Behaviour of iron chelates in calcareous soils

Summary A highly calcareous clay soil was treated with six iron chelates, those formed by RA 155, RA 156, RA 157, RA 159, ATA or HEG, and then extracted with an aqueous solution after intervals of up to 30 days.About 80% of total RA 155 was recovered at each sampling time, but after 15 days approximately one-third of the iron in it had been replaced by calcium. Some of the Fe-RA 156 and Fe-RA 159 was sorbed by the clay, but no calcium was found to have replaced iron chelated with RA 156, RA 157 or RA 159.The four chelates of the RA series were labelled with Fe⁵⁹. The amount of isotopic exchange taking place between the Fe⁵⁹ and soil iron was found to be negligible.A very low percentage of Fe-ATA and Fe-HEG was recovered from the soil. Approximately 50% of the Fe-ATA was sorbed by the clay, and in the remainder the chelated iron was replaced by calcium. The cause of the loss of Fe-HEG could not be determined.     

Behaviour of iron chelates in calcareous soils

Summary Fe-EDTA and Fe-HEEDTA, labelled with Fe⁵⁹, were applied at rates of 10 and 100 ppm iron to 50-g samples of dry soil, which were then stored for periods ranging from one to fifteen days before extracting with water.The analyses of the extracts lead to the following general conclusions.1. The decrease in soluble iron could be attributed to both sorption of chelate anions by the clay and to replacement of iron by calcium in the chelate molecule.2. The amount of each chelate sorbed changed little with time and was proportional to the quantity applied. More HEEDTA was sorbed than EDTA.3. The initial decrease in the concentration of soluble iron was rapid for both chelates, but was the greater for Fe-HEEDTA.4. The precipitation of iron from the soluble Fe-HEEDTA was slower than from Fe-EDTA, so that fifteen days after treatment more soluble iron was obtained from the Fe-HEEDTA treatments.5. Marked increases in the recoveries of Fe-EDTA were made when the treated soils were sealed within small containers, compared with those allowed free access to the air. Comparable treatments using Fe-HEEDTA had a much smaller effect.6. Isotopic exchange of Fe⁵⁹ with natural soil iron was greater in the treatments with 10 ppm chelated iron than the 100 ppm level. Fe-HEEDTA was subject to more exchange than Fe-EDTA at both levels.These results are discussed in relation to the treatment of soils with iron chelates for the control of lime-induced chlorosis, and to the importance of isotopic exchange when using chelates labelled with radioactive iron in soil.     

Reactions of iron chelates in calcareous soil and their relative efficiency in iron nutrition of corn

Summary Laboratory incubation studies on the reactions of Fe-DTPA, Fe-EDTA, Fe-citrate and Fe-fulvate with a calcareous soil indicated that Fe³⁺ was very rapidly displaced by Ca²⁺, Mg²⁺, Zn²⁺ and Cu²⁺ ions. The displacement of iron was in the reverse order of the stability of the Fe-chelates. The activity of Fe³⁺, Ca²⁺, Mg²⁺, Zn²⁺ and Cu²⁺ tended to attain a constant value with time. Application of chelating agents to a calcareous soil mobilized different amounts of iron as defined by their relative stability and cation competition. The degree of mobilization increased with increasing levels of applied chelating agents. A significant negative correlation (r = –0.77)^* was observed between pH and DTPA-extractable iron. Results of greenhouse experiment showed significant increase in the dry matter yield and iron uptake by corn plants upon application of iron-chelates. The chelates enhance the uptake of both native and applied sources. The effectiveness of the chelates used was in the order of their capacity to maintain iron in soluble form in the soil solution. These results suggest that iron nutrition of plants in calcareous soils can be effectively regulated by the application of iron chelated by natural or synthetic water-soluble chelating agents.     

