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  • 1
    ISSN: 1573-5036
    Keywords: chelate ; iron ; maize ; nutrition ; oat ; phytosiderophores ; siderophores ; trace metal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Collaborative experiments were conducted to determine whether microbial populations associated with plant roots may artifactually affect the rates of Fe uptake and translocation from microbial siderophores and phytosiderophores. Results showed nonaxenic maize to have 2 to 34-fold higher Fe-uptake rates than axenically grown plants when supplied with 1 μM Fe as either the microbial siderophore, ferrioxamine B (FOB), or the barley phytosiderophore, epi-hydroxymugineic acid (HMA). In experiments with nonsterile plants, inoculation of maize or oat seedlings with soil microorganisms and amendment of the hydroponic nutrient solutions with sucrose resulted in an 8-fold increase in FOB-mediated Fe-uptake rates by Fe-stressed maize and a 150-fold increase in FOB iron uptake rates by Fe-stressed oat, but had no effect on iron uptake by Fe-sufficient plants. Conversely, Fe-stressed maize and oat plants supplied with HMA showed decreased uptake and translocation in response to microbial inoculation and sucrose amendment. The ability of root-associated microorganisms to affect Fe-uptake rates from siderophores and phytosiderophores, even in short-term uptake experiments, indicates that microorganisms can be an unpredictable confounding factor in experiments examining mechanisms for utilization of microbial siderophores or phytosiderophores under nonsterile conditions.
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  • 2
    ISSN: 1573-5036
    Keywords: iron efficiency ; pH change ; reducing capacity ; release of reductants ; strategy I ; Zea mays L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The iron (Fe) efficient maize cultivar WF9 and the Fe inefficient maize mutant ys1 were grown in nutrient solutions with varied Fe supply. Changes in pH, reducing capacity of the roots and the release of Fe(III) reducing compounds were monitored over a period of 11 days. In both cultivars under Fe deficiency, there was no increased release of protons or reducing compounds and no increased reducing capacity of the roots. Indeed, the Fe(III) reduction of the roots of both cultivars tended to be higher in Fe sufficient plants. In contrast to some recent reports, these results demonstrate that the Fe efficient maize cultivar WF9 does not respond to Fe deficiency by strategy I mechanisms. This suggests that differences in Fe efficiency between the two cultivars are probably due to use of strategy II mechanisms for Fe acquisition.
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  • 3
    ISSN: 1573-5036
    Keywords: iron distribution in shoot organs ; iron uptake, Phaseolus vulgaris L., retranslocation of iron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A study has been made on the effect of primary leaves on iron (Fe) distribution in the shoot. Bean (Phaseolus vulgaris L.) seedlings were precultured in nutrient solution with 8×10-5 M FeEDTA for 4 days, and then grown further with either 8×10-5 M FeEDTA (+Fe) or without Fe supply (-Fe) for another 5 days. Thereafter, both +Fe and -Fe plants were treated in three different ways: undisturbed; one primary leaf removed; or one primary leaf shaded, starting two hours before supply 59FeEDTA to the roots. The +Fe plants were supplied with 8×10-5 M 59FeEDTA, and the -Fe plants with only 1×10-6 M 59FeEDTA. After 1 to 8 hour uptake periods, plants were harvested and 59Fe in different organs was determined. Removal or shading of one primary leaf did not affect 59Fe uptake by roots and 59Fe translocation to the shoot in +Fe plants. In the -Fe plants, however, removal of one primary leaf decreased 59Fe uptake by roots, whereas shading of one primary leaf had no effect on 59Fe uptake but slightly enhanced 59Fe translocation from roots to the shoot. The quantity of 59Fe in primary leaves was positively correlated with quantity of 59Fe in the stem in the -Fepplants, but not in the +Fe plants. In both, the +Fe and -Fe plants, the quantity of 59Fe in the shoot apex was positively correlated with 59Fe in primary leaves. The results suggest that irrespective of the Fe nutritional status of plants, the source of Fe for the shoot apex is Fe retranslocated from primary leaves.
