bluuebunny/crossref_metadata_2025 huggingface dataset:
Diversity and phylogeny of rhizobia
Authors: PETER J. , YOUNG W. , HAUKKA KAISA E.
Published: April 2006

Rhizobia are the bacteria that form nitrogen‐fixing nodules on legumes. The current list of four rhizobium genera and 17 species is reviewed, with some comments on likely future developments in the taxonomy. Sequences of the small subunit ribosomal RNA (SSU or 16S rRNA) support the well‐established subdivision of rhizobia into three genera: Rhizobium, Bradyrhizobium and Azorhizobium. These all lie within the alpha subdivision of the Proteabacteria, but on quite distinct branches, each of which also includes many bacterial species that are not rhizobia. Rhizobium, by this definition, is still broad and polyphyletic, so there have recently been suggestions that this genus should be split into four genera. SSU sequences may be the best phylogenetic tool we have, but they are not an infallible guide to evolutionary relationships, particularly among closely related species: slow evolution, recombination, intraspecinc variation and even intragenomic heterogeneity are all limitations that can be illustrated by examples from the rhizobia. It seems likely that the ability to form legume nodules was not present in the common ancestor of all rhizobia but that the nodulation genes were transferred between phylogenetically distinct bacteria, so that the phylogeny of nodulation genes will probably differ from that of the bacteria that carry them. Nitrogen fixation genes are often linked to nodulation genes, but they need not have the same evolutionary history.
Diversity of the ribosomal internal transcribed spacers within and among isolates of Glomus mosseae and related mycorrhizal fungi
Authors: LLOYD‐MACGILP S. A. , CHAMBERS S. M. , DODD J. C. , FITTER A. H. , WALKER C. , YOUNG J. P. W.
Published: April 2006

The internal transcribed spacer (ITS) region of the nuclear ribosomal RNA was amplified, cloned and sequenced from spores of five isolates of the arbuscular mycorrhizal fungus Glomus mosseae and one isolate each of G. fasciculatum, G. dimorphicum and G. coronatum. The sequences comprised ITSI (113–121 base pairs), 5.8S rRNA gene (154 base pairs) and ITS2 (222–230 base pairs). The ITS sequences were at least 84% identical, but only distantly related to other published sequences. Their identification as Glomus sequences was confirmed by sequencing part of the adjoining SSU rRNA gene from one isolate; it was 98% identical to the published G. mosseae sequence. Two to four clones were sequenced from each isolate, and in many instances these were substantially different (up to 6 % divergence) even when they were obtained from a single spore. Sequences from a single isolate were generally, but not always, more similar to each other than to those from different isolates. In addition to base substitutions, many ITS sequences differed slightly in length because of the insertion or deletion of up to three nucleotides within short runs of a single base, generally A or T. These changes were found at 22 separate sites within the ITS, and were more common between than within isolates. Phylogenetic relationships deduced from length variation and from base substitution were similar. The variation among isolates from different continents (Europe, Asia, South America) was no greater than among those from a smaller geographic range. The ITS1 and 2 sequences from G. caronatum were clearly distinct from the other isolates (11–16% divergence), but those of G. fasciculatum and G. dimorphicum fell within the range of variation exhibited by G. mosseae.
The choice of molecular marker methods for population genetic studies of plant pathogens
Authors: BROWN J. K. M.
Published: April 2006

DNA markers have been used in many studies of fungal plant pathogens, and in particular in investigations of mating systems, gene flow, the establishment of epidemics and adaptation to host crops. Many aspects of population structure can be analysed by means of contingency tables, using χ2 tests. Some extensions of such tests, with particular applications to plant pathology, are described. One test is applicable to situations where there is more than one level of subdivision of populations, while another is appropriate when there are two types of division, for instance by geographical area and by host crop. Furthermore, the χ2 test offers a convenient way of combining information from several independent markers. Tests for the differentiation of subpopulations are based on certain underlying assumptions, and it is argued that the primary consideration in choosing a marker system should be whether or not it fits the appropriate genetic criteria. Other considerations, such as time, cost and difficulty, should be evaluated if two or more methods are capable of generating markers which fit the genetic assumptions adequately. Although a large number of markers should be examined in order to estimate the extent of population subdivision, it might only be necessary to use a few markers to test whether such subdivision exists. Likewise, only a few markers may be needed to distinguish clones of a pathogen in a partially sexual population. However, in all of these tests, these markers should be well characterized genetically. It is shown that an existing genetic fingerprinting system for the barley powdery mildew fungus, Erysiphe graminis f. sp. hordei, is suitable for identifying clones but not for describing the differentiation of subpopulations. It may be possible to use markers based on random amplified polymorphic DNA (RAPD) or on amplified fragment length polymorphism (AFLP) in quantitative research in population genetics of E. graminis f. sp. hordei.
The interactive effect of irradiance and source of nitrogen on growth and root respiration ofCalamagrostis epigejos
Authors: GLOSER VIT , SCHEURWATER INGEBORG , LAMBERS HANS
Published: April 2006

