bluuebunny/crossref_metadata_2025 huggingface dataset:
Early processes involved in host recognition by arbuscular mycorrhizal fungi
Authors: GIOVANNETTI MANUELA , SBRANA CRISTIANA , LOGI CABLE
Published: April 2006

Plant species that are hosts of non‐arbuscular mycorrhizas were utilized to investigate the early processes involved in host recognition by arbuscular mycorrhizal fungi. The roots of plant hosts of ecto‐, arbutoid and ericoid mycorrhizas, as well as those of non‐mycorrhizal species, did not elicit the differential morphogenesis that occurred in the hyphae ofGlomus mosseae(Nicol. & Gerd.) Gerd. & Trappe when challenged with the roots of its hosts. In the absence of this morphogenetic response, infection structures were not formed, any further step in the recognition process was hindered, and defence reactions did not occur. The ability of arbuscular mycorrhizal fungi to discriminate their specific hosts from alt other plant species through a recognition process is probably determined by chemical signals.
Sinuous ordinary epidermal cells: behind several patterns of waviness, a common morphogenetic mechanism
Authors: PANTERIS E. , APOSTOLAKOS P. , GALATIS B.
Published: April 2006

Morphogenesis of sinuous epidermal cells in leaves of the fern Asplenium nidus and the monocotyledonous Cyperus papyrus, petals of the dicotyledonous Begonia lucerna. and in‐vitro‐grown leaves of the fern Adantum capillus‐veneris is controlled by the local differentiation of their walls. In all these cases wall pads, including radial cellulose microfibrils, arc deposited at the junctions of the external periclinal wall with the anticlinal ones. Moreover, in Asplenium nidus, similar wall pads form at the junctions of the internal periclinal wall with the anticlinal ones. The wall pads are connected to anticlinal cellulose microfibril bundles running the whole depth of the anticlinal walls nr part of it. This wall differentiation imposes a highly controlled cell wall expansion, a consequence of which is the waviness of the epidermal cell anticlinal, walls. The pattern of wall reinforcement varies among different species, resulting in differences in the pattern of waviness. Cortical microtubule arrays mirror the orientated deposition of cellulose microfibrils in the epidermal Cells.

These findings, derived from plants from different major groups, show a common epidermal cell morphogenetic mechanism depending on radial cellulose microfibrils and cellulose microfibril bundles. The facts that (a) epidermal cell morphogenesis in Adiantum copillus‐veneris leaves grown in vitro differs considerably from that of typical leaves and (b) petal epidermal cells in Begonia lucerna are sinuous, while leaf epidermal cells are not, suggest that this mechanism may he affected by epigenetic factors.
First evidence of myrmecochory in fleshy‐fruited shrubs of the Mediterranean region
Authors: ARONNE G. , WILCOCK C. C.
Published: April 2006

In the mediterranean ecosystems of South Africa and Australia, the role of ants in the dispersal of seeds is well known and antagonistic interactions as well as myrmecochory occur. The high prevalence of seed dispersal by ants, relative so that by vertebrates, is viewed as evidence of adaptation to the nutrient poor soils typical of these environments. Ant dispersal has been considered unimportant in the Mediterranean region and, until now, no systematic study of ant‐seed interaction has been undertaken.

In the Mediterranean shrubland of Southern Italy the seed content of functioning nests of the antMessor minor(André) has been quantitatively analyzed. The existence in the nest of seeds from shrub species, as well as those of the Fabaceae and Poaceae, suggest that ant dispersal may be much more widespread in the Mediterranean environments than has been realized. A large proportion of the seeds came from fleshy‐fruited shrub species previously reported to be bird dispersed, e.g.Rhamnus alaternusL.,Myrtus communisL.,Smilax asperaL.,Pistacia lentiscusL. andPhillyrea latifoliaL. Analysis of nest mounds showed that, although many seeds bad been partially predated by the ants, a very large number had been collected, transported to the nest and subsequently removed to the mound without damage.

Examination of the structure of the fruits and seeds ofR. alaternusandM. communis, and summer fruiting phenology ofR. alaternus, provided further evidence of specific adaptation to ant dispersal. The presence of an elaiosome on the seed is reported for the first time in both specific. Feeding trials showed that ants selectively remove specific diaspores, preferentially collecting the seeds with the elaiosome.
Predicting leaf gas exchange and δ13C responses to the past 30000 years of global environmental change
Authors: BEERLING D. J.
Published: April 2006

summary

Theoretical developments in our understanding of leaf gas exchange processes and carbon isotope composition (δ13C) mean that it should now be possible to model their responses to global environmental change. Such a model would be of use for process‐based interpretations of historical changes in leaf δ13C and for understanding the global stable carbon isotope balance. This paper describes the development and validation of a model towards this aim. The resulting model is used to simulate changes in leaf photosynthesis, stomatal conductance and δ13C of limber pine (Pinus flexilis) in response to the past 30000 y of global environmental change. The predictions of needle δ13C are in line with reported measurements of δ13C from fossilized Pinus flexilis needles preserved in packrat middens in western USA. Leaf gas exchange predictions show that the increased water use efficiency (WUE) of these trees growing in present‐day environments, relative to the past, was brought about through an increase in photosynthetic rates and a decrease in stomatal conductance. This contrasts with the explanation of the recent (past 200 y) increase in the WUE of temperate and Mediterranean ecosystems inferred from δ13C measurements which are predicted by the model to have arisen largely by a decrease in stomatal conductance in response to increases in the concentration of atmospheric CO2 since the pre‐industrial era.

