bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apoplastic permeability of sclerotia of Sclerotium rolfsii, Sclerotium cepivorum and Rhizoctonia solani
Authors: YOUNG NICOLA , ASHFORD ANNE E. 
Published: April 2006

summaryIntact mature sclerotia of Sclerotium rolfsii sacc, and Sclerotium cepivorum Berk, produced in culture are impermeable to the apoplastic tracer sulphorhodamine G. Both of these species produce sclerotia with rinds. Some movement of sulphorhodamine into sclerotia of Rhizoctonia solani Kühn, which have no rind, occurred but the fluorochrome was arrested after permeation of at most the outer five layers of cells. In all cases, low permeability depended on an intact outer layer, and when sclerotia of each species were bisected to provide direct access of sulphorhodamine to all tissue layers, the fluorochrome permeated the cell walls and extracellular matrix (where present) of many cells within the sclerotium. A marked reduction in permeability of intact sclerotia occurs at maturity in a number of species and might he important in long‐term Survival.
Dynamics of thermogenesis and structure of epidermal tissues in inflorescences of Arum maculatum
Authors: BERMADINGER‐STABENTHEINER EDITH , STABENTHEINER ANTON 
Published: April 2006

summaryThe temporal dynamics and spatial distribution of heat production by inflorescences of Arum maculatum L. were investigated by infra‐red thermography. Two centres of (teat production, the appendix and the male flowers, and three thermogenic phases, two of the male flowers and one of the appendix, could be observed. On the first day of flowering, when the spathe was still firmly closed, the male flowers became thermogenic (= first thermogenic phase Of the in florescence) and reached surface temperatures of 4.1–8.0 °C above ambient temperature. Afterwards the spathe unfolded and the appendix started heating to temperatures of 5.0–14.0 °C above ambient temperature (second thermogenic phase of the inflorescence). On the second day of flowering the male flowers revealed a second temperature maximum of 0.5–601 °C above ambient temperature third thermogenic phase of the inflorescence) which was followed by the release of the pollen grains. When the male flowers started heating, a fruit‐like and pleasant scent became evident and continued until the heat production in the male flowers stopped. Only during the heating phase of the appendix was this fruit‐like scent overlaid by the dung‐like odour typical of many aroid species. The surface of the spadix and the inner surface of the basal bulb (floral chamber) as investigated by scanning electron microscopy were characterized by smooth epidermal cells of papillate shape. These cells were rurgid before the onset of flowering and heat production and collapsed afterwards. Distinct intercellular spaces creating a lacunose epidermis (‘Lückenepidermis‘) were observed between the papillate epidermal cells of the inner surface of the basal bulb (floral chamber). This coincided with a high density of stomata on its outer surface. It is suggested that, beside other pathways, these structures contribute to the maintenance of sufficient oxygen support of the captured insects and the thermngenic tissues inside the floral chamber.
Impact of a fungal pathogen, Colletotrichum coccodes on growth and competitive ability of Abutilon theophrasti
Authors: DITOMMASO ANTONIO , WATSON ALAN K. 
Published: April 2006

summaryThe combined effects of planting density and of different inoculation frequencies ofColletotrichum coccodes (Wallr.) Hughes on growth and competitive performance of Abutilon theophrasti Medik. were studied using a soybean‐A. theophrasti target‐neighbour design in a controlled environment. In both trials of the experiment, A. theophrasti inoculated at the highest planting density (four plants per ppt) suffered significantly greater reductions in height (41%) than did A. theophrasti at the lowest density (one plant per pot) (7%). Above‐ground biomass and leaf area reductions, however were significantly greater at the highest density for only one of the trials. Soybean plants grown with inoculated A. theophrasti at the two highest planting densities had a significantly greater above‐ground biomass (61%) and leaf area (68%) than did plants grown with uninoculated A. theophrasti at the same densities. By contrast, at the two lower densities, soybean above‐ground biomass and leaf area were not increased significantly fallowing inoculation. Either one or two C. coccodes inoculations caused the greatest reductions in A. theophrasti growth compared with uninoculated plants. Conversely, three applications of the fungus generally resulted in less severe disease symptoms and resulted in the smallest decreases in A. theophrasti growth. Induced systemic resistance following two inoculations might have played an important role in limiting disease. However, the significantly greater biomass and height of A. theophrasti plants subjected to the triple C. caicudes treatment, compared with plants receiving either one or two inoculations in one of the trials, provides some evidence of a possible compensatory response in .4. theophrasti. The relevance of these findings for biological weed control is examined.
Increased growth efficiency ofQuercus albatrees in a CO2‐enriched atmosphere
Authors: NORBY RICHARD J. , WULLSCHLEGER STAN D. , GUNDERSON CARLA A. , NIETCH CHRISTOPHER T. 
Published: April 2006

