Impact of nitrogen form on iron uptake and distribution in maize seedlings in solution culture

Comparative studies on the effect of nitrogen (N) form on iron (Fe) uptake and distribution in maize (Zea mays L. cv Yellow 417) were carried out through three related experiments with different pretreatments. Experiment 1: plants were precultured in nutrient solution with 1.0x10(-4) M FeEDTA for 6 d and then exposed to NO3-N or NH4-N solution with 1.0x10(-)4 M FeEDTA or without for 7 d. Experiment 2: plants were precultured with (5)9FeEDTA for 6 d and were then transferred to the solution with different N forms, and 0 and 1.0x10(-4) M FeEDTA for 8 d. Experiment 3: half of roots were supplied with (5)9FeEDTA for 5 d and then cut off, with further culturing in treatment concentrations for 7 d. In comparison to the NH4-fed plants, young leaves of the NO3-fed plants showed severe chlorosis under Fe deficiency. Nitrate supply caused Fe accumulation in roots, while NH4-N supply resulted in a higher Fe concentration in young leaves and a lower Fe concentration in roots. HCl-extractable (active) Fe was a good indicator reflecting Fe nutrition status in maize plants. Compared with NO3-fed plants, a higher proportion of (5)9Fe was observed in young leaves of the Fe-deficient plants fed with NH4-N. Ammonium supply greatly improved (5)9Fe retranslocation from primary leaves and stem to young leaves. Under Fe deficiency, about 25% of Fe in primary leaves of the NH4-fed plants was mobilized and retranslocated to young leaves. Exogenous Fe supply decreased the efficiency of such (5)9Fe retranslocation. The results suggest that Fe can be remobilized from old to young tissues in maize plants but the remobilization depends on the form of N supply as well as supply of exogenous Fe.