levels, and therefore the use of a charcoal‐filtered treatment is probably unrealistic. In addition, charcoal filters will remove some of the NOx, and therefore on nutrient deficient soils (typical of many forest soils) the ‘control’ treatment might represent a reduced supply of nitrogen, making it difficult to disentangle the ozone effect per se.

The stage has therefore been reached where ‘level II’ ozone exposure mapping (i.e. based on effective dose at the physiological level) is possible for a number of species. As financial considerations become increasingly important, the scientific community must aim to provide better estimates of O3‐induced yield losses so that long‐term environmental audits can be performed.
The daily integral of nitrogen fixation by planktonic cyanobacteria in the Baltic Sea
Authors: STAL LUCAS J. , WALSBY ANTHONY E.
Published: March 2003

Measurements were made of the rates of nitrogenase activity (acetylene reduction) by cyanobacteria collected from the Baltic Sea at 2‐h intervals, over a period of 24 h, and incubated under natural light. By relating the chlorophyll‐specific rate of N2 fixation (PN) to the mean photon irradiance (I) at different periods, a PN/I curve was constructed. A mathematical description of this relationship was used in the calculation of rates of N2 fixation at different depths and times of day from continuous measurements of surface irradiance and light attenuation. By relating these calculations to the vertical distribution of chlorophyll due to Aphanizomenon flos‐aquae, an estimate of the daily integral of N2 fixation by the population of this cyanobacterium was obtained: it varied from 0·39 to 0·71 mmol m−2 with a mean value of 0·53 mmol−2 over 9 d. Comparisons with similar calculations of the daily integral of photosynthesis over the same period indicated the atomic ratio of N/C fixed is about 0·22, not very different from the N/C ratio expected for the elemental composition of these cyanobacteria. It is demonstrated that when buoyant gas‐vacuolate colonies float up during calm periods the increased irradiance that they experience supports an increased rate of N2 fixation. This increase is less than that seen for carbon fixation because photosynthesis is negated by respiration at low irradiances and is less inhibited at high irradiances.
Cytolocalization of glycogen, starch, and other insoluble polysaccharides during ontogeny of Paxillus involutus–Betula pendula ectomycorrhizas
Authors: JORDY M. N. , AZÉMAR‐LORENTZ S. , BRUN A. , BOTTON B. , PARGNEY J. C.
Published: March 2003

The Paxillus involutus (Fries) Karsten–Betula pendula Roth association was studied during the early stages of formation. Cytological studies revealed fungal colonization behind the root cap and gradually around the entire root apex. Ultrastructural investigations were carried out and insoluble polysaccharide distribution was followed. The density of starch grains increased in plant cells especially after 4 d of contact between the two partners, but later on decreased strongly in the root cap. Large amounts of glycogen were revealed in the hyphae in certain mycorrhizal regions after 6 d of contact: in the Hartig net, in the inner sheath but only near the net, and all along the outer sheath surrounding the mycorrhiza. Thickenings of the epidermal cell walls were detected as early as 2 d after contact and then varied according to the distance from the root tip. Such polysaccharide distributions are assumed to show a transfer of carbohydrates from the root to the fungus and are discussed in terms of carbon requirements for both partners.
Temperature and ontogeny mediate growth response to elevated CO2 in seedlings of five boreal tree species
Authors: TJOELKER M. G. , OLEKSYN J. , REICH P. B.
Published: March 2003

