bluuebunny/crossref_metadata_2025_split huggingface dataset:
Discrimination of some African Armillaria species by isozyme electrophoretic analysis
Authors: AGUSTIAN A. , MOHAMMED C. , GUILLAUMIN J. J. , BOTTON B. 
Published: April 2006

summaryTen Armillaria isolates, collected from various host plants and widespread geographical origins in tropical Africa, were cultivated on orange fragments in the presence of water and ran different culture media in order to optimize enzyme and mycelial cord production. Seven enzymes involved in the primary metabolism of nitrogen and carbon (glutamate dehydrogenases, aspartate aminotransferase, malate dehydrogenase, glucose n‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase and isocitrate dehydrogenase) were extracted from the mycelial cords and analyzed by polyacry lamide gel electrophoresis. Cluster analysis based on calculated similarity values derived from isozyme banding patterns separated the isolates into five groups. Two isolates considered as belonging to A. mellea ssp. africana (an African species closely related to European A. mellea) were present in a clearly Separated cluster when compared to the other isolate groups. Two Kenyan isolates, belonging to an as yet unnamed biological species, which were characterized by the production of few slow growing mycelial cords, were also found in a separate cluster with slightly greater similarity coefficients to the other isolates. The six other isolates, referred to as isolates of A. heimii (a highly variable species with different sexual systems) fell into three sub‐clusters of variable homology. The two homothallic heimii isolates from Tanzania and Malawi, which were very closely related, displaying 100% isozyme similarity, exhibited a higher degree of similarity with the two other homothallic heimii isolates from Zimbabwe and Congo, than with the two heterothallic unifactorial heimii isolates from Cameroon and Gabon. The value of isozymes in the classification of African Armillaria spp. is discussed.
Effect of drought stress on growth and essential oil metabolism in lemongrasses*
Authors: SINGH‐SANGWAN NEELAM , ABAD FAROOQI A. H. , SINGH SANGWAN RAJENDER 
Published: April 2006

summaryTwo lemongrasses. Cymbopogon nardus. (L.) Rendle var. confertiflorus (Steud.) Bor. and Cymbopogon pendulus (Steud.) Wats, were grown under mild and moderate water stress for 45 and 90 d. The impact of in situ drought stress on plants in terms of relative water content, $pS, concentration of proline, activities of PEP carboxylase and geraniol dehydrogenase, and geraniol and citral biogenesis, were investigated. The results revealed that the specific exhibited differential responses under mild and moderate stress treatments. In general, plant growth was reduced considerably whilst the level of essential oils was maintained or enhanced. Significant induction in catalytic activity of PKP carboxylase under water stress was one of the consistent metabolic responses of the aromatic grasses. The major oil constituents., geraniol and citral, increased substantially in both the species. Activity of geraniol dehydrogenase was also modulated under moisture stress. The responses varied depending Upon the level and duration of moisture stress. The observations have been analyzed in terms of possible relevance of some of these responses to their drought stress adaptability tolerance.
Pollen dispersal and representation on an isolated, forested plateau*
Authors: JACKSON STEPHEN T. , SMITH SUSAN J. 
Published: April 2006

summaryModern pollen assemblages from 18 small ponds and wetlands on the spatially isolated and forested Kaibab Plateau were studied to determine how the pollen assemblages recorded vegetation patterns. Vegetation of the Plateau consists of an inner core of subalpine Picca/Abies forests, surrounded by mixed Abies/Picea/ Pseudotsuga/Pinus ponderosa forests, which are in turn surrounded by extensive Pinus ponderosa forests. The flanks of the Plateau are vegetated by Pinus edulis/Juniperus woodlands, with scattered Quercus populations. Arboreal pollen assemblages were dominated by Pinus (70‐98 %), which was most abundant in the P. ponderosa forests. Picea, Abies, Pseudotsuga and Populus pollen were abundant only at sites in the mixed and subalpine conifer forests, where their combined abundance never exceeded 16% except at the site deepest in the subalpine forest (22%). Pollen percentages of Cupressaceae and Pinus Subsection Cembroides were highest in the outermost P. ponderosa forests (nearest the P. edulis/Juniperus woodlands) and in the mixed and subalpine conifer forests, where Quercus pollen was also highest. Percentage representation of the well‐dispersed pollen of Quercus, Cupressaceae and Pinus Subsect. Cembroides was amplified at these latter sites by the poor pollen representation of the dominant Picca, Abies and Pseudotsuga trees. This effect is similar to that recorded in many pollen assemblages from arctic and alpine tundra regions.
Size, distribution and biomass of genets in populations of Suillus bovinus (L.: Fr.) Roussel revealed by somatic incompatibility
Authors: DAHLBERG ANDERS , STENLID JAN 
Published: April 2006

