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  • root exudates  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Mobilization of iron and other micronutrient cations from a calcareous soil by plant-borne, microbial, and synthetic metal chelators (1989)
    Springer
    Plant and soil 114 (1989), S. 217-226 
    Details
    ISSN: 1573-5036
    Keywords: barley ; chelators ; copper ; iron ; manganese ; mobilization ; phytosiderophores ; root exudates ; siderophores ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Mobilization of Fe, Zn, Cu, and Mn by various chelators from a calcareous soil was measured using a simple dialysis tube/complexing resin system. Root exudates from Fe-deficient barley increased the concentrations of all four metals in solution by, on average, a factor of 20, and the addition of complexing resin as a sink for heavy metal cations forced steady state solution concentrations to be reached sooner. Root exudates mobilized increasing amounts of the various micronutrients in the following order: Cu〈Fe〈Zn〈Mn. Phytosiderophores isolated from root exudates of Fe-deficient barley mobilized similar amounts of Cu and Zn but somewhat more Fe and considerably more Mn than crude exudate. The synthetic chelators EDDHA and DTPA showed low specificity in micronutrient mobilization, but the microbial siderophore Desferal was relatively more specific, preferentially mobilizing Fe and Mn. The data indicates that phytosiderophores are capable of increasing the amount of complexed cations in solution. Despite their lack of specificity, phytosiderophores were just as effective as Desferal increasing the availability of Fe. Thus, phytosiderophores, as plant-borne chelators, are certainly of significance for the Fe nutrition of cereals grown in calcareous soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02220801
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of root exudates on mobilization in the rhizosphere and uptake of iron by wheat plants (1994)
    Springer
    Plant and soil 165 (1994), S. 213-218 
    Details
    ISSN: 1573-5036
    Keywords: calcareous soil ; iron ; iron mobilization ; phytosiderophores ; rhizosphere ; root exudates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To examine the effect of root exudates (e.g. phytosiderophores) on iron (Fe) mobilization in the rhizosphere and Fe uptake, wheat seedlings (Triticum aestivum L. cv. Ares) were precultured for 17 d in nylon bags filled with fine sand and provided with nutrient solution without or with Fe (0.1 mM FeEDTA). After the preculture the nylon bags with the roots of the seedlings (central root compartment, RC) were brought in contact for 4 d with nylon bags filled with calcareous soil (SC). In different distance from the RC (0, 2, 4 mm) the calcareous soil on each side of the RC had been amended with Fe rich sewage sludge resulting in an increase in DTPA-extractable Fe from 1.45 to 4.22 mg Fe kg−1 dry soil. Through the influence of roots in the RC extractable Fe increased in the SC between 2 and 133%. For the untreated soil this relative increase declined with the distance of 0, 2, and 4 mm from the RC from 86, 50, and 41% with Fe adequate plants and from 133, 86, and 35% with Fe deficient plants, respectively. The corresponding values for the sewage sludge treated soil was 13, 2, and 3% with Fe adequate plants and 24, 20, and 1% with Fe deficient plants, respectively. In accordance with the increased Fe solubility in the various SC Fe uptake and growth of wheat were also enhanced during the 4 d treatment. It can be concluded that the higher solubilization and uptake of Fe by the root of the Fe deficient (chlorotic) compared with the Fe sufficient (green) plants is mainly caused by enhanced release of phytosiderophores under Fe deficiency. The increased mobilization of Fe over a distance of up to 4 mm from the RC demonstrates the high capacity of root exudates (e.g. phytosiderophores) for Fe mobilization in the rhizosphere even under non-axenic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008064
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  • 3
    Electronic Resource
    Electronic Resource
    Strategies of plants for acquisition of iron (1994)
    Springer
    Plant and soil 165 (1994), S. 261-274 
    Details
    ISSN: 1573-5036
    Keywords: iron ; phytosiderophores ; root apoplasm ; root exudates ; siderophores ; standard reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two different types of root response to Fe deficiency (strategies) have been identified in species of the Plant Kingdom. In Strategy I which occurs in all plant species except grasses, a plasma membrane-bound reductase is induced with enhanced net excretion of protons. Often the release of reductants/chelators is also higher. In Strategy II which is confined to grasses, there is an increase in the biosynthesis and secretion of phytosiderophores which form chelates with FeIII. Uptake of FeIII phytosiderophores is mediated by a specific transporter in the plasma membrane of root cells of grasses. From results based mainly on long-term studies under non-axenic conditions this classification into two strategies has been questioned, and the utilization of Fe from microbial siderophores has been considered as an alternative strategy particularly in grasses. Possible reasons for controversial results are discussed in some detail. The numerous effects of microorganisms in non-axenic cultures, and the as yet inadequate characterization of the so-called standard (basic) reductase present major limitations to understanding different mechanisms of Fe acquisition. In comparison with the progress made in identifying the cellular mechanisms of root responses in Strategy I and Strategy II plants, our understanding is poor concerning the processes taking place in the apoplasm of root rhizodermal cells and of the role of low-molecular-weight root exudates and siderophores in Fe acquisition of plants growing in soils of differing Fe availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008069
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  • 4
    Electronic Resource
    Electronic Resource
    Genotypical differences among graminaceous species in release of phytosiderophores and uptake of iron phytosiderophores (1990)
    Springer
    Plant and soil 123 (1990), S. 147-153 
    Details
    ISSN: 1573-5036
    Keywords: barley ; chlorosis resistance ; cucumber ; genotypical differences ; grasses ; iron mobilization ; iron uptake ; maize ; microorganisms ; oat ; phytosiderophores ; rice ; root exudates ; root growth ; rye ; sorghum ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Graminaceous species can enhance iron (Fe) acquisition from sparingly soluble inorganic Fe(III) compounds by release of phytosiderophores (PS) which mobilize Fe(III) by chelation. In most graminaceous species Fe deficiency increases the rate of PS release from roots by a factor of 10–20, but in some species, for example sorghum, this increase is much less. The chemical nature of PS can differ between species and even cultivars. The various PS are similarly effective as the microbial siderophore Desferal (ferrioxamine B methane sulfonate) in mobilizing Fe(III) from a calcareous soil. Under the same conditions the synthetic chelator DTPA (diaethylenetriamine pentaacetic acid) is ineffective. The rate of Fe(III)PS uptake by roots of graminaceous species increases by a factor of about 5 under Fe deficiency. In contrast, uptake of Fe from both synthetic and microbial Fe(III) chelates is much lower and not affected by the Fe nutritional status of the plants. This indicates that in graminaceous species under Fe deficiency a specific uptake system for FePS is activated. In contrast, the specific uptake system for FePS is absent in dicots. In a given graminaceous species the uptake rates of the various FePS are similar, but vary between species by a factor of upto 3. In sorghum, despite the low rate of PS release, the rate of FePS uptake is particularly high. The results indicate that release of PS and subsequent uptake of FePS are under different genetic control. The high susceptibility of sorghum to Fe deficiency (‘lime-chlorosis’) is most probably caused by low rates of PS release in the early seedling stage. Therefore in sorghum, and presumably other graminaceous species also, an increase in resistance to ‘lime chlorosis’ could be best achieved by breeding for cultivars with high rates of PS release. In corresponding screening procedures attention should be paid to the effects of iron nutritional status and daytime on PS release as well as on rapid microbial degradation of PS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011260
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    Paper (German National Licenses)
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