Submitted to: Bioiron International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/1998
Publication Date: N/A
Technical Abstract: We have been interested in determining the whole-plant factors which coordinate iron acquisition at the root-soil interface and ensure adequate iron supply to developing vegetative and reproductive organs throughout the plant. In dicots, root Fe(III) reduction plays a significant role in providing the Fe2+ substrate for root iron influx; unfortunately, the regulation of the reductase system is poorly understood. Previous studies have shown that reductase activity can be increased when iron is withheld from the root environment. Young, iron-replete plants typically exhibit low reductase rates. We have recently characterized root Fe(III) reductase activity throughout the complete life cycle of pea (Pisum sativum L., cv. Sparkle); plants continuously supplied with iron demonstrated a dynamic modulation in reductase rates. Elevated rates were observed during the period of seed fill. Measurements of total plant iron throughout plant development showed that iron repartitioning from vegetative storage could not provide sufficient iron for seed fill requirements; continued and elevated root-iron reduction / root-iron acquisition was therefore essential. Because studies utilizing the removal of pods and the disruption of shoot-to-root communication resulted in a decline in root reductase rates, we postulate that phloem transport (to the roots) of an unidentified shoot signal can modulate root Fe(III) reductase activity. Shoot iron demand can be communicated to and perceived by the roots. Related studies involving shoot/root grafting experiments with the E107 and dgl pea mutants have also shown that a shoot signal can increase root reductase rates. We will discuss the nature of this iron demand signal and its significance to the enhancement of iron content in seed crops.