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  • 4
    ISSN: 1573-5036
    Keywords: Apoplast ; apoplastic root iron ; iron efficiency ; storage pool
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The concentration of apoplastic Fe in roots of soil-grown plants was determined in order to evaluate the possible significance of the root apoplast as storage pool for Fe. Roots were grown in membrane bags maintaining contact with the soil solution but without direct contact with the soil. It could be shown that the concentration of apoplastic Fe in roots grown in most soils was lower than 50 mg kg-1 root dry matter. This concentration is much lower than previously reported from nutrient solution and soil-grown cultures (about 1000 mg kg-1 dry matter). The concentration of apoplastic Fe in strategy I and strategy II plants was little affected by the different soils used. Direct contact of roots with soil led to soil contamination at the root surface and so to an overestimation of the apoplastic Fe pool. Soil contamination of roots grown in direct contact with soil was detected by measuring the soil markers Ti, Si and Al and was further shown by PIXE. In conclusion, the low concentration of apoplastic Fe in roots demonstrates that the root apoplast is less significant as storage pool for Fe than previously assumed.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 193 (1997), S. 71-83 
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The essentiality of B for growth and development of plants is well-known, but the primary functions of B still remain unknown. Evidence in the literature supports the idea that the major functions of B in growth and development of plants are based on its ability to form complexes with the compounds having cis-diol configurations. In this regard, the formation of B complexes with the constituents of cell walls and plasma membranes as well as with the phenolic compounds seems to be a decisive step affecting the physiological functions of B. Boron seems to be of crucial importance for the maintenance of structural integrity of plasma membranes. This function of B is mainly related to stabilisation of cell membranes by B association with membrane constituents. Possibly, B may also protect plasma membranes against peroxidative damage by toxic O2 species. In B-deficient plants, plasma membranes are highly leaky and lose their functional integrity. Under B-deficient conditions, substantial changes in ion fluxes and proton pumping activity of the plasma membranes were noted. Impairments in phenol metabolism and increases in levels of phenolics and polyphenoloxidase activity are typical indications of B deficiency, particularly in B deficiency-sensitive plant species, such as Helianthus annuus (sunflower). Enhanced oxidation of phenols is responsible for generation of reactive quinones which subsequently produce extremely toxic O2 species, thus resulting in the increased risk of a peroxidative damage to vital cell components such as membrane lipids and proteins. In B-deficient tissues, enhancement in levels of toxic O2 species may also occur as a result of impairments in photosynthesis and antioxidative defence systems. Recent evidence shows that the levels of ascorbic acid, non-protein SH-compounds (mainly glutathione) and glutathione reductase, the major defence systems of cells against toxic O2 species, are reduced in response to B deficiency. There is also increasing evidence that, in the heterocyst cells of cyanobacteria, B is involved in protection of nitrogenase activity against O2 damage.
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  • 6
    ISSN: 1572-8773
    Keywords: iron ; siderophores ; coprogen ; plant nutrition ; Penicillium chrysogenum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Cucumber, as a strategy I plant, and Maize as a strategy II plant, were cultivated in hydroponic culture in the presence of a ferrated siderophore mixture (1 μM) from a culture of Penicillium chrysogenumisolated from soil. The siderophore mixture significantly improved the iron status of these plants as measured by chlorophyll concentration to the same degree as a 100-fold higher FeEDTA supply. Analysis of the siderophore mixture from P. chrysogenum by HPLC and electrospray mass spectrometry revealed that besides the trihydroxamates, coprogen and ferricrocin, large amounts of dimerum acid and fusarinines were present which represent precursor siderophores or breakdown products of coprogen. In order to prove the iron donor properties of dimerum acid and fusarinines for plants, purified coprogen was hydrolyzed with ammonia and the hydrolysis products consisting of dimerum acid and fusarinine were used for iron uptake by cucumber and maize. In short term experiments radioactive iron uptake and translocation rates were determined using ferrioxamine B, coprogen and hydrolysis products of coprogen. While the trihydroxamates revealed negligible or intermediate iron uptake rates by both plant species, the fungal siderophore mixture and the ammoniacal hydrolysis products of coprogen showed high iron uptake, suggesting that dimerum acid and fusarinines are very efficient iron sources for plants. Iron reduction assays using cucumber roots or ascorbic acid also showed that iron bound to hydrolysis products of coprogen was more easily reduced compared to iron bound to trihydroxamates. Ligand exchange studies with epi-hydroxymugineic acid and EDTA showed that iron was easily exchanged between coprogen hydrolysis products and phytosiderophores or EDTA. The results indicate that coprogen hydrolysis products are an excellent source for Fe nutrition of plants.
