bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regeneration of bog liverworts
Authors: DUCKETT J. G. , CLYMO R. S. 
Published: April 2006

summaryLeafy liverworts of many species regenerate in slabs cut at various depths from peat cores from two widely different sites. Two patterns are recognizable. Species such as Calypogeia fissa (L.) Raddi, Lophocolea spp., Lophozia ventricosa (Dicks.) Dum., Barbilophozia floerkii (Web. & Mohr) Loeske and Riccardia latifrons (Lindb.) Lindb., which lack underground axes, regenerate most abundantly at the surface but not below 9 cm depth. Other species such as Kurzia pauciflora (Dicks.) Grolle, K. sylvatica (Evans) Grolle, Odontoschisma sphagni (Dicks.) Dum., O. denudatum (Mart.) Dum., Cladopodiella fluitans (Nees) Buch, Cephalozia bicuspidata (L.) Dum. and C. connivens (Dicks.) Lindb. which have underground axes, may regenerate poorly at the surface, much better down to 12 cm or so, and arc still found at 24–30 cm depth. These patterns were found in cores from a live Sphagnum‐covered surface and from a much older cut peat surface recently recolonized by liverworts. These results suggest that regeneration is mainly from underground axes rather than from spores or gemmae. The biomass of the underground axes seems to be large. All the axes have fungal associates, and it possible that they are partially saprophytic or parasitic.
The use of benomyl to control infection by vesicular–arbuscular mycorrhizal fungi
Authors: FITTER A. H. , NICHOLS R. 
Published: April 2006

SUMMARYThe effect of the fungicide, benomyl, on vesicular arbuscular (VA) mycorrhizal infection and phosphorus uptake was studied in two pot experiments, using pea Pisum sativum L., mustard Sinapis alba L. and red clover Trifolium pratense L. Benomyl was either incorporated into the soil or sprayed on to the surface of the pot. Benomyl had no effect on concentrations of water‐soluble P in soil but reduced VA mycorrhizal infection and P inflow in pea. Mustard plants were uninfected even in untreated pots and benomyl had no effect on P inflow in mustard. In clover, there was a positive correlation between shoot P concentration and percentage of root length infected with VA mycorrhizal fungi. Copper, zinc and manganese concentrations in clover shoots were affected by benomyl but this may not have been related to mycorrhizal infection. Benomyl is recommended as a treatment to control VA mycorrhizal infection, with many fewer undesirable consquences than result from soil sterilization.
The isolation of genomic DNA from cyanophage infecting Nostoc and Anabaena species of cyanobacteria
Authors: BANCROFT I. , SMITH R. J. 
Published: April 2006

SUMMARYThe preparation of genomic DNA from a recently isolated group of cyanophage which infect species of Nostoc and Anabaena (cyanobacteria) has been investigated. Factors which affect the yield of DNA, including culture density on infection, divalent cation requirements, NaCl tolerance and desorption from cell debris, have been assessed. These factors have been incorporated into optimized procedures for the isolation of genomic DNA from five cyanophage. The DNA isolated from the rive cyanophage species was identified using restriction endonuclease fragment patterns.
Photosynthetic characteristics of Spirulina platensis on solid support. Chlorophyll fluorescence kinetics
Authors: SIVAK MIRTA N. , VONSHAK AVIGAD 
Published: April 2006

