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

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4.6 Water Permeability of Isolated Astomatous Cuticular Membranes 109 Water permeance (m/s) 0.0 Lycopersicon F Capsicum F Citrus Lycopersicon F Clivia Solanum F 1/ Holdup time x 6 (s −1 ) 20 40 60 80 100 120 140 1.6e-4 1.4e-4 1.2e-4 1.0e-4 8.0e-5 6.0e-5 4.0e-5 2.0e-5 Capsicum F Ficus Ficus Solanum F Clivia Pyrus Pyrus Hedera Citrus Hedera Schefflera Schefflera 0.10 0.15 0.20 0.25 0.30 0.35 1/Thickness (1/µm) 160 6e-14 0.40 5e-14 4e-14 3e-14 2e-14 1e-14 Fig. 4.20 Test for homogeneity of cuticular membranes. Pwv was plotted vs 1/ℓ (circles), and Dw was plotted vs 1/6 ×te (squares). (Data from Becker et al. 1986) plot Pwv vs 1/ℓ should have a slope of DwKwv (2.18), while a plot Dw vs 1/6 × te should have a slope equal to ℓ 2 (2.5). These plots are shown in Fig. 4.20. The two plots are not linear, and there is considerable scatter. Pwv is highest with tomato and pepper fruit CM, and no dependence on 1/ℓ is detectable. Similarly, no dependence of Dw on 1/6 × te can be seen. With leaf CM and Solanum fruit CM, data are clustered and no dependence of Pwv on thickness or Dw on hold-up time is detectable. It is obvious that no simple relationship between Pwv and Dw on total thickness of CM exists. Such a dependence can not really be expected, because extracting small amounts of waxes increases permeance by orders of magnitude, and the weight fraction of waxes in cuticles is by no means constant (Table 4.6). Furthermore, even MX membranes are not homogeneous (Sect. 1.4), and CM contain waxes in addition to polar polymers and cutin. Polar polymers form a separate phase (Sects. 4.5 and 4.6.2, subsection: “Effect of Partial Vapour Pressure (Humidity) on Permeability of CM”), while waxes occur in cutin and on the surface of the cuticles (Sect. 1.3). 4.6.3.2 Estimation of Dw from Diffusion of Lipophilic Neutral Molecules Alternatively, the diffusion coefficients of water in wax can be estimated from diffusion coefficients of neutral solutes in cuticular waxes. Diffusion coefficients of a series of 14 C-labelled non-electrolytes in cuticular wax of different species were 0 Diffusion coefficient (m 2 /s)
110 4 Water Permeability measured (for details see Sect. 6.5). Plotting the logarithm as a function of the molar volume, good linearity was obtained for the wax of the three species Prunus laurocerasus, Ginko biloba and Juglans regia (Kirsch et al. 1997). Thus, with the molar volume known, Dw in cuticular waxes of any of other compound can be estimated. Using the molar volume of water (18cm 3 mol −1 ) and the equations in Table 6.10, diffusion coefficients of 1.19 × 10 −16 m 2 s −1 , 1.60 × 10 −16 m 2 s −1 and 1.06 × 10 −16 m 2 s −1 can be calculated for the three species Prunus laurocerasus, Ginko biloba and Juglans regia respectively. These are fairly low values, and compared to Dw obtained from extrapolated hold-up times (Table 4.9) they are by 1–2 orders of magnitude lower. However, Dw values in Table 4.9 were calculated using the thickness of the CM and not the thickness of the wax layer. Assuming that cuticular wax forms the transport-limiting barrier of the CM and not the thickness of the CM itself, Dw of most of the species shown in Table 4.9 can be recalculated (Table 4.10) if wax coverage of the CM is known. The thickness of the wax layer is calculated dividing the wax amount per area by wax density (0.9gcm −3 ). Depending on the wax amounts used for calculating the thickness of the wax layer, this estimation of diffusion coefficients results in values for leaf CM ranging from 0.11 ×10 −16 (Citrus) to 56.6 × 10 −16 (Nerium). Dw calculated for Nerium leaf CM and fruit CM from tomato and pepper clearly differ from the other CM of the data set. The reasons are not known. Most of the estimated Dw are around 10 −16 m 2 s −1 , and this agrees fairly well with the Dw estimated from diffusion of organic non-electrolytes in reconstituted cuticular waxes. If Dw calculated for CM is much higher than Dw values in reconstituted wax, some water flow in aqueous pores Table 4.10 Estimated diffusion coefficients (Dw) of water in cuticular waxes calculated from extrapolated hold-up times of water permeation across the CM. Thickness of the wax layers were calculated from amounts of wax per unit area (coverage) Species te(s) a Wax coverage ℓ(µm) d Dw in wax e (µgcm −2 ) (m 2 s −1 ) e Leaf CM Clivia miniata 770 106 b –113 c 1.17–1.25 2.96 × 10 −16 –3.38 × 10 −16 Hedera helix 933 64 c –85 b 0.71–0.94 0.90 × 10 −16 –1.58 × 10 −16 Nerium oleander 960 381 c –514 b 4.23–5.71 31.1 × 10 −16 –56.6 × 10 −16 Ficus elastica 512 87 c –114 b 0.97–1.26 3.06 × 10 −16 –5.16 × 10 −16 Citrus aurantium 264 12 b –32 c 0.13–0.35 0.11 × 10 −16 –0.77 × 10 −16 Pyrus communis 550 133 b 1.44 6.28 × 10 −16 Fruit CM Solanum melongena 640 48 b 0.53 0.73 × 10 −16 Capsicum annuum 361 96 c –197 b 1.06–2.18 5.18 × 10 −16 –21.9 × 10 −16 Lycopersicon esculentum 215 54 c –152 b 0.60–1.69 2.79 × 10 −16 –22.1 × 10 −16 a Data from Becker et al. (1986) b Data from Riederer and Schönherr (1984) c Data from Schreiber and Riederer (1996a) d Wax coverage divided by wax density of 0.9gcm −3 e D calculated from (2.5)
