bluuebunny/crossref_metadata_2025_split huggingface dataset:
The innervation of FGF‐induced additional limbs in the chick embryo
Authors: Turney B. W. , Rowan‐Hull A. M. , Brown J. M. 
Published: March 2003

AbstractMotoneurones that supply the vertebrate limb innervate their muscle targets in a highly reproducible manner. As development proceeds, these limb‐specific motoneurones send out axons, which grow towards the developing limb and then congregate at its base to form the plexus. In the plexus, in response to unknown positional cues, these axons rearrange, often changing their original spatial relationships, before sorting out to emerge in the defined nerve trunks that innervate the limb. Several proposals have been put forward to explain how this reproducible innervation pattern is achieved. These include (1) that early differences in the motoneurone identity dictate their future axonal trajectories, (2) that axons actively respond to attractive or repulsive positional cues provided by the limb bud itself, or (3) that motor axons are passively deployed, following pathways of least mechanical resistance. We have addressed the question of the relative roles of motoneurone identity and the signals that the axons encounter on their journey towards the limb bud. Using the developing chick embryo as our experimental model we tested the effect of providing an additional limb target for motor axons leaving the flank level of the spinal cord. To do this we placed FGF‐soaked beads in the presumptive flank of 2‐day‐old chick embryos. This treatment induces an additional limb containing muscles. We investigated whether such additional limbs are innervated and by which neurones. We show that rather than the additional limbs being solely supplied by axons diverted from the two existing limb plexuses, motoneurones that normally supply the flank alter their trajectories to enter the induced limb. Once in the limb, axons respond to positional cues within the bud to generate the stereotypical innervation pattern. Our results show that the tendency of ‘flank’ motoneurones to innervate flank can be overcome by the presence of an additional limb.
Regulation of myogenic differentiation in the developing limb bud
Authors: Francis‐West Philippa H. , Antoni Laurent , Anakwe Kelly 
Published: March 2003

AbstractThe limb myogenic precursors arise by delamination from the lateral dermomyotome in response to signals from the lateral plate mesoderm. They subsequently migrate into the developing limb bud where they switch on the expression of the myogenic regulatory factors, MyoD and Myf5, and coalese to form the dorsal and ventral muscle masses. The myogenic cells subsequently undergo terminal differentiation into slow or fast fibres which have distinct contractile properties determining how a muscle will function. In general, fast fibres contract rapidly with high force and are characterized by the expression of fast myosin heavy chains (MyHC). These fibres are needed for movement. In contrast, slow fibres express slow MyHC, contract slowly and are required for maintenance of posture. This review focuses on the molecular signals that control limb myogenic development from the initial delamination and migration of the premyogenic cells to the ultimate formation of the complex muscle pattern and differentiation of slow and fast fibres.
Root‐soil contact for the desert succulent Agave deserti in wet and drying soil
Authors: NORTH GRETCHEN B. , NOBEL PARK S. 
Published: March 2003

SUMMARYTo investigate the extent and size of root‐soil air gaps that develop during soil drying, resin casts of roots of the desert succulent Agave deserti Engelm. were made in situ for container‐grown plants and in the field. Plants that were draughted in containers for 7 and 14 d had 24 and 34% root shrinkage, respectively, leading to root‐soil air gaps that would reduce the hydraulic conductivity at the root‐soil interface by a factor of about 5. When containers were vibrated during drought, root‐soil air gaps were greatly diminished, and the predicted conductivity at the interface was similar to that of the control (moist soil). For plants in the field (4 and 6 wk after the last rainfall), root shrinkage was greater than for container‐grown plants, but root‐soil contact on the root periphery was greater, which led to a higher predicted hydraulic conductivity at the root‐soil interface. To test the hypothesis that root‐soil air gaps would help to limit water efflux from roots in drying soil, the water potentials of the soil, root, and shoot of plants from vibrated containers (with gaps eliminated or reduced) and non‐vibrated containers were compared. The soil water potential was lower for vibrated containers after 14 d of drought, suggesting more rapid depletion of soil water due to better root‐soil contact, and the root water potential was lower as well, suggesting greater water loss by roots in the absence of root‐soil air gaps. Thus, air gaps could benefit A. deserti by helping to maintain a higher root water potential in the early stages of drought and later by limiting root water loss at the root‐soil interface when the water potential exceeds that of the soil.
Production of pectin‐degrading enzymes by ericoid mycorrhizal fungi
Authors: PEROTTO SILVIA , COISSON JEAN DANIEL , PERUGINI IOLANDA , COMETTI VALERIA , BONFANTE PAOLA 
Published: March 2003

