bluuebunny/crossref_metadata_2025 huggingface dataset:
Axons and glial interfaces: ultrastructural studies*
Authors: Fraher John
Published: March 2003

At most vertebrate nerve transitional zones (TZs) there is a glial barrier which is pierced by axons passing between the CNS and PNS. Myelinated axons traverse this in individual tunnels. The same is true of larger non‐myelinated axons. This holds widely among the vertebrates, for example, the large motor axons of the sea‐lamprey Petromyzon (which also possess TZ specializations not found in mammals). Smaller non‐myelinated axons traverse the TZ glial tunnels as fascicles and so the barriers are correspondingly less comprehensive for them. Accordingly, in nerves composed of non‐myelinated axons, such as the vomeronasal or the olfactory, a TZ barrier stretching across the nerve is effectively absent. The chordate Amphioxus differs from the vertebrates in lacking a TZ barrier throughout. Invertebrates also lack glial barriers at the TZs between ganglia and interconnecting nerve trunks. The glial barrier at the dorsal spinal root TZ (DRTZ) has considerable value for analysing protocols aimed at achieving CNS regeneration, because it provides a useful model of the gliotic reaction at sites of CNS injury. Also, it is especially amenable to morphometric analysis, and so enables objective quantification of different protocols. Being adjacent to the subarachnoid space, it is accessible for experimental intervention. The DRTZ was used to investigate the value of neurotrophin 3 (NT3) in promoting axon regeneration across the TZ barrier and into the CNS following dorsal root crush. It promoted extensive regeneration and vigorous non‐myelinated axonal ensheathment. On average, around 40% of regenerating axons grew across the interface, compared with virtually none in its absence. These may have traversed the interface through loci occupied by axons prior to degeneration. Many regenerating axons became myelinated, both centrally and peripherally.
Regulation of microvascular permeability by vascular endothelial growth factors
Authors: Bates D. O. , Hillman N. J. , Pocock T. M. , Neal C. R.
Published: March 2003

Generation of new blood vessels from pre‐existing vasculature (angiogenesis) is accompanied in almost all states by increases in vascular permeability. This is true in physiological as well as pathological angiogenesis but is more marked during disease states. Physiological angiogenesis occurs during growth states, fat deposition, hair growth and wound repair, as well as during the female reproductive cycle in the endometrium. Pathological angiogenesis is seen in a wide variety of diseases, which include all the major causes of mortality in the west; heart disease, cancer, stroke, vascular disease and diabetes. Angiogenesis is regulated by vascular growth factors, particularly vascular endothelial growth factor (VEGF). These peptides act on 2 specific receptors in the vascular system (VEGF‐R1 and 2) to stimulate new vessel growth. VEGFs also directly stimulate increased vascular permeability to water and large molecular weight proteins. This increased vascular permeability appears to have a minor effect in physiological angiogenesis, but causes considerable damage in pathologies. VEGFs result in cerebral oedema in glioblastoma multiformae, ascites and pleural effusions in liver metastasis and lung cancer, respectively, may contribute to increased lipid deposition in atherosclerosis, substrate formation in neointimal hyperplasia, and neuropathy and nephropathy in diabetes. We have shown in MS222 anaesthetised frogs that VEGFs increase vascular permeability in mesenteric microvessels by stimulation of tyrosine autophosphorylation of VEGF‐R2 on endothelial cells, and subsequent activation of phospholipase C (PLC). This in turn results in increased production of diacylglycerol (DAG) and inositol tris phosphate (IP3). This PLC activation results in increased intracellular calcium through influx of calcium through store independent calcium channels, possibly the TrpC family of calcium channels). It is not known how this results in increased vascular permeability in endothelial cells in vivo. We have shown however, that VEGF can stimulate formation of a variety of pathways through the endothelial cell wall, including transcellular gaps, vesicoluvacuolar organelle formation, fenestrations and intercellular gaps. It is not clear whether these are all part of the same process.
The amounts and deposition patterns of fibrin‐type fibrinoid at the villous surface are altered in pregnancy at high altitude
Authors: Mayhew T. M. , Bowles C. , Yücel F.
Published: March 2003

In pregnancy at high altitude, there is preplacental (hypobaric) hypoxia and intrauterine fetal growth is restricted. Previous studies on placentas from Amerindian and nonindigenous women completing term pregnancies at low (LA; 400 m) and high (HA; 3600 m) altitudes in Bolivia showed that HA placentas had smaller surface areas of villi and smaller volumes of fibrin type fibrinoid (FTF). Recently we devised a stereological method for testing whether perivillous FTF (pFTF) is randomly distributed at the surface of villous trophoblast. Here the method is applied to test 2 experimental hypotheses: [1] deposition of pFTF is nonrandom regardless of altitude and [2] deposition patterns differ between altitudes. Uniform random samples of microscopical fields were drawn from Masson trichrome stained sections and intersection counts used to estimate the surface areas of, and patterns of pFTF on, 4 regions of trophoblast: nonsyncytial knots (nonSK), syncytial knots (SK), syncytial bridges (SB) and denudation sites (DEN). Absolute areas were compared by 2‐way analyses of variance. Expected and observed distributions were compared by (2 and contingency table analyses. At LA the mean (SEM) volume of FTF was 8.4 (1.54) cm3 and villous surface area was 7.0 (0.43) m2. At HA FTF volume was reduced by about 50% (P < 0.01) and villous surface by 20% (P < 0.01). The surface composition of trophoblast in LA placentas was nonSK (91%), SK (5%) and SB and DEN (both less than 3%). Relative surfaces were not significantly altered in HA placentas but, due to the impoverished growth of villi at HA, the changes represented a real decline in absolute surface of nonSK. At HA, the total surface of pFTF on trophoblast decreased by about 40%, from 4430 (564) cm2−2570 (406) cm2 (P < 0.01). At both altitudes pFTF deposition was preferentially found at DEN (12‐fold greater than expected for a random distribution). Pattern differences were detected between altitudes. In HA placentas the amount of pFTF deposited on nonSK regions was about 45% less (P < 0.05); apparent changes on SK and SB regions were not significant. These histometric findings suggest that the coagulation‐fibrinolysis steady state is altered at HA and favours greater fibrinolysis. At least some of the fibrinolytic or anticoagulant activity seems to reside in or on thinner regions of villous trophoblast and the placenta may be a relatively privileged site in terms of fibrinolysis. Also, reduced deposition of pFTF is probably linked to changes in the steady state of trophoblast turnover which seems to be perturbed in HA pregnancies.
Intracellular signalling involved in modulating human endothelial barrier function*
Authors: Van Hinsbergh Victor W. M. , Van Nieuw Amerongen Geerten P.
Published: March 2003

