bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of liming on ectomycorrhizal fungi infecting Pinus sylvestris L.
Authors: ERLAND SUSANNE , SÖDERSTRÖM BENGT
Published: April 2006

summary

Pinus sylvestris L. seedlings were grown in the laboratory in a forest humus which had been treated with different levels of CaO to give a soil pH gradient from 4 to 7. After 12 and 15 wk the resulting ectomycorrhizal infection was classified according to macroscopical morphology. The uniformity of the infection types distinguished was evaluated by isolating the fungi from the root tips and infecting seedlings with the isolates obtained. The isolation method was improved by using a medium containing benomyl and chlortetracyclin and by isolating from very small particles. For some mycorrhizal types the fungus was successfully isolated from 80% of the plated root particles.

The number of root tips that became mycorrhizal increased from 70% at pH 4 to nearly 100% around pH 5. Thereafter it decreased linearly to reach a minimum of slightly less than 40% at pH 7.5. Five different mycorrhizal types could be distinguished. They occurred with different abundance, distribution and pH optima. They were present throughout the entire pH range, except for a yellow type, identified as Piloderma croceum Erikss. & Hjortst., which was not found at values higher than 6–2. There was no great differences between infections on plants harvested after 12 and 15 wk. Seedling growth was constant to pH 5 then it increased up to about pH 7, at higher pH values growth declined.
Effect of nodulation, nitrogen fixation and CO2 enrichment on the physiology, growth and dry mass allocation of seedlings of Alnus rubra Bong.
Authors: ARNONE JOHN A. , GORDON JOHN C.
Published: April 2006

Inoculated and uninoculated Alnus rubra Bong, seedlings were grown for 47 days in atmospheres containing ambient (350 μ1 CO2 1−1) and elevated (650 μl CO2 1−1) levels of CO2, with and without combined nitrogen (20 mg 1−1) supplied as ammonium nitrate. Five plants from each treatment were harvested 15, 30, and 47 days after exposure to CO2 treatments began. Evidence for the presence of a positive feedback loop between nitrogen fixation and photosynthesis was observed in nodulated plants growing at elevated CO2. These plants had greater whole‐plant photosynthesis and nitrogenase activity, leaf area and nitrogen content, as well as nodule and plant dry mass, relative to nodulated plants grown at ambient CO2 and non‐nodulated plants grown at both CO2 levels. This feedback may be an important way in which the potential carbon drain of nitrogen fixation on the host plant could be compensated; increased nitrogen availability resulting in stimulated leaf area growth and whole‐plant photosynthesis. The relative amount of dry mass allocated below ground decreased for all seedlings over time, and the amount allocated above ground increased. This shift in allocation occurred slowly and at a constant rate in non‐nodulated plants and more rapidly and abruptly when plants were nodulated. The proportion of dry mass allocated below ground was consistently greater in non‐nodulated plants. Dry mass allocation to the stem was increased when combined nitrogen was applied and was greatest in nodulated plants grown at high CO2. Dry mass partitioning among other organs was not directly affected by nodulation, CO2 enrichment, or other treatment interactions.
Polyamine metabolism in ‘green‐islands’ on powdery mildew‐infected barley leaves: possible interactions with senescence
Authors: COGHLAN S. E. , WALTERS D. R.
Published: April 2006

Polyamine metabolism, lipoxygenase and catalase activities and ethylene production were examined in green‐islands induced to form on detached barley leaves infected with the powdery mildew fungus, Erysiphe graminis f. sp. hordei Marchal. Several‐fold increases in free polyamines were detected in green‐islands, which could not be accounted for by changes in polyamine biosynthetic and degradative enzymes: a small increase in ornithine decarboxylase (ODC) activity, greatly decreased arginine decarboxylase (ADC) activity, virtually unchanged activity of S‐adenosylmethionine decarboxylase (AdoMetDC) and greatly increased polyamine oxidase (PAO) activity. Changes in conjugated forms of polyamines suggest that elevated free polyamine concentrations might result from reductions in this pool. Green‐island tissues displayed a reduced activity of lipoxygenase, unchanged catalase activity and a greatly lowered rate of ethylene production. Chlorophyll concentration and rates of photosynthesis and dark respiration were slightly increased in these tissues.

In senescing regions of infected leaves, there was a small increase in free putrescine and spermine and a decrease in spermidine concentration, while concentrations of conjugated polyamines were substantially reduced. This was accompanied by an overall decrease in ODC and ADC activities and an increased activity of both AdoMetDC and PAO. These regions exhibited lowered lipoxygenase activity, greatly enhanced catalase activity and reduced rates of ethylene production. In addition, senescing regions exhibited a substantial reduction in chlorophyll concentration and the rate of photosynthesis, although dark respiration was similar to control values.