Growth and respiratory processes ofCalamagrostis epigejos(L.) Roth were studied as part of a comprehensive ecological project aimed at explaining the acclimation potential of some perennial grasses upon changes in climatic and edaphic factors after logging activity in forests. We investigated the relative growth rate (RGR), the respiration rate and the contribution of the different respiratory pathways in roots ofCalamagrostis epigejosgrown at two levels of irradiance and with nitrate or ammonium as N‐source. The respiration rate as well as the RGR decreased significantly but the leaf area ratio (LAR) increased upon transfer to shade. The LAR increase was caused by both a greater specific leaf area (SLA) and a greater leaf weight ratio (LWR). The relative contribution of the alternative (AP) and the cytochrome pathways to total respiration rate was the same in both radiation regimes. The ammonium form of N‐nutrition had a significant stimulative effect on AP activity in shaded plants. The AP capacity was significantly higher in ammonium‐fed plants grown at both irradiance levels. A possible role of the AP in plants with low energy input and with ammonium ions as N‐source is discussed.
Tissue level localization of acid invertase in leaves: an hypothesis for the regulation of carbon export
Authors: KINGSTON‐SMITH ALISON H. , POLLOCK CHRISTOPHER J.
Published: April 2006

Photoassimilate produced by mature leaves is usually loaded into the phloem as sucrose. Transport of sucrose from the mesophyll cells to the phloem might involve an apoplastic step or be entirely symplastic, depending on species. Acid invertase occurs as both soluble and cell‐wall‐bound forms and has been detected in mature leaves. However, the ability of this enzyme to act as a regulator of carbon export and storage depends on whether it occurs either in the sucrose transport path (which could decrease export), or is located within the mesophyll cells (potentially resulting in intracellular futile cycling between sucrose synthesis in the cytoplasm and hydrolysis in the vacuole). Tissue‐level localization of acid invertase was investigated by tissue printing, which establishes protein distribution within a leaf. Antiserum was raised against a synthetic peptide corresponding to a region close to the active site of acid invertase. Tissue prints from Pisum sativum L. and Hordeum vulgare L. showed invertase to be located in the vascular regions, which was not observed in Fuchsia hybrida L. This corresponds to differences in the presence of oligosaccharides in leaf extracts and in the pattern of plasmodesmatal connections between mesophyll cells and the vasculature. We hypothesize that the location of acid invertase activity is implicated in species‐specific differences in sucrose and oligosaccharide metabolism.
Effects of repeated parasitism byRhinanthus minoron the growth and photosynthesis of a perennial grass,Poa alpina
Authors: SEEL W. E. , PRESS M. C.
Published: April 2006

Plantlets ofPoa alpinaL. taken from a single viviparous mother plant in August 1991 were pot‐grown in an experimental garden in Abisko, Swedish Lapland. Half of the pots were infected with the annual hemiparasitic angiospermRhinanthus minorL. A proportion of the plants were harvested in August 1992: the infected grasses were less than half the mass of uninfected controls and had a higher proportion of brown (dead) tissue, but a similar partitioning of biomass into roots, stems and leaves. The grasses remaining after this harvest were divided into four groups: control (infected neither in 1992 nor in 1993 (−−)), newly infected (1993 only (−+)), not re‐infected (+–) and re‐infected (++). Total biomass accumulation by August 1993 was greatest in control grasses (−−) and least in those plants which had been infected for two consecutive years (++). Plants infected for the first time in their second year of growth (−+) showed fewer visible effects than those infected in their first year of growth (+–), but the relative biomass accumulation in 1993, when expressed per gram of dry matter existing at the end of the 1992 growing season, was least in those plants infected for the first time in 1993 ((‐ +) 6·41 g g−1) and greatest in those which had previously been infected but were relieved of infection in the second year ((+−) 12·65 g g−1). Unlike that in plants harvested in the first year of the investigation, the pattern of biomass partitioning differed between the groups of 2‐yr‐old plants depending on the year of infection. Uninfected plants (−−), and those plants infected for the first time in 1993 (−+) produced many viviparous plantlets. Those plants infected in 1992 ((+−) and (++)) showed negligible plantlet production, but had more numerous and larger leaves, which senesced more slowly and had higher nitrogen concentrations than those of uninfected controls. The maximum rate of host photosynthesis, photosynthetic light compensation point and quantum efficiency of photosynthesis, measured on a unit green‐leaf area basis in July 1993, did not differ significantly between the four groups.

Parasites which were grown on 6‐month‐old grass (1992 harvest) were only two thirds of the mass of those growing on older grasses (1993 harvest), and those on grass parasitized for two years (++, i.e. those without plantlets) accumulated twice as much biomass as those growing on grasses infected for the first time in 1993 (–+, i.e. those with plantlets). Parasites which were growing on previously parasitized hosts also had greater foliar nitrogen concentrations than those growing on hosts not parasitized until 1993 (−+).
Purification and characterization of a new fructan series from species of Asteraceae
Authors: ERNST MICHAEL , CHATTERTON JERRY , HARRISON PHILIP A.
Published: April 2006

A new fructan series, in addition to inulin, was identified in tissue extracts of Cichorium intybus L., Helianthus tuberosus L. and Taraxarum officinale Weber. The second fructan series was separated from the inulin series up to degree of polymerization (DP) 18 by ion chromatography. The DP 4 of this new fructan scries was purified and structurally analysed. Hydrolysis and methylation analysis of the DP 4 oligomer shows that this is a fructan series that contains only β‐2,1‐linked fructose molecules. We conclude that this new fructan series in species of Asteraceae comprises the inulo‐n‐ose series and probably consists of products of inulin hydrolysis that are formed during inulin mobilization.
Gender variation, partial male sterility and labile sex expression in gynodioecious Plantago coronopus
Authors: KOELEWIJN HANS P. , VAN DAMME JOS M. M.
Published: April 2006

