Cytosolic NADPH Is the Electron Donor for Extracellular FeIII Reduction in Iron-Deficient Bean Roots

Pyridine nucleotides were determined in lateral roots of iron-deficient and iron-sufficient Phaseolus vulgaris L. cv Prelude. In iron-deficient plants, total NADP per gram fresh weight and the NADPH/NADP(+) ratio were twice the values found in iron-sufficient plants. The NADPH/NADP(+) ratio in iron-deficient plants was considerably lowered after a 2 minute incubation in 1 millimolar ferricyanide. Total NAD was not influenced by growth conditions and was mainly present in oxidized form.These results indicate that NADPH is the electron donor for the high Fe(III) reduction activity found in iron-deficient roots, a process that is part of the Fe-uptake mechanism.