These results support the view that green‐islands represent areas of the infected leaf where senescence is retarded, biosynthetic activity is retained and in which polyamines may play an important role. On the other hand, although polyamine concentrations were reduced in senescing areas, other changes occurring there suggest that some functional integrity is maintained in that tissue.
Nitrogenase in Frankia from root nodules of Alnus incana (L.) Moench: immunolocalization of the Fe‐ and MoFe‐proteins during vesicle differentiation
Authors: HUSS‐DANELL KERSTIN , BERGMAN BIRGITTA
Published: April 2006

The localization of nitrogenase was studied in root nodules of Alnus incana (L.) Moench in symbiosis with a local source of Frankia. Nodules were fixed in glutaraldehyde and embedded in Epon or LR White. Ultrathin sections were examined by TEM after incubation with antisera against nitrogenase and gold‐conjugated secondary antibodies. Antisera against dinitrogenase reductase (Fe‐protein) from Rhodospirillum rubrum and dinitrogenase (MoFe‐protein) from Azotobacter vinelandii were used. Immunogold label density in hyphae and in spores of Frankia was low and similar to that of plant tissue. Very young vesicles without septa showed a label density of Fe‐protein similar to that of hyphae, while young vesicles with a few, usually non‐transversing, septa had a significant but still low density of label. Mature vesicles, highly compartmentalised due to transversing septa, contained statistically significantly more Fe‐protein label than all other cell types. Old degenerating vesicles always contained nitrogenase, about half as much as that of mature vesicles but often more than young vesicles. Similarly, MoFe label was not detected in hyphae, appeared in young but was greatest in mature vesicles. It is apparent that differentiation of vesicles reaches a certain stage of development prior to the onset of nitrogenase synthesis.
The control of ozone uptake by Picea abies (L.) Karst. and P. sitchensis (Bong.) Carr. during drought and interacting effects on shoot water relations
Authors: DOBSON M. C. , TAYLOR GAIL , FREER‐SMITH P. H.
Published: April 2006

Exposure to O3 alone has not yet been shown to reproduce the symptoms of the various types of spruce decline which have been identified in Europe. However, there is increasing evidence that this pollutant has physiological effects which interact with those of other environmental factors in ways which may be important in determining tree condition and growth. The effects of O3 episodes and drought on O3 uptake, gas exchange and water relations of Picea abies (L.) Karst. and P. sitchensis (Bong.) Carr. were investigated in two experiments. In the first a rapidly drying soil mixture was used, and seedlings of P. abies were exposed to short (2 h) daily episodes of O3 at 80 nl 1−1 on each day of a 5 d drought. Photosynthesis (A) and stomatal conductance (gs) were significantly decreased (P= 0.01) by water deficit and as a consequence, uptake of O3 by the plants was also significantly decreased. Exposure to O3 did not affect A or gs for this species. In the second experiment a soil mixture designed to give a slower development of water deficit was used and 1 + 1 transplants of P. sitchensis were exposed to a single O3 episode (up to 100 nl 1−1 for 3 h) after water had been withheld for 7 or 14 d. Hofler diagrams showed that mild water deficits did not affect shoot water relations. However, O3 significantly increased solute potential (Ψs) after 7 d of drought, an effect which was lost after 14 d of drought. Flux of O3 to the watered plants was greater than to the unwatered plants at all concentrations, the effect being more marked at higher concentrations. This effect was partly attributable to the greater stomatal conductances recorded for the well watered plants, but was also partly due to stomatal opening caused by O3, an effect which was diminished or reversed for unwatered plants.
A biophysical study of abscisic acid interaction with membrane phospholipid components
Authors: LESHEM YA'ACOV Y. , COJOCARU MIRIAM , MARGEL SHLOMO , EL‐ANI DALIA , LANDAU EHUD M.
Published: April 2006

Molecular area/surface pressure Langmuir isotherms of amphiphilic dipalmitoylphosphatidylcholine (DPPC) monolayers indicated that abscisic acid (ABA) has a marked rigidifying effect, expressed as reduction of molecular area and increase of monolayer collapse point. Moreover, ABA markedly increased aqueous droplet hydrophobicity, as indicated by a concentration‐dependent increase of contact angle when placed on a hydrocarbon chain surface; no such effects were obtained on either amphiphilic or octadecyltrichlorosilane surfaces. A combination of TLC and mass spectometry revealed the presence of DPPC in Vicia faba and Commelina communis guard‐cell protoplast membranes. ABA also increased plasma membrane rigidity as evidenced by probing with lipid specific membrane probes, namely diphenylhexatriene and its trimethyl derivative. Regarded together the results suggest a specific site of ABA binding to DPPC. The linkage between senescence and stomatal closure is discussed in the light of the new data presented here. It is suggested that DPPC in guard‐cell membranes may have a physical role in preventing collapse and/or bursting. In this connection an analogy is drawn with pulmonary mechanisms.
Ionic control of intracellular and extracellular Cd uptake by the moss Rhytidiadelphus squarrosus (Hedw.) Warnst
Authors: WELLS J. M. , BROWN D. H.
Published: April 2006

The effects of K, Ca, Mg and H ions on the kinetics of Cd uptake by the moss Rhytidiadelphus squarrosus (Hedw.) Warnst were investigated. The affinity of extracellular exchange sites for these ions decreased in the order Cd, H > Ca > Mg ≫ K and there were competitive interactions between ions. The affinity of the intracellular Cd transport site for these ions decreased in the order Ca > Cd > Mg ≫ K. Calcium was shown to be competitive and Mg a non‐competitive inhibitor of intracellular Cd uptake. Intracellular Cd uptake, optimal at about pH 5.6, was highly sensitive to pH, which primarily affected the Vmax. Potassium, supplied at less than 1 mM, had no significant effect on Cd uptake. However, at concentrations greater than 1 mM, KNO3 caused both a stimulation in transport site activity and reduced affinity for Cd.