summaryThe spatial distribution of genets in the ectomycorrhizal fungus Suillus bovinus (L.: Fr.) Roussel were studied in somatic incompatibility pairings of isolates from five Scots pine (Pinus sylvestris L.) stands differing in forest history and age, With increasing forest age, the size of genets increased while the number of genets and production of sporocarps per unit area decreased. There was an estimated 700–5700 genets ha−1 in younger forests and 30–120 ha−1 in older ones. The maximum size of genets was 1.7–5.3 m in the younger forest and to 17.5 m in the older ones. The production of sporocarps per unit area decreased with increasing forest age. Furthermore, production of sporocarps increased nonlinearly with the size of the genet, suggesting that genets become fragmented. Ergosterol measurements indicated that the fungal biomass of one genet consisted of 20–45% sporocarps and 55–80% mycorrhiza, not including extramatrical mycelia. Mycorrhizal aggregations in soil were mapped in two 5 m2 areas and, based on somatic incompatibility tests, all were round CO belong to the same genet as sporocarps present above ground. Production of spores per sporocarp was estimated to be 1.1–12.8 × 108. The observations are discussed in terms of population ecology.
The role of microclimate in determining the sensitivity ofQuercus rubraL. to ozone
Authors: SAMUELSON L. J. 
Published: April 2006

summaryMicroclimate has been suggested as a factor to consider when scaling ozone responses of forest trees from the seedling to tree level. To test whether microclimate influences the response of seedlings to ozone. 1‐yr‐oldOuercus rubraL, seedlings were grown in the shaded upper or lower canopy of 31‐yr‐old trees in open‐top tree chambers, or in more exposed open‐top seedling chambers, and received subambient(cumulativeSUM.M06*dose of (0 ppm‐h), ambient (cumulative SUM06 dose of l9 ppm‐h) or twice ambient (cumulative SUMU6 dose of 135 ppm‐h) exposures to ozone for one growing season. Seedlings exposed to warmer temperatures and greater PAR within the seedling chambers had greater biomass, total leaf nitrogen, second foliar flush net photosynthesis, leaf conductance and dark respiration than seedlings grown in either location within the tree canopies. However, microclimate did not influence the responses to ozone. Net photosynthesis, leaf conductance and apparent quantum yield of first flush leaves of seedlings exposed to the same leaf microclimate as trees were reduced between 16% and 20% by ozone treatment. Ozone induced larger reductions in the net photosynthesis, leaf conductance and apparent quantum yield of tree leaves. These results indicate that, although microclimate influenced seedling growth and physiology, microclimate did not play a dominant role in determining the sensitivity ofQ. rubraseedlings to ozone.
Effects of simulated acid rain on nitrogenase activity (acetylene reduction) in the lichen Stereocaulon paschale (L.) Hoffm., with special reference to nutritional aspects
Authors: KYTÖVIITA M.‐M. , CRITTENDEN P. D. 
Published: April 2006

summaryThe effects of SAR (simulated add rain using H2SO4 and HNO3 singly and combined) on ARA (acetylene reduction activity), and concentrations of N, K4, Mg2+ and Ca2− was investigated in Sterecaulon paschale (L.) Hoffm. ARA was significantly decreased after 4 months of SAR at pH 3.0. One year after spraying treatments had ceased, lichens treated at pH 3.0. showed no clear signs of recovery of ARA. After 5 y of acidification. ARA in lichens sprayed with combined H2SO4 and HNO3 at pH 2.9. was comparable to that observed after 4 months of pH 3.0.enhanced rain, i.e. close to zero. SAR at pH 4.0. had no marked effect on nitrogenase activity after 4 months' exposure, but ARA was significantly decreased after 5 y‐of pH 4.1. (H2SO4) treatment. There were no clear relationships between the inhibitory effects of acid additions and alterations in nutritional status in the lichen caused by SAR. Furthermore, no correlation between thallus N concentration and nitrogenase activity was observed.
Sulphate‐limited growth in the N2‐fixing unicellular cyanobacterium Gloeothece (Nägeli) sp. PCC 6909
Authors: ORTEGA‐CALVOH JOSE‐JULIO , STAL LUCAS J. 
Published: April 2006

