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PLANT DEFENSE
Warding off Attack by Pathogens,
Herbivores, and Parasitic Plants
Dale R. Walters
Crop&SoilSystemsResearchGroup
ScottishAgriculturalCollege
Edinburgh,UK
A John Wiley & Sons, Ltd., Publication
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PLANT DEFENSE
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ThisbookisdedicatedtoBeverley,for30yearsoflove
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PLANT DEFENSE
Warding off Attack by Pathogens,
Herbivores, and Parasitic Plants
Dale R. Walters
Crop&SoilSystemsResearchGroup
ScottishAgriculturalCollege
Edinburgh,UK
A John Wiley & Sons, Ltd., Publication
iii
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Thiseditionfirstpublished2011
(cid:1)C 2011byBlackwellPublishingLtd.
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LibraryofCongressCataloging-in-PublicationData
Walters,Dale.
Plantdefense:wardingoffattackbypathogens,herbivores,andparasiticplants/
DaleR.Walters.–1sted.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-1-4051-7589-0(pbk.:alk.paper) 1.Plants–Diseaseandpestresistance. I.Title.
SB750.W352011
632–dc22
2010011214
AcataloguerecordforthisbookisavailablefromtheBritishLibrary.
Setin10/12ptTimesbyAptara(cid:1)R Inc.,NewDelhi,India
PrintedinSingapore
1 2011
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Contents
Preface x
Chapter1 WhyDoPlantsNeedDefenses? 1
1.1 Plantsassourcesoffood 1
1.2 Organismsthatuseplantsasfood 2
1.2.1 Microorganisms 2
1.2.2 Parasiticangiosperms 3
1.2.3 Nematodes 5
1.2.4 Insects 5
1.2.5 Vertebrates 6
1.3 Impactofinfectionandherbivoryinnaturaland
agriculturalecosystems 6
1.3.1 Microorganisms 6
1.3.2 Parasiticangiosperms 7
1.3.3 Nematodes 8
1.3.4 Insects 8
1.3.5 Vertebrates 10
1.4 Conclusions 11
Recommendedreading 11
References 12
Chapter2 WhatDefensesDoPlantsUse? 15
2.1 Introduction 15
2.2 Defensesusedagainstpathogens 15
2.2.1 Background 15
2.2.2 Passiveorpreexistingdefenses 17
2.2.2.1 Preexistingstructuraldefenses 17
2.2.2.2 Preexistingchemicaldefenses 18
2.2.3 Activeorinducibledefenses 25
2.2.3.1 Induciblestructuraldefenses 25
2.2.3.2 Induciblechemicaldefenses 29
2.2.4 Defensesusedagainstpathogens—thenextstep 37
2.3 Defensesusedagainstparasiticplants 37
2.3.1 Background 37
2.3.2 Preattachmentdefensemechanisms 38
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2.3.3 Prehaustorialdefensemechanisms 38
2.3.4 Posthaustorialdefensemechanisms 40
2.4 Defensesusedagainstnematodes 41
2.4.1 Background 41
2.4.2 Passiveorpreexistingdefenses 42
2.4.3 Activeorinducibledefenses 43
2.4.3.1 Phenylpropanoidmetabolism 43
2.4.3.2 Hypersensitiveresponse 43
2.5 Defensesusedagainstherbivorousinsects 44
2.5.1 Background 44
2.5.2 Physicalbarriers 45
2.5.2.1 Waxesontheleafsurface 45
2.5.2.2 Trichomes 45
2.5.2.3 Secretorycanals 46
2.5.2.4 Leaftoughnessandleaffolding 47
2.5.3 Chemicaldefenses 49
2.5.3.1 Terpenes 50
2.5.3.2 Phenolics 52
2.5.3.3 Nitrogen-containingorganiccompounds 53
2.5.3.4 Arthropod-inducibleproteins 55
2.5.3.5 Volatilecompounds 56
2.6 Defensesusedagainstvertebrateherbivores 58
2.6.1 Background 58
2.6.2 Physicaldefenses 58
2.6.3 Chemicaldefenses 59
2.6.3.1 Phenoliccompounds 59
2.6.3.2 Terpenoids 62
2.6.3.3 Nitrogen-containingcompounds 63
2.6.3.4 Otherchemicals 64
2.6.3.5 Afinalwordonchemicaldefensesagainst
vertebrateherbivory 64
2.7 Defensesu sedagainstneighboringplants—allelopathy 64
2.7.1 Background 64