The endothelium dynamically regulates the extravasation of hormones, macromolecules and other solutes. In pathological conditions, endothelial hyperpermeability can be induced by vasoactive agents, which induce tiny leakage sites between the cells, and by cytokines, in particular vascular endothelial growth factor, which increase the exchange of plasma proteins by vesicles and intracellular pores. It is generally believed that the interaction of actin and non‐muscle myosin in the periphery of the endothelial cell, and the destabilization of endothelial junctions, are required for endothelial hyperpermeability induced by vasoactive agents. Transient short‐term hyperpermeability induced by histamine involves Ca2+/calmodulin‐dependent activation of the myosin light chain (MLC) kinase. Prolonged elevated permeability induced by thrombin in addition involves activation of the small GTPase RhoA and Rho kinase, which inhibits dephosphorylation of MLC. It also involves the action of other protein kinases. Several mechanisms can increase endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockage of specific receptors, and elevation of cyclic AMP by agents such as β2‐adrenergic agents. Depending on the vascular bed, nitric oxide and cyclic GMP can counteract or aggravate endothelial hyperpermeability. Finally, inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability‐reducing properties.
The development of the gubernaculum and inguinal closure in the marsupial Macropus eugenii
Authors: Coveney Douglas , Shaw Geoffrey , Hutson John M. , Renfree Marilyn B.
Published: March 2003

This study reports the developmental anatomy of testicular descent and inguinal closure of the tammar wallaby (Macropus eugenii) from birth to maturity. In females the ovary migrated caudally between days 10 and 20 after birth. The gubernaculum differentiates into the round ligament in the abdomen and extra‐abdominally as the ilio‐marsupialis muscle of the mammary glands. In males the testes migrated to the internal inguinal ring by day 20 post partum (pp), coinciding with the enlargement of the gubernaculum, and from the internal inguinal ring to the scrotum between days 20 and 65 pp. During descent there was an increase in the hyaluronic acid concentration in cells of the gubernaculum and scrotum. Development of the cremaster muscle began by day 10 pp on the periphery of the gubernaculum and its basic structure was completed by day 60 pp. After descent the inguinal canal closed between days 50 and 60 pp, but a small irregular lumen persisted, somewhat similar to that seen in the congenital scrotal hydrocoele of humans. Tammars have a hopping mode of locomotion and, like humans, are essentially bipedal. We suggest that inguinal closure evolved in these two species because their upright posture may otherwise lead to a high incidence of inguinal hernias.
The diaphragm: two physiological muscles in one
Authors: Pickering Mark , Jones James F. X.
Published: March 2003

To the respiratory physiologist or anatomist the diaphragm muscle is of course the prime mover of tidal air. However, gastrointestinal physiologists are becoming increasingly aware of the value of this muscle in helping to stop gastric contents from refluxing into the oesophagus. The diaphragm should be viewed as two distinct muscles, crural and costal, which act in synchrony throughout respiration. However, the activities of these two muscular regions can diverge during certain events such as swallowing and emesis. In addition, transient crural muscle relaxations herald the onset of spontaneous acid reflux episodes. Studying the motor control of this muscular barrier may help elucidate the mechanism of these episodes. In the rat, the phrenic nerve divides into three branches before entering the diaphragm, and it is possible to sample single neuronal activity from the crural and costal branches. This review will discuss our recent findings with regard to the type of motor axons running in the phrenic nerve of the rat. In addition, we will outline our ongoing search for homologous structures in basal vertebrate groups. In particular, the pipid frogs (e.g. the African clawed frog, Xenopus laevis) possess a muscular band around the oesophagus that appears to be homologous to the mammalian crural diaphragm. This structure does not appear to interact directly with the respiratory apparatus, and could suggest a role for this region of the diaphragm, which was not originally respiratory.
Regulation of the depth and composition of airway surface liquid
Authors: Widdicombe J. H.
Published: March 2003

