bluuebunny/crossref_metadata_2025 huggingface dataset:
Population dynamics of indigenous and genetically modified rhizobia in the field
Authors: HIRSCH PENNY R.
Published: April 2006

Many factors have been shown to affect rhizobial populations in soil. These include: soil fertility; physical properties such as pH and clay content; biotic factors such as distribution of the host plant and the prevalence of predators; and climatic effects including temperature and rainfall. Extremes of soil pH, temperature and moisture are not favourable to rhizobia. In certain circumstances, some rhizobial species seem to survive as part of the saprophytic soil microflora, whereas others cannot be detected unless their leguminous plant host is present. There have been numerous reports over the past century on factors which influence rhizobial survival, reflecting the importance of rhizobial inoculants in agriculture. Many of these results appear to be contradictory, presumably because of the complexity of the interactions between different influences, which this review of the literature attempts to clarify. Results from monitoring population dynamics of different rhizobial species and biovars under various crops at Rothamsted demonstrate that populations ofRhizobium leguminosarumbiovars survive in the absence of their host plants at c. 104–105modulating cells g‐1soil, and increase only about threefold following cultivation of the host. In contrast,Sinorhizobium meliloticould not be detected before its host was grown, but increased to 106nodulating cells g‐1soil when lucerne was cultivated. The behaviour of a genetically modifiedR. leguminosarumbv.viciaestrain, RSM2004, following field release as an inoculant, was similar to that of the indigenous population, numbers remaining stable in the absence of the host following an initial decline, with a small but significant numerical advantage being conferred by the presence of the host in the subsequent years. A second genetically modifiedR. leguminosarumbv.viciaeinoculant, CT0370, was found to survive in numbers similar to those of the indigenous population.
Resource re‐allocation following fruit removal in cucurbits: patterns in cantaloupe melons
Authors: EL‐KEBLAWY ALI , LOVETT‐DOUST JON
Published: April 2006

The effects of removal of fruits of marketable size on investment to male, female and vegetative activities., were evaluated using cantaloupe melons, Cucumis melo L., cv. Retata Degli Ortolani. Leaf and flower demography were used to examine the dynamics of potential trade‐offs among these activities. Treated plants and controls had similar total biomass, but it was distributed differently. Treated plants had more vegetative biomass, both above ground and in roots, whereas control plants allocated more, in both absolute and proportionate terms, to fruits. Treated plants produced more leaves than controls, but individual leaf life expectancies were the same. Developing fruits on control plants thus seem to act as sinks at the expense of new leaves. Fruit removal also significantly stimulated production of male flowers and fruit, though these fruits contained significantly fewer, and smaller, seeds. Once fruit removal had begun, lability of floral sex expression was evident. In treated plants there was a significant increase in the production of male flowers. Both treated and control plants produced the same number of pistillate flowers; adjustments of fruit production occurred because of differences in the rate of successful fertilization, and later, differences in fruit set. In control plants (but not in treated plants) there were obvious tradeoffs between yield components. The costs of fruit maturation in treated plants appeared to be decoupled from other yield components.
Responses to water stress in an ABA ‐ unresponsive hybrid poplar (Populus koreana×trichocarpa cv. Peace) I. Stomatal function
Authors: RIDOLFI M. , FAUVEAU M. L. , LABEL P. , GARREC J. P. , DREYER E.
Published: April 2006

The poplar cultivar ‘Peace’ (Populus trichocarpa×koreana) displays abnormal stomatal behaviour with a lack of sensitivity to exogenous abscisic acid (ABA) in mature leaves. We report details of the leaf‐age dependency of this feature, and present the responses of stomata to diverse closing stimuli in addition to ABA. Soil water depletion induced complete stomatal closure of the youngest leaves, whereas the oldest exhibited almost no closure. By contrast, no such age effect was observed in stomatal sensitivity to ABA: a complete lack of closure was observed on all leaves, even with 10‐3 M ABA. Moreover, a preconditioning by drought did not restore the ability of stomata to close in response to ABA. Supplying detached leaves with Ca2+ (5 × 10‐2 M) was effective in inducing stomatal closure in the youngest leaves, and reproduced the age‐dependent drought response. These results support the hypothesis that drought control of stomatal conductance in ‘Peace’ is ABA‐independent, and could involve calcium ions. A loss of stomatal sensitivity to calcium, with leaf maturation, could explain the dependency of stomatal closure on leafage. Xylem sap concentrations of calcium were lower than those required to close stomata, and no drought‐induced increase was recorded. The mature leaves were also insensitive to increased ambient CO2, but darkness promoted partial stomatal closure.
Responses to water stress in an ABA‐unresponsive hybrid poplar (Populus koreana×trichocarpa cv. Peace) II. Hydraulic properties and xylem embolism
Authors: COCHARD H. , RIDOLFI M. , DREYER E.
Published: April 2006

