bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: MEDINA E. , CRAM W. J. , LEE H. S. J. , LÜTTGE U. , POPP M. , SMITH J. A. C. , DIAZ M.
Published: April 2006

summary

This paper describes the ecology of a coastal alluvial plain at Chichiriviche in northern Venezuela. The area supports a great diversity of plant communities, ranging from mangroves on the seaward edge of the plain to non‐halophytic, fresh‐water communities on the landward side. Small differences on topography result in a mosaic of saline and less‐saline environments. Rainfall is strongly seasonal, causing superficial flooding of the alluvial plain in the rainy season and the creation of a hypersaline Substratum during the dry season. As a consequence, much of the plain is devoid or vegetation. Towards the landward side of the plain there are numerous small ‘vegetation islands’, fringed by halophilic succulent herbs, and made up of deciduous and semi‐deciduous shrubs and trees together with non‐halophytic CAM plants such as cacti and bromeliads. In subsequent papers the results of ecophysiological studies of these diverse plant species are presented.
The influence of photoperiod on incorporation of precursors into tocopherols and plastoquinone in Xanthium strumarium L.
Authors: TORRES J. MOLINA , LAIDMAN D. L. , GAUNT J. K.
Published: April 2006

summary

Radioactivity from tyrosine applied to leaves of Xanthium strumarium L. was incorporated into α‐ and γ‐tocopherol and plastoquinone. Time‐course studies on vegetative plants showed that γ‐tocopherol was rapidly labelled and turned over, while α‐tocopherol showed no sign of turnover. The same pattern was observed in the light and in darkness. Plastoquinone synthesis was rapid in the light but it was greatly reduced in the dark. Following floral induction the accumulation of radioactivity in γ‐tocopherol was at first slower, but it later readied higher levels than in the vegetative plants. Total incorporation into α‐tocopherol and plastoquinone was greatly reduced.
Peroxidase isoenzyme patterns of resistant and susceptible wheat leaves following stem rust infection
Authors: FLOTT BERENIKE E. , MOERSCHBACHER BRUNO M. , REISENER HANS‐JOACHIM
Published: April 2006

Near‐isogenic lines of the wheat (Triticum aestivum L.) cultivar Prelude, currying either the sr5 gene for susceptibility or the Sr5 allele for resistance to stem rust (Puccinia graminis Pers. f. sp. tritici Erics. & E. Henn.) were inoculated with race 32 of the fungus which possesses the P5 gene for avirulence. Enzyme extracts prepared at different times after inoculation were separated by non‐denaturing gel electrophoresis and the gels were stained for peroxidase activity using different substrates. Both anodic and cathodic gels were run.

In anodic separations, resistant and susceptible plants initially both exhibited decreases in the activity of two isoenzymes of low molecular mass, increases in two enzymes of intermediate molecular mass, and induction of two low high molecular mass isoperoxidases. In susceptible plants, these changes proceeded until 3 days after inoculation, when a general decrease in all isoenzymes was observed until 8 days after inoculation. In contrast, in resistant plants, the increases continued up to 7 days after inoculation. In addition, one isoperoxidase appeared about 2–3 days after inoculation only in the incompatible interaction.

Cathodic separations revealed that basic isoperoxidases increased after inoculation as well. In the group of small basic isoenzymes, two new bands appeared following inoculation. Only slight differences were seen between the two isolines.

Injecting an elicitor isolated from germinated urediniospores into the intercellular spaces of wheat leaves induces typical symptoms of the resistant reaction in both isolines. Correspondingly, the isoperoxidase pattern of the incompatible interaction, including the resistance related isoenzyme, was induced in both isolines.

The results are compared with previously reported changes in enzyme activities of the lignin biosynthetic Pathway, including the total activity of peroxidase. The relationship of different isoenzymes to the lignification response as a decisive mechanism of the hypersensitive resistant reaction is discussed.
Resource relationships of foraging mycelial systems of Phanerochaete velutina and Hypholoma fasciculare in soil
Authors: DOWSON C. G. , SPRINGHAM P. , RAYNER A. D. M. , BODDY LYNNE
Published: April 2006

summary

Inoculum blocks of wood colonized by the basidiomycetes Hypholoma fasciculare (Huds.: Fr.) Kummer and Phanerochaete velutina (DC: Pers.) Parmasto were placed in plastic trays containing moist (matric potential −0.007 MPa), unsterilized soil. When ‘baits’, in the form of beech (Fagus sylvatica L.) wood blocks, descaled pine (Primus sylvestris L.) cones, beech twigs, beech leaves or pine needles were introduced, H. fasciculare consistently responded by ramification of diffuse mycelium within and over the baits, inhibition of extension and regression of non‐connective mycelium, thickening of connective cords and polarized outgrowth from the baits. Decay of inoculum wood blocks was generally greater in the control than where baits were added. Whilst the decay rates of different types of baits varied, pine cones being least decayed, total loss of dry weight from the system (inocula and baits combined) was similar in all cases. The sparser, more independent and rapidly extending cords of P. velutina exhibited more varied responses to the introduction of baits, and only under certain circumstances exhibited the same responses as H. fasciculare. Although decay of inoculum blocks was generally greater in controls than where colonizable baits were added, total loss of dry weight in the latter systems was two‐ to fourfold greater than in controls.

Snowflake‐like mycelial growth patterns were induced in H. fasciculare by growing the fungus from an inoculum block placed in the centre of two concentric, hexagonal arrays of wood‐block baits. Selective removal of baits from the inner hexagonal array, after they had been colonized but before renewed outgrowth from them, either greatly delayed colonization of outlying blocks, if all six were taken out, or led respectively to symmetrical or asymmetrical ‘bypass’ systems if three alternating or adjacent blocks were taken.