The airways are lined with a film of liquid about 10 µm deep that is in two layers. Around the cilia is the watery periciliary sol. Over this is a mucous blanket that traps inhaled particles. The low viscosity of the periciliary sol allows the cilia to beat and propel the mucous blanket to the mouth. In large airways, mucus comes predominantly from the mucous glands but also from goblet cells in the surface epithelium. Water is added to the airway surface by gland secretion that is driven by active Cl secretion by serous cells. During inflammation elevation of the subepithelial hydrostatic pressure may also add significant volumes of water to the airway lumen. Water is removed by active Na transport across the surface epithelium. In airway diseases, the balance is shifted from water secretion to mucus secretion. In bronchitis and asthma this is due mainly to conversion of gland serous to mucous cells. In cystic fibrosis, gland serous cells cannot secrete water because they lack functioning CFTR in their apical membranes (CFTR is the cystic fibrosis transmembrane conductance regulator, a Cl channel that is abundant in serous cells). In all three diseases, the result is secretion of excessively concentrated gland secretions that are poorly moved by the cilia and accumulate. Altered salt and water transport by the surface epithelium may also contribute to the pathology of cystic fibrosis.
Laminar bone as an adaptation to torsional loads in flapping flight
Authors: De Margerie Emmanuel
Published: March 2003

Using a new histometric method, the orientation of primary osteons was measured in the main long bones of adult mallards (Anas platyrhynchos). In the light of previous biomechanical and ontogenetic studies, a functional hypothesis is proposed, explaining the histological differences observed between long bones; laminar bone tissue, mainly found in the wing bones, may be a biomechanical adaptation to torsional loads caused by flapping flight.
Dissolved inorganic carbon utilization and the development of extracellular carbonic anhydrase by the marine diatom Phaeodactylum tricornutum
Authors: IGLESIAS‐RODRIGUEZ M. D. , MERRETT M. J.
Published: March 2003

The presence of extracellular carbonic anhydrase (CA) in relation to medium composition was investigated using cultures of the marine diatom Phaeodactylum tricornutum Bohlin. Large‐volume cultures, with low initial cell inocula were grown on ASP‐2 (no dissolved inorganic carbon (DIC), 550 μM NOa−), f/2 (2–0 mM DIC, 880μM NO3−) and modified f/2 (2.0 mM DIC, 20 μM NO3− media. Cells growing on ASP‐2 showed extracellular CA in the early stages of growth, whereas extracellular CA was not detected until partial depletion of total DIC in the stationary phase for cultures on f/2 or modified f/2. Both HCO3− and CO2 were important in carbon limitation, extracellular CA being present when the free‐CO2 concentration fell below 5 μM, but the HCO3− concentration needed to be below 1 mM. When carbon‐replete cells were transferred to carbon‐limited conditions, extracellular CA was recorded within minutes, the process being light‐dependent and completely inhibited by 3,3,4‐dichlorophenyl‐l, 1‐dimethylurea (DCMU). The addition of DIC to carbon‐limited cells resulted in a rapid decrease in extracellular CA activity. The membrane‐impermeable inhibitor of carbonic anhydrase, dextran‐bound sulphonamide (DBS) was used to inhibit extracellular CA activity in relation to photosynthetic rate in carbon‐replete and carbon‐limited cells. At the lowest DIC concentration (O'lOniM), for cells with maximum external CA activity, DBS gave over 80% inhibition of the photosynthetic rate, demonstrating the key role of external CA in maintaining high photosynthetic rate under conditions of carbon limitation.

It is proposed that the key factor in the regulation of extracellular CA activity is the total Hux of inorganic carbon (C.) into the cell. This determines the Ci, flux into the chloroplast and when this is inadequate to support the photosynthetic rate attained by a carbon‐replete chloroplast at optimum photon flux density, extracellular CA is activated. This mechanism would explain the observed interaction of CO2 and HCO3− in the regulation of extracellular CA activity.
Involvement of the outer membrane lipopolysaccharides in the endophytic colonization of tomato roots by biocontrol Pseudomonas fluorescens strain WCS417r
Authors: DUIJFF BEN J. , GIANINAZZI‐PEARSON VIVIENNE , LEMANCEAU PHILIPPE
Published: March 2003

Previous studies demonstrated the role of the O‐antigenic side chain of the outer membrane lipopolysaccharides of Pseudomonas fluorescens strain WCS417r in its ability to induce resistance against fusarium wilt disease. The present study compared the colonization of tomato roots (Lycopersicon esculentum Mill.) by P. fluorescens strain WCS417r with that of a mutant of this strain, lacking the O‐antigenic side chain of its outer membrane lipopolysaccharides (OA −). Special attention was paid to colonization within root tissues and changes of the root ultrastructure induced by the bacterial strains. Experiments were performed with tomato plants rooted in rock wool and tomato seedlings grown on agar. Numeration of colony‐forming units showed that wild‐type strain WCS417r colonized the root interior of tomato grown in rock wool to a higher extent than its OA− mutant B4, whereas colonization of the rhizoplane did not differ between the two. Light microscopy observations of cross sections of roots grown on agar showed that (i) colonization of the root interior by both wild‐type and OA− mutant was inter‐ and intracellular, (ii) colonization of the internal root tissues mainly occurred if the Pseudomonas strains were inoculated at sites of lateral root emergence, (iii) the wild type colonized the root interior more frequently than did its OA− mutant. Thickening of the cortical cell walls, in reaction to the bacterial colonization of epidermal or hypodermal cells, or cortical intercellular spaces, suggested that local defence reactions of the plant occurred. Altogether, these results indicate the involvement of the O‐antigenic side chain of the outer membrane lipopolysaccharides in the endophytic colonization of the tomato root by P. fluorescens, WCS417r, and lead us to hypothesize that induction of disease resistance by strain WCS417r might be related to the extent of colonization of the internal root tissues.
Epicuticular wax of subarctic Scots pine needles: response to sulphur and heavy metal deposition
Authors: TURUNEN M. , HUTTUNEN S. , PERCY K. E. , McLAUGHLIN C. K. , LAMPPU J.
Published: March 2003