Pretreatment with KNO3 removed potentially competing ions from the cell wall, altering the subsequent chemical equilibria established when moss shoots were incubated in Cd solutions. Reduced competition from ions removed by KNO3 pretreatment resulted in a higher affinity of both transport sites and extracellular exchange sites for Cd, Ca and Mg. The results demonstrate quantitatively the regulatory effects on intracellular metal uptake of the extracellular ionic environment provided by the cell wall.
The role of free radicals and radical processing systems in loss of desiccation tolerance in germinating maize (Zea mays L.)
Authors: LEPRINCE OLIVIER , DELTOUR ROGER , THORPE P. CHRIS , ATHERTON NEIL M. , HENDRY GEORGE A. F.
Published: April 2006

On germination, maize seeds rapidly become intolerant of desiccation. Germinating seeds exposed to dehydrating conditions for 24 h show a significant rise in lipid peroxidation and the accumulation of an electron paramagnetic resonance‐detectable organic radical, in parallel with the development of desiccation intolerance. Throughout the 5‐d‐long germination phase and the period of loss of desiccation tolerance, the radical scavengers α‐ and γ‐tocopherol and glutathione accumulate in response to episodes of dehydration. However dehydration suppresses, or delays, increases in activity of superoxide dismutase, peroxidase and glutathione reductase, major components in the protection against activated forms of oxygen. We present evidence of a sequence of events in which activated oxygen plays an early and probably causative role in loss of tolerance of desiccation in these seeds.
Some effects of nitrogen, phosphorus, potassium and carbon dioxide concentration on the morphology and vegetative reproduction of Sphagnum cuspidatum Ehrh.
Authors: BAKER R. G. E. , BOATMAN D. J.
Published: April 2006

Five experiments are described which were designed to investigate the effects of varying the concentrations of nitrate, phosphate, potassium and carbon dioxide in the culture solution on the morphology and vegetative reproduction of Sphagnum cuspidatum Ehrh. The plants were grown axenically from spores sown on agar containing inorganic salts and then transferred to aqueous culture solutions through which air containing enhanced concentrations of carbon dioxide was passed.

In three of the experiments the plants were grown in a balanced inorganic salt solution at various dilutions and in two of these the concentration of carbon dioxide in the gas bubbled through the solution was varied. The concentrations of nitrogen, phosphorus and potassium were varied independently and in combination in the remaining experiments while the concentration of carbon dioxide was kept constant.

In some of the experiments the minimum concentrations of nitrogen and potassium supplied were considerably below the minimum average concentrations recorded in rain but the minimum concentration of phosphorus supplied was within the upper part of the range recorded in rain. Within the ranges supplied the concentrations of all three elements and of carbon dioxide affected interfascicle length and vegetative reproduction (innovation formation) but it was concluded that the element limiting innovation formation in natural conditions is phosphorus.
Kinetics of phosphorus uptake by the germ‐tubes of the vesicular–arbuscular mycorrhizal fungus, Gigaspora margarita
Authors: THOMSON B. D. , CLARKSON D. T. , BRAIN P.
Published: April 2006

We characterized kinetically the phosphorus (P) transport systems present in the germ‐tubes of the vesicular‐arbuscular (VA) mycorrhizal fungus, Gigaspora margarita Becker & Hall. Germinated spores of G. margarita were grown without P or with 1000 μM P for 10 d. The rate of P uptake by these spores and their associated germ‐tubes was measured at external P concentrations ranging from 1 to 10000 μM and in the presence or absence of an uncoupler of oxidative phosphorylation.

Two transport systems for P were identified in the germ‐tubes of G. margarita grown without P. System I, an active high affinity system with a Km of 1.8–3.1 μM and a Vmax of 3.1–3.6 nmol mg protein−1h−1and System II, a passive low affinity system with a Km of 10200–11 300 μM and a Vmax of 445–895 nmol mg protein−1h−1. These two systems operated simultaneously at concentrations of P ranging from 1 to 10000 μM. Two transport systems for P were also identified in the germ‐tubes of G. margarita grown with 1000 μM P. The Km of System I in these germ‐tubes (13.4 μM) was increased relative to the Km of System I in germ‐tubes grown without P. There was also evidence to suggest that the Km of System II was increased in germ‐tubes grown with 1000 μM P.

The values of Km and Vmax for the P transport systems in the germ‐tubes of G. margarita are similar to those observed in the hyphae of other fungi and in plant roots.
Aluminium polyphosphate in the ectomycorrhizal fungus Suillus variegatus (Fr.) O. Kunze as revealed by energy dispersive spectrometry
Authors: VÄRE H.
Published: April 2006

The aluminium detoxification mechanism of an ectomycorrhizal fungus, Suillus variegatus (Fr.) O. Kunze, grown on Petri dishes was studied using an atomic absorption spectrometer (AAS) and scanning transmission electronmicroscope with an electron dispersion photometer (STEM‐EDS). Higher concentrations of soluble Al in the growth medium resulted in abundant formation of aluminium polyphosphate granules in the hyphae, which have not been noted earlier in ectomycorrhizal fungi or in their mycorrhizas. EDTA washing and STEM‐EDS demonstrated that the granules were mainly located in the cell walls. The results suggest that growth of the fungal mycelium decreased as a result of higher Al and lower P concentrations inside the cells, as measured by AAS. The aluminium polyphosphate granules also contained varying amounts of other elements such as Ca, Cl, K, S, and Si.
Implication of ectomycorrhizal fungi in the cytokinin relations of loblolly pine (Pinus taeda L.)*
Authors: WULLSCHLEGER S. D. , REID C. P. P.
Published: April 2006

