bluuebunny/crossref_metadata_2025_split huggingface dataset:
The development of a CO2‐concentrating mechanism in Emiliania huxleyi
Authors: NIMER N. A. , MERRETT M. J. 
Published: April 2006

summaryThe development of an inorganic carbon concentrating mechanism (CCM) in relation to the expression of extracellular carbonic anhydrase (CAext) in cells from the stationary phase of Emiliania huxleyi cultures was investigated. Unlike exponential phase cells, those in the stationary phase showed a high affinity for CO2: the K0.5[CO2] (i.e. the CO2 concentration required for half‐maximal rate of photosynthesis) was 1.6μM at pH 8.3. Measurement of the internal inorganic carbon concentration by the silicone oil centrifugation technique showed that, with 1 mM external dissolved inorganic carbon (DIC), the intracellular inorganic carbon concentration was sixfold greater at pH 7.5 and twofold greater at pH 8.3, than the external concentration. The potent CAext inhibitor, dextran‐bound sulphonamide (DBS), gave an 80% inhibition of DIC‐dependent photosynthetic oxygen evolution. Similarly, DBS decreased the intracellular DIC concentration and inhibited photosynthetic 14CO2 fixation. The lipid‐permeable CA inhibitor, ethoxyzolamide (EZ), increased the intracellular DIC concentration but inhibited photosynthetic 14CO2 fixation. The observed intracellular DIC concentrations indicated that the stationary phase cells have the capacity to transport CO2 actively against a concentration gradient.
Response ofEriophorum vaginatumto CO2enrichment at different soil temperatures: effects on growth, root respiration and PO43−uptake kinetics
Authors: BASSIRIRAD H. , TISSUE D. T. , REYNOLDS J. F. , CHAPIN F. S. 
Published: April 2006

summaryIn a phytotron experiment, we examined responses of a tussock sedge,Eriophorum vaginatumL., to changes in atmospheric CO2, concentration and soil temperature. We were particularly interested in phosphorus (P) acquisition and below ground plant characteristics that regulated its uptake in response to CO2, enrichment. Plants were grown at two CO2, partial pressures, 35 and 70 Pa, three soil temperature regimes, 5, 15 and 25 °C and a constant ambient air temperature of 15 °C. Elevated CO2, increased total plant biomass production, but decreased tissue P concentration. Although high CO2, enhanced root carbohydrate concentration, it inhibited root respiration with no significant effect on root PO43−absorption capacity or root:shoot ratio. Surprisingly, there were no significant interactions between CO2, and soil temperature. The inability ofEriophorumto exhibit root–level compensatory adjustments, e.g. increased root: shoot ratio or PO43−absorption capacity, was largely responsible for the observed decline in tissue P concentration under elevated CO2, conditions. This could ultimately limit long–term growth responses ofEriophorumto CO2enrichment in the field where P availability is limiting. We found that uptake of PO43−in response to elevated CO2was independent of changes in root respiration, but changes in root respiration could have important implications for ecosystem carbon budget under elevated CO2levels. Our data indicated that although root respiration on a per unit biomass basis declined in response to CO2enrichment, this effect was counterbalanced by increased root biomass, so that high CO2stimulated root respiration on a whole‐plant basis by 30%. This might help to explain why long‐term exposure to high CO2increases CO2efflux fromEriophorum‐dominated ecosystems.
Distribution of phosphorus and calcium from nodal roots of Trifolium repens: the relative importance of transport via xylem or phloem
Authors: LÖTSCHER M. , HAY M. J. M. 
Published: April 2006

summaryThe intra‐plant distribution of radioactive phosphorus (32P) and calcium (45Ca) exported from a single nodal root of Trifolium repens (white clover) was measured to ascertain if initial allocation of radioisotopes via the xylem was significantly altered over time by redistribution via the phloem. The radioisotopes were simultaneously supplied in a 2 h pulse which was followed by supply of non‐radioactive nutrient solution until harvest 3, 6, 9, 21 or 72 h after the start of labelling. By the end of the 3 d experimental period net export from the source root was 94 % total absorbed 45Ca but only 56 % of 32P. After movement through the stolon of the parent axis, main sinks for both nutrients were the leaf and the branch at the second node distal to the source root (64 and 30 % of total absorbed 45Ca and 32P respectively after 72 h). Very little of either radioisotope moved into branches located along the stolon of the parent axis, on the side opposite to the source root (1 and 2% of total absorbed 45Ca and 32P respectively after 72 h). This evidence, along with knowledge of the vascular architecture of the genotype, indicated that the allocation of mineral nutrients was determined chiefly by the vascular links between the source root and sink organs rather than sink size or proximity to the source root. Data indicated that some distribution of 32P occurred via the phloem but that it was quantitatively small in relation to allocation via the xylem both in the short (3 h) and medium (72 h) terms.
Effect of arbuscular mycorrhizas on uptake of nitrogen byBrachiaria arrectaandSorghum vulgarefrom soils labelled for several years with15N
Authors: IBIJBIJEN J. , URQUIAGA S. , ISMAILI M. , ALVES B. J. R. , BODDEY R. M. 
Published: April 2006

