UV-B Radiation From Environmental Stressor to Regulator of Plant Growth

Ultraviolet-B (UV-B) is electromagnetic radiation coming from the sun, with a medium wavelength which is mostly absorbed by the ozone layer. The biological effects of UV-B are greater than simple heating effects, and many practical applications of UV-B radiation derive from its interactions with organic molecules. It is considered particularly harmful to the environment and living things, but what have scientific studies actually shown?

UV-B Radiation: From Environmental Stressor to Regulator of Plant Growth presents a comprehensive overview of the origins, current state, and future horizons of scientific research on ultraviolet-B radiation and its perception in plants. Chapters explore all facets of UV-B research, including the basics of how UV-B's shorter wavelength radiation from the sun reaches the Earth's surface, along with its impact on the environment's biotic components and on human biological systems. Chapters also address the dramatic shift in UV-B research in recent years, reflecting emerging technologies, showing how historic research which focused exclusively on the harmful environmental effects of UV-B radiation has now given way to studies on potential benefits to humans. Topics include:

• UV-B and its climatology
• UV-B and terrestrial ecosystems
• Plant responses to UV-B stress
• UB- B avoidance mechanisms
• UV-B and production of secondary metabolites
• Discovery of UVR8

Timely and important, UV-B Radiation: From Environmental Stressor to Regulator of Plant Growth is an invaluable resource for environmentalists, researchers and students who are into the state-of-the-art research being done on exposure to UV-B radiation.

ABOUT THE EDITORS
VIJAY PRATAP SINGH is Assistant Professor, Govt. Ramanuj Pratap Singhdev Post Graduate College, Chhattisgarh, India.

SAMIKSHA SINGH is Research Scholar, Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, India.

SHEO MOHAN PRASAD is Professor, Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, India.

PARUL PARIHAR is Research Scholar, Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, India.

List of Contributors xv

Preface xix

1 An Introduction to UV‐B Research in Plant Science 1
Rachana Singh, Parul Parihar, Samiksha Singh, MPVVB Singh, Vijay Pratap Singh and Sheo Mohan Prasad

1.1 The Historical Background 1

1.2 Biologically Effective Irradiance 2

1.3 UV‐B‐induced Effects in Plants 3

1.4 Conclusion and Future Prospects 5

Acknowledgements 6

References 6

2 Stimulation of Various Phenolics in Plants Under Ambient UV‐B Radiation 9
Marija Vidović, Filis Morina and Sonja Veljović Jovanović

