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

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136 5 Penetration of Ionic Solutes −ln (1−M t /M o ) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Populus 0.0 0 0 20 40 60 80 100 Time (h) Stephanotis Schefflera Pyrus Malus Fig. 5.8 Penetration of CaCl2 across astomatous CM isolated from Populus canescens, Pyrus communis, Malus domestica, Stephanotis floribunda and Schefflera actinophylla leaves. A 5-µl donor droplet containing 5gl −1 45 CaCl2 and 0.2 Glucopon 215 CSUP as wetting agent was applied to the outer surface of the CM and after droplet drying, penetration of CaCl2 was measured at 20 ◦ C and 90% humidity. Error bars are 95% confidence intervals. (Redrawn from Schönherr 2000) 5.3.3 Rate Constants Measured with Leaf CM from Different Species Rate constants for CaCl2 penetration differed considerably among species, and not all penetration plots were linear to the end (Fig. 5.8), but linearity was maintained until about 80% of the dose had penetrated. Populus CM (grey poplar) had the highest rate constants (8.4 × 10 −2 h −1 ), whereas lowest k (1.4 × 10 −2 h −1 ) were measured with Schefflera. This corresponds to a factor of 6 between the two species, with lowest and highest permeability for CaCl2. This shows that aqueous pores occur in CM of all of these species tested, but they may differ in number and/or size. These rate constants measured with CaCl2 may be compared with water permeance (Pw) in Table 4.8. Pw of poplar CM (26.8 × 10 −10 ms −1 ) was 5.7 times higher than Pw of Stephanotis CM (4.7 × 10 −10 ms −1 ). For rate constants of CaCl2 penetration, this ratio is only 2.9. This difference might be related to the fact that water also diffuses across the waxy pathway, which is excluded for CaCl2. Too much should not be made of this comparison, however, because different lots of CM were used for estimating Pw and k for CaCl2. Another factor should be pointed out which is not visible in Fig. 5.8. Reproducible data and reasonably short error bars are obtained only with very large sample sizes of 50–100 CM. Rate constants measured with individual CM vary greatly, and in each population cuticles occurred which were practically imperme- 98 97 95 92 87 78 63 39 Percent penetrated
5.3 Cuticular Penetration of Electrolytes 137 able. There are indications that frequency of aqueous pores in cuticles decreases during leaf expansion and maturation. Permeability to an Fe-chelate of Vitis vinifera and Prunus persica leaves decreased dramatically during leaf expansion (Schlegel et al. 2006). The upper astomatous leaf cuticle of poplar leaves can be isolated only from leaves which are just fully expanded. With these leaves, relatively high rate constants were measured for CaCl2, while permeability of the upper cuticle of older leaves is almost zero (unpublished data). These two facts indicate a considerable dynamic in development of aqueous pores and their closure in older leaves. 5.3.4 Size Selectivity of Aqueous Pores Citrus MX membranes were almost impermeable to raffinose (Fig. 4.9), having a molecular radius of 0.65 nm. The pentahydrate of raffinose has a molecular weight of 595gmol −1 . Estimates of pore radii of other species are not available. Cuticles over anticlinal walls and in cuticular ledges are permeable to berberine sulphate, which has a molecular weight of 769gmol −1 . In Sect. 4.5 we argued that diffusion of solutes in aqueous pores is increasingly hindered as solute size approaches pore size. Size selectivity of aqueous pores in grey poplar CM (Schönherr and Schreiber 2004b) and Vicia faba leaf disks (Schlegel et al. 2005) has been studied using calcium salts ranging in molecular weights from 111 to 755gmol −1 . Anhydrous molecular weight was used in the original literature, since the hydration numbers of these salts were not known. Size selectivity of the lipophilic or waxy pathway has been characterised using equivalent molar volumes (Vx) calculated according to McGowan and Mellors (1986). When size selectivity of aqueous pores and of the waxy pathway are to be compared, the same variable for size should be used. Vx of calcium salts was estimated based on a plot Vx vs molecular weight (Fig. 5.9). The training set was composed of aliphatic and aromatic organic molecules containing C, O and H atoms. With this set, Vx was smaller than the molecular weight by a factor of 0.895. This factor was used to estimate Vx of calcium salts (squares). A direct calculation of Vx was not possible since the equivalent molar volume of Ca 2+ was not available. Rate constants of penetration decreased with increasing molecular weight of the Ca 2+ salts (Fig. 5.10), showing again coupling of cation and anion fluxes. Each divalent calcium ion must be accompanied by two monovalent anions. Aqueous pores in all cuticles were large enough to accommodate Ca-lactobionate having a molecular weight of 755gmol −1 . A good linear correlation was obtained when logk was plotted against molecular weights (solid lines) or molar volumes (dashed lines). With Populus CM, rate constants decreased from 0.199 to 0.0285h −1 when molecular weight increased from 100 to 500gmol −1 . Rate constants measured with Vicia leaf disks were higher in light than in the dark, but slopes were similar. Broad bean leaves have stomata and glandular trichomes on both leaf surfaces, while poplar adaxial CM are astomatous and at the time of isolation unicellular trichomes have already all been shed. The cuticle over guard cells and glandular trichomes is probably
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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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Page 136 and 137: 126 5 Penetration of Ionic Solutes
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186 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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Water and Solute Permeability of Plant Cuticles: Measurement and ...

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