PLANT UTILIZATION OF IRON SOLUBILIZED BY OAT PHYTOSIDEROPHORE

Responses to Fe-deficiency stress have been classified as Strategies I and II. "Iron-efficient" cultivars within each strategy exhibit one or more of a combination of specific physiological responses to Fe-deficiency stress, while "Fe-inefficient" cultivars do not. Iron-efficient Coker 227 oat (Avena byzantina C. Koch.) is a Strategy II plant which produces an Fe-chelating compound (phytosiderophore) in response to Fe-deficiency stress. The objective of this paper is to summarize the results of studies in which the abilities of several plant species to utilize Fe solubilized by oat phytosiderophore were determined. Experiments were conducted in which Fe-deficiency stressed oat plants were grown in hydroponic solutions (1.2 mg Fe L-1 unchelated) in combination with three different species of both monocotyledonous and dicotyledonous plants which represented a wide range of Fe-efficiency. The cultivars varied in response to the oat phytosiderophore as follows: (a) WF9 maize (Zea mays L.), TAM 0-312 oat, 'Redlan' B-line sorghum (Sorghum bicolor (L.) Moench), fefe muskmelon (Cucumis melo L.), and T3238fer tomato (Lycopersicon esculentum Mill.) plants obtained more Fe when grown in combination with Coker 227 oat than when grown alone, (b) ys, (ys1/ys1) maize was unable to obtain Fe whether grown in the presence or absence of oat, and (c) A7, Dawson, Corsoy 79, Pride B-216, and T203 (PI-54619-5-1) soybean (Glycine max (L.) Merr.) did not obtain more Fe when grown in combination with oat--instead phytosiderophore prevented Fe uptake in relationship to the Fe-inefficiency of each soybean cultivar, The reasons for these differential responses are yet to be identified, but variation in root reductive capacity and/or presence or absence of specific uptake sites may be responsible.