SUMMARYProduction of enzymes which degrade plant cell wall macromoleculea has been studied in relatively few ericoid fungal isolates, although these polymers arc a major component of the organic litter and an important source of nutrients for these fungi. Our aims were to investigate whether the ability to degrade the wall pectic component, only reported for one isolate, is a general feature of ericoid fungi. Of about 35 isolates from different geographic regions, all were capable of growing on pectin as the sole carbon source. Polygalacturonase (PG) activity was detected to a different degree in the culture filtrates and independently of the fungal growth rate. Solid and liquid isoelectric focusing allowed separation and identification of several polygalacturonase isoforms. Among the fungal isolates investigated, those from the northern hemisphere produced mostly acidic isoforms, whereas isolates from South Africa secreted more abundantly basic isoforms. However, purification and biochemical characterization of several PG isoforms from the different isolates revealed an optimal activity in the acidic pH range for all the PG enzymes tested. Polygalacturonase enzymes seem to be an important component of the enzymatic arsenal secreted by ericoid fungi during their saprotrophic life. In addition, they could also play a role during root colonization, since penetration across the plant cell wall is a prerequisite for the establishment of endomycorrhizal symbiosis.
Leaf carbohydrate status in Lolium temulentum during the induction of flowering
Authors: PÉRILLEUX C. , BERNIER G. 
Published: March 2003

SUMMARYUnifoliated plants of Lolium temulentum L. ev. Ceres, a qualitative long‐day grass, were induced to flower by one 24‐h long day (LD) or by one 8‐h short day (SD) advanced by 1 2 h in the normal regime, so‐called ‘displaced short day’ (DSD). Standard light for SD and DSD was a mixture of fluorescence and incandescence at 400 μmol m−2 s−1whereas the extension period of the 24‐h LD was solely incandescence at 10–15 μmol m−2 s−1. The DSD system was first characterized by the timings of floral induction, stimulus translocation and apical development. Carbohydrates in the blade tissues and in leaf exudate were analysed comparatively in vegetative and induced plants.Fructans were not detected in the leaf tissues whereas sucrose and starch were found to be present in similar amounts. In SD, their contents exhibited a diurnal fluctuation and were not in large excess. The common change observed during the two inductive treatments was that starch remained at a high level during the LD extension, even though the lighting was unsuitable for photosynthesis, and increased transiently in DSD.Sucrose was the major sugar contained in the leaf exudate. Its content increased when flowering was induced, but not at the same time in the two systems. In LD, sucrose exudation rose when plants were returned to standard light after the inductive cycle, i.e. after the LD stimulus had left the leaf blade. By contrast, during the DSD, sucrose was transported at the same time as the floral stimulus. Results are discussed together with the methods used to time stimulus translocation and their implications.
Salinity stress inhibits calcium loading into the xylem of excised barley (Hordeum vulgare) roots
Authors: HALPERIN STEPHEN J. , KOCHIAN LEON V. , LYNCH JONATHAN P. 
Published: March 2003

