bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructural localization of ATPase activity in the Pinus sylvestris/Laccaria laccata ectomycorrhizal association
Authors: LEI J. , DEXHEIMER J.
Published: April 2006

Ultrastructural localization of the plasmalemmal ATPase activity has been studied in basidiomycete ectomycorrhizas synthesized between Pinus sylvestris L, and Laccaria laccata Scop, ex Fries.

The cortical cells showed a strong plasmalemma‐bound ATPase activity. The activity was also associated with the fungal plasmalemma in the external hyphae, sheath and Hartig net. The plasmalemmal ATPase activity disappeared in degenerating cortical cells. In the Hartig net, only the parts of the plasmalemma adjacent to other hyphae were active. When the Hartig net hyphae adjoined on one side a living cortical cell and, on the other side, a dead cortical cell, the ATPase activity of fungus plasmalemma was asymmetrically distributed. These observations are discussed in relation to the possible function of ATPase in ectomycorrhizas.
Reflectance of blue, green, red and near infrared radiation from wetland vegetation used in a model discriminating live and dead above ground biomass
Authors: LORENZEN BENT , JENSEN ARNE
Published: April 2006

Field measurements of canopy reflectance of wetland vegetation in the blue (450 ran), green (548 nm), red (655 nm) and NIR (805 nm) wavebands were correlated with plant biomass variables. Negative relationships, asymptotic in nature, were observed between visible wavebands, canopy reflectance and total live biomass as well as green biomass, with correlation coefficients r between −0·52 and −0·93. Curvilinear relations were observed between NIR canopy reflectance and total live biomass as well as green biomass, with r between 0·39 and 0·88. Different normalization indices (NIR blue−1, NIR red−1, VI, PI and NIRlbio) were tested and positive relations between these indices and total live biomass and green biomass were observed, with r between 0·69 and 0·96. Inverse relations of an asymptotic nature were observed between dead biomass as a percentage of total biomass and of green biomass, with r between 0·90 and 0·91. A model discriminating live and dead above‐ground biomass was developed to improve correlations between canopy reflectance and biomass variables. The model nearly doubled the correlation coefficient between reflectance and green biomass for a canopy containing large amounts of interfering dead biomass, but did not change this correlation for a canopy containing small amounts of dead biomass.
Effects of auxin and boron on nucleic acid metabolism and cell division during adventitious root regeneration
Authors: ALI A. H. N. , JARVIS B. C.
Published: April 2006

Treatment with indolebutyric acid (IBA) enhances root regeneration in stem cuttings of mung bean (Phaseolus aureus Roxb.) provided cuttings are supplied with borate. Treatment also increases the content of RNA in hypocotyls although RNA synthesis is inhibited by such treatment. Cell division in phloem parenchyma cells is evident 24 h after cuttings are prepared, irrespective of treatment with, or without, IBA. Following the preparation of cuttings, synthesis of RNA increases in the hypocotyl prior to the earliest mitoses in these cells and continues to increase in the presence of supplied borate. Autoradiographic investigation shows that, in the absence of supplied borate, synthesis of RNA within the nucleus decreases markedly in IBA‐treated cuttings 40 h after cuttings are made. Moreover, RNA synthesis is totally inhibited 24 h later whereas cell division does not cease until 60 h. Witholding supply of boron For up to 72 h after cuttings are made has no effect on DNA synthesis.
The influence of photosynthetically‐active radiation and simulated shadelight on the control of leaf growth of Betula and Acer
Authors: TAYLOR GAIL , DAVIES W. J.
Published: April 2006

The primary aim of the study was to quantify the effects of photosynthetically‐active radiation (PAR) on extension of leaves of silver birch (Betula pendula Roth.) and sycamore (Acer pseudoplatanus L.). Plants grown at 250 μmol m−2 s−1 were exposed to a range of fluence rates (0·680 μmol m− s−1) whilst enclosed in Perspex chambers in which temperature, vapour pressure deficit and photoenvironment were all controlled. Measurements of leaf extension, water relations, and cell wall extensibility (VVEX) were made at the end of a 3 h exposure period.

For leaves of birch, reducing the fluence rate resulted in reduced leaf extension and a lowering of WEX. Exposure of sycamore seedlings for 3 h to different values of PAR had little effect on the growth of leaves and WEX remained constant. The characteristics of net photosynthesis also differed for the two species and photosynthesis and wall loosening may be linked.

Since natural woodland shadelight, in addition to reduced PAR, also has a reduced R/FR ratio, a second group of seedlings were placed in a photoenvironment which simulated shadelight (low PAR, R/FR) for 28 d. This treatment reduced extension rate and final leaf size for both species. Measurements of extension, water relations and WEX made when seedlings were exposed to shadelight whilst held in the Perspex chambers revealed differences in the control of leaf growth for the two species.