The model as described offers the potential to contribute to our understanding of vegetation effects on the global carbon isotope balance during the glacial periods, and therefore to provide a further constraint on the carbon cycle models used to explain the low concentrations of atmospheric CO2 at these times.
Effect of nitrogen supply on frost hardiness in Calluna vulgaris (L.) Hull.
Authors: CAPORN S. J. M. , RISAGER M. , LEE J. A.
Published: April 2006

summary

Frost hardiness in Calluna vulgaris (L.) Hull, which had received ammonium nitrate applications in the field for 30 months, was assessed using scores of visible injury and measurements of the rate of total electrolyte leakage from excised shoots following controlled freezing treatments in the laboratory. There was good overall correlation between the two methods (Spearman correlation coefficient 0.77), but leakage measurements were more sensitive than injury scores to the effects of nitrogen. Visible injury was not significantly altered by nitrogen supply (Kruskal‐Wallis non‐parametric test). Ion leakage was analyzed in different ways, using either calculations of the first‐order rate coefficients or expressions of relative conductivity. These analyses produced similar results with respect to the effect of frost and nitrogen. Shoots of nitrogen‐fertilized (40, 80 and 120 kg ha−1 yr−1) C. vulgaris sampled in October 1991 showed significantly (P < 0.05) less leakage after overnight frosts of −15 and −20 °C than did the water‐treated controls. In October the temperature which killed 50% of the shoots (LT50), derived from the leakage data, was raised by at least 4 °C by the highest nitrogen treatments compared with the control plants. Frost treatments to pot‐grown C. vulgaris in November produced similar visible injury to attached and excised shoots from the same plants, both being significantly less damaged by a −18 °C frost after a 7‐month exposure to an NaNO3 mist solution (1.0 mM, pH 4.5) than were water‐misted controls. Ammonium‐mist treatments also marginally reduced frost injury, but the effects were not statistically significant. These results demonstrate that frost hardiness of C. vulgaris in the field can be assessed rapidly and accurately in the laboratory by analysis of electrolyte leakage from excised shoots.
Resistance to an ineffective Frankia strain type in Alnus glutinosa (L.) Gaertn.
Authors: VAN DIJK CORNELIS , SLUIMER ARIA
Published: April 2006

summary

Characteristics of natural resistance to the ineffective Frankia strain type AgI‐WD1 were investigated in different progenies of the host species Alnus glutinosa (L.) Gaertn. with the aid of nodulation experiments. This strain type of Frankia was abundant in the soil of an A. glutinosa stand at Voorne, The Netherlands. Soil suspensions from this site produced high numbers of ineffective root nodules on some of the A. glutinosa seedlings used in biotests, but ii significant number of the seedlings did not produce ineffective nodules. Resistance (R) or susceptibility (S) of the seedlings to Frankia strain type AgI‐WD1, as expressed by absence or presence of ineffective root nodules, proved to be persistent in cloned plants of each phenotype. Both R and S‐seedlings were susceptible to effective Frankia strains in the soil suspensions.

Variation in nodulation time was examined among cloned plants of S‐seedlings selected for this trait. Average nodulation times of three selected clones were 11, 26 and 39 d, respectively. Relative growth rates of cloned plants showed no relationship with nodulation time.

Both R and S phenotypes were present in all seed‐lots of A. glutinosa under study, but the frequency of R phenotypes of seed‐lots from different locations ranged from 24 to 100%. R‐frequencies of seed‐lots of nine trees from a small population of A. glutinosa segregated into two distinct frequency classes which suggested genotypic differentiation of the R‐trait among these trees. A significant correlation was found between R‐frequencies of seedlots from the same trees over successive years.
Effects of exposure to ozone at different stages in the development of Plantago major L. on chlorophyll fluorescence and gas exchange
Authors: REILING K. , DAVISON A. W.
Published: April 2006

summary

Similar ozone treatments were applied at different stages of growth to a population of Plantago major L., which is as sensitive to ozone as Bel‐W3 tobacco. Plants were grown from seed for 8 wk in controlled‐environment chambers and exposed to 70 μl O3 l−1 7 h d−1 for the whole period or for 2‐wk episodes during weeks 1 + 2, 3 + 4, 5 + 6 or 7 + 8. Controls had charcoal‐filtered air. Effects on stomatal conductance, chlorophyll fluorescence and net photosynthesis are described.

The fluorescence character, t1/2, proved to be very sensitive to ozone, and it responded at all stages of plant development, but the ratio of variable to maximum fluorescence decreased only when plants received ozone during the first 2 wk of growth. The reduction was caused by a drop in maximum fluorescence. Ozone had no effect on F0.