These observations are further support for the interpretation of basidiomycete mycelial cords as foraging systems and suggest experimental approaches which can help to elucidate their behaviour.
Protein secretion in plants
Authors: JONES RUSSELL L. , ROBINSON DAVID G.
Published: April 2006

summary

Protein secretion is an ubiquitous but poorly understood process in plants. Secreted proteins are synthesized on the membranes of the rough endoplasmic reticulum and transported to the cell surface by secretary vesicles formed at the Golgi apparatus. Whereas many of the structural details of this process are known the mechanisms underlying secretion are just beginning to be understood, in this article we review some of the recent developments in this field, and we compare the progress made with animal and plant cells.

CONTENTS

Summary
567

I.
Introduction
568

II.
Proteins secreted by plants
568

III.
Synthesis and post‐translational modification of secreted proteins
571

IV.
Molecular requirements for secretion
576

V.
Vehicles of secretory transport
581

VI.
Regulation of secretion
585

VII.
Conclusions and Perspective
587

Acknowledgements
588

References
588
Cadmium tolerance and co‐tolerance in Silene vulgaris (Moench.) Garcke [=S. cucubalus (L.) Wib.]
Authors: VERKLEIJ J. A. C. , PRAST J. E.
Published: April 2006

summary

This paper is the first to report cadmium tolerance in a dicotyledonous species, Silene vulgaris (Moench.) Garcke. The response to cadmium of five populations originating from one uncontaminated and various heavy‐metal contaminated sites was examined under standardized conditions for three weeks. The tolerance index (TI), based on the mean relative growth rate (R), was determined.

Populations originating from cadmium‐contaminated sites showed a distinct tolerance to cadmium. A population from a site enriched only with copper also exhibited a marked co‐tolerance to cadmium. A clear difference in biomass production between the sensitive and tolerant populations was attained at 1 μM cadmium. An optimum biomass production in tolerant populations at a metal concentration higher than in the control, as demonstrated for zinc and copper, could not be established for cadmium.

The pattern of cadmium uptake and translocation differed between tolerant and sensitive populations. All tolerant populations accumulated cadmium in the roots and showed some degree of restricted transport to the shoots. The effect of cadmium on the elemental distribution in roots and shoots was population‐independent for some elements (copper, zinc, potassium) and population‐specific for others (phosphorus, magnesium and sodium). The phenomenon of co‐tolerance to cadmium is discussed in relation to possible tolerance mechanisms, especially with regard to metal‐binding compounds (metallothioneins, phytochelatins).
A comparison of the effects on Canadian boreal forest lichens of nitric and sulphuric acids as sources of rain acidity
Authors: SCOTT MARTHA G. , HUTCHINSON T. C. , FETH MARILYN J.
Published: April 2006

The effects of different levels of nitrate and sulphate in acidic precipitation on the growth of the lichens Cladina rangiferina (L.) Wigg. and C. stellaris (Opiz.) Brodo were compared. Permanent Held plots in a Canadian boreal forest ecosystem received two years of spraying with artificial rains of pH 4.2 (ambient), 3.5 or 2.8, each containing one of four molar ratios of sulphate to nitrate, i.e. sulphuric acid alone, nitric acid alone: 2:1 or 1:2. A substantial fertilization effect was observed when C. rangiferina was watered with rain of pH 2.8, derived from nitric acid alone. Compared with before‐treatment values, gains in mean dry weight (+ 62%) and mean podetial height (+14%) were obtained for this species, in addition to elevated levels of N in air‐dried tissues. Post‐treatment values for the mean dry weight of C. rangiferina were significantly reduced for those podetia sprayed with rain of low pH, derived from sulphuric acid alone. Although podetia of C. stellaris were stimulated by rains of pH 4.2, based on a higher concentration of nitric acid, there was no N fertilization following the most acidic sprays. Data from this study support the view that the N content of acidic rain can cause a short‐term growth stimulation for those species able to absorb nitrate from solution. However, beneficial effects on growth of prolonged fertilization via acid rain inputs are unlikely.
Glutamate dehydrogenases in ectomycorrhizas of spruce (Picea excelsa L.) and beech (Fagus sylvatica L.)
Authors: DELL B. , BOTTON B. , MARTIN F. , LE TACON F.
Published: April 2006

summary

The ammonia assimilation enzyme glutamate dehydrogenase as studied in extracts of spruce (Picea excelsa L.) roots, mycelium of a mycorrhizal fungus (Hebeloma sp.) and associated ectomycorrhizas. Evidence from enzyme reactions in crude extracts, electrophoretic patterns and immunological tests Using antibodies raised against purified NADP‐GDH of Cenococcum geophilum Fr. consistently showed that Hebeloma NADP‐dependent GDH was active in spruce ectomycorrhizas. Histochemical studies associated some NADP‐GDH activity with the Hartig net. By contrast, the NADP‐GDH fungal pathway was strongly suppressed in beech (Fagus sylvatica L.) associations with Hebeloma crustuliniforme (Bull. ex St Amans) Quél. and Paxillus involutus (Batsch ex Fr.) Fr.
Ectomycorrhiza formation between Eucalyptus pilularis Sm. and Hydnangium carneum Wallr. in Dietr.
Authors: MOORE A. E. P. , MASSICOTTE H. B. , PETERSON R. L.
Published: April 2006

summary

Ectomycorrhizas were synthesized in growth pouches between Eucalyptus pilularis Sm. and Hydnangium carneum Wallr. in Dietr. Colonization of lateral roots occurred within 14 d after inoculation with the development of a dense white mantle and a paraepidermal Hartig net. Cystidium‐like structures and unusual hyphal coils were present on the surface of the mature mantle. The mantle consisted of distinctive outer and inner portions with small, uniform hyphae comprising the outer mantle and much enlarged and modified hyphae in the inner mantle. Granular deposits were abundant primarily in the inner mantle hyphae as shown by light and fluorescence microscopy. These granules were shown to be polyphosphate through cytochemical tests and the use of energy dispersive X‐ray microanalysis. Phosphorus and calcium were the main elements identified in these granules.
Interactions between desiccation and dark nitrogen fixation in tropical Nostoc commune
Authors: JONES K.
Published: April 2006

