Iron Stress as Related to the Iron and Citrate Occurring in Stem Exudate

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Abstract
Two soybean varieties that differ in their ability to absorb-translocate Fe were grown at different Fe levels to produce plants at different degrees of Fe stress or deficiency. There was a simultaneous occurrence of Fe and citrate in the exudate or both varieties dependent on the degree of Fe stress produced within the plant. A differential absorption of Fe was observed between the 2 soybean varieties resulting from differences in response to a given Fe stress. Despite this difference in response, there was a striking parallel between transported Fe and citrate in the exudate of each variety. When Fe increased, citrate increased; a decrease in Fe was paralleled by a decrease in citrate. This relationship held true whether Fe stress was produced in the plant by limiting the Fe supply or by using the inhibitors Zn or azide to stop the translocation of Fe.