summaryForests have a prominent role in the global carbon cycle, but their response to a changing atmosphere cannot be measured directly. Experimental observations of small trees in CO2‐enriched atmospheres must be interpreted carefully if they are to be relevant to the potential responses of forest trees. We grew1white oak (Quercus albaL.) saplings for four complete growing seasons in open‐top chambers with different partial pressures of atmospheric CO2White oak saplings produced 58% more dry mass in 50 Pa CO2and 135% more in 65 Pa, compared with plants in ambient (35 Pa) CO2Although this result might suggest a substantial potential for increased carbon storage in forests, the large difference in growth rate could be attributed to a stimulation of growth very early in the experiment. There was not a sustained effect of C2on relative growth rate after the first year, and the increased absolute growth rate could persist only so long as leaf area could increase, a condition that would not occur indefinitely in a forest. Nevertheless, annual stem wood production per unit area (growth efficiency) was 37 %, greater in elevated CO2. This increase in growth efficiency, a response that is consistent across diverse studies, implies a potential increase in carbon sequestration by forests, subject to critical assumptions about forest canopy development in a CO2‐enriched atmosphere
Effects of CO2 enrichment, leaf position and clone on stomatal index and epidermal cell density in poplar (Populus)
Authors: CEULEMANS R. , VAN PRAET L. , JIANG X. N. 
Published: April 2006

summaryThe effects of CO2, enrichment and leaf position on stomatal characteristics (stomatal density, stomatal index and stomatal pore length) and epidermal cell density were examined for two different Populus clones, Beaupre and Robusta, grown from cuttings in open‐top chambers under ambient and elevated atmospheric CO2 conditions. Both clones had amphistomatous leaves, and stomatal density was significantly larger on the abaxial leaf surface than on the adaxial. Significant interactions between CO2 enrichment, leaf position and clone were observed for most stomatal and epidermal characteristics. A significant reduction of the number of stomata mm−2 under elevated CO2 was observed in expanding leaves near the upper portion of the plant for both leaf surface sides and in both clones. For the abaxial leaf side only, this reduction under elevated CO2, was accompanied by a similar reduction of the stomatal index in both clones. In mature leaves on the middle and lower portion of the plants, there was no significant effect of the CO2 treatment on stomatal density. In young, expanding leaves near the upper part of the plant there were significant interactions between the CO2 treatment and leaf surface side for epidermal cell density. The latter increased under elevated CO2 at the abaxial leaf surface, but decreased at the adaxial surface on the upper part of the plant. Total epidermal cell numbers of mature, fully expanded leaves increased under elevated CO2, in both clones. The observation that interactions with leaf age and/or leaf position significantly confound the CO2, treatment effect on stomatal and epidermal cell densities, might contribute to the elucidation of the problem of the phenomenon of stomatal density reduction under elevated atmospheric CO2.
Root‐induced iron oxidation, pH changes and zinc solubilization in the rhizosphere of lowland rice
Authors: KIRK G. J. D. , BAJITA J.B. 
Published: April 2006