Gynodioecy is 8 breeding system consisting of male, steriles (MS, females) and hermaphrodites (H). There is however within such systems a third, often neglected, class of partially male sterile plants (PMS), i.e. plants with an intermediate sex expression, In natural populations of Plantago coronopus partially male sterile individuals were us common as male steriles (frequencies in the range 1·7–36·8%). These PMS plants constitute a continuous series, linking complete male sterility and hermaphroditism. We discovered that temperature influenced sex expression and the degree of male sterility of PMS individuals, but not of MS and H individuals. Thus, at higher temperatures PMS individuals became more male sterile. Difference in cytoplasmic background of the individuals did nut influence their response to temperature. It is argued that partial male sterility is a normal feature of gynodioecious species and not an abnormality.
Maternal effects on progeny inThymelaea hirsuta
Authors: EL‐KEBLAWY A. A. , SHALTOUT K. H. , DOUST J. LOVETT , DOUST L. LOVETT
Published: April 2006

In the evergreen desert shrub.Thymelaea hirsuta(L.) Endl., three major gender variants produce seed. ‘Stable females’ produce seed throughout the reproductive life of the individual, whereas the other two variants are dichogamous, producing both pollen and ovules at different limes, as ‘protandrous’, and ‘protogynous’ individuals. Seed was collected from individuals of the three maternal gender phenotypes, from six desert habitats in Egypt. Seed and seedling traits (seed mass, germination. Seedling emergence, growth and survival to 30 d, and to 1 yr) Were examined in laboratory and botanic garden experiments. Highly significant effects of maternal habitat were observed for most of these traits. Seedling height after 30 d differed significantly between habitats and maternal gender phenotypes. Plants from saline and non‐saline depressions were significantly taller than those from other sites, and progeny of females, overall, were taller than those of protandrous and protogynous seed parents. A significant interaction was observed between maternal habitat and maternal gender phenotype, for progeny height after 30 d and for per cent seed germination. We suggest that the three maternal gender phenotypes might be differentially favoured by selection.
Quantitative genetics of zinc hyperaccumulation in Thlaspi caerulescens
Authors: POLLARD A. JOSEPH , BAKER ALAN J.M.
Published: April 2006

We examined variation within and between populations of Thlaspi caerulescens J. & C. Presl (Brassicaceae). a plant species known to hyperaccumulate zinc to foliar concentrations exceeding 3 % (d.wt basis). Seeds were collected as sib families from two populations in Derbyshire, UK along with leaf samples from the parent plants. Offspring were grown hydroponically from seed, in culture solution containing 10 mg 1 −1Zn. Significant differences in zinc concentration and plant size were Found between populations and among sib families within populations. Heritability analysis based on resemblance among sibs revealed significant heritable variation within one population, but not the other. The characters of zinc accumulation and plant size were not correlated. Parent‐offspring recession did not prove useful for estimation of heritability, because of heterogeneity in metal availability to parents growing in the field. The results are relevant to attempts to exploit metal hyperaccumulation as a technology for remediation of contaminated soil, and to our understanding of the evolutionary origins of the phenomenon of hyperaccumulation.
The ozone sensitivity of birch (Betula pendula) in relation to the developmental stage of leaves
Authors: PÄÄkkÖNEN E. , METSÄRINNE S. , HOLOPAINEN T. , KÄRENLAMPI L.
Published: April 2006

Clonal birch (Betula pendula Roth.) seedlings at three different developmental stages were fumigated for 12h daily with 50, W and 130 ppb ozone for 25 d. When transferred to fumigation chambers, the leaves of plant group 1 were almost expanded, in group 2 they were fast enlarging, and in group 3 all the leaves emerged under the exposure. The plants in which the leaves emerged under the ozone stress were the most resistant to ozone. In groups 1 and 2 ozone treatments reduced the growth of leaf biomass, and induced more visible injuries on leaves and ultrastructural symptoms in chloroplasts than they did in group 3. The stomatal density of leaves increased in response to ozone in all the groups. The effects of ozone on stomatal conductance were complex. In groups 1 and 2 the 50ppb ozone exposure increased stomatal conductance whereas lowered conductances were observed in group 3 after fumigation with 90 and 130 ppb ozone. The results suggest that the leaves developing under ozone fumigation were better able of tolerate the ozone stress, as indicated by unaffected or stimulated growth and small amounts of visible and ultrastructural injuries and stomatal changes. It is possible to regard the changes as acclimation reactions.
Drought—CO2 interactions in trees observations and mechanisms
Authors: BEERLING D. J. , HEATH J. , WOODWARD F. I. , MANSFIELD T. A.
Published: April 2006

summary

It is sometimes assumed that because increases in atmospheric CO2 concentration usually enhance water use efficiency per unit leaf area, there will be a tendency for plants to show greater drought tolerance as well as increased biomass in the future. A critical examination of the responses to elevated CO2 in three temperate tree species shows that this assumption might be incorrect in the case of two of them. Both beech (Fagus sylvatica L.) and birch (Betula pubescens Ehrh.) display minimal stomatal closing responses to elevated CO2, and in the case of F. sylvatica the stomatal control of transpiration per unit leaf area appears to be unable to compensate for the greater development of leaf area. By contrast, the stomata of oak (Quercus robur L.) close appreciably in elevated CO2, to an extent which might be sufficient to compensate for an increase in total leaf area. A simple model for the controls on water supply and consumption for the whole tree suggests that in F. sylvatica the potential height attainment for a given sapwood area might decrease as the atmospheric CO2 concentration rises. The conclusions drawn from experimental data and from modelling are supported by field observations made in the UK in 1995, when the three species responded very differently to severe drought. We suggest that the progressive increase in the concentration of atmospheric CO2 over the past 200 yr might have accentuated differences in drought sensitivity between these species.
Absorption of atmospheric NO2 by spruce (Picea abies) trees
Authors: THOENE BARBARA , RENNENBERG HEINZ , WEBER PAUL
Published: April 2006