It is confirmed that leaves of birch are highly responsive to changes in PAR with cell wall loosening the most likely process controlling this response.
Altitudinal variation in nitrogenase activity of the Himalayan alder naturally regenerating on landslide‐affected sites
Authors: SHARMA EKLABYA
Published: April 2006

Natural regeneration, root nodule biomass and nitrogenase activity (acetylene reduction) of Alnus nepalensis D. Don (alder) were estimated at ten different landslide‐affected elevated (1000–2500 m) sites in the Kalimpong forest division of the Eastern Himalayas. Alder regeneration was best in the middle zone (1500–2000 m) of this altitude range. Nitrogenase activities were between 5 and 19 μmol C2H4 g−1 nodule d. wt h−1 in a peak activity month (July). The activity was largely dependent on mean soil temperature and root nodule moisture. The highest rate of acetylene reduction was found in the rainy season (July) at the 1830 m elevation site. Nitrogenase activity was negligible at night and increased during the day with a midday maximum. Alder regeneration, seedling growth, root nodule biomass and nitrogenase activity were temperature dependent along the gradient of altitude and fell off below 1500 m and above 2000 m.
Underground transfer of nitrogen between pasture plants infected with vesicular‐arbuscular mycorrhizal fungi
Authors: HAYSTEAD A. , MALAJCZUK N. , GROVE T. S.
Published: April 2006

Experiments were carried out to investigate the possibility that vesicular‐arbuscular (VA) mycorrhizal infection of grass (Lolium perenne L.) and clover (Trifolium repens L.) roots can enhance the exchange of nitrogen between the root systems of nitrogen‐fixing pasture legumes and associated grasses.

The results showed higher rates of transfer of 15N applied as (15NH4)2SO4 to the clover plants to companion grass plants when the roots were mycorrhizal. In some cases but not all the grass grew better in the mycorrhizal treatments.

An experiment in which the clover and grass roots were separated by a 60 μm (mean pore size) nylon mesh screen showed that translocation of the nitrogen was probably along the mycorrhizal hyphae. It was not clear from the data whether transfer was mediated by a common hyphal net or some other less direct means.
The biology of mycorrhiza in the Ericaceae XI. The distribution of nitrogen in soil of a typical upland Callunetum with special reference to the ‘free’ amino acids
Authors: ABUARGHUB S. M. , READ D.J.
Published: April 2006

The soil of a typical upland Callunetum was fractionated and the concentrations of nitrogenous components determined, emphasis being placed upon analysis of the distribution of ‘free’ amino acids both down the soil profile and through the year. The largest quantities of free amino‐compounds at all times of the year were found at the top of the profile, peak values occurring in September, October and November. Quantities of amino acids often exceeded those of extractable ammonium. The results are compared with those obtained in earlier studies of acidic organic soils and the significance of the findings is discussed with special reference to the nitrogen nutrition of mycorrhizal and non‐mycorrhizal ericaceous plants.
The biology of mycorrhiza in the Ericaceae
Authors: ABUARGHUB S. M. , READ D. J.
Published: April 2006

The results of qualitative and quantitative analysis of the individual ‘free’ amino acids of a Calluna heathland soil are reported. The distribution of each identified amino acid is described in relation both to its position in the soil profile and to time of year. The amino acids occurred in the following order of quantitative importance, histidine, glutamic acid, alanine, serine, aspartic acid, leucine, valine, glycine, arginine, isoleucine, lysine, phenylalanine, and tyrosine.

The concentrations of total free amino acids obtained by summing the individual values agreed remarkably closely with those obtained by the ninhydrin procedure. Analysis of the amino acids in terms of acidic, neutral and basic categories indicated that the neutral category was quantitatively the most important. The results are compared with those obtained in previous qualitative and quantitative analysis of individual amino acids from organic soils and their significance is discussed in relation to the mycorrhizal status of ericaceous plants.
Pine root exudate stimulates the synthesis of antifungal compounds by the ectomycorrhizal fungus Paxillus involutus
Authors: DUCHESNE LUC C. , PETERSON R. L. , ELLIS BRIAN E.
Published: April 2006

The ectomycorrhizal fungus Paxillus involutus Fr. was grown in the presence of root exudate of Pinus resinosa Ait, for two weeks. The effect of root exudate on the synthesis of ethanol‐soluble antifungal compounds by P. involutus was determined by a bioassay based on microconidial germination of Fusarium oxysporum Schlecht emend, Sny. & Hans f. sp. pini. Cultivation of P. involutus on root exudate led to a greater than two‐fold increase in fungitoxic activity when compared to cultivation on modified Melin Norkrans medium in Petri dishes. Inoculation of P. resinosa root exudate with both P. involutus and a spore suspension of F. oxysporum led to an 80 % suppression of the sporulation of F. oxysporum when compared to controls lacking P. involutus. The increased resistance of P. resinosa P. involutus associations to Fusarium root rot may, therefore, be the result of biosynthesis of antifungal compounds by P. involutus which is stimulated by P. resinosa root exudate.
Comparison of colonization among half‐sib families of Medicago sativa L. by Glomus versiforme (Daniels and Trappe) Berch.
Authors: LACKIE S. M. , BOWLEY S. R. , PETERSON R. L.
Published: April 2006

Twenty half‐sib families from within each of two populations of Medicago sativa L. (Pioneer 530 and OAC 78–101) were assessed for differences in ability to form vesicular‐arbuscular mycorrhizas (VAM) when grown in association with one VAM fungal species, Glomus versiforme (Daniels and Trappe) Berch. The families were grown under controlled environmental conditions using a culture‐pot system. Roots were cleared, stained and assessed for percent colonization. From the analyses of variance, the genetic variance and heritability of percent colonization were estimated. The mean percent colonization was 5.8 and 6.8% for the Pioneer 530 and OAC 78–101 populations, respectively. Significant (P < 0·05) differences in percent colonization were detected among half‐sib families derived from Pioneer 530 but not among half‐sib families derived from OAC 78–101. Significant (P < 0·05) pot and run effects were detected in the latter experiment which may have masked differences among the families. The estimate of narrow‐sense heritability of percent colonization in the Pioneer 530 population was 18·8% and the expected response to selection for percent colonization, if the top 10% of the population was selected, was 2·2% per cycle. This indicated that there was good potential for improving the extent of VAM colonization in the population of alfalfa. Further studies of host genotype‐VAM symbioses are warranted.
Recovery of net photosynthesis and dark respiration on rehydration of the lichen, Cladina mitis, and the influence of prior exposure to sulphur dioxide while desiccated
Authors: COXSON D. S.
Published: April 2006

