bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and assimilation of NH4+ and NO3− by Paxillus involutus in association with Betula pendula and Picea abies as affected by substrate pH*
Authors: EK H. , ANDERSSON S. , ARNEBRANT K. , SÖDERSTRÖM B.
Published: April 2006

summary

The influence of pH on the growth and assimilation of 15N‐labelled ammonium and nitrate was studied in intact ectomycorrhizal systems consisting of Betula pendula Roth and Picea abies (L.) Karst. colonized with a common mycelium of Paxillus involutus (Batsch) Fr. The plants were grown together in Plexiglass observation chambers containing non‐sterile peat with three different pH values, 4.11, 5.1 and 6.1. The mycorrhizal mycelium was allowed to prow over a barrier into an area of peat from which plant roots Here excluded. Labelled 15NH4NOa was supplied, either as 13NH4NO3 or as NH415NO2, exclusively to the fungal mycelium. Shoots and roots were analyzed for 15N in total nitrogen while the mycelium was analyzed for 15N in NH41, NO3− and free amino acids. The 15N labelling pattern indicated that ammonium was immediately assimilated into amino acids, primarily glutamine, by the fungal mycelium at the uptake site. The amino acids were then translocated to the mycorrhizal roots. In contrast, nitrate‐N was not assimilated in the mycelium but rather transferred to the mycorrhizal roots as nitrate. Mycelial uptake and transfer of N to the spruce and birch seedlings were significantly higher for NH4‐N than for NH4‐N. No firm conclusions about pH effects on the preferential uptake of ammonium and nitrate could he drawn. However, pH had a pronounced effect on the mycelial growth of P. involutus which was hampered severely at pH 6.1 and to a lesser extent at pH 5.1.
Auxin overproducer mutants of Hebeloma cylindrosporum Romagnesi have increased mycorrhizal activity
Authors: GAY G. , NORMAND L. , MARMEISSE R. , SOTTA B. , DEBAUD J. C.
Published: April 2006

summary

The ectomycorrhizal activity (expressed as the number of mycorrhizas per plant) of indole‐3‐acetic acid (IAA) overproducer mutants of Hebeloma cylindruspurum Rumagnesi and of their mono‐ and dikaryotic progenies has been studied in an attempt to clarify the role of fungal IAA in the establishment of ectomycorrhizal symbiosis, The original mutants obtained from the hi monokaryon produced a higher number of mycorrhizas than did the wild type. The study of the mycorrhizal activity of synthesized dikaryons heterozygous for the FIR (fluoroindoleresistant) mutations, which are responsible for IAA overproduction, showed that these mutations are recessive.

The vitro fruiting of a dikaryon heterozygous for a FIR mutation allowed the isolation of IAA‐overproducing sib‐monokaryons. Their average mycorrhizal activity was higher than that of non‐overproducers. indicating that, although the mycorrhizal activity of sib‐monokaryons is under polygenic control, high IAA production gives an advantage in mycorrhiza formation. This was confirmed by the higher number of mycorrhizas formed by synthesized dikaryons homozygous for a FIR mutation than by wild type mycelia.

The mycorrhizas formed by the mono‐ or dikaryotic wild types were characterized by a uniseriate Hartig net, whereas it was pluriseriate in the case of mycorrhizas formed by IAA overproducer mutants. The mutants stimulated the growth of the host plants to the same extent as did the wild types, indicating that growth stimulation is not a direct consequence of fungal auxin production. The usefulness of these mutants as a model to study the role of fungal IAA in mycorrhiza formation is discussed.
Influence of parental NaCl treatment on salinity tolerance of offspring in Sorghum bicolor (L.) Moench
Authors: AMZALLAG G. N.
Published: April 2006

summary

Adaptation and resistance responses to NaCl salinity Have been expressed in Sorghum bicolor (L.) Moench (genotype MP610) by exposure to 150 mol m−3 NaCl respectively 8 of 21 d after germination. Offspring of the adapted or the resistant plants (respectively named Al and Rl) were compared with offspring of control plants (Cl). Eighteen days after germination in presence nr absence of 75 mol m−3 NaCl, the Al plants showed a large increase in vigour, and a reduction in Na+ accumulation into the shoot, compared with the Cl plants. The Rl plants were widely heterogeneous and presented intermediate characteristics between the Al and Cl plants. When first exposed to salinity 21 d after germination, the AI plants showed a significant increase in salinity tolerance, when compared with Cl plants. Conversely, the Rl plants remained very similar to the Cl plants after late exposure to salinity. These results indicate that the exposure of Sorghum plants to salinity induced an increase in vigour in the progeny. Moreover, an enhanced salinity‐tolerance is specifically observed for offspring of adapted plants, suggesting that this property is not a simple consequence of parents grown in a saline environment. The possible nature of the observed effects on offspring is discussed.
The effectiveness of ectomycorrhizal fungi in increasing the growth of Eucalyptus globulus Labill. in relation to root colonization and hyphal development in soil
Authors: THOMSON B. D. , GROVE T. S. , MALAJCZUK N. , HARDY G.E. St J.
Published: April 2006

Forty‐seven different isolates of ectomycorrhizal fungi, from the different genera, were screened for their effectiveness in increasing the growth of Eucalyptus globulin La hi 11. where supply of P is deficient. Plants were grown in a P‐delicient sand, in pots, in a temperature‐ control led glasshouse. Seedlings we re harvested 6‐S and K7 d after planting, and were assessed for dry matter production and mywirrhizal colonization. Selected treatments were also assessed for P concentrations in the plant and hyphal development in the soil.