summaryThe unicellular diazotrophic cyanobacterium Gloeothece PCC 6909 was grown in batch and continuous culture, It was found that the organism scavenged sulphate from the medium and incorporated it in the polysaccharide sheath. As a result batch cultures became sulphur‐depleted whilst continuous cultures were sulphur‐limited. This was observed regardless of the nitrogen source of the culture. Sulphur‐depletion was the reason for the low nitrogenase activities usually observed in batch cultures of Gloeothece. Sulphate‐amended cultures showed sustained high nitrogenase activity in the light. Sulphate uptake from the medium was light‐dependent. Earlier work on N2 fixation in Gloeothece is discussed in the light of possible sulphur limitation.
Nitrogen‐fixing stem nodules of the Legume,Discolobium pulchellumBenth.
Authors: LOUREIRO M. F. , DE FARIA S. M. , JAMES E. K. , POTT A. , FRANCO A. A. 
Published: April 2006

summaryWe report on the structure of N2‐fixing nodules formed on the stem ofDiscolobium pulchellumBenth., an aquatic legume in the subfamily Pupilionoideae, tribe Aeschynomeneae, from the Hooded areas in the ‘Pantanal Matogrossense’ region of Brazil. The stern (and root) nodules were obligately aquatic, requiring permanent submergence in water or flooded soil, and receive oxygen via profuse aerenchyma covering The lower stem. Of the 69 isolates of rhizobia isolated from stem and root nodules, 70% were fast‐growing acid producers and 38% were slow growers. The rhizobia were not photosynthetic. Nodules were connected to the stem, and the vascular system from the stem branched throughout the nodule, penetrating the infected, tissue within finger‐like ingrowths of cortex. In both stem and root nodules, infected tissue was aeschynomenoid or desmodioid, that is, without uninfected (interstitial) cells. The infected cells in stem nodules were vacuolate, with visible infection threads. The inner cortex was rich in amyloplasts and contained the components of an oxygen diffusion barrier (a boundary cell layer without intercellular spaces and glycoprotein occlusions of intercellular spaces in other cell layers). The mid‐cortex, external to the boundary layer, consisted of loosely‐packed cells and these were continuous with stem aerenchyma. The outer part of the nodules was made up of phellogen‐derived cells forming a periderm, or ‘corky’ layer of cells. The periderm formed large lenticels above cortical vascular bundles. These lenticels also connected with the stem aerenchyma. Root nodules differed only in that infected cells were not vacuolate, bacteroids were larger and contained more poly‐β‐hydroxybutyrate (PHB) and there was less aerenchyma/lenticellular tissue. Stem and root nodule structure is discussed in terms of adaptations to O2constraints in an aquatic environment.
Capture of nitrate from soil by wheat in relation to root length, nitrogen inflow and availability
Authors: ROBINSON DAVID , LINEHAN DENIS J. , GORDON DENNIS C. 
Published: April 2006

summaryWe studied the interactions between nitrogen (N) inflow (uptake rate per unit root length) and root growth in the capture of nitrate by soil‐grown wheat (Triticum aestivum L. cv. Wembley). [l5N]‐nitrate was applied locally to soil overlying seminal roots of 42‐d‐old plants that had previously received K fertilizer (N +) or not (NO), [35S]‐sulphate was also applied to check the specificity of the plant's responses to nitrate. NO plants had exhausted soil nitrate by day 42. Over the next 7 d, inflow was stimulated in soil to which [15N]‐nitrate was supplied in the NO plants. NO plants increased their root length densities throughout the root system, not only around the point of [15N]‐nitrate application. Root length density did not change in the N+ plants. NO plants captured 73 % of the [l5NJ‐nitrate in 7d; N+ plants captured only 13%. There was no evidence that the plants' responses to the localized application of nitrate had an effect on the uptake of sulphate. The dominant influence on the capture of nitrate was inflow, rather than root growth.
Gaseous ammonia counteracts the response of Scots pine needles to elevated atmospheric carbon dioxide
Authors: PÉREZ‐SOBA MARTA , VAN DER EERDEN LUDGER J.M. , STULEN INEKE , KUIPER PIETER J. C. 
Published: April 2006

