A role for potassium in the use of iron by plants

Iron‐efficient T3238FER tomato (Lycopersicon esculentum Mill.) and A7 soybean [Glycine max (L.) Merr.] were unable to respond to iron (Fe) deficiency stress in the absence of potassium (K) in growth solutions. The lack of response in both FER tomato and A7 soybean was a diminished exudation of hydrogen (H+) ions and reductants and a lower level of Fe(III) reduction at the roots. This lack of Fe‐stress response resulted in reduced levels of leaf Fe and greater chlorosis in the absence of K in both species. Solution K was replaced with vary.ing equimolar levels of both sodium (Na) and rubidium (Rb) in growth solutions, but neither effectively substituted for K which appears essential in eliciting the Fe‐stress response mechanism resulting in the uptake of Fe by the plant. Potassium seems to have a very specific role in the plant for maximum utilization of Fe.