Dry weights of inoculated plants ranged from 50 to 350% of the dry Weights of uninoculated plants. Growth increases in response to ectorriycorrhizal inoculation corresponded with increased P uptake by the plant.‘Early’colonizing fungal species (Descolea maculata, Hebeloma westraliens, Laccaria laccata and Pisolithus tinctorius) were generally more effective in increasing plant growth than‘late’colonizing species (Cortinarius spp. and Hyutenmgium spp.), although there was also variation in effectiveness among isolates of the same fungal species. Plant dry weights were positively correlated (r2= 0·79‐0·84) with the length of colonized root, indicating that fungi which colonized roots extensively were The most effective in increasing plant growth. For some fungi, however, plant growth responses to inoculation were not related to colonized root length. These responses could not.be related to the development of hyphae in soil by the mycorrhizal fungi.
Fructan synthesis in oat
Authors: LIVINGSTON DAVID P. , KNIEVEL DANIEL P. , GILDOW FREDRICK E.
Published: April 2006

The accumulation of fructan oligomers in cold hardened oat stems was compared to oligomer synthesis in a crude enzyme extract. Water‐soluble carbohydrates were quantified at specified time intervals in three oat cultivars which had been hardened for a total of 5 wk at 2 °C. A crude enzyme extract was prepared from stems of one cultivar hardened for 6 d at 2 °C and incubated at 30 °C with 200 mM sucrose. 1‐Kestose was the first oligomer to accumulate in vitro but neokestose rapidly increased after 3 h of incubation and eventually surpassed the level of 1 ‐kestose. Neokestose and 1‐kestose accumulated at similar rates in vivo in the first week of hardening but after 1 week, 1‐kestose began to decrease while neokestose remained relatively constant. The same phenomenon was observed in vitro but after only 3 h. 6‐Kestose was not observed in vivo or in vitro, except for a trace before hardening began. The first tetramer to increase was 1&6G‐kestotetraose but it subsequently decreased and its concentration was surpassed by that of 6G,6‐kestotetraose. Similarities and differences between in vivo and in vitro patterns of fructan synthesis are discussed.
Identification of glycoproteins specific to biotrophic intracellular hyphae formed in the Colletotrichum lindemuthianum‐bean interaction
Authors: PAIN NAOMI A. , O'CONNELL RICHARD J. , MENDGEN KURT , GREEN JONATHAN R.
Published: April 2006

Monoclonal antibodies (MAbs) specific for intracellular for hyphae (IH, i.e. infection vesicles and primary hyphae). Appressoria/germ tubes and conidia of Colletotrichum lindemuthianum (Sace, & Magn.) Briosi & Cav. isolated from infected leaves of Phaseolus vulgoria L. were obtained using a co‐immunization procedure. One of the MAhs; UB25, bound specifically to IH in immunofluorescence immunogold and Western blot assays: it showed no affinity for conidia, conidial germ tubes, appressoria or appressorial germ tubes growing in vitro, of for any plant components. Immunogold labeling of infected tissue prepared by high pressure freezing, freeze‐substitution and low temperature embedding showed that the UB25 antigen was present in the interfacial matri surrounding IH and in the fungal wall. The antigen was confined to infection vesicles and primary hyphae in contact with host protoplast and could not be detected in primary hyphae growing in intercellular spaces. UB25 recognizes a protein epitope present in a set of N‐linked glycoproteins. These glycoproteins are expressed at an early stage of intracellular development, suggesting a possible role in biotrophy or recognition.
Purification and characterization of fructans with β‐2, 1‐ and β‐2, 6‐glycosidic linkages suitable for enzyme studies
Authors: BONNETT G. D. , SIMS I. M. , ST. JOHN J. A. , SIMPSON R. J.
Published: April 2006

Fructan pentasaccharides were purified, in quantities suitable for use as substrates for enzyme assays, from Neosugar‐p‐(Meijj Seika Kaisha Ltd. Japan), tubers of Helianthus tuberosus L., L., and stems and leaf sheaths of Triticum aestivum L by a combination of gel‐filtration and RP‐HPLC. Fructan of higher molecular mass (mean DP = 30) was purified from Leaves of Lolium rigidum Gaud, that had been induced to accumulate fructan and characterized along; with the commercially available fructan from Cichorium intybus L. (Sigma, St Louis, USA) (mean DP = 33). The fructan pentasaccharide purified from H. tuberosus was found to contain exclusively 2, 1‐linked fructose and terminal fructose and terminal glucose, and was identified as (1, 1, 1)‐kestopentatise. The fructan pentasaccharide purified from Neosugar‐P also contained (1,1,1)‐kestopentaose. although the presence of fructan Klinked glucose and 1 % 2, 6‐linked fructose indicated that a small proportion of other kestopentaoses were present, The fructan pentasaccharide purified from T aestivum consisted of almost exclusively 2,6‐linked fructose and terminal glucose and terminal fructose and was considered to contain predominantly (6,6,6)‐kestopentaose. The presence of 1 % 2,1,6)‐linked fructose indicated the sample also contained a small proportion of branched kestopentanse. The high molecular mass fructan from C. intybus was found to comprise linear molecules containing only 2,1‐linked fructose, terminal glucose and terminal fructose‐ High molecular mass fructan from L. rigidum contained predominantly 2. h‐linked fructose, had predominantly internal glucose, indicated by 2 %, 1.6‐linked glucose, low levels of branching, indicated 2 % 2,1,6‐linked fructose residues; and 1% of the residues were 2,1 ‐linked fructose.
Stimulation by auxin and sucrose of bulbil formation in vitro by single leaf cultures of Narcissus
Authors: STAIKIDOU I. , SELBY C. , ARVEY B. M. R.
Published: April 2006

