bluuebunny/crossref_metadata_2025_split huggingface dataset:
Postnatal development of the fore‐ and hindlimbs in the grey short‐tailed opossum, Monodelphis domestica
Authors: Martin Katherine E. A. , Mackay Sarah 
Published: March 2003

AbstractMarsupials are good experimental animals for developmental studies as their offspring are born at a stage comparable to embryonic stages of eutherian species. The South American opossum, Monodelphis domestica, is particularly useful because of its small size and easy maintenance. This study was carried out to compare development of opossum fore‐ and hindlimbs during postnatal life, using light microscopy and whole mount alizarin staining. At birth, well‐developed mobile forelimbs show cartilage models of bones and myotubular striated muscle fibres. However, hindlimbs are relatively underdeveloped paddle‐like outgrowths. Two days later mesodermal condensations form models of the future hindlimb bones and mononucleate myoblast aggregates are present; by 6 days post partum (dpp) the hindlimb has reached a stage of development similar to that of the forelimb at birth. At this stage, periosteal buds have invaded forelimb long bones and nuclei in forelimb muscle fibres have become displaced to the periphery. The 16 dpp hindlimb shows long bones invaded by periosteal buds and closely packed, striated muscle fibres. Epiphyseal plates are now seen in the forelimb long bones and forelimb muscle fibres show mature characteristics. Musculoskeletal development is well correlated with the functional demands of the limbs during postnatal development in the opossum, which provides an excellent model for investigations into the genes and molecules controlling limb development.
Changes in rice root architecture, porosity, and oxygen and proton release under phosphorus deficiency
Authors: KIRK G. J. D. , VAN DU LE 
Published: March 2003

SUMMARYEarlier work has shown that rice plants growing in reduced soil are able to solubilize P and thereby increase their P uptake by inducing an acidification in the rhizosphere; the acidification is caused by H+ produced in Fe2+ oxidation by root‐released O2, and by the direct release of H+ from the roots to balance cation‐anion intake. Here, we report rates of release of O2 and H+ from P‐stressed and P‐sufficient rice plants into sand cultures continuously perfused with deoxygenated nutrient solution. The P stress was sufficient to reduce plant dry mass by roughly half, but root dry mass increased roughly twofold and root surface area 2–5‐fold. The proportion of fine roots increased from 11 to 21 % of root length under P deficiency; root porosity, averaged over the whole root system, increased from 0–25 to 0.40. Apparent rates of O2 release were 0.8–3–3 μmol per plant d−1, or 22–87 μmol g−1 (root dry mass) d−1. Assuming that the bulk of the O2 was released from medium and fine roots, the fluxes of O2 were 0.02–0.13 nmol dm−2 (root surface) s−1, which is in the range found for soil‐grown plants. The release per plant was twofold greater in the low P treatment, although rates of release per unit root mass were slightly lower. The increased release under P deficiency is consistent with the increased length of fine roots and increased porosity. Rates of H+ release were 0.7–1.2 mmol per plant−1 d−1, or 1.4–6.1 mmol g−1 (root dry mass) d−1. The H+ release per unit plant dry mass was 60% greater in the low P treatment, but the release per unit root mass was 2.5‐fold lower. The increased H+ release under P deficiency was associated with increased NH4+ intake and decreased NO3− intake, and a tenfold increase in plant NO3‐N. This suggests that P deficiency reduced NO3−assimilation, causing reduced NO3− influx and/or increased efflux.
Longevity of leaves of a tropical tree, Theobroma cacao, grown under shading, in relation to position within the canopy and time of emergence
Authors: MIYAJI KEN‐ICHI , DA SILVA WALNY S. , DE PAULO T. ALVIM 
Published: March 2003

