The Chemical Biology of Plant Biostimulants

Editors Danny Geelen, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Belgium Lin Xu, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Belgium Series Editor Christian Stevens, Faculty of Bioscience Engineering, Ghent University, Belgium

List of Contributors xiii

Series Preface xv

Preface xvii

Part I Introduction 1

1 Agricultural Functions and Action Mechanisms of Plant Biostimulants (PBs): an Introduction 3
Patrick du Jardin, Lin Xu and Danny Geelen

1.1 The Biostimulant Concept 3

1.2 The Chemistry of Bioactive Ingredients 9

1.2.1 Striving to Identify the Active Ingredient 9

1.2.2 Chemical Characterization of Traditional Biostimulants 10

1.2.3 Novelty by Targeted Modification of Known Bioactive Molecules 11

1.2.4 Approaches to Screen for New Molecules with Biostimulatory Activity 12

1.3 Defining Mode and Mechanism of Action 14

1.3.1 Journey to the Site of Action 14

1.3.2 Multiple Functions of Bioactive Ingredients 15

1.3.3 Tools for a Multilevel Analysis of PBs Action 16

1.4 Focusing on Key Traits Influenced by Biostimulants 17

1.4.1 Nutrient Use Efficiency (NUE) 17

1.4.2 Increasing Tolerance to Abiotic Stress 19

1.4.3 Crop Quality 22

1.5 Perspective 23

1.5.1 Biostimulants: A New Bandwagon to Move Agriculture Forward? 23

1.5.2 Integration of Biostimulants with Precision Agriculture (PA) 24

1.5.3 What Do We Need for the Future? 24

Author Contributions 25

Acknowledgement 25

Further Reading 25

References 25

Part II Examples of Plant Biostimulants 31

2 Plant Biostimulants from Seaweed: An Overview 33
Wendy A. Stirk, Kannan R.R. Rengasamy, Manoj G. Kulkarni and Johannes van Staden

2.1 Introduction 33

2.2 Global Trends in Seaweed-Derived Plant Biostimulants 34

2.3 Production Technology 35

2.3.1 Methods of Production 35

2.3.2 Seaweed Biomass Variability 35

2.3.3 Shelf-Life 36

2.4 Beneficial Traits of Seaweed Biostimulants: Recent Developments 37

2.4.1 Improved Plant Growth 37

2.4.2 Increased Tolerance to Abiotic and Biotic Stresses 37

2.4.3 Biofortification 38

2.5 Major Biostimulants in Seaweed Extracts 38

2.5.1 Plant Hormones 38

2.5.2 Brassinosteroids 41

2.5.3 Betaines 42

2.5.4 Polyamines 42

2.5.5 Polymers 43

2.6 Concluding Remarks and Future Prospects 48

Acknowledgement 48

Abbreviations 48

References 50

3 Seaweed Carbohydrates 57
Oscar Goñi, Patrick Quille and Shane O’Connell

3.1 Introduction 57

3.2 Fucoidan from Brown Algae 60

3.2.1 Detailed Description of Chemical Composition and Structure of Fucoidan 60

3.2.2 Experimental Methods for Chemical Characterization of Fucoidan 63

3.2.3 Fucoidan PB Activity and Potential Applications 64

3.3 Alginate from Brown Algae 64

3.3.1 Detailed Description of Chemical Composition and Structure of Alginate 64

3.3.2 Experimental Methods for Chemical Characterization of Alginate 66

3.3.3 Alginate PB Activity and Potential Applications 67

3.4 Carrageenan from Red Algae 69

3.4.1 Detailed Description of Chemical Composition and Structure of Carrageenan 69

3.4.2 Experimental Methods for Chemical Characterization of Carrageenan 71

3.4.3 Carrageenan PB Activities and Potential Applications 71

3.5 Ulvan from Green Algae 74

3.5.1 Detailed Description of Chemical Composition and Structure of Ulvan 74

3.5.2 Experimental Methods for Chemical Characterization of Ulvan 75

3.5.3 Ulvan PB Activities and Potential Applications 75

3.6 Laminarin from Brown Algae 77

3.6.1 Detailed Description of Chemical Composition and Structure of Laminarin 77

3.6.2 Experimental Methods for Chemical Characterization of Laminarin 78

3.6.3 Laminarin PB Activities and Potential Applications 78

3.7 Cellulose and Hemicellulose Derived Oligosaccharides 79

3.7.1 Detailed Description of Chemical Composition and Structure of Cellulose and Hemicellulose Oligosaccharides 79

3.7.2 Experimental Methods for Chemical Characterization of Cellulose and Hemicellulose Oligosaccharides 80

3.7.3 Cellulose and Hemicellulose Oligosaccharides PB Activity and Potential Applications 80

3.8 Conclusions 81

Abbreviations 81

References 82

4 Possible Role for Electron Shuttling Capacity in Elicitation of PB Activity of Humic Substances on Plant Growth Enhancement 97
Richard T. Lamar