Seven ectomycorrhizal fungi were screened by a soybean cell division bioassay to determine their potential for cytokinin synthesis. Fungal isolates of Rhizopogon roseolus (Corda) Hollos and Suillus punctipes (Peck) Sing, released significant quantities of cytokinin‐like substances into the culture medium. In contrast, Cenococcum geophilum (Fr.), Hebeloma crustuliniforme (Bull. ex. St. Amans) Qual., Pisolithus tinctorius (Pers.) Coker and Couch, Suillus granulatus (L. ex. Fr.) O. Kuntze, and Thelephora terrestris (Ehrh.) Fr. failed to elicit a positive cytokinin response in the soybean bioassay. Purification of S. punctipes culture filtrates by cation exchange, organic solvent partitioning, and separation on Sephadex LH‐20 revealed the presence of compounds with the same retention volume as zeatin and zeatin riboside. Greenhouse studies with loblolly pine (Pinus taeda L.) indicated that, together with improved plant growth and enhanced mineral nutrition, P. tinctorius mediated a significant effect on host cytokinin relations. Cytokinin activity of extracted needles increased 44 and 30% for 12‐ and 14‐month‐old seedings, respectively, following ectomycorrhizal establishment. Axenically grown seedlings colonized by 5. punctipes showed no alterations in growth, nutrition, or cytokinin concentration, compared to non‐inoculated controls, even though mycorrhizal formation exceeded 30%. The ability of ectomycorrhizal fungi to affect host cytokinins was not dependent upon an ability to synthesize cytokinins in pure culture. Results are discussed in relation to improved mineral nutrition, enhanced root growth, and increased short‐root proliferation in the ectomycorrhizal association.
Production and development of seed and pollen in grafts of Picea sitchensis (Bong.) Carr. treated with gibberellin A4/7 to induce coning and the effect of forcing treatments
Authors: PHILIPSON J. J. , OWENS J. N. , O'DONNELL M. A.
Published: April 2006

Coning was induced on container‐grown grafts of Picea sitchensis (Bong.) Carr. by stem injection of gibberellin A4/7 in combination with heat and drought in a polythene house. After overwintering outdoors pollen and seed development in the following year were studied. Control grafts remained outdoors, except for a 16 d period (late April‐early May) in the polythene house to facilitate pollen shedding and pollinations. Pollen was at the 2‐ to 3‐cell stage when these grafts were placed in the polythene house and the grafts produced good quantities of high quality pollen and seed which could be used in tree improvement programmes. Placing grafts in warm conditions in January or March, when pollen was predominantly at a pre‐meiotic stage, advanced cone‐bud development but reduced the yield of pollen and seed, though forcing in March was less detrimental. Cytological study showed no meiotic irregularities in pollen mother cells forced in January or March, but abnormalities in later stages of pollen development included failure of tetrads to separate, retardation of development and degeneration of immature pollen. Poor seed development in January‐forced cones may be attributed to retarded development of the distal portion of the cones. Nucelli in the distal ovules had not become secretory at pollination and hence little or no pollen was taken into the micropyle, also there was retarded development of the megagametophyte which could adversely affect fertilization. More proximal ovules of forced cones, and ovules of control cones, had well developed nucelli which were actively secreting pollination droplets, pollen was commonly found in the micropyle and the megagametophyte was developing normally.
The effect of soil compaction on wheat during early tillering
Authors: ATWELL B. J.
Published: April 2006

summary

Wheat (Triticum aestivum L. cv. Eradu) was grown in the field on a deep loamy sand which had either a compact soil layer (compact soil) between 10 and 55 cm depth or a deep‐tilled profile (loosened soil). Between 33 and 62 d after sowing, shoots grew more slowly and had fewer tillers on the compact soil. Nitrogen and K (but not P) concentrations were 12–14% lower in shoots grown on the compact soil, suggesting that nutrient deficiencies might have contributed to impaired shoot growth.

Seminal root axes elongated at 0.60 and 1.78 cm d−1 in compact and loosened soil, respectively. At 47 d after sowing, roots in compact soil were short, thick and contorted; cortical cells expanded radially in response to high soil strength but were 66 % shorter, causing cortical cell volumes to be smaller than in roots from loosened soil. The diameter of the stele was not affected by soil compaction. In addition the zone of elongation was much nearer the apex and shorter in roots from compact soil. Overall, seminal roots in compact soil grew slowly and explored the soil profile inefficiently.
The effect of soil compaction on wheat during early tillering
Authors: ATWELL B. J.
Published: April 2006

summary

Wheat (Triticum aestivum L. cv. Eradu) was grown in the field or glasshouse on a deep loamy sand which had either a compact soil layer (compact soil) between 10 and 55 cm depth or a deep‐tilled profile (loosened soil). The pattern of assimilate transport to the roots was investigated. Previously reported growth rates and solute concentrations of the seminal root axes were coupled with rates of O2 uptake measured in the field to give estimates of dry weight import into the ethanol‐insoluble (structural), ethanol‐soluble (osmotic) and respiratory pools. The calculated daily import of dry weight was 28% less in mechanically impeded than unrestricted apices. However, the dry weight required to produce 1 cm of root was twice as high for axes in compact soil. In these roots, a greater proportion of imported substrates went into ethanol‐insoluble matter, probably cell walls. Non‐respired 14C lost from root systems into the rhizosphere was measured in the glasshouse and found to be less than 4% of the 14C fixed 72 h earlier, even in compact soil.