summary

The dynamic chamber technique was applied to investigate NO2 influx into Picea abies (L.) Karsten branches, and its effects on net photosynthesis and transpiration, as well as its dependency on irradiance, temperature and relative humidity. The study aimed to quantify effects of climate on atmospheric NO2 fluxes to spruce. Experiments were performed with 3‐ to 4‐yr‐old branches of 8‐ to 9‐yr‐old potted trees under controlled environmental conditions. With ambient NO2 concentrations increasing from 3.5 to 50 nl l−1a linear increase in the NO2 influx of up to c. 6.8 μmol m−2s−1was observed. From this increase a compensation point of 1.64 nl l−1NO2 was calculated by linear regression analysis. In the range of the NO2 concentrations studied, net photosynthesis of spruce was not affected. The responsiveness of the stomata to changes in irradiance and relative humidity was reduced at 45 nl l−1NO2 compared with 25 nl l−1NO2. With increasing irradiance up to 1000 μmol m−2s−1PAR, increasing NO2 flux to spruce branches was observed, which was attributed to a light‐dependent increase in stomatal aperture. Variation of the temperature between 14 and 35 °C did not affect the NO2 flux, in light or in darkness. Higher temperatures, up to 45 °C, resulted in an increase in NO2 influx in the light; in darkness, changes in NO2 flux were not observed under these conditions. An increase in relative humidity from 5 to 60 % in the light caused an increase in NO2 influx, whereas in darkness NO2 influx was not affected by changes in relative humidity. The increase in NO2 flux in response to r.h. observed in the light could not be explained by changes in stomatal aperture. A solution of NO2 in ultra‐thin water films covering the needle surface might explain this phenomenon.
Effect of artificial exclusion and augmentation of fungal plant pathogens on a regenerating grassland
Authors: PETERS J. C. , SHAW M. W.
Published: April 2006

summary

Plots of rough grassland dominated by Holcus lanatus L. were cleared of vegetation in three successive years and allowed to regenerate without grazing or harvesting. Vegetation cover and foliar disease severity were measured using pin sampling in each plot, two to four times per year. One third of plots were sprayed regularly with propiconazole to reduce fungal disease; one third of plots were sprayed with rust (Puccinia coronata f. sp. holci Corda.) urediospores in the second and third years of the study and with conidia of the leaf‐spotting fungus Ascochyta leptospora (Trail) Hara. In the third year. The fungicide had direct effects on the growth of perennial herbs and grasses, and indirect effects through disease control on perennial herbs. Both fungicide treatment and disease augmentation tended to raise diversity in plots where grasses were only partly dominant. Fungicides increased diversity because both direct and indirect effects were greater in perennial herbs than in grasses. Disease augmentation raised diversity because the diseases introduced were more specific to the most common component of the vegetation, H. lanatus.
Effect of 700 μmol mol −1CO2 and infection with powdery mildew on the growth and carbon partitioning of barley
Authors: HIBBERD J. M. , WHITBREAD R. , FARRAR J. F.
Published: April 2006

summary

The dry weight of barley plants in 700 μmol mol−1CO2 was increased by 19 d after planting relative to plants grown in 350 μmol mol−1CO2. Infection of the second leaf by powdery mildew led to reduced growth rates in both 350 and 700 μmol mol−1CO2, but the reduction in growth was transitory in 350 μmol mol−1CO2. Neither the allometric coefficient k between shoot and root, nor the leaf weight ratio, was altered by growth in 700 μmol mol−1CO2 or by infection with powdery mildew. The number of tillers produced increased per plant but not per unit d. wt in 700 μmol mol−1CO2. The growth response of barley to increased concentrations of CO2 and/or to infection with powdery mildew was not associated with alterations in net carbon partitioning, so a change in the ratio of photosynthetic to non‐photosynthetic tissue, contributed to neither the growth response of barley to 700 μmol mol−1CO2 nor to infection with powdery mildew. The increase in the growth rate of barley in 700 μmol mol−1CO2 and the reduction in the growth rate after infection occurred at the same time as increased and reduced rates of net photosynthesis respectively.
Vertical patterns of testate amoebae (Protozoa: Rhizopoda) and peat‐forming vegetation on cutover bogs in the Jura, Switzerland
Authors: BUTTLER ALEXANDRE , WARNER BARRY G. , GROSVERNIER PHILIPPE , MATTHEY YVAN
Published: April 2006

summary

The spatial and temporal processes of secondary vegetation development on abandoned cutover bog surfaces in the Jura region of northwest Switzerland have been examined. Descriptions of post‐abandonment development of peatland based on the vegetation composition of replacement series from previous studies of vegetation ecology have been confirmed by analysis of testate amoebae (Protozoa) in vertical sequences of secondary peat underlying the most advanced vegetation communities in the series. Recovery of bog habitats to conditions similar to those before cutting was rapid. Testate amoebae show this recovery occurred through several different developmental series, all of which led to a common convergence regardless of the initial condition of the old cutover surface. Cutover bogs can be fully restored and testate amoebae are a sensitive new means of monitoring habitat changes in bogs.
Phragmites die‐back: sulphide‐ and acetic acid‐induced bud and root death, lignifications, and blockages within aeration and vascular systems
Authors: ARMSTRONG J. , AFREEN‐ZOBAYED F. , ARMSTRONG W.
Published: April 2006

summary

Phragmites rhizome cuttings, and plantlets raised from seed, were exposed to the phytotoxins acetic acid or dissolved sulphide in unstirred solution cultures to determine whether die‐back symptoms found in field‐grown plants, and attributed to phytotoxin damage, could be induced. Many of the die‐back symptoms associated with field sites, namely stunted adventitious roots and laterals, bud death, callus blockages of the gas‐pathways, and vascular blockages, were all reproduced, and were particularly acute at the higher concentrations of the phytotoxins: acetic acid (1.67 mm), sulphide (1.4 mm).