We tested the extent to which growth responses to elevated carbon dioxide (CO2) are temperature‐dependent and change through early seedling ontogeny among boreal tree species of contrasting relative growth rates (rgr). Populus tremuloides Michx, Betula papyrifera Marsh, Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seeds for 3 months in controlled‐environment chambers at two CO2 concentrations (370 and 580 μmol mol−1) and five temperature regimes of 18/12, 21/15, 24/18, 27/21 and 30/24°C (light/dark). Growth increases in response to CO2 enrichment were minimal at the lowest temperature and maximal at 21/15°C for the three conifers and at 24/18°C or higher for the two broadleaved species, corresponding with differences in optimal temperatures for growth. In both CO2 treatments, rgr among species and temperatures correlated positively with leaf area ratio (lar) (r⩾0·90, P<0·0001). However, at a given lar, rgr was higher in elevated CO2, owing to enhanced whole‐plant net assimilation rate. On average in all species and temperatures at a common plant mass, CO2 enrichment increased rgr (9%) through higher whole‐plant net assimilation rate (22%), despite declines in lar in high CO2 (11%). Reductions in lar are thus an important feedback mechanism reducing positive plant growth responses to CO2. Proportional allocation of dry mass to roots did not vary between CO2 treatments. Early in the experiment, proportional increases in plant dry mass in elevated CO2 were larger in faster‐growing Populus tremuloides and B. papyrifera than in the slower‐growing conifers. However, growth increases in response to CO2 enrichment fell with time for broadleaved species and increased for the conifers. With increasing plant size over time, compensatory adjustments to CO2 enrichment in the factors that determine rgr, such as lar, were much larger in broadleaves than in conifers. Thus, the hypothesis that faster‐growing species are more responsive to elevated CO2 was not supported, given contrasting patterns of growth response to CO2 with increasing plant size and age.
Effects of elevated CO2 and soil quality on leaf gas exchange and above‐ground growth in beech–spruce model ecosystems
Authors: EGLI PHILIPP , MAURER STEFAN , GÜNTHARDT‐GOERG MADELEINE S. , KÖRNER CHRISTIAN
Published: March 2003

Responses of leaf gas exchange and above‐ground growth of beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) to atmospheric CO2 enrichment (374 μl l−1 vs. 590 μl l−1) and increased wet deposition of N (5 vs. 50 kg N ha−1 a−1) in combination with two natural forest soil types (‘acidic’ and ‘calcareous’) were studied in large open‐top chambers. Eight juvenile beech and spruce trees from different provenances, together with a ground cover composed of five understorey species, were established in each of 32 model ecosystems. Both beech and spruce showed sustained enhancement of photosynthesis in response to atmospheric CO2 enrichment during the first 2 yr of treatment. Nevertheless, switching measurement CO2 concentrations revealed partial downward adjustment of photosynthesis in trees grown in elevated CO2, beech generally showing more pronounced downward adjustment than spruce. The responsiveness of photosynthesis to CO2 enrichment did not vary significantly among trees from different provenances. Stomatal conductance was reduced under elevated CO2 in both tree species. In spruce, the radial growth of the main stem and the annual production of wood (shoot‐wood dry mass of current‐year lateral shoots), needle dry mass, and assimilation area per tree were stimulated both by CO2 enrichment and increased N deposition, but were not significantly affected by soil type by year 2. In contrast, in beech, the radial growth of the stem and the total leaf number, foliage dry mass, and assimilation area per tree were all not significantly affected by elevated CO2 and increased N deposition when responses of the two soil types were pooled, but were greater on calcareous than on acidic soil by year 2. However, CO2 interacted with soil type in beech: irrespective of the N deposition rate, saplings showed growth stimulation on the calcareous soil but responded negatively to CO2 enrichment on the acidic soil (where growth was slower). Our results suggest that complex interactions between CO2, species and soil quality need to be accounted for when attempting to predict forest development in a future CO2‐rich world.
The auxin transport inhibitor 2,3,5‐triiodobenzoic acid (TIBA) inhibits the stimulation of in vitro lateral root formation and the colonization of the tap‐root cortex of Norway spruce (Picea abies) seedlings by the ectomycorrhizal fungus Laccaria bicolor
Authors: KARABAGHLI‐DEGRON C. , SOTTA B. , BONNET M. , GAY G. , LE TACON F.
Published: March 2003

