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

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176 6 Diffusion of Non-Electrolytes 6.3 Diffusion with Changing Donor Concentrations: The Transient State Permeance (P) is a composite property (2.18). It is proportional to solubility (K) and mobility (D) of water and solutes in membrane, and inversely proportional to thickness of the membrane (ℓ). In homogeneous membranes, solute permeability is characterised using D and K because they are easily measured. Cuticles are highly asymmetrical (Sect. 1.4), and both water concentration and mobility vary with position (Chap. 4). Water transport occurs in aqueous pores, cutin and waxes, and their mutual arrangements determine water permeability. The question arises whether this also applies to solutes. In Sect. 6.2 we used permeances to characterise solute permeability, which can be measured easily in the steady state using various methods. Unfortunately, since P is a mixed quantity it is not possible to explain why permeances differ among cuticles from different species. In an attempt to obtain a better understanding of solute permeability in cuticles, we have developed methods to estimate solute mobility in CM, MX and in waxes. 6.3.1 Simultaneous Bilateral Desorption Diffusion coefficients can be estimated from sorption and desorption experiments (Sect. 2.6). We have used this approach to measure mobility of lipophilic 2,4-D in CM and MX membranes. Astomatous CM and MX membranes obtained from leaves and fruits were submerged in aqueous buffer (pH 3) containing 14 C-labelled 2,4-D. After equilibration they were removed from the buffer, blotted dry, flattened on a piece of Teflon and air-dried. Dry membranes were inserted between the two half-cells of a transport apparatus made of stainless steel (Fig. 9.4). This made it possible to desorb 2,4-D separately from the outer and inner surfaces of the membranes. Borax buffer (pH 9.18), in which 2,4-D is fully ionised, was used as desorption medium. By changing desorption media quickly and repeatedly, the amounts of 2,4-D desorbed at various times (Mt) were studied. Desorption was very rapid, and 90% of the 2,4-D initially contained in the CM and MX membranes were desorbed in 4 h (Fig. 6.15a). With a homogeneous membrane, 50% of solute should be desorbed from either side and the two desorption plots should be symmetrical. This was clearly not the case, neither with CM and MX. Only very small amounts (5%) were desorbed from the morphological outer surfaces of the Citrus CM, while 17% could be desorbed from the outer surface of the MX membranes. The largest fraction of 2,4-D was desorbed from the inner surface, as in 240 min 86% (CM) and 71% (MX) left the membranes through the morphological inner surfaces. Clearly, these membranes are highly asymmetrical, and this asymmetry can be characterised by comparing the initial rates of desorption from the inner and outer surfaces respectively. During the first 3 min, 163 times more 2,4-D was desorbed from the inner surface of the CM than from the outer. With
6.3 Diffusion with Changing Donor Concentrations: The Transient State 177 a M t/M o b M t/M o 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 0 CM inside MX inside CM outside MX outside 50 100 Time (min) 150 200 250 CM inside MX inside MX outside CM outside 0 20 40 60 80 100 120 (Time) 1/2 (s) 1/2 Fig. 6.15 Simultaneous bilateral desorption of 2,4-D from CM and MX membranes of Citrus aurantium leaves. The membranes had been preloaded with 14 C-2,4-D, and were desorbed at 25 ◦ C with borax buffer having a pH of 9.18. M0 is the amount of 2,4-D initially contained in the membrane and Mt is the amount desorbed at time t. In (a) Mt/M0 is plotted vs time, while in (b) it was plotted vs the square root of time. (Redrawn from Schönherr and Riederer 1988)
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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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226 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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