bluuebunny/crossref_metadata_2025_split huggingface dataset:
TILLERING AND LEAF AREA OF WINTER BARLEY EXPOSED TO SULPHUR DIOXIDE IN THE FIELD
Authors: BAKER C. K. , FULLWOOD A. E. , COLLS J. J. 
Published: April 2006

SummaryWinter barley (Hordeum vulgare L., cv. ‘Igri’), grown as a crop in the field, was exposed to SO2 concentrations ranging from 40 to 200 ppb [parts per billion (109) by volume] above ambient. From spring onwards, plants at 40 and 50 ppb were consistently the heaviest, having slightly more tillers than plants in the other plots. In the range 80 to 200 ppb SO2, the plants usually had fewer tillers than the controls, but this difference was not consistent throughout the season. Trends in the numbers and weights of tillers were interpreted as circumstantial evidence that 80 to 200 ppb of SO2 may have decreased assimilate production.Leaf area in May was markedly bigger in fumigated plants than in the controls. At 80 to 200 ppb the increases may have resulted from the plants having diverted a greater proportion of shoot dry weight into leaf tissue and from increased specific leaf area. These responses of ‘Igri’ barley in the field resembled those obtained by other workers for the same variety grown in controlled environments.
EVIDENCE THAT ARSENIC TOLERANCE IN HOLCUS LANATUS L. IS CAUSED BY AN ALTERED PHOSPHATE UPTAKE SYSTEM
Authors: MACNAIR MARK R. , CUMBES QUINTON 
Published: April 2006

SummaryThe uptake of arsenate by arsenic tolerant and non‐tolerant plants of Holcus lanatus L., and the interaction of this uptake with phosphate level, was studied. The tolerance of the different plants, as measured by root growth, was also investigated. Arsenate inhibited the root growth of non‐tolerant plants much more than that of tolerant ones, but at low levels of arsenate, the high phosphate treatment reduced the toxicity of arsenate in non‐tolerants but not in tolerants. Tolerant plants took up less arsenate than non‐tolerants. The effect of phosphate on arsenate uptake was very small in the tolerant plants, but in non‐tolerants phosphate inhibited arsenate uptake when the phosphate was at a higher concentration than arsenate. These results are compatible with the hypothesis that arsenate is taken up by the phosphate uptake system in non‐tolerant plants, but in tolerant plants this system has become altered so that it no longer recognizes arsenate.
REVERSAL OF CAESIUM INHIBITION OF GROWTH BY POTASSIUM IN HYPOCOTYLS OF TOMATO SEEDLINGS (LYCOPERSICON ESCULENTUM L.)
Authors: KORDAN H. A. 
Published: April 2006

SummaryStunted, misshapen, necrotic hypocotyls of tomato seedlings (Lycopersicon esculentum L.) germinated on caesium cations in continuous red or white light indicated caesium‐associated hypocotyl photo‐injury. Continuous, far red irradiation inhibited seedling germination in control and caesium treatments but was reversed by continuous white light. Hypocotyl photo‐injury also occurred in far red pretreated seedlings germinated on caesium in continuous white light. Except for suppressed elongation, hypocotyls of caesium‐treated seedlings were normal in appearance. Etiolated caesium‐treated seedlings placed in continuous white light also exhibited hypocotyl photo‐injury. The effects of caesium cations were reversed by potassium cations but not by cations of other alkali metals.
MORPHOLOGICAL PLASTICITY AND MINERAL NUTRIENT CAPTURE IN TWO HERBACEOUS SPECIES OF CONTRASTED ECOLOGY
Authors: CRICK J.C. , GRIME J.P. 
Published: April 2006

SummaryDevelopmental plasticity and nitrogen capture were compared in Agrostis stolonifera and Scirpus sylvaticus grown in compartmentalized root growth arenas which allowed simulation of the spatial and temporal patchiness distinguishing the conditions of mineral nutrient supply associated with fertile and infertile soils.Despite the small root system, higher rates of nitrogen capture and dry matter production were achieved by A. stolonifera at both high and low external concentrations of mineral nutrients. This species also showed a marked ability rapidly to adjust partitioning of growth between parts of the root system, thus allowing local proliferations of fine roots into sectors of high mineral nutrient concentration. Under the conditions of the experiment, this form of plasticity was only weakly developed in S. sylvaticus, which instead maintained a large but relatively unresponsive root mass under each experimental treatment.It is concluded that the high plasticity observed in A. stolonifera allows the dynamic exploitation of fertile soil by competing roots. It is predicted that the more stable pattern of root development in S. sylvaticus will confer a selective advantage in environments where mineral nutrients are strongly limiting upon productivity and become available in temporally unpredictable pulses.
INTERRELATIONSHIPS BETWEEN ASPECTS OF NITROGEN METABOLISM AND SOLUTE ACCUMULATION AND THE DISTRIBUTION OF SUBTROPICAL WOODY PLANTS IN SOUTHEAST AFRICA
Authors: PRIOR J. , TUOHY J. , WHITING J. 
Published: April 2006