The results accord with the hypothesis that phytotoxins may play a critical role in Phragmites australis die‐back.
Some foliar characteristics of ash trees (Fraxinus excelsior) exposed to ozone episodes
Authors: WILTSHIRE J. J. J. , WRIGHT C. J. , COLLS J. J. , CRAIGON J. , UNSWORTH M. H.
Published: April 2006

summary

Young ash trees (Fraxinus excelsiorL.) growing in the field were exposed to episodes of 150 nl 1−1ozone, or to clean air, in open‐top chambers at the University of Nottingham, Sutton Bonington Campus, UK, May–October, 1992–1994. The episodes were for 8 h daily and for 1–4 d in succession, with seasonal totals of 24–27 d. A nondestructive method for estimating whole‐tree leaf area was developed in 1992 and used to monitor leaf area, leaf number and leaf size in 1993 and 1994. Stomatal density and leaf abscission were also studied. No effects of exposure to ozone on leaf area and leaf number were detected. In 1994 there were consistent trends towards greater mean leaf size and higher stomatal density in trees exposed to ozone, but these effects were not significant at the 95% confidence level. Leaf abscission was slower in trees exposed to ozone in 1992 and 1994, but not in 1993 when there were fewer exposure days late in the season.
TheSauromatum guttatumappendix as an osmophore: excretory pathways, composition of volatiles and attractiveness to insects
Authors: SKUBATZ HANNA , KUNKEL DENNIS D. , HOWALD WILLIAM N. , TRENKLE ROBERT , MOOKHERJEE BRAJA
Published: April 2006

summary

This report combines chemical, electron microscopic and ecological studies on the volatiles liberated by theSauromatum guttatumappendix on D‐Day, the day of inflorescence‐opening and heat‐production. More than 100 compounds from at least nine different chemical classes (monoterpenes, sesquiterpenes, fatty acids, ketones, alcohols, aldehydes, indole, and phenolic and sulphur compounds) are liberated during the thermogenic activity. The volatiles were identified using gas chromatography‐mass spectrometry. Electron microscopy provides additional evidence that the endoplasmic reticulum (ER) interacts with the plasma membrane, creating novel routes of excretion of the volatiles to the exterior of the cell. It seems that the fusion event creates channels from the interior to the exterior of the cell. Furthermore, a multitubular body, conceivably originating in the ER, seems to fuse with the plasma membrane and to appear only on D‐day. This multitubular body is closely associated with lipid bodies during heat‐production and might be involved in the oxidation of lipids to volatile products. The foul odour produced by the appendix attracts at least 30 species of insects.
The effects of long‐term elevated ozone concentrations on the growth and photosynthesis of Sphagnum recurvum and Polytrichum commune
Authors: POTTER L. , FOOT J. P. , CAPORN S. J. M. , Lee J. A.
Published: April 2006

summary

Although ozone is generally accepted to be an important phytotoxic air pollutant, little is known of its effects on natural and semi‐natural vegetation. In this study two bryophyte species, Sphagnum recurvum P. Beauv. and Polytrichum commune Hedw., were exposed to long‐term chronic ozone concentrations, i.e. 70–80 ppb (nl 1−1), for 6–9 wk in summer conditions (mean 15°C) and in winter conditions (mean 6.4°C) in open‐top chambers (OTC), in the field, and at 15°C and 5°C in controlled‐environment chambers, under laboratory conditions.

Fumigation with ozone caused a significant reduction in the growth of treated plants in comparison with that of control plants. However, there were differences between species. S. recurvum was more affected than P. commune. In the controlled‐environment chambers growth of S. recurvum was reduced under both winter and summer conditions by 21 and 15%, respectively. In the OTCs, S. recurvum growth was reduced (by 17%) only under summer conditions. P. commune growth was only significantly reduced following ozone exposure in the OTCs under winter conditions. Here the growth reduction was by 22%.

Net CO2 assimilation of the two species was also significantly reduced by ozone exposure but only in the OTCs under winter conditions. Net CO2 assimilation of S. recurvum and P. commune was reduced by 60 and 80%, respectively.

The ratio of variable to maximal fluorescence (Fv/Fm ratio) was the least affected of the parameters measured. Only for P. commune fumigated in the OTCs under winter conditions was the Fv/Fm ratio significantly reduced (by 4.4%).

