Dependency of Iron Reduction on Development of a Unique Root Morphology in Ficus benjamina L

The activity of the Fe3+ reductase of excised adventitious roots of Ficus benjamina L., grown in hydroponic culture without iron, was determined by a colorometric assay simplified by the use of a microplate reader. Reductase activity remained the same from pH 4.5 to 6.5 and decreased sharply above pH 6.5. Acetate buffer inhibited reduction. During early stages of root growth, excised roots did not exhibit Fe3+ reductase activity. After several weeks and extensive root system development, Fe3+ reduction still was not detectable in primary roots, but intermediate and high rates of reduction occurred in lateral and newly formed root clusters, respectively. Clustered roots only developed on plants grown at 0 or very low (