SummaryLittle is known of the mechanisms governing nitrogen metabolism and stress tolerance in woody plants of subtropical southeast African savannas, although many of the more widely occurring genera, particularlyAcaciaandCombretumspecies, include valuable multi‐purpose trees. Basal nitrate reductase activities in vigorous leaves from 59 species and five savanna areas were used as a measure of nitrate availability. Consistently low activities were found in many of the legumes and in members of the Combretaceae. When shoots from 35 of these same species were provided with supplementary nitrate solution, increased reductase activity was recorded in a number of taxa, including non‐nodulating legumes belonging to the Caesalpinioideae. Nodulating legumes did not behave in the same way. Either proline or quaternary ammonium compounds, examples of stress metabolites, accumulated in the shoots of a range of taxa belonging to a number of families. The highest concentrations occurred in shoots collected from the driest areas. Amounts of tannin were high in some species but showed no consistent pattern.
ECTOMYCORRHIZAL VS ENDOMYCORRHIZAL FUNGI WITHIN THE SAME ROOT SYSTEM
Authors: CHILVERS G. A. , LAPEYRIE F. F. , HORAN D. P. 
Published: April 2006

SummaryVesicular‐arbuscular (VA) mycorrhizal fungi and ectomycorrhizal fungi were observed together in the same root system, and even within the same root apices, of seedlings of Eucalyptus dumosa A. Cunn. ex Schau. On a population basis, there was a succession of two overlapping mycorrhizal epidemics‐VA mycorrhizas followed by ectomycorrhizas.This succession was interpreted as follows. Early build‐up of VA mycorrhizas was related to initial higher inoculum potential of that fungus and to rapidity of colonization of individual roots. The ectomycorrhizal fungus was more successful later in achieving secondary infections by hyphal spread and in colonization of lateral root branches. The ectomycorrhizal fungus had no difficulty infecting pre‐existing VA mycorrhizas, but the ectomycorrhizal sheath provided a barrier to subsequent VA mycorrhizal infections. While the proportion of VA mycorrhizas to ectomycorrhizas changed between two and five months, the overall proportion of mycorrhizal roots remained constant, suggesting that there could be competition between the different fungi for limiting substrate.
THE INFLUENCE OF ROOT GROWTH AND INOCULUM DENSITY ON THE DYNAMICS OF ROOT DISEASE EPIDEMICS: THEORETICAL ANALYSIS
Authors: JEGER M. J. 
Published: April 2006

SummaryIncluding root growth and inoculum density as variables in a simple model of disease progress of a monocyclic root pathogen often leads to a sigmoid curve. If the product of root density and inoculum density is constant, then a monomolecular curve (without an inflexion point) results. When the product is a function of time, then either an asymptotic exponential or a sigmoid curve results, depending upon the parameter values. Where the product of root density and inoculum density increases exponentially, then a Gompertz function in the incidence of surviving plants results. Where root growth is fast relative to the reduction in inoculum through infection, then an asymptotic value of disease less than 1.0 is predicted.Detailed models of dynamics of root infection, incorporating root extension and loss of inoculum due to infection, and cases without and with lesion expansion, lead to the following conclusions: (1) increase in lesion numbers without lesion expansion, does not constrain or provide an upper limit to root growth; (2) where there is no root growth, then the proportion of root surface covered by lesions approaches an asymptote strictly less than 1.0 in the case without lesion expansion, but approaches 1.0 in the case with lesion expansion; (3) where the rate of infection is greater than the rate of root extension (without lesion expansion), then there is an upper limit to lesion surface area on roots; otherwise both root surface area and lesion numbers increase without limit; (4) where the rate of lesion expansion is greater than the rate of root extension, then the proportion of root surface area covered by lesions approaches 1.0 asymptotically. Explicit solutions giving the healthy root area as a function of time are obtained.Analysis of the dynamics of root infection indicates that root disease control strategies should aim to reduce pathogen density, maintain a low rate of root extension relative to root infection and restrict lesion expansion.
MODELS FOR THE CONTROL OF BRANCH POSITIONS AND FLOWERING SEQUENCES OF CAPITULA IN MYCELIS MURALIS (L.) DUMONT (COMPOSITAE)
Authors: JANSSEN J. M. , LINDENMAYER A. 
Published: April 2006