summary

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) needles to dry‐ and wet‐ deposited sulphur and heavy metals was investigated at six sites located 10–110 km from the Monchegorsk Cu‐Ni smelter on the Kola Peninsula, North‐West Russia, and in a long‐term irrigation experiment where pines were exposed over four growing seasons (1991–1994) to either acid rain treatment at pH 3.1 (H2SO4), metal treatment at pH 5.7 (Cu and Ni) or a combination of these at pH 3.1. Needle wettability exhibited a closer relationship with epistomatal wax tube distribution (WTD) than with chemical composition of epicuticular wax. Water droplet contact angles (DCA) decreased towards the smelter, and significant differences due to site were noted for 26‐month‐old and 38‐month‐old needles. Significant differences due to site were determined for secondary alcohols, dehydroabietic acid and hydroxy fatty acids, the proportions of which ranged from 22–5 to 48.9%, 6.2 to 224% and 0.6 to 2.6% respectively, depending on site and needle age class. The proportion of dehydroabietic acid increased towards the smelter, but no gradient was observed in the proportion of secondary alcohols or hydroxy fatty acids. No major effect of experimentally applied pollutants on the chemical composition or structure of the epicuticular wax was observed. The effect of treatment on DCA was significant in 1993 and 1994 due to a 6.5–13.2 degree greater wettability of the 37–49–month‐old acid‐treated needles relative to the irrigated or dry controls. Sulphuric acid at pH 3.1 did not increase needle wettability when combined with copper and nickel sulphate in similar concentrations. These data indicate that S deposition, especially H2SO4, plays a more important role in needle surface deterioration than Cu and Ni. Pollutant‐induced changes in epicuticular wax structure and needle wettability mimic natural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant‐induced metabolic changes in elongating needles.
Rise of fructan exohydrolase activity in stubble of Lolium perenne after defoliation is decreased by uniconazole, an inhibitor of the biosynthesis of gibberellins
Authors: MORVAN ANNETTE , CHALLE GAËLLE , PRUD'HOMME MARIE‐PASCALE , LE SAOS JOËLLE , BOUCAUD JEAN
Published: March 2003

The objectives of this study were (i) to evaluate the relative involvement of fructans from leaf sheaths and from elongating leaf bases to regrowth after defoliation of Lolium perenne L. by following fructan exohydrolase (FEH), sucrose‐sucrose fructosyl transferase (SST) and invertase (INV) activities and (ii) to examine whether gibberellins could be implicated in regulation of FEH activity. In stubble, 36% of fructans are located in leaf bases and 64% in leaf sheaths. During the first phase of regrowth, the depletion of carbohydrates was mainly due to the decline of fructans, which represented 76% and 50% of the carbohydrates mobilized from leaf sheaths and elongating leaf bases respectively. Despite a decrease in protein content, FEH activity increased 2·5‐fold in leaf sheaths and six‐fold in elongating leaf bases, so that the fructan‐hydrolysing activity was four times higher in growing leaves than in leaf sheaths, 2 d after defoliation. INV activity also increased, whereas the pattern of SST activity was inversely related to the variations of both hydrolysing activities. SST activity, which is highest in growing leaves, declined approximately threefold in leaf sheaths and elongating leaf bases at the beginning of regrowth.

The increase in activity of FEH in stubble was strongly inhibited by an inhibitor of the biosynthesis of gibberellin, uniconazole. FEH activity was decreased to c. 67%, 45% and 33% of the level in nontreated plants 24, 48 and 72 h following defoliation, respectively. The inhibition could be overcome by a subsequent treatment with gibberellic acids (GAs). For the first time, data are provided to support the view that GAs might play a role in the regulation of FEH activity, and the implication of this result is discussed.
Actinorhizal symbioses and their N2 fixation
Authors: HUSS‐DANELL KERSTIN
Published: March 2003

summary

More than 200 angiosperms, distributed in 25 genera, develop root nodule symbioses (actinorhizas) with soil bacteria of the actinomycetous genus Frankia. Although most soils studied contain infective Frankia, cultured strains are available only after isolation from root nodules. Frankia infects roots via root hairs in some hosts or via intercellular penetration in others. The nodule originates in the pericycle. The number of nodules in Alnus is determined by the plant in an autoregulated process that, in turn, is modulated by nutrients such as nitrogen and phosphate. Except in the genera Allocausarina and Casuarina, Frankia in nodules develops so‐called vesicles where nitrogenase is localized. Sporulation of Frankia occurs in some symbioses. As a group, actinorhizal plants show a large range of anatomical and biochemical adaptations in order to balance the oxygen tension near nitrogenase. In symbioses with well aerated nodule tissue like Alnus, the vesicles have a multilayered envelope composed mainly of lipids, bacterio‐hopanetetrol and their derivatives. This envelope is assumed to retard the diffusion of oxygen into the nitrogenase‐containing vesicle. In symbioses like Casuarina, the infected plant cells themselves, rather than Frankia, appear to retard oxygen diffusion, and high concentrations of haemoglobin indicate an infected region with a low oxygen tension. At least in Alnus spp., ammonia resulting from N2 fixation is assimilated by glutamine synthetase in the plant. The carbon compound(s) used by Frankia in nodules is not yet known. Nitrogenase activity decreases in response to a number of environmental factors but recovers upon return to normal conditions. This dynamism in nitrogenase activity is often explained by loss and recovery of active nitrogenase and has been traced to loss and recovery of the nitrogenase proteins themselves. Recovery is partly due to growth of Frankia and to development of new vesicles in the Alnus nodules. In the field, varying conditions continuously affect the plants and the measured rate of N2 fixation is a result not only of the conditions prevailing at the moment but also of the conditions experienced over preceding days. N2 fixed by actinorhizal plants is substantial and actinorhizal plants have great potential in soil reclamation and in various types of forestry. Several species are also useful in horticulture.