We compared the xylem hydraulic properties of potted cuttings of two poplar clones (Populus koreana×trichocarpa cv. Peace and P.×euramericana cv. Robusta) known to differ in their sensitivity to ABA and in their ability to close their stomata during a period of drought. ‘Robusta’ can control stomatal aperture, whereas ‘Peace’ can only close the stomata of immature leaves. ‘Peace’ did not exhibit any specific hydraulic property that could compensate for its lack of response to a water deficit. The two clones did not differ in their petiole or internode xylem vulnerability to embolism, both being highly vulnerable (onset of embolism observed at –1·2 MPa minimum leaf water potential, Ψwm). Both clones became embolised rapidly when pots were dehydrated, but the onset of embolism was slightly delayed in ‘Robusta.‘ Peace' was nevertheless capable of maintaining low xylem embolism near its apex and we associated this feature with the active stomatal control occurring in immature leaves. We conclude that efficient stomatal regulation is essential for maintaining the integrity of xylem sap flow under drought conditions and that ‘Peace’ shows an exception to the general rule of stomatal control of embolism.
Experiments on the causes of altitudinal differences in the leaf nutrient contents, size and δ13C of Alchemilla alpina
Authors: MORECROFT MICHAEL D. , WOODWARD F. IAN
Published: April 2006

This paper describes experiments carried out to investigate the causes of high leaf nitrogen concentrations and high δ13C values in Alchemilla alpina L. growing at high altitudes. We investigated whether genetic adaptation, high levels of nitrogen input or low temperatures could account for these trends. In a field experiment, plants from two altitudes in the Scottish Highlands were transplanted to Great Dun Fell, a site in the Pennines of northern England. The experimental design was fully factorial: two altitudinal origins × two altitudes of growth × two nitrogen levels. A second experiment used a controlled environment to test the effects of temperature alone.

The effects of altitude in the field transplant experiment were very similar to those in naturally growing plants. Leaf nitrogen concentration and δ13 were both higher at the high altitude, whilst growth declined and nitrogen per leaf was unaffected. An increase in potassium concentration with altitude was also found. Nitrogen addition caused increased leaf nitrogen concentrations but also increased nitrogen per leaf; δ13C was not affected and potassium and phosphorus concentrations decreased. The addition of nitrogen also increased mortality. Altitude of origin had relatively few effects but the population from the higher altitude did have a higher specific leaf area. Low temperature in the controlled environment caused increased δ13C, decreased leaf size and increased nitrogen and carbon contents, although the effect was less clear than the effects of altitude in the field. Gas exchange measurements suggested that the δ13C effect was caused by a reduction in stomatal conductance.

We conclude that the effects of altitude on this species are principally the result of direct environmental modifications to growth rather than genetic adaptation. Of the various factors that change with altitude, temperature and a short growing season are particularly important; enhanced nitrogen supply through atmospheric deposition promotes increasing leaf nitrogen concentrations but must be considered in conjunction with other variables.
Root hemiparasitism in a West African rainforest treeOkoubaka aubrevillei(Santalaceae)
Authors: VEENENDAAL E. M. , ABEBRESE I. K. , WALSH M. F. , SWAINE M. D.
Published: April 2006

We studied hemiparasitism inOkoubaka aubrevilleiPellegr. & Normand (Santalaceae), an uncommon West African rainforest tree of widespread distribution (Ivory Coast to Zaire) which attains heights of up to 40 m. It has a very large seed (mean fresh mass of 101 g), and slow accumulation of biomass characteristic of seedlings of shade‐tolerant rainforest trees.O. aubrevilleiseedlings became hemiparasitic within 6 months when grown next to seedlings of the tree speciesEntandrophragma angolense(Wei.) DC.,Pericopsis elata(Harms) Van Meeuwen,Pterygota macrocarpaK. Schum., andTieghemella heckeliiPierre ex Chev.P. macrocarpa, and the nitrogen‐fixing legume,P. elatawere most infected. Characteristically for hemiparasites, midday leaf water potentials inO. aubrevillei wereat – 2 MPa lower than those of the host seedlings. Stomatal conductance, however, was low, with a maximum of 111 mmol m2s‐1. After 1 yr, no significant effects of the hemiparasitism were observed on the growth ofO. aubrevilleior on its nutrient status as measured by foliar element concentrations. By contrast, the two most infected host species showed increased mortality and/or reduced growth. Foliar element concentrations were not, however, affected in host plants of the surviving species. Although the resources of a large seed might enable seedlings ofO. aubrevilleito grow independently from hosts for prolonged periods, their simultaneous strong effect on the mortality and growth of host seedlings might point to an alternative competitive function of hemiparasitism.
Polarity and endoplasmic microtubules in food‐conducting cells of mosses: an experimental study
Authors: LIGRONE ROBERTO , DUCKETT JEFFREY G.
Published: April 2006