Colonies of Nostoc commune in tropical Oahu have normally become desiccated and inactive in nitrogen fixation by between noon and 2 p.m. On rehydration, the desiccated colonies fix nitrogen at the same rate in the dark and the light for at least 2 h. When rewetted in the dark, desiccated colonies fix nitrogen at more than twice the rate of non‐desiccated colonies taken from the light and placed in the dark. The capacity of desiccated colonies to fix nitrogen in the dark when rehydrated is lost during storage for several months, but is rapidly regained after a short period of moist incubation in the light.

This ability to fix nitrogen on rewetting in the dark is well suited to a tropical climate where rainfall is mainly at night and when metabolic activity during the day is restricted by the rapid onset of desiccation.
Inhibition of phytopathogenic fungi in vitro by cell free culture media of ectomycorrhizal fungi
Authors: KOPE H. H. , FORTIN J. A.
Published: April 2006

The cell free culture media of 16 ectomycorrhizal fungi were tested for their ability to inhibit the growth of 23 phytopathogens and one ectomycorrhizal fungus. Extracellular metabolites of seven (44%) ectomycorrhizal fungi, Amanita citrina, Laccaria bicolor, Laccaria Iaccata, Pisolithus tinctorius, Suillns brevipes, Trircholomo flavovirens and Tricholoma pessundatum, inhibited the growth of up to 20 of 24 (83%) fungi tested. Two ectomycorrhizal fungi, P. tinctorius and T. pessundatum, were inhibitory to the ectomycorrhizal fungus, Sphaerosporella brunnea. A microscopic examination at the colony margin of confronted phytopathogenic fungi was made, noting changes in hyphal morphology. A novel feature, hyphal lysis, caused by the cell free culture medium of P. tinctorius, was seen in the two phytopathogens, Truncatella hartigii and Rhizoctonia praticola, and in the hyphae of the ectomycorrhizal fungus, S. brunnea.
Effects of simulated acid rain on growth parameters and yield components of two soybean cultivars
Authors: PORTER P. M. , BANWART W. L. , ZIEGLER E. L. , VASILAS B. L. , HASSETT J. J.
Published: April 2006

The effects of simulated acid rain on two soybean [Glycine max (L.) Merrill] cultivars were studied in field experiments in central Illinois. The cultivars,‘Amsoy 71’and‘Williams 82′, were shielded from ambient precipitation and treated twice weekly with applications of 1.05 cm of one of six simulated rain treatments which ranged in pH from 5.6 to 3.0. Each treatment was replicated 12 times in 1983, nine times in 1984, and six times in 1985. Measurements were taken for plant height, chaff dry weight, plant population, lodging, pods/plant, seeds/plant, seeds/pod, mass/seed, and number of low pods. There were small but significant (α= 0.10) effects of treatment acidity in some years for some of the parameters measured. For Amsoy 71, in one of three years, seeds/plant, seeds/pod, and chaff dry weight were reduced by increasing acidity of the simulated rain. In general, Amsoy 71 plants subjected to the more acidic treatments were shorter and had lower lodging in the second and third years of the experiments. For Amsoy 71 there were no significant linear contrasts for the effect of simulated acid rain on plants/ha, mass/seed, and protein concentration of the seed. For Williams 82 there was a small but significant trend for increased seed oil with decreasing pH in 1984 only. For this cultivar there were no significant linear contrasts for the effect of simulated acid rain on plants/hectare, plant height, lodging score, chaff dry weight, low pods, pods/plant, seeds/plant, seeds/pod, or mass/seed. Where changes in either cultivar occurred, the magnitude of these changes over the entire pH range studied was generally 6% or less. Not only was the magnitude of the responses minimal, but the response to simulated acid rain was not consistent between cultivars or in some cases within cultivars from year to year. The response to stimulated acid rain was also small when compared with the potential effect of other stresses such as drought, ozone, disease, insects, and weeds on soybean yield and growth parameters.
The effects of long‐term open‐air fumigation with SO2 on a field crop of broad bean (Vicia faba L.) I. Depression of growth and yield
Authors: KROPFF M. J. , MOOT J. , GOUDRIAAN J. , SMEETS W. , LEEMANS A. , KLIFFEN C. , van der ZALM A. J. A.
Published: April 2006

In an open‐air Held exposure system for the controlled release of air pollutants, broad bean (Vida faba L.) crops were exposed to elevated SO2 concentrations in three growing seasons, in order to analyse the effects on crop growth under field conditions. The treated plots were exposed to a mean concentration of 165μgm‐3 in 1985, 62μgm ‐3 in 1986 and 74μgm‐3 in 1988. The background concentration was about 10μ m‐3.