2.1 Introduction 9

2.2 UV‐B Radiation 10

2.2 Phenolics 12

2.2.1 Chemistry of Phenolic Compounds 13

2.2.2 Biosynthesis and Subcellular Localization of Phenolics 13

2.2.3 Functions of Phenolic Compounds Depend on Their Localization 15

2.4 UV‐B Radiation Stimulates Phenolic Induction 18

2.4.1 Mechanisms of UV‐B Perception 18

2.4.2 UV‐B‐Induced Accumulation of Phenolic Compounds 20

2.4.1 Interactive Effects of UV‐B with UV‐A Radiation and PAR on Phenolics Accumulation 28

2.4.2 Interactive Effects of UV‐B with other Environmental Factors on Phenolics Accumulation 30

2.5 UV‐B‐Induced Photomorphological Responses 31

2.5.1 Connection Between UV‐B‐Induced Morphological Responses and Phenolics 31

2.5.2 Effect of UV‐B Radiation on Root Morphology in Relation to Phenolics 32

2.6 Photosynthesis Under UV‐B Radiation 33

2.6.1 Interplay of Phenolics and Photosynthesis Under UV‐B Radiation 34

2.7 UV‐B Radiation Induces Phenolics Accumulation in Fruits 37

2.8 Conclusions and Future Perspectives 38

References 39

3 UV‐B Radiation: A Reassessment of its Impact on Plants and Crops 57
Krystyna Żuk‐Gołaszewska

3.1 Introduction 57

3.2 Plant Production 58

3.3 Plant protection Against UVB 60

References 60

4 Interaction of UV‐B with the Terrestrial Ecosystem 65
Rohit Kumar Mishra, Sanjesh Tiwari and Sheo Mohan Prasad

4.1 Introduction 65

4.2 Growth and Development 66

4.3 Secondary Metabolites 67

4.4 Susceptibility to Herbivorous Insects 67

4.5 Plant Sexual Reproduction 67

4.6 Genomic Level 68

4.7 Conclusion 69

References 70

5 A Review of Stress and Responses of Plants to UV‐B Radiation 75

Sonika Sharma, Soumya Chatterjee, Sunita Kataria, Juhie Joshi, Sibnarayan Datta, Mohan G. Vairale and Vijay Veer

5.1 Introduction 75

5.2 Morphological and Yield Response to UV‐B 76

5.3 Targets of UV‐B in the Carbon Fixation Cycle 79

5.4 Photoreceptors and Signalling Pathway in Response to UV‐B Radiation 80

5.5 Acclimatization and Protection in Response to UV‐B 82

5.6 Oxidative Stress and Antioxidant System in Response to UV‐B 82

5.7 DNA Damage and Repair Mechanism 83

5.8 Exclusion of UV Components: Experimental Approach to Study the Effect on Plants 85

5.9 Conclusion and Future Prospective 86

Acknowledgement 87

References 87

6 Oxidative Stress and Antioxidative Defence System in Plants in Response to UV‐B Stress 99
Sunita Kataria

6.1 Introduction 99

6.2 Plant Protection Against UV Radiation 101

6.3 UV‐B and ROS 103

6.4 UV‐B and Antioxidant Enzymes 104

6.5 UV‐B and Antioxidant 107

6.6 UV‐B and Signalling 108

6.7 Conclusions and Perspectives 110

References 111

7 Major influence on phytochrome and photosynthetic machinery under UV‐B exposure 123
Anita Singh, Gausiya Bashri and Sheo Mohan Prasad

7.1 Introduction 123

7.2 Photomorphogenesis in Higher Plants 124

7.2.1 Phytochrome system and its interaction with UV‐B 124

7.2.2 Photomorphogenic responses of UV‐B 125

7.2.3 UV‐B signal transduction (UV‐R8) 127

7.3 Effect of UV‐B Exposure on Photosynthetic Machinery 128

7.3.1 Direct effects of UV‐ B on photosynthetic machinery 128

7.3.1.1 Effects of UV‐B stress on components involved in light reaction 128

7.3.1.2 Effect of UV‐B stress on photosystems and cytochrome b6/f complex 129

7.3.2 Indirect effect of UV‐B stress on components involved in dark reaction 132

7.3.2.1 Impact on regulation of stomata and RuBisCO enzyme 132

7.3.3 UV‐B induced ROS production in plants 133

7.3.4 Protective adaptation 133

7.4 Conclusion and Future Perspectives 135

References 136

8 UV‐B Radiation‐Induced Damage of Photosynthetic Apparatus of Green Leaves: Protective Strategies vis‐a‐vis Visible and/or UV‐A Light 143
Padmanava Joshi

8.1 Introduction 143

8.2 UV‐B Effects on the Photosynthetic Apparatus of Leaves 143

8.3 UV‐A Effects on Photosynthetic Apparatus of Leaves (Damage and Promotion) 145

8.4 UV‐A‐Mediated Modulation of UV‐B‐Induced Damage 145

8.5 PAR‐Mediated Balancing of UV‐B‐Induced Damage 146

8.6 Photosynthetic Adaptation and Acclimation to UV‐B Radiation 146

8.7 Corroboration with Sensible Approach 147

8.8 Conclusion 149

Acknowledgements 149

References 149

9 Ultraviolet Radiation Targets in the Cellular System: Current Status and Future Directions 155

Parul Parihar, Rachana Singh, Samiksha Singh, MPVVB Singh, Vijay Pratap Singh and Sheo Mohan Prasad