The effects of decapitation and of drugs affecting microtubules, microfilaments and the endomembrane system, on the ultrastructure of food‐conducting cells have been studied in the sporophyte of the mosses Polytrichum juniperinum Hedw. and Mnium hornum Hedw. In both species decapitation caused a marked reduction of cellular polarity. Moreover in Mnium but not in Polytrichum decapitation induced the disappearance of endoplasmic microtubules (MTs), the loss of longitudinal alignment of organdies and the accumulation of abundant starch. Starch accumulated in the cortical parenchyma cells in Polytrichum. In both species extensive MT depolymerization was induced by 100 μM oryzalin, whereas 10 μM oryzalin was less effective and 2·5 mM colchicine had no apparent effect. Treatment with 100 μM oryzalin also caused disruption of organdie alignment, alterations in the shape and position of the nucleus and a marked reduction in, or disappearance of, endoplasmic reticulum, trans Golgi network and membrane‐bounded tubules, that were abundant in the controls. Treatment with 10 μM monensin partially mimicked the effects of oryzalin, causing a reduction of the endomembrane system and disappearance of most endoplasmic MTs. Neither oryzalin nor monensin suppressed cellular polarity. Cells treated with D2O or the actin microfilament inhibitor cytochalasin D showed no structural alterations. The data indicate that: (a) endoplasmic MTs have a major role in organelle alignment and shaping in food‐conducting cells of mosses; (b) cellular polarity depends on the presence of a source/sink gradient and is not directly associated with MTs; (c) interactions between MTS and organelles, notably the ER and other components of the endomembrane system, have mutually stabilizing effects.
Soybean roots infected by Glomus intraradices strains differing in infectivity exhibit differential chitnase and β‐1,3‐glucanase expression
Authors: LAMBAIS MARCIO R. , MEHDY MONA C.
Published: April 2006

Different species and strains of arbuscular mycorrhizal (AM) fungi show different efficiencies of root colonization depending on the genetic background of both symbionts and on the edaphic conditions. It has been shown previously that the expression of several plant defence‐related genes is differentially regulated in AM roots and some of these genes might be involved in controlling intraradical fungal growth. In this study we evaluated the expression of chitinases and β‐1,3‐glucanases in soybean roots infected by two strains of Glomus intraradices Shenck & Smith exhibiting different infectivities. G. intraradices strain 26 was shown to be more infective than G. intraradices strain 25. Endochitinase activities were suppressed approx. twofold throughout the time‐course in roots colonized by the more infective strain 26, but not strain 25, compared with uninfected controls. Exochitinase activities were threefold higher in roots colonized by the more infective strain 26 by the end of the experiment, but did not differ from controls in roots colonized by the less infective strain 25. Activities of β‐1,3‐endoglucanase were not affected in roots colonized by the more infective strain 26, and were suppressed in roots infected by the less infective strain 25 at 8 wk after planting (WAP). By contrast, the steady‐state levels of a basic β‐1,3‐endoglucanase mRNA (EG488) were two to threefold higher at 4 and 6 WAP in roots infected by either strain than in non‐infected controls. These data suggest that one factor contributing to the differential colonization of plant roots by AM fungi strains is their differential suppression of defence‐related gene expression, especially chitinases.
Tansley Review No. 86 Accumulation of phytoalexins: defence mechanism and stimulus response system
Authors: SMITH C.J.
Published: April 2006

Phytoalexin synthesis is a defence‐response‐ that is characterized by a requirement for a number of distinct elements, all of which must be present for the response to be expressed fully. These same elements: a signal, a cellular receptor, a signal transduction system and a responsive metabolic system, are also used to describe a stimulus‐response system. A number of molecular species can function as signal molecules or elicitors of phytoalexin synthesis, including poly‐ and oligosaccharides, proteins and polypeptides, and fatty acids. Few receptors for elicitors have been identified but those that have been are proteins located on the plasma membrane of the plant. Induction of phytoalexin synthesis involves selective and co‐ordinated activation of specific defence response genes, including those encoding the enzymes of phytoalexin synthesis, and these genes constitute the responsive metabolic system. The separate, and distant, locations of the receptor and the responsive genes means that the event in which the signal is perceived by the receptor must be relayed to the genes by means of a second messenger system. Several second messengers are candidates for such a coupling‐ or signal transduction‐system, including udenosine‐3′,5′‐cyclic monophosphate, Ca2+, diacylglycerol and inositol 1,4,5‐trisphosphate, active oxygen species and jasmonic acid. Each has been examined as a possible component of the signal transduction system mediating between the elicitor receptor interaction and the phytoalexin synthesis it induces. Analysis of the signalling events is made complex by the simultaneous solicitation by the invading micro‐organism of several defence responses, each of which might involve elements of a different signal system. The same complexity is evident which the role of phytoalexin accumulation in resistance is analysed. Evaluation of the contribution made by phytoalexin accumulation towards resistance has been attempted by the use of various inhibitors and enhancers of the process. Transgenic and mutant plants with specific alterations in one or more ot those elements necessary for the plant to respond to the signals for phytoalexin synthesis and other defence responses, are beginning to aid resolution of the complex pattern ot signalling events and the respective roles of the inducible defence mechanisms in resistance.