Behaviour of iron and manganese chelates in calcareous soils and their effectiveness for plants

Summary The behaviour of the metal chelates Mn-EDTA, Mn-DTPA, Mn-EDDHA, Fe-EDTA, Fe-DTPA and Fe-EDDHA in calcareous soils and their availability to plants were studied. The effectiveness of a metal chelate was shown to depend on its stability, the fixation capacity in the soil and its toxicity to the plant. Incorporation of Fe-DTPA into a framework of silica molecules prevents the fixation of Fe-DTPA in the soil. Fe-DTPA and Fe-EDDHA cause a reduction in the manganese uptake of the plant. The most striking result was the behaviour of Mn-DTPA in calcareous soils. Partial replacement of manganese in the chelate by iron from the soil makes this chelate useful for supplying the plant with both iron and manganese. Mn-DTPA appears to be the ideal type of chelate for the correction of chlorosis in the Netherlands, but unfortunately is not yet commercially available.     

Reactivity of synthetic Fe chelates with soils and soil components

The most effective and common Fe fertilisers in general are EDDHA and EDDHMA Fe chelates because they are highly stable ferric complexes in neutral and alkaline solutions. EDDHSA and EDDCHA iron chelates were introduced in the market recently. Commercial Fe chelates have two Fe fractions, chelated Fe and non-chelated Fe. The latter is bonded to by-products produced during the synthesis of the chelating agent. The effectiveness of Fe chelates depends on their ability to maintain Fe in the soil solution despite simultaneous equilibrium of Fe chelate with many cations, such as Ca²⁺. The main aim of this work was to test the possible agricultural use of EDDHSA and EDDCHA Fe chelates. The pH-Ca²⁺ effect on soluble and chelated Fe (pH ranging from 2 to 12) and the interaction of Fe chelates with soils and soil phases (ferrihydrite, acid peat, calcium carbonate and Ca montmorillonite) are presented. The results demonstrated that EDDHA, EDDHMA, EDDHSA and EDDCHA in solution remain fully associated with Fe from pH 4 to 9 despite competition with Ca. Among soil materials, ferrihydrite and acid peat retain both chelated and non-chelated Fe to the greatest extent. The type of chelating agent is a factor that affects chelated Fe availability in soil. FeEDDHA and FeEDDHMA were retained more by soil surfaces than FeEDDHSA and FeEDDCHA. Commercial Fe chelates present a large amount of soluble, non-chelated Fe and make Cu soluble in soils, which may be due to non-chelated Fe being displaced by Cu.     

BIOLOGICAL AVAILABILITY OF IRON TO THE FRESHWATER CYANOBACTERIUM ANABAENA FLOS‐AQUAE1

Iron acquisition from various ferric chelates and colloids was studied using iron‐limited cells of Anabaena flos‐aquae (Lyng.) Brèb UTEX 1444, a cyanobacterial strain that produces high levels of siderophores under iron limitation. Various chelators of greatly varying affinity for Fe³⁺ (HEDTA, EDDHA, desferrioxamine mesylate, HBED, 8‐hydroxyquinoline) were assayed for the degree of iron acquisition by iron‐limited cyanobacterial cells. Iron uptake rates (measured by graphite furnace atomic absorption spectrometry) varied approximately inversely with calculated [Fe³⁺] (calculated as pFe) and decreased with increasing chelator‐to‐iron ratio. No iron uptake was observed when Fe³⁺ was chelated with HBED, the strongest of the tested chelators. Iron‐limited Anabaena cells were able to take up iron from 8‐hydroxyquinoline (oxine or 8HQ), a compound sometimes used to quantify aquatic iron bioavailability. Iron bound to purified humic acid was poorly available but did support some growth at high humic acid concentrations. These results suggest that for cyanobacteria, even tightly bound iron is biologically available, including to a limited extent iron bound to humic acids. However, iron bound to some extremely strong chelators (e.g. HBED) is likely to be biologically unavailable.     