Whenever exposure occurred, O3 significantly reduced net CO2 assimilation and increased stomatal conductance. Unlike t1/2, the effects were persistent, affecting leaves that were in bud or enshrouded by leaves when the exposure occurred. It is suggested that these persistent effects may have been caused by changes in resource allocation, flowering and senescence, which resulted in altered hormonal balance.
Modelling of early infection of cereal roots by the take‐all fungus: a detailed mechanistic simulator
Authors: GILLIGAN C. A. , BRASSETT P. R. , CAMPBELL A.
Published: April 2006

summary

A stochastic model is constructed to simulate the spatial and temporal spread of infection of the take‐all fungus, Gaeumannomyces graminis var. tritici (Sacc.) Arx & Olivier var. tritici Walker on seminal roots of wheat. The model is designed to synthesize information on the dynamics and spatial orientation of the growth of main seminal root axes of wheat and the dynamics of primary and secondary infection of the pathogen. Primary infection is initiated by the soil inoculum. Three types of secondary infection by runner hyphal growth are distinguished; re‐infection of the same root, infection of another root on the same plant via the crown, and cross‐infection between roots on different plants. There are nine pathogen parameters, 14 host parameters, as well as four system parameters in addition to the location and orientation of seedlings. The pathogen parameters comprise estimates for the size and density of inoculum, the rate of growth of the fungus on roots, and the mean distances and probability of occurrence for primary and secondary infection. The host parameters concern orientation, density, emergence, rates of growth and size of roots. The principal output variables are total and infected root length, numbers of infections, proportion of infected roots and the numbers of primary and cross infections. Results of sensitivity analysis of the output variables to selected input parameters are presented. The model is tested against independent data‐sets from inoculum‐density experiments for different soil temperatures and ranges of inoculum density. Statistical methods of response curve analysis are used to compare the behaviour of inoculum density‐disease response curves for the simulated and experimental data. The model fitted the data satisfactorily for the majority of host and infection variables. Inclusion of secondary infection in the model improved the goodness‐of‐fit but the density of secondary infections was small relative to primary infections. Practical and conceptual problems in the validation of complex simulation models for fungal infection are discussed. The advantages and limitations of this and related models are critically assessed.
The dynamics of infection by the take‐all fungus on seminal roots of wheat: sensitivity analysis of a stochastic simulation model
Authors: GILLIGAN C. A.
Published: April 2006

summary

The effects and interactions of inoculum density (Iρ), rate of fungal growth (kf) and the maximum distances for primary (wp) and secondary (cross) (ws) infection on the temporal progress of infection of the take‐all fungus, Gaeumannomyces graminis, in small populations of contiguous wheat plants are examined in factorial combination using a stochastic simulation model. The effects are analyzed in relation to infection progress curves for the percentage infected roots, the total length of infected root, the density of separate infection and the mean length of separate infections as well as the densities of primary and cross infections. Linear models are used to analyze the effects of changing parameter values on components of the infection progress curves. Non‐linear, logistic models are used to summarize infection progress curves and to map the effects of changing simulation model parameters onto the parameters of the simpler, growth curve function. The proportion of infected roots was most influenced by Iρ and wp with a negligible effect due to ws. The density and length of infections on roots was principally controlled by kf. Changes in infection length were non‐monotonic. The average length of infections increased towards a temporary maximum, following the first wave of primary infections, dipped as infections overlapped and then increased rapidly as root colonization progressed. The first wave of cross infection occurred 7 d after the initiation of primary infection. The density of primary infections was controlled principally by Iρ and wp. The density of cross infections was controlled not only by kf and ws, which are directly involved in cross infection, but also by kf and wp which affect the amount of infected and susceptible tissue. The asymptotic parameter of the logistic model for the infection progress curves was the most frequently affected parameter, followed by the delay parameter, with relatively few changes affecting the rate parameter. Some problems in the use of complex, stochastic simulation models to simulate experimental conditions are discussed.
Regulation of somatic embryogenesis in long‐term callus cultures of sugarcane (Saccharum officinarum L.)
Authors: BRISIBE EBIAMADON ANDI , MIYAKE HIROSHI , TANIGUCHI TAKESHI , MAEDA EIZO
Published: April 2006

summary

Embryogenically competent callus was induced from in vitro grown Saccharum officinarum L. (NCo 310) plantlets by plating young leaf segments on MS basal medium supplemented with 30 μM dicamba for 21 d in darkness, and subsequently transferring to a medium (EFDM) on which embryos could form and develop. Embryogenic response was improved if the EFDM was supplemented with 1 or 5 μM dicamba, casein hydrolysate (1 g 1−1), and 6% maltose or 6–9% corn syrup. Calli maintained their embryogenic competence for up to 16 months under these conditions, and with alternate weekly subcultures on to fresh media containing 20 μM and 30 μM dicamba in the dark, embryogenic callus proliferation could be further increased. Additional improvements in embryogenic competence were optimized to over 40 months when primary callus was alternately precultured at weekly intervals either with 10‐5 M ABA or 5% sorbitol and then transferred to a medium containing 20 or 30 μM dicamba during maintenance. In general, medium plant growth regulator and nutritional cues, especially dicamha concentration, maltose/corn syrup levels and ABA/sorbitol preconditioning, were observed to influence critically both embryogenic callus proliferation and the frequency of somatic embryogenesis. The data are discussed within the context that these treatments can be successfully manipulated to enhance long‐term embryogenic competence and high‐frequency somatic embryogenesis in sugarcane.
A chamber system for exposing rice (Oryza sativa L.) to ozone in a paddy field
Authors: KOBAYASHI KAZUHIKO , OKADA MASUMI , NOUCHI ISAMU
Published: April 2006

