bluuebunny/crossref_metadata_2025_split huggingface dataset:
Population dynamics of indigenous and genetically modified rhizobia in the field
Authors: HIRSCH PENNY R. 
Published: April 2006

SUMMARYMany 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYWe 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

SUMMARYThis 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

SUMMARYWe 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

SUMMARYThe 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

SUMMARYDifferent 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

SUMMARYPhytoalexin 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

SUMMARYPlants 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

SUMMARY 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

SUMMARYRemoval 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

SUMMARYCurrent 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

summaryThis 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.