bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequential encounter of wood resources by mycelial cords of Phanerochaete velutina: effect on growth patterns and phosphorus allocation
Authors: HUGHES C. L. , BODDY LYNNE 
Published: April 2006

summaryThe effect of sequential encounter with wood resources (1 cm3 and 2 cm3‘baits’ in various combinations) by mycelial cords of Phanerochaete velutina (DC.: Pers.) Parmasto growing from 1 cm3 wood inocula was investigated in model soil systems in the laboratory. Encountering large wood baits (8 cm3), either next to the inoculum or after encounter of another bait, resulted in cessation of mycelial extension and regression of mycelium from the inoculum and small baits. Small wood baits had no effect on mycelial extension rates, even when encountered in rapid succession. All systems maintained a general polarity when growing out from a bait, but later often curved around the bait, extending over soil which had previously been explored. Allocation of 32P (taken up by the inoculum) between the three resource units (inoculum and two sequentially encountered baits) was investigated; significantly (P≤ 0.05) more 32P was allocated to the large wood baits (whether encountered first or second) than to the other bait; but the inoculum was usually allocated most. Wood inocula decayed more rapidly than baits. The significance of the results is discussed in relation to foraging.
Ensnaring microbes: the components of plant disease resistance
Authors: HAMMOND‐KOSACK KIM E. , JONES DAVID A. , JONES JONATHAN D. G. 
Published: April 2006

SUMMARYPlants activate an array of co‐ordinated defence responses to restrict microbial attack. Timely perception of foreign molecules appears to be critical for the success of these defences. However, the nature of the molecular events required for resistance is largely unknown. Recent isolation of disease resistance (R) genes, has revealed that R gene products have several features in common. This finding suggests that plants have evolved several common or similar signal transduction pathways to activate resistance to a range of unrelated microbes. R gene isolation and the genetic identification of other loci required for R function permits analysis of the structure and evolution of microbe‐perception mechanisms. Numerous types of activated defence responses are recognized. A requirement for salicylic acid in resistance has been established in some systems. Roles for other events, like reactive oxygen species and the hypersensitive (host cell death) response, remain enigmatic. A thorough understanding of the components leading to pathogen recognition and the expression of resistance should permit the design of novel strategies to engineer broad‐spectrum and durable plant disease control.
Diversity and phylogeny of rhizobia
Authors: PETER J. , YOUNG W. , HAUKKA KAISA E. 
Published: April 2006

SUMMARYRhizobia 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

SUMMARYThe 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

SummaryDNA 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

SUMMARYGrowth 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

SUMMARYPhotoassimilate 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

SUMMARYPlantlets 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

SUMMARYA 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

SUMMARYGynodioecy 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

SUMMARYIn 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

SUMMARYWe 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

SUMMARYClonal 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

summaryIt 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

summaryThe 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.