A reasonably uniform distribution of SO2 concentration was obtained over an area of 8m × 8m and concentrations exceeding the target concentration were rare. In 1985 and 1988, the growth rate of the crop was depressed at the end of the pod‐filling period. This resulted in a reduction of total dry‐matter production of 17% in 1985 and 9% in 1988, and a seed yield reduction of 23% in 1985 and 10% in 1988. In 1986, dry matter growth was not analysed up to the end of the growing season due to a severe infection of Botrytis fabae (Choclate spot disease) infection in the control plot in the middle of the pod‐filling period. Slight B. fabae infections in the control plots only were also observed in 1985 and 1988. In all experiments no significant reductions of dry matter growth were observed in the vegetative and early reproductive phases.
The effects of long‐term open‐air fumigation with SO2 on a field crop of broad bean (Vicia faba L.) II Effects on growth components, leaf area development and elemental composition
Authors: KROPFF M. J. , MOOI J. , GOUDRIAAN J. , SMEETS W. , LEEMANS A. , KLIFFEN C.
Published: April 2006

Faba bean crops (Vicia faba L.) were exposed to elevated SO2 concentrations in three different years in an open‐air field exposure system for the controlled release of air pollutants. The treated crops were exposed to an average SO, concentration of 165μg m‐3 in 1985, 62μg m‐3 in 1986 and 74μg m‐3 in 1988. The ambient SO2 concentration was about 10 μg m‐3. Plant height, number of internodes and number of pods were not affected by SO2. The specific leaf area was reduced in the plants exposed to SO2 at the end of the growing season. Leaf area development was strongly affected during the pod‐filling period in 1985 and 1988 as a result of leaf injury and defoliation in the fumigated plots. In 1986 a similar trend in leaf area reduction was observed in the early reproductive phase.

N and Mg content of the different organs was unaffected by SO2. The S content was strongly elevated in the leaves and pods of the fumigated plants, and the Ca content of the leaves was reduced by SO2. Chlorophyll content of different leaf numbers was unaffected by SO2.
Seasonal and altitudinal variation in Pteridium aquilinum (L.) Kuhn: frond and stand types
Authors: ATKINSON T. P.
Published: April 2006

The field ecology of Pteridium aquilinum (L.) Kuhn was studied through a growing season in the northern Malvern Hills. At lower altitudes, stands reached a biomass plateau by late July extending through to late September, while at higher altitudes biomass increment was delayed and curtailed by the shorter growing season. Pteridium retained several competitive characteristics even when altitude and exposure restricted its vigour. With increased altitude, biomass allocation favoured the lamina and the underground portion of the stipe; the stipe‐with‐rachis component was comparatively reduced with a dwarfing of the canopy but a dense packing of pinnae. Adjustment to conditions in the stand, by the emergence and die‐back of fronds, caused frond density to change through the growing season and at different altitudes. Two frond and associated stand types at contrasted altitudes were recognized by morphology and biomass.
Developmental changes in Sitka spruce as indices of physiological age I. Changes in needle morphology
Authors: STEELE M. J. , COUTTS M. P. , YEOMAN M. M.
Published: April 2006

There is a paucity of data regarding developmental changes in trees. Measurements of length, width, length/width ratio, perimeter/width and width/height ratios of tranverse sections, projected and total surface areas, dry weight, specific leaf area and the weight of epicuticular waxes per unit leaf area were made on needles sampled from the uppermost whorl of Sitka spruce trees aged 3, 5,10,15, 20 and 38 years. All characteristics, except needle length and the weight of epicuticular waxes, showed asymptotic changes with age that could adequately be described by the Gompertz growth function, and offer potential as indices of physiological age. Asymptotes were reached at different ages (width and the length/width ratio having the slowest rates of change and the perimeter/width ratio, specific leaf area, and the width/height ratio having the fastest) suggesting a predictable sequence of changes. The observed changes in needle morphology are interpreted as a transition from shade to sun leaves.
Cold‐induced dieback of montane spruce forests in the Swedish Scandes – a modern analogue of paleoenvironmental processes
Authors: KULLMAN LEIF
Published: April 2006

In 1987 particularly, but also in 1988, primaeval montane coniferous forests of northern Scandinavia experienced needle loss on an unprecedented scale, which affected the character of the entire landscape in certain regions. This study elucidates the dieback event For Norway spruce [Picea abies (L.) Karst.] in an area of the Swedish Scandes. The study includes visual assessment of percentage needle loss, age structure, radial growth and various environmental parameters, along altitudinal transects and within a larger sample plot. Frequency and magnitude of foliage damage were found to be related to elevation. The dieback process of closed forest stands was interpreted as a response to short‐term climatic variability. Damage mainly developed during one of the coldest early winters (December January 1986/7) of this century. In combination with sub‐normal depth of the snow caver, the severe cold promoted exceptionally deep and persistent soil frost in spruce forest stands. It is hypothesized that damage was mainly due to winter/spring drought (frost‐drought). Phenotypically closed forest stands may change in just a few years in response to cooling, a feature which has not been realized previously. The possibility of major retrogressive responses lo short‐term climatic events should therefore be considered in studies of historical biogeography and when modelling vegetation succession. The forest studied was probably established after a severe wind storm in 1837. The restocking process was facilitated by the post‐Little Ice Age warming, but the stands are at present suffering severe dieback due to the recent cooling of the climate. The results stress the potential importance of short‐term climatic disturbance in boreal forest succession. Reasonably, rapid cold‐induced dieback of forest stands may have been a recurrent feature of Holocene forest history in the Boreal zone.
Catabolism of chlorophyll in vivo: significance of polar chlorophyll catabolites in a non‐yellowing senescence mutant of Festuca pratensis Huds.
Authors: THOMAS HOWARD , BORTLIK KARLHEINZ , RENTSCH DORIS , SCHELLENBERG MAYA , MATILE PHILIPPE
Published: April 2006