summary

A field exposure chamber system was constructed in a paddy field. The system consisted of four ozone generators, five exposure chambers equipped with ventilation fans on both ends, and an ozone measurement and control system. Rice plants were exposed to ozone in the exposure chambers for the whole growing season. The ozone concentration in each chamber was maintained in a constant proportion to ambient ozone. The horizontal distribution of ozone concentration within a chamber showed ±10%, of variation with the lowest values at the centre and both ends of the chamber. Wind velocity showed a similar horizontal distribution as ozone but with a greater variation among the locations within a chamber. Diurnal as well as seasonal changes of ozone concentration in the chambers followed the targeted level rather closely except for several occasions of power failure or system malfunctioning. Temperature in the chambers was c. 1 °C higher in the daytime and 0.34 °C higher on daily average than in the field outside. Light flux density in the chambers was reduced to 75% of that outside with little seasonal variation. These results indicated a satisfactory performance of the field exposure chamber system for its intended use.
Corrigiola litoralis L. in the British Middle Pleistocene
Authors: FIELD MICHAEL H.
Published: April 2006

summary

Plant macrofossil analyses of fossiliferous silt and sand channel‐fill deposits from The Brays Pit near Mathon in the English West Midlands yielded the first record of Corrigiola litoralis L. in the British Middle Pleistocene. The presence of Corrigiola litoralis at this site shows that this taxon has occurred naturally in the British Isles. This may support the opinion that one of the extant populations of this species in south‐west England may be regarded as native. The stratigraphic context of the site is briefly considered followed by a description of the macroscopic remains.
Tansley Review No. 70 Signal transduction during fertilization in algae and vascular plants
Authors: BROWNLEE COLIN
Published: April 2006

summary

Fertilization involves interaction between two gametes and exchange of genetic information. In addition, information is transferred which results in triggering of the particular cellular and developmental responses of the organism. This review considers the cellular signals involved during different stages of gamete interactions in plants, including gamete attraction, recognition, fusion, zygotic activation and development. A wide range of signalling mechanisms can be seen to operate during fertilization, reflecting both the diversity of systems bringing gametes together and the different cellular responses to fertilization throughout the plant kingdom. Moreover, signals involved in triggering early development following gamete fusion appear to differ significantly even between species showing at least superficially similar cellular responses. Much of our current understanding comes from studies of a few easily accessible systems though recent developments in gamete isolation, in vitro fertilization and embryo culture should increase the scope for studies of signalling mechanisms in vascular plants.

Contents

Summary
399

I.
Introduction
400

II.
Chlamydomonas: interaction between structurally identical gametes
401

III.
Fucoid algae: a simple oogamous system
409

IV.
Vascular plants
412

V.
Concluding remarks
418

Acknowledgements
418

References
418
Tansley Review No. 71 Effects of elevated atmospheric CO2on woody plants
Authors: CEULEMANS REINHART , MOUSSEAU MARIANNE
Published: April 2006

summary

Because of their prominent role in the global carbon balance and their possible carbon sequestration, trees are very important organisms in relation to global climatic changes. Knowledge of these processes is the key to understanding the functioning of the whole forest ecosystem which can he modelled and predicted based on the physiological process information. This paper reviews the major methods and techniques used to examine the likely effects of elevated CO2on woody plants, as well as the major physiological responses of trees to elevated CO2. The available exposure techniques and approaches are described. An overview table with all relevant literature data over the period 1989‐93 summarizes the percent changes in biomass, root/shoot ratio, photosynthesis, leaf area and water use efficiency under elevated CO2. Interaction between growth, photosynthesis and nutrition is discussed with a special emphasis on downward regulation of photosynthesis. The stimulation or reduction found in the respiratory processes of woody plants are reviewed, as well as the effect of elevated CO2on stomatal density, conductance and water use efficiency. Changes in plant quality and their consequences are examined. Changes in underground processes under elevated CO2are especially emphasized and related to the functioning of the ecosystem. Some directions for future research are put forward.

ContentsSummary425I.Introduction426II.The special case of trees426III.Methodologies, strategies and techniques427IV.Physiological responses of trees to elevated CO2428V.Conclusions: Looking forward to the future at the ecosystem level441Acknowledgements442References442
Sulphate and antioxidants in needles of Scots pine (Pinus sylvestrisL.) from three SO2‐polluted field sites in eastern Germany
Authors: POLLE ANDREA , EIBLMEIER MONIKA , RENNENBERG HEINZ
Published: April 2006

summary

Needles from young and mature Scots pine trees (Pinus sylvestirs) were collected at three field sites in eastern Germany, i.e. Menz, Taura, and Gossa, which differed in SO2pollution. Current and previous year's needles from the polluted sites Taura and Gossa (yearly mean af SO2: 26 ppb) contained approximately 100‐120 μmol sulphate g−1d. wt, whereas needles tram the unpolluted site, Menz (yearly mean of SO2: 3 ppb) contained 30‐65 μmol sulphate g−1d. wt. The apoplastic sulphate content was in the order of o.3‐1% of total sulphate and corresponded to concentrations of 0.6‐1.2 mM in needles from Mtnz and to 1.5–2 mn in needles from Gossa. In needles from the polluted sites the contents of glutathione, cysteine, γ glutamyleysteine, and soluble protein were higher than in needles from Menz. Despite the clear increases in sulphur‐containing compounds, pigment content and activities of superoxide dismutase, total peroxidase and apoplastic peroxidase (on the basis of d. wt) were not significantly different. When enzymatic activities were related to protein, lowest activities were found in needles from the site with the highest SO2‐pollution. The results show that it is not possible to use the activities of peroxidases or superoxide dismutases as biomarkers for SO2‐mediated stress in pine needles. It remains open whether the needles from the polluted sites suffered from greater oxidative stress than the needles from the less polluted site.
Analysis of aspen foliage exposed to multiple stresses: ozone, nitrogen deficiency and drought
Authors: GREITNER CAROL S. , PELL EVA J. , WINNER WILLIAM E.
Published: April 2006

summary

Two field experiments were conducted to examine the impact of a foliar stress (ozone, O3), alone or in combination with a resource stress, on carbon gain of aspen (Populus tremuloides Michx.). The first experiment involved nitrogen deficiency, and the second, drought stress.

