Impact of nitrogen form on iron uptake and distribution in maize seedlingsin 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 thro ugh three related experiments with different pretreatments. Experiment 1: p lants 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 w ithout 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 treatme nt concentrations for 7 d. In comparison to the NH4-fed plants, young leave s of the NO3-fed plants showed severe chlorosis under Fe deficiency. Nitrat e 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 roo ts. HCl-extractable (active) Fe was a good indicator reflecting Fe nutritio n 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 primar y 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 yo ung leaves. Exogenous Fe supply decreased the efficiency of such (5)9Fe ret ranslocation. The results suggest that Fe can be remobilized from old to yo ung tissues in maize plants but the remobilization depends on the form of N supply as well as supply of exogenous Fe.