summarySalinity stress inhibits Ca translocation to the shoot, leading to Ca deficiency. The objective of this study was to determine whether salt stress inhibits Ca translocation through effects on younger root regions, where radial Ca transport is largely apoplastic, or through effects on mature regions of the roots, where radial Ca transport is largely symplastic. Roots were excised from 4‐d‐old dark‐grown barley seedlings. Calcium translocation was studied by application of 45Ca 3 or 6 cm from the root tip and measurement of its appearance in the root exudate. Calcium uptake along the axis of excised roots was studied with a vibrating Ca+2 microelectrode. Salt stress (60 mM NaCl) inhibited Ca translocation from the 6 cm region more than from the 3 cm region. Sodium sulphate treatments (30 and 36 mM) were more deleterious to Ca translocation than was NaCl in the 3 cm region, and 110 mM mannitol and 60 mM KC1 affected Ca translocation similarly to Na2SO4. The salt and mannitol treatments were more deleterious to Ca translocation in the 6 cm region than in the 3 cm region, and mannitol and KC1 inhibited Ca translocation more than the sodium treatments. Supplemental Ca could overcome the inhibition of Ca translocation by NaCl stress. Calcium uptake into the root at the 3 and 6 cm regions was not reduced by NaCl, but was retarded 0–05 cm from the apex. We conclude that symplastic Ca transport is more inhibited than apoplastic transport in salinized roots, and that the osmotic component of salt stress causes most of the inhibition. Since symplastic transport is inhibited, the possibility exists that research into the effects of salinity on the transport functions of endodermal cells will yield information that can be used to improve Ca translocation in salt‐affected plants.
Selecting for salt tolerance in white clover (Trifolium repens): chloride ion exclusion and its heritability
Authors: ROGERS M. E. , NOBLE C. L. , HALLORAN G. M. , NICOLAS M. E. 
Published: March 2003

SUMMARYThe potential to improve the salt tolerance of white clover (Trifolium repens L.) was evaluated in populations developed by selecting plants within the cv. Haifa which had high and low concentrations of Cl− in the shoots. Under saline conditions (40 mM NaCl), the low‐Cl populations consistently maintained lower concentrations of both Na and Cl in all plant parts and produced more dry matter than the original parent cultivar (Haifa), or the high‐Cl populations. Under non‐saline conditions, there were no differences between populations for these characters. In young seedlings, concentrations of Cl− in the shoots of the low‐Cl and high‐Cl populations started to diverge after 4 d exposure to saline conditions and there were significant differences between populations after 6 d growth at 40 mM NaCl. Results using 36C1 suggested that the salt‐tolerant low Cl population was better able to retain 36C1 in the roots and to limit its translocation to the leaves and petioles than the high‐Cl population. Realized heritability values for shoot Cl− concentration were found to be moderate in the first cycle of selection (0.24 and 0.37 for high and low Cl− concentrations respectively), but were substantially lower (0.10 and 0.09 respectively) in the second selection cycle. We propose that it is possible to increase levels of salt tolerance in white clover by selecting for low shoot Cl− concentrations under saline conditions and that this criterion could be used at very early stages of exposure to NaCl (i.e. day 4 or 6).
Survival of propagules of arbuscular mycorrhizal fungi in soils in eastern Australia used to grow cotton
Authors: McGEE P. A , PATTINSON G. S. , HEATH R. A. , NEWMAN C. A. , ALLEN S.J. 
Published: March 2003

SUMMARYSoil‐borne spores and hyphae of arbuscular mycorrhizal fungi are important propagules in cracking clay soils of northern NSW, Australia. In these soils, senescent roots were uncommon. Although c. 4–200 spores g−1 soil were found, less than 6% established arbuscular mycorrhizas in trap plants, and this percentage declined over 24 months. Using tetrazolium red as a vital stain, 16–21 % of spores from field soils were found to be viable in fresh soil and 6–7 % after 24 months of storage. Using fluorescein diacetate, the length of stained hyphae of c. 0–5 m g−1 soil was shown to be halved over 32 wk. The density of viable propagules of arbuscular mycorrhizal fungi in soil declined over time and was reduced by severe disturbance. The fungi that survived to 12 months included a species thought to form dormant spores, while those initiating infection after 24 months, did not.
Ultraviolet‐B radiation influences the abundance and distribution of phylloplane fungi on pedunculate oak (Quercus rohur)
Authors: NEWSHAM K. K. , LOW M. N. R. , McLEOD A. R. , GREENSLADE P. D. , EMMETT B. A. 
Published: March 2003

