Dr. Samiksha Singh, Assistant Professor in the Department of Botany, S.N. Sen B.V. Post Graduate College, Chhatrapati Shahu Ji Maharaj University, Kanpur, India. The Stanford University, USA, has named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2022 and 2023. Dr. Durgesh Kumar Tripathi, Associate Professor and Joint Coordinator (Research and Development) at Amity Institute of Organic Agriculture, Amity University Uttar Pradesh, Noida, India. Dr. Tripathi has worked extensively on heavy metals and toxic nanoparticles detoxification and has elaborated tolerance mechanisms in plants like rice, wheat, maize, tomato and brassica which could help in improving crop productivity benefitting for the society. Dr. Vijay Pratap Singh, Assistant Professor (Level 12) in the Department of Botany, C.M.P. Degree College, University of Allahabad, India. Clarivate Analytics has named Dr. Singh among the top 1% of the world’s most highly cited researchers for 2021–2023. Moreover, the Stanford University has also named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2019–2023.

• Contributors xiiiPreface xix1 Discovery and Background of GABA in Plants 1Gubbi Vani Ishika, Deepthi Puttegowda, Ranjith Raj, Manjunath Dammalli, and Ramith RamuAbbreviations 1Introduction 1History 2Background 3The GABA Metabolic Pathway in Plants 4Structure and Conformation of GABA 6Roles and Functions of GABA 7Plant Development 8Carbon and Nitrogen Metabolic Balance 8Enhancement of Storage Quality and Shelf Life 9pH Regulation 9Compatible Osmolyte 10Biotic and Abiotic Stress 10Temperature Stress 11Low Temperature 11High Temperature 11Drought 12Heavy Metals 12Ros 12Salt 13Conclusion 14What People Will Learn by Reading This Chapter 14How This Chapter Helps People Due to its Collective Content 15References 152 GABA Biosynthesis Pathways and its Signaling in Plants 19Nader Adamipour, Farzad Nazari, and Jaime A. Teixeira da SilvaGABA Production and Degradation Pathway 19Is GABA Only a Metabolite? 21Role of GABA in Signaling between Eukaryotes and Bacteria 22The Role of GABA Signaling in Regulating Pollen Tube Growth 23The Role of GABA Signaling in Regulating Stomatal Aperture 23Role of the GABA Shunt in Plants 24The Effect of GABA on Plant Growth 24The Effect of GABA on the Regulation of C:N Metabolism 25The Role of GABA in Improving Shelf Life and the Storage Quality of Products 26Role of GABA in Cytosolic pH Homeostasis 28The Impact of GABA on ROS 28Crosstalk of GABA with Other Signaling Molecules 29Abscisic Acid 29Ethylene 29Auxins 30Cytokinins 30Gibberellins 31Interaction of GABA, PAs, NO, and H 2 O 2 31GABA and Proline Interaction 32Conclusion and Future Prospects 32References 333 GABA and Its Crosstalk with Other Metabolites in Relation to Abiotic Stress Responses in Plants 43Akhilesh Kumar Pandey and Nishtha SrivastavaIntroduction 43Enzymes in GABA Metabolic Pathways 44Role of GABA Under Stressful Conditions in Plants 45GABA and Salt Stress 46GABA and Drought Stress 46GABA and Chilling Stress 48Crosstalk of GABA with Other Metabolites and Chemicals 48GABA with H 2 O 2 49GABA with Nitric Oxide (NO) 50GABA with Calcium 50Interplay of GABA with Plant Hormones 51GABA with Auxin 51GABA with Abscisic Acid 51GABA with Ethylene 52Mechanisms of Action of GABA in Plants Under Stress 52Conclusions and Future Perspectives 54References 544 GABA as a Signaling Molecule in Plants 65Navya Sreepathi, Deepthi Puttegowda, Nagma Firdose, Bhavya Somaplara Gangadharappa, V B Chandana Kumari, and Ramith RamuAbbreviations 65Introduction 66GABA in Plants as a Stress Response 67GABA as a Drought-Induced Stress Response in Plants 68GABA as a Stress Response in Plants Induced by Salinity 70GABA as a Temperature-Induced Stress Response in Plants 73GABA’s Role in Mediating Oxidative Stress-Induced Responses in Plants 74GABA’s Role in Mediating Pathogen and Herbivore Attack Stress-Induced Responses in Plants 76GABA Signaling in attKLM Operon (Bacteria) 76GABA Signaling Against Viruses, Fungi, and Insect Attack 77GABA Signaling in Plant Growth and Development 78GABA Signaling in Seed Germination 79GABA in ABA (Abscisic Acid) Signaling Pathway 80GABA Signaling for Auxin Biosynthesis for Plant Growth Under Fe Deficiency 81GABA in Root and Shoot Development 81GABA Influence in Pollen Tube Elongation 83GABA in