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

4.6 Water Permeability of Isolated Astomatous Cuticular Membranes 93
Since the effect of partial vapour pressure on permeance of cutin is probably small,
the wax-incrusted cutin may not respond at all to partial pressure of water vapour. In
this case, water vapour pressure would mainly affect permeance of the polar polymer
phase. This aspect is treated more comprehensively in the following section.
4.6 Water Permeability of Isolated Astomatous Cuticular
Membranes
4.6.1 Comparing Water Permeability of CM with that of MX
Cuticles are composed of a polymer matrix (Sect. 1.1) and various amounts of intraand
epicuticular waxes (Sect. 1.2). Permeances (Pw) of Citrus and pear CM are 8.3×
10 −10 and 4.9 × 10 −10 ms −1 respectively (Table 4.6). Jeffree (2006) has classified
these as Type 3 cuticles, which have an amorphous cuticle proper of low electron
density but lacking lamellae. The other species in Table 4.6 have a lamellated CP,
and Pw was lower and ranged from 1 to 3.2 × 10 −10 ms −1 .
Extracting cuticular waxes increased permeance by factors of 142–2,031 which
demonstrates that waxes play a major role in water permeability of CM. Inspection
of Table 4.6 shows that wax amounts, permeance and effect of extraction are
not correlated. A similar observation was made by Buchholz (2006), who reported
mobility of the lipophilic solute bifenox in CM from 22 different species. Mobility
was not related to thickness of CM or amounts of wax. The onion bulb scale cuticle
is about 1µm thick or less, and only 1µgcm −2 of wax could be extracted from these
thin cuticles. The waxes consisted mainly of C31 and C33 n-alkanes (together 79%
of total) and C44 and C46 n-alkyl esters (18% of total wax). The effect of extraction
of waxes on Pw of onion bulb scales is mainly due to the relatively high Pw of the
Table 4.6 Effect of extraction of waxes on water permeance at 25 ◦ C of astomatous isolated
cuticular membranes from leaves (L) or bulb scales (BS)
P(MX)
Species Pw (CM) Pw (MX) P(CM) Wax mass CM mass
(ms−1 ) (ms−1 ) (µgcm−2 ) (µgcm−2 )
Citrus aurantium L a 8.3 × 10 −10 1.6 × 10 −7 193 12 d 316 f
Pyrus communis L a 4.9 × 10 −10 1.1 × 10 −7 224 133 e 343 f
Allium cepa BS b 3.2 × 10 −10 6.5 × 10 −7 2,031 1 b 110 b
Clivia miniata L c 1.2 × 10 −10 1.7 × 10 −8 142 113 d 715 f
Hedera helix L a 1.0 × 10 −10 2.7 × 10 −8 270 64 d 476 f
a Schönherr and Lendzian (1981)
b Schönherr and Mérida (1981)
c Schmidt et al. (1981)
d Schreiber and Riederer (1996a)
e Riederer and Schönherr (1984)
f Becker et al. (1986)