ANALYSIS OF IRON-DEFICIENCY INDUCED HYDROGEN RELEASE BY PLANT-ROOTS USING CHEMICAL-EQUILIBRIUM AND PH-STAT METHODS

Iron (Fe) is an essential nutrient for plants. When Fe-deficient, most dicotyledonous and non-graminaceous monocotyledonous plants exhibit F e-deficiency stress responses, which may include proton (H+) release f rom roots. Proton release is considered to be one of the factors contr ibuting to plant Fe-deficiency resistance. Several methods, including the pH-stat, back-titration, and pH-drift procedures, have been used t o evaluate the Fe-deficiency induced acidification process. These meth ods actually determine total net acidity release, not H+ release. A me thod, based on the principles of chemical equilibrium, for the analysi s of net free H+ release is introduced in this paper. By comparing res ults of the chemical equilibrium method with those of a method measuri ng total net acidity release, such as the back-titration method, it is possible to determine the relative role of free H+ and organic acid t o total acidity release. The pH-stat method for analysis of total net acidity release, in which the pH of the incubation solution is held co nstant, eliminates the influence of pH decrease during plant incubatio n and thus results in a more accurate measurement of Fe-deficiency ind uced acidity release. The advantages and disadvantages of each individ ual method are discussed.