The partitioning of 14C‐labelled assimilate in plants from the two treatments was compared. The proportion of 14C in the ethanol‐soluble fraction was hardly affected by tissue age or soil strength. Furthermore, 62–82% of the soluble 14C was in the neutral (sugar) fraction in the roots. However, the 14C concentration (dry‐weight basis) in apices of seminal root axes was substantially greater when the roots grew in loosened soil. The greater sink strength of seminal root? growing in loosened soil was reflected in a 3‐fold larger incorporation of 14C into each gram of new ethanol‐insoluble material formed. In contrast, concentrations of 14C were similar in mature root tissues, nodal roots and shoots taken from both soil treatments.
Influence of ozone and soil magnesium status on the cold hardiness of loblolly pine (Finns taeda L.) seedlings
Authors: EDWARDS G. S. , PIER P. A. , KELLY J. M.
Published: April 2006

summary

One‐year‐old half‐sib loblolly pine (Pinus taeda L.) seedlings were planted in a sandy loam soil having approximately 15 or 35 mg kg−1 of exchangeable Mg and were exposed to subambient, ambient, or twice ambient (0.02, 0.05, or 0.09 μl O3 1−1, respectively) concentrations of O3 in open‐top chambers from April to October 1988. The cold hardiness of seedlings was tested on October 24, January 24, and March 21 by subjecting needle samples from the first and last growth flush to temperatures of ‐5, ‐10, ‐15, and ‐ 20 °C and determining relative electrical conductivity of the diffusate. Seedlings exposed to twice ambient O3 levels during the growing season were less hardened in early autumn and spring than seedlings exposed to ambient or subambient levels of O3, suggesting that O3 affects the plant's hardening and dehardening processes. Ozone and soil Mg treatments had no significant effects on visible injury of shoots following freezing treatments, nor were any visible symptoms of injury due to O3 evident during the study. Water potential components of excised shoots were estimated using pressure‐volume analysis. Osmotic potentials became more negative over the dormant period, suggesting that solutes had accumulated in the cells as seedlings hardened. Seedlings grown in high Mg soil had less negative osmotic potentials in January and March than those grown in low Mg soil, suggesting that seedlings in high Mg soil were more susceptible to cold temperatures, probably due to greater physiological activity.
Effects of low ozone concentrations on growth of Betula pubescens Ehrh., Betula verrucosa Ehrh. and Alnus incana (L.) Moench
Authors: MORTENSEN LEIV M. , SKRE ODDVAR
Published: April 2006

summary

Seedlings of Betula pubescens, Betula verrucosa and Alnus incana were grown for 50 days in growth chambers at four ozone concentrations (25, 35, 53 and 82 nl 1 −1) fot 7 h day−1. Shoot and root dry weight decreased almost linearly with increasing ozone concentration in the three species. Shoot/root and leaf/stem dry weight ratios were unaffected by ozone concentration, while leaf senescence was significantly enhanced by increasing the concentration. Visible ozone injury was observed at 53 nl 1−1 and above.
Dormancy break in seeds of Impatiens glandulifera Royle
Authors: MUMFORD PAULINE M.
Published: April 2006

summary

When dormancy is broken by chilling in Impatiens glandulifera Royle anthocyanin appears in the cells of the root cap acting as a marker of the physiological condition of the seeds. This precedes growth of the embryo as indicated by increase in seed weight. Abscisic acid at some concentrations can inhibit dormancy break and anthocyanin synthesis in the root cap. All tissues of the embryo, when excised, responded independently to the cold stimulus. Grafting pieces of dormant and non‐dormant seed showed the agent effective in breaking dormancy was not transmissible between a piece of chilled embryo placed in contact with a piece of dormant embryo.
Illtyd Pools, Brecon: description and conservation*
Authors: MEADE R. , WHEELER B. D.
Published: April 2006

summary

The Mires Research Group of the British Ecological Society examined Traeth Mawr and Traeth Bach, two closely‐adjoining mires near Brecon, Wales, in September 1984. Both occupy former lake basins with late‐glacial deposits overlain with fen peat. At Traeth Bach, this continues to the surface but, at Traeth Mawr, it is overlain by ombrotrophic peat with Sphagnum. The absence of this deposit from Traeth Bach may reflect differences in successional infilling or its removal by peat excavation (for which there is some evidence in both basins). It almost certainly does not reflect major differences in chemical conditions in the two basins as both contain base‐rich water (at least at depth). Such water (derived from springs and seepages) irrigates part of the margin of Traeth Mawr forming a base‐rich partial lagg and permits an unusual juxtaposition of plant species and vegetation types. Parts of the ombrotrophic surface are badly gullied and, perhaps in response to this, in places the surface is rather dry and degraded (with some trees). Moreover, marginal base‐rich water can now penetrate into the ombrotrophic area along the eroded gullies, leading to further changes in its floristic character. A plan for management is proposed.
The effect of atmospheric desiccation and osmotic water stress on photosynthesis and dark respiration of lichens
Authors: NASH T. H. , REINER A. , DEMMIG‐ADAMS B. , KILIAN E. , KAISER W. M. , LANGE O. L.
Published: April 2006

