Action of Plant Growth Regulators. III. Adsorption of Aromatic Acids to Oat Monolayers

Abstract

The paper is an extension of earlier work which led to the conclusion that the foundations of species resistance may be partly based on the extent of 2-methyl 4-chlorophenoxyacetic acid (MCPA) adsorption to sites in the plant not concerned in the physiological response. The adsorption of a number of methyl and/or chloro benzoic, phenyl acetic and phenoxyacetic acids on oat monolayers is reported. Adsorption isotherms were determined with a Langmuir trough at pH4.3 and 4.7 using (force and surface potential-area) characteristics of the films. These characteristics are used to build up a model of the mode of adsorption of the variojus acids. Also it was found that highly biologically active acids had adsorptions of intermediate value, whereas a number of inactive acids were highly adsorbed. It vas not possible however by this technique to conclude that acids which gave no change of surface potential were necessarily unadsorbed and hence no conclusions are drawn in this paper concerning unsubstituted and 26 di''substituted acids. Correlation of adsorption values with relevant biological data is deferred until all adsorption data are available.