Bryophytes, by the very nature of their morphology and physiology are, perhaps, more likely to be susceptible to ozone pollution than higher plants; these results are discussed in relation to their possible ecological significance.
The effect of different temperatures on the fatty acid composition of Rhizobium leguminosarum bv. viciae in the faba bean symbiosis
Authors: THÉBERGE MARIE‐CLAUDE , PRÉVOST DANIELLE , CHALIFOUR FRANÇOIS‐P.
Published: April 2006

summary

Fatty acid composition was determined in cells of strains CBhS and CBp7 of Rhizobium leguminosarum bv. viciae grown at four temperatures (10, 15, 22 and 30°C), and in bacteroids and nodules formed with faba bean (Vicia faba L.) grown at two day/night temperature regimes (22/15 and 15/10°C). Growth temperature markedly affected the fatty acid composition of free‐living bacteria in both strains studied, and both showed similar variations at each temperature. The proportion of unsaturated fatty acids increased significantly with lowering of temperature. The major fatty acid found in bacteria and bacteroids was cis‐vaccenic (C18: 1Δ11), which comprised up to c. 78 (bacteria) and 56% (bacteroids) of total fatty acids. The presence of polyunsaturated fatty acids (linoleic (C18:Δ,9,12) and linolenic (C18:3Δ9,12,15) acids) was noted only in bacteroids, indicating changes following the differentiation of bacteria into bacteroids in the nodules. The fatty acid composition of nodules was similar to that of bacteroids, although major differences were found in their proportions. The different day/night temperature regimes had contrasting effects in bacteroids and in nodules. In bacteroids of both strains, the proportions of stearic (C18:0) and linoleic (C18:Δ9,12) acids decreased at the lower temperature regime. In nodules, the proportion of stearic (C18:0) acid decreased, while that of linolenic (C18:3Δ9,12,15) acid increased at the lower temperature regime. However, those of cis‐vaccenic (C18:1Δ11), linoleic (C18:Δ9,12,15) and palmitic (C16:0) acids increased or decreased depending on the rhizobial strain. The proportion of unsaturated fatty acids increased with the lowering of temperatures in bacteroids of both strains, and varied in whole nodules depending on the strain. Strain CBp7 showed a greater symbiotic efficiency (dry matter yield) than strain CBh5 under both temperature regimes, but no relationship was found with the proportion of unsaturated fatty acids of bacteria, bacteroids or nodules.
Genetic selection of sox1GFP‐expressing neural precursors removes residual tumorigenic pluripotent stem cells and attenuates tumor formation after transplantation
Authors: Chung S. , Shin B.‐S. , Hedlund E. , Pruszak J. , Ferree A. , Kang Un Jung , Isacson Ole , Kim Kwang‐Soo
Published: April 2006

Because of their ability to proliferate and to differentiate into diverse cell types, embryonic stem (ES) cells are a potential source of cells for transplantation therapy of various diseases, including Parkinson's disease. A critical issue for this potential therapy is the elimination of undifferentiated cells that, even in low numbers, could result in teratoma formation in the host brain. We hypothesize that an efficient solution would consist of purifying the desired cell types, such as neural precursors, prior to transplantation. To test this hypothesis, we differentiated sox1‐green fluorescent protein (GFP) knock‐in ES cells in vitro, purified neural precursor cells by fluorescence‐activated cell sorting (FACS), and characterized the purified cells in vitro as well as in vivo. Immunocytofluorescence and RT‐PCR analyses showed that this genetic purification procedure efficiently removed undifferentiated pluripotent stem cells. Furthermore, when differentiated into mature neurons in vitro, the purified GFP+ cell population generated enriched neuronal populations, whereas the GFP– population generated much fewer neurons. When treated with dopaminergic inducing signals such as sonic hedgehog (SHH) and fibroblast growth factor‐8 (FGF8), FACS‐purified neural precursor cells responded to these molecules and generated dopaminergic neurons as well as other neural subtypes. When transplanted, the GFP+ cell population generated well contained grafts containing dopaminergic neurons, whereas the GFP– population generated significantly larger grafts (about 20‐fold) and frequent tumor‐related deaths in the transplanted animals. Taken together, our results demonstrate that genetic purification of neural precursor cells using FACS isolation can effectively remove unwanted proliferating cell types and avoid tumor formation after transplantation.
Sustained viral response prolonged survival of patients with C‐viral hepatocellular carcinoma
Authors: Akamatsu Masatoshi , Yoshida Haruhiko , Shiina Shuichiro , Teratani Takuma , Obi Shuntaro , Tateishi Ryousuke , Mine Norio , Kondo Yuji , Kawabe Takao , Omata Masao
Published: April 2006

Abstract: Background: We conducted this retrospective study to evaluate the position of interferon therapy in the curative treatment of hepatitis C virus‐associated hepatocellular carcinoma (HCC).

Methods: We compared overall and recurrence‐free survival rates between 191 patients who received interferon therapy before HCC development (15 with sustained virologic response (SVR)), 53 who received interferon therapy after HCC ablation (17 with SVR), and 399 HCC patients with Child–Pugh class A liver function who did not receive interferon (controls).

Results: The overall survival rate in the controls was 82.4%, 53.2%, and 28.3% at 3, 6, and 9 years, respectively, whereas that in patients who developed HCC after achieving SVR was 93.3%, 93.3%, and 93.3%; those with HCC after non‐SVR, 87.8%, 56.5%, and 35.8%; SVR after HCC, 100%, 87.5%, and 59.7%; and non‐SVR after HCC, 94.3%, 70.9%, and 53.2%. Cox proportional hazard regression analysis revealed that the risk of death was significantly reduced in patients with HCC after SVR and those with SVR after HCC, with a risk ratio of 0.124 (95% confidence interval (95% CI): 0.017–0.890, P=0.0378) and 0.388 (95% CI: 0.169–0.887, P=0.0250), respectively, compared with the controls. Improved survival was attributable mainly to sustained liver function among patients with SVR, and recurrence‐free survival did not differ significantly.