Norway spruce (Picea abies (L.) Karst.) seedlings were inoculated with the ectomycorrhizal fungus Laccaria bicolor ((Marie) Orton), strain S238 N, in axenic conditions. The presence of the fungus slowed tap–root elongation by 26% during the first 15 d after inoculation and then stimulated it by 136%. In addition, it multiplied in vitro lateral root formation by 4.3, the epicotyl growth of the seedlings by 8.4 and the number of needles by 2. These effects were maintained when the fungus was separated from the roots by a cellophane membrane preventing symbiosis establishment, thus suggesting that the fungus acted by non‐nutritional effects. We tested the hypothesis that IAA produced by L. bicolor S238 N would be responsible for the stimulation of fungal induced rhizogenesis. We showed in previous work that L. bicolor S238 N can synthesize IAA in pure culture. Exogenous IAA supplies (100 and 500 μm) reproduced the stimulating effect of the fungus on root branching but inhibited root elongation. The presence of 2,3,5‐triiodobenzoic acid (TIBA) in the culture medium significantly depressed lateral root formation of inoculated seedlings. As TIBA had no significant effect on IAA released in the medium by L. bicolor S238 N, but counteracted the stimulation of lateral rhizogenesis induced by an exogenous supply of IAA, we suggest that TIBA inhibited the transport of fungal IAA in the root. Furthermore TIBA blocked the colonization of the main root cortex by L. bicolor S238 N and the formation of the Hartig net. These results specified the role of fungal IAA in the stimulation of lateral rhizogenesis and in ectomycorrhizal symbiosis establishment.
Suppression of hyphal growth of soil‐borne fungi by dune soils from vigorous and declining stands of Ammophila arenaria
Authors: DE BOER W. , KLEIN GUNNEWIEK P. J. A. , WOLDENDORP J. W.
Published: March 2003

A study was carried out to determine whether expansion of marram‐grass stands (Ammophila arenaria (L.) Link) on acidic inner Dutch coastal dunes was caused by suppressiveness of soils from these stands against three potential pathogenic fungi of marram grass, namely Fusarium culmorum (W. G. Sm.) Sacc., Phoma exigua Desm. and a Ulocladium sp. The suppressiveness of the acidic inner dune soils was compared with that of lime‐rich dune soils from vigorous and declining marram‐grass stands. Suppressiveness of the dune soils against the saprotrophic fungi Chaetomium globosum Kunze: Fr, Mucor hiemalis Wehmer and Trichoderma harzianum Rifai was also determined. All fungi had been isolated from marram‐grass roots. Suppressiveness was determined by comparing the formation of hyphae from potato–dextrose agar discs into (layer method) or on top of (surface method) dune soils with that of controls consisting of sterile, acid‐washed beach sand. The growth of the three root‐infecting fungi was strongly inhibited in all soils regardless of the method used. Hence, there were no indications that the potential pathogenic fungi were selectively suppressed by the acidic dune soils and, consequently, the results did not give any indication for the involvement of a fungal component in the decline of marram grass. Growth of the saprotrophs C. globosum and M. hiemalis was much less inhibited than that of the root‐infecting fungi. Growth of T. harzianum was strongly inhibited in alkaline soils but not in the acid ones. The suppression of fungal growth could be partly or completely eliminated by a microwave treatment, indicating that biological components of the soil were essential to suppressiveness. The suppression of the fungi by colonies of dune soil micro‐organisms on water‐agar differed considerably from soil alone. Yet, all methods indicated the occurrence of general suppressiveness against fungi by dune soils, irrespective of the origin of the soil samples. This suppressiveness was probably not due to direct competition with other soil micro‐organisms for nutrients but to inhibiting compounds produced by the soil micro‐organisms.
Impacts of ozone on Plantago major: apoplastic and symplastic antioxidant status
Authors: LYONS TOM , OLLERENSHAW JOHN H. , BARNES JEREMY D.
Published: March 2003

