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Relatively elevated concentrations of naturally occurring radium isotopes ((226)Ra, (228)Ra and (224)Ra) are found in two main aquifers in the arid southern part of Israel, in activity concentrations frequently exceeding the limits set in the drinking water quality regulations. We aimed to explore the environmental implications of using water containing Ra for irrigation. Several crops (cucumbers, melons, radish, lettuce, alfalfa and wheat), grown in weighing lysimeters were irrigated at 3 levels of (226)Ra activity concentration: Low Radium Water (LRW)

The idea of immobilizing Fe and the formation of a slow-release fertilizer has been considered in several studies. However, none of the proposed materials were found efficient in correcting Fe deficiency. In the present study immobilization of Fe chelates on a solid matrix, as a first step in the production and supply process, is tested. The free forms of the siderophores desferrioxamine B (DFOB) and ethylendiaminebis(o-hydroxyphenyl-acetic acid) (EDDHA) were immobilized on p-nitrophenylchloroformate activated Sepharose and tested as Fe source for both strategy I (peanuts and cucumber, Arachis hypogeae L. and Cucumis sativus L., respectively) and strategy II (barley and wheat, Hordeum vulgare L. and Triticum aestivum L., respectively), plants. Plants grown in hydroponic cultures at pH 7.3 were supplied with the immobilized Fe-chelate either free in solution or confined in a dialysis tube with or without EDDHA in the outer solution as a carrier. Cucumber and barley plants were found efficient in acquiring Fe from the immobilized chelates. The effectiveness in utilizing the immobilized Fe-chelate differed among cultivars and was related to the efficiency of the reductases activity or phytosiderophores secretion systems, in Strategy I and Strategy II plants, respectively.

Iron chelators are the most effective Fe fertilizers known to date. However, due to their negative charge they are easily leached out of the root zone. Besides the risk of groundwater contamination with organic compounds and metals, repeated applications of expensive Fe chelates are often required. With the aim to reduce leaching, desferrioxamine B (DFOB) and ethylenediaminedihydroxyphenylacetic acid (EDDHA) were immobilized on Sepharose and tested as Fe sources to plants. Two cultivars of cucumber (Dlila and Kfir) grown in hydroponic cultures at pH 7.3, efficiently utilized Fe from immobilized FeDFOB, and immobilized FeEDDHA. In general, plant response to the immobilized fertilizers became comparable to that of soluble chelates within a period of 17 to 26 days. The kinetics of alleviating Fe induced chlorosis in plants treated with the immobilized chelates was slower than that obtained with soluble chelates. Moreover, the Fe3+ reduction rates obtained for immobilized FeDFOB were slower than thos...

Iron chelates are usually costly and easily leached beyond the root zone. This creates a need to frequently replenish the rhizosphere with chelated Fe and might contaminate groundwater with organic compounds and metals. The development of a slow-release Fe fertilizer that will efficiently supply Fe to plants while exhibiting high resistance toward leaching and/or degradation in the rhizosphere has been the focus of this study. Desferrioxamine B (DFOB) and ethylenediaminebis(o-hydroxyphenylacetic acid) (EDDHA) were immobilized on Sepharose. (13)C NMR and FTIR measurements confirmed that coupling of DFOB to the gel did not appear to influence its ability to chelate Fe(3+) or its binding nature. Isotherms for the immobilized ligands were determined in the presence of 1 mM HEDTA, at 25 degrees C and at an ionic strength of 0.1 M. The isotherms showed a high affinity of Fe(3+) to the ligands and binding up to saturation level throughout the pH range examined (4.0-9.0). The K(app) values for the immobilized Fe chelates were determined using a modified Scatchard model and found to be lower than the soluble ones. This decrease in K(app) might facilitate Fe uptake from these chelates by plants.

Although microbial siderophores are characterized by high affinity and selectivity for Fe3+, they are usually less efficient as Fe‐carriers to plants than synthetic chelates. An exception to this is rhizoferrin, a fungal siderophore produced by Rhizopus arrhizus isolated and purified by our group. A ferric complex of rhizoferrin was used in this study as an Fe source for tomato and cucumber ("strategy I") and barley and corn ("strategy II") plants grown in nutrient solutions. The Fe‐rhizoferrin complex was found to be an efficient carrier of Fe to these plants. The efficiency of this chelate is comparable with that of the commonly used ferric complexes of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine‐di(o‐hydroxyphenyl)acetic acid (EDDHA). The application of Fe‐rhizoferrin resulted in enhanced plant weight in barley and corn and higher leaf chlorophyll concentration in tomato, barley and com. Iron uptake by Fe‐stressed cucumber plants from the 59Fe chelate of rhizoferrin and other ch...

The siderophore rhizoferrin, produced by the fungus Rhizopus arrhizus, was previously found to be as an efficient Fe source as Fe-ethylenediamine-di(o-hydroxphenylacetic acid) to strategy I plants. The role of this microbial siderophore in Fe uptake by strategy II plants is the focus of this research. Fe-rhizoferrin was found to be an efficient Fe source for barley (Hordeum vulgare L.) and corn (Zea mays L.). The mechanisms by which these Gramineae utilize Fe from Fe-rhizoferrin and from other chelators were studied. Fe uptake from 59Fe-rhizoferrin, 59Fe-ferrioxamine B, 59Fe-ethylenediaminetetraacetic acid, and 59Fe-2[prime]-deoxymugineic acid by barley plants grown in nutrient solution at pH 6.0 was examined during periods of high (morning) and low (evening) phytosiderophore release. Uptake and translocation rates from Fe chelates paralleled the diurnal rhythm of phytosiderophore release. In corn, however, similar uptake and translocation rates were observed both in the morning and in the evening. A constant rate of the phytosiderophore's release during 14 h of light was found in the corn cv Alice. The results presented support the hypothesis that Fe from Fe-rhizoferrin is taken up by strategy II plants via an indirect mechanism that involves ligand exchange between the ferrated microbial siderophore and phytosiderophores, which are then taken up by the plant. This hypothesis was verified by in vitro ligand-exchange experiments.