SummaryThe development of highly branched inflorescences is considered. Two main characteristics of these structures are the flowering sequences (acropetal, basipetal or divergent) and the branch production (acrotonic, basitonic or mesotonic), which can be different on various branching orders (paracladia). A widespread pattern, found especially among Compositae, is a basipetal or divergent flowering sequence combined with basitonic or mesotonic branch production. We present quantitative models for this type of inflorescence development, based on the transport of a flower‐inducing hormone (florigen) and of a hormone responsible for apical dominance (auxin), together with some additional control factors. The computed structures obtained with these models are compared with observations on the inflorescence development of wall lettuce, Mycelis muralis.
INTERNAL AERATION AND DEVELOPMENT OF STELA ANOXIA IN SUBMERGED ROOTS
Authors: ARMSTRONG W. , BECKETT P. M. 
Published: April 2006

SummaryA case is presented for progressing from mathematical models of root aeration which assume complete radial homogeneity in respiratory demand and oxygen diffusivity to models which accommodate radial differences between the various tissue cylinders. The described model simulates aeration in submerged roots and allows for axial gas‐phase diffusion in the cortex and radial liquid‐phase diffusion elsewhere. It also accommodates diffusion into the rhizosphere and axial and radial differences in the root's properties on a tissue cylinder basis.The results, based on the characteristics of aerenchymatous graminean roots, highlight the potential for stelar anoxia and some wall‐layer anoxia in submerged, and even non‐submerged, roots. They show that, (1) stelar anoxia should raise oxygen levels elsewhere and enhance root extension; (2) with high and constant oxygen diffusivity in the stele, anoxia should first occur close to the apex and spread basally and laterally with further root extension; (3) there will be competition between the oxygen demands of the root and rhizosphere; (4) extension may be reduced by radial oxygen losses into the rhizosphere, but the subapical decline in root‐wall permeability in wetland species safeguards against this effect; (5) differences in critical oxygen pressure for extension growth (COPE) and respiration (COPR) may arise; and (6) survival may be helped by the manner in which anoxia spreads with aerobic conditions persisting in the phloem and pericycle until only traces of oxygen remain in the cortex. Sectional profiles of the roots show how oxygen gradients in the stele and wall layers will increase with increasing subapical impedance in these zones and, in the case of the wall layers, by oxygen throughflux to the rhizosphere.Some of the results suggest that inner‐stele anoxia might account for some of the hypoxic responses found in roots, and it is predicted that declining stelar oxygen diffusivity in subapical regions will raise COPR but not COPE, the inner‐stele becoming anoxic subapically and the apical regions remaining wholly aerobic. This implies the possibility that where roots are described in the literature as hypoxic, because of ethanol production, raised alcohol dehydrogenase activity and reduced energy charge, the symptoms may be sometimes indicative only of some subapical stelar anoxia.The results also serve to illustrate how variable the occurrence and shape of anoxic stelar zones might be. With only a slight alteration in subapical stelar oxygen diffusivity, anoxia could arise simultaneously in two positions along the root, or the first site of anoxia in the growing root might be both subapical and hypobasal. The likelihood of the endodermis in subapical parts being a possible cause of anoxia in roots is also considered.
REGULATORY ASPECTS OF NH4+ UTILIZATION IN THE ACIDOPHILIC THERMOPHILIC UNICELLULAR RED ALGA CYANIDIUM CALDARIUM
Authors: DI MARTINO RIGANO VITTORIA , VONA VINCENZA , DI MARTINO CATELLO , RIGANO CARMELO 
Published: April 2006

SummaryCyanidium caldarium is an acidophilic thermophilic red alga. At pH 1.9 with cells grown in batch culture with excess ammonium, removal of CO2 or darkness caused immediate inhibition of ammonium assimilation. By contrast, with cells grown in chemostat culture with nitrogen limitation, assimilation of ammonium was not inhibited by darkness, but it was inhibited by CO2 deprivation. In the case of these cells, inhibition was not immediate and behaved as a time‐dependent phenomenon. Ammonium assimilation was restored when CO2was supplied in either light or darkness.In contrast, at pH 7.4, ammonium assimilation decreased with time both in the presence and absence of CO2, and it ceased completely after about 90 min incubation at this pH. The inhibition was not due to the high pH per se. When resuspended at pH 2, these inhibited cells were unable to assimilate ammonium during a 25 min period in the presence of CO2. Thereafter, they become able to assimilate ammonium but at a rate which was only 30% of that of the control. If they were pre‐incubated at pH 2 in nitrogen‐free medium for 3 h, however, they then assimilated ammonium immediately after its addition. It is suggested that a reversible inactivation at pH 1.9 and a denaturation at pH 7.4 of the system for ammonium uptake occurs, and that this uptake system is stabilized by carbon compounds against inactivation at pH 1.9 but not against denaturation at pH 7.4.
THE INFLUENCE OF LOW TEMPERATURE ON DIEL PATTERNS OF CARBOHYDRATE METABOLISM IN LEAVES OF POA ANNUA L. AND POA×JEMTLANDICA (ALMQ.) RICHT.
Authors: BORLAND ANNE M. , FARRAR J. F. 
Published: April 2006