4.1 Introduction 97

4.1.1 Chemical Nature of HS 97

4.1.2 Sources of Commercial HS 98

4.1.3 Formation of Coal-Derived HS and its Effect on HS Chemical Variation 98

4.2 Similar Responses of Plants to HS and Abiotic and Biotic Stresses 99

4.2.1 Stress Elicitation, Plant Stress Sensing and Commonality of Physiological Responses 99

4.2.2 Redox Activity of HS and Possible Role in Elicitation of Biostimulant Response 100

4.2.3 Common Metabolic Events that are Shared by HS and Stress Elicitors 100

4.3 Humic/Fulvic Elicitation Mechanism 111

References 112

5 Auxin: At the Crossroads Between Chemistry and Biology 123
Sara Raggi, Siamsa M. Doyle and Stéphanie Robert

5.1 Introduction: What is an Auxin? 123

5.1.1 The Importance of Chemical Structure 123

5.1.2 The History of Natural Auxins 125

5.1.3 The Importance of Synthetic Auxins 126

5.1.4 Auxin Gradients and the Regulation of Plant Growth 126

5.2 Taking Advantage of Auxins: Industrial Applications 128

5.2.1 Auxins as Rooting Agents for Plant Propagation 128

5.2.2 Auxins as Herbicides 129

5.3 Understanding Auxin: The Importance of Chemical Tools in Research 130

5.3.1 Inhibitors of Auxin Metabolism as Research Tools 130

5.3.2 Unravelling Auxin Transport with a Plethora of Chemical Tools 134

5.3.3 Chemical Tools Reveal Complicated Auxin Perception and Signalling Pathways 140

5.4 Conclusions 145

Acknowledgement 146

References 146

6 Plant Biostimulants in Vermicomposts: Characteristics and Plausible Mechanisms 155
Wei San Wong, Hong Tao Zhong, Adam Timothy Cross and Jean Wan Hong Yong

6.1 Introduction 155

6.2 Advantages of Vermicomposting 157

6.3 General Characteristics of Vermicomposts 159

6.3.1 Mineral Nutrient Composition of Vermicomposts 159

6.3.2 Plant Growth Promoting Properties of Vermicompost 161

6.4 Plant Growth Promoting Substances in Vermicomposts 163

6.4.1 Phytohormones and Mass Spectrometric Evidence to Support Their Occurrence and Functions 163

6.4.2 Vermicompost-Derived Phytohormones as Biostimulants for Plant Growth 168

6.5 Benefits of Integrating Vermicomposts into the Current Plant Production Regime 172

6.6 Conclusion 173

References 173

Part III Methods to Screen for New Biostimulants 181

7 Exploring Natural Resources for Biostimulants 183
Giovanni Povero

7.1 Introduction 183

7.2 Biological Screening Technologies 187

7.2.1 Overview of Most Used Screening Protocols for Bioactives 187

7.2.2 In vitro Bioassays 187

7.2.3 ‘Acid Growth’ Tests 190

7.2.4 Microphenotyping 191

7.2.5 Genomic Investigation 194

7.2.6 Phenomic Studies 197

7.2.7 Other ‘-Omics’ 200

7.3 Conclusions 201

References 201

Part IV Biostimulants’ Mode of Action 205

8 Biostimulant Mode of Action: Impact of Biostimulant on Whole-Plant Level 207
Elizabeth Wozniak, Adam Blaszczak, Pawel Wiatrak and Michael Canady

8.1 Introduction 207

8.2 Crop Growth and Development 208

8.2.1 Crop Yield 208

8.2.2 Crop Quality and Post-Harvest Stability 210

8.2.3 Germination 212

8.2.4 Shoot Growth 213

8.2.5 Root Growth 214

8.2.6 Bloom and Fruit Set 215

8.3 Plant Physiology 216

8.3.1 Nutrient Uptake and Distribution 216

8.3.2 Abiotic and Biotic Stress 218

8.4 Conclusion 220

References 221

9 Biostimulant Mode of Action: Impact of Biostimulant on Cellular Level 229
Elizabeth Wozniak, Adam Blaszczak, Pawel Wiatrak and Michael Canady

9.1 Reactive Oxygen Species (ROS) Control 230

9.2 Membrane Stability and Function 232

9.3 Enzyme Activity 233

9.4 Production of Secondary Metabolites 234

9.5 Production of Plant Growth Regulators (PGRs) 235

9.6 Photosynthetic Pigments and Photosynthesis 236

9.6.1 Photosynthetic Pigments 236

9.6.2 Photosynthetic Processes 237

9.7 Conclusions 237

References 240

10 Biostimulant Mode of Action: Impact of PBs on Molecular Level 245
Lin Xu, Hoang Khai Trinh and Danny Geelen

10.1 Molecular Tools to Unravel Small Molecules Mode of Action 246

10.2 Biostimulant Impact on Plants on the Molecular Level 246

10.2.1 Transcriptional Analysis 247

10.2.2 Proteomic Studies 250

10.2.3 Metabolomic Studies 252

10.2.4 Multiple Approaches in Acquiring Omics Data: A Short Introduction 254

10.3 Conclusions 254

Acknowledgement 256

References 256

Part V Biostimulants – A Practical Guide 261

11 Use of Plant Metabolites to Mitigate Stress Effects in Crops 263
Nuria De Diego and Lukáš Spíchal

11.1 Introduction 263

11.2 Plant Metabolites Used for Stress Mitigation in Crops 264

11.2.1 Amino Acids 266

11.2.2 Polyamines 285

11.2.3 Hormones 286

11.2.4 Combined Application of Different Metabolites 287

11.2.5 Common Mode of Action of the Plant Metabolites to Mitigate Stress 287

11.3 Conclusion 289

Acknowledgement 290

References 290

Index 301