The pattern of resaturation respiration and of rehydration recovery of net photosynthesis has been examined after pretreatment of desiccated thalli of the mat‐forming lichen species Cladina mitis (Sandst.) Hale & Culb, with sulphur dioxide. The recovery of photosynthetic activity lagged behind that of dark respiration in all treatments, pointing to the necessity of monitoring both processes when investigating rehydration phenomena. The exposure of desiccated thalli to sulphur dioxide concentrations of 0·2 and 1·0 μ11−1 (v/v in air) for periods of 2 and 3 weeks prior to rehydration resulted in the enhancement of subsequent photosynthetic activity in all treatments. These effects were greatest in the 0·2 μ11−1 treatment where, after 2 weeks fumigation, rates of net photosynthesis on recovery were nearly 40% higher than that of control replicates receiving no SO2. These results point to the importance of considering the effects of dry deposition on physiological processes and suggest that in some cases limited SO2 exposure may result in short‐term enhancement of photosynthetic uptake.
Increases in δ13 values of radish and soybean plants caused by ozone
Authors: GREITNER CAROL S. , WINNER WILLIAM E.
Published: April 2006

This greenhouse study was undertaken to determine whether changes in photosynthesis and conductance caused by air pollution also affected the δ13C value of plant tissue. Experiments with radish (Raphanus sativus L. cv. Cherrybelle) and soybean (Glycine max L. Merr. cv. Williams) exposed to ozone (O3) at 0.12 μl 1−1 showed significant growth reductions, 14–20 μl l−1 reductions in CO2 internal (C1), and + 0.3 to + 0.7% shifts in the δ13C values of leaves and roots. These results indicate that ambient (O3) may influence the δ13C values of plants found in many agricultural and industrial regions, and that O3 may act simultaneously to suppress growth and increase water use efficiency (WUE). Stable carbon isotope techniques may be useful for integrating the metabolic effects of O3 over long exposures to air pollution.
Oxalate salts in the leaves of plum (Prunus salicina L.) and cherry (P. avium L.)
Authors: SANCHEZ‐ALONSO F. , LACHICA M.
Published: April 2006

Changes in the oxalate salts of plum (Primus salicina L., Golden Japan) and cherry (Prunus avium L., Napoleon) leaves have been studied over a single growing season. It has been shown that the oxalate content is higher in plum than in cherry trees; soluble oxalates are absent from the latter. In cherry trees all of the oxalic acid is precipitated as calcium oxalate. In plum trees, 2/3 of the content is present as calcium oxalate and the rest as potassium oxalate. The formation of calcium oxalate takes place in parallel with the formation and maturation of the fruit and ends once the fruit has been harvested. The substantial difference observed in oxalate content between the two species, despite their very similar total organic‐acid‐anion contents, indicates important differences in the mechanisms contributing to maintenance of charge balance.
Germination‐induced changes in acyl lipids and free sterols of olive pollen
Authors: RODRIGUEZ‐ROSALES M. P. , DONAIRE J. P.
Published: April 2006

The capacity of Olea europaea L. pollen grains to germinate has been studied. They germinated poorly when incubated in media with a pH higher than 5.55. However, germination was stimulated when a stream of air was passed through the incubation medium. Phosphatidylcholine, diacylglycerols, free fatty acids and triacylglycerols are the most abundant lipids in mature and germinated pollen. The level of diacylglycerol increases during germination while phosphatidylcholine, free fatty acids and triacylglycerols decrease, as compared with mature pollen. Overall, the fatty acid composition of mature pollen lipids is similar to that of germinated pollen. Compared to phospholipids and triacylglycerols, monoacyl‐, diacylglycerols and free fatty acids contain more laurate and myristate fatty acids. In relation to the amount of acyl lipids, free‐sterols are minor constituents of the lipid fraction from mature and germinated pollen, β‐sitosterol being the only significant component. The percentage of stigmasterol is significantly higher in mature than in germinated pollen.
The growth of dinoflagellates in laboratory cultures
Authors: DIXON G. K. , SYRETT P. J.
Published: April 2006

The growth rate ofAmphidinium carteraeHulburt in axenic culture was unaffected by gentle shaking (100 rpm); in contrast, growth rates ofAmphidinium klebsiiKof et Swezy,Scrippsiella trochoidea(Stein) Loeblich III andGyrodinium aureolumHulburt were lowered and the latter species was killed by shaking.

Amphidinium carteraeandScrippsiella trochoideagrew taster under continuous illumination than under the two light/dark regimes tested. However, growth ofGyrodinium aureolumwas much slower under continuous illumination (0·15 divs d‐1) than in the photoperiods (0·21–0·36 divs d‐1). Growth rates ofAmphidinium carteraeaerated with elevated CO2(0·5% v/v) were saturated at a photon flux density of 80μE m‐2s‐1. Cells grown at the lowest irradiance used (15 μE m2s‐1) had the highest pigment (chlorophylla, cand carotenoids) per cell and the highest rate of photosynthesis both on a unit cell and a unit chlorophyll a basis. However, these cells showed no photoinhibition of photosynthesis when rates were measured at photon flux densities up to 150 μE m‐2s‐1.