SUMMARYThe effects of u. v.‐B radiation (280–315 nm) on the fungi occurring on the lammas leaves of pedunculate oak (Quercus robur L.) were examined using saplings that were exposed at an outdoor facility to supplemental levels of u. v.‐B radiation under treatment arrays of cellulose diacetate‐filtered fluorescent lamps, which also produce u. v.‐A radiation (315–400 nm). Saplings were also exposed to u. v.‐A radiation alone under control arrays of polyester‐filtered lamps, and to ambient levels of solar radiation under arrays of unenergized lamps. The u. v.‐B treatment corresponded to a 30 % elevation above the ambient level of erythemally‐weighted u. v.‐B radiation. The fungi were examined weekly over a 4–month‐period in summer and autumn 1995 using two techniques, the spore fall and leaf impression methods, which differentiated between those fungi occurring on the upper (adaxial) and lower (abaxial) surfaces of the leaves. The abundances of Aureobasidium pullulans (De Bary) Arnaud and Sporobolomyces roseus Kluy. et van Niel, two leaf yeasts which had adaxial: abaxial ratios of < 1 under ambient levels of u. v.‐B radiation, were negatively correlated with increasing ambient levels of u. v.‐B radiation and were significantly reduced on adaxial leaf surfaces by supplemental levels of u. v.‐B. There were few effects of supplemental u. v.‐B radiation on the abundances of these yeasts on abaxial leaf surfaces. The abundances of the dematiaceous hyphomycetes, Cladosporium spp. and Epicoccum nigrum Link., species with adaxial: abaxial ratios of ≥ 1 under ambient levels of u. v.‐B radiation, were not correlated with ambient levels of u. v.‐B radiation, nor were they usually affected on either leaf surface by supplemental u. v.‐B radiation. Alternaria spp. and Microdochium nivale (Fr.) Samuels & Hallet showed consistent responses on adaxial leaf surfaces to u. v.‐A radiation applied under control and treatment arrays. Our results suggest that current levels of shortwave radiation already influence the distribution of fungi on leaf surfaces and that future increases in u. v.‐B radiation will directly affect the abundances of specific phylloplane fungi.
Zinc, lead and cadmium tolerance, uptake and accumulation byTypha latifolia
Authors: YE Z. H. , BAKER A. J. M. , WONG M. H. , WILLIS A. J. 
Published: March 2003

summaryZinc, lead and cadmium tolerance in four populations ofTypha latifoliaraised from seed collected from metal‐contaminated and uncontaminated sites were investigated. Metal concentrations in natural plant populations showed that Zn, Pb and Cd in the leaves were maintained at low levels (Zn: 22–122, Pb: 4.7–40 and Cd: 0.2–0.8 μg g−1d. wt), although concentrations of these metals in the associated soil‐sediments (total concentrations of Zn: 86–3009, Pb: 26–18894 and Cd: 1.4–26 μg−1d. wt) and in the roots (Zn: 46–946, Pb: 25–3628 and Cd: 1.0–17 μg g−1d. wt) varied widely. Some differences were found between metal‐contaminated and uncontaminated populations in terms of metal uptake under controlled conditions. Seedlings from metal‐contaminated populations accumulated considerably more metals (up to nearly twice as much Zn and Pb and three times as much Cd) in roots than the uncontaminated population in a pot trial. In general, however, different populations ofT. latifoliashowed similar growth responses (the longest leaf elongation, the longest root elongation, shoot and root d. wt), metal uptake and indices of metal tolerance when seedlings were grown in the same metal treatment solutions or in the same metal‐contaminated media under laboratory conditions. The data do not support the hypothesis that populations from metal‐contaminated sites have evolved tolerance to Zn, Pb and Cd, but rather thatT. latifoliashows constitutional tolerance.
Can an increased copper requirement in copper‐tolerant Mimulus guttatus explain the cost of tolerance?
Authors: HARPER FRANCES A. , SMITH SUZANNE E. , MACNAIR MARK R. 
Published: March 2003

