bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

SUMMARYSeven 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

SUMMARYConing 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

summaryWheat (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

summaryWheat (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

summaryOne‐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

summarySeedlings 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

summaryWhen 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

summaryThe 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

summaryFour 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

summaryGlycerol, 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

summaryWood 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

summaryWhen 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

summaryIn 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

summaryAlthough 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

summaryMeasurements 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.