summaryFour‐year‐old saplings of Scots pine (Pinus sylvestris L.) were exposed for 8 wk in controlled‐environment chambers to charcoal‐filtered air (FA), FA supplemented with 754 mg m−3 (650 μl 1−1)CO2, FA supplemented with l00 μ m13 NH3 and FA+CO2+NH3. Elevated CO2 induced a significant increase in the concentrations of NH4+ and NO3 in the soil solution, while exposure to NH3 enhanced the soil NH4− concentration. Elevated CO2 significantly increased needle biomass and area, and decreased specific leaf are (SLA) and N concentration in the needle. The activity of peroidase (POD) was decreased, while the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were only slightly affected. Gaseous NH3 enhanced the concentration of N. soluble proteins and the GS activity in the needless, while it decreased the POD and GDH activities. The effects of elevated CO2+ NH3 on needle biomass production, N Metabolism and POD activity were smaller than the effects of single exposures to elevated CO2 or NH3. Suggesting that elevated CO2 and NH3 counteract each other and disturb needle physiology. The possible mechanisms underlying the negative interactions of elevated CO2 and NH3 and discussed. The expected stimulation of biomass production by elevated CO2 my be reduced in the presence of atmospheric NH3.
Genotypic and environmental effects on endopolyploidy in the epidermal tissues of Lolium perenne L. and Lolium multiflorum Lam
Authors: GRIFFITHS P. D. , QUGHAM H. J. , JONES R. N. 
Published: April 2006

summaryC‐value determinations on nuclei of the adaxial epidermal bulliform cells of leaves of perennial (Lolium perenne) and Italian ryehgrass (Lolium multiflorum) show considerable levels of endopolyploidy. L. multiflorum has more endopolyploidy than L. perenne, and there is an environmental effect which reduces the level of endopolyploidy in L. multiflorum as the temperature is raised.
Changes in gene‐expression in response to sucrose accumulation in leaf tissue of Lolium temulentum L.
Authors: WINTERS A. L , WILLIAMS J. H. H. , THOMAS D. S. , POLLOCK C. J. 
Published: April 2006

summarySucrose accumulation and subsequent fructan synthesis was initiated in detached, mature leaves of Lolium temulentum by incubating them either in the light or with 200 mM sucrose in the dark. Fructan synthesis was also induced in intact seedlings by lowering root and shoot meristem temperature to 5 °C while maintaining aerial parts of the plant at 20 °C in the light. In this system, subsequent breakdown of fructans was induced by raising root and meristem temperature to 20 °C in the dark. Products of in vitro translations showed that transcripts encoding polypeptides of 17 and 35 kDa increased in sucrose accumulating‐tissue. Transcripts encoding 28 and 32 kDa polypeptide products appeared to be associated with leaf tissue actively exporting carbohydrate. Labelling studies in vivo in mature leaf tissue showed transient increases in the synthesis of polypeptides with MR 59, 60 and 70 kDa during the first 6 h of sucrose accumulation. Polypeptides with an MR of 74 and 27 kDa showed increased amounts later in induction.Cordycepin and cycloheximide were fed to mature leaf tissue at different stages during induction of sucrose accumulation in the light. Both control and cordycepin‐treated tissue showed higher levels of monosaccharide accumulation compared with cycloheximide‐treated tissue. Cordycepin applied during the first 2 h after excision blocked subsequent synthesis of all fructans. When applied at two‐hour‐stages between 2 and 8 h, subsequent accumulation of 1–kestose occurred without accumulation of higher fructans. Application after 8 h had no effect upon the pattern of fructan accumulation when compared to untreated controls. Application of cycloheximide during the first 8 h following excision blocked all fructan accumulation. Subsequent administration had no effect on the pattern of fructan accumulation. The results are discussed in relation to the changes in gene expression associated with induction of fructan synthesis.
The metabolism of fructans during seed development and germination in onion (Allium cepa L.)
Authors: POLLOCK C. J. , LLOYD E. J. 
Published: April 2006

summaryFructan metabolism was studied during maturation and germination in onion seeds. Fructans formed a significant transient store of carbon during the first 23 d following anthesis with an oligosaccharide distribution which closely resembled that observed in extracts from vegetative tissue. Seed maturation was accompanied by a decline in fructan content and a marked reduction in the number of separable oligosaccharides observed. During imbibition and germination. total fructan contents fell further; however, 4 d after imbibition, there was some elaboration ot higher oligosaccharides. The results are discussed in relation to the activity of the enzymes invoked in fructan metabolism in higher plants.
Response of growth and carbon allocation to elevated CO2 in young cherry (Prunus avium L.) saplings in relation to root environment
Authors: KERSTIENS G. , HAWES C.V. 
Published: April 2006