summary

Four species of epiphytic lichens from California with varying responses to salinity were studied to determine the response of CO2 exchange to decreasing water potential (Ψ). Changes in Ψ were induced either by allowing dry thalli to come into equilibrium with atmospheres of defined water vapour pressure, or by osmotic stress through incubation of the thalli in sea salt or sorbitol solutions. In two species the gradual decline of CO2 uptake rates with decreasing Ψ was independent of the method which was used to establish ft (and therefore relatively independent of the bulk water content of the thalli); measurable CO2 fixation occurred in Dendrographa minor Darb. and Ramalina menziesii Tayl. to values of Ψ as low as –38 and – 22 MPa, respectively. Photosynthesis of Evernia prunastri (L.) Ach. responded similarly to low Ψ which was induced either through atmospheric desiccation or osmotic dehydration (sorbitol). However, E. prunastri was much more sensitive to low Ψ when the thallus was treated with NaCl solutions. Photosynthesis in Pseudocyphellaria anthraspis Magn., the only species investigated with a blue‐green (cyanobacterial) photobiont, was strictly dependent on wetting of the thallus with water. Net photosynthesis was detectable to – 3−5 MPa in sorbitol and salt solutions, but in moist air of a similar Ψ P. anthraspis showed no CO2 uptake. In all four species, dark respiration was markedly less sensitive to osmotic dehydration in sorbitol or salt solutions than at the same Ψ under atmospheric desiccation. In E. prunastri, salt stress combined with high light resulted in a much more pronounced decrease in the rate of photosynthesis than either salt stress in low light, or high light alone. These species provide a model system to differentiate the effect of atmospheric desiccation and osmotic stress on lichen metabolism, and to study the interaction of drought per se with other stress factors such as salt and high light.
Compatible solutes – the mycological dimension and their role as physiological buffering agents
Authors: JENNINGS D. H. , BURKE R. M.
Published: April 2006

summary

Glycerol, mannitol and proline, compatible solutes produced by fungi in response to salt or water stress, can be involved in futile or substrate cycles. It is argued, on the basis of chemostat cultures with both bacteria and fungi, that substrate cycles which dissipate energy are necessary processes when fungi are subjected to osmotic or water stress. Whether or not the three compounds are also involved in overflow metabolism remains to be established. It is argued that substrate cycles may have more general importance when a fungus is growing under types of stress other than that caused by high concentrations of salt or low availability of water. The arguments put forward strengthen the case for considering the three compounds as part of a general class of physiological buffering agents. A modified version of the mannitol cycle is proposed.
Wood decay, and phosphorus and fungal biomass allocation, in mycelial cord systems
Authors: WELLS J. M. , BODDY LYNNE
Published: April 2006

summary

Wood block inocula, of different decay states, colonized by Phanerochaete velutina (D.C.: Pers.) Parmasto and Phallus impudicus (L.) Pers., were supplied with [32P]orthophosphate 1 wk after mycelium had made contact with newly supplied sterile wood baits. Inoculum decay state affected the initial pattern of mycelial outgrowth, biomass, phosphorus uptake and subsequent decay rates of newly supplied baits. P. velutina and P. impudicus translocated up to 75 and 13 % respectively of phosphorus accumulated by the inoculum to the new supplied bait, translocation being in proportion to the decay state of the inoculum. On contact with baits, biomass was preferentially allocated to connective rather than non‐connective mycelium. This was accompanied by regression of non‐connective mycelium, which depended on the decay state of the inoculum. Phosphorus movement via connective cords was up to ten times higher in non‐connective cords, maximal rates of 7225 nmol P cm−2 d−1 being recorded for cords from the most decayed P. velutina inocula.
Chemotropism – the key to ectomycorrhizal formation?
Authors: HORAN D. P. , CHILVERS G. A.
Published: April 2006

summary

When eucalypt mycorrhizal fungi were separated from eucalypt roots by interposing membrane niters, the fungal hyphae grew directly through these to contact the host root apices. The same mycelia grown on membrane filters over various agar media always remained above and readily detachable from the membranes, with no evidence of penetration. More significantly, these same eucalypt fungi did not grow through membranes towards the roots of several non‐host plants under the same circumstances, and mycorrhizal fungi of other plants such as birch and pine failed to penetrate membranes overlying eucalypt roots. It seems likely that there is a selective chemotropic attraction of these mycorrhizal fungi to substances diffusing from compatible host root apices. Such chemotropism could provide the signal which initiates the ectomycorrhizal infection process in the root cap region, and guides the inward growth of the hyphae through that tissue during the early stages of sheath formation.
Self‐Incompatibility inPapaver rhoeasL.: inhibition of incompatible pollen tube growth is dependent on pollen gene expression
Authors: FRANKLIN‐TONG VERNONICA E. , LAWRENCE MICHAEL J. , FRANKLIN F. CHRISTOPHER H.
Published: April 2006

summary

In order to gain an insight into the cellular activities which lead to the inhibition of pollen tube growth following a self‐incompatible response, we have been studying the effects of various metabolic inhibitors on pollen–stigmatic extract interactionsin vitro.The results indicate that both transcription and glycosylation are required for the full inhibition of pollen tube growth during an incompatible response inPapaver rhoeas.The ability of actinomycin D to partially alleviate an incompatible reaction suggests that during the response, pollen gene expression is induced; we have found that this is indeed the case and have identified novel proteins produced in the pollen which are associated with the incompatibility response. These findings give a clear indication thatde novotranscription of pollen genes which are specific to this response, play an important role in the inhibition of pollen tube growth in this species. This provides a significant step towards the elucidation of the mechanism whereby pollen tube growth is arrested following an incompatible reaction in this species.
Regulation of nutrient transfer between host and fungus in vesicular—arbuscular mycorrhizas
Authors: SCHWAB SUZANNE M. , MENGE JOHN A. , TINKER P. B.
Published: April 2006

