Plant Growth Inhibition and Membrane Penetration by a Homologous Series of Dichlorobenzoate Esters

The homologous series of n-alkyl esters (C₁–C₁₀) of 3,4-dichlorobenzoic acid was synthesized and their effects in inhibiting the growth of Nicotiana meristems were studied. The inhibition of growth was considered in terms of penetration of chemicals into the plant tissue and subsequent cell membrane disruption. Penetration was investigated by applying the emulsified ester to the meristem and then measuring the compound recovered with the isolated surface lipids. Decreasing amounts of 3,4-dichlorobenzoate esters penetrated into the plant as the alkyl chain length of the ester moeity was increased. Essentially no penetration occurred with the n-C₇ through C₁₀ esters tested. The effect of the ester homologues on cell membranes was studied by measuring the efflux of betacyanin from beet root cells. Decreasing amounts of pigments were released as the alkyl chain length of the ester was increased. Minimal cell membrane disruption was found for the C₇–C₁₀ esters. Inhibition of the plant meristem may result from the more rapid penetration of the short chain ester homologues into the plant.