SummaryThe effect of low temperature on diel changes in net gas exchange, carbohydrate content and export, and on the extractable activities of sucrose phosphate synthase and acid invertase from leaves of Poa annua (a ruderal grass) and Poa×jemtlandica (a subarctic grass) was investigated. Exposure for 5 d to a temperature of 7°C significantly reduced the rate of net photosynthesis of P. annua but had no effect that of P.×jemtlandica. In both species, soluble sugars constituted 20 % of the dry weight and showed net accumulation over 24 h. There was approximately twice the concentration of fructans in the leaves of P. x jemtlandica compared with P. annua.During the 16 h photoperiod, the leaves of P.×jemtlandica stored twice as much photosynthate as the leaves of P. annua. However, the higher rate of export from the leaves of P.×jemtlandica in the dark compared to P. annua resulted in the allocation of similar proportions of photosynthate to the processes of storage, respiration and export in leaf blades of both species over a 24 h period.Low temperature resulted in a decrease in the extractable activity of sucrose phosphate synthase from P. annua but not from P.×jemtlandica. The activity of acid invertase was reduced by exposure in both species.
VARIATIONS IN ACTIVITIES OF GLYCOGEN PHOSPHORYLASE AND TREHALASE DURING THE PERIODIC FRUITING OF THE EDIBLE MUSHROOM AGARICUS BISPORUS (LANGE) IMBACH.
Authors: WELLS TERENCE K. , HAMMOND JOHN B. W. , DICKERSON ANTHONY G. 
Published: April 2006

SummaryActivities of trehalase and glycogen phosphorylase were determined for stage 1 (pin) sporophores of Agaricus bisporus harvested daily throughout several fruiting cycles (flushes). Both enzymes exhibited maximum activity coincident with peak flush, as defined by maximum yield of stage 2 to 4 sporophores and minimum activity during the interflush periods. Glycogen phosphorylase activity sometimes peaked on more than one occasion during a flush, whereas trehalase gave only a single peak of activity per flush. These results are discussed in relation to metabolic events associated with carbohydrate changes during the periodic fruiting cycle of this fungus.
METABOLISM OF MANNITOL IN MYCORRHIZAL AND NON‐MYCORRHIZAL FUNGI
Authors: RAMSTEDT MAURITZ , JIRJIS RAIDA , SÖDERHÄLL KENNETH 
Published: April 2006

SummaryThe activity of mannitol dehydrogenase, mannitol 1‐phosphatase and mannitol 1‐phosphate dehydrogenase in five mycorrhizal basidiomycetes, one mycorrhizal ascomycete and five non‐mycorrhizal basidiomycetes was investigated. No mannitol 1‐phosphate dehydrogenase could be detected in any of the basidiomycetes. Mannitol dehydrogenase, present in all the tested fungi except Armillariella mellea, was strictly NAD‐dependent for the non‐mycorrhizal basidiomycetes, whereas in the mycorrhizal species it was mainly NADP‐dependent. The mannitol 1‐phosphatase of the mycorrhizal basidiomycetes was specific towards mannitol 1‐phosphate in contrast to that of the non‐mycorrhizal species, which was a non‐specific phosphatase. In the ascomycete Sphaerosporella brunnea all the mannitol metabolizing enzymes were found, including mannitol 1‐phosphate dehydrogenase. Growth of S. brunnea on mannitol slightly decreased the activity of the mannitol dehydrogenase (NADP) and mannitol 1‐phosphate dehydrogenase, but there was a slight increase in activity of glucose 6‐phosphate dehydrogenase.
THE EFFECT OF DESICCATION ON CELL SHAPE IN THE LICHEN PARMELIA SULCATA TAYLOR
Authors: BROWN D. H. , RAPSCH S. , BECKETT A. , ASCASO C. 
Published: April 2006

