Plant Tropisms »

Simon Gilroy, Ph.D., is Associate Professor of Biology at Pennsylvania State University.

Patrick Masson, Ph.D., is Professor of Genetics at the University of Wisconsin.

Tropisms, the defined vectorial stimuli, such as gravity, light, touch, humidity gradients, ions, oxygen, and temperature, which provide guidance for plant organ growth, is a rapidly growing and changing field. The last few years have witnessed a true renaissance in the analysis of tropisms. As such the conception of tropisms has changed from being seen as a group of simple laboratory curiosities to their recognition as important tools/phenotypes with which to decipher basic cell biological processes that are essential to plant growth and development. Plant Tropisms will provide a comprehensive, yet integrated, volume of the current state of knowledge on the molecular and cell biological processes that govern plant tropisms.

List of Contributors

Preface

Chapter 1 Mechanisms of Gravity Perception in Higher Plants Aline H. Valster Elison B. Blancaflor 3

1.1 Introduction 3

1.2 Identification and characterization of gravity perception sites in plant organs 4

1.2.1 Roots 4

1.2.2 Hypocotyls and inflorescence stems (dicotyledons) 6

1.2.3 Cereal pulvini (monocotyledons) 8

1.3 The starch-statolith hypothesis 9

1.3.1 A variety of plant organs utilize sedimenting amyloplasts to sense gravity 9

1.3.2 Amyloplast sedimentation is influenced by the environment and developmental stage of the plant 11

1.4 The gravitational pressure model for gravity sensing 11

1.5 The cytoskeleton in gravity perception 12

1.6 Concluding remarks and future prospects 14

1.7 Acknowledgment 15

1.8 Literature cited 15

Chapter 2 Signal Transduction in Gravitropism Benjamin R. Harrison Miyo T. Morita Patrick H. Masson Masao Tasaka 21

2.1 Introduction 21

2.2 Gravity signal transduction in roots and aboveground organs 22

2.2.1 Do mechano-sensitive ion channels function as gravity receptors? 24

2.2.2 Inositol 1, 4, 5-trisphosphate seems to function in gravity signal transduction 26

2.2.3 Do pH changes contribute to gravity signal transduction? 27

2.2.4 Proteins implicated in gravity signal transduction 28

2.2.5 Global '-omic' approaches to the study of root gravitropism 32

2.2.6 Relocalization of auxin transport facilitators or activity regulation? 37

2.2.7 Could cytokinin also contribute to the gravitropic signal? 38

2.3 Gravity signal transduction in organs that do not grow vertically 39

2.4 Acknowledgments 40

2.5 Literature cited 40

Chapter 3 Auxin Transport and the Integration of GravitropicGrowth Gloria K Muday Abidur Rahman 47

3.1 Introduction to auxins 47

3.2 Auxin transport and its role in plant gravity response 47

3.3 Approaches to identify proteins (hat mediate IAA efflux 51

3.4 Proteins that mediate IAA efflux 51

3.5 IAA influx carriers and their role in gravitropism 53

3.6 Regulation of IAA efflux protein location and activity during gravity response 55

3.6.1 Mechanisms that may control localization of IAA efflux carriers 56

3.6.2 Regulation of IAA efflux by synthesis and degradation of efflux carriers 58

3.6.3 Regulation of auxin transport by reversible protein phosphorylation 59

3.6.4 Regulation of auxin transport by flavonoids 61

3.6.5 Regulation of auxin transport by other signaling pathways 61

3.6.6 Regulation of gravity response by ethylene 64

3.7 Overview of the mechanisms of auxin-induced growth 65

3.8 Conclusions 67

3.9 Acknowledgements 68

3.10 Literature cited 68

Chapter 4 Phototropism and Its Relationship to Gravitropism Jack L. Mullen John Z. Kiss 79

4.1 Phototropism: general description and distribution 79

4.2 Light perception 80

4.3 Signal transduction and growth response 82

4.4 Interactions with gravitropism 83

4.5 Importance to plant form and function 84

4.6 Conclusions and outlook 85

4.7 Literature cited 86

Chapter 5 Touch Sensing and Thigmotropism Gabrele B. Monshausen Sarah J. Swanson Simon Gilroy 91