summary

Although the overwhelming majority of non‐aquatic vascular plants form vesicular‐arbuscular (VA) mycorrhizal associations, the extent of colonization of the host root by any given fungal symbiont varies considerably depending on host and environmental factors. Because VA mycorrhizal fungi are obligate biotrophs, transfer of photosynthate from host to fungus may be an important factor in regulating the extent of VA mycorrhizal formation. Host metabolites must cross the plasma membrane before becoming available to the fungus. Several studies on rates of root exudation under various environmental conditions show a strong correlation between rates of root exudation and percent of root length colonized by VA mycorrhizal fungi. However, passive leakage of simple metabolites from roots as the sole means of regulating fungal colonization seems improbable for an obligate biotroph which has not yet been successfully cultured on any artificial medium. So far there has been insufficient investigation of hormone interactions between symbionts, and of the interference by the fungus in host cell wall synthesis, to evaluate the possible role of these factors in controlling growth of VA mycorrhizal fungi. Cytochemical studies of the host‐fungus interface suggest modification of host plasma membrane ATPase activity as arbuscules develop, but the function of this altered activity remains unresolved. The presence of a linked P1‐photosynthate exchange mechanism on the host plasma membrane analogous to the P1‐photosynthate translocator known to exist in the outer membrane of chloroplasts remains an uninvestigated possible mechanism for balancing photosynthate demand by the fungus with enhanced P uptake.
Ecophysiological comportment of the tropical CAM‐tree Clusia in the field
Authors: BALL E. , HANN J. , KLUGE M. , LEE H.S.J. , LÜTTGE U. , ORTHEN B. , POPP M. , SCHMITT A. , TING I. P.
Published: April 2006

summary

Clusia rosea Jacq. is abundant in the moist parts of the Caribbean island of St John (US Virgin Islands, Lesser Antilles) but relatively rare along the dry south coast. Three types of seedlings were encountered, terrestrial seedlings, seedlings growing as humus‐epiphytes on other trees, and seedlings growing inside the tanks of the bromeliad Aechmea lingulata (L.) Baker. Free‐living trees grow from terrestrial seedlings or from epiphytic seedlings strangling and shading their host trees. Leaf‐Na+ levels were always low (1–4 mequiv I−1 tissue water); trees close to the shore were not affected by salinity. In leaves of mature C. rosea trees, levels of Ca2+, Mg2+ and K+ were about 60–90, 40–50, 45–55 mequiv I−1 tissue water, respectively. Epiphytic seedlings tended to contain lower levels of these inorganic cations than seedlings growing terrestrially or in the tanks of Ae. lingulata. Epiphytic seedlings contained significantly less nitrogen than terrestrial seedlings. In the leaves of mature trees N‐levels were independent of altitude and location on the island, but shaded leaves had significantly higher N‐levels than exposed leaves. Light compensation point of photosynthesis in epiphytic seedlings performing C3‐photosynthesis was 17–5 (μmol photons m−2 s−1), photosynthesis was saturated at about 300μmol photons m−2 s−1 showing a maximum rate of CO2‐uptake of 2–3 μmol m−2 s−1.
Ecophysiological comportment of the tropical CAM‐tree Clusia in the field
Authors: BALL E. , HANN J. , KLUGE M. , LEE H. S. J. , LÜTTGE U. , ORTHEN B. , POPP M. , SCHMITT A. , TING I. P.
Published: April 2006

summary

Measurements were performed on leaves of Clusia rosea Jacq. trees in the moist central mountains (330 to 365 m above sea level) and at the dry south coast of St John Island (US Virgin Islands, Lesser Antilles). Seedlings of C. rosea were also studied in the central hills.

During the study period (March 1989) all trees showed crassulacean acid metabolism (CAM), in which net CO2uptake extended for a remarkably long time in the morning (phase II of CAM: until about 11 to 12 h) and contributed about 1/3 of total net CO2‐uptake. During the night (phase I of CAM) malic acid and citric acid were accumulated concurrently at a molar ratio of malic: citric acid of about 1.6.

Internal recycling of respiratory CO2 was 20% of total CO2 fixed during the night. Water‐use‐efficiency (mol CO2 taken up: mol H2O transpired) was 0.014 to 0.022. The pH of leaf‐cell sap at the end of the dark period was 2.85. This would still allow an H+‐ATPase at the tonoplast to transport 2H+ into the vacuole per ATP hydrolysed when operating near thermodynamic equilibrium.

Free sugars, glucose and fructose, and starch were used as precursors for the CO2‐acceptor phosphoenolpyruvate during the dark period; contributions of the two hexoses were about equal and together four‐times that of starch.

Xylem tensions showed increases of up to 8 bar during day‐time. Leaf‐sap osmotic pressures did not change significantly; the trend was a small decline during day‐time.

Among the seedlings, three different modes of photosynthesis were encountered, namely C3‐photosynthesis in terrestrial and in epiphytic seedlings, continuous stomatal opening and CO2‐uptake day and night in epiphytic seedlings, and CAM in seedlings growing in the tanks of Aechmea lingulata (L.) Baker.
Acclimation to ozone stress in radish: leaf demography and photosynthesis
Authors: HELD A. A. , MOONEY H. A. , GORHAM JAMES N.
Published: April 2006

summary

Whole plant acclimation to ozone exposure in growth‐chamber cultivated radish (Raphanus sativus L. cv. Cherry Belle) was investigated. The primary goal was to separate developmental from physiological ozone acclimation processes. Plants were grown for 37 days at two different lengths of ozone exposure and a control treatment. After germination, seedlings were transplanted into controlled growth chambers and exposed to daytime (10 h) ozone (0.12 μl 1−1) either on the next day (continuous ozone treatment) or three days later (intermediate treatment) and compared to a control (average ambient ozone concentration (0.01–0.02 μml 1−1). Plants grown in ozone after transplanting accumulated considerably less biomass than the controls, but had higher dry weights than the intermediate treatment, implying an acclimation response. Photosynthetic capacity and nitrogen content of leaves decreased at high levels of ozone exposure resulting in an accelerated leaf senescence. No distinct leaf‐level physiological acclimation to ozone exposure was seen based on gas exchange measurements. As an apparent compensatory response, plants exposed to ozone had higher leaf production rates than control plants, at the expense of root and hypocotyl growth. This developmental, whole‐plant response appeared to be the most effective acclimation response to ozone exposure seen in radish. However, it did not fully compensate for the damage caused by ozone, since plants still showed considerable reductions in growth.
Transition metals and the ability of Sphagnum to withstand the phytotoxic effects of the bisulphite ion
Authors: BAXTER R. , EMES M. J. , LEE J. A.
Published: April 2006

