bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological and histochemical characteristics of the lamina propria in scrotal and abdominal testes from postpubertal boars: correlation with the appearance of the seminiferous epithelium
Authors: PINART E. , BONET S. , BRIZ M. , PASTOR L. M. , SANCHO S. , GARCÍA N. , BADIA E. , BASSOLS J.
Published: March 2003

This study was undertaken to investigate the morphological characteristics and lectin affinity of the testicular lamina propria in healthy boars and in unilateral and bilateral abdominal cryptorchid boars. The lamina propria of scrotal testes from healthy boars and unilateral cryptorchid boars was constituted by an innermost noncellular layer, the basal lamina, and by 2 layers of peritubular cells, each separated by a fibrous layer. The noncellular layers contained collagen fibres and glycoconjugates with abundant N‐acetylgalactosamine, galactose, fucose, N‐acetylglucosamine and neuraminic acid residues. The inner peritubular cell layer was composed of myoid cells, the outer layer of fibroblasts. In the abdominal testes of unilateral and bilateral cryptorchid boars, the lamina propria of nondegenerating and degenerating seminiferous tubules appeared thickened due to an increased content of collagen fibres and glycoconjugates. Glycoconjugates showed decreased amounts of fucose, neuraminic acid and galactose, and increased amounts of N‐acetylglucosamine residues. The basal lamina formed infoldings toward the seminiferous epithelium and contained small cells. Both inner and outer peritubular cells were fibroblasts of immature appearance. In degenerated seminiferous tubules of bilateral cryptorchid boars, the lamina propria was composed of a thickened and collagenised basal lamina, without peritubular cells and with a low content of glycoconjugates. In scrotal testes, therefore, the lamina propria was implicated in tubular contractility and in mediating the communication and the substrate diffusion between seminiferous tubules and interstitial tissue. Cryptorchidism induced morphological and histochemical alterations in the lamina propria of abdominal testes, which may be linked to evidence from other studies of lack of tubular contractility and defective cell–cell communication and substrate diffusion. The severity of these anomalies correlated with the severity of Sertoli cell alterations.
Osteological features in pure‐bred dogs predisposing to cervical spinal cord compression
Authors: BREIT S. , KÜNZEL W.
Published: March 2003

Relative to body size, midsagittal and interpedicular diameters of the cranial and caudal aspects of cervical vertebral foramina (C3–C7) were found to be significantly (P < 0·05) larger in small breeds than in large breeds and Dachshunds, and also larger in Dachshunds (P < 0·05) than in large breeds. This condition increases the risk for spinal cord compression resulting from relative stenosis of the cervical vertebral foramina, especially in large dogs, and this is also exacerbated by the typical shape of the vertebral foramina (i.e. dorsoventrally flattened cranially and bilaterally narrowed caudally). Within large dogs those breeds highly predisposed to cervical spinal cord compression were Great Danes (the breed with the smallest midsagittal vertebral foramen diameters from cranial C6 to cranial T1) and Doberman Pinschers, because of the most strikingly cranially dorsoventrally narrowed cone‐shaped vertebral foramina at C6 and C7. The existence of a small midsagittal diameter in the cranial cervical spine was a high risk factor predisposing to spinal cord compression in small breeds and Dachshunds. Remarkable consistency was noted between the spinal level of the maximum enlargement of the spinal cord which previously was reported to be at C6, and the site of maximum enlargement of the vertebral canal currently stated in Dachshunds and small breeds. In large breeds the maximum enlargement of the vertebral canal tended to be located more caudally at the caudal limit of C7. The average age at which large dogs were most susceptible to noxious factors causing abnormal growth of the pedicles was determined to be 16 wk.
Regional differences in innervation of lymph nodes in the Wistar rat
Authors: LI Y. , NOVOTNY G. E. K.
Published: March 2003

Previous light microscopic investigations have indicated that, in the rat, the innervation of mesenteric lymph nodes may be less dense than that of axillary nodes. However, nerves of the enteric system are difficult to visualise by light microscopy. Therefore we quantified the density of innervation of axillary and mesenteric lymph nodes at the ultrastructural level. The results show a highly significant difference in the density of innervation between these 2 groups of lymph nodes, but morphologically the type of the innervation does not seem to differ. In previous studies, nerves were found predominantly in regions characterised by aggregations of plasma cells. In view of this association, we suggest that the difference in innervation may reflect the migration of plasma cells out of mesenteric nodes and into the mucosa of the gut wall. By contrast, in peripherally located nodes, plasma cells tend to remain within the lymph nodes, and hence the density of innervation of these nodes is greater.
In situ hybridization and immunohistochemistry of bone sialoprotein and secreted phosphoprotein 1 (osteopontin) in the developing mouse mandibular condylar cartilage compared with limb bud cartilage
Authors: Shibata Shunichi , Fukada Kenji , Suzuki Shoichi , Ogawa Takuya , Yamashita Yasuo
Published: March 2003