Culture filtrates failed to support any further growth ofA. carterae, S. trochoideaorO. aureolumwhen reinoculated with the same dinoflagellate species. However, the growth ofA. carterae, but not that of the other two species, resumed when fresh nutrients were added to culture filtrates.

Cell yields ofA. carteraewere increased by over 50% by doubling the nutrient addition to be medium. The nutrient responsible for this increase appears to be nitrate. Nitrate and arginine were also good sole nitrogen sources for the growth ofA. carterae. However, ammonium supplied at the same concentration (1 mg atom N NI‐1) was toxic; growth was slower, motility was impaired and cells become enlarged and rounded. Lowering the ammonium concentration to 0·2 mg atom N 1‐1restored growth and cellular morphology to normal.
Ethylene and the responses of roots of maize (Zea mays L.) to physical impedance
Authors: MOSS G. I. , HALL K. C. , JACKSON M. B.
Published: April 2006

The response of the roots of maize seedlings to physical impedance was studied in glass chambers that enabled oots to be grown either unimpeded or in loosely packed small glass spheres (ballotini) and flushed with humidified iir or other gas mixtures. Impedance decreased root length when measured after approximately 40 h by 30‐60% and increased root diameter 10 cm behind the tip by a similar percentage. Fresh weight was reduced by up to 28‐40% while ethylene evolution from roots was increased 2‐ to 2·5‐fold. Supplying ethylene (5‐13 μl 1‐1) in the air flow to unimpeded roots simulated closely the effects of impedance.

The volatile inhibitor of ethylene action, 2,5‐norbornadiene (approx. 900μl 1‐1), overcame the effects of ethylene (5·4 μl 1‐1) completely, but the growth of impeded roots was unchanged by norbornadiene. Similarly, aminoethoxyvinylglyeine ((0·5‐0·75 mmol M‐3) inhibited endogenous ethylene formation, but did not modify the growth responses of roots to impedance, even though ethylene production was suppressed to rates well below those of unimpeded roots. The concentration of abscisic acid was not affected by impedance.

It is concluded that despite a widespread view to the contrary, ethylene is not the cause of the morphological ‐esponse of roots to physical impedance. Abscisic acid is also unlikely to be involved.
Authentic activity of the ethylene‐forming enzyme observed in membranes obtained from kiwifruit (Actinidia deliciosa)
Authors: MITCHELL THOMAS , PORTER ANDREW J. R. , JOHN PHILIP
Published: April 2006

Membrane vesicles in the juice squeezed from the pericarp of ripe kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson, formerly Actinidia chinensis Planch.] possess an activity of the ethylene‐forming enzyme which showed the essential features of the in vivo enzyme: a preference for the racemic mixture containing the (IR, 2S)‐enantiomer of 1 ‐amino‐2‐ethylcyclopropanc‐ 1 ‐carboxylic acid; a relatively high affinity for the natural substrate 1‐aminocyclopropane‐ 1 ‐carboxylic acid (Km of 125μM); only partial inhibition by excess eatalase and mM concentrations of FDTA, dithiothreitol and ascorbate. During post‐harvest ripening enzyme activity assayed in vitro developed in parallel with enzyme activity assayed in vivo. The kiwifruit enzyme was sensitive to salicylhydroxatnic acid and to a loss of structural integrity of the membrane vesicles. Although only 0·% of the activity measurable in vivo was recovered in vitro. the kiwifruit membranes provide a useful, easily prepared system for studying the ethylene‐forming enzyme in vitro.
Inoculation of mycelial cord‐forming basidiomycetes into woodland soil and litter II. Resource capture and persistence
Authors: DOWSON C. G. , RAYNER A. D. M. , BODDY LYNNE
Published: April 2006

Substantial mycelial cord systems of Hypholoma fasciculare (Huds. ex Fr.) Kummer, Phallus impudicus (L.) Pers., Phanerochaete (Ph.) velutina (DC ex Pers.) Parmasto, Phanerochaete laevis (Fr.) Erikss. & Ryv. and Steccherinum fimbriatum (Pers. ex Fr.) Erikss. had developed 2 years alter direct inoculation into the soil and litter of a range of woodland sites. Where species had been inoculated individually, the distribution patterns of the cord systems were strongly related m the availability and colonizability of various litter components. Where different species were co‐inoculated in columns and rows 14 × 17 cm apart. Ph. velutina frequently replaced the other species, forming extensive mycelial systems and bringing about considerable decay of the original inocula. However, established systems of S. fimbriatum often developed in close proximity to Ph. velutina. Where inoculum blocks were implanted amongst litter containing few available resources for colonization, outgrowth was strongly directed along rows of nearest‐neighbouring blocks.
The effect of the fungus, Balansia cyperi Edg., on growth and reproduction of purple nutsedge, Cyperus rotundus L.
Authors: STOVALL MARY E. , CLAY KEITH
Published: April 2006

