IRON-EFFICIENT AND IRON-INEFFICIENT OATS AND CORN RESPOND DIFFERENTLY TO IRON-DEFICIENCY STRESS

Iron-efficient (WF9 corn and Coker 227 oat) and Fe-inefficient (ys1 corn and TAM 0-312 oat) cultivars were comparatively tested for their response to Fe-deficiency stress induced by the use of either ferrous or ferric chelators. Corn and oats were grown in 20-mu-M Fe with 0, 60, and 120-mu-M BPDS and 40-mu-M Fe with 0, 120, and 240-mu-M BPDS and 20-mu-M Fe with 0 and 40-mu-M EDDHA. All four cultivars tested, both Fe-efficient and Fe-inefficient, continuously reduced Fe3+ to Fe2+ at a low level as evidenced by the production of Fe2+ (BPDS)3 in test nutrient solutions over time. Severity of chlorosis increased as more BPDS was added to the nutrient solutions for both WF9 and ys1 corn, but unlike corn, Coker 227 and TAM 0-312 oats were both able to obtain Fe from the Fe2+ (BPDS)3 complex and were less chlorotic as a result. In short-term (4-hour) in vivo measurements, iron-stressed WF9 (Fe-efficient) corn reduced more Fe3+ to Fe2+ than similarly stressed ys1 corn, Coker 227 oat or TAM 0-312 oat. Thus, at the same time that Fe-efficient WF9 corn reduces more Fe than the other cultivars, it is also unable to compete with BPDS for that Fe in the nutrient solution. These differences coupled with the observation that only Coker 227 oat produced measureable iron solubilizing substances (phytosiderophores) suggest that these two species differ in their mechanisms for obtaining Fe during Fe-deficiency stress.