summaryRice plants (Oryza sathiva L., cv. IR34) were grown with their roots sandwiched between cylinders of an anaerobic low‐Zn Mollisol. After periods of root‐soil contact of up to 12 d (total plant age c. 28 d) the profiles of different Zn fractions, reduced and oxidized Fe, and pH in the soil near the root plane' were determined. The concentration of easily plant‐extractable Zn in the soil (measured by extraction in I M KCl) was negligible, and so it was necessary for the plants to induce changes in the soil to solubilize Zn. After 6 d, there was a substantial accumulation of Zn associated with organic matter and amorphous ferric hydroxide within 4–5 mm of the root plane. Over the next 6 d, the accumulation continued but there was a substantial depletion of the accumulated fractions within 2 mm of the root plane. The zones of accumulation and depletion coincided with zones of Fe(III) accumulation and soil acidification in which the pH decreased from the bulk soil value of 7.3 by over 0.2 pH units; i.e. a two‐fold increase in H+ concentration, The acidification was the result of H+ released from the roots to balance excess intake of cations over anions, and H+ generated in the oxidation of Fe(H) by root‐released O2. At the high pH and CO., pressure of the experimental soil (7.3 and c. 0.9 kPa. respectively), soil acidity diffusion is fast and consequently the pH drop at the root surface was small. The rate of Fe oxidation peaked before 6 d, but the acidification and Zn accumulation continued beyond 6 d unabated. It is concluded that Fe oxidation released Zn from highly insoluble fractions, and that this Zn was re‐adsorbed on Fe(OH)3 and on organic matter in forms that were acid‐soluble and therefore accessible to the plants.
Estimates of fungal biomass in Scots pine stands on an urban pollution gradient
Authors: MARKKOLA A. M. , OHTONEN R. , TARVAINEN O. , AHONEN‐JONNARTH U. 
Published: April 2006

summaryBiomasses of ectomycorrhizal and saprotrophic fungal communities partitioned into sporophores and non‐reproductive structures were estimated in mature Scots pine (Pinus sylvestris L.) stands along an urban nitrogen and sulphur pollution gradient in northern Finland. The average total biomass of fungi varied in the four pollution zones from 14.6 to 20.2 g d. Wt kg−1 soil d. wt and from 73.3 to 108.0 g d. Wt m−2, the mycelia of both mycorrhizai and saprotrophic fungi in the soil comprising 72–80% of the total. The annual carbon allocation to the fungal communities was calculated to vary between 9 and 26% of the estimated annual carbon assimilation at the Scots pine sites. The size of the mean fungal biomass fractions decreased in the following sequence: mycelia in the soil > fungal biomass in fine roots estimated in terms of chitin > sclerotia > fungal biomass in fine roots estimated in terms of ergosterol > sporopbores of mycorrhizal fungi > sporophores of saprotrophie fungi. A positive correlation was obtained between the number of Scots pine mycorrhiza and the average sporophore yield of mvcorrhiaal fungi for three successive years. Tbe sporophore biomass of the mycorrhizal fungi was smaller at the most polluted than at the least polluted sites. The total fungal biomass allocation was not affected by urban pollution.
Assessment of photosynthetic radiation‐use efficiency with spectral reflectance
Authors: PEÑUELAS JOSEP , FILELLA IOLANDA , GAMON JOHN A. 
Published: April 2006

summaryReflectance changes at 531 nm, associated with the zeaxanthin‐antheraxanthin‐violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance (‘PRI’, Photochemical Reflectance Index calculated as (R531− R570)/(R531+ R570)) as an indicator of efficiency of photosynthetic radiation use in seven species representing both C3 and CAM photosynthetic pathways. Leaves exposed to a dark‐lighted ark transition in a steady‐state laboratory gas exchange system exhibited nearly parallel changes in PRI and PS II quantum yield (ΔF/Fm′). Similar PRI and ΔF/Fm′ responses were seen in leaves exposed to diurnally changing sunlight levels outdoors. PRI was linearly related to ΔF/Fm′, and both ΔF/Fm′ and PRI were exponentially related to instantaneous efficiency of photosynthetic radiation‐use in different species over a range of different field conditions. These results extend previous studies by indicating a functional relationship between PRI. ΔF/Fm′, and photosynthetic radiation‐use efficiency. The narrow‐band PRI index offers a simple, portable means of assessing PS II radiation‐use efficiency, analogous to ΔF/Fm′, and with the potential for remote applications at scales larger than the leaf.
A three‐dimensional representation of the relationship between penetration of u.v.‐B radiation and u.v.‐screening pigments in leaves of Brassica napus
Authors: ÅLENIUS CAMILLA M. , VOGELMANN THOMAS C. , BORNMAN JANET F. 
Published: April 2006

