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

4.6 Water Permeability of Isolated Astomatous Cuticular Membranes 99
Table 4.7 Water permeance Pw of CM, diffusion coefficient DSA of stearic acid in reconstituted
wax, mass mcm of the CM, and mass mwax of the wax obtained from the investigation of 24 species.
(Data from Schreiber and Riederer 1996a, b)
Species Pw × 10 11 DSA × 10 19 mCM mWAX
(ms −1 ) (m 2 s −1 ) (µgcm −2 ) (µgcm −2 )
Leaf CM
Vanilla planifolia (vanilla) 1.7 12.3 359 122
Monstera deliciosa (breadfruit-vine) 4.3 25.8 808 242
Philodendron selloum 6.6 8.9 335 54
Ficus elastica (Assam rubber plant) 9.4 25.1 510 87
Ficus benjamina (Java fig) 13.0 29.3 306 64
Hedera helix (ivy) 5.70 2.7 337 114
Clivia miniata 15.7 36.0 1,020 285
Camellia sinensis (tea-plant) 10.8 8.1 252 11.8
Prunus laurocerasus (cherry laurel) 13.3 63.0 333 83
Nerium oleander (oleander) 52.2 55.7 664 113
Olea europaea (olive-tree) 12.6 59.8 661 88
Citrus aurantium (bitter orange) 12.8 38.3 369 32
Citrus limon (lemon) 47.0 77.9 1,373 381
Euonymus japonicus (evergreen e.) 35.8 70.0 403 64
Liriodendron tulipifera (tulip-poplar) 42.0 74.6 233 72
Juglans regia (English walnut) 45.8 99.8 125 27
Ginkgo biloba (ginkgo) 52.2 100.5 342 40
Cydonia oblongata (quince) 62.9 34.1 191 51
Ligustrum cf. vulgare (prim) 43.4 42.7 227 39
Forsythia suspensa (golden bells) 38.7 80.2 955 137
Maianthemum bifolium (false lilly-of-the 111.0 152.3 68 36
valley)
Fruit CM
Lycopersicon esculentum (tomato) 62.2 121.0 1,554 54
Capsicum annuum (bell-pepper) 134.5 222.3 2,162 96
Malus domestica (apple) 207.0 290.5 3,217 1,317
the measured value of 1.3 × 10 −10 ms −1 . Since the y-intercept lowers calculated
permeance, it is not related to water permeation in a hypothetical parallel aqueous
pathway. These data are consistent with model III A.
The good correlation between Pw of CM and DSA in reconstituted wax is
amazing, because permeance is a composite quantity and depends on mobility
and solubility of water in wax and thickness of the CM. According to (2.18),
Pw = Dw × Kww/ℓ, while DSA is a pure mobility parameter. In Chap. 2 we defined
ℓ as thickness of a membrane, while in reality the lengths of the diffusion path can
be much larger due to the tortuosity factor τ. Thus, linearity implies that Kww/ℓτ is
equal to the slope of 6.6 × 10 7 m −1 , which is the same with all species. However,
Kww and ℓτ are likely to vary independently among species, and it is not very likely
that they are the same for all species. High permeance could be the consequence
of large Kww or a short diffusion path, that is, thin CM and low τ. Cuticular wax
is composed of crystalline and amorphous fractions (Reynhardt and Riederer 1991;
1994), and both sorption and diffusion of water should exclusively take place in