Pitfalls and Uncertainties of Using Potentiometric Titration for Estimation of Plant Roots Surface Charge and Acid-Base Properties

Grzegorz Jozefaciuk,Malgorzata Lukowska,Alicja Szatanik-Kloc,Justyna Szerement

doi:10.4236/ajps.2014.513200

Abstract

Amount and properties of roots surface charge are important for nutrient uptake and balance in plants. Roots surface charge markedly varies at different rizosphere conditions (particularly pH and ionic strength), which can markedly alter during vegetation season. Among recently available measuring methods, surface charge-pH dependence of roots (as well as other biological objects) is most easily evaluated by potentiometric titration. Use of this method is also easy at different ionic strengths. Potentiometric titration also allows for estimation of the distribution of charge generating surface groups. However, many applications of this method seem to be based either on incorrect methodical or theoretical approaches. In this paper we discuss the methodical and theoretical backgrounds of the titration method. Basing on experimental titration curves of roots of barley grown in nutrient solution, we show inconsistency of surface charge results obtained at different measuring conditions. Limitations of theoretical interpretations of the results are outlined also.

Highlights

The simplest and most convenient method used for estimation of plants root charge versus pH characteristics and to characterize acidic strength of surface charge generating groups is back-titration [1]-[8]
Since titration results have to be expressed on unit mass of the roots, we propose to use the mass of 105 ̊C dried roots for this purpose
The most important element in measurements of titration curves of plant roots is maintaining acid-base equilibrium, it is not easy to get it in practice, even for long time static titration

Summary

Introduction

The simplest and most convenient method used for estimation of plants root charge versus pH characteristics and to characterize acidic strength of surface charge generating groups is back-titration [1]-[8]. At any pH, the amount of base consumed by the roots themselves can be found by subtracting the amount of base consumed by the supernatant from this consumed by the whole suspension In this way the titration curve of the roots solid phase is obtained which serves for estimation of roots charge-pH dependence and for characterization of acidic strength (dissociation or proton binding constants) of charge-generating surface functional groups. These groups have been usually modeled as one or more negatively charged biotic ligands. In this paper we consider plant roots as an example

Methods

Results

Conclusion