Two growth trials were conducted in the greenhouse to determine the effects of the systemic clavicipitaceous fungus, Balansia cyperi Edg, on growth and tuber production of purple nutsedge (Cyperus rotundus L.). In the field, tubers collected from populations of infected plants were significantly smaller than tubers from populations of uninfected plants. There were no differences in percentage of tubers sprouting, or in time to sprouting, between infected and uninfected tubers collected and planted in the greenhouse in September 19S5. Infected tubers collected and planted in January 1986 showed significantly decreased percentage sprouting, and increased time to sprouting, compared with uninfected tubers. In both trials, after correcting for differences in initial tuber size, vegetative tiller (shoot) number increased and inflorescence number decreased for infected purple nutsedge compared to uninfected purple nutsedge. Plants were harvested after 20 weeks in the second trial. Total dry weight of infected plants was greater than total dry weight of uninfected plants, but ratios of below‐ground: above‐ground dry weight were the same. Infected plants produced significantly more, but smaller, tubers than uninfected plants. Greater vegetative growth and production of more tubers may provide and advantage to infected purple nutsedge in mixtures with uninfected plants and other plant species.
A pollen diagram from an interglacial deposit at Trysull, Staffordshire, England*
Authors: MORGAN A. V. , WEST R. G.
Published: April 2006

A pollen diagram from freshwater sediments resting on glacio‐fluvial outwash at Trysull, Staffordshire, England shows a sequence relating to the development of temperate stage forest. Correlation with a nearby Hoxnian site at Nechells, Birmingham is suggested.
Cell expansion rate, temperature and turgor pressure in growing leaves of Lolium temulentum L.
Authors: THOMAS A. , TOMOS A. D. , STODDART J. L. , THOMAS H. , POLLOCK C. J.
Published: April 2006

Leaf growth rate and the turgor pressure of cells in the expanding zone of leaves of Lolium temulentum were measured simultaneously. Growth rate was reduced over a range from 30μm min−1 to zero by reducing the temperature of the expanding zone from 20 to 2 °C. Turgor pressure remained constant at 05 MPa. This implies that growth reduction by low temperature is due to changes in cell wall rheology. Cell membrane hydraulic conductivity (Lp) was reduced with temperature as expected, but this was not sufficient to influence growth rate detectably.
The level of injury and needle ultrastructure of acid rain‐irrigated pine and spruce seedlings after low temperature treatment
Authors: REINIKAINEN JAANA , HUTTUNEN SATU
Published: April 2006

Frost injury in three Finnish provenances of acid rain‐treated (pH 4 and 3) pine [Pinus sylvestris (L.)] and spruce [Picea abies (L.) Karst.] seedlings was studied by microscopical methods. Seedlings from southern and northern provenances were watered for seven weeks with artificially acidified rain during the hardening period in 1986. A cold treatment on the winter hardened seedlings was carried out in January by lowering the temperature gradually to −55°C. Afterwards the development of injury symptoms was followed visually and microscopically. The most prominent sign of freezing injury was needle discoloration. In addition, the stems and buds of the seedlings showed signs of severe injury. Under the light microscope the injury was exhibited as largened intercellular spaces and increased numbers of disintegrating cells. Diminution of the membraneous structures within the cytoplasm of mesophyll cells and rupturing of plasmalemma and tonoplast, as well as swelling of chloroplasts, were seen in damaged cells. The symptoms of freezing injury at ultrastructural level differed from those found in needles exposed to air pollutants.
Effects of forest soil acidification on ectomycorrhizal and vesicular—arbuscular mycorrhizal development
Authors: DANIELSON R. M. , VISSER S.
Published: April 2006

Seedlings of Pinus contorta Dougl. and Phleum pratense L. were grown in the greenhouse in forest floor (F/H horizons) and mineral soil from a P. contorla stand which had been acidified (pH 1.6 5.2) with S° dust over a 5‐year period. Although S° dust was the primary treatment it was assumed that acidification accounted for the major effects on the plants and mycorrhizas. Pinus contorla failed to grow below pH 2.8 and ectomycorrhizas were absent below pH 3.3. Pheleum pratense ceased growth at pH 3.3 and no vesicular‐arbuscular (VA) mycorrhizas were formd below pH 4.0. There did not appear to be any relationship between the relative abundance of coarse and fine VA mycorrhizal endophytes and soil acidity. Cenococcum geophilum L. was a common ectomycorrhizal associate of pine seedlings grown in the F/H soil, and E‐strain fungi (Complexipes), Mycelium radicis atrovirens Melin, Tomentella sp. and Suillus sp. were all more common in the mineral soi than in the F/H soil. Piloderma bicolor (Peck) Julich was observed to occur in large, discrete patches in the undisturbed natural stand but did not form ectomycorrhizas in the greenhouse. Both P. pratense and P. contorla were capable of good growth in extremely acid soils in a non‐mycorrhizal state.
The role of proteins in the nitrogen nutrition of ectomycorrhizal plants
Authors: ABUZINADAH R. A. , READ D. J.
Published: April 2006

Seedings of Betula pendula L. were grown aseptically in the non‐mycorrhizal condition and in association with the mycorrhizal Fungi Hebeloma crustuliniforme (Bull, ex St. Am.) Quél Amanita muscaria (L. ex Fr.) Hooker or Paxillus incolutus (Batsch) Fr. They were supplied with the amino‐acid l‐alanine, or with peptides of between 2 and 6 alanine units, as sole nitrogen (N) sources. The ability of the different categories of plants to use these N sources was measured in terms of dry weight yield and nitrogen content of roots and shoots.