Antioxidant effect of bovine serum albumin on membrane lipid peroxidation induced by iron chelate and superoxide

Albumin is supposed to be the major antioxidant circulating in blood. This study examined the prevention of membrane lipid peroxidation by bovine serum albumin (BSA). Lipid peroxidation was induced by the exposing of enzymatically generated superoxide radicals to egg yolk phosphatidylcholine liposomes incorporating lipids with different charges in the presence of chelated iron catalysts. We used three kinds of Fe³⁺-chelates, which initiated reactions that were dependent on membrane charge: Fe³⁺-EDTA and Fe³⁺-EGTA catalyzed peroxidation in positively and negatively charged liposomes, respectively, and Fe³⁺-NTA, a renal carcinogen, catalyzed the reaction in liposomes of either charge. Fe³⁺-chelates initiated more lipid peroxidation in liposomes with increased zeta potentials, followed by an increase of their availability for the initiation of the reaction at the membrane surface. BSA inhibits lipid peroxidation by preventing the interaction of iron chelate with membranes, followed by a decrease of its availability in a charge-dependent manner depending on the iron-chelate concentration: one is accompanied and the other is unaccompanied by a change in the membrane charge. The inhibitory effect of BSA in the former at high concentrations of iron chelate would be attributed to its electrostatic binding with oppositely charged membranes. The inhibitory effect in the latter at low concentrations of iron chelate would be caused by BSA binding with iron chelates and keeping them away from membrane surface where lipid peroxidation is initiated. Although these results warrant further in vivo investigation, it was concluded that BSA inhibits membrane lipid peroxidation by decreasing the availability of iron for the initiation of membrane lipid peroxidation, in addition to trapping active oxygens and free radicals.     

Iron requirement and iron uptake from various iron compounds by different plant species

The Fe requirements of four monocotyledonous plant species (Avena sativa L., Triticum aestivum L., Oryza sativa L., Zea mays L.) and of three dicotyledonous species (Lycopersicum esculentum Mill., Cucumis sativus L., Glycine maxima (L.) Merr.) in hydroponic cultures were ascertained. Fe was given as NaFe-EDDHA chelate (Fe ethylenediamine di (O-hydroxyphenylacetate). I found that the monocotyledonous species required a substantially higher Fe concentration in the nutrient solution in order to attain optimum growth than did the dicotyledonous species. Analyses showed that the process of iron uptake was less efficient with the monocotyledonous species. When the results obtained by using chelated Fe were compared with those using ionic Fe, it was shown that the inefficient species were equally inefficient in utilizing Fe³⁺ ions. However, the differences between the efficient and the inefficient species disappeared when Fe²⁺ was used. This confirms the work of others who postulated that Fe³⁺ is reduced before uptake of chelated iron by the root. In addition, it was shown that reduction also takes place when Fe is used in ionic form. The efficiency of Fe uptake seems to depend on the efficiency of the root system of the particular plant species in reducing Fe³⁺. The removal of Fe from the chelate complex after reduction to Fe²⁺ seems to present no difficulties to the various plant species.     

Remedying the iron-deficient maize plants by new synthetic macromolecular chelating agents

The efficacy of Fe³⁺ complexes of polyethers with 8-quinolinol (8QOH) chelating groups attached to the polymer chain at different positions of the aromatic ring or having different chain length for remedying the iron-deficient maize plants was evaluated. The efficacy of chelates of polymers having terminal 8QOH residues was compared with that of complexes of ethylenediaminetetraacetic acid, 8QOH, mixtures of commercial polyethers with isopropylamino end-groups and 8QOH or FeCl₃.6H₂O. It was found that at 30/25 °C (day/night) and photosynthetic photon flux density 1100–1300 μmol m⁻² s⁻¹, the chlorotic maize plants recovered for 4 days of iron re-supply. An increase in the fresh and dry weight, leaf area, net photosynthetic CO₂ uptake of maize leaves, leaf pigment composition and chlorophyll fluorescence was more pronounced in the plants supplied with Fe³⁺ chelates of polymers bearing 8QOH groups attached at 5-position, compared to the other tested Fe³⁺complexes. The importance of the stability of Fe³⁺ complexes, structure of the chelating agent and the necessity of effective ligand exchange between synthetic chelators and free phytosiderophore in iron uptake by strategy II plants was discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of Iron Uptake from Ferrioxamine B by Chlorella vulgaris