SUMMARYSeveral aspects of photosynthesis in vivo (CO2 and O2 exchange, chlorophyll fluorescence and its quenching components) were measured in Spirulina platensis after filtering suspensions of this cyanobacteria through fibre glass filters. This simple procedure allowed the use of methods which previously could be applied only to leaves. Fluorescence characteristics displayed by Spirulina in suspension or collected on the solid support were similar, indicating that filtration and assay did not by themselves affect the photosynthetic process. When oxygen evolution and carbon dioxide uptake were followed simultaneously their kinetics differed, and the rate of O2 evolution was often higher than the rate of CO2 uptake. Slow kinetics and other fluorescence characteristics were strongly modified in aged cultures or when nutrient supply during growth was not optimal, or after exposure to photoinhibitory photon flux densities. Photoinhibition and recovery were studied in two strains differing in their sensitivity to high photon flux densities. During illumination using high photon flux densities two phases could be determined. After a few minutes variable fluorescence decreased and ‘dark fluorescence’(Fo) was unchanged, but after prolonged illumination Fo increased. The latter phase appeared earlier in the more sensitive strain and could be brought forward by increasing photon flux densities or, in some circumstances, by increasing [O2].Results are discussed in terms of the underlying relationships between electron transport and photosynthetic carbon assimilation and of the use of chlorophyll fluorescence as a diagnostic probe. It is suggested that measurement of chlorophyll fluorescence (by itself or in conjunction with quantum yield) on cyanobacteria or algae collected on solid support could provide a convenient screening procedure to assess sensitivity to photoinhibition and to other kinds of stress likely to be encountered in large‐scale culture.
The effect of the gp gene on fruit development in Pisum sativum L.
Authors: PRICE D. N. , SMITH C. M. , HEDLEY C. L. 
Published: April 2006

SUMMARYThe effect of the yellow‐podded (gp) gene on pea fruits was studied with reference to changes in their plastids. The main effect of the gene was on the mesocarp. The chlorophyll concentration of this layer was depressed to less than 5% of that in normal green pods, allowing considerably higher light transmission through the pod wall. Ultrastructural studies showed that the mesocarp of yellow pods contained plastids with an internal membrane system restricted to single and paired membranes and vesicles. Unlike the chloroplasts of green mesocarps they lacked grana. Large starch grains were found in the plastids of mesocarps from both yellow and green pods.Well‐developed chloroplasts, lacking starch grains, were found in the thin parenchymatous lining of the endocarp in yellow and green pods. Here chlorophyll concentrations were comparable in the two pod types and considerably higher than those found in the normal green mesocarp. However, the higher light levels transmitted to this layer in yellow pods correlated with a higher chlorophyll a:b ratio compared with that in the green pod.
Studies on the tolerance to SO2 of grass populations in polluted areas
Authors: Taylor H. J. , Bell J. N. B. 
Published: April 2006

SUMMARYGrass populations were collected from two sites, Philips Park and Rainham, with different pollution characteristics. They were screened for acute and chronic air pollution injury caused by nitrogen dioxide (NO2) and by sulphur dioxide(SO2) in combination with NO2 in comparison with bred cultivars of the same species grown at a clean air site. No evidence of tolerance of acute NO2 or NO2/SO2, injury was found at Philips Park. A Dactylis glomerata L. population from Rainham showed tolerance to both types of injury. There was also some evidence to suggest that there was a relationship between NO2 and NO2/SO2 tolerance. Chronic NO2 fumigation of Lolium perenne L. was shown to have apparently beneficial effects such as increased growth, increased chlorophyll content and reduced rate of senescence. The Rainham population of this species appears to have a requirement for low concentrations of NO, in the atmosphere. There was an indication that plants which were most tolerant of acute doses of NO2 were those which most benefited from low concentrations of NO2L. perenne and D. glomerata were adversely affected by chronic exposure to a mixture of NO2 and SO2 The Rainham populations of both species were more tolerant of the mixture than bred cultivars. Chronic NO2/SO2 injury was found to be more severe when soil nitrogen was high.
Dynamics of arbuscule development and degeneration in mycorrhizas of Triticum aestivum L. and Avena sativa L. with reference to Zea mays L.
Authors: ALEXANDER TOM , MEIER ROSE , TOTH RONALD , WEBER HANS CHRISTIAN 
Published: April 2006