5.1 Introduction 91

5.2 Plant mechanoresponses 91

5.2.1 Specialized touch responses 92

5.2.2 Thigmomorphogenesis and thigmotropism 94

5.3 General principles of touch perception 95

5.3.1 Gating through membrane tension: the mechanoreceptor for hypo-osmotic stress bacteria, MscL 98

5.3.2 Gating through tethers: the mechanoreceptor for gentle touch in Caenorhabditis elegans 99

5.3.3 Evidence for mechanically gated ion channels in plants 101

5.4 Signal transduction in touch and gravity perception 103

5.4.1 Ionic signaling 103

5.4.2 Ca²⁺ signaling in the touch and gravity response 103

5.5 Insights from transcriptional profiling 107

5.6 Interaction of touch and gravity signaling/response 110

5.7 Conclusion and Perspectives 113

5.8 Acknowledgements 114

5.9 Literature cited 14

Chapter 6 Other Tropisms and their Relationship to Gravitropism Gladys I. Cassab 123

6.1 Introduction 123

6.2 Hydrotropism 123

6.2.1 Early studies of hydrotoprism 124

6.2.2 Genetic analysis of hydrotropism 125

6.2.3 Perception of moisture gradients and gravity stimuli by the root cap and the curvature response 126

6.2.4 ABA and the hydrotropic response 128

6.2.5 Future experiments 129

6.3 Electrotropism 129

6.4 Chemotropism 131

6.5 Thermotropism and oxytropism 132

6.6 Traumatropism 134

6.7 Overview 135

6.8 Acknowledgments 135

6.9 Literature cited 135

Chapter 7 Single-Cell Gravitropism and Gravitaxis Markus Braun Ruth Hemmersbach 141

7.1 Introduction 141

7.2 Definitions of responses to environmental stimuli that optimize the ecological fitness of single-cell organisms 141

7.3 Occurrence and significance of gravitaxis in single-cell systems 142

7.4 Significance of gravitropism in single-cell systems 143

7.5 What makes a cell a biological gravity sensor? 144

7.6 Gravity susception-the initial physical step of gravity sensing 145

7.7 Susception in the statolith-based systems of Chora 145

7.8 Susception in the statolith-based system Loxodes 149

7.9 Susception in the protoplast-based systems of Euglena and Paramecium 150

7.10 Graviperception in the statolith-based systems of Cham 150

7.11 Graviperception in the statolith-based system Loxodes 151

7.12 Graviperception in the protoplast-based systems Paramecium and Euglena 151

7.13 Signal transduction pathways and graviresponse mechanisms in the statolith-based systems of Chara 153

7.14 Signal transduction pathways and graviresponse mechanisms in Euglena and Paramecium

7.15 Conclusions 155

7.16 Acknowledgements 156

7.17 Literature cited 156

Color Section

Chapter 8 Space-Based Research on Plant Tropisras Melante J. Correll John Z. Kiss 161

8.1 Introduction-the variety of plant movements 161

8.2 The microgravity environment 162

8.3 Ground-based studies: mitigating the effects of gravity 165

5.4 Gravitropism 166

8.4.1 Gravitropism: gravity perception 166

8.4.2 Gravitropism: signal transduction 168

8.4.3 Gravitropism: the curving response 169

8.5 Phototropism 171

8.6 Hydrotropism, autotropism, and oxytropism 172

8.7 Studies of other plant movements in microgravity 174

8.8 Space flight hardware used to study tropisms 175

8.9 Future outlook and prospects 177

8.10 Literature cited 177

Chapter 9 Plan(t)s for Space Exploration Christopher S. Brown Heike Winter Sederoff Eric Davies Robert J. Ferl Bratislav Stankovic 183

9.1 Introduction 183

9.2 Human missions to space 184

9.3 Life support 184

9.4 Genomics and space exploration 185

9.5 Nanotechnology 187

9.6 Sensor, biosensors, and intelligent machines 187

9.7 Plan(t)s for Space Exploration 188

9.8 Imagine 192

9.9 Literature cited 192

Index 197