Conclusion: Interferon therapies before and after HCC development were both significantly associated with prolonged survival when SVR was achieved.
The natural history of parallel transjugular intrahepatic portosystemic stent shunts using uncovered stent: the role of host‐related factors
Authors: Helmy Ahmed , Redhead Doris N. , Stanley Adrian J. , Hayes Peter C.
Published: April 2006

Abstract: Objectives: Parallel shunts (PS) are used in the management of transjugular intrahepatic portosystemic stent‐shunt (TIPS) insufficiency, a major limitation of the technique. This study describes the natural history of PS, and uses them as a model to assess the role of host factors in the development of primary shunt insufficiency.

Methods: Out of 338 patients with TIPS, 40 (11.8%) patients required insertion of a PS. Baseline and follow‐up data of these patients were collected. Regular shunt surveillance involved biannual clinic visits and transjugular portography.

Results: The non‐PS group (group 1; n=298) and the PS group (group 2; n=40) had similar baseline demographic and disease characteristics. Index shunts of both groups and the PS produced a significant portal pressure gradient drop (P<0.001), which was less in the index shunts of Group 2 (P<0.02 for both). PS had similar cumulative shunt patency rates to those of the index shunts of Group 1, and both were greater than those of index shunts in Group 2 (P<0.001 for both). The intervention rate (number of interventions/number of check portograms × 100) was similar for PS and the index shunts of Group 1 (38.7% and 43% respectively), but was significantly higher in the index shunts of Group 2 (85.6%; P<0.01 for both). In Group 1 and Group 2, 144 patients (48.3%) and 21 patients (52.5%) died during follow‐up after a median period of 23.4 and 8.9 months respectively.

Conclusions: These findings do not support the hypothesis that shunt insufficiency is related to host factors.
Activated hepatic stellate cells overexpress p75NTR after partial hepatectomy and undergo apoptosis on nerve growth factor stimulation
Authors: Asai Keiko , Tamakawa Susumu , Yamamoto Masahiro , Yoshie Masumi , Tokusashi Yoshihiko , Yaginuma Yuji , Kasai Shinichi , Ogawa Katsuhiro
Published: April 2006

Abstract: Background: Expression of neurotrophins (NTs) and their receptors is increased during hepatic regeneration, but their role is not well understood.

Methods: NTs and their receptors were investigated by RT‐PCR and immunostaining in regenerating livers after two‐thirds hepatectomy (PH) and in hepatocytes and hepatic stellate cells (HSCs) isolated from regenerating livers in mice. Induction of apoptosis after treatment with NGF and the expression of α‐smooth muscle actin (SMA), interleukin 6 (IL‐6) and hepatocyte growth factor (HGF) were also investigated in regenerating HSCs.

Results: Nerve growth factor (NGF) and p75 NT receptor (p75NTR) mRNA were elevated after PH, while other NTs and NT receptors showed no remarkable change. NGF was detected in regenerating hepatocytes, but not in normal hepatocytes. Regenerating HSCs expressed increased p75NTR and SMA in vivo and showed an activated phenotype and the high expression of HGF and IL‐6 in vitro. Enhanced cell death was seen in HSCs, both from normal and regenerating liver, after treatment with NGF.

Conclusions: Although activated HSCs may produce the factors that regulate liver regeneration, the de novo NGF production by regenerating hepatocytes may induce the death of activated HSCs via p75NTR, leading to termination of hepatic regeneration.
Consensus on extra‐hepatic portal vein obstruction
Authors: Sarin Shiv Kumar , Sollano Jose D. , Chawla Yogesh Kumar , Amarapurkar Deepak , Hamid Saeed , Hashizume Makoto , Jafri Wasim , Kumar Ashish , Kudo Masatoshi , Lesmana Laurentius A , Sharma Barjesh C. , Shiha Gamal , Janaka de Silva H. ,   and Members of the APASL Working Party on Portal Hypertension
Published: April 2006

Abstract: The Asian Pacific Association for the Study of the Liver (APASL) had set up a working party on portal hypertension in 2002 with a mandate to develop consensus on various aspects of portal hypertension. The first of these consensuses has been developed on extra‐hepatic portal vein obstruction (EHPVO). It was discussed and prepared by the experts in this field from the Asian region and was presented at the annual meeting of the APASL, at Bali in August 2005. This article summarizes all the consensus statements approved by the APASL on various aspects of EHPVO.
Preloads Generated with Repeated Tightening in Three Types of Screws Used in Dental Implant Assemblies
Authors: Byrne Declan , Jacobs Stuart , O'Connell Brian , Houston Frank , Claffey Noel
Published: April 2006

Purpose:
Abutment screw loosening, especially in the case of cemented single tooth restorations, is a cause of implant restoration failure. This study compared three screws (titanium alloy, gold alloy, and gold‐coated) with similar geometry by recording the preload induced when torques of 10, 20, and 35 Ncm were used for fixation.

Materials and Methods: Two abutment types were used—prefabricated preparable abutments and cast‐on abutments. A custom‐designed rig was used to measure preload in the abutment–screw–implant assembly with a strain gauge. Ten screws of each type were sequentially tightened to 10, 20, and 35 Ncm on ten of the two abutment types. The same screws were then loosened and retightened. This procedure was repeated. Thus, each screw was tightened on three occasions to the three insertion torques. A linear regression model was used to analyze the effects on preload values of screw type and abutment type for each of the three insertion torques.

