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

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8.1 Sorption from Aqueous Solutions 237 partition coefficients was exclusively due to a temperature effect on solute activity in the aqueous phase, that is, on water solubility of 4-NP. With increasing temperature water solubility increased, and as a consequence partition coefficients decreased. Sorption in tomato fruit MX differed. Here, k ′ increased with temperature from about 5 to 14, showing that the number of available sorption sites increased with temperature. The plot k ′ vs T has plateaus at 7–22 ◦ C and 22–32 ◦ C. A gradual increase occurred between 22 and 47 ◦ C (Riederer and Schönherr 1986a). This indicates structural changes in the cutin matrix, and the step character can be interpreted as phase transitions which lead to a loosening of the polymer chains, with a concomitant increase in number of sorption sites. 8.1.2 Thermodynamics of Sorption Sorption in cuticles can be further characterised by Gibbs free energy (∆G) involved in transfer of 1 mol of 4-NP from the aqueous phase to the cuticle phase. ∆Gsorption = −RT lnK (8.3) ∆Gsorption is proportional to ln K, and since ln K is always >1, Gibbs free energy is always negative. This is expected for a spontaneous (exergonic) process. ∆Gsorption was largest at low internal concentrations (about −12 to −10kJ mol −1 ), and decreased with increasing internal 4-NP concentration to about −9 to −8kJ mol −1 . At low internal concentration, ∆Gsorption was larger with MX than with CM (Riederer and Schönherr 1986a). ∆Gsorption depends on heat of sorption (Hs) and entropy (Ss): Substituting (8.3) into (8.4) leads to ∆Gsorption = ∆Hs − T∆Ss lnK = ∆Hs RT + ∆Ss R (8.4) (8.5) Plotting ln K vs T −1 (in Kelvin) results in a straight line having the slope ∆Hs/R, and the y-intercept is ∆Ss/R. A large entropy is characteristic for sorption on solid substrates, which leads to a higher degree of order. For ∆Gsorption to be negative, the large T∆Ss term must be overcompensated by the heat of sorption (∆Hs). This was the case at all temperatures and concentrations (Riederer and Schönherr 1986a). With both species, a striking difference between CM and MX exists for the effect of sorbate concentration on ∆Hs. At low concentration the heat of sorption of CM was constant, and decreased only if the internal concentration exceeded 10 −2 mol kg −1 (Fig. 8.2a). Sorption sites in the CM seemed to be energetically homogeneous as long as the internal concentration was
238 8 Effects of Temperature on Sorption and Diffusion of Solutes and Penetration of Water a ∆H sorption (kJ/mol) b ∆S sorption (kJ mol −1 Kelvin −1 ) −15 −20 −25 −30 −35 −40 −45 −50 −20 −40 −60 −80 −100 −120 0.014 0.139 1.39 13.9 139 −4 CM Lycopersicon MX Ficus Internal concentration (g/kg) CM MX −3 −2 −1 0 log Internal concentration (mol/kg) Ficus MX Ficus CM Lycopersicon MX Lycopersicon CM ∆S = 3.78 x ∆H + 47.1(r 2 = 0.995) −140 −50 −45 −40 −35 −30 −25 −20 −15 ∆H sorption (kJ mol −1 ) Fig. 8.2 (a) Change in molar enthalpy due to transfer of 4-NP from the aqueous to the cuticle phase. ∆HS for various concentrations was calculated at 25 ◦ C. (b) Entropy–enthalpy relationship at 25 ◦ C and internal concentrations shown in (a)
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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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3.3 Partition Coefficients 59 The d
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Chapter 4 Water Permeability All te
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4.1 Water Permeability of Synthetic
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4.2 Isoelectric Points of Polymer M
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4.2 Isoelectric Points of Polymer M
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4.3 Ion Exchange Capacity 69 The hi
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4.3 Ion Exchange Capacity 71 has an
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4.3 Ion Exchange Capacity 73 Counte
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4.4 Water Vapour Sorption and Perme
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4.4 Water Vapour Sorption and Perme
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4.5 Diffusion and Viscous Transport
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4.6 Water Permeability of Isolated
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Problems 121 Our present knowledge
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Solutions 123 5. Ca 2+ , because se
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126 5 Penetration of Ionic Solutes
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146 6 Diffusion of Non-Electrolytes
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Page 196 and 197: 186 6 Diffusion of Non-Electrolytes
Page 216 and 217: 206 7 Accelerators Increase Solute
Page 242 and 243: Chapter 8 Effects of Temperature on
Page 244 and 245: 8.1 Sorption from Aqueous Solutions
Page 248 and 249: 8.2 Solute Mobility in Cuticles 239
Page 256 and 257: 8.3 Water Permeability in CM and MX
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Page 260 and 261: 8.4 Thermal Expansion of CM, MX, Cu
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Page 266 and 267: Problems 257 E D (kJ/mol) DH S (kJ/
Page 268 and 269: Chapter 9 General Methods, Sources
Page 270 and 271: 9.2 Testing Integrity of Isolated C
Page 272 and 273: 9.4 Distribution of Water and Solut
Page 274 and 275: 9.6 Cutin and Wax Analysis and Prep
Page 276 and 277: 9.7 Measuring Water Permeability 26
Page 278 and 279: 9.8 Measuring Solute Permeability 2
Page 284 and 285: 276 Appendix A Abbreviations (conti
Page 286 and 287: 278 Appendix A Symbols (continued)
Page 288 and 289: 280 Appendix B Physico-chemical pro
Page 290 and 291: Appendix C Index of Plants Botanica
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Page 294 and 295: 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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