The ferric chelate reductase activities of leaf plasma membranes isolated from
the leaves of Fe-deficient and Fe-sufficient sugar beet have been
characterized. Substrates used were the complexes of ferric iron with ethylene
diamine tetraacetic acid, citric acid and malic acid. Iron deficiency was
associated with 1.5- to 2-fold increases in leaf plasma membrane ferric
chelate reductase activity when rates were calculated on a protein basis. The
natural complexes of ferric iron with citrate and especially with malate were
good substrates for the ferric chelate reductase enzyme present in leaf plasma
membrane preparations. The apparent affinities were higher for the ferric
malate complex. The optimal pH for the activity of the ferric chelate
reductase in sugar beet leaf plasma membranes was in the range 6.5–7.0.
The ferric chelate reductase activity decreased by approximately 30%
when the assay pH was decreased to 5.8 or increased to 7.5. Therefore, our
data provide evidence against the hypothesis that changes in apoplastic pH
could decrease markedly the activity of the ferric chelate reductase enzyme in
plasma membrane preparations from the leaves of Fe-deficient plants.
CIPK23 is involved in iron acquisition of Arabidopsis by affecting ferric chelate reductase activity