Mandibular condylar cartilage is often classified as a secondary cartilage, differing from the primary cartilaginous skeleton in its rapid progress from progenitor cells to hypertrophic chondrocytes. In this study we used in situ hybridization and immunohistochemistry to investigate whether the formation of primary (tibial) and secondary (condylar) cartilage also differs with respect to the expression of two major non‐collagenous glycoproteins of bone matrix, bone sialoprotein (BSP) and secreted phosphoprotein 1 (Spp1, osteopontin). The mRNAs for both molecules were never expressed until hypertrophic chondrocytes appeared. In the tibial cartilage, hypertrophic chondrocytes first appeared at E14 and the expression of BSP and Spp1 mRNAs was detected in the lower hypertrophic cell zone, but the expression of BSP mRNA was very weak. In the condylar cartilage, hypertrophic chondrocytes appeared at E15 as soon as cartilage tissue appeared. The mRNAs for both molecules were expressed in the newly formed condylar cartilage, although the proteins were not detected by immunostaining; BSP mRNA in the condylar cartilage was more extensively expressed than that in the tibial cartilage at the corresponding stage (first appearance of hypertrophic cell zone). Endochondral bone formation started at E15 in the tibial cartilage and at E16 in the condylar cartilage. At this stage (first appearance of endochondral bone formation), BSP mRNA was also more extensively expressed in the condylar cartilage than in the tibial cartilage. The hypertrophic cell zone in the condylar cartilage rapidly extended during E15–16. These results indicate that the formation process of the mandibular condylar cartilage differs from that of limb bud cartilage with respect to the extensive expression of BSP mRNA and the rapid extension of the hypertrophic cell zone at early stages of cartilage formation. Furthermore, these results support the hypothesis that, in vivo, BSP promotes the initiation of mineralization.
The phenotype of the human materno‐fetal endothelial barrier: molecular occupancy of paracellular junctions dictate permeability and angiogenic plasticity*
Authors: Leach Lopa
Published: March 2003

In vitromodels predict that molecular occupancy of endothelial junctions may regulate both barrier function and angiogenesis. Whether this is true in human vascular beds undergoing physiological angiogenesis has not been shown. This review presents data which demonstrate there are two distinct junctional phenotypes, ‘activated’ and ‘stable’, present in the vascular tree of the human placenta taken from two distinct highly angiogenic gestational periods (first and last trimester). Stability is conferred by the presence of occludin in tight junctions and plakoglobin in adherens junctions. Their localization may be influenced by vascular endothelial growth factor and angiopoietins 1 and 2 that have a similar temporal and site‐specific differential expression. The junctional phenotypes are reversible, as shown in studies with endothelial cells isolated from placental microvessels and grown in the presence/absence of cAMP‐enhancing agents. Reductions in protein levels and loss of junctional localization of adhesion molecules result in increased permeability to macromolecules, whilst up‐regulation and re‐targeting of these molecules inhibit cell proliferation and increase transendothelial resistance. These studies suggest junctional adhesion molecules can regulate physiological angiogenesis and vascular re‐modelling. Moreover, the activated junctional phenotype of placental microvessels allows them to participate in increased growth and proliferation. This junctional immaturity appears to be at the expense of barrier function resulting in sites of maximal materno‐fetal solute exchange.
The role of mitochondria, cytochrome c and caspase‐9 in embryonic lens fibre cell denucleation
Authors: Sanders E. J. , Parker E.
Published: March 2003

During the differentiation of secondary lens fibre cells from the lens epithelium, the fibre cells lose all of their cytoplasmic organelles as well as their nuclei. The fibre cells, containing crystallins, which confer optical clarity, then persist in the adult lens. The process of denucleation of these cells has been likened to an apoptotic event which is not followed by the plasma membrane changes that are characteristic of apoptosis. We have examined the expression and subcellular translocation of molecules of the apoptotic cascade in differentiating lens epithelial cells in culture. In this culture system, the epithelial cells differentiate into lentoids composed of lens fibre cells. We find that caspase‐9, which is expressed and activated before embryonic day 12 in intact lenses, is localized in the cytosol outside mitochondria in non‐differentiating cultured cells. In lentoid cells, caspase‐9 migrates into mitochondria after the latter undergo a membrane permeability transition that is characteristic of apoptotic cells. At the same time, caspase‐9 co‐localizes with cytochrome c in the cytosol. The cytochrome c is apparently released from the mitochondria in lentoid cells after the mitochondrial membrane permeability transition and during the period of nuclear shrinkage. Also during this time, the mitochondria aggregate around the degenerating nuclei. Cytochrome c disappears rapidly, while mitochondrial breakdown occurs approximately coincident with the disappearance of the nuclei, but mitochondrial remnants persist together with cytochrome c oxidase, which is a mitochondrial marker protein. Apaf‐1, another cytosolic protein of the apoptotic cascade, also migrates to the permeabilized mitochondria and also co‐localizes with caspase‐9 and cytochrome c in the cytosol or mitochondria of denucleating cells, thus providing evidence for the formation of an ‘apoptosome’ in these cells, as in apoptotic cells. At no time did we observe the translocation of molecules between cytoplasmic compartments and the nucleus in differentiating lentoid cells. We suggest that the uncoupling of nuclear and membrane apoptotic events in these cells may be due to the early permeability changes in the mitochondria, resulting in the loss of mitochondrial signalling molecules, or to the failure of molecules to migrate to the nucleus in these cells, thus failing to activate nuclear‐plasma membrane signalling pathways.
Airway and blood vessel interaction during lung development
Authors: Hislop Alison A.
Published: March 2003

