Studies on octylphenoxy surfactants. 7. Effects of Triton X-100 on sorption of 2-(1-naphthyl)acetic acid by tomato fruit cuticles

Abstract

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.

Urea Penetration of Isolated Tomato Fruit Cuticles

“…ex Hornem) leaves. The excised tissue was incubated in a mixture of cellulase (0.2% w/v, Sigma, St. Louis), pectinase (4% w/v, ICN Nutritional Biochemicals, Costa Mesa, Calif.), and NaN 3 (1 mM to prevent fungal and bacterial growth) in sodium citrate buffer (50 mM, pH 4.0) prepared in distilled water (Shafer and Bukovac, 1987;Yamada et al, 1964). Enzyme solution was changed several times over a 2week period.…”

Influence of some nonionic surfactants on water sorption by isolated tomato fruit cuticles in relation to cuticular penetration of glyphosate

“…Wyrill and Burnside' reported that surfactants were more effective for glyphosate toxicity to common milkweed and hemp dogbane with increased ethoxylation. Gaskin and Holloway4 observed, with wheat and field bean, an optimum EO chain length (1 [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] for glyphosate uptake, as well as an influence of the hydrophobic moiety. Stevens and Bukovac" showed that the foliar uptake in maize of 2-deoxy-D-glucose, used as a model of a hydrophilic compound, was positively correlated with the hygroscopicity of octylphenoxy surfactants.…”

Characterizing pesticide and surfactant penetration with isolated plant cuticles

“…4). 55 The sorption isotherm remains linear for 'Triton X-100' up to c. 1 glitre-'. Suppression of NAA sorption by cuticles in the presence of surfactant micelles can be attributed to solubilization of NAA in the m i c e l l e~.~~ UV spectroscopy confirms the presence of NAA molecules in the micelles at surfactant concentrations above the CMC.55,57,58 Micellar solubilization is greater when the NAA molecule is in the nondissociated form.58 These data show that micelles reduce the effective NAA concentration (driving force for sorption) in the sorbate solution and, thus, compete with the cuticle for the available NAA.…”

“…One can visualize curve C for a weak organic acid pesticide, where the pH is decreased, with reference to the pK,, resulting in a higher concentration of the more readily sorbed nondissociated species; and curve D, as the pH is increased above the pK,, yielding a higher concentration of the dissociated species.22* 4 4 9 7 2 Also, a response depicted by curve D may be obtained in the presence of a surfactant at a concentration above the CMC if the micelles of the surfactant solubilize the a.i. 55 Curve E suggests that the spray additive induced a change in the sorptive properties of the cuticle, thus delaying sorption equilibrium. Such changes may be caused by solubilizing and removing waxes, plasticizing or causing membrane swelling and, thus, increasing the mobility of the chain segments of the cutin polymer.…”

“…54 The shape of the sorption isotherm was not changed in the presence of 'Triton X-100'. 55 In contrast, the sorption isotherm for 'Triton X-100' is multiphasic ( Fig. 3B).…”