Iron uptake from two Fe³⁺-hydroxamate siderophores, ferrioxamine B and Fe³⁺-rhodotorulate, by iron-stressed Chlorella vulgaris (ATCC strain 11468) was evaluated with some comparison to iron uptake from synthetic and organic acid ferric chelates. Iron-stress induced iron uptake from ferrioxamine B. Dissipation of the electrochemical gradient, via uncouplers, inhibited iron uptake. Respiratory inhibitors gave variable results, an indication that a direct link to respiration was not apparent. Vanadate inhibition of iron uptake indicated that an ATPase or phosphate intermediate could be involved in the uptake mechanism. Divalent cations manifested variable effects dependent on the cation and chelator used. These data confirm that C. vulgaris has an inducible iron-uptake system for Fe³⁺-hydroxamic acid siderophores which may involve a different mechanism than that observed for other chelates.     

Chemical equilibrium and E value of Zn (ZnE) in inceptisols and entisols of tropical india

Summary The chemical equilibrium and E value for Zn was calculated in 9 soils of Haryana (India) which represented mainly entisol and inceptisols. The rate of isotopic exchange between⁶⁵Zn and native soil Zn was quite rapid and radioactivity reduced to about 0.2 per cent of initial activity after 3 days but total Zn concentration in soil solution did not decrease. In 5 out of 9 soils equilibrium was established in 2 to 3 days. In typic ustochrepts having high clay content (3,4) equilibrium was attained in two days. In typic udipsamments (2), typic camborthids (8) and aquic vertic ustichrepts (9) it took 3 days to set equilibrium. Typic ustochrepts (5) took 5 days for equilibrium whereas typic ustipssaments (6) and typic camborthids of high O.C. did not attain equilibrium even in 7 days. This indicated that the chemistry and availability of Zn in soil would depend on soil types. When Zn_E was estimated by applying activity after equilibrium with carrier Zn and by applying activity with carrier Zn before equilibrium was set, there was no agreement in Zn_E in two methods. Increasing Zn_E with increasing Zn dose was observed by both methods only in alkaline typic ustochrept (4). In some soils higher E values than added amounts were observed, whereas, in soil 8 negative E values were obtained. The E values become erratic and are over estimated where complex reactions take place due to high pH, high O.C. and high complex forming elements.     

Iron (II) Activated Persulfate Oxidation of MGP Contaminated Soil

The persulfate anion (S₂O₈ ^2?) is a strong oxidant with a redox potential of 2.01 V. However, when mixed with iron (II), it is capable of forming the sulfate radical (SO₄ ^?.) that has an even higher redox potential (E ^o = 2.6 V). In these studies the sulfate radical was investigated to determine if it was a feasible oxidant for the destruction of BTEX and PAH compounds found in MGP contaminated soil. The sulfate radical was generated by either the sequential addition of iron (II) solutions or by a single addition of a citric acid chelated iron (II) solution. The sequentially added iron destroyed 86% of the total BTEX concentration and 56% of the total PAH concentration in the soil. The citric acid chelated iron destroyed 95% of the total BTEX concentration and 85% of the total PAH concentration. A second dose of persulfate and citric acid chelated iron (II) resulted in the destruction of 99% of the total BTEX concentration and 92% of the total PAH concentration. In both the sequential and chelated iron studies the lower molecular weight BTEX compounds were oxidized to a greater extent than the higher molecular weight BTEX compounds, whereas the oxidation of PAH compounds showed no preference to molecular weight.     

Zusammenhänge zwischen der Eisenaufnahme und dem Eisentransport in der Pflanze

Zusammenfassung Junge Sonnenblumenpflanzen nahmen 8 Std. lang nicht markiertes und danach 15 Std. lang mit Fe⁵⁹ markiertes Eisen in Form von Fe-Chlorid, Fe-EDTA oder Fe-Citrat auf. 1. Bei allen drei Eisenformen absorbierten die Pflanzenwurzeln mehr Eisen aus der N?hrl?sung mit 0,1 ppm Fe als aus der mit 1,0 ppm Fe. 2. Die Wurzeln der mit Fe-Chlorid ern?hrten Pflanzen enthalten den h?chsten Gehalt an Fe⁵⁹. 3. Das Stengelexsudat der 0,1 ppm Fe-Reihe enthielt weniger Fe⁵⁹ als das Exsudat der 1,0 ppm Fe-Reihe. 4. Eine sichere Beziehung zwischen der Ern?hrung mit den verschiedenen drei Eisenformen und der ausgeschiedenen Exsudatmenge konnte nicht festgestellt werden. Ebenfalls bestand kein Zusammenhang zwischen der ausgeschiedenen Exsudatmenge und ihrem Fe⁵⁹-Gehalt. 5. Der Gehalt des Stengelexsudats an Fe⁵⁹ war bei der Ern?hrung mit Fe-EDTA und Fe-Citrat h?her als bei Fe-Chlorid.