summaryTo gain detailed information on the structure and dynamics of the foliage within a canopy, the longevity of leaves of cacao trees (Theobroma cacao L.) growing under normal commercial planting shade in Bahia State, Brazil, was determined relative to their position within the canopy and the time of leaf emergence.In the experimental stand, the relative light intensity above the cacao canopy ranged between 30 and 100% of full daylight, and 4–10% at ground level. The mean leaf area index for the canopy, and the extinction coefficient of the foliage were 3–9 and 0–61, respectively.The longevity of leaves of adult trees of cacao with closely packed crowns varied with their position within the canopy, and/or the irradiance received, and the time of emergence. In particular longevity decreased greatly with the height of the leaf from ground level. The mean longevity for the upper foliage (more than 220 cm above the ground) within the canopy was 181 d; the mean longevity of the lower leaves (0–150 cm above the ground) was about twice that of the upper leaves.Approximately 23% of emergent leaves fell within 60 d of emergence, following infection (about 14% of loss) or as a result of wind damage (about 5 % of loss). Thereafter, in mature and senescent leaves, leaf fall followed normal physiological changes.
Irradiance and nitrate‐dependent variation in growth and biomass allocation of Mycelis muralis. An analysis of its significance for a functional categorization of ‘sun’ and ‘shade’ plants
Authors: CLABBY GERARD , OSBORNE BRUCE A. 
Published: March 2003

summaryThe biomass of Mycelis muralis (L.) Dumort plants increased with increases in growth irradiance and nitrate supply. Comparisons of the data from this study with published information indicate that biomass production and growth rate of M. muralis are comparable to that of a number of slow‐growing species from resource‐poor environments. Biomass allocation varied with growth irradiance and nitrate supply. At high irradiances and low nitrate supplies there was a significantly greater allocation of plant mass to roots, resulting in a lower leaf area ratio (LAR) and leaf mass ratio (LMR). In contrast to the findings of a number of other studies, light level and nitrate supply had interactive effects on leaf mass per unit area (LMA). Changes in LAR due to variations in irradiance were mainly a consequence of changes in LMR. Given the ability of M. muralis to grow in deep shade, this suggests that large changes to within‐leaf allocation (LMA) are not an essential requirement for growth at low irradiances. Conversely, because M. muralis can also grow in fully exposed situations, these traits might not exclude some shade species from high irradiance habitats. However, a low growth rate, or traits which result in a low growth rate, might be advantageous in a number of resource‐poor environments.
Callose deposition during the interaction between cowpea (Vigna unguiculata) and the monokaryotic stage of the cowpea rust fungus (Uromyces vignae)
Authors: ŠKALAMERA DUBRAVKA , JIBODHAND STEFAN , Heath Michele C. 
Published: March 2003

summaryThe interaction between the race 1 of the cowpea rust fungus (Uromyces vignae Barclay) and the resistant cowpea (Vigna unguiculata (L.) Walp.) ev. Queen Anne is characterized by the deposition of callose around intracellular fungal structures. Ultrastructural examination of the early stages of infection by basidiospores of the fungus revealed two types of deposits induced by intracellular hyphae: a non‐callose collar at the penetration site and a callose encasement around the invasion hypha. The callose encasement was developed from the site where the fungus encountered the inside of the plant cell wall and was separated from the fungus by the extrahyphal membrane and an extension of plant plasma membrane. The incidence of encasements was reduced in plants treated with inhibitors of transcription (actinomycin D), protein synthesis (cycloheximide), protein glycosylation (tunicamycin) and microfilament polymerization (cytochalasin E). Inhibitors of Golgi‐associated vesicle transfer (monensin, brefeldin A) and anti‐microtubule agents (colchicine, oryzalin) had no effect. When the fungus was killed by heat treatment in either the resistant or the susceptible cultivar, callose was deposited at various locations along the fungus, mostly in the extrahyphal matrix. The data suggest that unlike the extrahaustorial membrane surrounding D‐haustoria of this fungus, the extrahyphal membrane is capable of generating callose. Since this process does not normally occur in the susceptible or the resistant cv. even when callose is deposited in the latter by regions of the plasma membrane not associated with the fungus, we conclude that the deposition of callose by the extrahyphal membrane is inhibited by the living fungus.
Natural 15N abundance in fruit bodies of ectomycorrhizal fungi from boreal forests
Authors: TAYLOR ANDREW F. S. , HÖGBOM LARS , HÖGBERG MONA , LYON ANTHONY J. E. , NÄSHOLM TORGNY , HÖGBERG PETER 
Published: March 2003