CONTENTS

Summary
375

I.
Introduction
376

II.
The partners of actinorhizal symbioses
377

III.
Root nodules
380

IV.
Nitrogen fixation and related processes
385

V.
Environmental effects on nitrogen fixation
389

VI.
Ecological role
397

VII.
Concluding remarks
398

Acknowledgements
398

References
398
Multiple tolerance and co‐tolerance to heavy metals in Silene vulgaris: a co‐segregation analysis
Authors: SCHAT HENK , VOOIJS RIET
Published: March 2003

summary

Plants from metalliferous soils often exhibit combined tolerance to different heavy metals. Such tolerance could rely either on the possession of a combination of different metal‐specific tolerance mechanisms (‘multiple tolerance’), or on less specific mechanisms that pleiotropically confer tolerance to different metals (‘co‐tolerance’). In this study, we examined the co‐segregation of tolerances to Cu, Zn, Ni, Co and Cd in crosses between distinctly tolerant ecotypes of Silene vulgaris (Moench) Garcke. The results demonstrate non‐pleiotropic genetic control of tolerance to Cu, Zn and Cd. Tolerance to Ni and Co, on the other hand, seems to represent the pleiotropic byproduct of the tolerance allele of one particular locus for zinc tolerance.
From phenotype via QTL to virtual phenotype in Microseris (Asteraceae): predictions from multilocus marker genotypes
Authors: BACHMANN KONRAD , HOMBERGEN ERIK‐JAN
Published: March 2003

summary

Microseris douglasii (DC.) Sch.‐Bip. and M. bigelovii (Gray) Sch.‐Bip. are two small annual autogamous species of Compositae with nearly non‐overlapping distribution ranges in Western North America. Specifically, M. bigelovii occurs directly along the Pacific coast, whilst M. douglasii has an inland distribution including patches of serpentine soil. Both species are variable, and artificial hybrids between them vary widely in fertility depending on the individual parents. Segregating offspring of one hybrid (strain H27) is being used to analyse the genetic basis of characters differentiating the two species by QTL mapping with RAPDS and ALFPs as molecular markers. Technical problems with mapping dominant markers in a wide cross will be briefly listed and QTL analysis will be discussed. For the genetic analysis of physiological characters, the precise definition of the characters is crucial and the methods of scoring or measuring phenotypes in different environments eventually require more time and effort than the molecular characterization. We are establishing recombinant inbred lines to provide material for more complex physiological analyses requiring several plants per genotype. An increasing number of characters is being studied in this cross, and the possibility of shared pleiotropic QTLs is high. The potential number of QTL genotypes by far exceeds the number of actual genotypes in these lines. We are characterizing the gene interactions as closely as possible and making quantitative genetic models to predict the genotypes corresponding to all possible genotypes. These predictions are converted via computer modelling into an increasingly realistic three‐dimensional representation of the growing plant useful for a simulation of plant evolution.
Dissecting drought‐ and cold‐tolerance traits in the Lolium–Festuca complex by introgression mapping
Authors: HUMPHREYS MIKE , THOMAS HUW‐MARTIN , HARPER JOHN , MORGAN GARETH , JAMES ANEURIN , GHAMARI‐ZARE ABBAS , THOMAS HENRY
Published: March 2003

summary

Recent advances in the cytogenetics of the Lolium–Festuca complex provide new opportunities for understanding and manipulating complex physiological mechanisms such as drought and cold resistance. This paper describes breeding programmes involving hybrids between two species: L. multiflorum, which offers good early growth and high nutritive value, and F. arundinacea, which is more stress tolerant. The programmes are designed to allow a rapid recovery of the Lolium genome and to restrict numbers of recombinants derived from Festuca. Use of genomic in situ hybridization (GISH) and an isozyme marker demonstrates how gene complexes from any part of the Festuca genome can be introgressed into Lolium. This enables us to construct genotypes combining desirable traits of both Lolium and Festuca species. By introgressing different Festuca genes into Lolium, quantitative traits such as tolerance to drought and cold can be ‘dissected’ into their different components, to clarify their function. Festuca genes for stress tolerance can be located by genomic in situ hybridization (GISH) and assigned to regions of chromosome arms in Lolium. Two Lolium genotypes are described, in which genes for drought resistance transferred from the F. pratensis sub‐genome of F. arundinacea onto chromosome 2 of Lolium. The two drought‐resistant lines have the high water conductance of Festuca on their adaxial leaf surface and the low abaxial conductance of Lolium. The paper also describes how androgenesis of L. multiflorum×F. arundinacea hybrids has led to the selection and characterization of genotypes with coacclimation to drought and freezing stress, in some cases exceeding that in the Festuca parent.
Growth and fruiting of tomato as influenced by elevated carbon dioxide and ozone
Authors: REINERT RICHARD A. , EASON GWEN , BARTON JEFFORY
Published: March 2003

