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Title: Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots. [Phadeolus vulgaris L. var Prelude]

Abstract

The recent proposal of Tipton and Thowsen that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prelude) plants. The role of O/sub 2/ in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O/sub 2/. However, in the presence of O/sub 2/ the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O/sub 2//sup -/, as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O/sub 2//sup -/ may have in the acquisition of ferric iron by dicotyledonous plants.

Authors:
; ; ;
Publication Date:
Research Org.:
Universitaet Hohenheim, Stuttgart (West Germany)
OSTI Identifier:
6998485
Resource Type:
Journal Article
Resource Relation:
Journal Name: Plant Physiol.; (United States); Journal Volume: 85:1
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; IRON COMPOUNDS; REDUCTION; PHASEOLUS; NUTRITIONAL DEFICIENCY; ROOTS; SUPEROXIDE DISMUTASE; BIOCHEMICAL REACTION KINETICS; INHIBITION; MEMBRANE TRANSPORT; OXYGEN; PH VALUE; RESPONSE MODIFYING FACTORS; SCAVENGING; SUPEROXIDE RADICALS; BACTERIA; CHEMICAL REACTIONS; ELEMENTS; ENZYMES; KINETICS; LEGUMINOSAE; MICROORGANISMS; NONMETALS; OXIDOREDUCTASES; PLANTS; RADICALS; REACTION KINETICS; RHIZOBIUM; TRANSITION ELEMENT COMPOUNDS 550200* -- Biochemistry

Citation Formats

Cakmak, I., van de Wetering, D.A.M., Marschner, H., and Bienfait, H.F. Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots. [Phadeolus vulgaris L. var Prelude]. United States: N. p., 1987. Web.
Cakmak, I., van de Wetering, D.A.M., Marschner, H., & Bienfait, H.F. Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots. [Phadeolus vulgaris L. var Prelude]. United States.
Cakmak, I., van de Wetering, D.A.M., Marschner, H., and Bienfait, H.F. 1987. "Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots. [Phadeolus vulgaris L. var Prelude]". United States. doi:.
@article{osti_6998485,
title = {Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots. [Phadeolus vulgaris L. var Prelude]},
author = {Cakmak, I. and van de Wetering, D.A.M. and Marschner, H. and Bienfait, H.F.},
abstractNote = {The recent proposal of Tipton and Thowsen that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prelude) plants. The role of O/sub 2/ in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O/sub 2/. However, in the presence of O/sub 2/ the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O/sub 2//sup -/, as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O/sub 2//sup -/ may have in the acquisition of ferric iron by dicotyledonous plants.},
doi = {},
journal = {Plant Physiol.; (United States)},
number = ,
volume = 85:1,
place = {United States},
year = 1987,
month = 9
}
  • The tandem gene clusters orfR-ombB-omaB-omcB and orfS-ombC-omaC-omcC of the metal-reducing bacterium Geobacter sulfurreducens PCA are responsible for trans-outer membrane electron transfer during extracellular reduction of Fe(III)-citrate and ferrihydrite [a poorly crystalline Fe(III) oxide]. Each gene cluster encodes a putative transcriptional factor (OrfR/OrfS), a porin-like outer-membrane protein (OmbB/OmbC), a periplasmic c-type cytochrome (c-Cyt, OmaB/OmaC) and an outer-membrane c-Cyt (OmcB/OmcC). The individual roles of OmbB, OmaB and OmcB in extracellular reduction of Fe(III), however, have remained either uninvestigated or controversial. Here, we showed that replacements of ombB, omaB, omcB and ombB-omaB with an antibiotic gene in the presence of ombC-omaC-omcC had nomore » impact on reduction of Fe(III)-citrate by G. sulfurreducens PCA. Disruption of ombB, omaB, omcB and ombB-omaB in the absence of ombC-omaC-omcC, however, severely impaired the bacterial ability to reduce Fe(III)-citrate as well as ferrihydrite. These results unequivocally demonstrate an overlapping role of ombB-omaB-omcB and ombC-omaC-omcC in extracellular Fe(III) reduction by G. sulfurreducens PCA. Involvement of both ombB-omaB-omcB and ombC-omaC-omcC in extracellular Fe(III) reduction reflects the importance of these trans-outer membrane protein complexes in the physiology of this bacterium. Moreover, the kinetics of Fe(III)-citrate and ferrihydrite reduction by these mutants in the absence of ombC-omaC-omcC were nearly identical, which clearly show that OmbB, OmaB and OmcB contribute equally to extracellular Fe(III) reduction. Finally, orfS was found to have a negative impact on the extracellular reduction of Fe(III)-citrate and ferrihydrite in G. sulfurreducens PCA probably by serving as a transcriptional repressor.« less
  • Eight strains of Thiobacillus ferrooxidans and three strains of Thiobacillus were grown on ferrous iron (Fe{sup 2+}), elemental sulfur (S{sup 0}), or sulfide ore (Fe, Cu, Zn). The cells were studied for their aerobic Fe{sup 2+} and S{sup 0}-oxidizing activities (O{sub 2} consumption) and anaerobic S{sup 0}-oxidizing activity with ferric iron (Fe{sup 3+}) (Fe{sup 2+} formation). Results show that all the T. ferrooxidans strains studied have the ability to produce cells with Fe{sup 2+} and S{sup 0} oxidation and Fe{sup 3+} reduction activities, but their levels are influenced by growth substrates and strain differences.
  • Acidophilic bacteria of the genera Thiobacillus and Sulfolobus are able to reduce ferric iron when growing on elemental sulfur as an energy source. It has been previously thought that ferric iron serves as a nonbiological oxidant in the formation of acid mine drainage and in the leaching of ores, but these results suggest that bacterial catalysis may play a significant role in the reactivity of ferric iron.
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