In the adult lung the pulmonary arteries run alongside the airways and the pulmonary veins show a similar branching pattern to the arteries, though separated from them. During early fetal development the airways act as a template for pulmonary blood vessel development in that the vessels form by vasculogenesis around the branching airways. In later lung development the capillary bed is essential for alveolar formation. This paper reviews evidence for the interaction of the airways and blood vessels in both normal and abnormal lung development.
Elastic fibre organization in the intervertebral discs of the bovine tail
Authors: Yu Jing , Peter C. , Roberts Sally , Urban Jill P. G.
Published: March 2003

Elastic fibres have been revealed by both elastin immunostaining and conventional histological orcein‐staining in the intervertebral discs of the bovine tail. These fibres are distributed in all regions of the disc but their organization varies from region to region. In the centre of the nucleus, long (> 150 µm) elastic fibres are orientated radially. In the transitional region between nucleus and annulus, the orientation of the elastic fibres changes, producing a criss‐cross pattern. In the annulus itself, elastic fibres appear densely distributed in the region between the lamellae and also in ‘bridges’ across the lamellae, particularly in the adult. Elastic fibres are apparent within the lamellae, orientated parallel to the collagen fibres of each lamella, particularly in the young (12‐day‐old) discs. In the region between the disc and the cartilaginous endplate, elastic fibres appear to anchor into the plate and terminate there. The results of this study suggest that elastic fibres contribute to the mechanical functioning of the intervertebral disc. The varying organization of the elastic fibres in the different regions of the disc is likely to relate to the different regional loading patterns.
Molecular control of arterial–venous blood vessel identity
Authors: Adams Ralf H.
Published: March 2003

Recent research has demonstrated that not only haemodynamic factors but also genetic programmes control arterial–venous cell fate and blood vessel identity. The identification of arteries and veins was previously based solely on morphological criteria and is now greatly facilitated by specific molecular markers. Moreover, signalling pathways controlling the arterial–venous decision during embryonic development have been outlined for the first time. This review gives an up‐to‐date overview of differentially expressed genes and the regulatory processes leading to the differentiation of arteries and veins.
Epithelial mesenchymal interactions, the ECM and limb development
Authors: Lonai Peter
Published: March 2003

It has been long since recognized that cellular interactions are not always direct, i.e. they do not always take place between cells contacting each other, or between cells that emit soluble factors and other cells, which respond to it. In contrast, cross‐talk between cells is frequently based on signals attached to the extracellular matrix (ECM). Thus besides proximate cell‐to‐cell contact, certain interactions are mediated by the ECM in a sequence: cell‐to‐matrix, matrix‐to‐cell. ECM‐mediated interactions may take place within a group or sheet of cells or across adjacent cell sheets. A modified mat‐like ECM, the basement membrane, separates adjacent cell sheets and mediates their interactions. Since cell sheets separated by basement membranes are an elementary feature of metazoan histology, interactions with the basement membrane have considerable importance. Recently accumulated evidence emphasizes the importance of ECM‐mediated interactions. It is becoming increasingly evident that the ECM functions not only as an architectural component, but it is involved also in signal transduction. This evidence derives from four main sources: from the structure of receptor‐ligand complexes, from Drosophila and C. elegans genetics, from cell biological observations and from the analysis of mammalian development. In this review, I will touch upon recent evidence, illustrated by examples of FGF signalling in vertebrate limb development. Although the involvement of matrix components is not yet proven for all cases directly, the strength of multiple indications suggests that a better understanding of ECM‐mediated interactions will shed new light on cell differentiation.
Carbohydrate allocation patterns in citrus genotypes as affected by phosphorus nutrition, mycorrhizal colonization and mycorrhizal dependency
Authors: GRAHAM J. H. , DUNCAN L. W. , EISSENSTAT D. M.
Published: March 2003

