bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations in the normal anatomy of the collateral ligaments of the human elbow joint
Authors: BECKETT K. S. , McCONNELL P. , LAGOPOULOS M. , NEWMAN R. J.
Published: March 2003

The variations which occur in the medial and lateral ligament complexes of the elbow were investigated. These occurred frequently with the standard appearances occurring in no more than half the specimens on the medial side and one quarter of those on the lateral side. Surgeons who regularly perform elbow arthroplasty must be aware of these considerations, especially with the introduction of unconstrained prostheses which rely upon the ligament complex for their postoperative stability.
Symposium on Mechanisms of Ageing and Longevity
Authors: COWEN T.
Published: March 2003

The Symposium on ‘Mechanisms of Ageing and Longevity’ was held at the Royal Free Campus, Royal Free and University College Medical School, London, on 17 September 1999. It was organised and sponsored by the Anatomical Society of Great Britain and Northern Ireland with generous contributions from BBSRC, AgeNet and Research into Ageing.

The Symposium was organised as a result of recent discoveries in two principal areas: the genetics of longevity regulation in the nematode worm, Caenorhabditis elegans, and the cell biology of ageing in mammalian cells. Papers were presented covering the role of insulin‐like signalling, free radical damage and caloric restriction in ageing of invertebrate and mammalian systems. One of the principal aims was to examine the idea that a genetically conserved signalling pathway might regulate ageing processes at both a cellular and an organismal level.
Forkhead transcription factors are targets of signalling by the proto‐oncogene PKB (C‐AKT)
Authors: KOPS G. J. P. L. , BURGERING B. M. T.
Published: March 2003

Following the discovery that the proto‐oncogene protein kinase B (PKB) functions as a downstream element in signalling from phosphoinositide 3′‐kinase (PI3‐kinase) (Burgering & Coffer, 1995), PKB has been shown to mediate a diverse array of PI3‐kinase dependent cellular responses. Most recently PKB‐dependent phosphorylation of 3 members of the family of Forkhead transcription factors has been demonstrated to play a role in PI3‐kinase dependent effects on transcription. This review focuses on this newly discovered function of PKB in conveying the diversity of PI3‐kinase dependent cellular responses.
Intracellular and extracellular regulation of ureteric bud morphogenesis
Authors: DAVIES JAMIE
Published: March 2003

The urinary collecting duct system of the permanent kidney develops by growth and branching of an initially unbranched epithelial tubule, the ureteric bud. Formation of the ureteric bud as an outgrowth of the wolffian duct is induced by signalling molecules (such as GDNF) that emanate from the adjacent metanephrogenic mesenchyme. Once it has invaded the mesenchyme, growth and branching of the bud is controlled by a variety of molecules, such as the growth factors GDNF, HGF, TGFβ, activin, BMP‐2, BMP‐7, and matrix molecules such as heparan sulphate proteoglycans and laminins. These various influences are integrated by signal transduction systems inside ureteric bud cells, with the MAP kinase, protein kinase A and protein kinase C pathways appearing to play major roles. The mechanisms of morphogenetic change that produce branching remain largely obscure, but matrix metalloproteinases are known to be necessary for the process, and there is preliminary evidence for the involvement of the actin/myosin contractile cytoskeleton in creating branch points.
Investigation of a cyclopic, human, term fetus by use of magnetic resonance imaging (MRI)
Authors: Situ D. , Reifel C. W. , Smith R. , Lyons G. W. , Temkin R. , Harper‐Little C. , Pang S. C.
Published: March 2003

Using magnetic resonance imaging (MRI), the internal neural and craniofacial malformations of a cyclopic fetus are described. External facial features were characterized by a tubular proboscis situated above a single eye slit. The brain was recognized as ‘pancake’ type alobar holoprosencephaly (a condition where the undifferentiated telencephalon partially surrounds a monoventricle). Displacement of some bones that normally contribute to the orbit could be clearly discerned. Absence of neural structures (e.g. falx cerebri, corpus callosum) and missing components of the ethmoid bone indicated a midline deficit. This correlates with proposed theories of cyclopic embryopathy, which suggest that the prechordal plate and the neural crest cells are affected during the third week of gestation in cyclopia.
Anatomical relationship between specialized astrocytes and leptin‐sensitive neurones
Authors: Young John K.
Published: March 2003