summaryA pot experiment was conducted under glasshouse conditions to investigate the effect of the inoculation of arbuscular mycorrhizal (AM) fungi on the growth and N uptake of two graminaceous plants:Brachiaria arrecta(Hack. ex. Th. Dur & Schinz) Stent andSorghum vulgare(Pers.) growing in four fumigated soils which had been labelled for several years with15N. The four soils had different chemical characteristics, especially in their P availability. The levels of root colonization by AM fungi were inversely related to the P concentration in these soils. Positive responses to AM fungal inoculation were observed for all the yield parameters except in the soil with the highest P availability (40 μg P g−1soil, extractant Mehlich‐1). In the other three soils, AM fungal inoculation of both crops increased N accumulation by between 17 and 46%, but the15N enrichment of the N absorbed was significantly lower in the mycorrhizal plants than in those not colonized by mycorrhizal fungi. This suggests that some of the N absorbed from the soil by the mycorrhizal roots was derived from N sources other than the mineral N.
Effects of NO (+ NO2) pollution on growth, nitrate reductase activities and associated protein contents in glasshouse lettuce grown hydroponically in winter with CO2 enrichment
Authors: HUFTON CAROLINE A. , BESFORD ROBERT T. , WELLBURN ALAN R. 
Published: April 2006

summaryWinter hydroponic growth of several lettuce cultivars under glass showed considerable inhibition (up to 47%) of growth after 6 wk exposure to concentrations of NO (+ NO2 450 nl −1 in total) typical of emissions from propane burners used for direct heating and CO2 enrichment. After a further 4 wk under similar conditions, however, these growth depressions were replaced by a swing into benefit so that, by harvest, pollutant‐exposed lettuces were bigger and had faster assimilation rates than those growing in clean CO2‐enriched air. This adaptation may partly be explained by enhanced use of NO2‐derived N by lettuce leaves, a consequence of increased nitrate reductase (NaR) activities and amounts of associated NaR proteins, despite adequate nitrate also being available in the hydroponic fluid. Rates of NaR activity in the roots, by contrast, were depressed by NO (+ NO2) pollution. NaR activities were highest in early afternoon in clean or polluted air but these daily patterns did not coincide with the content of NaR‐associated proteins determined by ELISA. Other mechanisms of modulating NaR activity must therefore be responsible.
Ultrastructure and supramolecular organization of photosynthetic membranes of some marine red algae
Authors: TSEKOS I. , REISS H.‐D. , ORFANIDIS S. , OROLOGAS N. 
Published: April 2006