During dark incubation of excised leaf tissue from Bf 993, a senescence mutant of Festuca pratensis Huds., a highly polar green pigment fraction (PC) increased from negligible amounts at day 0 to maximal concentrations at days 4–6 and declined thereafter. Over the same time‐scale, chlorophyll (chl) was lost from leaves of the normal genotype Rossa without any detectable accumulation of PC. Chromatographic analysis established that PCs are a group of dephytylated derivatives of chl a. Chl‐ protein complexes from 4–day‐senesced Bf 993 tissue were isolated by sucrose gradient centrifugation and PCs identified by thin‐layer chromatography. High levels of PC were associated with the light‐harvesting complex of Photosystem II; Photosystem I yielded none. Cycloheximide, at a concentration sufficient to inhibit yellowing in the normal genotype, completely abolished the appearance of PC in Bf 993. Accumulation of PC‐like pigments in Rossa leaf tissue could be induced by anoxia. It is proposed that PCs are normal intermediates in chl catabolism, which begins with a protein synthesis‐dependent dephytylation, followed by oxidation leading ultimately to open‐chain pyrrole derivatives. The first steps in the breakdown sequence take place while the pigment is associated with proteins in the thylakoid membrane. The metabolic lesion in the Festuca mutant appears to be located downstream of the dephytylation step, leading to an abnormal accumulation of PCs in this genotype.
Pollination, fertilization and fruit development in sycamore (Acer pseudoplatanus L.)
Authors: PIGOTT C. D. , WARR S. J.
Published: April 2006

Sycamore (Acer pseudoplatanus L.) regenerates freely from seedlings in northern England. Even when temperatures are below average in early May, pollen germinates and pollen tubes grow to the base of the style within 3‐5 d of the flowers opening. In (lowers at constant temperatures from 5.5 to 15.5°C, pollen germinates rapidly and a high proportion of pollen tubes reach the base of the style within four days. In natural conditions proembryos are present in fertile ovules 3 weeks after pollination. Fertile fruits grow rapidly until July and then more slowly until September. Large crops of fertile fruit are formed even when temperatures are below normal at flowering and subsequent development proceeds in both warm and cool summers.
Structure and function of the interfaces in biotrophic symbioses as they relate to nutrient transport
Authors: SMITH S. E. , SMITH F. A.
Published: April 2006

Summary

In this review we compare the structure and function of the interfaces between symbionts in biotrophic associations. The emphasis is on biotrophic fungal parasites and on mycorrhizas, although necrotrophic parasitic associations and the Rhizobium/legume symbiosis are mentioned briefly. We take as a starting point the observations that in the parasitic associations nutrient transport is polarized towards the parasite, whereas in mutualistic associations it is bidirectional. The structure and function of the interfaces are then compared. An important common feature is that in nearly all cases the heterotrophic symbiont (whether mutualistic or parasitic) is located topologically outside the cytoplasm of the host cells, in an apoplastic compartment. This means that nutrient movements across the interface must involve transport into and out of this apoplastic region through membranes of both organisms.

Basic principles of membrane transport in uninfected cells are briefly reviewed to set the scene for a discussion of transport mechanisms which may operate in parasitic and mycorrhizal symbioses. The presence and possible roles of ATPases associated with membranes at the interfaces are discussed. We conclude that cytochemical techniques (used to demonstrate the activity of these enzymes) need to he extended and complemented by biochemical and biophysical studies in order to confirm that the activity is due to transport ATPases. Nevertheless, the distribution of activity appears to he in accord with polarized transport mechanisms in some pathogens and with bidirectional transport in mycorrhizas. The absence of ATPases on many fungal membranes needs re‐examination.

We emphasize that transport mechanisms between mycorrhizal symbionts cannot be viewed simply as the exchange of carbon for phosphate. Additional features include provision for transport of carbon and nitrogen as amino acids or amides and for ions such as K+ and H+ involved in the maintenance of charge balance and pH regulation, processes which also occur in parasitic associations. Interplant transport of nutrients via mycorrhizal hyphae is discussed in the context of these complexities. Some suggestions for the directions of future work are made.

CONTENTS

Summary
1

I.
Introduction
2

II.
The availability of nutrients to the symbionts
3

III.
Structure of interfaces between symbionts
4

IV.
Identity of nutrients transferred: an overview
12

V.
Membrane transport: basic principles
14

VI.
Transport at the interface of biotrophic symbioses
15

VII.
Regulation of pH in biotrophic symbioses
25

VIII.
Conclusions:
26
Effects of high soil moisture on formation of ectomycorrhizas and growth of karri (Eucalyptus diversicolor) seedlings inoculated with Descolea maculata, Pisolithus tinctorius and Laccaria laccata
Authors: BOUCHER N. L. , MALAJCZUK N.
Published: April 2006

Summary

Seedlings of Eucalyptus diversicolor P. Muell. I noculated with the ectomycorrhizal fungi Descolea maculata Bougher (two isolates), Pisolithus tinctorius (Pers.) Coker & Couch and Laccaria laccata (Scop, ex Fr.) Berk. & Br. were raised under glasshouse conditions in a yellow sand at a gradient of four soil moisture levels ranging from above field capacity to near waterlogged. All fungi enhanced growth of seedlings above that of uninoculated seedlings, but in soils near saturation there was no response to inoculation. Reduced mycorrhizal formation in relation to increasing soil moisture occurred to various degrees for all fungi. This was particularly marked with Pisolithus tinctorius. In contrast, Laccaria laccata maintained a relatively high number of mycorrhizal roots at all moisture levels applied, except at the wettest soil treatment. An isolate of D. maculata from a swamp environment did not produce a greater number of mycorrhizal roots at high soil moisture than an isolate of this species from a forest environment.
Botrytis cinerea kills groundsel (Senecio vulgaris) infected by rust (Puccinia lagenophorae)
Authors: HALLETT S. G. , PAUL N. D. , AYRES P. G.
Published: April 2006