summary

‘Tiny Tim’ tomato plants were exposed to five CO2 treatments (375 (ambient), 450, 525, 600 or 675 μmol mol−1) in combination with 03 (0 or 80 nmol mol−1. Biomass was evaluated following 3,5,7 and 13 wk exposure. Biomass following 13 wk exposure also included weekly harvests of mature tomato fruit beginning week 8. Carbon dioxide enrichment significantly enhanced total vegetative plant d. wt at each harvest, as well as cumulative yield of mature fruit, whereas O3 significantly suppressed total vegetative plant d. wt at each harvest and reduced total cumulative fruit yield. The magnitude of these changes varied with the development of tomato from early growth to mature fruit yield. Carbon dioxide enrichment reduced the detrimental effects of O3 on total vegetative plant d. wt of tomato following 3, 5, 7 and 13 wk exposure. Final mature fruit yield was 24% higher under enriched GO2 treatments than in ambient CO2. Ozone suppressed final yield by 31%, following exposure to 80 nmol mol−1 O2, when compared with exposure to charcoal‐filtered (CF) air. The impacts of both CO2 and O3 on yield were, however, dependent upon the presence or absence of the other gas. In the absence of O3, yields were very similar for the ambient and elevated CO2 treatments, but in the presence of O3, yields under ambient CO2 were greatly suppressed whereas yields under elevated CO3 were similar to those in the absence of O3. Thus, enriched CO2 ameliorated most of the suppressive effect of O3 on yield of mature fruit.
Colonization of tomato root by a non‐pathogenic strain of Fusarium oxysporum
Authors: OLIVAIN CHANTAL , ALABOUVETTE CLAUDE
Published: March 2003

summary

A strain of non‐pathogenic Fusarium oxysporum Schlecht. emend, Snyd. & Hans. has been selected for its capacity to reduce the incidence of Fusarium wilt of tomato. Among the possible modes of action of this strain, competition with the pathogen for the colonization of the root surface and tissues has been proposed. In order to study the pattern of root colonization, young Lycopersicon etculentum Miller (tomato) plants grown in a nutrient solution were inoculated by a suspension of F. oxysporum microconidia and processed at time‐intervals for microscopic observations. The fungal strain was transformed with the Gus reporter gene to facilitate the observations. Within 24 h of inoculation the root surface was colonized by a dense network of hyphae, with the exception of the apex, which was colonized only after 48 h. A few hyphae were observed penetrating into the epidermis, leading to the internal colonization of the root cortex. This colonization was always discontinuous, since defence reactions of the plant limited the extension of the fungus. The barrier formed by thickenings and coilings of the cell walls and hypertrophied cells was most frequently observed in the external cortex and, sometimes, deeper in the internal cortex, close to the vessels which were never colonized. Typical defence reactions such as wall appositions, intercellular plugging and intracellular osmiophilic deposits, were frequently observed. This is the first report, based on microscopic observations, of the capacity of a non‐pathogenic strain of F. oxysporum to colonize roots of tomato.
Role of auxin and gibberellin in regenerative differentiation of tracheids in Pinus pinea seedlings
Authors: KALEV NATALIE , ALONI RONI
Published: March 2003

A new experimental system was developed for studying the hormonal mechanisms which control tracheid differentiation. In this system the tracheids redifferentiated from parenchyma cells in the hypocotyl of young Pinus pinea L. seedlings. The experimentally induced tracheids have unique shapes and patterns, and are therefore easily distinguished from the primary and secondary tracheids formed before the experiments. Auxin (0·1–1% NAA) alone sufficed to cause the redifferentiation of short tracheids, usually in discontinuous patterns across the hypocotyl. Gibberellin by itself did not induce redifferentiated tracheids. Combinations of auxin with gibberellin (0·1% NAA+0·1–1% GA3) promoted the differentiation of long tracheids (up to threefold greater than those induced by auxin) in continuous patterns along the stem axis. Gibberellin in the presence of auxin promoted tracheid elongation by stimulating intrusive growth of both the upper and lower ends of the differentiating tracheids. The role of auxin and gibberellin in controlling the evolution of tracheary elements, from tracheids to vessels and fibres, is discussed.
Effect of physical conditions on the spatial and temporal dynamics of the soil‐borne fungal pathogen Rhizoctonia solani
Authors: OTTEN W. , GILLIGAN C. A.
Published: March 2003