Bulbil formation in vitro by single leaf explains from shoot clump cultures was investigated for Narcissus cultivars St Keverne and Havera. Single leaf explants (30–50 mm leaf with attached basal plate tissue) formed bulbils very infrequently unless cultured on media containing both auxin and a high concentration of sucrose whereas auxin was not necessary for bulbil formation by shoot dump cultures. As well as showing much stronger stimulation by auxin, bulbil initiation and development were more strongly inhibited In BA in single leaf cultures than in shoot dump cultures. Partitioning of dry matter into bulbils was generally lower in single lent cultures than in shoot clump cultures but was more sensitive to growth regulators.

Optimal sucrose and auxin concentrations for bulbil development by single leaf cultures were investigated. Bulbil formation in the presence of NAA was strongly stimulated by 176 mM sucrose for both cultivars but there were genotypie differences in auxin responses, St Keverne showing good bulbil development with 0.54 μM NAA, 5.4 μ 1AA and 5.4 μM 1BA und Hawera responding only to 27 μM LAA.

It is concluded that single leaf cultures could provide a simple system for investigation of the regulation of the regulation of Narcissus bulb initiation and development.
Influence of episodes of summer O3 on δ5and δ9 fatty acids in autumnal lipids of Norway spruce [Picea abies (L.) Karst]
Authors: WELLBLRN ALAN R. , ROBINSON DEBORAH C. , THOMSON ALAN , LEITH IAN D.
Published: April 2006

Current year needles from 5 yr‐old Norway spruce trees, which had been exposed to either episodes of atmospheric O3, or periodic mistings with simulated acid rainwater throughout three summer periods, were‐analyzed for changes in molar percentages and ratios of fatty acids isolated from different lipids at the time of maximum winter hardening. No significant changes due to acidic misting were detected but significant decreases in the degree of unsaturation off both C 16 and C18, fatty acids, the molar percentage of δ5,9,12,15, and the molar ratio δ5,918: 2 to δ9,1218:2 in monogalactosyl diglyceride (MGDG) due to summer 03 exposures were found. Molar percentages and ratios of fatty acids did not change much in other lipids bur these changes in plastidie MGDG could be traced to a significant effect of summer O3 on the δ4‐ and δ12 ‐desaturases acting upon phosphatidyl choline (PC) in the endoplasmic reticulum. The replacement of the δ6‐subset of C18 fatty acids by an equivalent δ5‐series throughout was confirmed by Gas chromatography and mass spectrometry Molecular modelling also showed that the δ5 forms, which resembled the δ5‐isomers, are very different in shape to the δ5‐series and this may account, in part, for the extremely low winter temperatures from which Norway spruce needles may recover.
Fructan biosynthesis in excised leaves of Lolium temulentum L.
Authors: CAIRNS ANDREW J. , ASHTON JENNIFER E.
Published: April 2006

A crude enzyme preparation from excised illuminated leaves of Lolium temulentum L. catalyzed the de novo synthesis of fructan of apparent degree of polymerization 3–20.

In the absence of sucrose, the fructan synthetic activity (FSA) was labile at temperatures above 10 °C, but could be stored at 5 °C for 6 h with the loss of only 20% of the initial activity. Sucrose stabilized the FSA such that high rates of fructan synthesis continued for at least 6 h at 30 °C. By comparison, in the absence of sucrose 80% of the FSA was lost in 2 h at 30 °C.

The FSA was maximal at pH 6·0 in citrate‐phosphate buffer and at 43 °C. It was not possible to saturate the FSA even at 1500 mol m−3 sucrose, or to calculate meaningful kinetic parameters for enzymatic fructan synthesis. 150 mill m−3 sucrose was the highest substrate concentration practically feasible and imposed an arbitrary maximum concentration for use in enzyme assays. Pyridoxal‐hydrochloride was found to reduce invertase activity by 40%, but also inhibited FSA by 20% at 1500 mol −3 sucrose and pH 6.0.
Flow cytometric probing of chromatin condensation in maize diploid nuclei
Authors: BIRADAR D. P. , RAYBURN A. LANE
Published: April 2006

Nuclei were isolated from stems, mesocotyls, nodal roots and root tips of two maize hybrids. The fluorochrome, propidium iodide (PI), was used to stain the nuclei that were passed through a flow cytometer‐cell sorter. Significant differences in fluorescence intensities were observed among the diploid nuclei from the different plant organs. These observations, in conjunction with previously reported DAPI fluorescence data, reflect the state of chromatin condensation in diploid nuclei isolated from meristematic and differentiating tissues. Nuclei from root meristematic tissues showed no or very little chromatin condensation. Mesocotyls and nodal roots, 1‐wk‐old, appeared to contain chromatin in a more diffuse state owing to completed differentiation which allows more DNA to be accessible to PI. Mesocotyls, 2‐wk‐old owing to senescence, contained degraded chromatin in which DNA was more accessible to PI because it lacked associated proteins. The diploid nuclei from stems had the highest amount of chromatin condensation. The results show the usefulness of flow cytometry for analyzing chromatin condensation in plant nuclei. The study also shows the importance of selecting a particular type of fluorochrome in the analysis of nuclear chromatin.
Ultrastructure of the endophyte and localization of nifH transcripts in root nodules of Coriaria nepalensis Wall, by in situ hybridization
Authors: MIRZA M. SAJJAD , PAWLOWSKI K. , HAFEEZ F. Y. , CHAUDHARY A. H. , AKKERMANS A. D. L.
Published: April 2006

