Table Of ContentWater and Solute Permeability of Plant Cuticles
Lukas Schreiber (cid:129) Jörg Schönherr
Water and Solute Permeability
of Plant Cuticles
Measurement and Data Analysis
123
ProfessorDr.LukasSchreiber Dr.JörgSchönherr
EcophysiologyofPlants Rübeland6
InstituteofCellular 29308Winsen-Bannetze
andMolecularBotany(IZMB) Germany
UniversityofBonn [email protected]
Kirschallee1
53115Bonn
Germany
[email protected]
ISBN978-3-540-68944-7 e-ISBN978-3-540-68945-4
LibraryofCongressControlNumber:2008933369
(cid:2)c 2009Springer-VerlagBerlinHeidelberg
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Preface
Transport properties of plant cuticles are important for different fields of modern
plant sciences. Ecologists and physiologists are interested in water losses to the
environment via the cuticle. Penetration of plant protecting agents and nutrients
into leaves and fruits is relevant for research in agriculture and plant protection.
Ecotoxicologists need to know the amounts of environmental xenobiotics which
accumulateinleavesandotherprimaryplantorgansfromtheenvironment.Forall
ofthesestudiessuitablemethodsshouldbeused,andasoundtheoreticalbasishelps
to formulate testable hypotheses and to interpret experimental data. Unnecessary
experimentsandexperimentswhichyieldambiguousresultscanbeavoided.
In this monograph, we have analysed on a molecular basis the movement of
moleculesacrossplantcuticles.Basedoncurrentknowledgeofchemistryandstruc-
ture of cuticles, we have characterised the aqueous and lipophilic pathways, the
nature and mechanisms of mass transport and the factors controlling the rate of
movement.Wehavefocusedonstructure–propertyrelationshipsforpenetranttrans-
port,whichcanexplainwhywaterandsolutepermeabilitiesofcuticlesdifferwidely
amongplantspecies.Basedonthisknowledge,mechanismsofadaptationtoenvi-
ronmentalfactorscanbebetterunderstood,andratesofcuticularpenetrationcanbe
optimisedbyplantphysiologistsandpesticidechemists.
Thismonographisamechanisticanalysisoffoliarpenetration.Wehavemadeno
attempttoreviewandsummarisedataonfoliarpenetrationofspecificsolutesinto
leavesofspecificplantspeciesunderaspecificsetofenvironmentalconditions.A
numberofreviewscanbeconsultedifthisisofinterest(Cottrell1987;Cutleretal.
1982;Hollowayetal.1994;Kerstiens1996a;RiedererandMüller2006).Awealth
ofadditionalliteratureiscitedinthesebooks.
Once synthesised, the plant cuticle is a purely extra-cellular membrane, and
metabolism or active transport which greatly affect transport across cytoplasmic
membranesare notinvolvedin cuticularpenetration.For thisreason, a numberof
booksonsorptionanddiffusioninman-madepolymericmembranesweresources
ofinspirationinwritingthismonograph.Wedrewheavilyontheclassicalbooksby
Crank(1975),CrankandPark(1968),Israelachvili(1991)andVieth(1991).
v
vi Preface
Thisisnotareviewaboutfoliarpenetration.Weaimedatwritingageneraltext-
bookonsorptionanddiffusionincuticles.Basedoncharacteristicandrepresentative
examples we show (1) how problems related to water and solute transport across
cuticlescanexperimentallybeapproachedusingsuitablemethodsdevelopedinthe
past,(2)thewayinwhichthesedatacanbeanalysed,andwhatwecanlearnfrom
these resultsaboutstructureandfunctioningofcuticles, andfinally(3)the limita-
tionsandproblemsindatainterpretation.Attheendofeachchapter,problemsand
solutionscan be found.Some of them summarise the highlightsof the text, some
illustrateimplicationsandothersareintendedasexercisesofcalculations.