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Relationships between iron uptake and iron transport in plants

Summary The uptake of unlabelled iron for 8 h and of Fe⁵⁹, given as Fe chloride, Fe EDTA and Fe citrate for 15 h, was investigated in young sunflower plants. 1. In all three iron forms the roots absorbed more iron from the nutrient solution with 0.1 ppm Fe than with 1.0 ppm Fe. 2. The roots of those plants, supplied with Fe-chloride contained the highest amount of Fe⁵⁹. 3. The stem exudate of plants, given a nutrient solution with 0.1 ppm Fe contained less Fe⁵⁹ than the exudate of plants, grown in a nutrient solution containing 1.0 ppm Fe. 4. No close relationship between the nutrition with the three iron forms and the produced amount of exudate could be established. Furthermore no correlation between the produced amount of exudate and its Fe⁵⁹ content could be found. 5. The content of Fe⁵⁹ in the stem exudate was higher when Fe EDTA and Fe citrate were given as compared with Fe chloride.

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Auszug aus der Dissertation des Verfassers.     

Evidence for a specific uptake system for iron phytosiderophores in roots of grasses

Roots of grasses in response to iron deficiency markedly increase the release of chelating substances (`phytosiderophores') which are highly effective in solubilization of sparingly soluble inorganic Fe<sup>III</sup> compounds by formation of Fe<sup>III</sup>phytosiderophores. In barley (Hordeum vulgare L.), the rate of iron uptake from Fe<sup>III</sup>phytosiderophores is 100 to 1000 times faster than the rate from synthetic Fe chelates (e.g. Fe ethylenediaminetetraacetate) or microbial Fe siderophores (e.g. ferrichrome). Reduction of Fe<sup>III</sup> is not involved in the preferential iron uptake from Fe<sup>III</sup>phytosiderophores by barley. This is indicated by experiments with varied pH, addition of bicarbonate or of a strong chelator for Fe<sup>II</sup> (e.g. batho-phenanthrolinedisulfonate). The results indicate the existence of a specific uptake system for Fe<sup>III</sup>phytosiderophores in roots of barley and all other graminaceous species. In contrast to grasses, cucumber plants (Cucumis sativus L.) take up iron from Fe<sup>III</sup>phytosiderophores at rates similar to those from synthetic Fe chelates. Furthermore, under Fe deficiency in cucumber, increased rates of uptake of Fe<sup>III</sup>phytosiderophores are based on the same mechanism as for synthetic Fe chelates, namely enhanced Fe<sup>III</sup> reduction and chelate splitting. Two strategies are evident from the experiments for the acquisition of iron by plants under iron deficiency. Strategy I (in most nongraminaceous species) is characterized by an inducible plasma membrane-bound reductase and enhancement of H<sup>+</sup> release. Strategy II (in grasses) is characterized by enhanced release of phytosiderophores and by a highly specific uptake system for Fe<sup>III</sup>phytosiderophores. Strategy II seems to have several ecological advantages over Strategy I such as solubilization of sparingly soluble inorganic Fe<sup>III</sup> compounds in the rhizosphere, and less inhibition by high pH. The principal differences in the two strategies have to be taken into account in screening methods for resistance to `lime chlorosis'.     

