Microbial siderophores

Z. Yehuda, M. Shenker, V. Romheld, H. Mar.schner, Y. Hadar, and Y. Chen. The role of ligand exchange in uptake of iron from microbial siderophores by graminaceous plants. Plant Physiol. 112 [213 (1996). 

Recently, exchange of metals between siderophores and phytosiderophores has been proposed as a primary mechanism for plant use of microbial siderophores (20,21). Conversely, it has also been shown that microbial siderophores... 

The use of microbial siderophores by dicotyledonous plants appears to involve uptake of the entire metallated chelate (42-44), or an indirect process in which the siderophore undergoes degradation to release iron (45). As demonstrated in initial studies examining this question, there was concern that iron uptake from microbial siderophores may be an artifact of microbial iron uptake in which radiolabeled iron is accumulated by root-colonizing microorganisms (46). Consequently, evidence for direct uptake of iron from microbial siderophores has required the use of axenic plants. In experiments with cucumber, it was shown that the microbial siderophore ferrioxamine B could be used as an iron source at concentrations as low as 5 pM and that the siderophore itself entered the plant (42). 

The po.ssible role of a chelate reductase for iron uptake from microbial siderophores has been examined for several plant species (30,47). With certain microbial siderophores such as rhizoferrin and rhodotorulic acid, the reductase may easily cleave iron from the siderophore to allow subsequent uptake by the ferrous iron transporter. However, with the hydroxamate siderophore, ferrioxamine B, which is produced by actinomycetes and u.sed by diverse bacteria and fungi, it has been shown that the iron stress-regulated reductase is not capable... 

E. BarNess, Y. Hadar, Y. Chen, and V. Romheld, Short term effects of rhizosphere microorganisms on Fe uptake from microbial siderophores by maize and oat. Plant Phy.siol. 700 451 (1992). 

F. A. Fekete. Assays for microbial siderophores. Iron Chelation in Plants and Soil Microorganisms. (L Barton, ed.). Academic Press, San Diego, 1993, pp. 399-417. 

E. Bar Ness, Y. Hadar, Y. Chen, and A. Shanzer, Iron uptake by plants from microbial siderophores—a study with 7 nitrobenz-2oxa-1,3-diazole desferrioxamine as fluorescent ferrioxamine B analog. Plant Physiol. 99 1329 (1992). 

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