SUMMARYThe 15N natural abundance and N concentrations of fruit bodies from 70 species (23 genera) of ectomycorrhizal fungi found in boreal forests are presented. Large intraspecific and intrageneric differences were found, e.g. 8.3‰15N in the species Dermocybe crocea and 12.6‰ in the genus Cortinarius. In addition, significant differences in both δ15N and %N were found between different parts of fruit bodies, with cap material giving consistently higher values. Proteins and amino acids were enriched by 9.7±0.4‰ (mean ± 1 SE) relative to chitin, irrespective of the part of the fruit body examined. Chitin had δ15N values similar to that of plant hosts. The higher δ15N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps. The δ15N of mycorrhizal fungi can be a function of the N species used (organic N, NH4+, NO3−), the depth of soil at which the mycelium occurs, and metabolic fractionations. The metabolic fractionations, e.g. potential transaminations during the flux of N from the soil through the fungus to the plant, make it difficult, at present, to make inferences about sources of N based on δ15N values alone. No effect of sample drying temperature on δ15values of fungal material was detected.
Abscisic acid (ABA) relations in the aquatic resurrection plant Chamaegigas intrepidus under naturally fluctuating environmental conditions
Authors: SCHILLER PETRA , HEILMEIER HERMANN , HARTUNG WOLFRAM 
Published: March 2003

SUMMARYThe resurrection plant Chamaegigas intrepidus Dinter (Scrophulariaceae) grows as a typical hydrophyte in shallow rock pools on granitic outcrops in arid areas of Namibia. During the rainy season, the rock pools are temporarily filled with water. When the pools dry up, C. intrepidus desiccates and survives in an air‐dry condition for at least 8 months. After rewatering, the plants regain their metabolic activity in under 2 h. The desiccation of the vegetative organs is accompanied by a dramatic accumulation of abscisic acid (ABA). Beyond this, desiccation of roots is accompanied by the occurrence of specific dehydration‐related proteins, whereas the leaves of C. intrepidus show high levels of dehydrins in the dehydrated as well as in the hydrated state.Investigations in Namibia showed drastic diurnal fluctuations in the pH of the rock pools. The pH value increased from slightly acidic or neutral conditions during the morning to alkaline conditions (up to pH 12) during late afternoon. Since compartmental ABA distribution depends strongly on pH gradients across membranes, the external pH would be expected to affect the ABA relations in the plant. According to the anion trap concept, an alkaline pH in the surrounding medium should cause a release of ABA from the roots, although C. intrepidus appeared to release less ABA than the terrestrial rosettes of Valerianella locusta.
Photosynthesis and photoinhibition in a tropical alpine giant rosette plant, Lobelia rhynchopetalum
Authors: FETENE M. , NAUKE P. , LÜTTGE U. , BECK E. 
Published: March 2003

summaryCarbodioxide uptake, oxygen evolution and chlorophyll fluorescence of leaves of Lobelia Lobelia rhynchopetalum Hemsl., a giant rosette plant of the tropical alpine regions of Ethiopia, were studied under field conditions at 4000 m above sea level. Our objective was to investigate the photosynthetic adaptation to the combination of wide fluctuation in diurnal temperature, high photon flux densities (PFD) and low CO2 partial pressure encountered in these regions. At an ambient CO2 partial pressure of c. 17 Pa, maximal rates of CO2 uptake were low, ranging between 4 and 6 μmol m−2 s−1. Such rates, however, required high PFDs and were observed only at levels of 1500 μmol photons m−2 s−2. Carbon dioxide uptake was significantly inhibited when PFD was ≤ 2000 μmol photons m−2 s−1. On the other hand, at saturating CO2 levels, maximal photosynthetic oxygen evolution was higher (30 μmol C2 m−2 s−1). saturating at the same PFD as CO2 uptake. Quantum efficiency of CO2 uptake (0.006 mol CO2 mol photons−1, at high altitude and a low CO, partial pressure of 17 Pa) and even of oxygen evolution under CO2‐saturating conditions in the leaf O2 electrode (0.05 mol O2 mo) photons−1) indicated reduced photosynthetic efficiency. Electron transport rate (ETR) was strongly correlated with the leaf temperature. Non‐photochemical quenching (NPQ) responded inversely to leaf temperature and stomatal conductance.The results indicated that in the morning, when the sun irradiates the partly frozen leaves with closed stomata, NPQ is the principal mechanism by which Lobelia leaves protect their photosynthetic apparatus. However, during the day, the predominant upright inclination of the leaves significantly contributes to protecting the leaves from excess light absorption. A comparison of the chlorophyll fluorescence of young and old leaves revealed that the former had high ETR and quantum efficiency of photosynthetic electron transport but a lower capacity for NPQ. Extremely high NPQ values but low ETR and low quantum efficiency were recorded for the old leaves. Thus, in the course of maturation the leaves apparently lose photosynthetic efficiency but increase their capability for protective non‐photochemical quenching.
Anti‐transpiration and anti‐growth activities in the xylem sap from plants under different types of soil stress
Authors: ZHU XIAOHONG , ZHANG JIANHUA 
Published: March 2003