The patterns of change in leaf area, photosynthetic rate and carbon pain with leaf position from root to apex were altered by O3 alone. Net photosynthesis, and carboxylation capacity of older leaves decreased, and of younger leaves increased, in response to O3. Thus younger leaves partially compensated for the decreased photosynthetic capacity of older leaves. Physiological maturity and senescence were accelerated by O3. Whole plant carbon gain declined with O3 due to reductions in both leaf area and photosynthetic rate.

Nitrogen deficiency alone decreased carbon gain via reductions in both leaf area and photosynthetic rate across leaf position. The effects of O3 and nitrogen deficiency together on both leaf area and photosynthetic rate were additive, Aspen seedlings compensated to O3 stress regardless of nitrogen level. Plant responses to both of these stresses may have been mediated by ribulose bisphosphate carboxylase/oxygenase (Rubisco) content or activity, and thus indirectly by nitrogen content.

In the second experiment, seedlings were subjected to drought during the first six weeks of exposure to O3 and were measured several weeks after termination of the drought treatment. Drought caused aspen seedlings to produce fewer and smaller leaves. After termination of drought, they produced larger new leaves, and net photosynthesis of most leaves was greater than in continuously well‐watered plants. In plants not exposed to O3, enhanced photosynthetic rate partially compensated for the smaller leaf area. O3 generally decreased leaf area and photosynthesis, and hence carbon gain. The effects of prior exposure to drought and O3 together were additive for whole‐plant photosynthetic rate, but less than additive for whole‐plant leaf area.
Tansley Review No. 75 Arabidopsis– its use in the genetic and molecular analysis of plant morphogenesis
Authors: PYKE KEVIN
Published: April 2006

summary

In the last decade, the weed Arabidopsis thaliana has come to prominence as a major new model system for investigating genetic and molecular aspects of developmental plant morphology. Extensive genetic and molecular information about the Arabidopsis genome, facilitated by international collaborations and the production of novel mutagenic systems, has enabled a vast array of mutants to be identified, most of which reveal nuclear genes that control different aspects of plant developmental processes. An ever increasing number of these newly identified genes have been isolated and within the next few years an overall view of the molecular control of plant development is likely to emerge. Particularly prevalent amongst these Arabidopsis mutants are those which alter morphogenic processes cither by changes in differentiation patterns of specific cell types, homeotic conversion of entire structures or abnormal patterns of cell division.

Mutants in the control of morphogenesis of most parts of the Arabidopsis plant have been identified and characterized. The most abundant classes are in embryogenesis including seedling pattern formation, root morphogenesis, floral morphology (including pollen and anther formation) and mutunts affecting shoot apical inenstern morphology. The first genes to be isolated from morphological mutants have been identified as transcription factors capable of controlling expression of other gene classes as part of a hierarchy of gene control. The relative ease with which many interesting and potentially important genes in morphogenesis have been revealed by identificatic.n of mutants makes it highly likely that with the aid of Arabidopsis thatiana, an understanding of the extremely complex molecular basis of plant morphogenesis may at last be Hirbin reach.

Contents

Summary
19

I.
Introduction
19

II.
Why Arabidopsis?
20

III.
The developing seed
22

IV.
The root
25

V.
The shoot apex
27

VI.
The Leaf
28

VII.
Whole plant morphology
30

VIII.
Floral development
31

IX.
Sub‐cellular tnorphology
32

X.
Discussion and future possihihties
32

XI.
Acknowledgements
32

XII.
References
34
Radial fibres in aggregate rays ofQuercus calliprinosWebb. – evidence for radial signal flow
Authors: LEV‐YADUN SIMCHA
Published: April 2006

summary

Radial fibres differentiate in many aggregate rays ofQuercus CalliprinosWebb. The occurrence of radial fibres in rays suggests a radial flow of developmental stimuli for fibre differentiation.
Cytological events induced by arachidonic acid in potato tubers
Authors: ALTAMURA M. M. , CASTORIA R. , FABBRI A. A. , TOMASSI M. , FANELLI C.
Published: April 2006

summary

Necrosis of potato tuber cells is enhanced, after 24 h incubation, by arachidonic acid (AA), an elicitor of the hypersensitive response in Solarium tuberosum L. and also by Fenton's reagents (a hydroxyl radical‐generating system) either alone or in association with AA. The phenomenon is independent of tuber age. In aged tubers, phenylthiourea (PTU) causes a significant reduction of AA‐induced cell necrosis. Necrosis observed in the presence of PTU alone is lower than in other treatments, and neither different from the controls nor affected by‐tuber age. Cell size is not affected by treatments or ageing. Nuclear hypertrophy occurs independently of tuber ape, with the highest values after treatment with AA and Fenton's reagents. Nucleolar extrusion is observed in all treatments but earliest in the presence of AA. AA also enhances the number of lignified parenchymal cells and, to a lesser extent, the number of traeheary elements.
Interactions between arbuscular mycorrhizal fungi and foliar‐feeding insects inPlantago lanceolataL.
Authors: GANGE A. C. , WEST H. M.
Published: April 2006