The transmission of infection by many soil‐borne fungal parasites of plants depends on the ability of the fungus to grow on or through soil. Progress in analysing the effects of soil physical factors on the temporal and spatial dynamics of fungal growth has been hindered by technical difficulties of quantifying fungal biomass in soil and heterogeneity in soil properties. In this paper we use a combination of a monoclonal antibody‐based immunosorbent assay and microscopy to analyse the effects of soil physical properties on the spatial and temporal dynamics of colonies of the economically important fungus Rhizoctonia solani Kühn growing in two dimensions and three dimensions in a sand. Combinations of different particle‐size distributions and matric potential are used to manipulate the air‐filled pore volume and pore‐size distribution independently of each other. Temporal dynamics are measured by the change in fungal biomass over time whereas spatial dynamics relate to fungal spread and are measured by the colony size, the rate of colony expansion and the biomass distribution within colonies. We show that the fungus spreads more than three times further over surfaces than through sand, even though the same amount of biomass is produced in each case. Pore‐size distribution and air‐filled pore space both affected the extent and rate of fungal spread in three dimensions within sand, with more rapid and extensive spread in a coarse sand compared with a fine sand at identical air‐filled pore volume. The spread of fungal hyphae along surfaces was affected neither by differences in surface texture nor by air‐filled volume, and was substantially more homogeneous than for three‐dimensional spread. We argue that the relative impermeability of sand surfaces to penetration by hyphae might be influenced by the ability of the fungus to branch within a confined space rather than simply to penetrate the pores. The broader epidemiological and ecological consequences of preferential spread by parasitic and saprophytic fungi along surfaces rather than through the dense soil volume are discussed.
Multiple‐host fungi are the most frequent and abundant ectomycorrhizal types in a mixed stand of Douglas fir (Pseudotsuga menziesii) and bishop pine (Pinus muricata)
Authors: HORTON THOMAS R. , BRUNS THOMAS D.
Published: March 2003

The ectomycorrhizal fungal associations of Douglas fir (Pseudotsuga menziesii D. Don) and bishop pine (Pinus muricata D. Don) were investigated in a mixed forest stand. We identified fungi directly from field‐collected ectomycorrhizal (ECM) root tips using PCR‐based methods. Sixteen species of fungi were found, of which twelve associated with both hosts. Rhizopogon parksii Smith was specific to Douglas fir. Three other species colonized only one of the hosts, but were too infrequent to draw conclusions about specificity. Seventy‐four percent of the biomass of ECM root tips sampled in the stand were colonized by members of the Thelephoraceae and Russulaceae. All 12 species of fungi that associated with both tree species did so within a 10×40 cm soil volume, suggesting that individual fungal genotypes linked the putatively competing tree hosts.
Changes in root hydraulic conductance (KR) of Olea oleaster seedlings following drought stress and irrigation
Authors: LO GULLO MARIA A. , NARDINI ANDREA , SALLEO SEBASTIANO , TYREE MELVIN T.
Published: March 2003

Quasi‐steady‐state measurements of root hydraulic conductance (KR) of Olea oleaster Hoffmgg. et Link potted seedlings were performed using a pressure chamber with the aim of: (a) measuring the impact of different water‐stress levels on a KR; (b) measuring the kinetics of KR recovery several days after soil rewetting; (c) relating changes in KR to changes in root anatomy and morphology. Increasing water‐stress was applied in terms of ratio of leaf water potential (ΨL) measured at midday to that at zero turgor (ΨTLP), i.e. ΨL/ΨTLP=0·5, 1·0, 1·2, 1·6; KR was measured initially and at 24, 48, 72, 96 h after irrigation.

Values of KR in seedlings stressed to ΨL/ΨTLP=1·2 increased for 48 h after irrigation from 0·23 to 0·97×10−5 kg s−1 m−2 MPa−1 i.e. from 16% to 66% of that measured in unstressed seedlings. A marked shift of the x‐axis intercept of the straight line relating flow to pressure (zero flow at non‐zero pressure) was recorded initially after irrigation and persisted up to 48 h. Recovery of KR occurred within 24 h after irrigation in seedlings at ΨL/ΨTLP=0·5 and 48 h later in those at ΨL/ΨTLP=1·0.

Severe drought stress (ΨL/ΨTLP=1·6) caused anatomical changes to roots which formed a two‐layered exodermis with thicker suberized walls and a three‐ to four‐layered endodermis with completely suberized tangential walls. Recovery of KR in these roots required resumed growth of root tips and emergence of new lateral roots.
Plant hybridization
Authors: RIESEBERG LOREN H. , CARNEY SHANNA E.
Published: March 2003

Most studies of plant hybridization are concerned with documenting its occurrence in different plant groups. Although these descriptive, historical studies are important, the majority of recent advances in our understanding of the process of hybridization are derived from a growing body of experimental microevolutionary studies. Analyses of artificially synthesized hybrids in the laboratory or glasshouse have demonstrated the importance of gametic selection as a prezygotic isolating barrier; the complex genetic basis of hybrid sterility, inviability and breakdown; and the critical role of fertility selection in hybrid speciation. Experimental manipulations of natural hybrid zones have provided critical information that cannot be obtained in the glasshouse, such as the evolutionary conditions under which hybrid zones are formed and the effects of habitat and pollinator‐mediated selection on hybrid‐zone structure and dynamics. Experimental studies also have contributed to a better understanding of the biology of different classes of hybrids. Analyses of morphological character expression, for example, have revealed transgressive segregation in the majority of later‐generation hybrids. Other studies have documented a high degree of variability in fitness among different hybrid genotypes and the rapid response of such fitness to selection – evidence that hybridization need not be an evolutionary dead end. However, a full accounting of the role of hybridization in adaptive evolution and speciation will probably require the integration of experimental and historical approaches.