Summary

Inoculation of healthy groundsel (Senecio vulgaris L.) with Botrytis cinerea Pers at 1.24 × 106conidia ml −1 caused 10% mortality, and only 40%, mortality when plants were abiotically wounded before inoculation. However, all plants previously infected by rust (Puccinia lagenophorae Cooke) died after inoculation with B. cinerea. Mortality was most rapid it plants were inoculated with B. cinerea as rust colonies first erupted through the host's epidermis. A reduction in the concentration of conidial inoculum increased time to death, and concentrations below 015 × 103 conidia ml−1 failed to cause 100 % mortality within the 32 d of the experiment. Death of plants was associated with the growth of B. cinerea into stem bases; a reduction in the density of rust lesions on leaves had no effect on the time from inoculation to the appearance of foliar symptoms, but increased time‐to‐kill. There was little variation m virulence between isolates of B. cinerea made from different groundsel or ragwort (Senecio jacobaea L.) populations. Similar interactions between biotrophic fungi and opportunistic pathogens have occasionally been noted previously; their importance in natural vegetation processes and possible relevance to the biocontrol of weeds is discussed.
Foliar uptake of peroxyacetyl nitrate (PAN) by herbaceous species varying in susceptibility to this pollutant
Authors: OKANO K. , TOBE K. , FURUKAWA A.
Published: April 2006

Summary

Foliar uptake of peroxyacetyl nitrate (PAN) was measured by the gas exchange method on nine herbaceous species. Susceptibility to PAN was also examined in the tested species in order to seek correlations with the uptake rate of PAN. PAN was synthesized by the nitration of peracetic acid in n‐tridecane.

Uptake rate of PAN by the leaves was kept at a steady level during the 90 min light period, while in the dark it declined rapidly and reached almost zero within 30–45 min. This suggests that adsorption of PAN on to the surface of the leaves is very small and most of it enters the leaf through open stomata.

Among the species tested, sunflower showed the highest rate of PAN uptake, followed by radish, tomato and spinach. Maize and soyabean exhibited the lowest rate. A highly significant correlation was observed between the rate ol PAN uptake and stomatal conductance among the tested species.

Petunia was most susceptible to PAN, followed by radish and tobacco, but maize and peanut were tolerant. There was no significant correlation between the uptake rate of PAN and susceptibility to it among the species. A higher susceptibility of petunia to PAN was not characterized by a higher rate of pollutant uptake. These results show that the main factor determining the differences between species in susceptibility to PAN is not the amount that gains access to the tissues, but some internal metabolic processes.
The history of the endemic flora of St Helena: late Miocene:‘Trochetiopsis‐like’ pollen from St Helena and the origin ofTrochetiopsis
Authors: CRONK Q. C. B.
Published: April 2006

Summary

Re‐examination of a fossiliferous sediment from St Helena has revealed the presence in the late Miocene of pollen grains very similar to modernTrochetiopsispollen.Trochetiopsisis found only in St Helena and is assumed to be a palaeoendemic genus. The late Miocene material provides striking confirmation of this view.

The two extantTrochetiopsisspecies are compared with other species in the Sterculiaceae: Dombeyeae, using multivariate methods. It is suggested that the two extantTrochetiopsisspecies diverged on St Helena comparatively recently, probably as a result of disruptive selection followed by ecological isolation caused by environmental change at the beginning of the Quaternary.

It is also suggested that the ancestor of the extantTrochetiopsisspecies arrived in St Helena by long distance dispersal from African or Madagascar Dombeyeae stock at least 9 million years ago. However, since this time the pollen morphology of theTrochetiopsislineage has changed little. The taxonomic isolation ofTrochetiopsiscan thus be explained partly by evolution on St Helena, but mainly by evolution and extinction in the Dombeyeae elsewhere (reliction).
Oligosaccharides in foliage of Agropyron, Bromus, Dactylis, Festuca, Lolium and Phleum*
Authors: CHATTERTON N. J. , HARRISON P. A. , THORNLEY W. R. , DRAPER E. A.
Published: April 2006

Temperatures are frequently too cool on rangelands of the western United States for plant growth to occur during much of the time when soil moisture is most readily available. Altering plant metabolism to facilitate growth under cool temperatures holds considerable potential for improving forage production on these ranges. Sucrosyloligosaccharides in representative grasses were characterized. Sucrosyloligosaccharides facilitate the partitioning of carbohydrates outside the chloroplasts during growth at cool temperatures. Eight grasses (Bromus inermis Leys., B. tectorum L., Dactylis glomerata L., Lolium perenne L., Festuca arnndinacea Schreb., Phleum pratense L., and two accessions of ‘Hycrest’ a cross between Agropyron desertorum (Fischer ex. Link) Schultes and A. cristatum L. Gaertner were grown in controlled environments at 10/5 ± 1 °C day/night temperatures. Oligosaccharides extracted from lyophilized leaves were separated using anion exchange chromatography. The relative amounts and kinds of trisaccharides varied among species. All grass contained both raffinose and 1‐ketose. Neoketose was the dominant trisaccharide in Lolium and Festuca but was absent from both Agropyron hybrids. 6‐Kestose was present in all species except L. perenne. Extracts of L. perenne and F. arundinacea contained a trisaccharide containing glucose, fructose and galactose (1:1:1), tentatively given the trivial name ‘loliose’. The oligosaccharide pattern in L. perenne, both Bromus species, D. glomerata and P. pratense suggest the presence of simple polymeric fructan series. However, the series are different from the inulin series in Jerusalem artichoke tubers. In contrast, chromatograms of leaf extracts of F. arundinacea and both Agropyron accessions have complicated profiles which may reflect the presence of both linear and branched polymers in those species. The oligosaccharide profiles determined by anion exchange chromatography may have useful chemotaxonomic applications.
Lodging of winter barley (Hordeum vulgare L.) in relation to its degree of exposure to sulphur dioxide
Authors: BAKER C. K. , FULLWOOD A. E. , COLLS J. J.
Published: April 2006