We have previously reported that a specialized subpopulation of astrocytes in the arcuate nucleus of the hypothalamus show an unusually intense immunoreactivity for brain fatty acid binding protein (bFABP). Since bFABP has been shown to regulate the activity of an enzyme, fatty acid synthase, that has a potent influence upon the regulation of feeding by the hypothalamus, it was of interest to determine if bFABP + astrocytes are positioned to potentially influence the activity of feeding‐regulating neurones. In this study, we examined the anatomical relationship between specialized arcuate astrocytes immunoreactive for bFABP and feeding‐regulating neurones that are responsive to leptin and which are immunoreactive for the transcription factor STAT3. The results show that both cell types are abundant in the arcuate nucleus of the hypothalamus and are frequently closely adjacent to each other. This study provides an anatomical basis for the possibility that specialized arcuate astrocytes regulate the function of leptin‐sensitive, feeding‐regulating neurones of the arcuate nucleus.
Immunohistochemistry of the lymphoid tissues of the tammar wallaby,Macropus eugenii
Authors: Old Julie M. , Deane Elizabeth M.
Published: March 2003

The lymphoid tissues of the metatherian mammal, the adult tammar wallaby,Macropus eugenii, were investigated using immunohistochemical techniques. Five cross‐reactive antibodies previously shown to recognize surface markers in marsupial tissues and five previously untested antibodies were used. The distribution of T‐cells in the tissue beds of spleen, lymph node, thymus, gut‐associated lymphoid tissue (GALT) and bronchus‐associated lymphoid tissue (BALT) was documented using antibodies to CD3 and CD5. Similarly, B‐cells were identified in the same tissues using anti‐CD79b. Antibodies to CD8, CD31, CD79a and CD68 failed to recognize cells in these tissue beds. In general the pattern of cellular distribution identified using these antibodies was similar to that observed in other marsupial and eutherian lymphoid tissues. This study provides further information on the commonality of lymphoid tissue structure in the two major groups of extant mammals, metatherians and eutherians.
Why study human limb malformations?
Authors: Wilkie Andrew O. M.
Published: March 2003

Congenital limb malformations occur in 1 in 500 to 1 in 1000 human live births and include both gross reduction defects and more subtle alterations in the number, length and anatomy of the digits. The major causes of limb malformations are abnormal genetic programming and intra‐uterine disruption to development. The identification of causative gene mutations is important for genetic counselling and also provides insights into the mechanisms controlling limb development. This article illustrates some of the lessons learnt from the study of human limb malformation, organized into seven categories. These are: (1) identification of novel genes, (2) allelic mutation series, (3) pleiotropy, (4) qualitative or (5) quantitative differences between mouse and human development, (6) physical and teratogenic disruption, and (7) unusual biological phenomena.
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

Motoneurones 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

The 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

To 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

Production 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

Unifoliated 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

summary

Salinity 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

The 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

Soil‐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.
Fructan metabolism in two species of Bromus subjected to chilling and water stress
Authors: PUEBLA ANDREA F. , SALERNO GRACIELA L. , PONTIS HORACIO G.
Published: March 2003

Two species of Bromus adapted to different climatic conditions were studied to determine their responses to chilling and water stress. Enzymes of sucrose and fructan metabolism as well as fructoside content were measured in roots and shoots. The results indicate that Bromus pictus (adapted to a cold desert area) has a constitutive fructan synthesis, whilst B. auleticus (adapted to a warmer northern climate) only accumulated fructan under cold stress. Microscopic observations of roots exposed to fluorescent probes ascertained cell viability and showed that the apex of roots in the northern species were more affected by the water‐deficit treatment than the southern species. The presence of fructans in B. pictus and their absence in B. auleticus support the hypothesis that fructans play a role in plant tolerance to environmental stress.
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

The 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

summary

Zinc, 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

summary

If 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

summary

In 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

summary

Two 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

summary

Interspecific 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.
Effects of ambient ozone concentrations on contents of non‐structural carbohydrates in young Picea abies and Fagus sylvatica
Authors: LUX D. , LEONARDI S. , MÜLLER J. , WIEMKEN A. , FLÜCKIGER W.
Published: March 2003

