Analysis of iron‐deficiency induced hydrogen release by plant roots using chemical equilibrium and pH‐stat methods

Abstract

Iron (Fe) is an essential nutrient for plants. When Fe‐deficient, most dicotyledonous and non‐graminaceous monocotyledonous plants exhibit Fe‐deficiency stress responses, which may include proton (H⁺) release from roots. Proton release is considered to be one of the factors contributing to plant Fe‐deficiency resistance. Several methods, including the pH‐stat, back‐titration, and pH‐drift procedures, have been used to evaluate the Fe‐deficiency induced acidification process. These methods actually determine total net acidity release, not H⁺ release. A method, based on the principles of chemical equilibrium, for the analysis of net free H⁺ release is introduced in this paper. By comparing results of the chemical equilibrium method with those of a method measuring total net acidity release, such as the back‐titration method, it is possible to determine the relative role of free H⁺ and organic acid to total acidity release. The pH‐stat method for analysis of total net acidity release, in which the pH of the incubation solution is held constant, eliminates the influence of pH decrease during plant incubation and thus results in a more accurate measurement of Fe‐deficiency induced acidity release. The advantages and disadvantages of each individual method are discussed.

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