IRON INEFFICIENCY IN MAIZE MUTANT YS1 (ZEA-MAYS L CV YELLOW-STRIPE) IS CAUSED BY A DEFECT IN UPTAKE OF IRON PHYTOSIDEROPHORES

To determine the Fe inefficiency factors in the maize mutant ys1 (Zee mays L. cv Yellow Stripe), root exudates of Fe-inefficient ys1 and of two Fe-efficient maize cultivars (Alice, WF9) were collected in axenic nutrient solution cultures. Analysis by thin-layer chromatography and high-performance liquid chromatography revealed that under Fe deficiency ys1 released the phytosiderophore 2'-deoxymugineic acid (DMA) in quantities similar to those of Alice and WF9. Under nonaxenic conditions, DMA released by plants of all three cultivars was rapidly decomposed by microorganisms in the nutrient solution. Uptake experiments with Fe-59-labeled DMA, purified from root exudates of either Fe-deficient Alice or ys1 plants, showed up to 20 times lower uptake and translocation of Fe-59 in ys1 than in Alice or WF9 plants. The presence of microorganisms during preculture and short-term uptake experiments had no significant effect on uptake and translocation rates of Fe-59 in Alice and ys1 plants. We conclude that Fe inefficiency in the maize mutant ys1 is the result of a defect in the uptake system for Fe-phytosiderophores.