Flowering, Fruit Development, and Ripening 83GABA-Mediated Regulation of Stomatal Aperture in Plants 85GABA Regulation in Stomatal Closure 85GABA Signaling for GORK Channels Under Hypoxia 86GABA in Ion-Exchange Regulation 86GABA’s Interplay with Diverse Signaling Pathways in Plants 88Conclusion and Future Prospectives 89References 905 GABA and Drought Stress 97Petronia Carillo and Andrea CarraIntroduction 97GABA Shunt in Plants 99GABA Accumulates in Plants Under Drought Stress 99GABA Accumulation Increases Drought Tolerance 100GABA Signaling and the Regulation of Stomatal Opening 102Conclusion 105References 1056 The Role of GABA on Programmed Cell Death and Senescence in Plants 111Fazilet Özlem Albayrak, Filiz Vardar, and Nihal Gören-SağlamIntroduction 111GABA Pathways 112The Roles of GABA under Stress Conditions 113GABA as a Signal Molecule 115GABA-Mediated Avoidance from PCD 116The Role of GABA on Leaf Senescence 118Conclusions 121References 1217 GABA and Nodulation in Plants 129Shubhra Khare, Ajey Singh, Km Niharika, Nimisha Amist, Zeba Azim, Rangoli Krishna, Nishtha Srivastava, and Narsingh Bahadur SinghIntroduction 129Nodulation in Leguminous Plants 130Functioning of γ-Aminobutyric Acid in Plants 132Functioning of GABA in Nodulation 134Conclusions and Future Prospects 136References 1378 GABA and Wounding Stress in Plants 143Neeraj Kumar Dubey, Vijay Bahadur Yadav, Kunwar Deelip Singh, Satyendra Kumar Yadav, Ran Vijay Singh, Amarjeet Singh, and Jogeswar PanigrahiIntroduction 143GABA: An Important Molecule for Plant 144GABA and Abiotic Stress 145Biotic Stress and Wound-Mediated GABA Fluctuation 146Transgenic Plants Expressing GABA and Effect on Herbivorous Performance 147References 1489 GABA in Plant Stress Response and Tolerance Mechanisms 155Şerife Palabıyık, İrem Çetinkaya, Tülay Öztürk, and Melike BorIntroduction 155Abiotic Stress and GABA 158Salt Stress and GABA 159Drought and GABA 161High Temperature and GABA 162Cold Stress and GABA 163Heavy Metal Stress and GABA 164Biotic Stress and GABA 165Conclusion and Future Prospects 166References 16610 GABA Priming Induced Modulations in the Redox Homeostasis of Plants under Osmotic Stress 173Kakkuzhiyulla Parambath Raj Aswathi, Kolothodi Chandran Jisha, Mathew Veena, Akhila Sen, Nair Gopalakrishnan Sarath, and Jos Thomas PuthurIntroduction 173Role of GABA in Plants 174GABA Priming and Oxidative Stress Mitigation 174Morphological Response 176Physiological Response: With Special Emphasis on ROS and Antioxidant Machinery 176Molecular Response 180Stress Signaling Cross-Talk 181Conclusion and Future Prospects 182Acknowledgments 182References 18211 Gamma-Aminobutyric acid-Mediated Heavy Metal Stress Tolerance in Plants 189Srijita Ghosh and Aryadeep RoychoudhuryIntroduction 189Health Benefits of GABA 191Biosynthesis of GABA 191GABA Transport in Plants 192Role of GABA in Abiotic Stress Tolerance 194GABA and Drought Stress 194GABA and Polyamines in Drought Stress 197GABA and Salt Stress 198GABA and Heat Stress 199GABA and Cold Stress 200GABA and Heavy Metal Stress 200Conclusion 202Acknowledgments 202References 20312 GABA and Heat Stress 211Zeba Azim, Shubhra Khare, Narsingh Bahadur Singh, Km Niharika, Ajey Singh, Ravi Kumar Yadav, and Nimisha AmistIntroduction 211GABA-Biosynthesis and Transport/Pathways in Plant 213GABA Morphological and Physiological Functions within Plants 213GABA and Abiotic Stress 214GABA and Heat Stress 215Conclusion 217References 21813 GABA and Oxidative Stress and the Regulation of Antioxidants 225Somayeh Rastegar and Pegah Sayyad-AminIntroduction 225Types and Characteristics of ROS 226ROS Generation in Plants under Normal and Stress Conditions 227The Importance of ROS Compartmentation for Plant Stress Adaptation 228Antioxidant Defense System in Plants 229Nonenzymatic Antioxidants 229Enzymatic Antioxidants 231Relationships of GABA Shunt and ROS during Stress Conditions 233The Response of GABA under Abiotic Stress Conditions 235Synthesis of Ascorbic Acid (AsA) 235Synthesis of Phenolic Compounds 236Conclusion 237References 23814 GABA in Relation to Cold and Chilling Stress 243Somayeh Rastegar and Emad Hamdy KhedrIntroduction 243Plant Strategies to Overcome Cold Stress 245γ-Aminobutyric Acid (GABA) 247GABA Biosynthesis in Plants 247Response Strategies of GABA in Cold Stress Tolerance 