9.1 Introduction 155

9.2 Absorption Characteristics of Biomolecules 156

9.3 Action Spectrum 156

9.4 Targets of UV‐B 157

9.4.1 Interaction with Biomolecules 157

9.4.2 Nucleic Acids 158

9.4.3 Ribonucleic Acids 159

9.5 UV‐B Interaction with Proteins 159

9.5.1 Tryptophan 160

9.5.2 Tyrosine 160

9.5.3 Phenylalanine 162

9.5.4 Histidine 162

9.6 The Photosynthetic Machinery 163

9.6.1 Photosystem I and II 164

9.6.2 The Light‐Harvesting Complexes 165

9.7 Cell Division and Expansion 167

9.8 Conclusion and Future Directions 168

Acknowledgements 169

References 169

10 Silicon: A Potential Element to Combat Adverse Impact of UV‐B in plants 175
Durgesh Kumar Tripathi, Shweta, Shweta Singh, Vaishali Yadav, Namira Arif, Swati Singh, Nawal Kishor Dubey and Devendra Kumar Chauhan

10.1 Introduction 175

10.2 The role of Silicon Against UV‐B Exposure on Morphology of Plants 178

10.3 The defensive role of silicon against UV‐B exposure on physiological and biochemical traits of plants 179

10.4 Silicon repairs anatomical structures of plants damaged by UV‐B exposures 180

10.5 UV‐B‐induced oxidative stress and silicon supplementation in plants 181

10.6 Silicon supplementation and the status of antioxidant enzymes in plants exposed to UV‐B 183

10.7 Silicon and level of phenolic compounds under UV‐B stress 184

10.8 Present status and future prospectives 186

References 187

11 Sun‐Screening Biomolecules in Microalgae: Role in UV‐Photoprotection 197
Rajesh P Rastogi, Ravi R Sonani, Aran Incharoensakdi and Datta Madamwar