Plots in a field crop of winter barley (Hordeum vulgare L. ev.‘Igri’) were exposed to SO2 concentrations of 50, 100 and 200 nl l−1 above ambient. During May 1984 the crop lodged owing to wind and heavy rain, and the severity of lodging was clearly related to the gas concentrations that the plants had experienced.

Samples of stems from the experimental plots were tested to find how much force was needed to bend the basal internode. Stems of plants that had experienced SO2 elevations of 100 and 200 nl l−1 were weaker than those from control plots; stems of the plants exposed to 50 nl l−1 were the strongest of all. Investigation of stem anatomy showed that lodging resistance was correlated with stem anatomical attributes, and particularly with the thickness of pairs of contiguous walls of sclerenchyma cells.

The differences in stem strength in the SO2 treatments probably arose from the effects of SO2 on plant growth earlier in the season.
Morphogenetic modifications induced by the mycorrhizal fungus Glomus strain E3 in the root system of Allium porrum L
Authors: BERTA G. , FUSCONI A. , TROTTA A. , SCANNERINI S.
Published: April 2006

Morphometric analysis, modelling and histological techniques were used to study root morphogenesis in nonmycorrhizal and mycorrhizal plants of Allium porrum infected by a Glomus sp., strain E3, during the first 105 days after sowing. They showed that morphogenetic changes were induced by the fungus in the root system of the host.

Adventitious roots of mycorrhizal plants became more numerous and shorter than those of controls, as mycorrhizal infection proceeded. Increase in number was fitted by logistic curves in mycorrhizal and control plants; increase in length was fitted in both cases by logistic curves. Mycorrhizal roots became progressively more branched than controls: branching increased linearly with time in mycorrhizas, whereas in the controls it showed an almost constant frequency from day 49 onwards and was fitted by a logistic curve. There was a significant depression of mitotic index demonstrated in the apical meristems of vesicular‐arbuscular mycorrhizas.
Effect of nitrate and ammonium nutrition on the metabolism of the ectomycorrhizal basidiomycete, Hebeloma cylindrosporum Romagn
Authors: SCHEROMM P. , PLASSARD C. , SALSAC L.
Published: April 2006

Hebeloma cylindrosporum Romagn. grown on a nitrate medium exhibits a growth rate ten times greater than that on an ammonium medium lacking organic acids. Nitrate reduction is accompanied by a low rate of synthesis of organic anions and an elevated excretion of OH− ions into the external medium. The addition of a Krebs cycle organic acid, e.g., malate, citrate, succinate or pyruvate to the ammonium medium induces a strong increase in the growth of the thalli which then equals that obtained on a nitrate medium. The absorption of such precursors to 2‐oxoglutarate could permit the recharging of the Krebs cycle, otherwise inhibited because the assimilation of ammonium causes an important re‐routing of 2‐oxoglutarate. In these thalli, the soluble nitrogen content shows a clear reduction compared with the thalli cultured on ammonium medium lacking organic acids. The poor growth observed on an ammonium medium may be due in part to insufficient CO2 fixation by anaplerotic reactions which, in Hebeloma cylindrosporum Romagn., is carried out by phosphoenolpyruvate carboxykinase.
Helianthemum—Terfezia relations in different growth media
Authors: ROTH‐BEJERANO N. , LIVNE D. , KAGAN‐ZUR V.
Published: April 2006

The Israeli desert truffle, Terfezia leonis Tul., failed to enter into association with its plant symbiont, Helianthemum sessiliflorum (Defs.) Pers., when cultivated together on an agar medium consisting of inorganic salts. Addition of activated charcoal to the growth medium brought about rapid and extensive association. Activated charcoal did not enhance fungal growth in the absence of the plant seedling. The stimulating effect of the charcoal is probably related to its adsorption characteristics and may not be due to contact or abrasion between seedling roots and charcoal particles.
Leaf polymorphism in Ranunculus nanus Hook. (Ranunculaceae)
Authors: MENADUE Y. , CROWDEN R. K.
Published: April 2006

The Tasmanian endemic species Ranunculus nanus Hook, has variable leaf morphology, the range of which frequently overlaps that of other co‐occurring Ranunculus species. Thus, identification of vegetative material is difficult and often there is taxonomic confusion.

Transplant and controlled‐environment experiments have shown that the variations in leaf form are largely plastic growth responses to localised environmental conditions.

In general, the morphological variation is greater between populations than within populations, suggesting that selection pressures at different sites have produced a range of genotypically different populations, each with a varying phenotypic response to their particular environment.