Characterization of siderophore-mediated iron transport inGeotrichum candidum,a non-siderophore producer

Summary Geotrichum candidum is capable of utilizing iron from hydroxamate siderophores of different structural classes. The relative rates of iron transport for ferrichrome, ferrichrysin, ferrioxamine B, fusigen, ferrichrome A, rhodotorulic acid, coprogen B, dimerium acid and ferrirhodin were 100%, 98%, 74%, 59%, 49%, 35%, 24%, 12% and 11% respectively. Ferrichrome, ferrichrysine and ferrichrome A inhibited [⁵⁹Fe]ferrioxamine-B-mediated iron transport by 71%, 68% and 28% respectively when added at equimolar concentrations to the radioactive complex. The inhibitory mechanism of [⁵⁹Fe]ferrioxamine B uptake by ferrichrome was non-competitive (K _i 2.4 M), suggesting that the two siderophores do not share a common transport system. Uptake of [⁵⁹Fe]ferrichrome, [⁵⁹Fe]rhodotorulic acid and [⁵⁹Fe]fusigen was unaffected by competition with the other two siderophores or with ferrioxamine B. Thus,G. candidum may possess independent transport systems for siderophores of different structural classes. The uptake rates of [¹⁴C]ferrioxamine B and⁶⁷Ga-desferrioxamine B were 30% and 60% respectively, as compared to [⁵⁹Fe]ferrioxamine B. The specific ferrous chelates, dipyridyl and ferrozine at 6 mM, caused 65% and 35% inhibition of [⁵⁹Fe]ferrioxamine uptake. From these results we conclude that, although about 70% of the iron is apparently removed from the complex by reduction prior to being transported across the cellular membrane, a significant portion of the chelated ligand may enter the cell intact. The former and latter mechanisms seem not to be mutually exclusive.     

Active Transport of Iron in Bacillus megaterium: Role of Secondary Hydroxamic Acids

Kinetics of radioactive iron transport were examined in three strains of Bacillus megaterium. In strain ATCC 19213, which secretes the ferric-chelating secondary hydroxamic acid schizokinen, ⁵⁹Fe³⁺ uptake from ⁵⁹FeCl₃ or the ferric hydroxamate Desferal-⁵⁹Fe³⁺ was rapid and reached saturation within 3 min. In strain SK11, which does not secrete schizokinen, transport from ⁵⁹FeCl₃ was markedly reduced; the two ferric hydroxamates Desferal-⁵⁹Fe³⁺ or schizokinen-⁵⁹Fe³⁺ increased both total ⁵⁹Fe³⁺ uptake and the ⁵⁹Fe³⁺ appearing in a cellular trichloroacetic acid-insoluble fraction, although 10 min was required to reach saturation. Certain characteristics of transport from both ferric hydroxamates and FeCl₃ suggest that iron uptake was an active process. The growth-inhibitory effect of aluminum on strain SK11 was probably due to the formation of nonutilizable iron-aluminum complexes which blocked uptake from ⁵⁹FeCl₃. Desferal or schizokinen prevented this blockage. A strain (ARD-1) resistant to the ferric hydroxamate antibiotic A22765 was isolated from strain SK11. Strain ARD-1 failed to grow with Desferal-Fe³⁺ as an iron source, and it was unable to incorporate ⁵⁹Fe³⁺ from this source. Growth and iron uptake in strain ARD-1 were similar to strain SK11 with schizokinen-Fe³⁺ or the iron salt as sources. It is suggested that the ferric hydroxamates, or the iron they chelate, may be transported by a special system which might be selective for certain ferric hydroxamates. Strain ARD-1 may be unable to recognize both the antibiotic A22765 and the structurally similar chelate Desferal-Fe³⁺, while retaining its capacity to utilize schizokinen-Fe³⁺.     

