Journal of Experimental Botany, Vol 49, 1219-1226, Copyright © 1998 by Oxford University Press
U Eckhardt and T Buckhout
The mechanism of adaptation to Fe-deficiency stress was investigated in the
unicellular green alga, Chlamydomonas reinhardtii.
Upon removal of nutritional Fe, the activity of a cell surface
Fe(III)-chelate reductase was increased by at least 15-fold within 24 h.
This increase was negatively corelated with the Fe concentration in the
growth media. Incubation of cells in the presence of the
Fe2+-specific chelator,
bathophenanthrolinedisulphonic acid, led to an increased
Fe3+ reductase activity, even when sufficient Fe was
present. Growth of cells in Cu-free media for 48 h led to no statistically
significant increase in Fe3+ reductase activity. The
Fe(III)-chelate reductase activity in Fe-starved cells was saturable with
an apparent Km of 31
ARTICLES
Iron assimilation in Chlamydomonas reinhardtii involves ferric reduction and is similar to Strategy I in higher plants
Angewandte Botanik, Humboldt Universitat zu Berlin, Invalidenstrasse 42, D-10115 Berlin, Germany; Corresponding author; e-mail: Thomas-Buckhout@biologie.hu-berlin.de
M
and was inhibited by uncouplers of the transmembrane proton gradient but
not by SH-specific reagents.Fe uptake was only observed in Fe-deficient
cells. Uptake was specific for Fe in that at 100-fold excess of a number of
metal ions in the transport assay did not inhibit uptake activity. However,
a 100-fold excess of Cu resulted in a 87% inhibition of Fe uptake. The
Vmax for Fe3+ reduction
activity was 250-fold greater than for Fe uptake; although the
Km values for both processes differed by only 10-fold.
Thus, the rate limiting step in Fe assimilation was transport and not
reduction. These results indicate that Fe assimilation in C.
reinhardtii involves a reductive step and thus resembles the
mechanism of Fe uptake in Strategy I higher plants.Keywords:
Ferric chelate reduction, iron assimilation, iron uptake,
unicellular green algae, Chlamydomonas.
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