summary

Sphagnum cuspidatum Ehrh. (ex Hoffm.) and Sphagnum recurvum P. Beauv. were collected from the hog surface and minerotrophic lagg zones of two relatively remote ‘unpolluted’ sites in Northern England and North Wales, and two ‘polluted’ sites in the S. Pennines. In addition, surface peat and surface water samples were taken adjacent to the sample points.

Sphagnum recurvum from mire surfaces in the S, Pennines and drainage channels at remote sites was exposed to the phytotoxic bisulphite ion (HSO3−), which subsequently rapidly disappeared from the bathing solution (< 6 b). When the same species, taken from mire surfaces at remote sites, was exposed to HSO3−, a much slower disappearance of this ion occurred. Sphagnum cuspidatum from remote sites showed a similar response. Both became bleached and eventually died. Sphagnum recurvum, growing in the drainage channel at the remote site showed a higher extracellular concentration of transition metals an cation exchange sites; a consequence of a higher concentration of the same ions in these telluric waters. At the S. Pennine sites transition metal concentrations in the surface peat were high. Here, as in the drainage channels at the remote sites, the extracellular metal concentrations imparted to the moss the ability rapidly to remove HSO3−, from the growth medium.
The hydraulic architecture of trees and other woody plants
Authors: TYREE MELVIN T. , EWERS FRANK W.
Published: April 2006

summary

In this paper, we have reviewed how the hydraulic design of trees influences the movement of water from roots to leaves. The hydraulic architecture of trees can limit their water relations, gas exchange throughout the crown of trees, the distribution of trees over different habitats and, perhaps, even the maximum height that a particular species can achieve. Parameters of particular importance include: (1) the vulnerability of stems to drought‐induced cavitation events because cavitation reduces the hydraulic conductance of stems, (2) the leaf specific conductivity‐of stems because it determines the pressure gradients and most negative water potentials needed to sustain evaporation from leaves, (3) the water storage capacity of tissues because this might determine the ability of trees to survive long drought periods. All of these parameters are determined by the structure and function of anatomical components of trees. Some of the ecological and physiological trade‐offs of specific structures are discussed.

CONTENTS

Summary

I.
Introduction
346

II.
Water flow through pipes and the unit pipe model
347

III.
Parameters and concepts to describe hydraulic architecture
349

IV.
Patterns of hydraulic architecture in woody plants
350

V.
Vulnerability to cavitation: relation to hydraulic architecture and drought resistance
354

VI.
Dynamic and steady state models of water flow in trees
355

VII.
The segmentation hypothesis
357

References
359
Evidence for a role for the cell membrane in copper tolerance of Mimulus guttatus Fischer ex DC.
Authors: STRANGE JULIE , MACNAIR MARK R.
Published: April 2006

summary

The effect of copper on root growth, K+ efflux and short‐term copper uptake by three isogenic genotypes of Mimulus guttatus Fischer ex DC. differing only in their copper tolerance gene is studied. The tolerant homozygotes do not differ in any way from the heterozygotes. The non‐tolerant homozygotes show greater root inhibition, greater K+ efflux, and greater short‐term Cu2+ uptake. The difference in the uptake parameters is best described by a greater linear diffusion term in the non‐tolerant genotypes. These results suggest that copper damages the cell membrane, and that this damage leads to an increase in the leakiness of the membrane, leading to both greater K+ efflux and Cu2+ influx via diffusion. This suggests that the primary copper tolerance mechanism probably resides in the cell membrane. The rapidity with which the differences between the genotypes is established suggests that the differences are constitutive. It is argued that these results provide further evidence against the involvement of phytochelatins in the primary tolerance mechanism.
Post‐glacial vegetational history of the Oxford region
Authors: DAY S. P.
Published: April 2006

summary

The results of pollen, sedimentological, magnetic susceptibility and charcoal particle analysis of two radiocarbon‐dated sequences of organic deposits from the Oxford region are presented. The record from one of the sites, Cothill Fen, extends from c. 10000 to c. 6500 BP, while that from the other site, Sidlings Copse, covers the period from c. 9500 BP to the present.

The post‐glacial landscape was initially open, with some Betula and Pinus sylvestris woodland. At Cothill Fen, Corylus avellana populations began to expand at c. 9400 BP, followed by Ulmus at c. 9100 BP, Quercus at c. 8800 BP, and Tilia cordata and Alnus glutinosa at c. 6800 BP. T. cordata probably became dominant on well‐drained soils in the region. At Sidlings Copse, P. sylvestris declined as populations of Quercus and Ulmus expanded, but P. sylvestris persisted around Cothill Fen until t. 7700 BP, perhaps connected with human disturbance of the vegetation.

The Ulmus decline at Sidlings Copse is suggested to have resulted from a combination of disease and exploitation of leaf‐fodder, with no major clearance until c. 3800 BP. By c. 3 700 BP no woodland remained around the site, but local regeneration began at c. 1000 BP.