A kinetic method for determining iron reducing activity released from plant roots

This paper describes the development and validation of a new method for determining the iron reducing activity of nutrient solutions supporting plant growth. The method depends on the rate at which an aliquot of nutrient solution reduces the iron of Fe3+‐nitrilotriacetate (NTA). The reduced iron is bound by bath‐ophenanthroline sulfonate (BPS) and the rate of Fe2+‐BPS formation is measured at 535 nm. Fe3+‐NTA was chosen as the test iron reagent, since it is susceptible to reduction, yet, nonpolymeric and stable in solution. Reducing agents showed a wide spectrum of activity in this test. The rate at which they reduce Fe3+‐NTA is not a function of their standard oxidation reduction potential alone. Use of the method is illustrated in a study of the release of iron reducing activity by the roots of a tomato plant. The test proved to be simple, fast, and precise. The advantages and limitations of the method are discussed.