Among closely related citrus genotypes growing in high phosphorus (P) orchard soils, there is a tendency for less mycorrhizal‐dependent (M‐dependent) species to have lower rates of root colonization than more M‐dependent species. We hypothesized that the less M‐dependent the citrus species the more limited is their carbohydrate (CHO) allocation to the M fungus. In a glasshouse study at low and high P supply, lower total incidence of Glomus intraradices FL 208, intensity of vesicles formation, and accumulation of 16: W5cis fungal fatty acid as measures of root colonization were related to lower mycorrhizal dependency (MD; M plant d. wt/non‐mycorrhizal (NM) plant d. wt expressed at low P supply) in five citrus genotypes. At high P supply, when host carbon (C) production was not affected by P nutrition, less M‐dependent genotypes had consistently lower starch concentrations in their root and shoot tissues than did more M‐dependent genotypes, irrespective of M inoculation. At low P supply, M plants were more heavily colonized by G. intraradices and had lower starch levels than the M plants supplied with additional P. At high P, M plants of the more dependent genotypes allocated more C to starch pools relative to the NM plant than the least dependent genotype. Concentration of sucrose in tissues did not vary consistently with the dependency of citrus genotypes or with M inoculation except in high P NM plants, when less M‐dependent genotypes had lower levels of sucrose in their roots than the more dependent species. At high P supply, sucrose concentrations were lower in colonized roots than in NM roots. Across citrus genotypes, sucrose in M fibrous roots decreased relative to that in NM roots with increase in root colonization suggesting that more sucrose was allocated for growth and maintenance of G. intraradices in roots of M‐dependent species. The concentration of reducing sugars in root tissues varied in relation to MD of citrus genotypes in the same way as that of starch and sucrose, but was less responsive to M colonization. Responses of total non‐structural CHO in tissues indicated that more heavily colonized plants at low P expended more C to acquire P than did M plants of similar biomass and P status grown at high P supply. Total CHO pools increased with MD of citrus genotypes, providing evidence than C allocation patterns in the host affect M colonization.
Physiological effects of copper on iron acquisition processes in Plantago
Authors: SCHMIDT W. , BARTELS M. , TITTEL J. , FÜHNER C.
Published: March 2003

In Plantago lanceolata L. the effect of Cu(II) additions to the nutrient solution on root‐associated Fe(III) reductase was studied in a factorial design with different Cu(II) and Fe(III) concentrations. Iron starvation resulted in approx. an eightfold increase in root Fe reduction at the level of intact plants and twofold enhancement in the specific activity of both NADH‐linked FeEDTA reductase and H+‐ATPase in isolated root plasma membrane vesicles. In plants exposed to low (0.3–0.7 μM.) Cu and suboptimal Fe levels, reduction activity at the root surface was further increased and associated with more severe interveinal chlorosis than plants grown in Cu‐free medium. In Fe‐sufficient plants, withholding Cu over a prolonged period slightly enhanced the reduction activity.

Addition of high (5 μM) Cu concentrations to Fe‐free medium inhibited the induction of the physiological responses by Fe‐deficiency stress. In plants without Fe supply but with adequate Cu supply, short‐term application of 5 μM CuSO4 completely inhibited the reduction activity. Neither incubation of the plasma membrane vesicles before measurement nor incubation of intact plants with Cu before isolation caused a significant decrease in reductase activity. The results are interpreted as indicating different mechanisms underlying Cu‐induced alterations in iron nutrition.
Intraspecific variation of leaf pubescence and drought response in Encelia farinosa associated with contrasting desert environments
Authors: SANDQUIST DARREN R. , EHLERINGER JAMES R.
Published: March 2003

Traits associated with leaf energy balance are especially important for desert plants because decoupling leaf and ambient temperatures can be critical for maximizing productivity and survival in these hot, dry regions. Deserts are also one of the most climatically unpredictable and heterogeneous biomes; thus, variation of energy balance characters due either to plasticity or genetic differentiation might also be crucial to the success of desert plant species. In a common garden environment we examined variation in the traits associated with energy balance and productivity in Encelia farinosa A. Gray (brittlebush) plants. Comparing two populations from contrasting rainfall and drought climates, we found that plants from the wetter site (Superior, Arizona) always maintained higher leaf absorptances than plants from the more xeric region (Oatman, Arizona) when at similar water potentials. Superior plants also increased stomatal conductance and photosynthesis in response to mid‐spring rainfall, whereas Oatman plants did not. Oatman plants, however, tended to have greater leaf areas and continuous spring growth, which made them larger than Superior plants, yet both populations produced the same number of flower heads. The differences for these traits, and the associations among them, agree with predictions based on the contrasting drought and rainfall environments of these two populations. Our results suggest that the differences might represent alternative suites of characters of selective importance for maximizing carbon gain over the climatically variable range of this widespread species. Furthermore, these differences, detected in common environment conditions, might have a genetic basis, which might contribute to a greater potential for local adaptation in this species.
Growth and fructan content of plants of Vernonia herbacea (Asteraceae) regenerated from rhizophores
Authors: MACHADO DE CARVALHO M. ANGELA , ZAIDAN LILIAN B. P. , DIETRICH SONIA M. C.
Published: March 2003

The growth and fructan contents of plants of Vernonia herbacea (Vell.) Rusby regenerated from fragments of the underground organ (rhizophore) were analysed during two developmental cycles. When cultivated away from their natural ecosystem, these plants went through the same phenological phases as those naturally grown in the cerrado. The first aerial shoots started developing from initial fragments before the new underground system, the former acting as the main metabolic sink for the fructan present in the initial fragments. The new rhizophores started to develop by the sixth month, as photosynthates were transformed into fructans. Growth parameters measured reached higher values in the second growth cycle, exhibiting growth curves synchronized with those obtained for fructan contents in the new rhizophores. Fructo‐oligosaccharides were available mostly during the period of fast growth of aerial organs whilst the fructo‐polysaccharides were reduced. Fructan variation indicates that these compounds are metabolized during development. Additionally, the rapid growth, intense production of rhizophores and high fructan content make Vernonia herbacea a promising source of fructan for commercial use.
Effects of a rapid, unseasonal rewetting event on mineral location in Antarctic lichens
Authors: HOVENDEN MARK
Published: March 2003