CONTENTSSummary1I.Introduction2II.Chemistry of phytoalexins3III.Phytoalexin accumulation as a determinant of resistance6IV.Elicitation of phytoalexin accumulation11References34
Influence of cucumber mosaic virus infection on the intraspecific competitive ability and fitness of purslane (Portulaca oleracea)
Authors: FRIESS N. , MAILLET J.
Published: April 2006

Plants of purslane (Portulaca uleracea L.), either inoculated with cucumber mosaic virus CMV) or not, were grown to seeding at a range of densities up to 628 plants m−2, both in monoculture and together. CMV infection reduced vegetative growth and flower production in monoculture and in mixture. However, in mixture, unequal interference amplified the effect of infection on growth. At high densities, intraphenotypic interference between healthy plants grown in monoculture was very important, whereas it did not affect infected plants. When grown in mixture, infected plants had a weaker competitive ability than did healthy plants. Healthy plants showed a plasticity which allowed them to compensate for she reduced growth of infected plants when in mixture. It is concluded that partial infection of a natural population causes no overall decrease in production, but might induce a qualitative change owing to the reduced participation of infected plants in providing seed for the next generation.
Survival and spread of the endophyte Stagonospora pteridiicola in Pteridium aquilinum, other ferns and some flowering plants
Authors: FISHER P. J.
Published: April 2006

Pteridium aquilinum (L.) Kuhn was sampled for colonization by Stagonospora pteridiicola in Great Britain, Hungary and Australia. British samples gave the highest incidence of 68% during September and 12% at the beginning of the growing season. Hungarian samples showed a similar frequency. The fungus was not found in Australian bracken. Five field‐collected fern species other than bracken did not contain the fungus in May when bracken already had a colonisation frequency of 12% in the pinnules. Sampling after the bracken had died in November demonstrated that the fungus had continued growth as a saprobe. Glasshouse‐grown bracken sprayed with a spore suspension showed 96% colonization after 21 d, whereas four fern species and five flowering plants, similarly treated, gave colonization frequencies of 0–3%. Other glasshouse‐grown bracken, similarly sprayed, showed that colonization declined over 5 months from 75% to 40%, and that the fungus showed little spread into fresh unsprayed growth on these plants. The possible species specificity of the fungus is discussed.
Experimental studies of hypothallus growth in the lichen Rhizocarpon geographicum
Authors: ARMSTRONG R. A. , SMITH S. N.
Published: April 2006

Removal of the areolae of the crustose lichen Rhizocarpon geographicum (L.) DC. resulted in either low or no measurable radial growth of the marginal hypothallus. Radial growth of the hypothallus was also significantly reduced compared with intact thalli when (I) aerolae were removed to within 1 and 2 mm of the hypothallus and (2) a 5 mm wide ‘moat’ was created between the areolae and the hypothallus. Adding ribitol (0.01 M) to isolated hypothalli at 3‐month intervals over 15 months resulted in total radial growth c. 60% that of intact thalli. Adding an arabitol/mannitol mixture (0.05 M arabitol, 0.03 M mannitol) increased radial growth compared with deionized water and ribitol treatments. Adding ribitol (0.7M), arabitol (0.2 M) and mannitol (0.08 M) to the areolae of intact thalli had no significant effects on radial growth of the hypothallus. On a south‐facing rock surface, isolated hypothalli grew at a similar rate to intact thalli for 2 months. Growth then declined and the hypothalli disappeared from the rock surface within 6 months. The effects of addition of carbohydrate suggests that the marginal hypothallus has the capacity to utilize exogenous materials. However, in intact thalli in the field, the radial growth of the hypothallus is likely to be a result of transfer of materials from the areolae through hyphal connections.
Determination of the number of zones in a biostratigraphical sequence
Authors: BENNETT K. D.
Published: April 2006

Current methods for numerical zonation of biostratigraphic sequences neither assess the reliability of zones identified nor provide any means of determining the number of zones that are ‘significant’ (based on structure in the data set, rather than the stochastic element). These problems can be overcome by using the broken‐stick model to assess the significance of zones against a model of random distribution of zones within a sequence. The broken‐stick model is described and its application demonstrated on actual data sets. Additionally, simulation modelling is used to assess the uncertainty of the location of individual zone markers, given the errors of the original data. These widely‐applicable methods make it possible to identify zones rigorously and consistently. The potential in biostratigraphy and correlation includes the recognition, correlation and subdivision of chronostratipraphic units in long Quaternary sequences.
A method for rapid quantification of sucrose and fructan oligosaccharides suitable for enzyme and physiological studies
Authors: JOHN J. A. ST. , BONNETT G. D. , SIMPSON R. J.
Published: April 2006

summary

This paper presents a method for rapid quantification of sucrose and fructans by thin‐layer chromatography (TLC) and densitometry. In the optimized protocol, glass‐backed TLC plates were developed in a solution of propan‐1‐ol: ethyl acetate: water (45:35:20, v/v/v) for 3.5 h at 30 °C. In this system, sucrose, the fructan trisaccharides: 1‐kestose, 6G‐kestose and 6‐kestose, fructan tetrasaccharide and fructan pentasaccharide were separated. An internal standard of stachyose was useful for most of the applications examined. The fructans were detected by spraying with urea‐phosphoric acid and heating at 110 °C for 6 min. The blue colour developed was stable for 18 h provided that plates were kept in the dark. Quantification was achieved by reflectance densitometry and comparison with standards. The standard curves for the oligosaccharides were not linear, owing to the spreading of spots on the TLC plates, but were highly repeatable. The TLC quantification method provided a more rapid analysis of sucrose and fructan oligosaccharides than was possible by high‐performance liquid chromatography analysis because time‐consuming pre‐treatment of samples was not needed. The method will be useful for both enzyme and physiological studies.
Comparative measurements of gas‐exchange, acid accumulation and chlorophyllafluorescence of different species ofClusiashowing C3photosynthesis, or crassulacean acid metabolism, at the same field site in Venezuela
Authors: HAAG‐KERWER A. , GRAMS T. E. E. , OLIVARES E. , BALL E. , ARNDT S. , POPP M. , MEDINA E. , LÜTTGE U.
Published: April 2006

summary

Four differentClusiaspecies showing C3photosynthesis (C. multiflora) or crassulacean acid metabolism (CAM) (C. rosea, an unidentifiedClusiasp. andC. alata)co‐occur in the same habitat in the northwest of Venezuela. The aim of this field study was to correlate the adaptive changes in chlorophyll a fluorescence with gas exchange patterns and deacidification of nocturnally accumulated organic acids.