summaryThe ultrastructure and supramolecular organization of photosynthetic membranes in four species of marine red algae (Porphyra yezoensis, Porphyra leucosticta, Erythrocladia subintegra, Pterothamnion crispum) were studied both in replicas of rapidly frozen cells and in ultrathin sections. Because the thylakoids in red algal chloroplasts are not stacked, freeze‐fractured thylakoid membranes exhibit only two types of fracture faces (EF and PF). In all four species the PF reveals numerous, tightly packed, but randomly distributed particles (density range from 3530 to 4970 particles μm−2 for Porphyra yezoensis). The particle size distribution is uniform in the two types of fracture faces with an average diameter of about 11.3–11.6 nm in all four algae.The phycobilisomes of Porphyra yezoensis and Erythrocladia subintegra have the approximate shape of a compressed rotation ellipsoid with the following dimensions; Porphyra yezoensis, length 52.8±1.2 nm, thickness 24.4±0.6 run, height 34.6±1 nm; Erythrocladia subintegra, length 45.1±0.7 nm, thickness 23.1±0.5 nm, height 29.4±0.9 nm. In Porphyra yezoensis, Porphyra leucosticta and Erythrocladia subintegra both the phycobilisomes and EF particles are organized into rows with a spacing of 70–80 nm in Porphyra yezoensis, 65–75 nm in Porphyra leucosticta and 53.8–55 nm in Erythrocladia subintegra. EF particle complexes with four subunits were found in Porphyra yezoensis. In Pterothamnion crispum the shape of the phycobilisomes is hemiellipsoidal. The phycobilisomes seem to be organized into rows; their centre to centre periodicity is c. 60 nm. Porphyra yezoensis cells possess about 770±58 phycobilisomes μm−2 of thylakoid surface, whereas the number of EF particles is about 1270±203 μm−2 Thus, the ratio of phycobilisomes to EF particles is c. 0.6. In Erythrocladia subintegra the ratio of phycobilisomes to EF particles is about 0.7.Of special interest is the ocurrence of a crystalline matrix in pyrenoids of Porphyra leucosticta and the absence of phycobilisomes in the intrapyrenoid thylakoids of Porphyra yezoensis and Erythrocladia subintegra.
Cell ultrastructural evidence of accelerated ageing of Norway spruce needles in industrial areas
Authors: WULFF A. , AHONEN J. , KÄRENLAMPI L. 
Published: April 2006

summaryNeedle mesophyll cell ultrastructure of 1st to 9th yr needles from Norway spruce (Picea abies (L.) Karst.) trees of different ages was studied at three different sites to determine the normal features of needle ageing, and the impact of air pollution on the needle ageing process. The sites included one rural area and two industrial environments, of which one contained SO2 emissions and the other SO2 and F emissions. The ultrastuctural features of needle mesophyll cells of different ages were found to be remarkably similar when young (20‐yr‐old) and mature (> 50‐yr‐old) trees were compared. Senescence‐related ultrastructural symptoms such as increase in the number and size of plastoglobuli and an increase in the large lipid accumulations were observed with increasing needle age. In addition, the occurrence of lipid bodies in the central vacuole and an increased number of dark grains in the cell wall were detected in ageing needles. No changes in chloroplast length were observed during the ageing of needles, although the width of the chloroplasts showed a tendency to increase. A poor differentiation of granal membranes and an increase in small cytoplasmic lipid bodies and irregularly‐shaped lipid material were symptoms typical of needles in the industrial areas. The ageing symptoms appeared in younger needles and were more evident in industrial areas than at the control site, suggesting an accelerated ageing process in the industrial areas.
The effect of elevated CO2 and grazing by Gastrophysa viridula on the physiology and regrowth of Rumex obtusifolius
Authors: PEARSON MARK , BROOKS GEORGINA L. 
Published: April 2006

summaryPlants of Rumex obtusifolius L. were grown in Solardomes under ambient and elevated (+ 250 μmol mol−1) mole fractions of CO2 and were exposed to two levels of herbivory by Gastrophysa viridula Degeer larvae. The herbivory treatment lasted 1 month, thereafter half of the plants were harvested and over the following month during a period of regrowth physiological measurements were made on the remaining plants. At the termination of the herbivory treatment uninfested plants showed no damage, whereas the low and high herbivore treatments caused 20–40% and 50–70% loss of leaf area as a proportion of total leaf area, respectively. The CO2 treatment did not affect the degree of defoliation. Total leaf area was not significantly affected by either CO2 or herbivory. Uninfested plants grown in elevated concentrations of CO2 showed increased growth, root‐to‐shoot ratios (RS), rates of photosynthesis and reduced stomatal conductance compared with uninfested plants grown in ambient CO2. A/C1 analysis revealed that plants grown in elevated CO2 showed reductions in Vcmax. For plants grown in ambient CO2 the high herbivory treatment led to increased rates of photosynthesis and decreased rates of dark respiration per unit leaf area, and caused increases in stomatal conductance and RS. For plants grown in elevated CO2 the high herbivory treatment increased plant biomass and RS. The increases in RS in response to elevated CO2 and herbivory appeared to be additive. Defoliation did not reduce the degree of photosynthetic down‐regulation caused by growth in elevated concentrations of CO2, but appeared to reduce the rate of ontogenic decline in photosynthesis in ambient CO2.
Interactions between the parasitic angiosperm Orobanche aegyptiaca and its tomato host: growth and biomass allocation
Authors: BARKER E. R. , PRESS M. C. , SCHOLES J. D. , QUICK W. P. 
Published: April 2006