summaryAnti‐transpiration and anti‐growth activities of xylem sap were studied for maize, sunflower, cotton and castor bean, which were subjected to several stress treatments: soil drying, flooding and salinity. All samples of xylem sap showed an increased concentration of proteins when plants were either soil‐dried, salt‐treated or flooded. The protein transportation flux in xylem sap, i.e. the product of protein concentration and volume flux, was also increased as a result. Electrophoresis using SDS‐PAGE analysis showed that xylem proteins were of variable size. When samples of xylem sap were used to feed detached leaves or shoots in a bioassay system for their anti‐transpiration and anti‐growth activities, such xylem proteins in their original concentrations apparently showed neither direct inhibition nor enhanced effects of ABA. All samples of xylem sap from plants subjected to different stresses showed anti‐transpiration and anti‐growth activities that could be fully accounted for by their ABA concentration. In cases where such activities were more than could be explained by the ABA concentrations, filtration with a 0–20 μm microfilter removed the discrepancies.
The long‐term epidemic of Claviceps purpurea on Spartina anglica in Poole Harbour: pattern of infection, effects on seed production and the role of Fusarium heterosporum
Authors: RAYBOULD A. F. , GRAY A. J. , CLARKE R. T. 
Published: March 2003

An epidemic of the ergot fungus (Claviceps purpurea (Fr.) Tul), a non‐systemic floral pathogen, appeared in populations of Spartina anglica C. E. Hubb in Poole Harbour in the 1980s. Over 70% of inflorescences were infected between 1985 and 1995. Between 1983 and 1995, there was no consistent pattern in the rank order of sites with respect to the proportion of inflorescences infected, and variation in the amount of infection was not related to inflorescence density. Among years, there was significant variation in the total biomass of ergot per inflorescence, but no significant difference in the number of ergots per inflorescence. Log–log regressions of total weight of ergot per inflorescence against the number of ergots per inflorescence showed that in all years resources for each additional ergot were limited.There was no statistically significant difference between the number of seed set on infected and uninfected inflorescences in 1985 or 1995. Further analysis showed that, compared with uninfected inflorescences, there was higher seed output from inflorescences with fewer than 10% of spikelets infected, which balanced reduced seed output from heavily infected inflorescences. At high levels of ergot infection, a lower proportion of uninfected spikelets set seed, compared with spikelets on uninfected inflorescences. This suggests that conditions which favour ergot growth are detrimental to seed production. Compared with uninfected inflorescences, mean and total seed weights were significantly lower in inflorescences with >10% of spikelets infected.The fungus Fusarium heterosporum Nees ex Fr. was found in association with the ergots on Spartina. There was a significant positive correlation between the average severity of Fusarium infection and the number of ergots on an inflorescence. There was a non‐significant negative correlation between severity of Fusarium and mean ergot weight, when ergot number per inflorescence was held constant. These data suggest that any negative effect of Fusarium on Claviceps is small.The high, and temporally and spatially uniform levels of ergot infection probably result from genetic uniformity of Spartina and the lack of zonation in the salt marshes of Poole Harbour. This situation is likely to persist for the foreseeable future.
Germination and post‐germination growth to carrot seedling emergence: predictive threshold models and sources of variation between sowing occasions
Authors: FINCH‐SAVAGE W. E. , STECKEL J. R. A. , PHELPS K. 
Published: March 2003

