Studies on Foliar Penetration: VIII. EFFECTS OF CHLORINATION ON THE MOVEMENT OF PHENOXYACETIC AND BENZOIC ACIDS THROUGH CUTICLES ISOLATED FROM THE FRUITS OF LYCOPERSICON ESCULENTUM L.

The effects of chlorine substitution on the movement of phenoxyaceticand benzoic acids through enzymatically-isolated cuticles ofLycopersicon fruits were determined by following the transferof each acid containing ¹⁴C from a donor to a receiver solution.This cuticle is characterized by an isotropic cutin matrix,within which patches of birefringent cuticular waxes are foundnear the outer surface. The outer, morphological surface isrelatively smooth while at the junction with the outer wallsof the epidermal cells there is extensive cuticular developmentextending down between the anticlinal walls. The epicuticularwax appears as a soft sheet-like covering of which the surfaceis relatively featureless. Chlorination of phenoxyacetic acid results in an enhanced transferacross the isolated cuticle. The order was 2,4,5- and 2,4,6-trichlorophenoxyacetic> 2,4- and 3,5-dichlorophenoxyacetic > 2-chlorophenoxyacetic> phenoxyacetic acid. Removal of the epicuticular wax resultedin greater permeability for all compounds; transfer of the morepolar acids was favoured. In contrast, chlorination of benzoicacid decreases passage through the cuticle; the rate is highestfor benzoic acid followed in descending order by 2-chlorobenzoic,2,4- and 2,5-dichlorobenzoic and 2,3,6-trichlorobenzoic acid.Chlorination also depresses the passage of both phenoxyaceticand benzoic acid through a dialysis membrane. The effects ofchlorination on the lipid solubility of both series of compoundsare discussed in relation to differences in transfer acrossthe cuticle.