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

5.3 Cuticular Penetration of Electrolytes 141
Relative rate constant (%)
100
90
80
70
60
50
40
30
20
10
0
betaine
CaCl 2
proline
K-glyphosate
70
putrescine
80
Ca-glyphosate
Humidity (%)
Fig. 5.11 Permeability of Populus canescens CM to selected organic ions and to CaCl2 as affected
by humidity and POD. Donor solutions contained 0.2gl −1 Glucopon 215 CSUP as wetting agent;
solute concentration was 5gl −1 and temperature 20 ◦ C. Maximum rate constants at 100% humidity
were 0.99h −1 (putrescine), 0.66h −1 (CaCl2,, proline and betaine) and 0.33h −1 (IPA-glyphosate).
(Redrawn from Schönherr 2006, and Schönherr and Schreiber 2004a, b)
log Rate constant (h −1 )
−0.2
−0.4
−0.6
−0.8
−1.0
−1.2
−1.4
−1.6
Ca-chloride
K-GLY
y = −3.63 x 10 −3 x −0.16 (r 2 = 0.97)
Molar volume (cm3 −1.8
50 100 150 200 250 300 350 400
/mol)
90
14 C
45 Ca
Fig. 5.12 Effect of molar volume of selected ionic compounds on rate constants of penetration
across Populus canescens CM at 20 ◦ C and 100% humidity. Donor solutions contained 5gl −1
solutes and 0.2gl −1 Glucopon 215 CSUP as wetting agent. The same set of CM was used for
all experiments, and duplicate determinations were made with all compounds. The calcium salt of
glyphosate was labelled either as 45 Ca-glyphosate and or as Ca- 14 C-glyphosate. The slope of the
regression line is 3.63 × 10 −3 molcm −3 (Schönherr and Schreiber 2004a)
Ca-GLY
100
Ca-Gluconate