The results indicate that inC. roseaandClusiasp. a lowering of the potential quantum yield, measured as Fv/Fmafter 10 min of dark adaptation, is restricted to the early morning hours. With the onset of deacidification there was no further decline in Fv/Fm, although the irradiance upon the leaves remained high. For the C3‐plant,C. multiflora, changes in Fv/Fmwere correlated with changes in irradiance incident on the leaves before predarkening for 10 min for Fv/Fmmeasurements. The fast relaxation of Fv/Fmunder low light indicates thatC. multiflorawas not suffering photoinhibitory damage. Effective quantum yield as determined by ΔF/Fm, was low under high irradiances forC. roseaandClusiasp. and did not change significantly forC. roseaduring phase III of CAM. During the time of low incident irradianceC. alataandC. multiflorareached an effective quantum yield that was close to the optimal quantum yield of electron transport. It is noteworthy that apparent electron transport rates through photosystem II (PS II) (ΔF/F'm) × PPFD) were highest forC. rosea, Clusiasp. andC. alataduring phase III of CAM. Electron transport rates inC. multiflorawere lower under high irradiance and did not differ from those found in phases II and IV of CAM. The possible role of CO2, evolution from acid decarboxylation with respect to photosynthetic efficiency is discussed.
Rise and demise of cold‐climatePicea abiesforest in Sweden
Authors: KULLMAN LEIF
Published: April 2006

summary

The study focuses on structural and compositional dynamics of high‐elevation (boreal) mixedPicea‐Betulaforest in the Swedish Scandes. Data from seven years' monitoring of crown condition (defoliation), seed viability, soil and air temperatures, a tree‐ring chronology and the age structure ofPiceaare presented. Real long‐term dynamism of the tree cover was inferred from radiocarbon dates of buried subfossil wood. At all time‐scales, the forest has responded sensitively to thermal variability.Piceaseed viability, demography and radial growth correlated positively with summer temperature. The currentPiceapopulation largely results from warming during the first half of the 20th century. However, cooler climate in the pastc.five decades has led to reduced population and radial growth as well as accelerating crown defoliation. This decline is related primarily to winter soil temperatures. The mechanism of needle loss is deduced to be winter desiccation and resulting cavitation of the xylem. It is hypothesized that previous similar episodes have been balanced by periods of spruce expansion. The successional history leading up to the present stage includes fire disturbance and subsequent cooling during the Little Ice Age, which prolonged and consolidated the early post‐fireBetulaphase.Pinuswas incapable of penetrating these unusually dense birch stands, whereas the shade‐intolerant spruce could establish progressively as climate warmed. This course of structural and compositional dynamism relates to complex interactions of disturbance, climate change and reproductive responses.
The effect of ozone fumigation over one season on photosynthetic processes of Quercus robur seedlings
Authors: FARAGE P. K.
Published: April 2006

summary

Quercus robur saplings were exposed to elevated O3 (80 nmol mol‐1) in hemispherical glasshouses for one growing season in order to assess the effects of this pollutant on photosynthesis. Measurements of chlorophyll fluorescence induction kinetics in mid‐summer showed that plants exposed to both control O3 (20 nmol mol−1) and elevated O3 treatments experienced significant photoinhibition of photosynthesis. Elevated O3 increased photoinhibition. At the end of the summer, photosynthetic CO2 uptake, measured at either light saturation or under light‐limiting conditions, was not significantly different between plants from the two O3 treatments. Although the maximum rate of carboxylation velocity, as estimated from the response of CO2 uptake to intercellular CO2 concentration, the maximum quantum efficiency and the maximum rate of electron transport measured in vivo were decreased by O3 exposure, the responses differed between plants and, overall, the decreases were not statistically significant. The results suggest that O3 levels that are at present reached for a few days during photochemical episodes in the summer are not sufficient to cause measurable lasting damage to photosynthetic CO2 uptake in oak saplings assessed over one growing season.
The effects of fertilizer and root competition on seedlings of Orchis morio and Dactylorhiza fuchsii in chalk and clay soil
Authors: MCKENDRICK S. L.
Published: April 2006