Studies on the root nodules of Coriaria nepalensis Wall. using light and electron microscopy revealed that infected cortical cells are enlarged and form a compact kidney‐shaped region with an acentric stele. Within a single cell, the actinomycetous endophyte has branched hyphae and elongate vesicles. Hyphae penetrate the host cell wall in different directions. Inside the host ceil, the hyphae are located in the peripheral region of the cytoplasm near the host cell whilst the vesicles are positioned towards the centre of the cell around the central vacuole. No septa formation was observed in the microsymbiont vesicles. Host cell mitochondria were aggregated near the hyphal/vesicular junction of the endophyte. In situ hybridization studies demonstrated that the nifH transcripts are unequally distributed over the infected cortical cells. In infected cells, nifH mRNA was located in the region occupied by the elongate vesicles of the endophyte near the host cell central vacuole. The results indicate that the elongate vesicles of the nodule endophyte of C. nepalensis are functionally identical to the spherical vesicles of the nodule endophyte of Alnus.
A palaeobotanical study of paludifying pine forest on the island of Hailuoto, northern Finland
Authors: HULME P. D.
Published: April 2006

Soil profile, macrofossil and pollen analysis investigations were carried out at two sites within paludifying pint forest to determine the vegetation succession and paludification history of the area. Isostatic uplift raised the area above sea level less than 500 y ago. Before the land emerged from the sea, Phragmites and Schoenoplectus beds grew in shallow water close to the shore. As the area emerged, shore meadows dominated by grasses, sedges and forbs became established and were in turn replaced by alder woods. Mixed birth and alder woods then developed and the formation of an organic layer started with the accumulation of humus. Birch then largely replaced alder but both were superseded by pine forest about 50 y before the start of the investigation. After pine forest establishment, Sphagnum invaded, peat accumulation started and paludification was under way. Soil waterlogging necessary for paludification to proceed was a result of a low hydraulic head and shallow hydraulic gradient between the study area and the sea. The vegetation succession is comparable with contemporary succession around the present coastline of Hailuoto and on other Finnish islands. Paludification of the area was an autogenic process; no anthropogenic influences were detected. The relevance of this to the origin of blanket mire in Britain during prehistoric times is discussed. It is suggested that more evidence is required to clarify the roles of forest clearance and climate in the inception of blanket mire in Britain.
Salt tolerance and ion relations of Salsola kali L.: differences between ssp. tragus (L.) Nyman and ssp. ruthenica (Iljin) Soó
Authors: REIMANN CHRISTINE , BRECKLE SIEGMAR‐W.
Published: April 2006

summary

The effect of increasing salt concentrations (up to 200 mmol l−1 Cl−1 on growth, succulence and mineral composition has been studied in some accessions of Saltola kali L. ssp. tragus (L.) Nyman and ssp. ruthenica (Iljin) Soó Differences between accessions corresponded to the taxonomic distinction of subspecies. Dry weight was increased by 50 mmol l−1 NaCl in ssp. tragus, but not in ssp. ruthenica. Rising salinity increased shoot water content in both subspecies, but ssp. tragus was more succulent than ssp. ruthenica. ssp. tragus potassium content decreased after NaCl treatment, and the accumulation of sodium was significantly higher than in ssp. ruthenica. Chloride content and total cation concentration were similar in all accessions. The results indicate a positive correlation between salt tolerance, succulence and low K/Na‐ratios in leaves.
Physical injury, re‐crystallization of wax tubes and artefacts: identifying some causes of structural alteration to spruce needle wax
Authors: BERMADINGER‐STABENTHEINER EDITH
Published: April 2006

summary

The study presents investigations of epicuticular wax morphology on spruce needles (Picea abies (L.) Karst.) performed by ambient temperature scanning electron microscopy. To use alterations to epicuticular wax morphology as a successful tool in forest damage research, it is necessary to distinguish environmental influences and artefacts from common pollution effects, The present paper summarizes observations of alterations to epicuticular waxes independent of pollution effects, recorded in various field studies. These observations are supplemented by controlled experiments to investigate wax alterations owing to solvents and mechanical injury. Fissures in the antechamber wax were the result of needle shrinkage during drying. Wax alterations, where only the antechamber wax was affected by a continuous loss of the structural integrity of wax tubes, were classified as storage artefacts since they occurred exclusively on needles stored in air‐tight glass vials and were unrelated to needle age, sampling site or pollution influence. Such wax alterations were never observed in needles stored in air‐permeable paper bags. Mechanical injury also resulted in severe morphological alterations to epicuticular wax structures. The wax tubes on the surface as well as in the antechamber were squashed and flattened. On smoothed and squashed wax layers a significant regrowth of wax tubes was occasionally observed, unrelated to needle age. Though the tubular form of the re‐crystallized waxes was similar to those originally present on the surface, the tube diameters were much wider. Since redeveloped wax tubes also occurred on dead needles which had been artificially injured, this process could be classified as re‐crystallization analogous to wax re‐crystallization out of solvent extracts. The re‐crystallization took place within 48 h after the mechanical injury occurred. The implications of the reported wax alterations for a successful use of epicuticular wax morphology as a bioindicator are discussed.
Plant growth and cell division in Pisum sativum L. and Picea sitchensis (Bong.) Carr. exposed to ozone
Authors: BAMBRIDGE LORRAINE , MACLEOD RONALD , HARMER RALPH
Published: April 2006

