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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.

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.