While non‐mycorrhizal plants were unable to use any of these compounds as N sources, mycorrhizal infection provided the plants with some access to all of the N sources. The fungi differed, however, in the extent to which they mobilized the nitrogen, H. crustuliniforme being generally a more effective symbiont than A. muscaria which was, in turn, more effective than P. involutus. The yields and N contents of infected plants were normally higher on the peptides than on the amino acid, and in the two most effective fungi, the highest yield and nitrogen content were obtained in the treatments containing the largest peptide units. The physiological and ecological significance of these observations is discussed with particular attention being given to the role of mycorrhizas in the nitrogen nutrition of plants in natural ecosystems.
New aspects on the acquisition of biotrophic status by a vesicular—arbuscular mycorrhizal fungus, Gigaspora margarita
Authors: BÉCARD G. , PICHÉ Y.
Published: April 2006

An in vitro system for culturing the vesicular arbuscular (VA) mycorrhizal fungus Gigaspora margarita Becker & Hall with Ri T‐DNA transformed roots of carrot has been used to investigate the progressive dependency of a VA mycorrhizal fungus on its host during mycorrhizal establishment. The growth of hyphae from germinating spores of G. margarita was measured under different combinations of the following treatments: in absence or presence of root, with or without mycorrhizal colonization, with or without spore removal. Two distinct mechanisms of hyphal growth stimulation have been identified. The first required the presence of the root hut remained spore dependent. The second is exclusively root dependent. It has been demonstrated that the second mechanism is triggered when arbuscules are forming, indicating they are necessary for establishment of biotrophy. It is proposed that roots contribute to fungal growth by an inductive action, in addition to providing nutrients.
Early stages in colonization of Allium porrwn (leek) roots by the vesicular—arbuscular mycorrhizal fungus, Glomus versiforme
Authors: GARRIOCK M. L. , PETERSON R. L. , ACKERLEY C. A.
Published: April 2006

Leek (Allium porrum L. cv. Titan) roots wore colonized by the vesicular arbuscular (VA) mycorrhizal fungus Glomus versiforme (Daniels and Trappe) Berch. External hyphae were of varying sizes and had a single‐layered wall surrounding a vacuolate cytoplasm. Intra‐hyphal hyphae were frequent in the extraradical mycelium. Some external hyphae formed small branches which initiated simple appressoria over the outer tangential wall of epidermal cells. Appressoria were multinucleate and possessed many structures which we have interpreted to be bacterium‐like organclles (BLOs). Infection hyphae formed by appressoria penetrated the radial cell walls of epidermal cells and were surrounded by an electron dense substance and host cell wall. Epidermal and cortical cells reacted frequently by forming cell wall thickenings. Hyphae in the exodermis formed coils which were surrounded by host plasma membrane but not host cell wall, and had many nuclei and BLOs.
Soil disturbance reduces the infectivity of external hyphae of vesicular—arbuscular mycorrhizal fungi
Authors: JASPER D. A. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

We conducted two glasshouse experiments to determine the effect of soil disturbance on the infectivity of external hyphae of vesicular–arbuscular (VA) mycorrhizal fungi. A nylon mesh was used to exclude plant roots while allowing fungal hyphae to grow into soil contained by the mesh. Hyphae of VA mycorrhizal fungi that had been separated from the original host plant root were still able to colonize bioassay plants rapidly and extensively. However, disturbance of the soil inside the mesh, by mixing for 1 min, almost eliminated subsequent VA mycorrhiza formation in that soil. Damage to the soil hyphal network by soil disturbance may contribute to the losses in mycorrhizal infectivity that have been observed after mining and cultivation.
Hyphae of a vesicular—arbuscular mycorrhizal fungus maintain infectivity in dry soil, except when the soil is disturbed
Authors: JASPER D. A. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

We examined the hypothesis that hyphae of a VA mycorrhizal fungus in dry soil remain infective, but that the infectivity decreases if the soil is disturbed. We used split‐pots, and sealed cylinders of nylon mesh, to create volumes of dry soil which contained hyphae of Acaulospora laevis Gerd. and Trappe that were attached, outside the mesh, to roots of living plants of Acacia satigna. (Labill.) H. Wendl. After the soil was dried in situ, the hyphae were detached from the roots without soil disturbance, or the soil containing the hyphae was disturbed. The infectivity of the hyphae after these treatments was then compared with that of intact hyphae.

External hyphae of A. laevis remained highly infective in soil in which the matric potential had reached −21 MPa. Hyphae detached from the original host plant roots were equally infective. However, disturbance of the dry soil containing the external hyphae severely reduced the infectivity of the hyphae. After fluorescent staining, fungal structures with fluorescing nuclei were readily visible both within, and attached to, roots of A. Saligna which had no fluorescing nuclei.
Interpreting long‐term exponential growth of plant populations in a 250000‐year pollen record from Valle di Castiglione (Roma)
Authors: MAGRI DONATELLA
Published: April 2006

The pollen concentration diagram of a long core drilled in the lacustrine sediments of Valle di Castiglione (Roma) indicates that the increase of different plant populations is often exponential. Increases of trees, shrubs, herbs, aquatic plants and pteridophytes have been examined; their doubling times vary from a few to many hundreds of years. The durations of exponential growth last up to 6000 years.