Novel chelating agents as manganese and zinc fertilisers: characterisation,theoretical speciation and stability in solution

Abstract

Mineral, complex and chelated micronutrient fertilisers are widely used in agriculture. However, there have been few studies on manganese and zinc fertilisers. In fact, specific chelating agents to provide these micronutrients to plants have not been found, in contrast to iron. This work considers the interactions of novel and traditional ligands in micronutrient mixtures used in hydroponics and fertigation. Theoretical speciation studies comparing the stability in solution have been carried out to simulate the possible interactions that can affect Fe, Mn and Zn in aqueous formulations containing these micronutrients. Unknown stability constants of ligands with Zn and Mn have been determined. Also, theoretical speciation investigations in hydroponic conditions have been carried out. It has been found that the new chelating agents, IDHA and EDDS, and the poorly studied o,p-EDDHA, can be good alternatives to the traditional sources such as EDTA, HEEDTA and DTPA principally for Zn fertilisers. The Mn and Zn chelates with o,p-EDDHA and complexes with lignosulfonate and gluconate have also shown high stability in a hydroponic nutrient solution, maintaining more than 80% Mn in solution until pH 10. The presence of o,o-EDDHA/Fe³⁺ and o,p-EDDHA/Fe³⁺ enhances the stability of Zn in solution in the mixed fertilisers. More studies with substrates are necessary to confirm these results and to extend them to other agronomic conditions.     

Lolium multiflorum uptake of iron supplied as different synthetic chelates

The plant availability of Fe from synthetic chelates has not been examined extensively for plants having the second strategy in iron uptake. Since these plants also excrete chelating agents, competition between natural and synthetic ligands is expected. This research was conducted to study the efficiency of different iron-chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA and a commercial product, Rexene) inLolium multiflorum iron nutrition. Plants were grown in a greenhouse with hydroponic culture using a buffered nutrient solution at pH 8. Initial iron concentration in the nutrient solution was near 0.5 mgl^–1 and solutions were replaced weekly. In an other Fe-EDTA treatment the same amount of chelate was supplied by four additions during each week.Changes of iron concentration in the nutrient solution, harvestable yield, Fe, Mn, Cu and Zn content in plant tissue and chlorophylllevels in leaves are discussed as parameters to evaluate chelate efficacy. Fe-EDDHA, without inorganic iron in the medium was not as effective as the commercial product Rexene, containing Fe-EDDHA and some extra weakly complex iron, which gave the highest yields. Fe-EDTA applied once a week with fresh nutrient solution was less effective than a four part addition as seen from Chl₁/[Fe] ratios.     

Metal chelates in the storage and transport of neurotransmitters: interactions of metal ions with biogenic amines

Abstract— Equilibrium studies on the interaction of biogenic amines with iron (Fe²⁺ and Fe³⁺) and magnesium (Mg²⁺) were undertaken in an attempt to correlate the stabilities of metal-amine chelates and the reported granule-binding affinities of the biogenic amines. By means of potentiometric equilibrium measurements at 25°C and an ionic strength of 10 (KNO₃) the formation constants of the Fe²⁺ chelates with norepinephrine (NE) and adenosine-S-triphosphate (ATP) were determined. Possible structures were derived for the co-ordinate binding of Fe^{2 +} with NE. The interactions of Fe²⁺ and Fe²⁺-ATP with NE were investigated and the formation of Fe²⁺-NE-ATP (1:1:1) mixed ligand ternary chelate was proposed on the basis of the equilibrium data. Information obtained from chelation studies of Fe²⁺ with pyrocatechol and ethanolamine taken together with the data obtained on the Fe²⁺-NE system indicated that the binding of Fe²⁺ by NE was probably via the pyrocatechol moiety. Equilibrium constants for the binding of tyramine (TA) dopamine (DA) and NE with Mg²⁺ were also determined. The equilibrium data obtained on the Mg²⁺-amine systems indicated a correlation between the metal-amine binding affinities and the structure and amine-release (and storage) activities of the biogenic amines. A consideration of the stabilities of the Fe²⁺ and Mg²⁺ chelates together with the occurrence of these metal ions in synaptosomes suggests their possible involvement in the intra vesicular amine-binding and storage sites.     

Soil water uptake by trees using water stable isotopes (δ2H and δ18O)−a method test regarding soil moisture,texture and carbonate

Aims

Stable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition.

Methods

In the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry.

Results

The isotopic composition of extracted soil water was similarly depleted in both ¹⁸O and ²H with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the δ¹⁸O composition while δ²H was not affected.

Conclusions

Our results indicate that soil carbonate can cause artifacts for ¹⁸O isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for δ¹⁸O and δ²H in plant water uptake studies.