summary

During the middle of the 1992 austral winter in the northern Windmill Islands, continental Antarctica, a highly unusual climatic event occurred in which the air temperature exceeded 0°C for some 60 h, at the end of which there was a significant rain shower before the ambient temperature returned to subzero conditions. This event caused most of the snow cover to melt and refreeze as clear ice. Lichens were thus rehydrated in the dark, in some places completely inundated, then frozen in ice. The effect that these conditions had on the distribution of K, Na, Mg and Ca within the thallus was estimated for two of the dominant macrolichen species, Umbilicaria decussata (Vill.) Zahlbr. and Usnea sphacelata R.Br, from three sites on a knoll on Clark Peninsula. One site acted as a natural control, owing to the very deep snow cover at the site, which protected lichens from the rewetting event. Despite persistent differences between species and the various sites, there was no overall effect of the climatic event on the membrane integrity of either lichen species. Only Usnea sphacelata from the most exposed site showed a significant leakage of K across the cell membrane, which indicated a loss of membrane integrity. Overall, both species were tolerant of the extreme conditions, although Umbilicaria decussata was the more tolerant.
Development of laboratory‐based methods for assessing seedling thermotolerance in pearl millet
Authors: HOWARTH CATHERINE J. , POLLOCK CHRISTOPHER J. , PEACOCK JOHN M.
Published: March 2003

summary

In this paper, the response to temperature of three physiological processes has been examined in detail in seedlings of sorghum and pearl millet. These have been compared with their field performance under high temperature conditions with the aim of developing laboratory‐based screening techniques for seedling thermotolerance. Membrane thermostability, as assessed by electrolyte leakage, seedling re‐growth and protein synthetic ability were measured in seedlings exposed to a range of temperatures using a thermal gradient bar. The effect of genotype, seedling age and pre‐treatment was examined. Differences between genotypes were only apparent after seedlings had been given a brief high temperature pre‐treatment (2 h at 43 °C). Similar results were found with all three methods used and their suitability for use in the screening of large numbers of entries is discussed. Significant correlation was found between the ability of membrane thermostability to acclimate and seedling survival in the field.
Outcome of interactions between genets of two Suillus spp. and different Pinus sylvestris genotype combinations: identity and distribution of ectomycorrhizas and effects on early seedling growth in N‐limited nursery soil
Authors: TIMONEN SARI , TAMMI HANNA , SEN ROBIN
Published: March 2003

summary

The identity of individual ectomycorrhizas, root colonization patterns and early growth responses of interconnected Scots pine (Pinus sylvestris L.) seedlings were investigated following interactions between local genets of Suillus bovinus (L. ex Fr.) O. Kuntze (SBK4b and SBK5b) and S. variegatus (Swartz ex Fr.) O. Kuntze (SVK3b) and different host‐genotype combinations. Three equidistant 39‐d‐old seedlings, in pots that contained sterile N‐limited nursery soil, were each inoculated with one of the three genets in the multiple inoculation treatment (MIT). Single inoculation treatments (SITs), involving inoculation of only one seedling in the triad with one of the three genets, and a similarly configured uninoculated treatment (UIT), were also prepared for comparative analysis. All seedling roots in the inoculated treatments, except for one SIT/SBK4b combination, hosted large numbers (>150) of Suillus‐type ectomycorrhizas after 23–25 wk growth without additional fertilization. Esterase (EST) isozyme analysis of individual ectomycorrhizas from all SIT and MIT combinations enabled efficient interspecific and intraspecific typing of fungal (genet) colonization (89 and 72 %, respectively) and identification of host genotype variation (Z locus polymorphism) at a lower rate (51 %). Species, but not 5. bovinus genet, typing within randomly sampled individual ectomycorrhizas from selected SITs was successful (50–70%) following PCR/RFLP analysis of diagnostic sequences of fungal rRNA genes. In the SITs, only the inoculated fungal genet was detected in ectomycorrhizas on all three seedlings. Roots were predominantly colonized by SBK4b in one, and SBK5b in three, of the MIT combinations, although ectomycorrhizas of the former genet were detected at low frequencies on nearly all seedlings. In the remaining MIT combination, both SBK4b and SVK3b were found to co‐dominate as ectomycorrhizas on the seedling roots. Small numbers of the latter genet were detected in ectomycorrhizas of two SBK5b‐dominated MIT combinations. However, no significant trends in host‐mycorrhiza interactions were detected using a log‐linear analysis. Compared with the UIT, significant positive mycorrhizal plant growth responses, particularly increased needle length, were recorded in all the heavily colonized seedlings in most SIT and all MIT combinations. Intermediate seedling growth was restricted to the one SIT/SBK4b combination where seedlings supported limited numbers of ectomycorrhizas. The general host‐fungal colonization patterns observed provide further below‐ground evidence supporting genet interactions previously detected through sporocarp population analyses in young Scots pine reforestation sites.
Air today – gone tomorrow?
Authors: THOMAS HOWARD
Published: March 2003