The interpretation of this phenomenon takes into account the close relation between climate, soil and vegetation. Under climatic conditions suitable for the expansion of a given population, growth depends on soil fertility, which, in turn, increases as the population grows. The process may be self‐fertilizing, producing in the long run a sum of nutrients greater than their consumption. Competition does not seem decisive in determining patterns and times of increase of plant populations.
Respiration and microalgal growth: a review of the quantitative relationship between dark respiration and growth
Authors: J.GEIDER RICHARD , OSBORNE BRUCE A.
Published: April 2006

Biomass‐specific, dark respiration rates of microalgae vary by almost two orders of magnitude from 0.01 to 0.6 d−1. In general, dark respiration rates increase with growth rates in both intraspecitic and interspecific comparisons, but the precise relationship between respiration and growth rate varies. Under optimal conditions, respiration rates are about 20‐30% of growth rates, but the ratio of respiration to growth increases under suboptimal conditions. The intercept of plots of respiration rate vs. growth rate varied from < 0.01 to 0.4 d1, and the slopes of these relationships varied from < 0.1 to 1.0. Minimum maintenance metabolic rates of about 0.01 d 1 have been estimated for some microalgae by extrapolation of the initial slope of the light curve for growth to a hypothetical negative growth rate in darkness. The dimensionless total energy cost of synthesis and maintenance for heterotrophie growth of microalgae using either endogenously or exogenously supplied carbohydrates is typically 0.4‐1.2 for growth with ammonia or urea as a nitrogen source and 0.7‐1.4 for growth with nitrate as the nitrogen source.
Development of lines of radish differing in resistance to O3 and SO2
Authors: GILLESPIE CHRIS T. , WINNER WILLIAM E.
Published: April 2006

The potential for developing intraspecific lines of radish (Raphanus sativus L. cv, Cherry Belle) based on their relative resistance to either O3 or SO2 was examined using growth‐analysis techniques. Plants were exposed to either 0–10μ 1−1 O3 or 0.50 μ 1 −1 SO2 for 4 h day−1, 3 days week−1, for 3 weeks. Resistant and sensitive individuals were then selected and divided into four groups: O3 resistant (O3R), O3 sensitive (O3S), SO2 resistant (SO2R), and SO2 sensitive (SO2S) Cross‐pollinations were made among plants within the selected groups and seed collected. F1 populations were raised from the resulting seed and exposed to the same exposure regime. Net photosynthesis and stomatal conductance were measured during the final two fumigations, and plants were harvested immediately following the final exposure, divided into component parts, dried and weighed.

O3 and SO2 generally caused biomass reductions in all the F1 groups. O3 reduced below ground growth more than SO2 leading to greater reductions in root/shoot ratios. O3R plants were resistant to both pollutants, showing little biomass reduction particularly from O3. Root/shoot ratios of these plants were altered less by pollutant exposure than non‐selected radishes. Shoot growth of SO2R plants was greater in O3 or SO2 than non‐selected plants, but below ground growth was similar. Selection for plants sensitive to either pollutant was not apparent from growth analysis, as growth of the sensitive plants was generally the same as that of non‐selected plants. Gas exchange results indicated greater stomatal conductance in O3S plants in filtered air than either non‐selected or O3R plants, while O3S plants had lower conductance rates in the O3 treatment.
Physiology and yield of field‐grown Brassica oleracea L. exposed to acidic fog
Authors: TAKEMOTO B. K. , JOHNSON A. G. , PARADA C. R. , OLSZYK D. M.
Published: April 2006

Field‐grown Brassica oleracea L. ev. Emperor (broccoli) plants were exposed to a range of treatments with simulated acidic fog in open‐field plots to examine the effect of fog chemistry on yield and growth, and to determine whether alterations in yield or growth were related to the development of foliar injury and/or the inhibition of net photosynthesis. Simulated fogs (i.e. pH values of 1.76, 2.23, 2.72, 3.22 or 5.48) with a liquid water content of 0.20–0.25 g m−3 were applied twice weekly for 10 weeks. Applications of pH 1.76 fog caused significant yield reductions (37%) relative to pH 5.48. Leaf dry weight responses were more sensitive to fog chemistry than yield. Leaf dry weight was significantly inhibited by 53, 25 and 9% in the pH 1.76, 2.23, and 2.72 fog treatment groups, respectively.

The depression of yield by fog of pH 1.76 was closely correlated with the development of foliar injury and the inhibition of net photosynthesis on a percentage basis. Plants exposed to pH 2.23 or 1.76 fog consistently displayed amounts of injury ranging from 5 to 7% or 20 to 31%, respectively, whereas plants exposed to pH 2.72 fog or higher exhibited less than 5% injury throughout the study. Whole‐study average rates of net photosynthesis were significantly depressed by pH 1.76 fog (30% lower). The inhibition of net photosynthesis was coincident with increases in both mesophyll and stomatal resistances to CO2, but the ratio of mesophyll to stomatal resistance was not significantly altered.

These findings provide evidence that repeated exposures to highly acidic fog (pH 1.76 or 2.23) may cause significant reductions in marketable yield and/or growth of B. oleracea, but substantive adverse effects would not be expected from exposures to fog of lower acidic strength. Although the inhibition of net phososynthesis in B. oleracea by acidic fog was coincident with decreased yield, reduced rates of CO2 assimilation appear to be due to the development of foliar injury (i.e. reduced photosynthetically active leaf area per plant) rather than a specific alteration in mesophyll or stomatal resistance to CO2.
Translocation of lysine from the host Melicope simplex to the parasitic dwarf mistletoe Korthalsella lindsayi (Viscaceae)
Authors: COETZEE J. , FINERAN B. A.
Published: April 2006