These findings have taxonomic implications. Because of phenotypic plasticity, the characters, leaf size, leaflet number, hairiness and petiole length, are of little value in diagnostic keys.
Holocene vegetational and environmental history at Loch Lang, South Uist, Western Isles, Scotland
Authors: BENNETT K. D. , FOSSITT J. A. , SHARP M. J. , SWITSUR V. R.
Published: April 2006

A Holocene record of pollen, charcoal, magnetic susceptibility and sediment chemistry from South Uist, Western Isles, is described and discussed. The vegetation of eastern South Uist included areas of woodland over as much as half of the available landscape during the early postglacial. This woodland was dominated by Betula and Corylus, but Quercus, Ulmus, Alum glutinosa and Fraxinus excelsior were also present. The status of Pinus sylvestris is uncertain. Quercus, Ulmus and A. glutinosa are now extinct as native trees in the Western Isles. During the later half of the Holocene (from about 4000 BP), woodland declined, possibly as a result of the use of hill land as grazing. Blanket peat vegetation, which had begun to spread from about 5500 BP, became the dominant feature of the landscape as the woodland areas decreased. The physical and chemical data from Loch Lang sediments suggest that little erosion of soils took place until about 550 years ago, when there was a marked increase, possibly attributable to increasing grazing pressure.
Photosynthetic acclimation in a terrestrial CAM bromeliad, Bromelia humilis Jacq
Authors: FETENE M. , LEE H. S. J. , LÜTTGE U.
Published: April 2006

Photosynthetic acclimation of a terrestrial CAM bromeliad –Bromelia humilis Jacq. to irradiance and nitrogen supply during growth was investigated under controlled conditions. Considerable acclimation to shade was realized through an increase in total chlorophyll, accessory pigments, an increase in chloroplast size and appressed to non‐appressed thylakoid membrane ratio, and a reduction in chlorophyll a/b ratio. A relatively high apparent photon yield in shade was associated with a low light‐compensation point and low dark‐respiration rate.

Light saturation of integrated dark CO2 uptake occurred at a relatively low total daily photosynthetic photon flux density (PPFD) and was not influenced by growth PPFD level. Maximum photosynthetic capacity expressed per unit chlorophyll and nitrogen use efficiency were significantly higher in high‐PPFD‐grown plants. In addition, apparent photon yield was only slightly reduced in high‐PPFD‐grown plants with nitrogen, while maximum photosynthetic rate remained the same indicating radiationless dissipation of excess light.

Very high levels of recycling of respiratory carbon were observed under nitrogen deficiency in plants grown in both high and low PPFD. The extensive photosynthetic acclimation of B. humilis is discussed in terms of contrasting exposure and limitations of its natural environment.
Transport and assimilation of inorganic carbon byLichina pygmaeaunder emersed and submersed conditions
Authors: RAVEN JOHN A. , JOHNSTON ANDREW M. , HANDLEY LINDA L. , McINROY SHONA G.
Published: April 2006

Photosynthetic O2evolution by the upper littoral lichen,Lichina pygmaea(Lightf.) C.Ag., under light‐saturated conditions at 5 °C is saturated by the 2 mol m−3inorganic C found in seawater at pH 8.0. Photosynthesis is not reduced when pH is increased to pH 9.4, and is slightly reduced at pH 10.0, when submersed in seawater with 2 mol m−3inorganic C. The rate of photosynthesis at pH 10 greatly exceeds the rate of uncatalysed conversion of HCO3−. It is concluded that HCO3−is used in photosynthesis. Since extracellular carbonic anhydrase is present, it is possible that CO2enters the photobiont (Calothrix) cells even during HCO3use. pH drift experiments support the notion of HCO3−use. Emersed photosynthesis at 5 °C is more than half‐saturated by 35 Pa (normal atmospheric) CO2; the light‐ and CO2‐saturated emersed photosynthetic rate is not significantly different from the light and inorganic C‐saturated photosynthetic rate when submersed. Inorganic C diffusion from the thallus surface to the photobiont needs, at least under some conditions, carbonic anhydrase activity which permits HCO3−fluxes to supplement CO2movement. The CO2compensation partial pressure at 5 °C is 0.83 Pa, i.e. at the low range of values found for terrestrial cyanobacterial lichens. Dark14C‐inorganic C assimilation when submersed is a small fraction of the dark respiratory rate, consistent with the observed absence of diel CAM‐like variation in intracellular titratable acidity. The high value (−11.5%) of δ13C, the low CO2compensation partial pressure, and the relatively high affinity for inorganic C., are consistent with the operation of an inorganic C concentrating mechanism such as occurs in free‐living cyanobacteria and probably occurs in terrestrial cyanobacterial lichens and in most intertidal algae.
Ammonium assimilation by the nitrate‐utilizing yeast, Candida nitratophila
Authors: HIPKIN C. R. , FLYNN K. J. , MARJOT E. , HAMOUDI Z. S. , CANNONS A. C.
Published: April 2006

Ammonium‐nitrogen was assimilated rapidly by nitrogen‐replete cultures of the nitrate‐utilizing yeast, Candida nitratophila as long as a suitable source of carbon was available. These cultures contained high activities of an NADPH‐dependent glutamate dehydrogenase with a relatively high affinity for ammonium (Km= 0.27 mM) and high glutamine synthetase activity. Both enzyme activities were apparently derepressed when glutamine‐grown cultures were starved of nitrogen or transferred to nitrate medium. Nitrogen‐deficient cultures also contained NADH‐dependent glutamate synthase activity that was inhibited by azaserine in vitro. Ammonium assimilation in vivo, was inhibited by methionine sulphoximine whilst addition of azaserine resulted in an accumulation of intracellular glutamine and an inhibition of glutamate production. Our results suggest that, in C. nitratophila, there is a potential for ammonium assimilation via both the glutamate dehydrogenase pathway and the glutamine synthetase/glutamate synthase pathway with the latter pathway predominating in nitrogen‐deficient cells.