This paper discusses ways in which plant metabolism, development and survival influence, and are influenced by, gaseous pollutants. When amino acids are used as carbon and energy sources by plants and other organisms, reduced inorganic nitrogen is released, with wide‐ranging implications for the N cycle. Plants can detect the presence and amounts of deposited N and ozone in the environment, not only by direct metabolic incorporation but probably also via distinct signalling systems. Low‐nutrient communities and ecosystems, such as temperate conifer forest, are often protected against N overnutrition by adaptations that insulate plant metabolism and growth from the fertilizing effects of deposited pollutant N. Changes in ecosystem balance and biodiversity are not related in any simple way to differential injury responses of constituent species. The question of what happens when a particular component of a changing plant community fails is considered in terms of the relationship between phases of development and the turnover of tissues and organisms.
Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability
Authors: NAVAS MARIE‐LAURE , FRIESS NATHALIE , MAILLET JACQUES
Published: March 2003

The study characterized the influence of cucumber mosaic virus (CMV) on the growth response of two annual weeds to nitrogen. Plants were grown individually along a N gradient from 4 to 32 mmol l−1 and data were interpreted using growth analysis. Plant biomass increased with N concentration and was significantly higher for healthy than infected plants at the two highest N concentrations. Healthy plants of Portulaca oleracea L. were characterized by lower biomass allocation to leaves and higher biomass allocation to roots than infected plants; no change in biomass allocation was recorded for Stellaria media Vill. Relative growth rate (rgr), net assimilation rate (nar) and specific leaf area (sla) of plants increased with increasing N concentration. Healthy plants of P. oleracea were characterized by a higher rgr and nar and a lower sla than infected plants, whereas healthy S. media had a higher rgr but a similar nar and sla or leaf weight ratio (lwr) compared with infected plants. The consequences of these results on the population dynamics of weeds and virus spread are discussed.
The effect of fungicides on vesicular–arbuscular mycorrhizal symbiosis. III. The influence of VA mycorrhiza on phytotoxic effects following application of fosetyl‐Al and phosphonate
Authors: SUKARNO N. , SMITH F. A. , SCOTT E. S. , JONES G. P. , SMITH S. E.
Published: March 2003

This study compares the effects of the fungicide Aliette® (fosetyl‐Al) on non‐mycorrhizal and mycorrhizal onion (Allium cepa L.) with effects of the degradation products, aluminium (applied as aluminium chloride) and phosphonate (applied as dimethyl phosphonate). We sought to determine the extent to which the plants absorb and accumulate phosphonate and ascertain why, as shown previously, toxic effects of fosetyl‐Al on mycorrhizal plants are less severe than effects on equivalent non‐mycorrhizal plants.

Fosetyl‐Al markedly reduced growth, especially of roots, and also inhibited mycorrhizal colonization. Dimethyl phosphonate caused smaller effects on growth and did not decrease colonization. Aluminium chloride did not affect growth of non‐mycorrhizal or mycorrhizal plants, or mycorrhizal colonization. In all cases, mycorrhizal plants grew better than equivalent non‐mycorrhizal plants (with no added soil phosphate), and non‐mycorrhizal plants given supplementary soil phosphate grew best.

Concentrations and contents of total P in shoots were increased by dimethyl phosphonate and more so by fosetyl‐Al. Concentrations of P were also increased in roots. 31P nuclear magnetic resonance (NMR) spectroscopy was used to determine relative concentrations of phosphonate and phosphate. Application of fosetyl‐Al led to accumulation of more phosphonate than did application of dimethyl phosphonate, and non‐mycorrhizal plants treated with fosetyl‐Al accumulated much more phosphonate than did equivalent mycorrhizal plants (both with no added soil phosphate). Internal phosphate concentrations increased, especially in mycorrhizal plants, following application of both dimethyl phosphonate and fosetyl‐Al. Non‐mycorrhizal plants given supplementary soil phosphate also showed restricted growth when treated with fosetyl‐Al even though they accumulated phosphate in relatively high amounts and had lower ratios of phosphonate to phosphate, particularly in shoots. In general, high internal concentrations of phosphonate were correlated with large reductions in plant growth among treatments.

Possible causes of these effects include conversion of phosphonate to phosphate in the tissues (especially in mycorrhizal plants), enhanced uptake of phosphate via mycorrhizal fungi and additional accumulation of P in plants with restricted growth. Competition for uptake between phosphate and phosphonate is also discussed.
Changes of enzyme activities associated with the mobilization of carbohydrate reserves (fructans) from the stem of wheat during kernel filling
Authors: WILLENBRINK J. , BONNETT G. D. , WILLENBRINK S. , WARDLAW I. F.
Published: March 2003