2.7.2 Allelopathyandtheblackwalnut 65
2.7.3 AllelopathyandtheCalifornianchaparral 65
2.7.4 Allelopathyandspottedknapweed 65
2.8 Conclusions 66
Recommendedreading 67
References 67
Chapter3 SoundingtheAlarm:SignalingandCommunicationin
PlantDefense 77
3.1 Introduction 77
3.2 Signalinginplant–pathogeninteractions 77
3.2.1 Introduction 77
3.2.2 Localsignalingandbasalresistance 78
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3.2.2.1 SAsignaling 78
3.2.2.2 JAsignaling 79
3.2.2.3 ETsignaling 80
3.2.2.4 Signalinginvolvingotherplanthormones 83
3.2.3 Systemicsignalingandinducedresistance 84
3.2.3.1 Inducedresistance 84
3.2.3.2 SignalingduringSAR 84
3.2.3.3 SignalingduringISR 85
3.2.3.4 Priming 86
3.2.4 Volatilesignaling 90
3.3 Signalinginplant–nematodeinteractions 91
3.3.1 Introduction 91
3.3.2 SAsignaling 92
3.3.3 JAsignaling 92
3.4 Signalinginplant–insectherbivoreinteractions 93
3.4.1 Introduction 93
3.4.2 Localsignaling 95
3.4.2.1 JAsignaling 95
3.4.2.2 ETsignaling 97
3.4.2.3 SAsignaling 97
3.4.2.4 Specificityandregulationof
jasmonate-baseddefenses 97
3.4.3 Systemicsignaling 99
3.4.3.1 Systemin 99
3.4.3.2 JAsignaling 100
3.4.3.3 Withinleafsignaling 101
3.4.4 Volatilesignaling 103
3.4.5 Priming 106
3.5 Signalingininteractionsbetweenplantsandvertebrateherbivores 110
3.6 Signalingininteractionsbetweenplantsandparasiticplants 110
3.7 Conclusions 111
Recommen dedreading 112
References 112
Chapter4 PlantDefenseintheRealWorld:MultipleAttackersand
BeneficialInteractions 125
4.1 Introduction 125
4.2 Dealingwithmultipleattackers:cross-talkbetween
signalingpathways 126
4.2.1 Trade-offsassociatedwithtriggeringSA-mediated
defenses 126
4.2.1.1 SAsuppressionofJA-induceddefenses 126
4.2.1.2 MolecularbasisofSAsuppressionofJA
defenses 128
4.2.1.3 Ecologicalcostsofresistancetobiotrophic
versusnecrotrophicpathogens 130
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4.2.1.4 Trade-offswithmutualisticsymbioses 131
4.2.1.5 EffectsofSA-andJA-mediateddefenses
onbacterialcommunitiesassociatedwithplants 132
4.2.2 TriggeringSA-dependentdefensesdoesnotalways
compromisedefenseagainstinsectherbivores 133
4.2.3 Trade-offsandpositiveoutcomesassociatedwith
triggeringJA-dependentdefenses 134
4.2.4 Puttingitalltogether:orchestratingtheappropriate
defenseresponse 137
4.3 Canbeneficialplant–microbeinteractionsinduce
resistanceinplants? 143
4.3.1 Introduction 143
4.3.2 Inductionofresistancebymycorrhizas 143
4.3.3 Resistanceinducedbyendophyticandother
beneficialfungi 145
4.4 Conclusions 146
Recommendedreading 147
References 147
Chapter5 TheEvolutionofPlantDefense 153
5.1 Introduction 153
5.2 Hypothesesofplantdefense 153
5.2.1 Thegrowth–differentiationbalancehypothesis 155
5.2.2 Optimaldefensehypotheses 157
5.2.3 Plantapparencyhypothesis 160
5.2.4 Thecarbon–nutrientbalancehypothesis 160
5.2.5 Thegrowthratehypothesis 161
5.2.6 Hypothesesofplantdefense—wherenext? 163
5.3 Evolutionofplantdefensestrategies 163
5.3.1 Theunivariatetrade-offhypothesis 163
5.3.2 Theresistance–regrowthtrade-offhypothesis 165
5.3.3 The plantapparencyhypothesis 165
5.3.4 Theresourceavailabilityhypothesis 167
5.3.5 Plantdefensesyndromes 167
5.4 Patternsofplantdefenseevolution 169
5.4.1 Adaptiveradiation 170
5.4.2 Escalationofdefensepotency 170
5.4.3 Phylogeneticconservatism 171
5.4.4 Phylogeneticescalationanddeclineofplant
defensestrategies 171
5.5 Whydoplantshaveinduceddefenses? 172
5.5.1 Costs 172
5.5.1.1 Allocationcostsassociatedwithinduced
responsestoherbivory 175