summaryA three‐dimensional (3–D) representation of the penetration of u.v.‐B (280–320 nm) radiation using fibre‐optic microprobes, and of the spectrophotometric analysis of u.v.‐.screening pigments in leaves of Brassira napus, L. ev. Ceres is presented. In this way the results from radiation measurements were directly related to the distribution of u.v.‐screening pigments. Brasssica napus was grown in a greenhouse chamber with a photon flux density of 740μmol m−2 s−1 photosynthetieally active radiation (400–700 nm) with or without the addition of u.v.‐B radiation. The amount of u.v‐B added was equivalent to 9 kJ m−2 d−1 biologically effective u.v.‐B. Growth parameters measured lncluded leaf thickness and dry weight. Ultraviolet‐B radiation stimulated the accumulation of increased amounts of screening pigments, located mostly beneath the adaxial surface of the leaf. Leaf dry weight decreased by 15% in u.v.‐treated plants and, on a dry weight basis, chlorophyll content increased by 19% in treated leaves. The chlorophyll profiles within leaves from both control and u.v.‐treated plants showed an increase from the adaxial surface to a plateau in the middle of the leaf, at a leaf depth of c. 150–320μm. Relatively large amounts of 285 nm radiation penetrated into leaves of u.v.‐B treated plants to sites located within the initial 40μm of the leaf. Thus, despite the presence of additional screening pigments, u.v.‐B radiation was capable of reaching potential targets within the epidermis and mesophyll.
Mesophyll structure during leaf development in Ballota acetabulosa
Authors: PSARAS G. K. , RHIZOPOULOU S. 
Published: April 2006

summaryMesophyll structure and water relations were studied in expanding and expanded dorsiventral leaves of Ballota acetabulosa Benth., a wild perennial shrub from the Mediterranean. The spongy mesophyll was developed earlier than the palisade in expanding leaves and exhibited a larger internal exposed surface. By contrast, in fully expanded leaves the internal exposed surface was much larger in the palisade than in spongy mesophyll. The development of chloroplasts in cells of both mesophyll tissues, as well as their arrangement along the cell walls exposed to intercellular canals, coincided with the formation of intercellular spaces. Leaf expansion appears to be positively related to increasing internal exposed surface and declining water potentials. As a result, mature leaves possess a high ratio of internal exposed surface per leaf area and low values of turgor. It is considered that an increase in the internal exposed surface might be an adaptive feature for small‐leaved shrubs, grown under water deficiency.
Exudation rate and hydraulic conductivity of maize roots are enhanced by soil drying and abscisic acid treatment
Authors: ZHANG JIANHUA , ZHANG XIAOPING , LIANG JIANSHENG 
Published: April 2006

summaryWhen young maize seedlings were fed with abscisic acid (ABA) into their root systems, the exudation rate from roots through cut stems was enhanced more than leaf diffusive resistance. Enhanced root exudation was also observed when mildly droughted plants were re‐watered. To compare the mechanisms involved in this response under these two treatments, we examined solute transport in exudates and in situ whole root hydraulic conductivity following ABA feeding to the roots or soil drying/re‐watering treatment. Increases of both solute concentration and delivery rate in the exudates of pre‐droughted plants appeared to account for about half of the enhanced exudation rate. ABA‐fed plants showed only a marginal increase of solute delivery rate and in fact a somewhat reduced concentration of solutes in their exudates. In situ root hydraulic conductance, assessed by the pressure‐How method on undisturbed roots, was greatly increased by ABA or soil drying treatments. The results indicate that drought‐induced ABA in roots improved root hydraulic conductivity and raised root pressure when droughted plants were re‐watered.
Ammonium toxicity and nitrate response of axenically grown Dactylorhiza incarnata seedlings
Authors: DIJK EEUWE , ECK NELLY 
Published: April 2006

summaryThe response to ammonium‐ and nitrate‐nitrogen of seedlings of the calcicole orchid species Dactylorhiza incarnata (L.) Soó was tested in axenic in vitro culture of c. 3‐momh‐old protocorms. A pronounced toxicity of ammonium ions was observed. Seedlings raised from plants of a coastal population (f. dunensis (Druce) Soó) and those from plants of an inland population (f. incarnata) showed a different response to nitrogen form. Although ammonium toxicity was similar for seedlings of both sites, those of the coastal population showed a positive response to nitrate ions whereas those of the inland population did not. These differences could not be interpreted unequivocally as population differentiation. Ammonium toxicity was reduced in alkaline conditions. Yields increased with increasing pH and reached a maximum at pH 8.0. Calcium concentrations of 1 mM were optimal, but calcium levels did not affect the ammonium response. Seedlings did not respond to potassium concentrations in the range of 0.0–4.0 mM superimposed on a basal level of 0.4 mM. No interaction could be demonstrated between ammonium toxicity and potassium levels. Response to pH and ammonium provides a plausible mechanism for the sensitivity of the species to soil decalciftcation and decrease in seepage intensity of calcium rich groundwater in the field.
The biology of mycorrhiza in the Ericaceae
Authors: KERLEY SIMON J. , READ DAVID J. 
Published: April 2006