Theideaofanalysingpermeabilityofcuticlesbasedonstructure–propertyrela-
tionships was born during a stay (1967–1972) by one of us (JS) as a doctoral
studentinBukovac’slaboratoryatMichiganStateUniversity,USA.Later,thecon-
ceptsdevelopedinthetwovolumesbyHartleyandGraham-Bryce(1980)wereof
immense help to us in formulatingtestable hypotheses.In writing, we have relied
greatlyon ourown work conductedat the Botany departmentsof the Universities
of München,Bonnand Hannover,butthe bookcouldnothave beenwritten with-
out the collaborative research in the last decades with M. Riederer (University of
Würzburg), K. Lendzian (Technische Universität München), B.T. Grayson (Shell,
Sittingbourne, England), P. Baur (now Bayer Crop Science) and Anke Buchholz
(nowSyngenta,Switzerland).
Itwasoneofouraimstoprovideabetterunderstandingofcuticularpenetration,
and to formulate some basic rules for predicting and optimising rates of cuticular
penetration. This requires some elementary mathematics, but we have kept equa-
tions simple and calculus is not required to follow our arguments or to solve the
problems. Some basic knowledge of chemistry and physics are helpful but not
mandatory.WehopethisbookwillbeusefultoMasteranddoctoralstudentswork-
ing in different fields of plant sciences (ecology, physiology, molecular biology,
ecotoxicology,plantnutrition,horticulture,pesticide science andplantprotection)
whenfacedforthefirsttimewithproblemsrelatedtopermeabilityofplantcuticles
to water and solutes. Researchers at universities, applied research institutions and
those in the agrochemical industry working on transport across cuticles will find
numeroususeful hints. This book was written as a text book and can be used for
teaching,sinceineachchapter(1)westatetheproblem,(2)wedescribeanexperi-
mentalsolution,(3)wepresentacriticalanalysisoftheexperimentaldata,and(4)at
theendofeachchapterwe addproblemsintendedtohelpthestudentinverifying
understandingofconceptsandcalculations.
Germany LukasSchreiber
November2008 JörgSchönherr
Acknowledgements
WegratefullyacknowledgereadingofpreliminarychaptersbyDr.AnkeBuchholz,
Dr. Andrea Faust, Dr. Rochus Franke, Dr. Klaus Lendzian, Dr. Jurith Montag,
Dr. Kosala Ranathunge and Dr. Jiri Santrucek. Their corrections and suggestions
wereofimmensehelp,andsubstantiallyimprovedthefinalversionofthisbook.
We are thankful to Sylvia Eifinger for preparing the drawings of models and
experimentalequipments.
Oneofus(LS)isindebtedtotheUniversityofBonnandtheFacultyofMathe-
maticsandNaturalSciencesforgrantingasabbaticalleaveduringthewinterterm
2007/2008forwritingthisbook.
We also acknowledge with gratitude constant support and help by Dr. Jutta
Lindenborn,Dr.ChristinaEckeyandDr.DieterCzeschlikfromSpringerVerlag.
Finally, we thank our families for their understanding and patience during the
writingandpreparationofthisbook.
vii
Contents
1 ChemistryandStructureofCuticlesasRelatedtoWaterandSolute
Permeability................................................... 1
1.1 PolymerMatrix ............................................ 2
1.2 CutinComposition ......................................... 3
1.3 SolubleCuticularLipids..................................... 8
1.3.1 ExtractionandClassificationofWaxes .................. 8
1.3.2 ChemistryofWaxes.................................. 10
1.3.3 SpecialAspectsofWaxAnalysis ....................... 11
1.4 FineStructureofCuticles.................................... 14
1.4.1 Nomenclature ....................................... 15
1.4.2 TransversalHeterogeneity............................. 15
1.4.2.1 LightMicroscopy............................ 15
1.4.2.2 ScanningElectronMicroscopy................. 18
1.4.2.3 TransmissionElectronMicroscopy ............. 20
1.4.3 CuticleSynthesis .................................... 26
1.4.4 LateralHeterogeneity................................. 27
Problems ...................................................... 27
Solutions ...................................................... 28
2 QuantitativeDescriptionofMassTransfer ........................ 31
2.1 ModelsforAnalysingMassTransfer .......................... 32