summary

A field experiment was conducted to investigate whether infection by arbuscular mycorrhizal (AM) fungi has any effect on herbivory by foliar‐feeding insects. Plantsof PI ant ago laureolataL. were grown in a randomized block design and natural levels of mycorrhizal infection reduced by the application of the granular fungicide iprodione. Plant growth responses were examined and herbivore bioassays performed by rearing both a chewing and sucking insect on the leaves of mycorrhizal and fungicide‐treated plants.

Fungicide application successfully reduced mycorrhizal infection, and this led to reductions in foliar biomass, caused by lower leaf number. However, fungicide‐treated plants suffered consistently higher levels of damage by centralist chewing and leaf‐mining insects, which colonized the plants. The chewing insect bioassay confirmed the field results, in that larvae ofArttia cajaL. (Lepidoptera: Arctiidae) consumed more leaf material from plants in which infection was reduced.

There was no evidence that AM fungi altered food quality for the chewing insect. Instead, infection caused an increase in the carbon/nutrient balance, which in turn led to increased levels of the carbon‐based feeding deterrents, aucubin and catalpol,

The sucking insect,Mvzus perskae(Sulzer) reacted in an opposite fashion to the ehewtr. with performance being greater on mycorrhizal plants. Again, there was no evidence that an alteration in food Quality was the cause, and in this case infection may result in changes in leaf morphology which benefit the insect.

We suggest that under conditions of high light and low nutrient availability. AM infection can alter the carbon/nutrient balance of plants, leading to an increased allocation to carbon‐based defences. This can have important consequences for insect herbivore performance and the patterns of herbivory in field situations.
A new method to quantify the inoculum potential of arbuscular mycorrhizal fungi
Authors: LIU R.‐J. , LUO X.‐S.
Published: April 2006

summary

Previously described concepts of inoculum potential (IP) and methods to measure the IP of arbuscular mycorrhizal fungi (AMF) are reviewed. The concept of IP is elusive and needs developing‐ A new definition of IP is described here us the number of viable fungal propagules and structures coupled with their initial infectivity, and the IP can be calculated from the formula IP =(N × H × K)+S or IP = (N × L) +S, where N= numbers of vesicles in roots and points of hyphae connected with the roots per unit length of the roots; W= root weight; K= root length per unit weight of the roots; L= root length: S= numbers of viable spores in an inoculum. For the AMF that product spores in roots, few spores, or no spares, the formula becomes IP =N × W × K = N × L. The parameter of the IP is therefore the total numbers of vesicles and/or spores in roots, points of hyphae connected with roots, and viable spores in an inoculum of any type. The correlation coefficients between the IP of the inoculum of Glamus Mossear (Nicol. &Gerd.) Gerdemann &Trappe, Glomus versiforme (Karsten) Berth,or Sclerocystis sinuosa Gerdemann &Bakhi and the amount of early stage infection produced by the corresponding were all > 0.93 (P < 0.01)on three host plants. Gassypium hirsutum L., or Sarghum Sudanense L., It is suggested that the IP should be easily and rapidly estimated with accuracy by the present method.
Discrimination of some African Armillaria species by isozyme electrophoretic analysis
Authors: AGUSTIAN A. , MOHAMMED C. , GUILLAUMIN J. J. , BOTTON B.
Published: April 2006

summary

Ten Armillaria isolates, collected from various host plants and widespread geographical origins in tropical Africa, were cultivated on orange fragments in the presence of water and ran different culture media in order to optimize enzyme and mycelial cord production. Seven enzymes involved in the primary metabolism of nitrogen and carbon (glutamate dehydrogenases, aspartate aminotransferase, malate dehydrogenase, glucose n‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase and isocitrate dehydrogenase) were extracted from the mycelial cords and analyzed by polyacry lamide gel electrophoresis. Cluster analysis based on calculated similarity values derived from isozyme banding patterns separated the isolates into five groups. Two isolates considered as belonging to A. mellea ssp. africana (an African species closely related to European A. mellea) were present in a clearly Separated cluster when compared to the other isolate groups. Two Kenyan isolates, belonging to an as yet unnamed biological species, which were characterized by the production of few slow growing mycelial cords, were also found in a separate cluster with slightly greater similarity coefficients to the other isolates. The six other isolates, referred to as isolates of A. heimii (a highly variable species with different sexual systems) fell into three sub‐clusters of variable homology. The two homothallic heimii isolates from Tanzania and Malawi, which were very closely related, displaying 100% isozyme similarity, exhibited a higher degree of similarity with the two other homothallic heimii isolates from Zimbabwe and Congo, than with the two heterothallic unifactorial heimii isolates from Cameroon and Gabon. The value of isozymes in the classification of African Armillaria spp. is discussed.
Effect of drought stress on growth and essential oil metabolism in lemongrasses*
Authors: SINGH‐SANGWAN NEELAM , ABAD FAROOQI A. H. , SINGH SANGWAN RAJENDER
Published: April 2006