summary

Pea (Pisum sativum L. cv. Feltham First) and clonal Sitka spruce plants (Picea sitchensis (Bong.) Carr.) were exposed to ozone concentrations of 0–90 ppb to investigate effects on both shoot and root growth and also cell division in the apical mm of roots. P. sativum plants were maintained under these conditions for 3 wk whilst P. sitchensis were left for 3 months. After 3 wk in the presence of 90 ppb ozone the mitotic index in the root apical mm of P. sativum was reduced compared with control plants (0 ppb ozone), whereas the number of primordia along the length of the main root in P. sativum plants increased at 90 ppb ozone. The smallest concentration of ozone (30 ppb) had no effect on leaf area, shoot dry weight and number of leaves of P. sativum. However, the number of second order lateral roots and total root dry weight were reduced at concentrations of 60 ppb and above while leaf size, plant height and shoot dry weight were only reduced in the presence of 90 ppb ozone. Cell doubling time in the root apical mm of P. sitchensis increased in plants which had been grown in the presence of 30 ppb ozone and decreased in those plants grown in chambers containing 90 ppb ozone. Ozone did not appear to have any other effects on those aspects of the cell cycle examined in either P. sativum or P. sitchensis.
Temperature sensitivities of Festuca arundinacea Schreb. and Dactylis glomerata L. ecotypes
Authors: THOMAS HOWARD , STODDART JOHN L.
Published: April 2006

summary

The thermal responses of leaf growth and senescence were measured in four populations of Festuca arundinacea Schreb. and three of Dactylis glomerata L. with a range of geographical origins. Leaf extension was quantified by fitting logistic curves to lengths measured for up to 120 d in controlled environments at 20 °C or after transfer to 5 °C at emergence of the fourth leaf. Electronic position transducers were employed to observe rapid adjustments in leaf elongation rate in response to changes in the temperature experienced by the growing zone. Leaf segments were incubated in darkness on a thermal gradient bar giving a range of temperatures between 0 and 20 °C, and chlorophyll and protein were determined after 4 d of senescence. For each process, temperature sensitivities were determined as 010, to give a profile of thermal response for each ecotype. Correlations between processes across ecotypes enabled possible relationships between temperature perception mechanisms to be identified. In their responses to chilling temperatures, mean extension rates measured over a period of one or more plastochrons were not closely related to short‐term rates. There was a significant negative correlation between chlorophyll stability in excised leaf tissue and mean long‐term extension rates. In general, ecotypes from the coldest habitats were the most sensitive to low temperature inhibition.
Structural changes and permeability of ivy (Hedera helix L.) leaf cuticles in relation to leaf development and after selective chemical treatments
Authors: VIOUGEAS M. A. , ROHR R. , CHAMEL A.
Published: April 2006

summary

The fine structure of ivy leaf cuticles was investigated as a function of leaf development before and after cuticle isolation as well as after selective extraction of cuticle components. Cuticle mass increased with increasing age from 234°3 to 539.1 μg cm−2 Waxes increased from 12.3 to 18.6%, of cuticle mass from young to old leaves. However, percentages of cutin and non‐lipid constituents did not vary significantly with leafage. They represented approx. 58 and 26%, of the cuticle mass, respectively. Cuticle thickness determined from electron and light microscopy increased 12–fold during leaf growth to reach 4.25 μm for mature leaves. Transmission electron microscopy of transverse sections of non‐isolated and isolated cuticles showed an outer lamellate zone gradually merging from an inner reticulate zone the thickness of which increased with leaf growth. The lamellate zone appeared very early (in vitro unexpanded leaf) and was characterized by a constant thickness (0.2 μm). Cuticle lamellation seemed to disappear after extraction of soluble cuticular wax, which confirmed intracuticular wax localization in lamellae. Electron‐dense fibrillae observed in the reticulate zone disappeared after acid hydrolysis showing that they are made of non‐lipid components. X‐ray diffraction confirmed the presence of crystalline structures and revealed a cuticle disorganization alter wax extraction. Permeability measurements showed an increase rather than a decrease in glyphosate and isoproturon diffusion through cuticles with increasing leafage, suggesting that the main barrier to diffusion is the outer lamellate zone. A considerable increase in isoproturon penetration through cuticles resulted from the wax extraction, demonstrating the major role of wax in the control of cuticular permeability to this herbicide.
Changes in quercetin concentration in onion (Allium cepa L.) owing to location, growth stage and soil type
Authors: PATIL B. S. , PIKE L. M. , HAMILTON B. K.
Published: April 2006

summary

A study with onion investigated the variation in the concentration of the potentially anticarcinogenic flavonol, quercetin owing to location, soil type and growth stage. Seven genotypes grown at two locations were analysed for aglycone and total quercetin concentration by reverse‐phase high‐performance‐liquid‐chromatography (RP‐HPLC). Out of seven genotypes investigated, four showed significant differences (P= 0.05) in total quercetin concentration between two locations. In 1993, ‘Texas Grano 10I5Y’ (TG1015Y) bulbs collected at five growth stages were analysed for quercetin concentration by RP‐HPLC. Quercetin concentration in ‘TG1015Y’ at different growth stages showed slight differences. Furthermore, quercetin concentration in bulbs harvested at second growth stage (23 March) was significantly (P= 0.05) greater than at the first growth stage (23 March). A slight difference in total quercetin concentration due to soil was noticed. This study shows that the site of growth of union is a major environmental factor in determining quercetin concentration but soil type and growth stage are not important.
The use of an unenclosed field fumigation system to determine the effects of elevated ozone on a grass–clover mixture
Authors: WILBOURN S. , DAVISON A. W. , OLLERENSHAW J. H.
Published: April 2006

summary

A mixture of Trifolium repens L. (var. Grasslands Huia) and Lolium perenne L. (var. Melle) was established in an area with low ambient ozone concentrations and exposed to episodes of ozone using a simple, unenclosed field fumigation system. Control plots were exposed to ambient air. There were two cutting frequencies to simulate grazing and silage production respectively. This paper reports on the performance of the system and the effects on yield and species composition in the first year of fumigation.

