CUTICULAR PENETRATION OF 2,4-D AS AFFECTED BY INTERACTION BETWEEN A DIETHYLENE GLYCOL MONOOLEATE SURFACTANT AND APPLE LEAF CUTICLES

Impacts of pH and sorption-desorption of 'Pegosperse' 100-O (PEG 100-O ; diethylene glycol monooleate, containing 15% diester) surfactant by apple (Malus pumila M.) leaf cuticles on surfactant-enhanced cuticular penetration of 2,4-D [(2,4-dichlorophenoxy)acetic acid] were studied. Glass cylinders were affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been soaked in 10 ml lite r-1 PEG 100-O solution and washed for 20 and 120 min, respectively. Qu antities of [C-14]2,4-D in the glass-cuticle chambers passing through the cuticles at pH values from 1 to 6.5 were determined. PEG 100-O sig nificantly increased cuticular penetration of dissociated 2,4-D at pH 4.5; the surfactant had no effect on penetration of undissociated 2,4- D at pH 1.0. Surfactant-enhanced penetration of 2,4-D occurred only wh en the surfactant was in the cuticles, while the process of surfactant sorption-desorption alone had no effect on penetration. These results support a 'hydrophilic channel' hypothesis, i.e. that surfactants may create hydrophilic channels or increase the area of the channels in t he cuticle and, consequently, enhance the passing of polar molecules l ike dissociated 2,4-D through the cuticle.