Abstract
AbstractTwo soybean varieties that differentially absorb and translocate iron were used to compare root‐sap citrate with stem‐exudate citrate as they are involved in the uptake of Fe and Ca. The status of Fe and PO4 in the prenutrient solution determined the citrate concentration in the root sap and the citrate translocated in the stem exudate. There was a parallel between the iron and the citrate translocated in the stem exudate, but this relationship did not appear to exist for the citrate and Fe concentrations in the root sap.Iron stress (deficiency) promoted the accumulation of citrate in the root‐sap, but there was not a concomitant increase of citrate in the stem exudate. In iron‐deficient soybeans, phosphate stress also promoted the accumulation of citrate in the root sap, and here, stem‐exudate citrate and root‐sap citrate more nearly followed the same trends. The citrate pool in the root appears to result from a deficiency of iron and may not be directly involved in the absorption and translocation of iron from the growth medium. Increasing amounts of phosphate in the prenutrient decreased both the citrate and Fe in the root sap and stem exudate.The factors controlling the uptake of Fe are rather specific and are not related to the uptake of radioactive Ca 45 in soybeans regardless of soybean variety, degree of iron stress, or citrate concentration in the root.
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