summaryIn acid mor‐humus soils of heathland ecosystems fungi are a significant part of the soil biomass. In these organic soils chitin and hyphal wall hexosamines are major potential sources of nitrogen (N). The ability of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan to degrade purified chitin and the hexosamines, N‐acetylglucosamine, glucosamine and galactosamine when supplied as sole sources of N, was investigated in aseptic liquid culture. The fungus grew rapidly on all the organic N sources, producing the largest dry weight increase when supplied with galactosamine and similar yields on the other nitrogenous sources. Mycelial N contents of fungus grown on the hexosamines reflected the dry weight yields with the fungus grown on galactosamine haying the highest N content. After 20 d only tract quantities of N‐acetylglucosamine and glucosamine were present in culture filtrate, and 15% of the galactosamine remained at the final harvest. Plants of Vaccinium macrocarpon Ait. and Calluna vulgaris (L.) Hull were grown aseptically in the mycorrhizal or non‐mycorrhizal condition on agar media containing chitin or a hexosamine and compared with yields and N contents in the absence of an N source. It was revealed that significant quantities of N were transferred to the host in the mycorrhizal condition that led to enhanced growth rates. The highest yields of V. macrocarpon were observed with N‐acetylglucosamine, with the other hexosamines giving yields slightly below that on chitin. The yields were reflected in the calculation of the percentage of available substrate present in the plant; up to 40% of the N‐acetylglucosamine was present in the plants after 40 d.
Cadmium toxicity in Nostoc UAM208: protection by calcium
Authors: FERNANDEZ‐PIÑAS F. , MATEO P. , BONILLA I. 
Published: April 2006

summaryThe interactive effects of cadmium (Cd) and calcium (Ca) on growth, photosynthesis (O2 evolution), nitrogenase, respiration, developmental cycle and Cd bioaccumulation by the N2 fixing cyanobacterium Nostoc UAM208 have been studied. Ca was found to exert a detoxifying role towards Cd inhibition of these physiological processes. Finally, the mechanisms by which Ca might protect the cyanobacterium against Cd toxicity are discussed.
Fungal biomass in roots and extramatrical mycelium in relation to macronutrients and plant biomass of ectomycorrhizal Pinus sylvestris and Alnus incana
Authors: EKBLAD ALF , WALLANDER HÅKAN , CARLSSON ROLF , HUSS‐DANELL KERSTIN 
Published: April 2006

summaryWe studied the effects of macronutrients on the production and distribution of fungal biomass and plant biomass in ectomycorrhizal (Paxillus involutus (Fr.) Fr.) or non‐mycorrhiza] Pinus sylvestris L, and Alnus incana (L.) Moench. Fungal biomass was measured as ergosterol content in roots and extramatrical mycelium, Alnus infants was nodulated with Frankia. All six macronutrients were varied according to a two‐level fractional factorial design, The plants were grown in pots during two growing periods in a growth chamber. Levels of N, P and sometimes K and interactions between them, had highly significant effects, whereas Ca. Mg and S had no significant effects. The production of extramatrical mycelial biomass peaked when P was low and other nutrients were high. This investment in extramatrical mycelium resulted in a 660%, higher biomass in mycorrhizal compared with non‐mycorrhizal P. sylvestris at this nutrient regime. The proportion of fungal biomass in roots was stable in P. sylvestris hut more variable in A. incana. Alnus incana grew less when mycorrhizal then when non‐mycorrhizal. The growth responses to mycorrhiza and to the different nutrient treatments were evident at the end of the first growing period. Non‐mycorrhizal P. sylvestris did not respond to P limitation by a production of proportionally more roots. This might be a reflection of an obligate dependency on mycorrhiza for effective P uptake. By contrast, the root/shoot ratio in both mycorrhizal and non‐mycorrhiza] P. sylvestris decreased strongly in response to increased N. The opposite root/shoot response was found in Alnus incana, and the ratio decreased strongly in response to increased P and increased in response to increased N.