Wheat plants were grown at a day/night temperature of 18/13°C under glasshouse conditions. Twenty‐two d after anthesis, one set of plants was shaded to 50% of the normal photon fluence rate, another was ‘degrained’ by selective spikelet removal which left only the grains in the five central spikelets; a further set was left as control. Individual plants were harvested at days 22, 30 or 42 after anthesis. Extracts from the peduncle and the penultimate internode were prepared to determine the activities of sucrose phosphate synthase, sucrose synthase, fructan exohydrolase and acid invertase, and to assess the concentration of hexose sugars, sucrose and fructans. Measurements were also made of ear and individual grain weights, and stem f. wt and d. wt. There was a decline in the amount of fructans with time, more pronounced in ‘shaded’ (source‐limited) than in control plants. By contrast, in ‘degrained’ (sink‐limited) plants, the amount of fructans in the stem initially rose, then decreased, with a concomitant increase in the amount of fructose. The shifts in sugar content of the wheat culm reflected both the sink demand of the ear and source activity. The activity of fructan exohydrolase correlated with the carbohydrate changes. Under limited photosynthate assimilation, the mobilization of fructans from the internodes towards the ear was related to an increase in this enzyme, whereas the other enzymes played a less direct role in the mobilization of fructan reserves from the wheat stem.
The release of genetically engineered micro‐organisms and viruses into the environment
Authors: GIDDINGS GLYNIS
Published: March 2003

This review considers the reasons for, and research governing, the regulation and monitoring of genetically engineered micro‐organisms and viruses (GEMs) released into the environment. The hazards associated with releasing GEMs into the environment are the creation and evolution of new pests and diseases, and damage to the ecosystem and non target species. The similarities and differences between GEMs and conventional micro‐organisms are discussed in relation to risk assessment. Other issues covered include the persistence of micro‐organisms in the environment, transgene dispersal to non‐engineered microbes and other organisms, the effects of transgenes and transformation on fitness, and the evolution of pests and pathogens that are given or acquire transgenes. Areas requiring further research are identified and recommendations for risk assessment made.

CONTENTS

Summary
173

I.
Introduction
173

II.
A comparison of genetically engineered micro‐organisms and viruses and conventional micro‐organisms
174

III.
Persistence in the environment
175

IV.
Transfer of transgenes to other species
176

V.
The evolution of genetically engineered micro‐organisms and viruses and natural micro‐organisms acquiring transgenes
178

VI.
Damage to non‐target species and ecosystem function
178

VII.
Influences on the evolution of other organisms
179

VIII.
Conclusions and discussion
180

References
181
Natural occurrence of ampelomyces intracellular mycoparasites in mycelia of powdery mildew fungi
Authors: KISS LEVENTE
Published: March 2003

This is the first extensive investigation that quantifies natural mycoparasitic relationships in the phyllosphere. The presence of Ampelomyces spp. was quantified in naturally occurring powdery mildew fungi collected in Hungary and Romania between 1992 and 1995. A total of 570 samples was studied representing 27 species (nine genera) of the Erysiphaceae infecting 41 host plant genera. The incidence of Ampelomyces spp., determined as the proportion of samples in which intracellular pycnidia were present, varied between 4.3 and 68.8% in the host fungal genera studied. The intensity of mycoparasitism, defined as a percentage of the powdery mildew mycelia parasitized by Ampelomyces, ranged from 0.15 to 65%. Both the incidence and the intensity of mycoparasitism showed the lowest values in Blumeria graminis (DC.) Speer collected from wild and cultivated monocotyledons, while the highest values were found in Arthrocladiella mougeotii (Lév.) Vassilkov infecting Lycium halimifolium Mill. plants. The paper reports for the first time the natural occurrence of Ampelomyces in Sawadaea bicornis (Wallr.∶Fr.) Homma on maple.
Anatomical characteristics of roots of citrus rootstocks that vary in specific root length
Authors: EISSENSTAT D. M. , ACHOR D. S.
Published: March 2003

Among citrus rootstocks, higher specific root length (SRL, root length/d. wt) has been linked to several specific morphological and physiological traits, including smaller average root diameter, higher root hydraulic conductivity and higher rates of root proliferation. In this study, thickness of the outer tangential exodermal (hypodermal) wall and its suberin layer, number of passage cells, presence of epidermis, and stelar anatomy were examined and related to variation in root diameter of field roots of known maximum age. We also compared root morphology and anatomy of young roots in the field with those of potted rootstock seedlings in the glasshouse. Fibrous roots were measured separately from pioneer (framework) roots. Among the fibrous roots, only the first‐order (root links having a root tip) and second‐order (root links bearing first‐order roots) laterals were examined. Among first‐order field roots, larger root diameter was caused by larger rather than more numerous cells in the cortex. Root diameter of first‐order roots was positively correlated with both number of passage cells in the exodermis and thickness of the secondary walls of the exodermis in both field and potted plants.

Exodermal walls were about 80% thicker in field‐ than pot‐grown roots. In the field, in more than 50% of the first‐order roots examined less than 30% of the root surface was still covered by epidermis, with few differences among rootstocks. In contrast, in roots of 19‐wk‐old glasshouse plants generally 70–100% of the epidermis was still intact. There was no evidence of secondary xylem development in second‐order fibrous roots in the field; in seedling, pot‐grown rootsystems, 75–97% of second‐order roots had formed secondary xylem despite their small diameter (<0.8 mm).

