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

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138 5 Penetration of Ionic Solutes Molar volume (cm 3 /mol) 800 700 600 500 400 300 200 100 0 chloride propionate glutamate pantothenate heptaglutamate V x = 0.895 MW (r 2 = 0.90) 0 100 200 300 400 500 600 700 800 Molecular weight (g/mol) Fig. 5.9 Molar volumes (Vx) of a set of aliphatic and aromatic organic compounds plotted against their molecular weights (green circles). The slope (0.895) was used to estimate Vx of calcium salts (red squares) used in Fig. 5.10 log Rate constant −0.4 −0.6 −0.8 −1.0 −1.2 −1.4 −1.6 −1.8 Molar volume (cm 3 /mol) 0 100 200 300 400 500 600 700 800 1.8 Populus canescens Vicia faba, light Molecular weight (g/mol) Vicia faba, dark 0 100 200 300 400 500 600 700 800 Fig. 5.10 Effect of molecular weight (solid lines) or molar volumes (dashed lines) of salts on rate constants and half-times of penetration of Ca salts into adaxial epidermis of Vicia faba leaf disks and across CM of Populus canescens at 20 ◦ C and 100% humidity. (Redrawn from data of Schönherr and Schreiber 2004a, b and Schlegel et al. 2005) lactobionate 2.8 4.4 7.0 11 18 28 44 Half time (h)
5.3 Cuticular Penetration of Electrolytes 139 Table 5.1 Parameters of the regression lines shown in Fig. 5.10 and rate constant (k) calculated for salts having molar volumes of 100 or 500cm 3 mol −1 Species log k0(h −1 ) σ ′ (molcm −3 ) k(100) (h −1 ) k(500) (h −1 ) k(100) k(500) Vicia light (MW) −0.37 −1.15 × 10 −3 – – – Vicia light (Vx) −0.37 −1.28 × 10 −3 0.32 0.098 3.3 Vicia dark (MW) −0.63 −1.21 × 10 −3 – – – Vicia dark (Vx) −0.63 −1.35 × 10 −3 0.17 0.050 3.4 Populus (MW) −0.49 −2.11 × 10 −3 – – – Populus (Vx) −0.49 −2.34 × 10 −3 0.19 0.022 8.7 logk0 is the y-intercept, and σ ′ corresponds to the slope of the regression lines in Fig. 5.10 responsible for the difference in rate constants between broad bean and poplar. This is in accord with preferential penetration of berberine chloride at these sites (Fig. 5.1). Slopes and y-intercepts of the straight lines which quantify selectivity of poplar and broad bean cuticles (Fig. 5.10) have physical meaning. The y-intercepts are the log k0 values for a hypothetical compound of zero molecular weight or molar volume (cf. Sect. 6.3.2, subsection: “Variability of Solute Mobility with Size of Solutes”). The slopes (σ ′ ) of the lines characterise size selectivity. These parameters are summarised in Table 5.1. These k0-values characterise permeability of cuticles from different species and at different experimental conditions. With broad bean (dark) k0 is 0.23h −1 , while with poplar CM lacking stomata the k0 was 0.32h −1 . Since slopes also differ, the difference between species increases with molar volume of solutes (Fig. 5.10). Permeability of broad bean in light (k0 = 0.40h −1 ) was 1.7 times higher than in the dark. As was already pointed out, the difference indicates that cuticles over stomata are more permeable when stomata are open (cf. Fig. 6.13). As size selectivity was not affected by light, higher permeability appears to be due to an increased number of pores. Since k0-values mark permeability of a salt having zero molar volume or molecular weights, they are the same no matter which size variable is used in calculation. Slopes of the lines (σ ′ ) are negative, which implies that logk decreases by the factor σ ′ ×Vx. Size selectivity of aqueous pores was larger with poplar CM than with bean leaf cuticles. Size selectivity was not very pronounced, because increasing molar volume by a factor of 5 decreased rate constants by factors of only 3.3–8.6 (Table 5.1). Size selectivity of the lipophilic path (β ′ ) in cuticles has been studied [(6.21) and (6.23); Table 6.8] and was found to be the same with all species investigated. Average sized dependence β ′ is 9.5 × 10 −3 mol cm −3 . Thus, size discrimination of lipophilic solutes in the waxy pathway is 4–7.4 times larger than discrimination of ionic solutes in aqueous pores. Rate constants are proportional to permeance (2.26), and permeance depends on the diffusion coefficient, partition coefficient and on thickness of the membrane (2.18). For a given species, the thickness of the cuticle or the lengths of the aqueous
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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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188 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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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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