The system operated satisfactorily when the wind speed was between 1 and 5 m s−1. When the wind dropped suddenly below 1 m s−1there were short periods with high concentrations but these events were rare and did not last more than a few minutes. Above 5 m s−1there was lateral downwind spillage of ozone and at higher wind speeds it was not possible to maintain the target concentration of 50–70 nl 1−1. The plots were fumigated only when the weather was suitable for ozone formation and when the wind speed was stable. Because the weather was poor, fumigation was restricted to 22 d between July and September. The mean 4–7 h concentrations were 50–70 nl l−1. Seven‐hour mean ambient concentrations over the same period were 10–28 nl 1−1.

There were significant effects of ozone on yield and herbage composition. The effects varied between harvests, probably because of differences in the timing of cutting relative to the episodes, and to the differences in phenology between the species. Most of the loss of yield was due to effects on Trifolium, which was much more sensitive than Lolium. There was a persistent effect of ozone on the stolon density of Trifolium which lasted into the following year. It is suggested that this arose because the clover replaced damaged leaves very quickly, maintaining the canopy at the expense of the stolons. Persistent effects on stolons might lead to poorer winter survival and lower nitrogen fixation. Gaps in the sward as a result of loss of Trifolium might allow rapid weed invasion. There was no interaction between cutting frequency and ozone, which may have been due to the fact that the poor summer restricted the number of cuts and therefore decreased the difference between the two cutting frequencies.
Variation in susceptibility and tolerance within and between populations of Tussilago farfara L. infected by Coleosporium tussilaginis (Pers.) Berk.
Authors: DE NOOIJ MARIANNE P. , PAUL NIGEL D. , AYRES PETER G.
Published: April 2006

summary

Quantitative variation in susceptibility to infection by the rust Coleosporium tussilaginis, and in reduction in growth owing to the infection, were determined in 30 clonally propagated genotypes of Tussilago farfara sampled from three geographically isolated sites, Arnhem (The Netherlands), Lancaster and Sheffield (both UK). Populations, and genotypes within populations showed no significant variation in intensity of disease after artificial inoculation under ideal conditions with a fungal isolate collected from the Lancaster population. By contrast, significant differences between and within populations were observed after natural secondary infection by spores produced from the artificially inoculated plants. Genotypes differed considerably in the reduction in growth caused by the infection, but this was not correlated with the extent of symptoms shown by the plants. Low resistance was associated with high tolerance, as in the Lancaster and Sheffield populations, while high resistance was associated with low tolerance, as in the Arnhem population. The evolutionary significance of these associations is discussed.
Phosphorus and carbon budgets: mycorrhizal contribution in Hyacinthoides non‐scripta (L.) Chouard ex Rothm. under natural conditions
Authors: MERRYWEATHER JAMES , FITTER ALASTAIR
Published: April 2006

summary

The extent of host benefit from arbuscular mycorrhiza (AM) in terms of phosphorus (P) assimilation under natural conditions has rarely been demonstrated or quantified. An apparently obligately mycorrhizal host, Hyacinthoides non‐scripta (L.) Chouard ex Rothm., was selected and, throughout the season September‐July 1989–90, entire clones were collected from a field site at frequent intervals without experimental modification of the host, its mycosymbiont or their environment. In a concurrent glasshouse experiment, sand‐cultured non‐mycorrhizal plants given a nutrient solution containing a supply of P were unable to assimilate sufficient to maintain tissue P content.

We provide correlative evidence of mycorrhizal behaviour in an undisturbed, natural ecosystem by demonstrating the temporal coincidence of root colonization by mycorrhizal fungi and the inflow of phosphorus in adult H. non‐scripta. Annual carbon (biomass) and phosphorus budgets are described. Carbon was reallocated from the resting bulb, first for root production and, later, to developing leaves and inflorescences. A similar pattern was observed in P allocation. A substantial amount of P was lost in seed, leaves, roots and scapes shed at the end of a season, when bulb biomass had increased, but P content had not.
Interactions between native prairie grasses and indigenous arbuscular mycorrhizal fungi: implications for reclamation of taconite iron ore tailing
Authors: NOYD ROBERT K. , PFLEGER F. L. , RUSSELLE M. P.
Published: April 2006