2.1.1 Model1 ............................................ 33
2.1.2 Model2 ............................................ 35
2.1.3 Model3 ............................................ 37
2.1.4 ConductanceandResistance........................... 37
2.2 SteadyStateDiffusionAcrossaStagnantWaterFilm ............ 38
2.3 SteadyStateDiffusionAcrossaStagnantWaterFilmObstructed
byCelluloseandPectin ..................................... 39
2.4 SteadyStateDiffusionofaSoluteAcrossaDense
Non-PorousMembrane...................................... 40
2.4.1 TheExperiment ..................................... 43
ix
x Contents
2.5 DiffusionAcrossaMembranewithChangingConcentrations ..... 45
2.5.1 TheExperiment ..................................... 46
2.6 Determination of the Diffusion Coefficient from Sorption
orDesorptionKinetics ...................................... 48
2.6.1 TheExperiment ..................................... 49
2.7 Summary ................................................. 51
Problems ...................................................... 51
Solutions ...................................................... 51
3 Permeance,DiffusionandPartitionCoefficients:UnitsandTheir
Conversion .................................................... 53
3.1 UnitsofPermeability ....................................... 53
3.1.1 Example............................................ 55
3.2 DiffusionCoefficients....................................... 58
3.3 PartitionCoefficients........................................ 58
Problems ...................................................... 60
Solutions ...................................................... 60
4 WaterPermeability............................................. 61
4.1 WaterPermeabilityofSyntheticPolymerMembranesandPolymer
MatrixMembranes:AComparisonofBarrierProperties.......... 61
4.2 IsoelectricPointsofPolymerMatrixMembranes ................ 65
4.3 IonExchangeCapacity...................................... 68
4.3.1 CationSelectivity.................................... 72
4.4 Water VapourSorptionandPermeabilityasAffectedbypH,
CationsandVapourPressure ................................. 74
4.5 DiffusionandViscousTransportofWater:EvidenceforAqueous
PoresinPolymerMatrixMembranes .......................... 78
4.5.1 LipophilicandHydrophilicPathwaysinthe
PolymerMatrix...................................... 88
4.5.2 PermeabilityofthePoreandCutinPathways ............. 89
4.5.3 EffectofPartialPressureofWaterVapouronPermeances
ofthePoreandCutinPathways ........................ 92
4.6 WaterPermeabilityofIsolatedAstomatousCuticularMembranes .. 93
4.6.1 ComparingWaterPermeabilityofCMwiththatofMX .... 93
4.6.2 WaterPermeabilityofCM............................. 94
4.6.2.1 Chemical Composition of Wax and Its
RelationshiptoWaterPermeability ............. 96
4.6.2.2 WaterPermeabilityofCMandDiffusion
ofStearicAcidinWax........................ 98
4.6.2.3 Co-PermeationofWaterandLipophilicSolutes...101
4.6.2.4 EffectofPartialVapourPressure(Humidity)
onPermeabilityofCM .......................104
4.6.2.5 EffectofAgClPrecipitatesonWaterPermeance ..105
Contents xi
4.6.3 DiffusionCoefficientsofWaterinCMandCuticularWax ..107
4.6.3.1 MeasurementofD forWater in CM from
w
Hold-upTimes ..............................107
4.6.3.2 EstimationofD fromDiffusionofLipophilic
w
NeutralMolecules ...........................109
4.6.4 WaterPermeabilityofParaffinWaxes ...................111
4.6.4.1 WaterPermeanceofPolyethylene
andParaffinWax ............................111
4.6.4.2 WaterPermeabilityofLipidMonolayers.........114
4.6.4.3 Estimation of Water Sorptionin Wax and
ThicknessoftheWaxyTranspirationBarrier .....116
4.7 PermeancesofAdaxialandAbaxialCuticles....................118
4.8 WaterPermeabilityofIsolatedCuticularMembranes
asComparedtoIntactLeaves ................................119
4.9 TheShapeoftheWaterBarrierinPlantCuticles.................120
Problems ......................................................121
Solutions ......................................................122
5 PenetrationofIonicSolutes .....................................125