summaryThe hypothesis that inadequate rooting volume may reduce the growth stimulation by elevated CO2 in ported tree seedlings and saplings was tested experimentally and by surveying the literature. One‐year‐old cherry saplings were grown for one season in naturally lit growth chambers in eight combinations of CO2 concentration (ambient: ambient+ 250 ppm) and root environment (four types), The latter included (1) moderately restrictive pot volume (41) in combination with two levels of fertilizer addition (la. 1b); (2) 10 l pots with total fertilizer content per pot as in treatment la, and (3) 20 l pots with five plants sharing live times the space and nutrient resources of treatment la. Plants were harvested in April, May, June, August and September. The overall mean effect of high CO2 on plant dry mass by the end of the season was +24%. Interactive effects of root environments and CO2 concentrations on dry mass were not significant at the 5% level, but repealed measurements of basal stem diameter of individual plants indicated a significant impact of root environment on the response to CO2. Overall growth enhancement by elevated CO2 did not differ significantly between harvests, but it tended to increase during the season in those root environments which restricted growth in ambient CO2 most strongly (la and 3). The hypothesis was rejected for this experiment. Leaf area and stem height were not affected by any treatment. The variation of carbon allocation to roots and shoots with plant size was very similar in all treatments. Plants grew faster in elevated CO2 very early in the season, and this resulted in small but significant differences between seasonal patterns of biomass partitioning in ambient and elevated CO2. A survey of 33 studies on growth responses of 47 tree species to elevated CO2 (600–800 ppm) showed that the relative change in biomass was not related to the ratio of plant biomass and pot volume found in either ambient or elevated CO2. We conclude that there is no evidence that inadequate pot volume had a negative impact on the stimulation of growth of true species in elevated CO2.
Effect of magnesium‐deficiency on antioxidative systems in needles of Norway spruce [Picea abies (L.) Karst.] grown with different ratios of nitrate and ammonium as nitrogen sources
Authors: POLLE ANDREA , OTTER TILMAN , MEHNEJAKOBS BEATE 
Published: April 2006

summaryThe effect of magnesium deficiency and variations of the ammonium to nitrate ratio on chlorophyll, soluble protein and antioxidative systems was investigated in current year's needles of clonal spruce trees [Picea abies (L.) Karst.]. The trees were grown for 1 yr in sand culture with circulating nutrient solutions containing sufficient (0.2 mM) or limiting (0.041 mM) concentrations of Mg. The nitrogen concentration of the nutrient solutions was not varied (5 mM) but the NO3−/NH4+‐ratio was adjusted TO 0.76 in Mg‐sufficient and to 1.86, 0.76 and 0.035 in Mg‐limited plants, Under Mg‐limitation, the chlorophyll, soluble protein and Mg‐contem were lowest in needles of trees supplied with NH4+ and highest in trees supplied with NO4− as major N‐source. Apoplastic peroxidase activities were not affected by changes in nutrition. In total needle extracts, NADH oxidase, ascorbate peroxidase, mimodehydroascorbate reductase, glutatkione reductase and asoorbate content were not, or only little, affected by changes in nutrition, except for trees grown with the highest N4+‐concentrations. Glutathtone content and guaiacol peroxidase were increased in Mg‐deficient needles. Superoxide dismutase activity was decreased in Mg‐limited needles of trees grown with N4+ and increased in needles of trees grown with NO3− as a major N‐source, Except for superoxide dismutase, the activities of antioxidant enzymes and substrates were not correlated with the decree of needle chlorosis. Superoxide dismurase activity was low compared to enzymatic activities involved in H2O2 detoxification. Supposing that the needles suffered from enhanced oxidative stress, these results suggest that scavenging of O2− was a limiting factor in stress compensation rather than the detoxification of H2O2.
Structural aspects of ectomycorrhiza ofPinus pinaster(Ait.) Sol. formed by an IAA‐overproducer mutant ofHebeloma cylindrosporumRomagnési
Authors: GEA L. , NORMAND L. , VIAN B. , GAY G. 
Published: April 2006

summaryMycorrhizas formed onPrinus pinasterby an IAA‐overproducer mutant strain (h1 FIR 4 h1 F1 331) ofHebeloma cylindrosporumare described. The wild strain (hl) was used as reference. The wild type mycorrhiza had a thin mantle and a uniseriate Hartig net, which reached the second layer of cortical cells, as generally described. Conversely, the mutant type mycorrhiza had special features; a large mantle and a highly developed Hartig net (up en seven layers of hyphae in width) which reached the endodermis. Even when the Hartig net was formed of several layers of hyphae, the cortical cells remained alive, indicating that the fungus may aid survival of the host cells. Intracellular hyphae surrounded by invaginated host plasmalemma and by interfacial material, were frequently seen in cortical cells, In this case, both fungal and host cells were alive. Even if the mutant strain is more invasive, the IAA overproduction dries not seem to modify its symbiotic status. It is possible that IAA plays a role in cell wall loosening, allowing the fungus to overcome barriers which normally prevent the invasion of living cortical cells.