Electrochemical evaluation on the distribution and diffusion of ions in the plant cuticular membrane

Abstract

Cuticular membranes (M) isolated from green or red tomatoes and apples were equilibrated with an aqueous solution, and were set between the aqueous solution (W) and the organic solution (O). Voltammetry for ion transfer from W to O through M was carried out by cyclic voltammetry (CV) and potential step chronoamperometry (PSCA). Various quaternary ammonium ions were examined as an alternative of organic ions such as pesticides. When CV or PSCA was repeated every 5 or 10 minutes, the measured current for ion transfer from M to O decreased at every measurement. The decrement rate was damped with the repeat number of measurements. The current decrement was not observed at the W|O interface in the absence of a cuticular membrane, and was caused by both a slow distribution of ions at the W|M interface and slow diffusion inside the M. The distribution rate constant at the W|M interface and the diffusion coefficient in M were evaluated from PSCA and a simple simulation, and were obtained with various viewpoints, such as the difference of the face or back of membrane, the kind of plants, the degree of maturation of fruits, the hydropobicity of tested ion and the role of lenticel in apple membrane.