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

5.3 Cuticular Penetration of Electrolytes 133
5.3 Cuticular Penetration of Electrolytes
5.3.1 Effect of Wetting Agents
Leaf surfaces are difficult to wet by water, and good contact of donor solutions
with the waxy surface of the CM is essential. Rates of salt penetration could be
significantly increased by adding small amounts of surfactants, which decrease surface
tension (Fig. 5.6). Plantacare 1200P, APG 325 and Glucopon 215 CSUP are
alkyl polyglucosides (Henkel, Düsseldorf, Germany). Average degree of polymerisation
of glucose is about 1.4–1.5, and fatty alcohols linked to the sugar moieties
have 8–14 carbon atoms. These surfactants have a good ecotoxicological profile,
and phytotoxicity has not been observed.
At a concentration of 0.2gl −1 , surface tension was reduced from 72 to
30–32mNm −1 , and rate constants were increased by a factor of 12. There was no
difference among the three surfactants. The wetting agent Glucopon 215 CSUP at a
concentration of 0.2gl −1 was used in all subsequent experiments with CM and leaf
disks.
Similar experiments were conducted using poplar CM and the isopropylamine
(IPA) salt of glyphosate. In the control experiment, 0.2gl −1 of Glucopon 215 CSUP
was added as wetting agent, and the rate constant was about 0.1h −1 . If accelerator
− ln (1 −M t/M o)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
APG 325
Plantacare 1200 P
0
0 20 40 60 80 100
Time (h)
Glucopon 215 CSUP
no surfactant
Fig. 5.6 Effects of wetting agents (0.2gl −1 ) on rates of penetration of CaCl2 across astomatous
isolated CM of Pyrus communis leaves. A 5-µl drop containing 6gl −1 of 45 CaCl2 was added to the
surface of the CM, and after drying, penetration was measured at 20 ◦ C and 90% humidity. Error
bars are 95% confidence intervals. The same set of 100 CM was used as control (no surfactant) and
with surfactants. (Redrawn from Schönherr 2001)
98
97
95
92
87
78
63
39
Percentage penetrated