summary

Two lemongrasses. Cymbopogon nardus. (L.) Rendle var. confertiflorus (Steud.) Bor. and Cymbopogon pendulus (Steud.) Wats, were grown under mild and moderate water stress for 45 and 90 d. The impact of in situ drought stress on plants in terms of relative water content, $pS, concentration of proline, activities of PEP carboxylase and geraniol dehydrogenase, and geraniol and citral biogenesis, were investigated. The results revealed that the specific exhibited differential responses under mild and moderate stress treatments. In general, plant growth was reduced considerably whilst the level of essential oils was maintained or enhanced. Significant induction in catalytic activity of PKP carboxylase under water stress was one of the consistent metabolic responses of the aromatic grasses. The major oil constituents., geraniol and citral, increased substantially in both the species. Activity of geraniol dehydrogenase was also modulated under moisture stress. The responses varied depending Upon the level and duration of moisture stress. The observations have been analyzed in terms of possible relevance of some of these responses to their drought stress adaptability tolerance.
Pollen dispersal and representation on an isolated, forested plateau*
Authors: JACKSON STEPHEN T. , SMITH SUSAN J.
Published: April 2006

summary

Modern pollen assemblages from 18 small ponds and wetlands on the spatially isolated and forested Kaibab Plateau were studied to determine how the pollen assemblages recorded vegetation patterns. Vegetation of the Plateau consists of an inner core of subalpine Picca/Abies forests, surrounded by mixed Abies/Picea/ Pseudotsuga/Pinus ponderosa forests, which are in turn surrounded by extensive Pinus ponderosa forests. The flanks of the Plateau are vegetated by Pinus edulis/Juniperus woodlands, with scattered Quercus populations. Arboreal pollen assemblages were dominated by Pinus (70‐98 %), which was most abundant in the P. ponderosa forests. Picea, Abies, Pseudotsuga and Populus pollen were abundant only at sites in the mixed and subalpine conifer forests, where their combined abundance never exceeded 16% except at the site deepest in the subalpine forest (22%). Pollen percentages of Cupressaceae and Pinus Subsection Cembroides were highest in the outermost P. ponderosa forests (nearest the P. edulis/Juniperus woodlands) and in the mixed and subalpine conifer forests, where Quercus pollen was also highest. Percentage representation of the well‐dispersed pollen of Quercus, Cupressaceae and Pinus Subsect. Cembroides was amplified at these latter sites by the poor pollen representation of the dominant Picca, Abies and Pseudotsuga trees. This effect is similar to that recorded in many pollen assemblages from arctic and alpine tundra regions.
Size, distribution and biomass of genets in populations of Suillus bovinus (L.: Fr.) Roussel revealed by somatic incompatibility
Authors: DAHLBERG ANDERS , STENLID JAN
Published: April 2006

summary

The spatial distribution of genets in the ectomycorrhizal fungus Suillus bovinus (L.: Fr.) Roussel were studied in somatic incompatibility pairings of isolates from five Scots pine (Pinus sylvestris L.) stands differing in forest history and age, With increasing forest age, the size of genets increased while the number of genets and production of sporocarps per unit area decreased. There was an estimated 700–5700 genets ha−1 in younger forests and 30–120 ha−1 in older ones. The maximum size of genets was 1.7–5.3 m in the younger forest and to 17.5 m in the older ones. The production of sporocarps per unit area decreased with increasing forest age. Furthermore, production of sporocarps increased nonlinearly with the size of the genet, suggesting that genets become fragmented. Ergosterol measurements indicated that the fungal biomass of one genet consisted of 20–45% sporocarps and 55–80% mycorrhiza, not including extramatrical mycelia. Mycorrhizal aggregations in soil were mapped in two 5 m2 areas and, based on somatic incompatibility tests, all were round CO belong to the same genet as sporocarps present above ground. Production of spores per sporocarp was estimated to be 1.1–12.8 × 108. The observations are discussed in terms of population ecology.
The role of microclimate in determining the sensitivity ofQuercus rubraL. to ozone
Authors: SAMUELSON L. J.
Published: April 2006

summary

Microclimate has been suggested as a factor to consider when scaling ozone responses of forest trees from the seedling to tree level. To test whether microclimate influences the response of seedlings to ozone. 1‐yr‐oldOuercus rubraL, seedlings were grown in the shaded upper or lower canopy of 31‐yr‐old trees in open‐top tree chambers, or in more exposed open‐top seedling chambers, and received subambient(cumulativeSUM.M06*dose of (0 ppm‐h), ambient (cumulative SUM06 dose of l9 ppm‐h) or twice ambient (cumulative SUMU6 dose of 135 ppm‐h) exposures to ozone for one growing season. Seedlings exposed to warmer temperatures and greater PAR within the seedling chambers had greater biomass, total leaf nitrogen, second foliar flush net photosynthesis, leaf conductance and dark respiration than seedlings grown in either location within the tree canopies. However, microclimate did not influence the responses to ozone. Net photosynthesis, leaf conductance and apparent quantum yield of first flush leaves of seedlings exposed to the same leaf microclimate as trees were reduced between 16% and 20% by ozone treatment. Ozone induced larger reductions in the net photosynthesis, leaf conductance and apparent quantum yield of tree leaves. These results indicate that, although microclimate influenced seedling growth and physiology, microclimate did not play a dominant role in determining the sensitivity ofQ. rubraseedlings to ozone.
Effects of simulated acid rain on nitrogenase activity (acetylene reduction) in the lichen Stereocaulon paschale (L.) Hoffm., with special reference to nutritional aspects
Authors: KYTÖVIITA M.‐M. , CRITTENDEN P. D.
Published: April 2006