SUMMARYA quantitative light and electron microscope study of developing and degenerating arbuscules of the mycorrhizal fungus Glomus fasciculatum (Thax. sensu Gerd.) Gerd. & Trappe in Triticum aestivum L. (wheat) and Avena sativa L. (oats) was carried out in order to estimate three parameters during the colonization cycle and to compare these parameters to those in Zea mays L. The parameters are: (1) Vv (f,c), the fraction of the host cell volume (c) occupied by a volume of fungus (f); (2) Vv,(cy, c), the fraction of the host cell volume occupied by host cytoplasm (cy); (3) Sv(p,c) the surface area‐to‐volume ratio of the host protoplast (p) to the whole host cell. Uninfected cortical cells of wheat had an Sv,(p,c) of 0.11 μm2μm −3 and those of oats 0.10 μm2μm −3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in St. In wheat this increase reached 1.17 μm2μm−3 and in oats, 1.04 μm2μm−3. When the arbuscule is mature, the fungus occupies 35% of the cell in wheat with 20% as branches and 15% as trunk. In oats, the fungus occupies 36% of the cell, with 23 % as branches and 13 % as trunk. In wheat, host cell cytoplasm was initially 39 % and increased to 21.6% and in oats, from 3.6 to 28.8%. These values are similar to those observed in Zea mays. The rates at which the parameters Vv(f,c) and Sv(p,c) changed during arbuscule development and degeneration were similar. The amount of encasement and host cell cytoplasm showed the greatest variation among host species.
Photosynthesis in discrete regions of leek leaves infected with the rust, Puccinia allii Rud.
Authors: Roberts A. M. , Walters D. R. 
Published: April 2006

SUMMARYPhotosynthesis was examined in discrete regions of leek (Allium porrum L.) leaves infected with the rust, Puccinia allii Rud. Oxygen evolution, expressed on both a chlorophyll and a leaf area basis, was significantly reduced in pustule regions, coupled with an increase in rates of dark respiration, for the duration of the experiment. The activity of ribulose bisphosphate carboxylase (RuBPcase) was reduced in pustule areas and losses in total soluble protein and chlorophyll were observed. Areas between pustules exhibited photosynthetic rates (on a chlorophyll basis) near to control values and dark respiration was reduced for at least part of the experiment. No significant alteration in RuBPcase activity, total soluble protein or chlorophyll concentrations was detected in interpustule regions. The physiological mechanisms underlying the changes in photosynthesis and respiration within discrete regions of rusted leeks are discussed.
Effects of the fairy ring fungus Agaricus arvensis on nutrient availability in grassland
Authors: Edwards P. J. 
Published: April 2006

SUMMARY Agaricus arvensis Schaeff. ex Fr. produced a pattern (a fairy ring) in the vegetation consisting of three concentric zones of scorched or reddened foliage alternating with zones of more vigorous growth. The outermost zone contained active mycelium; the inner zones were thought to represent the positions of the mycelium in previous years.Soil samples were taken from the various zones of affected vegetation, and from outside and inside the rings. Concentrations of total nitrogen, phosphorus (total and acetic acid extractable), potassium and magnesium were highest in the active zone; concentrations of these nutrients inside the zones were lower than those outside.Leaf blades of Agrostis capillaris L. in all zones of affected vegetation had enhanced concentrations of nitrogen. Phosphorus and potassium concentrations in leaves were reduced within the fairy rings, especially in the zones of reddened foliage. It is concluded that the growth habit of the fungus allows it to accumulate nutrients very effectively and may cause nutrient deficiencies in higher plants.The investment of potassium in sporophores was equivalent to 23 % of that in the soil volume exploited by the mycelium in 1 year. For phosphorus the corresponding percentages were 1–3 of total soil phosphorus and 63 % of acetic acid‐extractable phosphorus. However for nitrogen, calcium and magnesium the quantity in the sporophores was & 1 % of that in the soil.
Phragmites australis: a critical appraisal of the ventilating pressure concept and an analysis of resistance to pressurized gas flow and gaseous diffusion in horizontal rhizomes.
Authors: ARMSTRONG J. , ARMSTRONG W. , BECKETT P. M. 
Published: April 2006

