Effects of accelerators on mobility of ~(14)C-2,4-dichlorophenoxy butyric acid in plant cuticles of Stephanotis

摘要

Effects of diethylsuberate (DESU), diethyl sebacate (DES), dibutyl suberate (DBSU), dibutyl sebacate (DBS) and tributyl phosphate (TBP) on diffusion of ~(14)C-2,4-dichlorophenoxy butyric acid (2,4-DB) across cuticular membranes (CM) was studied. Astomatous CM were isolated enzymatically from Stephanotis leaves and diffusion was measured at 20 °C. The alkyl substituted dicarboxylic acids constitute a homologous series with carbon numbers increasing from C_(12) to C_(18). Molecular weights increased only moderately from 230.0 (DESU) to 314.5 (DBS), while partition coefficients amounted to 92 (DESU), 1213 (DES), 15,988 (DBSU) and 210,762 (DBS). All above compounds turned out to be accelerators as they increased 2,4-DB mobility by up to 40-fold, with accelerator concentrations in the CM ranging from only 10 to 105 g kg~(-1). Efficacy (2,4-DB mobility in presence/mobility in absence of accelerators) increased with increasing concentrations of accelerators in CM or in reconstituted cuticular waxes. Plotting efficacy vs. accelerator concentration in the CM resulted in straight lines and slopes increased in the order DBS (0.14), DBSU (0.31), DES (0.51) and DESU (0.85). Hence, DESU was the most powerful accelerator in this series as it increased 2,4-DB mobility in the CM about 6 times more than DBSU. Waxes constitute the major barrier in plant cuticles and plots efficacy vs. accelerator concentration in Stephanotis wax were also linear, but compared to CM slopes were steeper by factors of 3.20 (DBS), 2.97 (DBSU), 2.70 (DES) and 1.62 (DESU). TBP was similarly effective as DESU, but plots efficacy vs. concentration were not linear and curves approached a plateau at 60 to 80 g kg~(-1). These data are discussed with regard to suitability of these accelerators for formulating systemic pesticides.