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

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174 6 Diffusion of Non-Electrolytes Fig. 6.12 Penetration units consisting of bean leaf disks (17 mm in diameter) and glass tubes (10 mm in diameter) attached with silicon rubber. The units were positioned on moist filter paper in Petri dishes which permitted studying the effect of light on rates of penetration (taken from Schönherr 1969) Amount penetrated (mol/cm 2 ) 6e-10 5e-10 4e-10 3e-10 2e-10 1e-10 light light LS+Tween 20 (45 x 10 -12 mol cm -2 h -1 ) LS(32 x 10 -12 mol cm -2 h -1 ) US+Tween 20 (15 x 10 -12 mol cm -2 h -1 ) US(9 x 10 -12 mol cm -2 h -1 ) 0 0 3 6 Time (h) 9 12 Fig. 6.13 Penetration of succinic acid-2,2-dimethylhydrazide (Alar) into primary leaves of kidney bean at 25 ◦ C. Donor concentration was 5×10 −4 mol l −1 and was buffered with citrate–phosphate buffer at pH 5. Upper (US) and lower (LS) leaf surfaces are marked on the plots. Fluorescent light (5.25mW m −2 ) was used when indicated and Tween 20 was added to the donor at 0.1%. Rates of penetration are given in parentheses on the plots. (Data taken from Schönherr and Bukovac 1978)
6.2 Steady State Penetration 175 effect on rates was shown to be caused by stomatal opening which increased permeability of cuticular ledges (Schönherr and Bukovac 1978). Alar is an electrolyte, and at pH 5 it is neutral because negative and positive charges are present in equal amounts (Schönherr and Bukovac 1972b). The role of stomata in foliar penetration of ionic compounds is treated comprehensively in Chap. 5. Alar penetration into bean leaves using the leaf disk method with attached wells is a good example to demonstrate the merits of the method. The main advantages are the facts that permeability of large leaves can be measured, and it is possible to test if permeability of lower and upper leaf surfaces differ. With submerged leaves this is not possible. Kirsch et al. (1997) have used this method to compare solute permeability of isolated CM with non-isolated cuticles (Sect. 6.5). It is a somewhat laborious undertaking, since sampling is destructive and when rates of penetration (that is the time course of penetration) are studied, different leaf disks must be used for each time interval. This increases variability, and a large number of leaf disks (25 and more) must be used for representative sampling and for testing linearity. We have shown above why this is absolutely essential. Autoradiography makes it possible to study distribution of radioactive labels, provided the leaves are freeze-dried quickly to avoid redistribution and metabolism. Autoradiographs of selected bean leaf disks show that in the presence of Tween 20 more succinic acid-2,2-dimethylhydrazide penetrated and radio-label was much more uniform (Fig. 6.14). Sometimes the label spread along the veins and reached the cut edges. In later experiments with CaCl2, this was avoided by placing the leaf disks on stainless steel washers rather than directly on moist filter paper (Fig. 5.4b). Permeances for non-ionised 2,4-D, salicylic acid and benzoic acid were measured using the upper, astomatous leaf surfaces or CM obtained from Prunus laurocerasus, Ginkgo biloba and Juglans regia leaves (Kirsch et al. 1997). With leaf disks and CM, penetration plots were linear and permeances could be calculated from slopes. Permeances measured with leaf disks and CM did not differ significantly with all three species and compounds. Clearly, enzymatic isolation of cuticles did not affect permeability of cuticles. Fig. 6.14 Autoradiographs of bean leaf disks after penetration of 14 C labelled succinic acid-2,2dimethylhydrazide (Alar) in light for 12 h. Penetration without (a) and with 0.1% Tween 20 (b) as wetting agent
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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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224 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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