summary

Young spruce (Pirea abies [L.] Karst; 2‐yr) and beech trees (Fagus sylvatica L.; current‐year and 1‐yr‐old seedlings) were grown under field conditions at a rural site near the city of Base] (Schonenbuch; 400 m above sea level) and 2‐yr‐old spruce trees at an elevated montainous site (Wengernalp; 1890 m above sea level). The plants were exposed in open‐top‐chambers (OTC) either to charcoal‐filtered air or ambient air with ozone being the predominant air pollutant at both sites. The exposures lasted up to 1 yr. At the end of the growth period the plants were harvested and the pool sizes of the major non‐structural carbohydrates were determined. Exposure to ambient air compared with filtered air controls caused an increase of glucose, fructose, pinitol, starch and, in some cases, sucrose in needles whereas carbohydrate contents in roots and twigs of spruce were reduced, in particular at Wengernalp. In beech saplings at Schönenbuch, a significant rise of sucrose and, in some cases, of raffinose, together with a significant reduction of glucose and fructose was observed in buds, leaves, twigs, and roots in ambient air compared with filtered air. In phloem exudates of current year beech seedlings, a 54–160 higher content of carhohydrates was found in ambient air than in filtered air. In roots of the beech saplings, the amount of soluble carbohydrates increased and starch contents mostly decreased. In general, starch storage in roots and stems was more abundant in beech trees. Spruce, especially at the mountainous site, accumulated high amounts of soluble carbohydrates in needles, in particular glucose.
Growth and survival of Azolla filiculoides in Britain. II. Sexual reproduction
Authors: JANES RACHEL
Published: March 2003

Sporulation in the floating fern Azolla filiculoides Lam. is both frequent and widespread in Britain and might therefore play a greater part in the population dynamics of the species than
has been suggested by earlier reports. In laboratory experiments, increasing plant density and/or phosphorus supply resulted in increased sporulation. It was estimated that a thick mat of 8 kg m2 fresh biomass can produce 380000 microsporocarps and 85000 megasporocarps per m2.

Light and temperatures >10°C were necessary for sporocarp germination. Sporocarps could survive exposure to both low temperatures (5°C for at least 3 months) and sub‐zero temperatures (−10°C for at least 18 d). Sporocarps were found to survive storage in water for 3 yr and to germinate from mud samples collected in the field. In laboratory culture, sporeling growth and survival were optimal at 15°C.

There is some evidence that A. filiculoides might have adapted to the British climate since its introduction.
Effect of enhanced atmospheric CO2 on mycorrhizal colonization by Glomus mosseae in Plantago lanceolata and Trifolium repens
Authors: STADDON PHILIP L. , GRAVES JONATHAN D. , FITTER ALASTAIR H.
Published: March 2003

Plantago lanceolata L. and Trifolium repens L. were grown for 16 wk in ambient (360 μmol mol−1) and elevated (610 μmol mol−1) atmospheric CO2. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and given a phosphorus supply in the form of bonemeal, which would not be immediately available to the plants. Seven sequential harvests were taken to determine whether the effect of elevated CO2 on mycorrhizal colonization was independent of the effect of CO2 on plant growth. Plant growth analysis showed that both species grew faster in elevated CO2 and that P. lanceolata had increased carbon allocation towards the roots. Elevated CO2 did not affect the percentage of root length colonized (RLC); although total colonized root length was greater, when plant size was taken into account this effect disappeared. This finding was also true for root length colonized by arbuscules. No CO2 effect was found on hyphal density (colonization intensity) in roots. The P content of plants was increased at elevated CO2, although both shoot and root tissue P concentration were unchanged. This was again as a result of bigger plants at elevated CO2. Phosphorus inflow was unaffected by CO2 concentrations. It is concluded that there is no direct permanent effect of elevated CO2 on mycorrhizal functioning, as internal mycorrhizal development and the mycorrhizal P uptake mechanism are unaffected. The importance of sequential harvests in experiments is discussed. The direction for future research is highlighted, especially in relation to C storage in the soil.
Carbon dioxide‐concentrating mechanism and the development of extracellular carbonic anhydrase in the marine picoeukaryote Micromonas pusilla
Authors: IGLESIAS‐RODRÍGUEZ M. D. , NIMER N. A. , MERRETT M. J.
Published: March 2003

A range of marine photosynthetic picoeukaryote phytoplankton species grown in culture were screened for the presence of extracellular carbonic anhydrase (CAext), a key enzyme in inorganic carbon acquisition under carbon‐
limiting conditions in some larger marine phytoplankton species. Of the species tested, extracellular carbonic anhydrase was detected only in Micromonas pusilla Butcher. The rapid, light‐dependent development of CAext when cells were transferred from carbon‐replete to carbon‐limiting conditions was regulated by the available free‐
CO2 concentration and not by total dissolved inorganic carbon. Kinetic studies provided support for a CO2‐
concentrating mechanism in that the K0.5[CO2] (i.e. the CO2 concentration required for the half‐maximal rate of photosynthesis) was substantially lower than the Km[CO2] of Rubisco from related taxa, whilst the intracellular carbon pool was at least seven fold greater than the extracellular DIC concentration, for extracellular DIC values ⩽1.0 mm.

