Water and Solute Permeability of Plant Cuticles: Measurement and ...

222 7 Accelerators Increase Solute Permeability of Cuticles
Effect (D/D control)
100
80
60
40
20
SA
2,4-D
MET
TRI
TB
C 8E 4
C 12E 8
0
0 10 20 30 40 50 60
1/D control . 10 −16 (m 2 /s)
Fig. 7.12 Effects of the two accelerators octaethylene glycol monododecyl ether (C12E8; black
symbols) and tetraethylene glycol monooctyl ether (C8E 4; red symbols) on diffusion (D/Dcontrol)
of lipophilic solutes in barley wax. Salicylic acid (SA), 2,4-dichlorophenoxyacetic acid (2,4-D),
metribuzin (MET), triadimenol (TRI), tebuconazole (TB), bitertanol (BIT). Data redrawn from
Burghardt et al. (1998)
7.4 Effects of Plasticisers on Transport in Cuticles
In the field, spray droplets containing both active ingredients and adjuvants are
sprayed on the foliage, and there they interact with the cuticles. Adjuvants affect
both driving force (partition coefficient) and solute mobility (Chap. 6). For example,
cuticle/water or wax/water partition coefficients of solutes can be greatly reduced
when solutes are dissolved in a neat adjuvant phase, and this reduces driving
force and rates of penetration (Schönherr and Baur 1994; Baur et al. 1997b, 1999;
Marzouk et al. 1998; Baur 1998; Buchholz 2006). This effect can partially or totally
mask a plasticising effect. In mechanistic studies with isolated cuticles, this problem
can be avoided by applying the solutes and the plasticisers to different sides of
the CM. The plasticiser to be studied can be directly used as desorption medium
in the receiver compartment facing the morphological outer surface of the CM.
The radio-labelled solute is applied to the inner surface of the CM (Sect. 6.4). With
surfactants it is convenient to work at concentrations above the cmc as receiver
solutions. The plasticiser can penetrate into the CM, while at the same time solutes
which appear in the receiver are trapped in micelles (Schönherr et al. 2001).
BIT