3H‐lysine was administered to severed ends of host stems infected by the parasitic mistletoe Korthalsella lindsayi (D. Oliver) Engl. Autoradiography at the ultrastructural level revealed that the tracer is transported from host to parasite and that it accumulates in lipid bodies in the haustorial parenchyma. At the host/parasite interface phloem is generally absent and the number of direct xylem tracheary to tracheary contacts are limited. In the interface area no cytoplasmic continuity could be observed between host and parasite, but numerous plasmatubules were present. It is concluded that organic substances such as the amino acid lysine can be translocated apoplastically from the host to the parasite and that plasmatubules are probably implicated in this process.
Effects of ectomycorrhiza on host growth and carbon balance in a semi‐hydroponic cultivation system
Authors: NYLUND JAN‐ERIK , WALLANDER HÅKAN
Published: April 2006

Ectomycorrhizal and control Pinus sylvestris L. seedlings were grown under steady‐state nutritional conditions in a semi‐hydroponic system. Free access to balanced low concentrations of mineral nutrients did not inhibit mycorrhiza formation. The large variations in relative growth rate observed after inoculation with different fungi demonstrated that the mycobiont has a substantial influence over the proportion of host photosynthate allocated for maintaining the symbiosis. Analyses with 14C‐tracer demonstrated that photosynthesis was considerably enhanced in mycorrhizal seedlings, even though N and Mg concentrations were similar in mycorrhizal and uninoculated seedlings. Although translocation and respiration were highly variable, they were enhanced in some seedlings. Nutrition had no demonstrable effects on shoot or root carbohydrate content, but auxin (IBA and IAA) treatments increased the carbohydrate concentrations. Several auxin treatments also accelerated translocation and respiration, but their effects on photosynthesis were variable. The results contradict some of the basic tenets in Björkman's (1942) carbohydrate theory, while providing circumstantial evidence in favour of Slankis's (1973) hormone hypothesis.
Time‐course of N2‐fixation (15N) in the field by clover growing alone or in mixture with ryegrass to improve pasture productivity, and inoculated with vesicular—arbuscular mycorrhizal fungi
Authors: BAREA J. M. , AZCÓZ R. , AZCÓN‐AGUILAR C.
Published: April 2006

The isotope 15N was used to estimate N2‐fixation by white clover, and N‐transfer from clover to perennial ryegrass. Pure stands of each of these pasture plants and a mixed sward of both were established in a field soil in which it had been demonstrated that vesicular‐arbuscular mycorrhizal inoculation was necessary for suitable development of the clover. All plants, whether clover or ryegrass, received the same amount of a selected mycorrhizal inoculum. The 15N/14N ratio of the grass in pure stands was used to evaluate N2,‐fixation by clover growing alone, and that of the grass in the mixture to estimate that by the companion clover. Tentative evidence of N‐transfer was obtained by comparing the 15N/11N ratio in the grass growing alone with that when mixed with the legume.

In spite of a decline with time in 15N enrichment, the N2‐fixation rates were about the same throughout the growing season and for the two cropping systems. The total N, P and dry matter yields in the grass/clover mixture were greater than in monocultures. A lower 15N enrichment of the grass growing mixed compared to that growing alone, suggesting N‐transfer, was only obtained at the second harvest. The mycorrhizal colonization of the grass in the mixed grass/closer sward was significantly enhanced, as compared with that of the grass in pure stands. Mycorrhizal hyphae are known to be involved in NH4+ uptake, translocation and transfer to the host plants, and this may partly explain the improvement of pasture productivity when grass and mycotropic legumes are grown together.
Effects of soil and plant phosphorus concentrations on vesicular‐arbuscular mycorrhiza in sorghum plants
Authors: De MIRANDA J. C. C. , HARRIS P. J. , WILD A.
Published: April 2006

The effect of soil and plant phosphorus (P) on mycorrhiza was studied using a split‐root technique. In this experiment, sorghum (Sorghum bicolor (L.) Moench.) plants inoculated with the vesicular‐arbuscular (VA) mycorrhizal fungus Glomus macrocarpum (Tul. & Tul.), were subjected simultaneously to low and high phosphate concentrations applied to a phosphorus deficient Brazilian Dark Red Latosol. Phosphorus was translocated from one half of the root system to the other. When small additions of P were made to the soil, mycorrhizal infection. spore numbers and external hyphae increased compared with the unsupplemented soil. Translocation of phosphorus into roots growing in unsupplemented soil had little effect on percentage root infection, spore number or external hyphae in that compartment although infected root length increased slightly. In the treatment where soil P and plant P were high, percentage root infection and external hyphal growth were both similarly reduced. In the high phosphate treatments although percentage root infection was reduced, the total length of mycorrhizal root was not affected by phosphate fertilization.
Root temperature affects mycorrhizal efficacy in Fraxinus pennsylvanica Marsh
Authors: BORGES RITA G. , CHANEY WILLIAM R.
Published: April 2006

Growth parameters and carbohydrate contents were determined for Fraxinus pennsylvanica Marsh, seedlings inoculated with Glomus macrocarpum Tul. and Tul. or Glomus fasciculatum (Thaxt.) Gerd. and Trappe, and for uninoculated controls that were grown in a greenhouse for 16 weeks at root temperatures of 15, 25 or 35 °C. Seedling growth responded rapidly to mycorrhizal inoculation when root temperatures were 25 or 35 °C. Response to inoculation at 15 °C was delayed but seedlings at this temperature finally attained the size of those grown at 25 and 35 °C. Growth of noninoculated plants was best at 15 and 25 °C. Inoculation with mycorrhizal fungi moderated the adverse effect of higher root temperature. Infection of roots by both fungal species was greater at 25 °C than at 15 or 35 °C. Sugar content increased as root temperature increased whereas starch content was inversely related. Both soluble sugar and starch content were less in mycorrhizal than in nonmycorrhizal seedlings.