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  • 7
    ISSN: 1432-2048
    Keywords: Key words: Acid phosphatase ; Lupinus ; Organic acids ; Phosphorus (deficiency ; uptake) ; Root exudates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Release of large amounts of citric acid from specialized root clusters (proteoid roots) of phosphorus (P)-deficient white lupin (Lupinus albus L.) is an efficient strategy for chemical mobilization of sparingly available P sources in the rhizosphere. The present study demonstrates that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly restricted to mature root clusters in the later stages of P deficiency. Inhibition of citrate exudation by exogenous application of anion-channel blockers such as ethacrynic- and anthracene-9-carboxylic acids may indicate involvement of an anion channel. Phosphorus-deficiency-induced accumulation and subsequent exudation of citric acid seem to be a consequence of both increased biosynthesis and reduced metabolization of citric acid in the proteoid root tissue, indicated by increased in-vitro activity and enzyme protein levels of phosphoenolpyruvate carboxylase (EC 4.1.1.31), and reduced activity of aconitase (EC 4.2.1.3) and root respiration. Similar to citric acid, acid phosphatase, which is secreted by roots and involved in the mobilization of the organic soil P fraction, was released predominantly from proteoid roots of P-deficient plants. Also 33Pi uptake per unit root fresh-weight was increased by approximately 50% in juvenile and mature proteoid root clusters compared to apical segments of non-proteoid roots. Kinetic studies revealed a K m of 30.7 μM for Pi uptake of non-proteoid root apices in P-sufficient plants, versus K m values of 8.5–8.6 μM for non-proteoid and juvenile proteoid roots under P-deficient conditions, suggesting the induction of a high-affinity Pi-uptake system. Obviously, P-deficiency-induced adaptations of white lupin, involved in P acquisition and mobilization of sparingly available P sources, are predominantly confined to proteoid roots, and moreover to distinct stages during proteoid root development.
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  • 8
    ISSN: 1432-1890
    Keywords: Key words Arbuscular mycorrhiza ; Iron ; Peanut ; Phosphorus ; Sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The influence of an arbuscular mycorrhizal (AM) fungus on phosphorus (P) and iron (Fe) uptake of peanut (Arachis hypogea L.) and sorghum (Sorghum bicolor L.) plants was studied in a pot experiment under controlled environmental conditions. The plants were grown for 10 weeks in pots containing sterilised calcareous soil with two levels of Fe supply. The soil was inoculated with rhizosphere microorganisms only or with rhizosphere microorganisms together with an AM fungus (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe). An additional small soil compartment accessible to hyphae but not roots was added to each pot after 6 weeks of plant growth. Radiolabelled P and Fe were supplied to the hyphae compartment 2 weeks after addition of this compartment. After a further 2 weeks, plants were harvested and shoots were analysed for radiolabelled elements. In both plant species, P uptake from the labelled soil increased significantly more in shoots of mycorrhizal plants than non-mycorrhizal plants, thus confirming the well-known activity of the fungus in P uptake. Mycorrhizal inoculation had no significant influence on the concentration of labelled Fe in shoots of peanut plants. In contrast, 59Fe increased in shoots of mycorrhizal sorghum plants. The uptake of Fe from labelled soil by sorghum was particularly high under conditions producing a low Fe nutritional status of the plants. These results are preliminary evidence that hyphae of an arbuscular mycorrhizal fungus can mobilise and/or take up Fe from soil and translocate it to the plant.
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  • 9
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The influence of soluble phenol concentration and polyphenoloxidase activity in leaves of both B-deficient and B-sufficient sunflower plants (Helianthus annuus L. cv. Frankasol) on plasma membrane permeability was investigated, A study was also undertaken as to whether or not the incubation of B-deficient leaves in ascorbate- and calcium-containing solutions has a beneficial effect on plasma membrane integrity. Plants were cultivated under controlled environmental conditions with deficient and sufficient B supply and different light intensity to provoke changes in phenol metabolism. Analysis of membrane permeability (measured by potassium efflux), soluble phenol concentration and polyphenoloxidase (EC 1.10.3.1) activity of leaves showed that there was no correlation between these parameters. Furthermore, incubation in solutions containing ascorbate and calcium did not decrease the enhanced membrane permeability due to B deficiency, which could, however, be lowered by boric acid application. In summary, the results suggest that B does not maintain plasma membrane integrity by complexing phenols or inhibiting polyphenoloxidase activity, thereby preventing damage by oxygen free radicals. Ascorbate metabolism or calcium-related disorders seem also not to be involved. It is therefore likely that B has a direct function at the membrane, possibly by stimulating membrane-related enzymes, or in a structural role similar to that reported for the cell wall.
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  • 10
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Iron inefficiency in the maize (Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of 59Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar Km (∼ 10 μM) in both genotypes. In contrast. Vmax was 5.5 μmol Fe-DMA g−1 dry weight [30 min]−1 in Alice, but only 0.6 μmol Fe-DMA g−1 dry weight [30 min]−1 in ysl. Uptake experiments with double-labeled 59Fe-[14C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.
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