SUMMARYThe concept of plant ‘ventilating pressures’ is considered by comparing the pressures required to cause various rates of gas‐How through rhizomes of Phragmites australis venting either beneath water or into air. The resistances to pressurized flow in nodal and internodal regions are quantified, and the pressure: flow data analysed mathematically to deduce effective pore‐space diameter in the nodal diaphragms, and the diffusive resistances of the diaphragms and intemodes.The value traditionally termed ‘ventilating‐pressure’, the minimum pressure required to cause a venting of gas into water, is shown to be a function of surface tension effects at the venting surfaces and not a measure of gas‐flow resistance within the plant.With venting to air rather than water, gas flows occurred at all applied pressures greater than atmospheric and pressure‐flow resistance within the plant was determined from the gas flow: pressure relationship. Pressure‐flow resistance was much greater in the nodal pith diaphragms (6–210 MPa s m−3) than in internodal pith cavities (0.001 5.040 MPa s m−3; path length, 100 mm) and was chiefly a function of pore‐size, pore numbers and path length within the small stellate parenchyma layers of the diaphragms. The domed nature of diaphragms reduces resistance by increasing the pore numbers. The effective pore diameters within the small stellate parenchyma of the diaphragms were estimated from the pressure: flow data using a modification of the Poiseulle equation. The values obtained ranged from c. 3.7 μm, and corresponded closely with diameters found previously by scanning electron microscopy.It is concluded that both large and small stellate parenchyma must contribute significantly to the diffusive resistance of tile diaphragms in accordance with path lengths and porosity; and that, in contrast with pressure‐flow resistance, the internodes because of their length, should have the greater impedance. Estimated values for the pith diaphragm diffusive resistance were 1–13 Ms m−3 (path length, 1.7–3 mm), whilst pith cavity resistances, (path length 100 mm), were 25–1100 Ms m−3. In the latter, the variation was attributable chiefly to the widely varying rhizome diameters: porosities of wide rhizomes were greater than those of narrower ones because of large pith cavities. The fractional porosity due to cortical aerenchyma channels (10–20%) was not related to rhizome thickness.It is concluded that gas‐flow resistances in Phragmites are sufficiently small to allow for substantial long‐distance transport by convection or diffusion.
The response of stomata to ring‐substituted indolylacetic acids
Authors: THOMSON A. , COX R. C. , MANSFIELD T. A. 
Published: April 2006

summaryIndol‐3‐ylacetic acids with substituents in the aromatic ring have been synthesised and their effect on stomata on isolated epidermis tested. Unlike indol‐3‐ylacetic acid which induces stomatal opening, all the substituted acids caused closure. The perception mechanism in the guard cells may therefore involve receptors with high specificity for IAA. The ability of guard cells to discriminate IAA from closely related molecules may be higher than in other cellular systems.
Urban distribution of Rhytisma acerinum (Pers.) Fries (tar spot) on sycamore
Authors: LEITH I. D. , FOWLER D. 
Published: April 2006

SUMMARYThis study examined ecological aspects of the distribution of tar spot disease caused by the fungus Rhytisma acerinum (Pers.) Fries on Acer pseudoplatanus L. (sycamore). The host is abundant in Edinburgh and surrounding areas yet no tar spots were found in the city, although they were abundant on sycamore in the surrounding countryside, especially at sheltered sites. The vertical distribution from a localized source of leaf litter from infected sycamore showed an approximately linear relationship between tar spot index of attached leaves (TSI = no. of tar spots per 100 cm2 of leaf) and the log of height of such infected foliage above the ground. The distribution of tar spots was controlled primarily by the presence or absence of overwintered sycamore leaves infected with R. acerinum. In Edinburgh these leaves are actively removed by man and passively by wind, so reducing the potential source of inoculum by the following spring.The presence of SO2 was unimportant in the distribution of R. acerinum. An experiment to study the relative importance of current air concentrations of SO2 on the incidence of infection by R. acerinum showed that the average SO2 concentration of < 50 μg m‐3 hail no effect. The observed distribution of tar spot throughout the city and surrounding countryside could be explained entirely by distance from the nearest source of inoculum without involving a role for air pollutants.
Effects of microwave treatment of soil on growth of birch (Betula pendula) seedlings and infection of them by ectomycorrhizal fungi
Authors: GIBSON FIONA , FOX FRANCES M. , DEACON J. W. 
Published: April 2006

