Remedy of chlorosis induced by iron deficiency in plants with the fungal siderophore rhizoferrin

Although microbial siderophores are characterized by high affinity and sele ctivity for Fe3+, they are usually less efficient as Fe-carriers to plants than synthetic chelates. An exception to this is rhizoferrin, a fungal side rophore 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 t omato and cucumber ("strategy I") and barley and corn ("strategy II") plant s grown in nutrient solutions. The Fe-rhizoferrin complex was found to be a n efficient carrier of Fe to these plants. The efficiency of this chelate i s comparable with that of the commonly used ferric complexes of ethylenedia minetetraacetic acid (EDTA) and ethylenediamine-di(o-hydroxyphenyl)acetic a cid (EDDHA). The application of Fe-rhizoferrin resulted in enhanced plant w eight in barley and corn and higher leaf chlorophyll concentration in tomat o, barley and corn. Iron uptake by Fe-stressed cucumber plants from the Fe- 59 chelate of rhizoferrin and other chelators followed the order: EDDHA > r hizoferrin > EDTA greater than or equal to desferrioxamine B (DFOB); Fe-59 translocation from roots to shoots Followed the order: rhizoferrin = EDDHA > EDTA greater than or equal to DFOB. The high availability of Fe complexed by rhizoferrin for "strategy I" plants is related to its relatively high r edox potential and low affinity to Fe2+. The high availability of Fe-rhizof errin to "strategy II" plants is related to its relatively low apparent sta bility constant with Fe3+, which results in the ability of this compound to transfer Fe3+ via ligand exchange to the phytosiderophores which is specif ically taken up by the roots.