Results: The results indicated that the gold‐coated screw generated the highest preloads for all insertion torques and for each tightening episode. Further analysis focused on the effects of screw type and abutment type for each episode of tightening and for each fixation torque. The gold‐coated screw, fixed to the prefabricated abutment, displayed higher preloads for the first tightening at 10, 20, and 35 Ncm. Conversely, the same screw fixed to the cast‐on abutment showed higher values for the second and third tightening for all fixation torques. All screws showed decay in preload with the number of times tightened. Given the higher preloads generated using the gold‐coated screw with both abutment types, it is more likely that this type of screw will maintain a secure joint when tightened for the second and third time.

Conclusion:
All screw types displayed some decay in preload with repeated tightening, irrespective of abutment type and insertion torque. The gold‐coated screw showed markedly higher preloads for all insertion torques and for all instances of tightening when compared with the uncoated screws.
Transformation‐Induced Twinning: The 90° and 180° Ferroelectric Domains in Tetragonal Barium Titanate
Authors: Cheng Shun‐Yu , Ho New‐Jin , Lu Hong‐Yang
Published: April 2006

Ferroelectric twin domains resulting from the cubic (c) to tetragonal (t) phase transformation at the Curie point TC≈130°C in pressureless‐sintered BaTiO3 ceramics, using TiO2‐excess powder, have been investigated using scanning and transmission electron microscopy. Both 90° and 180° domains were identified by spot splitting along characteristic crystallographic directions in the selected‐area diffraction patterns and/or from the shape of domain boundaries. Lamellar domains were found predominantly with the 90° types. The 180° domain boundaries mostly appeared wavy in shape, while the 90° ones, having sharpened ends, attained a dagger shape. Failure of Friedel's law in the non‐centrosymmetric t‐BaTiO3 was adopted to validate the existence of the 180° domains. The 90° domains with boundaries lying in

are reflection–inversion twins, and the 180° domains lying in {100)t and }220)t are inversion twins. Convergent‐beam electron diffraction was performed to ensure that changing of the polar direction [001]t across the 90° and the 180° domain boundaries was consistent with the domain type. It was also used to confirm whether the 180°‐type walls are inversion domain boundaries produced by the loss of an inversion center when the cubic phase transforms into tetragonal symmetry. The formation of such ferroelectric domains is discussed with reference to the crystal symmetry reduction from

(c‐phase) to P4mm (t‐phase) with a loss of mirror plane (m) and roto‐inversion axis

upon c→t phase transformation.
Influence of Non‐Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: I. Substitution of Ba3W2O9
Authors: Wu Hui , Davies Peter K.
Published: April 2006

A narrow region of Zn‐vacancy‐containing cubic perovskites was formed in the (1−x)Ba3(ZnNb2)O9−(x)Ba3W2O9 system up to 2 mol% substitution (x=0.02). The introduction of cation vacancies enhanced the stability of the 1:2 B‐site ordered form of the structure, Ba(Zn1−x□x)1/3(Nb1−xWx)2/3O3, which underwent an order–disorder transition at 1410°C, ∼35° higher than pure Ba(Zn1/3Nb2/3)O3. The Zn vacancies also accelerated the kinetics of the ordering reaction, and samples with x=0.006 comprised large ordered domains with a high lattice distortion (c/a=1.226) after a 12 h anneal at 1300°C. The tungstate‐containing solid solutions can be sintered to a high density at 1390°C, and the resultant ordered ceramics exhibit some of the highest microwave dielectric Q factors (Q×f=1 18 000 at 8 GHz) reported for a niobate‐based perovskite.
Influence of Non‐Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: III. Effect of the Muffling Environment
Authors: Wu Hui , Davies Peter K.
Published: April 2006

The effect of different muffling environments on the structure and dielectric losses of Ba(Zn1/3Nb2/3)O3 (BZN) microwave ceramics was investigated. The microwave dielectric losses of stoichiometric BZN pellets heated in ZnO‐rich environments were severely degraded (e.g. Q×f∼15 000 in ZnO powder) compared with samples muffled in their own powder (Q×f∼80 000). Structure analyses and gravimetric measurements confirmed that the ceramics muffled in ZnO powder or vapor absorb excess ZnO to form non‐stoichiometric solid solutions with reduced cation order and Q. By using starting compositions in the (1−x)BZN−(x)BaNb4/5O3 binary (x=0.04), the stoichiometry can be tailored to ensure that after the uptake of ZnO, the ceramics remain well ordered and are located in a high Q region of the system. For example, ZnO‐vapor‐protected (0.96)BZN−(0.04)BaNb4/5O3 reached a very high Q×f (∼1 05 000) after sintering at 1400°C for 5 h.
Effect of Particle Sizes of Starting Materials on Microstructure Development in Textured Bi0.5(Na0.5K0.5)0.5TiO3
Authors: Fuse Kaori , Kimura Toshio
Published: April 2006

Microstructure development in Bi0.5(Na0.5K0.5)0.5TiO3 prepared by a reactive‐templated grain growth process was dependent on the sizes of platelike Bi4Ti3O12 (BiT) and equiaxed TiO2 particles used as starting materials. Calcined compacts were composed of large, platelike template grains and small, equiaxed matrix grains, the sizes of which were determined by those of the BiT and TiO2 particles, respectively. Texture was developed by the growth of template grains at the expense of matrix grains during sintering, and a new mechanism of grain growth was proposed on the basis of microstructure observation. The grain growth rate was determined by the template and matrix grain sizes, and a dense ceramic with extensive texture was obtained using small BiT and TiO2 particles.