SUMMARYSeedlings of birch (Betula pendula Roth.) were grown for 12 weeks in small volumes of field soils heated in a microwave (MW) oven for different times and then either supplemented or not with inocula of ectomycorrhizal fungi and, in one case, with fresh agricultural soil. Growth of roots and shoots was assessed, and the incidence of different mycorrhizal types, distinguished by colour and morphology, was recorded. Bacterial and fungal populations were determined by dilution plating after MW treatment of soils.In four soils, shoot and root growth were markedly enhanced by MW treatments that raised the soil temperature to 60°C or more, irrespective of the exposure times (20–50 s) needed for this. Shoot dry weights were increased 1·9‐ to 2·9‐fold by MW treatment of two soils from young (11–16 years) birch stands, compared with 8·0‐ and 11·4‐fold for two soils from old birchwoods. But MW treatment of a colliery spoil reduced shoot growth 5‐fold. The growth responses were not related to the size of seedlings in untreated soils. The responses coincided with substantial reductions in the total populations of bacteria and fungi. Hebeloma subsaponaceum Karsten developed similar numbers of mycorrhizas from mycelial inoculum added to untreated and MW treated soil. But Lactarius pubescent (Fr. ex Krombh.) Fr. developed significantly more mycorrhizas from inoculum added to MW‐treated soil than to untreated soil. This difference between the fungi accords with their classification as, respectively, early stage and late stage in reported mycorrhizal successions on birch.Some mycorrhizal types developed on seedlings from resident inoculum in soil. Their incidence was reduced by different amounts following MW treatment, suggesting differences in heat‐tolerance of their propagules. Hebeloma sacchariolens Quel., which forms sclerotium‐like bodies and which probably developed from resident inoculum, was unaffected by MW treatment of soil. Some mycorrhizal fungi, notably Thelephora terrestris (Ehrh.) Fr., developed in place of others in soils treated for long times (80–180 s), and they probably developed from airborne spores.
Early events of vesicular–arbuscular mycorrhiza formation on Ri T‐DNA transformed roots
Authors: BÉCARD G. , FORTIN J. A. 
Published: April 2006

SUMMARYAn in vitro system using Ri T‐DXA transformed roots and the vesicular–arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall has been developed to study the initial events of mycorrhiza formation. Sucrose, sodium and phosphorus were found to be critical components of the medium used to establish the dual culture. Using a single spore as inoculum it was consistently possible to obtain colonization of a preselected point on the root and to time the colonization process (within 5 days). Abundant viable and aseptic spores can be obtained. The system is especially appropriate for studying the triggering of the fungal biotrophy towards the root.
Time sequence of the infection process eucalypt ectomycorrhizas
Authors: HORAN D. P. , CHILVERS G. A. , LAPEYRIE F. F. 
Published: April 2006

SUMMARYThe paper‐sandwich technique for simultaneous inoculation of populations of root apices, was used to produce numbers of synchronously developing ectomycorrhizas, and to permit direct time‐sequencing of stages in the infection process in eucalypts. After one day there was evidence of chemical interaction between fungus and host. By two days, sheath formation had started in the cap region, cap cells were invaded by fungus, and apical root tissues commenced to swell. By four days all the anatomical features of an ectomycorrhiza were present, including the Hartig net. Thereafter, mycorrhizal features were merely enhanced and perpetuated by subsequent acrogenous development of the fungus‐root dual organ. The process of mycorrhizal perpetuation involved the same sequence of events (sheath development at the apex associated with invasion of cap cells, modification of other root tissues, then finally formation of Hartig net) as did the initial infection process.
Root hydraulic conductivity of vesicular–arbuscular mycorrhizal green ash seedlings
Authors: ANDERSEN C. P. , MARKHART A. H. , DIXON R. K. , SUCOFF E. I. 
Published: April 2006

SUMMARYGreen ash (Fraxinus pennsylvanica Marsh.) was either inoculated or not with Glomus etunicatum Becker and Gerd. and grown for 37 d to permit root colonization. Root hydraulic conductivity (Lpp) per unit length was measured on excised root systems to examine the influence of vesicular arbuscular (VA) mycorrhiza inoculation, seedling size, phosphorus (P) nutrition, and biomass distribution. Fertilization with P eliminated significant differences in seedling size and dry matter distribution between mycorrhizal (M) and non‐mycorrhizal (NM) seedlings, but VA mycorrhizas increased root and leaf P concentration. Root Lp was similar in M and NM seedlings of similar size, and was lower in M seedlings for a given root P concentration. Root Lp decreased with age and weight, and increased as the proportion of dry weight in the leaves increased in both M and NM seedlings. Mycorrhizal colonization had no significant effect on root Lp in the absence of a significant growth response.