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

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8.5 Water Permeability of Synthetic Polymers as Affected by Temperatures 253 a glassy/rubbery transition. At room temperatures, cutin has the consistence of chewing gum and it did not undergo a phase transition. It is in the rubbery state from the beginning. Citrus waxes associated with cutin exhibited a first-order phase transition at 38 ◦ C when CM were moist during DSC measurements (Eckl and Gruler 1980). The latent heat associated with this transition was small (0.4kJ kg −1 CM), and it is not clear if this transition is due to waxes or wax/cutin interactions. Reynhardt and Riederer (1991) also used DSC, but their samples were under dry nitrogen and temperature was increased at a rate of 10 ◦ C min −1 . This is 100 times faster than that of Eckl and Gruler, and it probably reduced resolution. Further, Eckl and Gruler (1980) did not find any phase transitions with CM and MX when samples were dry, and there are doubts that DSC with dry CM scanned at very high rates can produce useful data for interpreting water permeability of CM. With this meagre data base, the role of waxes in the kink of Arrhenius plots of Pw remains obscure. The absence of kinks in thermal expansion of cutin and their presence with CM and MX leaves little doubt that they are related to polysaccharides. Double refraction of cuticles is evidence that some of the polysaccharides are crystalline (Sect. 1.4.2), most probably cellulose. Unfortunately, we have no data as to the type of structural changes which occur in cellulose of cuticular origin between 35 and 50 ◦ C, and as to which role water plays in these changes. Crystal structure of cellulose involves intermolecular hydrogen bonds, and it is probable that water is involved in structural changes. This needs to be investigated, and before this has been done it is futile to speculate if the kinks seen in Arrhenius plots of water permeance reflect a glass/rubbery phase transition. 8.5 Water Permeability of Synthetic Polymers as Affected by Temperatures Water permeance depends on sorption and diffusion of water in the constituents of cuticular membranes. Neither sorption of water nor its diffusion in waxes or MX has been studied so far, and this prevents any thermodynamic analysis of water permeability of cuticles. In an attempt to overcome these limitations, Riederer (2006) studied permeance of isolated CM and assumed that all water diffuses in aqueous pores. No attempt was made to demonstrate the presence of aqueous pores in the CM studied. Enthalpy of sorption in CM was assumed to be identical to that measured for wetting of wood. Wood consists of lignin and cellulose, but lignin is not a constituent of cuticles. These assumptions are arbitrary and in conflict with current knowledge (Chap. 4). There can be no doubt that a large fraction of water diffuses across the cutin and waxy pathways. Due to the heterogeneity of cuticles, it is extremely difficult to actually measure diffusion and sorption in the constituents of cuticles such as waxes, cutin and polar polymers. In an attempt to better understand penetration of water across cuticles, we searched the literature for information obtained with homogeneous synthetic membranes.
254 8 Effects of Temperature on Sorption and Diffusion of Solutes and Penetration of Water 8.5.1 EP, ED and ∆HS Measured with Synthetic Polymers Doty et al. (1946) measured water vapour permeability of a number of synthetic polymers in the temperature range between zero and 60 ◦ C. PHg was calculated from the steady state increase in vapour pressure on the receiver side. We converted these PHg values to Pwv as explained in Chap. 3. Temperature effects were analysed using the Arrhenius equation (8.15). Water permeability of most polymers increased with temperature, but slopes of Arrhenius plots differ greatly (Fig. 8.8). All slopes are linear, and there are no kinks visible. Polystyrene has the highest permeability (Pwv), and between 25 and 45 ◦ C permeability was not affected by temperature. Polyvinylidene chloride has the lowest Pwv and the steepest Arrhenius slopes. Pwv varied among polymers by a factor of 440. EP varied from about zero (polystyrene) to 85kJ mol −1 (polyvinylidene chloride), and the pre-exponential factor log Po varied among polymers by orders of magnitude from 4 to −9 (m 2 s −1 ). There was a good(r 2 = 0.95) negative linear correlation between EP and log Pwv. The regression equation EP = −31.7 ×log Pwv −291 was calculated from the data in Fig. 8.8. A similar dependence was observed with plant CM, where Hedera helix had the lowest permeance and the highest EP (62kJ mol −1 ), while Forsythia and Vicia had the highest permeance and the lowest EP of 27kJ mol −1 (Schreiber 2001). log P wv (m 2 /s) -9.0 -9.5 -10.0 -10.5 -11.0 -11.5 Temperature (∞C) 60 50 40 30 21 13 5 -3 Polystyrene PVC-Ac PVC-Ac PVC -12.0 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 PE 1/T x 1000 (Kelvin -1 ) PE Rubber hydrochloride Polyvinylidene chloride Fig. 8.8 Arrhenius plots showing the effect of temperature on water vapour permeability (Pwv in m 2 s −1 ). Two lots of polyvinyl chloride-acetate copolymer (PVC-Ac) and polyethylene (PE) were used. PVC is polyvinyl chloride. Data from Doty et al. (1946) were re-calculated and re-plotted
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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 212 and 213: 202 6 Diffusion of Non-Electrolytes
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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 246 and 247: 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
Page 258 and 259: 8.3 Water Permeability in CM and MX
Page 260 and 261: 8.4 Thermal Expansion of CM, MX, Cu
Page 264 and 265: 8.5 Water Permeability of Synthetic
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
Page 292 and 293: References Abraham MH, McGowan JC (
Page 294 and 295: References 287 Doty PM, Aiken WH, M
Page 296 and 297: References 289 Kolattukudy P (2004)
Page 298 and 299: References 291 Sabljic A, Güsten H
Page 300 and 301: References 293 Schreiber L, Schönh
Page 302 and 303: Index 2,4-D, 46 2,4-Dichlorophenoxy
Page 304 and 305: Index 297 leaf disks, 130 leaf surf
Page 306: Index 299 water molar volume, 110 p
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