summary

The responses of two native British orchids, Orchis morio L. and Dactylorhiza fuchsii (Druce) Soó, to fertilizer and root competition were tested in pots of natural soil. Seedlings were raised from seed in symbiotic culture, set into pots of natural soil and grown for 10 wk in a controlled environment chamber with and without the grass Festuca rubra L. on clay, chalk and fertilized chalk soil. The growth of O. morio was not significantly affected by fertilization. Fertilization of D. fuchsii produced a marked reduction in growth, particularly of the roots. Root competition had little effect on either of the orchids, except that plants of O. morio grown with F. rubra had a greater allocation to thicker, tuber‐bearing roots relative to fine roots (c. 1 mm diameter or less) compared with those grown without grass. These results were in marked contrast to those obtained for the typical grassland perennial Leontodon hispidus L., in which fertilization led to a very large increase in growth, and root competition greatly reduced growth.
The effects of shade on seedlings of Orchis morio and Dactylorhiza fuchsii in chalk and clay soil
Authors: MCKENDRICK S. L.
Published: April 2006

summary

The responses of two native British orchids, Orchis morio L. and Dactylorhiza fuchsii (Druce) Soó, to shading were tested using 7‐ and 8‐month‐old symbiotically propagated seedlings. Seedlings were raised in culture, set into tubes of clay and chalk soil and grown under shade screens for 10‐wk in a controlled environment chamber in deep green shade, green shade, neutral shade, and unshaded (photosynthetic photon fluence rates (PPFR) 24, 54, 54 and 225 μmol m−2s−1respectively). The dicotyledonous perennial Leontodon hispidus L. was also tested for comparison. The orchids tolerated shade more than did L. hispidus, in which a decrease in PPFR led to a decrease in d.wt, an increase in specific lead area (SLA) and elongation of the petioles. In O. morio, lower PPFR led to only a slight decrease in d.wt in the most shaded treatment, an increase in SLA similar to that of L. hispidus, and an increase in the vertical inclination of some leaves. In D. fuchsii lower PPFR led to a reduction in d.wt, mainly in the roots at higher, and in the leaves at lower, photon irradiance. A change from neutral to green shade reduced growth in L. hispidus, but had no effect on either orchid. The physiological and ecological implications of shade tolerance in orchid seedlings are discussed.
Manipulating secondary metabolism in cultured plant cells
Authors: YEOMAN M. M. , YEOMAN C. L.
Published: April 2006

summary

This review attempts to present an overall strategy for the production of useful secondary metabolites by cultured plant cells. After consideration of the nature and utility of secondary metabolites and the possible role of these substances to the plant, the review focuses attention on the properties of the plant cells in culture and how the cell populations and their physical and chemical environment can be manipulated to encourage the synthesis and accumulation of secondary products. Finally, consideration is given to the involvement of genetic engineering in the production of cells to perform particular metabolic tasks and how these techniques might contribute to the development of a new strategy to enable the production of useful secondary metabolites on a commercial scale.

CONTENTS

Summary
553

I.
Introduction
553

II.
Development of a strategy
555

III.
Concluding remarks
565

Acknowledgements
565

References
565
A bean epicuticular glycoprotein is present in the extracellular matrices around infection structures of the anthracnose fungus, Colletotrichum lindemuthianum
Authors: HUTCHISON KATIE A. , O'CONNELL RICHARD J. , PAIN NAOMI A. , GREEN JONATHAN R.
Published: April 2006

summary

Monoclonal antibodies were raised to Colletotrichum lindemuthianum (Sacc. & Magn.) Briosi & Cav. infection structures which had been isolated from leaves of Phaseolus vulgaris L. by isopycnic centrifugation and immunomagnetic separation. One of the antibodies, UB29, recognized a carbohydrate epitope in a 200 kDa glycoprotein present on the surface of conidia, germ‐tubes and appressoria when they developed on host tissue. Intracellular hyphae were not labelled. Immunogold labelling showed that the antigen was confined to the extracellular matrices around such structures. No such antigen was detected by immunofluorescence or Western blotting when the fungus developed in vitro. UB29 recognized a glycoprotein of identical Mr located in the epicuticular wax layer of uninoculated bean hypocotyls. The results suggest that a host epicuticular glycoprotein is present in the extracellular matrices of fungal structures during growth on the plant surface.
Mass and energy exchange between the atmosphere and leaf influence gas pressurization in aquatic plants
Authors: STEINBERG S. L.
Published: April 2006

summary

A mechanistic model was used to describe how mass and energy exchange between a leaf and air affect internal pressurization in aquatic plants. The core of the model is the calculation of the temperature of a leaf for which the energy balance is zero. The leaf temperature and water vapour gradient between leaf and air are then used to calculate potential pressurization. Simulations with the model were used to demonstrate the sensitivity of gas pressurization in aquatic plants to key environmental and physiological factors including radiation, temperature, humidity, wind speed, leaf size and leaf conductance. The model confirms other published data showing that humidity‐induced pressurization is the dominant mode of pressurization under most conditions. The simulations also demonstrated that thermal transpiration and humidity‐induced pressurization are not separate phenomena, but are dependent on the energy balance of the leaf, which in turn is affected by complex interactions between the leaf and environment.
Prediction of the growth response to elevated CO2: a search for physiological criteria in closely related grass species
Authors: ROUMET C. , ROY J.
Published: April 2006

summary

Using 11 closely related grass species, we tested the capacity of physiological criteria to predict the growth response to elevated CO2 and to categorize the species with regard to their CO2 response. A growth analysis was conducted under productive conditions both at ambient (350 μmol mol−1) and elevated (700 μmol mol−1) CO2. The relative growth rate stimulation was regressed against each of the growth rate components measured at ambient CO2.