Cumulative germination curves were recorded for carrot (Daucus carota L.) seeds at a range of constant temperatures (T) and water potentials (Ψ) in the laboratory and under variable soil conditions in 15 seed‐bed environments in the field. A single base temperature (Tb), a distribution of base water potentials (Ψb(G)) for percentiles (G) of the population and the hydrothermal time constant (Hg) were determined from laboratory data. Although less effective at low Ψ, it was possible, using these germination parameters, to satisfactorily describe the effect of T and Ψ on germination rates under constant conditions according to the threshold models of thermal and hydrothermal time. These models were applied to field data with the condition that the germination process ceased if T<Tb for thermal time and additionally Ψ<Ψb(G) for hydrothermal time.Neither model accurately predicted germination patterns in the field. However, the pattern of germination was adequately described in most situations by a modified threshold model in which the predicted progress towards germination was unaffected by soil Ψ, provided it remained above Ψb(G), and was therefore more rapid under variable seed bed conditions than hydrothermal time. In this modified threshold model, the condition Ψ<Ψb(G) had to be fulfilled at the initiation of radicle extension before germination occurred. This result implies that the initiation of radicle growth operates as a moisture‐sensitive step that can determine germination and seedling emergence timing under variable soil‐moisture conditions.Seedling emergence was also recorded in the field and used to determine, separately, the impact of germination and post‐germination growth on the variation in seedling emergence patterns. The analysis suggests that delays in seedling emergence occur largely in the germination phase, but that seedling losses and variation in the spread of seedling emergence times within the population occur largely during the post‐germination growth phase.
Competition under high and low nutrient levels among three grassland species occupying different positions in a successional sequence
Authors: SCHIPPERS PETER , SNOEIJING INEKE , KROPFF MARTIN J. 
Published: March 2003

To clarify the role of seasonal change, competitive response and nutrient availability in the competitive asymmetry of grassland species a competition experiment was conducted on Holcus lanatus, Anthoxanthum odoratum and Festuca ovina, which represent a successional sequence of decreasing nutrient availability. Seven harvests were taken over two growing seasons. At each harvest the dry weight of plant parts, dead leaves, leaf area and plant height were measured. Three key traits that determine the successional status of the species were studied: specific leaf area, specific shoot height, and dead leaf fraction.The response of these traits to competition appeared to be limited and insufficient to change the competitive relations in the experiment. However, all three traits showed marked seasonal changes which resulted in superior growth and survival in winter of the species adapted to nutrient‐poor environments. The findings support the theory that competitive asymmetry increases at higher nutrient levels. It is postulated that the directionality of light makes it possible for the dominant species to monopolize this resource more easily than nutrients.
Responses of two Sphagnum moss species and Eriophorum vaginatum to enhanced UV‐B in a summer of low UV intensity
Authors: Niemi Riikka , Martikainen Pertti J. , Silvola Jouko , Sonninen Eloni , Wulff Anu , Holopainen Toini 
Published: March 2003

Summary•   The flux of ultraviolet (UV)‐B radiation to the Earth's surface is increasing, particularly in high latitudes. We studied the sensitivity of some dominant plant species of boreal and subarctic peatlands to this increase.•   Intact peat monoliths with the mosses Sphagnum balticum and Sphagnum papillosum, and cotton grass (Eriophorum vaginatum) were exposed to ambient solar UV‐B or ambient solar UV‐B supplemented by 30% in a field experiment in central Finland.•   Although the UV‐B dose was low during the growing season, owing to frequent cloudiness, both Sphagnum species showed significantly higher membrane permeability under enhanced UV‐B. In S. balticum, UV‐B tended to decrease the capitulum dry mass and induced a 30–40% increase in the concentration of chlorophyll and carotenoid pigments. Enhanced UV‐B had no effects on leaf morphology, chlorophyll fluorescence or stomatal functioning in E. vaginatum.•   The various UV‐B responses in the Sphagnum species under investigation indicate that they may be sensitive even to small increases in solar UV‐B radiation. By contrast, E. vaginatum appeared to tolerate the UV‐B fluxes of the experiment.
Sources of family income and expenditure on children's private, after‐school education in Korea
Authors: Chung Young Sook , Choe Minja Kim 
Published: March 2003

AbstractThis paper examines the relationship between sources of family income and household expenditure on private, after‐school education for children in secondary schools in Korea in the context of educational ‘credentialism’, which values evidence of college education highly. Data from a survey of 514 parents of secondary school students are used. Estimated ordinary least squares coefficients indicate that the wife's income, but not the husband's, was positively associated with the amount of spending on children's education at private, after‐school programmes. This finding suggests that some married women with children in Korea seek employment in order to earn the money needed for their children's private, after‐school education.