It is proposed that when the flux of CO2 into the cell is insufficient to support the photosynthetic rate at an optimum photon irradiance, the development of CAext increases the availability of CO2 at the plasma membrane. This ensures rapid acclimation to environmental change and provides an explanation for the central role of M. pusilla as a carbon sink in oligotrophic environments.
Response of photosynthesis of Sphagnum species from contrasting microhabitats to tissue water content and repeated desiccation
Authors: SCHIPPERGES B. , RYDIN H.
Published: March 2003

The response of photosynthetic CO2 exchange to tissue water content in five spp. of Sphagnum from contrasting microhabitats (S. fuscum (Schimp.) Klinggr., S. papillosum H. Lindb., S. magellanicum Brid., S. balticum (Russ.) C. Jens. and S. cuspidatum Ehrh. ex Hoffm.) was measured in the laboratory using an infrared gas analyser technique. Experiments were designed to test recovery of net photosynthesis after periodic and long lasting desiccation.

The contact between capitula and basal parts of the mosses seems to be important for survival. Isolated capitula cut off from any contact with the water table were not able to recover after complete desiccation (at 15°C for 2–4 d). When contact with the water table is lost, e.g. during long periods of desiccation, recovery of net photosynthesis can take place but only if the water content of the capitula does not fall too far below c. 10–20% of the water content at compensation point.

There was no relationship between the ability of net photosynthesis to recover from desiccation and the wetness of the natural microhabitat. Sphagna survive dry periods by avoidance of drying out by high capillarity or dense growth form (as in S. fuscum).
Neither compatible nor self‐incompatible pollinations of Brassica napus involve reorganization of the papillar cytoskeleton
Authors: DEARNALEY J. D. W. , CLARK K. M. , HEATH I. B. , LEW R. R. , GORING D. R.
Published: March 2003

Compatible pollination of Brassica napus necessitates pollen hydration, pollen germination and growth of the pollen tube through the loosened walls of stigmatic papillar cells, whereas self‐incompatible (SI) pollinations fail at one of these stages. Analyses of the early stages of pollination show that at high (but not low) relative humidities, both compatible and SI pollen hydrates, but SI germination is reduced and the rare pollen tubes generally fail to penetrate the papillar walls, although there is some wall loosening. Inside the papillae, both compatible and SI interactions may induce the formation of callose, but there is no evidence for a major accumulation of cytoplasm or secretory vesicles in the vicinity of the pollen tubes and neither microtubule nor F‐actin patterns re‐arrange in this zone. These observations indicate that the source of the wall‐loosening enzymes is probably the pollen tube or pollen coat, and that the common cellular responses of plants to attempted invasions have become suppressed in the papilla–pollen tube interaction.
The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea
Authors: RAYBOULD A. F. , MASKELL L. C. , EDWARDS M‐L. , COOPER J. I. , GRAY A. J.
Published: March 2003

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus‐derived genes.
Colonization of wheat para‐nodules by the N2‐fixing cyanobacterium Nostoc sp. strain 2S9B
Authors: GANTAR M. , ELHAI J.
Published: March 2003

The treatment of wheat roots with 2,4‐dichlorophenoxyacetic acid (2,4‐D) led to the formation of tumour‐like structures, para‐nodules, which were readily colonized by cyanobacteria. The amount of cyanobacteria found on 2,4‐D treated roots was 3.6 times higher than that found on untreated roots. Cyanobacteria penetrated the para‐
nodules by migrating in between loosely arranged cells that covered their surfaces or by penetrating the space at the junction of root and para‐nodule. In plants treated with 2,4‐D and co‐cultivated with cyanobacteria in medium without combined nitrogen, the rate of acetylene reduction was three times that seen in untreated but colonized roots. Addition of 2,4‐D itself did not change the rate of acetylene reduction in free‐living culture of Nostoc sp. strain 2S9B. In plants treated with 2,4‐D and co‐cultivated with Nostoc sp. strain 2S9B in medium without combined nitrogen the nitrogen content of roots but not shoots was significantly increased.
Interactive effects of arbuscular mycorrhizal symbiosis, intraspecific competition and resource availability on Trifolium subterraneum cv. Mt. Barker
Authors: FACELLI E. , FACELLI J. M. , SMITH S. E. , MCLAUGHLIN M. J.
Published: March 2003

