HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Shenker, M. Articles by Hadar, Y. Search for Related Content PubMed Articles by Shenker, M. Articles by Hadar, Y. Agricola Articles by Shenker, M. Articles by Hadar, Y.

Stability Constants of the Fungal Siderophore Rhizoferrin with Various Microelements and Calcium

Dep. of Soil and Water Sciences, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, Israel

Y. Hadar

Dep. of Microbiology and Plant Pathology, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, Israel

*Corresponding author (deanagri{at}agri.huji.ac.il).

ABSTRACT

Stability constants of metal-ligand complexes determine their speciation in solution at equilibrium. Therefore, stability constants of siderophore-metal complexes are of crucial importance in studies of their efficiency as Fe mediators. In this study, potentiometric titrations were used to determine protonation and stability constants of Fe³⁺, Fe²⁺, Cu²⁺, Ca²⁺, and Zn²⁺ with rhizoferrin, a siderophore produced by Rhizopus arrhizus, which has been shown in previous studies to be an effective carrier of Fe to plants. Rhizoferrin was found to be a specific Fe³⁺ chelator but with a stability constant lower than most microbial siderophores. The ferric complex of rhizoferrin is anionic throughout the pH range prevailing in soils, and therefore, it is expected to be mobile in the rhizosphere. The following log K_app values at 25°C, pH 7.0, and 0.1 M ionic strength were determined: 19.1, 7.5, 6.2, 6.0, and 4.4 for Fe³⁺, Fe²⁺, Cu²⁺, Ca²⁺, and Zn²⁺, respectively. The apparent stability constant (K_app) value for the ferric complex of rhizoferrin suggests that ligand exchange with mugineic acid is the mechanism facilitating the efficiency of rhizoferrin as an Fe carrier to graminaceous plants.

Received for publication June 20, 1995.

This article has been cited by other articles:

				M. Shenker, T.W.-M. Fan, and D.E. Crowley Phytosiderophores Influence on Cadmium Mobilization and Uptake by Wheat and Barley Plants J. Environ. Qual., November 1, 2001; 30(6): 2091 - 2098. [Abstract] [Full Text] [PDF]

				M. Shenker, Y. Hadar, and Y. Chen Kinetics of Iron Complexing and Metal Exchange in Solutions by Rhizoferrin, A Fungal Siderophore Soil Sci. Soc. Am. J., November 1, 1999; 63(6): 1681 - 1687. [Abstract] [Full Text] [PDF]