Plant Physiol, March 2002, Vol. 128, pp. 1022-1030
Ferrous Ion Transport across Chloroplast Inner Envelope
Membranes1
Richard
Shingles,*
Marisa
North, and
Richard E.
McCarty
Department of Biology, Johns Hopkins University, Baltimore,
Maryland 21218-2685
The initial rate of Fe2+ movement across the inner
envelope membrane of pea (Pisum sativum) chloroplasts
was directly measured by stopped-flow spectrofluorometry using membrane
vesicles loaded with the Fe2+-sensitive fluorophore, Phen
Green SK. The rate of Fe2+ transport was rapid, coming to
equilibrium within 3s. The maximal rate and concentration dependence of
Fe2+ transport in predominantly right-side-out vesicles
were nearly equivalent to those measured in largely inside-out
vesicles. Fe2+ transport was stimulated by an inwardly
directed electrochemical proton gradient across right-side-out
vesicles, an effect that was diminished by the addition of valinomycin
in the presence of K+. Fe2+ transport was
inhibited by Zn2+, in a competitive manner, as well as by
Cu2+ and Mn2+. These results indicate that
inward-directed Fe2+ transport across the chloroplast inner
envelope occurs by a potential-stimulated uniport mechanism.
1
This work was supported by the U.S. Department
of Energy (grant no. DE-FG02-92ER 200 280).
*
Corresponding author; e-mail shingles{at}jhu.edu; fax
410-516-5213.
© 2002 American Society of Plant Physiologists
