Iron uptake

Waheed A et al Regulation of transferrin-mediated iron uptake by HFE, the protein defective in hereditary hemochromatosis. Proc Natl Acad USA 2002 99 3117. 

Soft rot spreading depends on the efficiency of the iron uptake pathway mediated by the siderophore chrysobactin. Biosynthesis of the ferrichrysobactin outer membrane receptor (Fct) and of the chrysobactin precursor, i.e. the activated form of 2,3-dihydroxybenzoic acid, are encoded by an operon,/cr ebsCEBA [3]. 

The mutant L37 cbrA21 is affected as regards to its iron uptake pathway mediated by the siderophore achromobactin. Because this mutation results in derepression of the chrysobactin mediated iron transport pathway, the mutant is probably less susceptible to iron deprivation than wild-type cells are, when entering the host. This results in a delay in Pels production thus leading to delayed symptoms, as reported by Sauvage and Expert (1994). 

D. L. Jones, P. R. Darrah, and L. V. Kochian, Critical evaluation of organic acid mediated iron dissolution in the rhizo.sphere and its potential role in root iron uptake. Plant Soil 180 51 (1996). 

H. Marschner, V. Romheld, and M. Kissel, Localization of phytosiderophore re-lea.se and iron uptake along intact barley roots. Physiol. Plant. 71 51 (1987). 

V. Romheld, and H. Marschner, Mechanisms of iron uptake by peanut plants 1. Reduction, chelate splitting, and release of phenolics. Plant Physiol. 77 949 (1983). 

K. Venkat Raju, H. Marschner, and V. Riimheld, Effect of iron nutritional. status on iron uptake, substrate pH and production and release of organic acids and riboflavin by sunflower plants. Z. Pflanzenerenaehr. Bodenk. I32 ll (1972). 

S. Tagaki, Mechanism of iron uptake regulation in roots and genetic differences. Agriculture, Soil Science and Plant Nutrition in the Northern Part of Japan. (Japanese Society of Soil Science and Plant Nutrition eds.), 1984, Tokyo, Japan, p. 190. 

Under aerated conditions at neutral to alkaline pH, inorganic iron is extremely insoluble (8), such that plants and microorganisms rely absolutely on iron uptake from organic matter complexes or iron that has been solubilized by siderophores and organic compounds contained in root exudate. Low-molecular-weight root exudates that dissolve iron include organic acids that are secreted by plant roots as a specific response to iron deficiency (9) or that are released constitutively at... 

IV. IRON UPTAKE MECHANISMS FROM SIDEROPHORES AND PHYTOSIDEROPHORES... 

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... 

Iron uptake by bacteria at sites of lateral root emergence has been further confirmed using another technique employing 7-nitrobenz-2-oxa-l,3-diazole-desferrioxamine B, which is a derivitized siderophore that becomes fluorescent after it is deferrated (78). In this case, iron uptake from the siderophore ferrox-amine B was a.ssociated primarily with microbially colonized roots, but both plant and iron uptake from this chelate occurred in the regions just behind the root tips. 

H. F. Bienfait, Regulated redox proces.ses at the plasmalemma of plant root cells and their function in iron uptake. J. Bioenerg. Biomemhr. 17 13 (1985). 

D. E. Crowley. V. Romheld, H. Marschner, and P. J. Szaniszlo. Root-microbial effects on plant iron uptake from siderophores and phytosiderophores. Plant Soil 142 1 (1992). 

H. Marschner, V. Romheld, and M. Kissel, Localization of phytosiderophore release and of iron uptake along intact barley roots. Physiol. Planta. 77 157 (1987). V. Romheld, The role of phytosiderophores for acquisition of iron and other micronutrients in graminaceous species An Ecological Approach Iron Nutrition and Interactions in Plants (Y Chen and Y Hadar, eds.), Kluwer Academic Publishers, Boston, 1991, pp. 159-166. 

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). 

G. L. Boyer, Iron uptake and siderophore formation in the actinorhizal symbiont Frankia Biochemistry of Metal Micronutrients in the Rhizosphere (J. A. Manthey, D. E. Crowley, and D. G. Luster, eds.). CRC Press, Boca Raton, Florida, USA London, England, UK, 1994, pp. 41-54. 

J. S. Duhan, S. S. Dudeja, and A. L. Khurana. Siderophore production in relation to N fixation and iron uptake in pigeon pea-Rhizobium symbiosis. Folia Microbiol. 45 421 (1998). 

W. Schmidt, Mechanisms and regulation of reduction-based iron uptake in plants. New Phytol. I4I (1999). 

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