summaryIf metal tolerant plants, by virtue of their tolerance mechanism, are less efficient at the uptake, distribution or utilization of metals then essential micronutrient deficiency may occur at the low levels of metal supply found on non‐mine soils. This argument forms the basis of the metal requirement hypothesis put forward to explain the lower fitness of tolerant individuals on uncontaminated soil, the so called‘cost of tolerance’. In this paper, copper balance was investigated in Mimulus guttatus Fischer ex. DC (the yellow monkey flower) for plants with or without the major tolerance gene which confers primary tolerance, and plants with few or many modifier genes which control degree of tolerance. No conclusive evidence to support an increased copper requirement in plants with the major tolerance gene, and/or many modifier genes was shown. Any differences in copper requirement found during vegetative growth were small, and were deemed insufficient to explain the apparent cost of tolerance.
The ferredoxin‐encoding fdxN gene of the filamentous cyanobacterium Anabaena variabilis ATCC 29413 is not essential for nitrogen fixation
Authors: MASEPOHL BERND , GÖRLITZ KIRSTEN , MONNERJAHN URSULA , MOSLERAND BRITTA , BÖHME HERBERT 
Published: March 2003

summaryIn contrast to that of Anabaena sp. PCC7120, the fdxN gene in Anabaena variabilis ATCC 29413 is not interrupted by a 55‐kb DNA element, making this strain more suitable for genetic analysis of fdxN independent of the developmentally regulated excision during heterocyst formation. As a basis for mutational analysis, the fdxN gene of A. variabilis was cloned and sequenced. The deduced FdxN protein sequence was highly homologous to the Anabaena 7120 fdxN gene product including eight cysteine residues that are known to be conserved among ferredoxins containing two [4Fe‐4S] clusters. The fdxN gene of A. variabilis was disrupted by insertion of an interposon within the fdxN coding region resulting in mutant strain KG29. Diazotrophic growth and in vivo nitrogenase activity of KG29 were similar to those of the wild‐type, indicating that FdxN was not essential for N2 fixation in A. variabilis.
Looking for molecular and physiological markers of osmotic adjustment in sunflower
Authors: JAMAUX I. , STEINMETZ A. , BELHASSEN E. 
Published: March 2003

summaryTwo families of Helianthus lines, T−S (low desiccation rate) and T+ (low desiccation rate), with contrasting osmotic adjustment (OA), obtained from a divergent selection programme, were compared for several morphological traits, ecophysiological parameters and molecular markers. The physiological analysis in a glasshouse experiment showed that the two families were identical in irrigated conditions except for a single trait, relative water loss (RWL: water loss rate of excised leaves). RWL could be used for these genotypes as a physiological marker of OA. A molecular analysis of the two contrasting lines, using differential screening of cDNA libraries, led to the isolation of three specific cDNAs, one of which, DRS26, showed high sequence homology with a mammalian amino‐acid transporter. Subsequent RFLP and STS studies, using DRS26 and RAPD bulked analysis, enabled the identification of putative molecular markers of RWL and OA in T−:T+ sunflower.
Reciprocal transfer of carbon isotopes between ectomycorrhizal Betula papyrifera and Pseudotsuga menziesii
Authors: SIMARD SUZANNE W. , JONES MELANIE D. , DURALL DANIEL M. , PERRY DAVID A. , MYROLD DAVID D. , MOLINA RANDY 
Published: March 2003

summaryInterspecific C transfer was studied in laboratory microcosms containing pairs of 6‐month‐old Betula papyrifera Marsh, and Pseudotsuga menziesii (Mirb.) Franca seedlings growing in individual, root‐restrictive (28μm pore size) pouches filled with field soil. Interspecific transfer was examined by reciprocal labelling of seedlings with 13CO2(gas) and 14CO2(gas). At the time of labelling, the root zones of ectomycorrhizal (EM) B. papyrifera and P. menziesii were interconnected by an extensive network of EM mycelium. Carbon transferred through EM connections was distinguished from that through soil pathways by comparing microcosms where interconnecting hyphae were left intact vs. those where they were severed immediately before labelling.Transfer was bidirectional, and represented 5 % of total isotope uptake by both B. papyrifera and P. menziesii together. P. menziesii received on average 50% more 14C and 66% more 13C from paper birch than vice versa, however, differences between species were not statistically significant. Neither net nor bidirectional transfer differed between severing treatments, leaving in question the relative importance of EM hyphae versus soil transfer pathways. The tendency for P. menziesii to receive more isotope than B. papyrifera corresponded with a 10‐fold greater net photosynthetic rate per seedling and two‐fold greater foliar N concentration of B. papyrifera than P. menziesii.