summary

In a glasshouse experiment using coarse taconite iron ore tailing as the substrate, we examined interactions between the warm‐season grasses Andropogon gerardii (big bluestem) and Schizachyrium scoparium (little bluestem), and the cool‐season grass Elymus canadensis (Canada wild rye), and indigenous arbuscular mycorrhizal (AM) fungi from an adjacent fine tailing basin. Shoot dry mass (DM), P uptake, shoot P concentration, root DM, root length, spore density, percentage root length colonized, and length of external AM fungal hyphae were measured over a gradient of phosphate availability. Andropogon gerardii was highly dependent and responsive to inoculation at low P, whereas inoculation had no significant effect on the growth of 5. scoparium. Root DM and root lengths of both warm‐season grasses were unaffected by mycorrhizal inoculation. Elymus canadensis was responsive only at the lowest P level and not dependent on mycorrhizas; in fact, shoot DM, P uptake, root DM and root lengths were all greater in control than inoculated plants at moderate P levels. Despite a growth suppression, colonized root lengths for E. canadensis were approximately five times longer than warm‐season grasses at low P levels, making it suitable as an early succession species for increasing mycorrhizal inoculum potential and thus enhancing the successful reclamation of coarse tailing deposits by more persistent, mycorrhizal‐dependent species.
Influence of potassium nutrition on germinability, abscisic acid content and sensitivity of the embryo to abscisic acid in developing seeds of Sorghum bicolor (L.) Moench
Authors: ARNOLD R. L. BENECH , FENNER M. , EDWARDS P. J.
Published: April 2006

summary

Pre‐harvest sprouting in maturing seeds of Sorghum bicolor (L.) Moench is a major problem in the cultivation of this crop plant. The influence of potassium nutrition on germinability, abscisic acid (ABA) content and embryo ABA sensitivity in its developing seeds was investigated. Plants were grown in sand culture under three different potassium treatments: K1 (control), K2 (one third of the control potassium supply), and K3 (one ninth of the control potassium supply). Reduced potassium increased the germinability of developing seeds during the late stages of maturation (31 and 36 days after pollination, DAP), particularly in K2 grains. These changes in seed germinability were paralleled by a reduced ABA content in the seed and by a lower embryonic sensitivity to ABA. The ABA content of K2 intact grains peaked at 25 DAP and then decreased sharply, being 30–50% lower than that in the controls at 31 and 36 DAP. ABA content in the control gains peaked later in the developmental period (at 31 DAP). By contrast K3 grains had a remarkably constant ABA content during most of the developmental period (20–36 DAP). Sensitivity to ABA was markedly reduced in the embryos from both the low potassium treatments, particularly when tested at an ABA concentration of 5μM. The data indicate that potassium supply influences germinability, ABA concentrations and embryo ABA sensitivity in developing seeds in this species.
Fungal slime and its role in the mycorrhizal amelioration of zinc toxicity to higher plants
Authors: DENNY H. J. , RIDGE I.
Published: April 2006

summary

The degree of sliminess of a range of fungal isolates which form endomycorrhizas with Calluna vulgaris L. was investigated and related to their performance in the presence of potentially toxic concentrations of zinc. Some fungal isolates possess, to a greater or lesser extent, a mass of loosely adherent slime (LAS). The amount of this was proportional to the ability of the fungal mycelium to take up zinc from solution, the zinc tolerance of the fungal isolates, and the amount of growth enhancement exhibited by the associated C. vulgaris plants in the presence of potentially toxic concentrations of zinc. Furthermore the amount of LAS was inversely proportional to the concentration of zinc found in the shoots of the associated C. vulgaris plants. These observations support the hypothesis that LAS plays a central role in removing zinc ions from solution, removal which in turn determines the zinc tolerance of the fungus itself and the degree of amelioration of zinc toxicity to the host plant.
Holocene vegetation history and human impact at Bryn y Castell, Snowdonia, north Wales
Authors: MIGHALL T. M. , CHAMBERS F. M.
Published: April 2006

summary

Three radiocarbon‐dated pollen diagrams are presented from Holocene peat and lake deposits in Snowdonia, close to the Late Iron Age/Romano‐British ironworking hill‐tort of Bryn y Castell, Gwynedd, in upland north Wales. This paper discusses pollen, charcoal and peat‐stratigraphic evidence for major local vegetation changes and for the development of the surrounding cultural landscape during the last 10000 radiocarbon yr. Pollen data from one of the sites (BYC 2) provided a vegetational record for most of the Holocene. The early part of the sequence suggests an oligotrophic lake in a landscape that is being colonized by birch‐pine woodland; later, mixed deciduous woodland surrounds an infilling lake basin. Dating of peat deposits at two of the sites (BYC, BYC H) indicated that their pollen records commenced between 5500 and 5000 yr BP. By this time, the lake basin was fringed by alder carr. There followed a gradual and then, c. 2700 yr BP, a more abrupt decline in woodland, such that, by the end of the Bronze Age and with the basin largely terrestrialized, the local landscape became dominated by mire vegetation communities, which have persisted to the present. Human activity seems to have been a major factor in the loss of woodland cover. Although there is some circumstantial evidence for earlier phases of human disturbance at BYC 2, human activity becomes increasingly apparent from c. 5000 yr BP. During the mid Holocene, the impact of Neolithic and early‐ to mid‐Bronze Age cultures appears to be characterized by temporary woodland clearances, for arable and pastoral agriculture. By c. 2700 yr BP the majority of woodland cover seems to have been permanently removed from the landscape, but as there is scant archaeological evidence for late Bronze Age cultures in this part of Snowdonia, other factors, especially climate change, could be implicated. During the late Holocene, especially during part of the late Iron Age and Romano‐British period, remaining local stands of woodland seem to have been exploited for iron smelting, although the overall impact of ironworking was limited.
Quantitative imaging of chlorophyll fluorescence
Authors: ROLFE STEPHEN A. , SCHOLES JULIE D.
Published: April 2006

