CHELATION EFFECTS ON THE IRON REDUCTION AND UPTAKE BY LOW-IRON STRESS TOLERANT AND NONTOLERANT CITRUS ROOTSTOCKS

The relative rates of ferric-iron (Fe3+) reduction and uptake by two citrus rootstocks were measured for a series of synthetic Fe3+ chelates and microbial siderophores. The rates of Fe3+ reduction by the citrus seedlings followed the order: FeHEDTA much less than FeDPTA > FeCDTA. No reduction occurred for FeDFOB (ferrioxamine B) and FeTAF (ferric triacetylfusagen). Low rates of Fe3+ reduction occurred for Fe2RA3 (ferric rhodotorulic acid). The levels of Fe-55 taken up the citrus seedlings showed good correlations with the reduction rates. These results indicate the importance of Fe3+ reduction in the Fe uptake by citrus rootstocks. The immobility of a large percent of the Fe-55 taken up by the roots is attributed to the accumulation of Fe in the root apoplasts.