SummaryComparisons have been made of the shape of algal cells in the lichen Parmelia sulcata which was subjected to controlled desiccation regimes inducing substantial water loss. The spherical appearance of algal cells obtained by conventional techniques for transmission electron microscopy (TEM) was shown by low temperature scanning electron microscopy (LTSEM) to be the consequence of rapid rehydration during fixation. Collapse of the walls of algal cells and fungal hyphae in the medulla and algal layer when desiccated were observed with LTSEM and shown to be reversible on rehydration. Desiccation‐induced contraction of cortical fungal protoplasts was detected with LTSEM. Fixation with osmium vapour only before TEM demonstrated a similar contraction of algal protoplasts.
PHENOTYPIC FLEXIBILITY OF CAREX FLACCA SCHREB.
Authors: HEATHCOTE C. A. , DAVIES M. S. , ETHERINGTON J. R. 
Published: April 2006

SummaryNine populations of Carex flacca Schreb., collected from sites which vary widely in their liability to soil flooding, were grown on an experimental soil with free drainage, transient flooding or continuous flooding for 26 weeks. Although the flooding treatments resulted in low redox potentials and high concentrations of reduced iron and manganese in the soil, the growth of C. flacca plants was little affected by flooding. All populations grew equally well on the flooded soils. All populations produced adventitious roots at the soil surface in the flooded treatments; these were absent from plants grown on the freely drained soil. Flooding produced an increase in the manganese concentration of roots and shoots but, although the iron content of roots was markedly increased by flooding, there was no increased transport to the shoots.In view of the absence of detectable phenotypic differentiation between these populations from widely contrasting sites and their unimpaired growth on severely waterlogged soils, it is argued that C. flacca plants have a broad tolerance (phenotypic flexibility) of soil flooding. This may be important in the wide ecological amplitude of this species.
MORPHOLOGICAL AND ANATOMICAL EFFECTS OF SEVERE DROUGHT ON THE ROOTS OF LOLIUM PERENNE L.
Authors: JUPP A. P. , NEWMAN E. I. 
Published: April 2006

SummaryThree experiments using soil‐grown Lolium perenne plants were performed in order to investigate the effects of a gradually increasing drought stress on the death of root cells and the growth of lateral roots. Water potentials of ‐2 to ‐10 MPa caused death of the root cortex, but death of root tips occurred only at soil water potentials below ‐10 MPa. Low soil water potentials promoted lateral root initiation and elongation, the total length of lateral roots being between three and five times that of control plants. On rewetting severely droughted plants, root growth continued by elongation of existing, previously initiated, lateral roots.
ECTOMYCORRHIZA FORMATION IN EUCALYPTUS
Authors: MALAJCZUK N. , DELL B. , BOUGHER N. L. 
Published: April 2006

Summary Cortinarius and Hysterangium species are a dominant component of the macrofungi in eucalypt forests of Western Australia, and their hyphae occupy 10 % of the soil surface area. Anatomical studies of jarrah (Eucalyptus marginata Donn ex Sm.) and karri (E. diversicolor F. Muell) roots collected in association with hyphae of Cortinarius globuliformis Boug., C. ochraceus Clel. and Hysterangium inflatum Rodway showed mycorrhizal structures with mantles one to five cells thick and Hartig nets penetrating to the hypodermis. These superficial ectomycorrhizas were similar in size to those of non‐colonized feeder roots and lacked the expanded cortex and broad mantle of pyramidal ectomycorrhizas formed by Laccaria laccata (Scop, ex Fr.) Berk. & Br. Colonized host roots responded with polyphenol accumulation in the epidermis/hypodermis and lignification of the outer cortex for both the superficial and pyramidal types.
IN VITRO FRUITING UNDER CONTROLLED CONDITIONS OF THE ECTOMYCORRHIZAL FUNGUS HEBELOMA CYLINDROSPORUM ASSOCIATED WITH PINUS PINASTER
Authors: DEBAUD J. C. , GAY G. 
Published: April 2006

SummaryThe ectomycorrhizal fungus Hebeloma cylindrosporum Romagnési produced sporulating fruit bodies under axenic conditions on a synthetic medium when cultivated with its usual host plant Pinus pinaster (Sol.). In the absence of the host plant, H. cylindrosporum only formed primordia or immature fruit bodies. In 11 Erlenmeyer flasks, the fungal fruiting started about one and half months after the inoculation of one‐month‐old P. pinaster plants by the mycelium of H. cylindrosporum, and a total of 144 fruit bodies appeared in 45 flasks during a 9.5‐month fruiting period. At 18 °C, the mean number of basidiomes developed per flask was about 3–5. A thermal shock of ± 6 °C for 5 d did not significantly affect the mean number of basidiomes per flask but modified the time course of their rate of formation. Spores were collected from the fruit bodies and were found to be capable of germinating.