On the Action of Plant Growth Regulators. II. Adsorption of MCPA to Plant Components.

Abstract

Interactions between a plant growth regulator, 2-methyl-4-chlorophenoxyacetic acid (MCPA) and monolayers produced directly from plant tissue squashes were studied at pH 4.1, 4.3 and 4.7. The interactions were carried out on a Langmuir trough using force-area (F-A) curves and surface potential-area ( [DELTA] V-A) curves to assess the degree of adsorption of MCPA to the plant monolayers. Estimates were also made of the amount of adsorbing material present in the various tissues. This was done by homogenizing the plant tissue and by noting the volume of filtered homogenate required to form a given area of film on a Langmuir trough. Total adsorption of MCPA, which is a function of the degree of adsorption and the amount of adsorbing material present, was calculated for selected organs from 16 plant species. A broad correlation was found between the resistance of a plant to MCPA and its ability to adsorb the growth regulator, thus lending support to the suggestion that the foundation of species resistance may be partly based upon the extent of MCPA adsorption to sites not concerned in the physiological response.