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Water and Solute Permeability of Pl
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Professor Dr. Lukas Schreiber Ecoph
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vi Preface This is not a review abo
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Contents 1 Chemistry and Structure
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Contents xi 4.6.3 Diffusion Coeffic
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Contents xiii 7.4.2 Effects of Plas
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2 1 Chemistry and Structure of Cuti
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10 1 Chemistry and Structure of Cut
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Chapter 2 Quantitative Description
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2.1 Models for Analysing Mass Trans
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2.3 Steady State Diffusion Across a
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2.4 Steady State Diffusion of a Sol
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2.4 Steady State Diffusion of a Sol
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2.5 Diffusion Across a Membrane wit
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2.5 Diffusion Across a Membrane wit
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2.6 Determination of the Diffusion
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Solutions 51 2.7 Summary In this ch
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Chapter 3 Permeance, Diffusion and
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3.1 Units of Permeability 55 3.1.1
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3.1 Units of Permeability 57 identi
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Page 72 and 73: Chapter 4 Water Permeability All te
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Page 76 and 77: 4.2 Isoelectric Points of Polymer M
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Page 132 and 133: Problems 121 Our present knowledge
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Page 136 and 137: 126 5 Penetration of Ionic Solutes
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160 6 Diffusion of Non-Electrolytes
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206 7 Accelerators Increase Solute
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Chapter 8 Effects of Temperature on
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8.1 Sorption from Aqueous Solutions
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8.1 Sorption from Aqueous Solutions
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8.2 Solute Mobility in Cuticles 239
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8.3 Water Permeability in CM and MX
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8.3 Water Permeability in CM and MX
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8.4 Thermal Expansion of CM, MX, Cu
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8.5 Water Permeability of Synthetic
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8.5 Water Permeability of Synthetic
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Problems 257 E D (kJ/mol) DH S (kJ/
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Chapter 9 General Methods, Sources
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9.2 Testing Integrity of Isolated C
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9.4 Distribution of Water and Solut
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9.6 Cutin and Wax Analysis and Prep
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9.7 Measuring Water Permeability 26
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9.8 Measuring Solute Permeability 2
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276 Appendix A Abbreviations (conti
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278 Appendix A Symbols (continued)
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280 Appendix B Physico-chemical pro
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Appendix C Index of Plants Botanica
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References Abraham MH, McGowan JC (
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References 287 Doty PM, Aiken WH, M
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References 289 Kolattukudy P (2004)
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References 291 Sabljic A, Güsten H
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References 293 Schreiber L, Schönh
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Index 2,4-D, 46 2,4-Dichlorophenoxy
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Index 297 leaf disks, 130 leaf surf
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Index 299 water molar volume, 110 p
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