It is argued that there can be suites of physiological, morphological and anatomical traits in roots that co‐vary with specific root length. Investigations of how root morphology and anatomy are linked to root function, moreover, need to recognize trait variability and the potentially important differences between field‐ and pot‐ grown (seedling) roots.
Phragmites die‐back: toxic effects of propionic, butyric and caproic acids in relation to pH
Authors: ARMSTRONG J. , ARMSTRONG W.
Published: March 2003

Symptoms which are associated with die‐back in Phragmites: growth inhibition, root and bud death, premature shoot senescence, blocked aeration and vascular systems, especially in rhizomes and roots, and abnormal surface and internal cell‐wall lignification and suberization of roots were induced by each of three of the lower volatile organic acids, propionic, butyric and caproic. These acids were applied in nutrient media in concentrations similar to those previously associated with die‐back sites and/or in sediments containing rotting rhizomes and roots of the plant. At concentrations of 1.4 and 0.56 mM, respectively, butyric and caproic acids were each found to be highly toxic at pH 4.5, but relatively innocuous at pH 6. Propionic acid, applied at a much higher concentration of 10.4 mM, was highly toxic at both pH 4.5 and 6. The results support previous findings that the undissociated forms of the organic acids are the more toxic. Rhizomes and roots, rotting in water or waterlogged sand, released cocktails of acids and produced pH in the range 4.8–5.4. Phragmites seedlings planted in these media died within 12 h. Overall, the results support the theory that die‐back in Phragmites can be induced and/or perpetuated by organic acids released from the decaying underground parts of the plant or other sources of organic matter.
The influence of dissolved inorganic carbon in the rhizosphere on carbon and nitrogen metabolism in salinity‐treated tomato plants
Authors: CRAMER M. D. , GAO Z. F. , LIPS S. H.
Published: March 2003

The influence of variation in the concentration of dissolved inorganic carbon (DIC) in the form of CO2 and HCO3− in the root media on the C and N metabolism of Lycopersicon esculentum cv. F144 was investigated under both saline and non‐saline conditions. Tomato seedlings were grown in hydroponic culture (pH 6.5) with or without NaCl, and the root solution was aerated with either ambient CO2 (360 μmol mol−1) or CO2‐enriched air (5000 μmol mol−1). Nitrate uptake and root tissue NO3− concentrations were increased slightly by elevated rhizosphere DIC concentrations in both control and salinity‐treated plants. This was associated with 46% higher nitrate reductase activity in the roots of control plants supplied with elevated DIC than in those supplied with ambient DIC. The activity of phosphoenolpyruvate carboxylase (PEPc) in vitro in control and salinity‐treated plants was unaffected by the supply of elevated rhizosphere DIC concentrations. However, PEPc activity in vitro was considerably higher than the rates of PEPc activity in vivo reported previously, indicating that PEPc activity was not in itself a limitation on the provision of anaplerotic C. Therefore elevated DIC concentration in the rhizosphere stimulated the uptake of NO3− and provided alternative C skeletons for the assimilation of the NH4+ resulting from NO3− reduction into amino acids within the roots. Salinity stimulated root glutamine synthetase (GS) activity up to double that in control plants. Furthermore, elevated DIC caused an increase in leaf and root GS activity of control plants while inhibiting GS activity in the roots of salinity‐treated plants. Glutamine∶2‐
oxoglutarate aminotransferase (GOGAT) activity of salinity‐treated plants was doubled by elevated rhizosphere DIC concentrations. These changes in GS and GOGAT activity must reflect changes in amino acid synthesis. Under saline conditions the xylem transport of NO3− is partly blocked and a larger root assimilation develops, requiring not only the transamination of 2‐oxoglutarate to glutamate but also that of oxaloacetate to aspartate and the transamidation of aspartate to asparagine.
Underground starch storage in Erica species of the Cape Floristic Region – differences between seeders and resprouters
Authors: BELL TINA L. , OJEDA FERNANDO
Published: March 2003

Concentrations of starch in roots of seeder species of Erica from the Cape Floristic Region, South Africa were found to be considerably less than in resprouters. Shoot starch was highly variable but mean values were similar in both seeder and resprouter species of Erica. Three distinct patterns of starch storage in roots were recognized. All seeder species fell within definitions of Categories 1 (narrow major and minor parenchymatous rays, one to two cells wide with no inter‐ray storage) or 2 (thick major rays up to seven cells wide and thin minor rays with small amounts of inter‐ray storage) whereas resprouter species were consistently within Categories 2 or 3 (broad major and minor rays, up to eight cells wide and conspicuous inter‐ray starch storage). Results are discussed in light of similar studies of the related Epacridaceae. ‘Mixed’ species (i.e. with seeder or resprouter individuals present, often in distinct populations) were always classified as belonging to Category 2. Studies of populations of three ‘mixed’ species confirmed that seeder forms had consistently lower amounts of root starch than resprouters. Rays of xylem parenchyma were the main sites for starch storage in roots of both seeders and resprouters and greater proportions of cross‐sectional area of roots were consistently devoted to such storage tissues in resprouter forms of the three ‘mixed’ species. Analyses of a number of seeder and resprouter Erica coccinea populations showed that differences in amounts of realised and potential root starch storage are best explained by the effect of regeneration behaviour rather than by among‐population variability.