The aim of this work was to examine the correspondence between apoplastic/symplastic antioxidant status and previously reported plant age‐related shifts in the ozone (O3) resistance of Plantago major L. Seed‐grown plants were fumigated in duplicate controlled environment chambers with charcoal/Purafil?‐filtered air (CFA) or CFA plus 70 nmol mol−1 O3 for 7 h d−1 over a 42 d period. Measurements of stomatal conductance and antioxidants were made after 14, 28 and 42 d fumigation, on leaves at an equivalent stage of development (youngest fully expanded leaf, measured c. 9 d after emergence). Ozone exposure resulted in a similar decline in stomatal conductance across plant ages, indicating that increases in O3 resistance with plant age were mediated through changes in the tolerance of leaf tissue rather than enhanced pollutant exclusion. Leaf apoplastic washing fluid was found to contain ‘unspecific’ peroxidase, ascorbate peroxidase, superoxide dismutase and ascorbate, but not glutathione and the enzymes required to facilitate the regeneration of ascorbate from its oxidized forms. A weak induction in the activity of certain symplastic antioxidants was found after 14 d O3 fumigation, despite a lack of visible symptoms of injury, but shifts in symplastic antioxidant enzyme activity were not consistent with previously observed increases in resistance to O3 with plant age. By contrast, changes in ‘unspecific’ peroxidase activity and in the small pool of ascorbate in the leaf apoplast were found to accompany age‐related shifts in O3 resistance. It is concluded that constituents of the leaf apoplast may constitute a potentially important front line defence against O3.
Characterization of PSII photochemistry in salt‐adapted cells of cyanobacterium Spirulina platensis
Authors: LU CONGMING , VONSHAK AVIGAD
Published: March 2003

The changes in pigment composition, photosynthesis and PSII photochemistry were investigated in cells of Spirulina platensis adapted to salt stress (<0.75 M NaCl). A decrease in the phycocyanine/chlorophyll and no significant change in the carotenoid/chlorophyll ratio were observed in salt‐adapted cells. Salt stress inhibited the apparent quantum efficiency of photosynthesis and PSII activity while stimulating PSI activity and dark respiration significantly. Salt stress also resulted in a decrease in overall activity of the electron transport chain, which could not be restored by diphenylcarbazide, an artificial electron donor to the reaction centres of PSII. Measurements of the polyphasic fluorescence rise in fluorescence transients including phases O, J, I and P showed that salt stress had no effect on the fluorescence yield at phase O but decreased the fluorescence yield at phases J, I and P. Analyses of the JIP test developed from the polyphasic rise of fluorescence transients showed that salt stress led to a decrease in both the maximum quantum efficiency of PSII photochemistry and the maximum quantum efficiency of electron transport beyond the primary quinone electron acceptor. However, salt stress induced no significant changes in the probability of transporting an electron beyond QA, the trapping flux per PSII reaction centre, or the electron transport flux per PSII reaction centre. A theoretical analysis of fluorescence parameters indicated a decrease in the rate constant of excitation energy trapping by PSII reaction centres. In addition, salt stress induced an increase in the complementary area above the fluorescence induction curve in the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea, suggesting an increase in the proportion of closed PSII reaction centres in salt‐adapted cells. Based on these results, it is suggested that modifications in PSII photochemistry in salt‐adapted Spirulina cells maintained a high conversion efficiency of excitation energy, such that no significant change was observed in either the trapping flux or the electron transport flux per PSII reaction centre.
Specific PCR‐primers as a reliable tool for the detection of white truffles in mycorrhizal roots
Authors: MELLO ANTONIETTA , GARNERO LILIA , BONFANTE PAOLA
Published: March 2003

During their symbiotic phase, white truffles are barely distinguishable morphologically, and molecular probes are needed for their identification. Here we report the design of species‐specific primers for two white truffles (Tuber magnatum and T. borchii) on the basis of their ITS sequence. Their efficiency has been successfully tested on fruit bodies of the same species, many related and unrelated fungal species, as well as mycorrhizal roots in direct, nested and multiplex PCR experiments. They have allowed us to identify T. magnatum mycorrhizas for the first time.
Culture senescence and abscisic acid induce saporin production in cultured roots of Saponaria officinalis
Authors: DI COLA ALESSANDRA , POMA ANNA , SPANÒ LAURA
Published: March 2003

The presence and variation of activity of the type 1 ribosome‐inactivating protein saporin has been evaluated in cultured roots of the soapwort Saponaria officinalis. Results from western analysis and in vitro protein synthesis inhibition indicate that saporin production is increased in senescing cultures, reaching a maximum value during the late stationary phase. Accordingly, cultures treated with the senescence‐related hormone abscisic acid show a significant increase in saporin activity, independently from the culture growth phase. Stress conditions, such as the presence of hydrogen peroxide in the culture medium, had no effect on the modulation of enzymatic activity. The putative regulation of saporin production by abscisic acid and its possible role in accomplishing the ageing programme is discussed.