Growth response to CO2 was positively correlated with specific leaf area (sla, the leaf surface area per unit of leaf weight), leaf area ratio (the leaf area per unit of total plant dry weight) and negatively correlated with net assimilation rate and leaf nitrogen concentration, both per unit of leaf area. We suggest that sla has a predominant role in these relationships. Different hypotheses are proposed and discussed in order to explain why species with low sla are less responsive to elevated CO2. Neither biomass allocation, relative growth rate, shoot or root specific activities per unit of mass, nor chemical composition were significantly correlated with growth response to CO2.

The four predictive criteria mentioned above coherently differentiate the five wild annual species (higher sla, stronger growth response to CO2) from the four wild perennials. The two perennial crop species, with the highest sla, were more responsive than the wild species.
Cytogenetic evidence for autopolyploidy in Parnassia palustris
Authors: WENTWORTH J. E. , GORNALL R. J.
Published: April 2006

summary

Diploid populations of Parnassia palustris L. var. palustris and var. condensata Travis & Wheldon have a highly symmetrical karyotype, consisting of seven metacentrk and two submetacentric chromosomes. The gross morphology of the karyotype of tetraploid populations is indistinguishable from that of the diploids. Studies of meiosis in tetraploids of both varieties demonstrated a high frequency of quadrivalent formation, strongly suggesting an autopolyploid origin. Later stages of meiosis in the tetraploids are regular and the pollen shows no decrease in stainability compared with that of the diploids. Some evidence is presented to show that tetraploids of both varieties may have a wider ecological amplitude than do diploids.
Inoculum potential of ericoid endophytes of Western Australian heaths (Epacridaceae)
Authors: HUTTON B. J. , DIXON K. W. , SIVASITHAMPARAM K. , PATE J. S.
Published: April 2006

summary

The nature and location of infective inocula of ericoid endophytes were examined in habitat soil sampled dry during midsummer from different depths down the rooting profile of an Epacridaceae‐rich mediterranean‐type ecosystem in south‐western Australia. Efficacy of soil inocula was tested using aseptically germinated seedlings ofLysinema ciliatumR. Br. grown in a glasshouse. Hair roots, the principal structures colonized by endophytes, constituted c. 70% of the total length of root systems formed under glasshouse culture. Colonization of these hair roots by endophytes was greatest (17%) when seedlings had been inoculated with habitat soil from the upper 24 cm zone and declined to less than 1% following inoculation with soil obtained from a depth of 36 cm and beyond. By contrast, sampling of a naturally growing epacrid (Leucopogon conostephioidesD.C.) at the same study site during the wet midwinter growing season showed uniformly high (34–43 %) infection of hair roots down to maximum rooting depth at 70 cm. The infectivity of sieved soil fractions from bulk habitat soil was considerably greater (mean of 17 % hair root infection) for glasshouse‐culturedLysinema ciliatuminoculated with the 251–305 μm particle size fraction than for that inoculated with coarser (306–5000 μm) and finer (39–250 μm) sieve fractions (0–6% infection). Dilution of bulk soil with sterilized soil indicated maximum infection at 1:16 dilution, declining to negligible infectivity at a dilution of 1:100. The data support the hypothesis that inoculum persists through summer principally in relatively coarse fractions of organic matter near the soil surface. With the onset of autumn rains, downward mycelial growth emanating from this upper zone rapidly recolonizes the soil profile and eventually promotes extensive colonization of hair roots produced that season by the epacrid root system.
Physiological heterogeneity within fungal mycelia: an important concept for a functional understanding of the ectomycorrhizal symbiosis
Authors: CAIRNEY J. W. G. , BURKE R. M.
Published: April 2006

summary

Individual mycelia of filamentous fungi display considerable heterogeneity at the physiological level. Important physiological processes such as nutrient absorption, extracellular enzyme secretion and solute translocation occur differentially within an individual mycelium, and vary according to spatio‐temporal changes in patterns of gene expression as the mycelium develops and senesces. In ectomycorrhizal (ECM) fungi, gene expression appears to be strongly influenced by interaction with the soil environment and the host root. The ECM mycelium is thus a complex and dynamic entity wherein discrete regions display particular physiological attributes. Physiological heterogeneity is important in the overall functioning of the symbiosis. In the particular case of movement of phosphorus from soil to host root in the ECM symbiosis, heterogeneity might provide the driving force for the integrated processes of absorption, translocation and transfer. It is suggested that it is only by considering the sum of the seemingly disparate physiological processes within the heterogeneous mycelium that mycorrhizal functioning can be fully understood.
A conceptual model for the development of Phytophthora disease in Quercus robur
Authors: Jönsson U.
Published: April 2006

Here, a conceptual model is presented for the development of Phytophthora disease in pedunculate oak. The model is presented using the causal loop diagram tool and gives an overview of how various abiotic and biotic factors, such as soil moisture, nutrient availability and mycorrhizal colonization, may affect the reproduction and the infective capacity of soil‐borne Phytophthora species, the susceptibility of the host and subsequent disease development. It is suggested that the link between the root damage caused by Phytophthora species and overall tree vitality is in the assimilation and allocation of carbon within the plants. The potential impact of environmental factors on these processes is discussed. The model is presented with reference to scenarios related to variation in soil moisture and nutrient availability. The need for species‐specific validation of the model and the implications of the model are discussed.
Immunocytochemical localization of 3‐methylcrotonyl‐CoA carboxylase in cultured ependymal, microglial and oligodendroglial cells
Authors: Murín Radovan , Verleysdonk Stephan , Rapp Mirna , Hamprecht Bernd
Published: April 2006