summary

The effects of SAR (simulated add rain using H2SO4 and HNO3 singly and combined) on ARA (acetylene reduction activity), and concentrations of N, K4, Mg2+ and Ca2− was investigated in Sterecaulon paschale (L.) Hoffm. ARA was significantly decreased after 4 months of SAR at pH 3.0. One year after spraying treatments had ceased, lichens treated at pH 3.0. showed no clear signs of recovery of ARA. After 5 y of acidification. ARA in lichens sprayed with combined H2SO4 and HNO3 at pH 2.9. was comparable to that observed after 4 months of pH 3.0.enhanced rain, i.e. close to zero. SAR at pH 4.0. had no marked effect on nitrogenase activity after 4 months' exposure, but ARA was significantly decreased after 5 y‐of pH 4.1. (H2SO4) treatment. There were no clear relationships between the inhibitory effects of acid additions and alterations in nutritional status in the lichen caused by SAR. Furthermore, no correlation between thallus N concentration and nitrogenase activity was observed.
Sulphate‐limited growth in the N2‐fixing unicellular cyanobacterium Gloeothece (Nägeli) sp. PCC 6909
Authors: ORTEGA‐CALVOH JOSE‐JULIO , STAL LUCAS J.
Published: April 2006

summary

The unicellular diazotrophic cyanobacterium Gloeothece PCC 6909 was grown in batch and continuous culture, It was found that the organism scavenged sulphate from the medium and incorporated it in the polysaccharide sheath. As a result batch cultures became sulphur‐depleted whilst continuous cultures were sulphur‐limited. This was observed regardless of the nitrogen source of the culture. Sulphur‐depletion was the reason for the low nitrogenase activities usually observed in batch cultures of Gloeothece. Sulphate‐amended cultures showed sustained high nitrogenase activity in the light. Sulphate uptake from the medium was light‐dependent. Earlier work on N2 fixation in Gloeothece is discussed in the light of possible sulphur limitation.
Nitrogen‐fixing stem nodules of the Legume,Discolobium pulchellumBenth.
Authors: LOUREIRO M. F. , DE FARIA S. M. , JAMES E. K. , POTT A. , FRANCO A. A.
Published: April 2006

summary

We report on the structure of N2‐fixing nodules formed on the stem ofDiscolobium pulchellumBenth., an aquatic legume in the subfamily Pupilionoideae, tribe Aeschynomeneae, from the Hooded areas in the ‘Pantanal Matogrossense’ region of Brazil. The stern (and root) nodules were obligately aquatic, requiring permanent submergence in water or flooded soil, and receive oxygen via profuse aerenchyma covering The lower stem. Of the 69 isolates of rhizobia isolated from stem and root nodules, 70% were fast‐growing acid producers and 38% were slow growers. The rhizobia were not photosynthetic. Nodules were connected to the stem, and the vascular system from the stem branched throughout the nodule, penetrating the infected, tissue within finger‐like ingrowths of cortex. In both stem and root nodules, infected tissue was aeschynomenoid or desmodioid, that is, without uninfected (interstitial) cells. The infected cells in stem nodules were vacuolate, with visible infection threads. The inner cortex was rich in amyloplasts and contained the components of an oxygen diffusion barrier (a boundary cell layer without intercellular spaces and glycoprotein occlusions of intercellular spaces in other cell layers). The mid‐cortex, external to the boundary layer, consisted of loosely‐packed cells and these were continuous with stem aerenchyma. The outer part of the nodules was made up of phellogen‐derived cells forming a periderm, or ‘corky’ layer of cells. The periderm formed large lenticels above cortical vascular bundles. These lenticels also connected with the stem aerenchyma. Root nodules differed only in that infected cells were not vacuolate, bacteroids were larger and contained more poly‐β‐hydroxybutyrate (PHB) and there was less aerenchyma/lenticellular tissue. Stem and root nodule structure is discussed in terms of adaptations to O2constraints in an aquatic environment.
Capture of nitrate from soil by wheat in relation to root length, nitrogen inflow and availability
Authors: ROBINSON DAVID , LINEHAN DENIS J. , GORDON DENNIS C.
Published: April 2006

summary

We studied the interactions between nitrogen (N) inflow (uptake rate per unit root length) and root growth in the capture of nitrate by soil‐grown wheat (Triticum aestivum L. cv. Wembley). [l5N]‐nitrate was applied locally to soil overlying seminal roots of 42‐d‐old plants that had previously received K fertilizer (N +) or not (NO), [35S]‐sulphate was also applied to check the specificity of the plant's responses to nitrate. NO plants had exhausted soil nitrate by day 42. Over the next 7 d, inflow was stimulated in soil to which [15N]‐nitrate was supplied in the NO plants. NO plants increased their root length densities throughout the root system, not only around the point of [15N]‐nitrate application. Root length density did not change in the N+ plants. NO plants captured 73 % of the [l5NJ‐nitrate in 7d; N+ plants captured only 13%. There was no evidence that the plants' responses to the localized application of nitrate had an effect on the uptake of sulphate. The dominant influence on the capture of nitrate was inflow, rather than root growth.