PLANT PHYSIOLOGY , Vol 112, Issue 3 1273-1280, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
The Role of Ligand Exchange in the Uptake of Iron from Microbial Siderophores by Gramineous Plants
Z. Yehuda, M. Shenker, V. Romheld, H. Marschner, Y. Hadar and Y. Chen
Department of Soil and Water Sciences (Z.Y., M.S., Y.C.), and Department of Microbiology and Plant Pathology (Y.H.), Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
The siderophore rhizoferrin, produced by the fungus Rhizopus arrhizus, was
previously found to be as an efficient Fe source as
Fe-ethylenediamine-di(o-hydroxphenylacetic acid) to strategy I plants. The
role of this microbial siderophore in Fe uptake by strategy II plants is
the focus of this research. Fe-rhizoferrin was found to be an efficient Fe
source for barley (Hordeum vulgare L.) and corn (Zea mays L.). The
mechanisms by which these Gramineae utilize Fe from Fe-rhizoferrin and from
other chelators were studied. Fe uptake from 59Fe-rhizoferrin,
59Fe-ferrioxamine B, 59Fe-ethylenediaminetetraacetic acid, and
59Fe-2[prime]-deoxymugineic acid by barley plants grown in nutrient
solution at pH 6.0 was examined during periods of high (morning) and low
(evening) phytosiderophore release. Uptake and translocation rates from Fe
chelates paralleled the diurnal rhythm of phytosiderophore release. In
corn, however, similar uptake and translocation rates were observed both in
the morning and in the evening. A constant rate of the phytosiderophore's
release during 14 h of light was found in the corn cv Alice. The results
presented support the hypothesis that Fe from Fe-rhizoferrin is taken up by
strategy II plants via an indirect mechanism that involves ligand exchange
between the ferrated microbial siderophore and phytosiderophores, which are
then taken up by the plant. This hypothesis was verified by in vitro
ligand-exchange experiments.
