排序方式: 共有16条查询结果,搜索用时 8 毫秒
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NICOLA TOMASI TOBIAS KRETZSCHMAR LUCA ESPEN LAURE WEISSKOPF ANJA THOE FUGLSANG MICHAEL GJEDDE PALMGREN GÜNTER NEUMANN ZENO VARANINI ROBERTO PINTON ENRICO MARTINOIA & STEFANO CESCO 《Plant, cell & environment》2009,32(5):465-475
White lupin ( Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H+ -ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H+ -ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H+ -ATPase gene, an increased amount of H+ -ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H+ -ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H+ -ATPase-catalysed proton efflux. 相似文献
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Modifications which enable simpler operation of the Cunningham-Barth-Kirk microrespirometer are described and an example of its use is quoted. Added advantages include easy positioning of indicator drop in the capillary and thermal equilibration at atmospheric pressure. 相似文献
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A simulation model incorporating structural, biochemical andphysiological features of root nodules of soyabean is described.The simulation is used to examine the effects of varying thelocation and kinetics of leghaemoglobin within infected cells.A striking feature is the capacity of the simulated nodule tomaintain its activity in the face of these changes, in spiteof relatively large changes in concentrations of free O2, andleghaemoglobin oxygenation with the cells. These propertiesarise from the diffusion resistance and intracellular demandfor O2, due to the respiratory activities of the bacteroids. Nitrogen fixation, diffusion, oxygen, model 相似文献
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The spatial, habitat and dietary overlap of two breeding goose species was studied in Sassendalen, Svalbard, in summer 2003 based on abundance within 500 × 500‐m grid squares and faecal diet analyses during pre‐breeding, nesting and post‐hatching periods. More than half of all Pink‐footed Geese Anser brachyrhynchus occurred in the absence of Barnacle Geese Branta leucopsis during nesting and post‐hatching periods compared to c. 20% when concentrated by pre‐breeding snow cover. In contrast, only 5% of Barnacle Geese were observed in the absence of Pink‐footed Geese pre‐breeding, 15% during nesting, and 35% post‐hatching. Among six defined habitat types, Barnacle Geese resorted more to ‘upland’ habitats during pre‐breeding and nesting and to lowland lakes post‐hatching when compared to Pink‐footed Geese. Although Pink‐footed Geese showed less change in seasonal habitat preference, many shifted to the river valley bottom post‐hatching, giving access to open water (predator avoidance) and lush green vegetation (foraging for goslings). The smallest extent of distributional overlap between the two species occurred post‐hatching, but each species was also highly restricted by snow cover during pre‐nesting. The greatest extent of overlap in distribution and diet occurred during incubation, when large dietary variation between different breeding valleys reflected local food availability around nests (probably a result of nest‐site preference rather than food selection per se). Whether this means that increased interactions within and between the two goose species with future increases in local density are most likely to be manifest at this stage of the summer is impossible to determine without knowledge of available food resources and manipulative experiments. More detailed investigations of the effects of foraging by both species on plant structure, quality and community composition are necessary to predict likely outcomes of future changes in population densities of both species. 相似文献
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A simulation of a normally functioning soyabean nodule, witha variable gaseous diffusion barrier in the inner cortex, hasbeen used to calculate rates of nitrogen fixation and the concentrationsof O2, CO2, H2 and N2 at various tissue locations, in responseto variations in diffusion-resistance and external O2 concentration. A small diffusion-resistance allowed increased nitrogen fixationin air, but lead to diminished rates at increased external O2concentrations. Large diffusion-resistances provide increasedprotection against the effects of high O2 concentrations butdiminish nitrogen fixation in air. These effects depend on therespiratory activity (Vmax) of the bacteroids. In general, efficiency(moles of N3 fixed/moles of O2 used) is affected more than N2fixation rates at increased external O2 concentrations. As a result of differential fluxes and solubilities of the gasesinvolved in nitrogen fixation, significant negative pressuredifferences (about 24 kPa in air) would be generated betweenthe outer cortex and the nodule central tissues, provided thatthe structure is sufficiently inflexible, and the central tissueis isolated from undue influences of water and gas. The calculations also show that the concentrations of H2 nearthe bacteroids remain low (23 per cent of concentrationsof dissolved N2) and are thus unlikely to inhibit N2 fixationexcept at high values of the diffusion resistance. Nitrogen fixation, diffusion, pressure 相似文献