summaryThe influence of the parasitic angiosperm Orobanche aegyptiaca on the growth and shoot/root allometry of tomato plants was studied in two experiments. In the first, the density of infection was manipulated, with host and parasite biomass being measured 56 d after planting (d.a.p.). In the second, multiple harvests were made from 14 to 91 d.a.p. at one level of infection (20 mg seed dm−3). The first experiment demonstrated an approximately linear reduction in host biomass up to 10 mg seed dm−3 soil, beyond which there was no further reduction. The parasite also depressed shoot/root ratio, which changed prior to any decrease in total biomass. These trends were maintained in the second experiment, becoming more pronounced with time. Significant reductions were observed in host biomass compared with that of uninfected controls from 42 d.a.p., following the emergence of the parasite above ground, and corresponded with the onset of lower relative growth rates (RGRs) in the infected plants. Infection also influenced components of RGR: there was a stimulation of leaf area ratio (LAR) and a depression of unit leaf rate (ULR). The data are discussed with respect to the influence of other parasitic weeds on host growth.
Carbohydrate metabolism in source leaves of barley grown in 700 μmol mol−1 CO2and infected with powdery mildew
Authors: HIBBERD J. M. , WHITBREAD R. , FARRAR J. F. 
Published: April 2006

summarySoluble carbohydrate accumulated faster in second leaf blades of barley when plants were grown in 700 μmol mol−1 CO2 rather than 350 μmol mol−1 CO2. Infection of the second leaf blade by powdery mildew had no effect on the concentration of soluble carbohydrate until 6 d after inoculation when it was lower than in controls. The accumulation of soluble carbohydrate in the second leaf of uninfected plants grown in 700 μmol mol−1 CO2 was due largely to earlier and faster accumulation of fructan. TLC showed that the series of fructan was not different in plants grown in 700 μmol μmol−1 CO2 relative to plants grown in 350 μmol mol−1 CO2, neither did infection by powdery mildew affect the series of fructan present in the second leaf blade. The rate constant for phloem loading obtained by compartmental analysis of 14C efflux from the leaf blade was not reduced in plants grown in 700 μmol mol−1 CO2, indicating that carbohydrate accumulation was not caused by reduced ability of the leaf to export carbon.
Effects of mycorrhizal colonization byPaxillus involutuson uptake of Ca and P byPicea abiesandBetula pendulagrown in unlimed and limed peat
Authors: ANDERSSON SOLBRITT , JENSÉN PAUL , SÖDERSTRÖM BENGT 
Published: April 2006

summaryUptake of P(32P) and Ca(45Ca) by seedlings ofPicea abies(L.) Karst andBetula pendulaRoth, non‐mycorrhizal or mycorrhizal withPaxillus involutus(Batsch: Fr) Fr. was studied. Seedlings were grown in unamended peat (pH 4.0) or in peat limed (CaO) to pH 5.1 or 6.1. A double‐labelled (32P and45Ca) complete nutrient solution was added to the peat 7 wk after planting. An 8 d period was allowed for uptake of the isotopes before the seedlings were harvested.Mycorrhizal colonization clearly increased the uptake of P(32P) in the unlimed substrate and in the substrate limed to a pH of 5.1. At the highest lime rate, the uptake of P(32P) was greatly reduced in both mycorrhizal and non‐mycorrhizal seedlings. The difference in P uptake between mycorrhizal and non‐mycorrhizal seedlings was small at this lime rate. The mycorrhizal colonization of the roots was not affected by liming. How‐ever, it is possible that the mycelial growth into the substrate was inhibited. The reduction in uptake could thus be an effect of a lower availability of P in combination with a decreased fungal uptake surface at the highest lime rate.The mycorrhizal effect on uptake of Ca was much smaller than its effect on uptake of P. Mycorrhizal colonization increased the Ca(45Ca) uptake in the unlimed treatment, where the Ca content in the substrate was very small. In the limed substrates the uptake of Ca was as high or higher in the non‐mycorrhizal than in the mycorrhizal seedlings.
Nitrogen metabolism of external hyphae of the arbuscular mycorrhizal fungus Glornus intraradices
Authors: JOHANSEN ANDERS , FINLAY ROGER D. , OLSSON PÅL AXEL 
Published: April 2006