CONTENTS

Summary
599

I.
Introduction
599

II.
Concepts and terminology
600

III.
Historical background
600

IV.
Studies of experimental hybrids
601

V.
Experimental manipulations of natural hybrid populations
609

VI.
The biology of different classes of hybrids
612

VII.
Conclusions and future research
619

Acknowledgements
620

References
620
Seasonal changes of leaf surface contamination in beech, oak, and ginkgo in relation to leaf micromorphology and wettability
Authors: NEINHUIS C. , BARTHLOTT W.
Published: March 2003

The leaf surfaces of beech, oak and ginkgo have been investigated with respect to contamination with particles during one growing season. Based on the observation that particles are removed from water‐repellent leaves by rain (Lotus effect) the three species were selected because they differ in leaf surface micromorphology and wettability. Leaves of beech are smooth, lacked wax crystals and were ±wettable. Those of ginkgo were rough because their cells were convex and were densely covered by wax crystals, resulting in permanent water repellency. Leaves of oak were covered by waxes and were water repellent when young, but, a few weeks after leaf expansion had ceased the waxes were rapidly eroded. These differences in wettability resulted in different amounts of contamination. Ginkgo collected a very small number of particles during the whole vegetation period. In beech the contamination was significantly higher, but fairly constant, whereas oak leaves accumulated particles with age.
Sink to source transition in developing leaf blades of tall fescue
Authors: BRÉGARD A. , ALLARD G.
Published: March 2003

This study aims to characterize the translocation of photosynthates within and from developing tall fescue (Festuca arundinacea) leaves at the time of transition from sink to source. The developing leaf contains a source, the exposed tip, and a sink, the growing basal portion. When the exposed tip of the developing blade is labelled with 14CO2, it exports photosynthates exclusively to sinks within the developing blade until the blade reaches 80% of its final length, when photosynthates begin to be exported from the blade and pass through the collar to reach the growing sheath and the next expanding leaf. Concurrently, the previous mature leaves reduce their level of photosynthate export to the developing blade; export stops as soon as the sheath of the developing leaf elongates beyond 10 mm. Export from the mature leaves to the growing sheath and to the next expanding leaf blade increases rapidly. Thus, in a developing tall fescue leaf blade photosynthate importation and exportation are exclusive events: the expanding blade imports photosynthate from mature leaves until it reaches 80% of its final length, then exportation begins and importation ceases.
Influence of an arbuscular mycorrhizal fungus on Pseudomonas fluorescens DF57 in rhizosphere and hyphosphere soil
Authors: RAVNSKOV SABINE , NYBROE OLE , JAKOBSEN IVER
Published: March 2003

The influence of Glomus intraradices (BEG87) on Pseudomonas fluorescens DF57 in hyphosphere and rhizosphere soil was examined. Cucumis sativus (Aminex, F1 hybrid) was grown in symbiosis with the arbuscular mycorrhizal fungus G. intraradices in PVC tubes, consisting of a central root compartment and two lateral root‐free compartments. Two Tn5‐luxAB‐marked strains of P. fluorescens DF57 were used. Strain DF57‐P2, which has an insertion of Tn5∶∶luxAB in a phosphate starvation‐inducible locus, was used as a phosphate starvation reporter. Another lux‐tagged strain DF57‐40E7, which carries a constitutively expressed luxAB fusion, was used as control for strain DF57‐P2 and for measuring the metabolic activity of P. fluorescens DF57. A strain of P. fluorescens DF57, which carries a constitutively expressed gfp gene, was used in studies of attachment between the bacteria and the hyphae. G. intraradices decreased the culturability of P. fluorescens DF57 significantly, both in rhizosphere and hyphosphere soil, whereas the total number of P. fluorescens DF57 measured by immunofluorescence microscopy was decreased in hyphosphere soil only. G. intraradices did not induce a phosphorus starvation response in P. fluorescens DF57, and the metabolic activity of the bacteria was not affected by the fungus after 48 h. P. fluorescens DF57 did not attach to G. intraradices hyphae and was not able to use the hyphae as carbon substrate. The negative effect of G. intraradices on culturability and on number of P. fluorescens DF57 in hyphosphere soil is discussed.
Partitioning of sugars in Lolium perenne (perennial ryegrass) during drought and on rewatering
Authors: THOMAS HENRY , JAMES ANEURIN R.
Published: March 2003

Simulated swards of perennial ryegrass (Lolium perenne) growing in 1‐m3 soil blocks in the glasshouse were either well watered or deprived of water for 57 d and then rewatered. The first aim was to measure effects of drought on sugar (water‐soluble carbohydrate) composition of laminae and sheaths of mature laminae, and bases and laminae of young (growing) leaves. The second aim was to use pulse labelling with 14CO2 to follow the partitioning of recently‐fixed assimilates, and the assembly and consumption of reserve sugars (fructans). Over the last 7 d of drought growth almost stopped, old leaves died faster than they were replaced, and total sugar (which had doubled in concentration during drought) was rapidly consumed. Leaf laminae had lower content of total sugars and of large fructan (DP>5) than did growing bases and sheaths. Drought greatly reduced the rate at which sugar was exported from the laminae to the sheaths and growing leaf bases, and the rate at which it was converted to fructan. Nevertheless, fructan accumulated over the first 50 d of drought. Rewatering did not result in depolymerization and remobilization of sugars that had been formed during the last 7 d of drought, but stimulated their further assembly into high‐DP fructans. Our hypothesis, that accumulation of neo‐kestose (a DP‐3 fructan) in droughted laminae was a symptom of sugar remobilization just before death, was disproved. It is concluded that sugar reserves contribute to drought resistance only under extreme conditions. The specific role of fructan in dry environments might be to improve regrowth when drought is relieved, rather than to enhance growth during drought.