11.1 Introduction 197

11.2 Global Climate Change and UV Radiation 198

11.3 Effects of UV Radiation on Microalgae 199

11.4 UV‐induced Defence Mechanisms 201

11.5 Sun‐Screening Biomolecules as Key UV Photoprotectants 201

11.5.1 Mycosporine‐Like Amino Acids (MAAs) 202

11.5.2 Scytonemin 204

11.6 UV‐Induced Biosynthesis 206

11.7 Photoprotective Function 207

11.8 Conclusions 208

Acknowledgements 208

References 208

12 Plant Response: UB‐B Avoidance Mechanisms 217
Sunil K Gupta, Marisha Sharma, Farah Deeba and Vivek Pandey

12.1 Introduction 217

12.2 Ultraviolet Radiation: Common Source, Classification and Factors 219

12.2.1 Common Sources of UV‐R 219

12.2.2 Classification 219

12.2.3 Environmental Factors Affecting UV Level 220

12.3 UV‐B and Human Health 220

12.3.1 Effects on the Skin 220

12.3.2 Effects on the Eyes 220

12.4 UV‐B and Plant Responses 220

12.4.1 Morphological Responses 220

12.4.1.1 Visible Symptoms 220

12.4.1.2 Plant Growth and Leaf Phenology 221

12.4.1.3 Reproductive Morphology 222

12.4.1.4 UV‐B‐induced photomorphogenesis 222

12.4.2 Leaf Ultrastructure and Anatomy 222

12.4.3 Crop Yield 223

12.4.4 Photosynthesis 225

12.4.4.1 Pigments 225

12.4.4.2 Photosynthetic Machinery 225

12.4.5 Biochemical Responses 226

12.4.5.1 ROS Production in Plants 226

12.4.5.2 Free Radical Scavenging Mechanism 227

12.4.6 Molecular Responses 227

12.4.6.1 UV‐B and Genes 227

12.4.6.2 UV and Proteins 230

12.5 UV‐B Avoidance and Defence Mechanism 234

12.5.1 Avoidance at Morphological Level 234

12.5.1.1 Epicuticular Waxes 234

12.5.2 Avoidance at Biochemical Level 235

12.5.2.1 Possible Role of Pectin Endocytosis in UV‐B Avoidance 235

12.5.3 Avoidance at the Molecular Level 236

12.5.3.1 DNA Repair 236

12.5.3.2 Genes and Avoidance 237

12.5.3.3 UV‐B perceived by UVR8 Strongly Inhibits Shade Avoidance 237

12.5.4 UV‐B and Secondary Metabolites 238

12.5.4.1 Plant Phenolics 238

12.5.4.2 Anthocyanin 239

12.5.4.3 Alkaloids 240

12.5.4.4 Isoprenoids 240

12.5.4.5 Glucosinolates 240

12.6 UV‐B and its Significance 240

12.6.1 Ecological Significance 240

12.6.2 UV‐B and Plant Competition 241

12.7 Conclusion 242

Acknowledgments 243

References 244

13 Impact of UV‐B Exposure on Phytochrome and Photosynthetic Machinery: From Cyanobacteria to Plants 259
Shivam Yadav, Alok Kumar Shrivastava, Chhavi Agrawal, Sonia Sen, Antra Chatterjee, Shweta Rai and LC Rai

13.1 Introduction 259

13.2 Effect of UV‐B Irradiation on Photosynthetic Machinery of Cyanobacteria 260

13.2.1 Pigments 260

13.2.2 Photosynthetic Electron Transport System 261

13.2.3 Photophosphorylation and CO2 fixation 262

13.3 Effect of UV‐B Irradiation on Photosynthetic Machinery of Algae 262

13.4 Effect of UV‐B Irradiation on Photosynthetic Machinery of Higher Plants 264

13.4.1 Pigments 264

13.4.1.1 Phytochrome 264

13.4.1.2 Chlorophylls, carotenoids and other pigments 265

13.4.2 Photosystem II 265

13.4.2.1 Oxygen‐evolving complex 266

13.4.2.2 Plastoquinones and redox‐active tyrosines 266

13.4.2.3 D1 and D2 proteins 267

13.4.3 Photosystem I 267

13.4.4 Cytochrome B6F complex, ATP synthase and RuBisCO 267

13.4.5 Net photosynthesis 268

13.5 Conclusion and future perspective 268

Acknowledgements 268

References 269

14 Discovery of UVR8: New Insight in UV‐B Research 279
ShivamYadav and Neelam Atri

14.1 Introduction 279

14.2 Photoperception in Plants 280

14.3 Discovery of UVR8: UV‐B Photoreceptor 280

14.4 UVR8 Structure 281

14.4.1 Salt Bridge Interactions Mediate UVR8 Dimerization 281

14.4.2 Chromophore and Key Tryptophan Residues 281

14.5 Physiological Roles of UVR8 283

14.5.1 Photomorphogenic Response Regulation by UVR8 283

14.5.2 Regulation of Flavonoid Biosynthesis 284

14.5.3 Plant‐Pathogen and Plant‐Herbivore Interactions 284

14.6 Conclusion and Future Perspectives 284

References 285

15 UVR8 Signalling, Mechanism and Integration with other Pathways 289
Antra Chatterjee, Alok Kumar Shrivastava, Sonia Sen, Shweta Rai, Shivam Yadav and LC Rai

15.1 Introduction 289

15.2 UVR8‐Arbitrated Signalling 290

15.2.1 Constitutively Photomorphogenic 1 (COP1) 290

15.2.2 Elongated Hypocotyl 5 (HY5) and HYH 291

15.2.3 Repressor of UV‐B Photomorphogenesis 1 (RUP1) and RUP2 292

15.3 Molecular Mechanism of Photoreceptor‐Mediated Signalling 293

15.4 UVR8 Involvements in Different Pathways 296

15.4.1 Protection from Photo‐Inhibition and Photo Oxidative Stress 297

15.4.2 Flavonoid and Alkaloid Pathways 298

15.4.3 DNA Damage Repair 299

15.4.4 Defence Against Pathogens 299

15.4.5 Inhibition of Plant Shade Avoidance 300

15.4.6 Regulation of Leaf Morphogenesis 300

15.4.7 Regulation of Root Growth and Development 300

15.4.8 Circadian Clock 301

15.5 Conclusion and Future Perspectives 301

Acknowledgements 302

References 302

Index 309

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