summaryThe arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith was grown in symbiosis with Cucumis sativus L. ev. Aminex (Fl hybrid) in mesh bags surrounded by a sand‐filled hyphal compartment (HC), allowing only the fungal hyphae to protrude into the HC. The hyphae in the HC were supplied with 15N‐labelled NH4+ or NO3− after 60 d (expt 1). Following a 48 h labelling period, the sand was removed from the HC and the hyphae extracted. In another experiment (expt 2), the hyphae were extracted from the sand before being incubated in vitro in a nutrient solution containing 15N‐labelled NH4+ for 15 h. The hyphal material was incubated in a 0 or 2.5 mM solution of the GOGAT‐inhibitor albizzine prior to labelling. In both experiments the hyphal content of free amino acids and fatty acids were measured as well as the ammo acid l5N enrichment.Asparagine was the hyphal amino acid measured in highest concentration followed by glutamine, glutamate, aspartate and alanine. Ornithine, serine and glycine were detected in lower concentrations, but γ‐aminobutyric acid and citrulline were not detectable. This pattern was the same in both experiments and was unaffected by the type of N applied to the hyphae or by preincubation with albizzine, although the amino‐acid concentration decreased considerably in expt 2 compared with expt 1. Both NH4+‐N and NO3−‐N were assimilated into amino acids but the levels of l0N enrichment following application of NO3− were much lower than those following application of NH4+ indicating that the latter was more readily assimilated. Albizzine decreased the hyphal amino acid concentration by c. 30% (without affecting the 15N enrichment of the individual amino acids) indicating that the AM‐fungal hyphae might possess a GS‐GOGAT enzyme system for assimilation of inorganic N. The fatty‐acid profiles (especially phospholipid fatty acids 16: 1ω5 and 20:5) obtained from the hyphae of G. intraradices showed that contamination of the samples by fungi other than G. intraradices and bacteria was insignificant, and confirmed the usefulness of specific fatty‐acid measurement to estimate soil AM‐fungal content.
Physiological responses of Festuca arundinacea to fungal endophyte infection
Authors: MARKS SUSAN , CLAY KEITH 
Published: April 2006

summaryEnhanced growth rates of several grass species infected by fungal endophytes are known, but the underlying changes in plant physiology are not. Carbon exchange rates (CER) and leaf conductances (g) of 13 genotypes of tall fescue (Festuca arundinacea Schreb. var. KY 31) infected by the fungal endophyte Acremomum coenophialum Morgan‐Jones and Gams were measured at ambient conditions. Endophyte‐free ramets of the same genotypes were also measured. Correlations were calculated between environmental conditions at the time of measurement, and physiological responses. The only differential response of infected and uninfected ramets was to temperature. At low leaf temperatures no difference was seen between infected and uninfected plants. However, at leaf temperatures above 35°C infected tall fescue plants photosynthesized at a significantly greater rate (20–25%) than uninfected plants. This resulted from a decrease in the CER of uninfected plants, not an increase in the rate of infected plants, at high temperature. There were also significant infection × genotype interactions, indicating that the response to infection was specific to a given genotype. These results indicate that physiological responses of host plants to fungal endophyte infection depend both on the physical environment and the genotype of the plants.
Reduction of risk for growers: methods for the development of disease‐resistant crops
Authors: UKNES SCOTT , VERNOOIJ BERNARD , MORRIS SHERICCA , CHANDLER DANIELLE , STEINER HENRY‐YORK , SPECKER NICOLE , HUNT MICHELLE , NEUENSCHWANDER URS , LAWTON KAY , STARRETT MARK , FRIEDRICH LESLIE , WEYMANN KRIS , NEGROTTO DAVID , GÖRLACH JÖRN , LANAHAN MIKE , SALMERON JOHN , WARD ERIC , KESSMANN HELMUT , RYALS JOHN 
Published: April 2006

SummarySystemic acquired resistance (SAR) appears to be a ubiquitous higher plant defence response. Resistance is dependent on the high‐level expression of SAR genes. Mutations, transgenes or chemicals that cause high‐level SAR gene expression also cause resistance to pathogens. Furthermore, when SAR is eliminated, through the reduction of salicylic acid accumulation or activity, generalized severe disease‐susceptibility occurs. Therefore, SAR appears to be an essential component of the defensive repertoire that ensures plant health in nature. Chemicals that activate SAR in the field, as well as crop varieties with constitutive SAR gene expression, will provide new solutions to disease problems for growers in the near future.