summary

A computer‐controlled video system is described where images of chlorophyll fluorescence from oat (Arena saliva L.) leaves are captured throughout an induction curve. The fluorescence parameters φ11 and ΔFm/F'm which represent photosystem II photochemical efficiency and non‐photochemical quenching respectively are calculated from images taken under actinic and saturating illumination. They are compared with the equivalent parameters determined from simultaneous measurements made with a non‐imaging modulated fluorimeter. The leaves are imaged in the chamber of an infra‐red gas analyser, allowing the relationship between the fluorescence parameters and CO2 assimilation to be determined. Under a series of illumination conditions and partial pressures of CO2, the values of φ11 determined by image analysis are in close agreement with those obtained by modulated fiuorimetry and are linearly related to CO2 assimilation. The values of ΔFm/Fm determined by image analysis are linearly related to those obtained by modulated fluorimetry but the absolute values differ between the two systems. The video system described can be used to examine quantitative changes in fluorescence parameters in a heterogeneous system.
Uptake of15NO2by sunflower (Helianthus annum) during exposures in light and darkness: quantities, relationship to stomatal aperture and incorporation into different nitrogen pools within the plant
Authors: SEGSCHNEIDER HANS‐JOSEF , AND JÜRGEN WILDT , FÖRSTEL HILMAR
Published: April 2006

summary

Exposures of sunflowers (Helianthus annuusL. var. Giganteus) to15NO2, at concentrations between 5.0 and 72.9 ppb resulted in its uptake by the plants during illumination as well as during darkness. The NO2, flux increased linearly with increasing NO2, concentrations in both treatments. Evolution of NO2by sunflowers was not observed. During illumination, measured and potential N Of uptake were equal, which indicates that the uptake of NO2was only limited by stomatal resistance, whereas in darkness, an additional internal resistance to NO. cannot be excluded. After15NO2, exposures, the highest proportions of the15N tracer were fixed as protein nitrogen or as heterocyclic nitrogen compounds and glucosamine. Under both treatments there were remarkably high15N enrichments in the fraction ‘soluble amino acid nitrogen’, indicating a rapid assimilation of the nitrogen derived from15NO2, A linear relation was found between the δ15N values of nitrogen pools investigated and the15NO2concentrations after exposures in light as well as after night‐time fumigation. Apparently, all the enzyme systems involved in the assimilation of the NO2nitrogen must be available in sufficient amounts in plant tissues during exposures. Even after exposures in the dark, about 95% of the absorbed15NO2, nitrogen was fixed in reduced organic nitrogen compounds, which indicates that the assimilation of atmospheric NO2, might not depend on the production of reduction equivalents by photosynthesis. The mechanism of NO, assimilation via nitrate/nitrite reductase within the exposed sunflowers is discussed.
Predictions of where minimal damage to jarrah roots could result in tree death
Authors: DAVISON E. M. , TAY F. C. S.
Published: April 2006

summary

Field observations of Eucalyptus marginata Dorm ex Smith (jarrah) trees on sites infested with Phytophthora cinnamomi Rands showed that sudden and sustained stem shrinkage at 1–3 m preceded crown death. This was interpreted as indicating severe water deficiency in the stem base before the foliage died. Reduced mot conduction might be an important factor leading to tree death. Measurements of conduit length in stems and roots showed that c. 15% were 1 m long and the remainder 40–50 cm long. Qualitative measurements of sap wood conduction were made in 20 cm‐long segments of large horizontal jarrah roots using gas flow at positive pressure. Conduction. expressed as cm3 gas flow mm −2 min−1 increased with increasing distance from the tree bole. This increase was associated with an increase in vessel cross‐sectional area, not with increasing vessel number or a decrease in the proportion of tylosed vessels. Observations on roots from trees from two sites, part of each site being infested with P. cinnamomi, indicated that maximum conduction mm−2 along a root was associated with site, not whether or not the site was infested with P. cinnamomi. Our calculations show that conduction in large horizontal roots is not constant, but decreases dose to the base of a jarrah tree, so that damage close to the bole will have the greatest effect on water movement to the foliage.
Mycorrhizal fungus propagules in the jarrah forest
Authors: BRUNDRETT MARK C. , ABBOTT L. K.
Published: April 2006

summary

Spatial variations in the capacity of propagules of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi to form associations in their natural habitats were investigated using bioassays with bait plants grown in intact cores of forest soil. These cores were collected from a sclerophyllous forest community dominated by Eucalyptus marginata Donn ex Smith (jarrah) and E. calophylla Lindley (marri) trees with a diverse shrub understorey in the mediterranean (winter rainfall) climatic zone of Western Australia. Small‐scale (adjacent core) variations in the capacity of AM fungi to form associations were found to be as substantial as differences between locations 1 5 m apart. Comparisons of AM fungus colonization patterns within the roots of seedlings growing in the same core indicated that there was considerable spatial heterogeneity in the inoculums potential of ‘individual’ fungi within these 1 1 volumes of soil. A second experiment included bait plants to measure ECM formation as welt as AM formation and also considered the impact of soil disturbance. The disruption of hyphal networks reduced mycorrhizal formation somewhat, but it still remained highly variable. Some of this spatial heterogeneity could be attributed to differences in the organic matter content, length of fungal hyphae, or length of old mycorrhizal roots, measured within soil cores. In jarrah forest soil, mycelial systems of AM and ECM fungi apparently were localized in separate domains, and there were also zones where non‐mycorrhizal roots (mostly cluster roots produced by members of the Proteaceae) predominated. More research is required to determine the size of domains of mycorrhizal mycelial systems in soils, how these spatial patterns change with time, and if they are associated with zones of resource utilization by different ‘functional groups’ of roots.