To evaluate the ability of ependymal, microglial and oligodendroglial cells to degrade leucine, the presence of 3‐methylcrotonyl‐CoA carboxylase (MCC) was investigated in cultures of these cells. MCC is a biotin‐containing heterodimeric enzyme that is specific for the irreversible part of the leucine catabolic pathway. It has been reported previously that in cell culture MCC is expressed in astrocytes and a subpopulation of neurones. In the present study ependymal, microglial and oligodendroglial cell cultures, derived from the brains of newborn rats, were examined for the expression of MCC by RT–PCR, western blotting and immunocytochemistry. The results of RT–PCR and western blotting showed the presence of mRNA as well as protein of both subunits of MCC in ependymal, microglial and oligodendroglial cell cultures. Immunocytochemical investigation of the cellular and subcellular distribution of MCC demonstrated a mitochondrial location of MCC in all neuroglial cell types investigated. The ubiquitous expression of MCC in glial cells demonstrates the ability of the cells to engage in the catabolism of leucine transported into the brain, mainly for the generation of energy.
Substance P release evoked by capsaicin or potassium from rat cultured dorsal root ganglion neurons is conversely modulated with bradykinin
Authors: Tang He‐Bin , Inoue Atsuko , Iwasa Mikiko , Hide Izumi , Nakata Yoshihiro
Published: April 2006

To clarify the molecular mechanism of substance P (SP) release from dorsal root ganglion (DRG) neurons, we investigated the involvement of several intracellular effectors in the regulation of SP release evoked by capsaicin, potassium or/and bradykinin. Bradykinin‐evoked SP release from cultured adult rat DRG neurons was attenuated by either the mitogen‐activated protein kinase kinase (MEK) inhibitor (U0126) or cycloheximide. As the long‐term exposure of DRG neurons to bradykinin (3 h) resulted in extracellular signal‐regulated kinase (ERK) phosphorylation at an early stage and thereafter induced cyclooxygenase‐2 (COX‐2) protein expression, which both contribute to the SP release triggered by bradykinin B2 receptor. The long‐term exposure of DRG neurons to bradykinin enhanced the SP release by capsaicin, but attenuated that by potassium. Interestingly, the inositol 1,4,5‐triphosphate (IP3)‐induced calcium release blocker [2‐aminoethyl diphenylborinate (2‐APB)] not only inhibited the potassium‐evoked SP release, but also completely abolished the enhancement of capsaicin‐induced SP release by bradykinin from cultured DRG neurons. Together, these findings suggest that the molecular mechanisms of SP release by bradykinin involve the activation of MEK, and also require the de novo protein synthesis of COX‐2 in DRG neurons. The IP3‐dependent calcium release could be involved in the processes of the regulation by bradykinin of capsaicin‐triggered SP release.
Investigating the factors influencing professional identity of first‐year health and social care students
Authors: Adams Kim , Hean Sarah , Sturgis Patrick , Clark Jill Macleod
Published: April 2006

Interprofessional education (IPE) involves students from different professions being brought together to learn about each other's profession. Several models of IPE exist, and central to the debate around which of these models is the most appropriate is the question of the stage of training in which to implement these programmes. Currently, however, there is no consensus on this question. Debate so far has revolved around the strength of professional identities, or lack thereof, amongst pre‐qualifying students and how this may influence interprofessional learning. The potential role of professional identity in IPE seems to be unresolved. The present article adds to this debate by investigating the level of professional identity when students commence their professional studies; the differences in the level of professional identity between students from a range of professions; and the factors which may affect the initial levels of professional identification. Data were collected by questionnaire from the first‐year cohort of Health and Social Care (H&SC) students embarking on IPE as an embedded part of an undergraduate pre‐qualifying programme. A sample of 1254 students was achieved. Professional identity was measured using an adaptation of a previously described scale. Our findings suggest that a degree of professional identity is evident before students begin their training. Differences in strength of initial professional identity were observed across professions, with physiotherapy students displaying the highest levels of professional identification. To test for associations between professional identity and a number of independent variables, an ordinary least squares (OLS) regression model was estimated. The variables that were found to be significant predictors of baseline professional identity were: gender; profession; previous work experience in H&SC environments; understanding of team working; knowledge of profession; and cognitive flexibility. Some explanations for these findings are presented and the implications are discussed.
Reviewing experience and testimony as pedagogical resources in open learning
Authors: Shakespeare Pam
Published: April 2006

Accounts of experience and direct testimony are used extensively in health and social care education. In the sphere of open and distance learning (ODL) they both offer a richness and texture in the materials and form the focus for the use of a spectrum of ‘human data’, which are central to the health and social care professions. This article discusses some of the uses of experience and testimony in ODL relating to health and social care and examines ways in which testimony is transformed for pedagogic purposes in open and distance learning.