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

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8.4 Thermal Expansion of CM, MX, Cutin and Waxes 251 This again points to a change in structure of the MX rather than to an effect of temperature on structure of waxes. Schreiber and Schönherr (1990) took a closer look at thermal expansion of CM, MX and cutin. 8.4 Thermal Expansion of CM, MX, Cutin and Waxes Thermal expansion was measured by stuffing wet cuticular materials in a specific gravity bottle (1cm 3 ), and after exhaustive aspiration to remove all air bubbles from cuticles and water the bottle was closed with a very fine calibrated capillary. Gravity bottle and capillary, with the exception of its tip, were submerged in a water bath at constant temperature (±0.01 ◦ C). The bath temperature was raised from 5 to 65 ◦ C at a rate of 0.25 ◦ C min −1 , and the position of the meniscus in the capillary was continuously read using a travelling microscope (cathetometer). From the total volume expansion, the volume of the cuticular materials was calculated by subtracting the volume of the water in the bottle. Specific volume (cm 3 kg −1 ) was plotted vs temperature, and the volume expansion coefficient (cm 3 kg −1 K −1 ) was calculated from the slope of the plots. Total volume expansion in the range of 5–65 ◦ C of Ficus, Capsicum (fruit) and Citrus increased in the order CM < MX < cutin. Plots for cutin from Ficus, Citrus and Capsicum (fruit) were linear over the entire temperature range. Phase transitions were observed only with CM and MX. With Ficus and Citrus CM, two phase transitions were detected in the range of 17–20 ◦ C and 42–50 ◦ C. All other CM and MX investigated had only one phase transition between 40 and 55 ◦ C (Table 8.1). Table 8.1 Thermal expansion coefficients for the temperature range 25–65 ◦ C Polymer PTT Volume expansion coefficient (cm 3 kg −1 K −1 ) ◦ C below 42 ◦ C above 42 ◦ C above/below Citrus CM 17 and 42 0.53 0.74 1.40 Citrus MX 21 and 44 0.50 0.65 1.30 Citrus cutin none 0.95 – 1.0 Ficus CM 18 and 50 0.55 0.95 1.73 Ficus cutin none 0.96 Capsicum CM 42 0.56 0.60 1.07 Capsicum cutin none 0.82 – 1.0 Lycopersicon CM 46 0.57 0.69 1.21 Pyrus CM 46 0.62 1.41 2.27 Nerium CM 39 0.39 0.62 1.59 Olea CM 55 0.45 0.70 1.56 PEMA a 65 0.275 0.27 0.98 Polyvinylacetat a 32 0.24 0.45 1.88 PVA-Cl copolymer a 30 0.20 0.24 1.20 PETP amorph a 67 0.19 0.80 4.21 PTT is the phase transition temperature a Taken from Stannett and Williams (1965). All other data from Schreiber and Schönherr (1990)
252 8 Effects of Temperature on Sorption and Diffusion of Solutes and Penetration of Water Volume expansion coefficients were always larger by a factor of 1.07–2.27 above the phase transition. Expansion coefficients of cutin were much larger than with CM and MX. Volume expansion of cutin is linear in the range of 5–65 ◦ C, hence it cannot be responsible for the phase transition observed with CM and MX. Volume expansion was larger with MX than CM, but the difference is related to the fraction of wax contained in the CM. Correcting for the wax fraction, volume expansion of CM is the same as that of MX. Volume expansion of MX is the sum of expansion of its components cutin and polar polymers. Expansion coefficients of cutin are much higher than those for MX (Table 8.1), and it follows that volume expansion of MX is hindered by polar polymers, probably by embedded cellulose. Volume expansion of cuticular waxes was not measured. Rosenberg and Brotz (1957) measured volume expansion of natural and synthetic waxes, and found them to be linear. Relative expansion was 0.057% per ◦ C, which is lower than that for Citrus MX (0.074% per ◦ C above 45 ◦ C) and cutin (0.098% per ◦ C) measured by Schreiber and Schönherr (1990). Relative expansion of crystalline cellulose is 0.057% per ◦ C (Banderup and Immergut 1966), which is also lower than expansion of MX and cutin. These data indicate that the kinks observed in Arrhenius plots of water permeance (ln Pw vs. T −1 ) may have been caused by strains arising from different expansion of waxes, cutin and polar polymers in MX. Volume expansion of amorphous and crystalline waxes could not keep pace with that of cutin and MX, and this induced micro-defects in the wax. These cracks are new pathways for diffusion and water, and permeance increases much more rapidly than below 40 ◦ C. No kinks were observed with Citrus MX membranes, because in these membranes waxes are absent and new defects cannot arise at higher temperatures. The convex curvature of the Arrhenius graphs at high temperatures (Fig. 8.6) could have been caused by reduced sorption of water in cutin and polar polymers (Sect. 8.5). Cracks in paraffin wax films formed by sudden cooling led to relatively high water permeability, but these cracks disappeared during storage and water permeability decreased significantly (Table 4.12). Water permeance of freshly isolated CM from Citrus leaves decreased by factors of two to three during storage (Geyer and Schönherr 1990). Water permeance of Citrus CM at 25 ◦ C increased upon heating to 65 ◦ C, and after subsequent cooling to 25 ◦ C, Pw was larger by a factor of 2.8 than before heating (Schreiber and Schönherr 2001), indicating that wax structure differed after re-solidification. When these CM were stored for 100 days in the dry form, permeance was greatly reduced and nearly reached permeances measured before heating. These results very much resemble those observed with paraffin waxes, and demonstrate the capacity of waxes to change structure when stored at room temperature. Reduction in free energy probably is the driving force for these structural changes (Fox 1958). Four synthetic polymers are included in Table 8.1. Their thermal expansion coefficients are a little smaller below the PTT, while above the PTT expansion coefficients are similar as with CM. The phase transition temperatures given for the synthetic polymers refer to a transition from the glassy to the rubbery state, and this poses the question as to whether the transition observed with CM also represent
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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 210 and 211: 200 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 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 262 and 263: 8.5 Water Permeability of Synthetic
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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