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The effects of a polyethoxy (EO) derivative of octylphenol (OP) with 9.5 ethyleneoxy groups (OP + 9.5EO) on 2-(l-naphthyl)acetic acid (NAA) sorption by cuticles enzymatically isolated from mature tomato (Lycopersicon esculentum Mill. cv. Sprinter) fruit were studied at pH 3.2 and 25 "C. Time to reach NAA sorption equilibrium by cuticular membranes (CM) or dewaxed CM (DCM) was not affected by OP + 9.5EO. At concentrations below the critical micelle concentration (CMC), OP + 9.5EO had little effect on NAA sorption. However, at concentrations above the CMC, NAA sorption was inversely related to OP + 9.5EO concentration. The amounts of NAA sorbed by CM and DCM for the lowest OP + 9.5EO concentration examined (0.001 %, w/v) were approximately 50 and 60 pmolekg-', respectively. At concentrations above 4 % , no detectable amount of NAA was sorbed by CM. Sorption of NAA by CM was inversely related to solution pH (2.2-6.2), and OP + 9.5EO (0.1%) lowered NAA sorption at all pH levels examined. The amount (micromoles per kilogram) of NAA sorbed by CM increased with increasing NAA concentration (micromolar to millimolar). OP + 9.5EO (0.1%) decreased NAA sorption by CM over the entire NAA concentration range examined.

14C-urea penetration of isolated tomato (Lycopersicon esculentum Mill. cv. `Pik Red') fruit cuticular membranes (CM) was studied as a function of concentration and temperature. There was no significant effect of cuticular wax on urea penetration at 25C, permeances for the CM being 8.4 × 10-10 and dewaxed CM (DCM) 11.1 × 10-10·m·s-1. Time lags were near zero for both CM and DCM. Steady-state diffusion analysis suggests that the relatively low cuticular permeance of urea is due to low partitioning that offsets high diffusivity. Urea flux through the CM and DCM showed ≈1.5- and 1.9-fold increases, respectively, for each 10C increase between 5 and 45C. Urea flux across CM and DCM increased linearly with concentration (10 μm to 1 m) and, thus, was a first-order process.

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ABSTRACISorption characteristics of 2-(1-naphthyl)acetic acid (NAA), 2-(1-naphthyl)acetamide (NAAm), and 2,4-dichlorophenoxyacetic acid (2,4-D) were determined for cuticles enzymicaliy isolated from mature tomato (Lycopersicon esculentum Mill. cv Sprinter) and pepper (Capsicum annuum L.) fruit. Sorption equilibrium for NAA and 2,4-D by tomato cuticular membranes (CM) and dewaxed cuticular membranes (DCM) was achieved within 24 hours at 25°C. The average K (partition coefficient) values for NAA in tomato CM and DCM were 166 and 204, respectively, whereas the corresponding K values for 2,4-D were 292 and 383, respectively. Sorption equilibrium for 2,4-D and NAA in pepper cuticles was not achieved after 18 and 63 days, respectively. Sorption equilibrium for NAAm in tomato and pepper CM and DCM was attained within 48 hours. Acid pretreatment (2.0 N HCI, 10 minutes) had no effect on NAA, 2,4-D, or NAAm sorption by tomato CM and DCM, or on NAAm sorption by pepper CM and DCM. Acid pretreatment of pepper CM and DCM led to slightly lower KPH (apparent partition coefficient) values for both NAA and 2,4-D. More significantly, sorption equilibrium for NAA and 2,4-D in pepper CM and DCM was achieved within 24 hours after acid treatment.The plant cuticle is a continuous nonliving, lipophilic membrane that forms the interface between the plant and its environment (17). It is a heterogeneous membrane, consisting of a polyester matrix, cutin, and cuticular lipids (2,10,11,16). Carbohydrates, phenolic compounds and polypeptides may also be present ( 17). Cuticular penetration is a prerequisite for the absorption of foliar-applied substances (12). Since the cuticle is the major barrier to foliar absorption (4, 9, 27), numerous studies have focused on cuticular sorption and/or permeability using various organic and inorganic substances (9,13,25