5.1 LocalisationofAqueousPoresinCuticles......................126
5.2 ExperimentalMethods ......................................129
5.3 CuticularPenetrationofElectrolytes...........................133
5.3.1 EffectofWettingAgents..............................133
5.3.2 PenetrationofCalciumandPotassiumSalts ..............134
5.3.3 RateConstantsMeasuredwithLeafCMfromDifferent
Species.............................................136
5.3.4 SizeSelectivityofAqueousPores ......................137
5.3.5 PenetrationofOrganicIonsandZwitterIons .............140
5.4 CuticularPenetrationofFeChelates...........................142
Problems ......................................................143
Solutions ......................................................144
6 DiffusionofNon-Electrolytes....................................145
6.1 SorptioninCuticularMembranes,PolymerMatrix,
CutinandWaxes ...........................................145
6.1.1 DefinitionandDeterminationofPartitionCoefficients .....145
6.1.2 Cuticle/WaterPartitionCoefficientsK .................146
cw
6.1.3 Wax/WaterPartitionCoefficientsK ...................148
ww
6.1.4 ConcentrationDependenceofPartitionCoefficients .......149
6.1.5 PredictionofPartitionCoefficients......................149
6.1.6 Problems Related to the Measurementof Partition
Coefficients.........................................151
6.1.6.1 SoluteswithIonisableAcidicandBasicGroups ..151
6.1.6.2 HydrophobicSoluteswithExtremely
LowWaterSolubility.........................151
xii Contents
6.1.6.3 PolarSoluteswithExtremely
HighWaterSolubility ........................152
6.2 SteadyStatePenetration.....................................153
6.2.1 PermeanceofIsolatedCuticularMembranes .............153
6.2.2 Steady State Penetration into Detached Leaves:
TheSubmersionTechnique............................159
6.2.2.1 PenetrationintoCutEdges ....................160
6.2.2.2 CuticularPenetration.........................161
6.2.2.3 CompartmentalAnalysis......................163
6.2.2.4 ProjectedandSpecificSurfaceArea ............168
6.2.2.5 EvaluationofCompartmentalAnalysis..........170
6.2.3 SteadyStatePenetrationintoLeafDisksUsing
theWellTechnique...................................171
6.3 DiffusionwithChangingDonorConcentrations:
TheTransientState .........................................176
6.3.1 SimultaneousBilateralDesorption......................176
6.3.2 UnilateralDesorptionfromtheOuterSurface.............180
6.3.2.1 EstimatingSoluteMobilityfromRateConstants ..183
6.3.2.2 VariabilityofSoluteMobilityamongDifferent
PlantSpecies................................186
6.3.2.3 VariabilityofSoluteMobility
withSizeofSolutes ..........................187
6.4 SimulationofFoliarPenetration ..............................190
6.5 DiffusioninReconstitutedIsolatedCuticularWaxes .............192
6.5.1 ExperimentalApproach...............................193
6.5.2 DiffusionCoefficientsinReconstitutedCuticularWax .....195
6.5.3 RelationshipBetweenDandP .........................198
Problems ......................................................200
Solutions ......................................................202
7 AcceleratorsIncreaseSolutePermeabilityofCuticles ..............205
7.1 SorptionofPlasticisersinWaxandCutin ......................206
7.1.1 SorptionofAlcoholEthoxylatesinWax .................206
7.1.2 Sorptionof AlcoholEthoxylatesin PolymerMatrix
Membranes .........................................210
7.1.3 Sorptionofn-AlkylEstersinWax ......................211
7.2 PlasticisationofCuticularWax:EvidencefromSpectroscopy......212
7.3 EffectsofPlasticisersonDiffusionofLipophilicSolutesinWax ...215
7.3.1 EffectofC E onSoluteDiffusioninReconstitutedWax ..215
12 8
7.3.2 PlasticisingEffectsofOtherAlcoholEthoxylates .........217
7.3.3 PlasticisingEffectsofn-AlkylEsters....................218
7.3.4 DependenceofthePlasticisingEffectonMolarVolume
ofSolutes...........................................220
7.4 EffectsofPlasticisersonTransportinCuticles ..................222
7.4.1 ReversibilityofPlasticiserEffects ......................223