We performed two glasshouse experiments to determine whether the presence of arbuscular mycorrhizal symbiosis reduces the intensity of intraspecific competition at low concentrations of available phosphorus (P), and whether this effect is modified by a reduction in light intensity. In the first experiment, Trifolium subterraneum cv. Mt. Barker was grown at different densities in controlled conditions of light and temperature, and half of the pots were inoculated with spores of the arbuscular mycorrhizal fungus, Gigaspora margarita. In the second experiment, the plants were grown in similar controlled conditions but the light intensity received by half of the pots was reduced by >50%. The biomass and P content of individual mycorrhizal plants and the biomass response to mycorrhizal infection were drastically reduced as plant density increased. The effects of density on percentage infection, shoot and root P concentrations, and root: shoot ratios were inconsistent. Generally reduction in light intensity did not alter these effects. Mycorrhizal symbiosis increased intraspecific competition intensity through an increase in the availability of soil P. This increase in competition was reflected in the greater size inequality of low density mycorrhizal treatments. Our results emphasize that the main effects of mycorrhizas at the individual level cannot be expected to be apparent at the population level, because they are overridden by density‐dependent processes.
Growth response of branches of Picea sitchensis to four years exposure to elevated atmospheric carbon dioxide concentration
Authors: BARTON C. V. M. , JARVIS P. G.
Published: March 2003

Branch bags were used to expose branches on mature Sitka spruce trees to either ambient [CO2] (A) or elevated [CO2] (E) for 4 yr. This paper reports the effects of this treatment on the growth, development and phenology of the branches, including shoot expansion, shoot numbers, needle dimensions, needle numbers and stomatal density. The effect of elevated [CO2] on the relationship between leaf area and sapwood area was investigated. Exposure to elevated [CO2] doubled photosynthetic rates in current‐year shoots and, despite some down‐regulation, 1‐yr‐old E shoots also had higher rates of photosynthesis than their A counterparts. Thus, the amount of assimilate fixed by E branches was substantially more than that fixed by A branches; however, this increase in the local production of assimilate did not lead to an increase in non‐structural carbohydrate or stimulate growth or meristematic activity within the E branches. There was a very consistent relationship between leaf area and stem cross‐sectional area that was not influenced by [CO2]. However, unbagged branches had thicker stems than bagged branches, resulting in a slightly lower ratio of leaf area to cross‐sectional area. The implications of the results for the modelling of growth and allocation and the potential utility of the branch bag technique are discussed.
Evolutionary divergence in the pan‐Atlantic mangrove Avicennia germinans
Authors: DODD R. S. , AFZAL RAFII Z. , BOUSQUET‐MÉLOU A.
Published: March 2003

Cuticular hydrocarbon composition was determined for 18 populations of Avicennia germinans (Avicenniaceae) collected from West Africa, Florida, the Pacific coast of Mexico and French Guyana. Variation in covariance structure among the hydrocarbons was evaluated from correlations among the traits for each of the populations and from a hierarchical common principal components analysis. Principal components ordinations of populations based on the 171 z* transformed correlation coefficients, onto which a minimal spanning tree was superimposed, suggested a network in which French Guyanan populations formed a nexus from which African populations differentiated biochemically from Floridan and Mexican groups. Common principal components analysis provided further support for the differentiation in covariance structure among these biochemical traits of African populations. Pacific coast Mexican populations appeared to have diverged less in covariation among traits from Atlantic American sources than did the northern (Floridan) and southern (French Guyanan) Atlantic American populations from one another. The complete isolation of Pacific coast sources after emergence of the Central American isthmus during the Pliocene provides a reference for comparison of levels of differentiation among regions that suggests an underlying pattern of divergence in this species. Partial Mantel matrix tests revealed significant geographic effects, with no significant climatic effects. Our results provide support for recognition of a major differentiation between Old and New World sources within the taxon and indicate the need for a full revision of this species.