248Mitigating ROS Generation and Improving Antioxidant Systems During Cold Stress in Plants 248GABA Improves Nonenzyme Antioxidant System 250Regulating Phenol Metabolism 250Regulating Ascorbic Acid Metabolism 251Promoting Polyamine Synthesis 252Protecting Chloroplast Integrity 253Maintaining Higher ATP Content and Energy Charge 254Future Perspectives, Challenges, and Conclusion 256Future Perspectives 256Challenges 256Conclusion 256References 25715 Role of GABA Under Bacterial Stress in Plants 263Kuldeep Lahry, Akhilesh Kumar Pandey, and Sudhir SinghIntroduction 263GABA and Biotic Stress in Plants 266GABA and Bacterial Stress Response in Plants 267Molecular Basis of GABA Accumulation in Response to Bacterial Pathogens 269Glu-dependent Accumulation of GABA 269Glu-independent Accumulation of GABA 270The Involvement of GABA in the Interaction of Microbes with Plants 270Ralstonia solanacearum 270Pseudomonas syringae pv. tabaci 271Conclusions and Future Perspectives 272References 27316 GABA-Mediated Salt Stress Tolerance Through Physiological and Molecular Mechanisms 287Riya Johnson, Joy Mulakkal Joel, Koravantakamparambil Sulaiman Anjitha, Louis Noble, Parammal Faseela, and Jos Thomas PuthurIntroduction 287Concept of Salt Stress to Plants 288Salt Stress and Related Metabolic Changes 289GABA and Salinity Stress Tolerance 290GABA Improves Photosynthesis and Chlorophyll Fluorescence Parameters Under Salt Stress 291GABA Alleviates Oxidative Injury Induced by Salt Stress via Accumulation of the Osmolytes in Plants 295Molecular Changes Associated with GABA-Induced Salinity Stress Tolerance 298Conclusion 299Acknowledgments 299References 29917 GABA and Nutrient Deficiency 305Km Niharika, Shubhra Khare, Ajey Singh, Zeba Azim, Nimisha Amist, and Narsingh Bahadur SinghIntroduction 305An Overview of GABA 306Role of GABA in Plant Development 306Role of GABA in Different Stress Tolerance 307Different Mineral Nutrients and Their Role in Plant Development 308Different Nutrient Deficiencies in Plants 310Role of GABA in Nutrient Deficiency 311Concluding Remarks 315References 31518 GABA and Plant-Derived Therapeutics 321Lakshmi Jayaram, Deepthi Puttegowda, V. H. Pushpa, Shashank M. Patil, and Ramith RamuList of Abbreviations 321Introduction 322The Mechanism of GABA in Action: Neurotransmission and Its Effect on Neurons 322Plants with Reported GABAergic Activity: A Novel Source of Therapeutics 325Passiflora incarnata (Passion Flower) 327Piper methysticum (Kava) 328Withania somnifera (Ashwagandha, Indian Ginseng, Winter Cherry) 328Valeriana officinalis, (Valeriana) 329Scutellaria lateriflora, (Scullcap, Blue Skullcap) 330Melissa officinalis, (Lemon Balm) 330Ginkgo biloba, (Maiden Hair) 330Humulus lupulus, (Hops) 331Matricaria recutita, (True Chamomile) 331Centella asiatica, (Gotu Kola) 332Conclusion and Future Perspective 332References 333Index 343

Dr. Samiksha Singh, Assistant Professor in the Department of Botany, S.N. Sen B.V. Post Graduate College, Chhatrapati Shahu Ji Maharaj University, Kanpur, India. The Stanford University, USA, has named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2022 and 2023. Dr. Durgesh Kumar Tripathi, Associate Professor and Joint Coordinator (Research and Development) at Amity Institute of Organic Agriculture, Amity University Uttar Pradesh, Noida, India. Dr. Tripathi has worked extensively on heavy metals and toxic nanoparticles detoxification and has elaborated tolerance mechanisms in plants like rice, wheat, maize, tomato and brassica which could help in improving crop productivity benefitting for the society. Dr. Vijay Pratap Singh, Assistant Professor (Level 12) in the Department of Botany, C.M.P. Degree College, University of Allahabad, India. Clarivate Analytics has named Dr. Singh among the top 1% of the world’s most highly cited researchers for 2021–2023. Moreover, the Stanford University has also named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2019–2023.

• Contributors xiiiPreface xix1 Discovery and Background of GABA in Plants 1Gubbi Vani Ishika, Deepthi Puttegowda, Ranjith Raj, Manjunath Dammalli, and Ramith RamuAbbreviations 1Introduction 1History 2Background 3The GABA Metabolic Pathway in Plants 4Structure and Conformation of GABA 6Roles and Functions of GABA 7Plant Development 8Carbon and Nitrogen Metabolic Balance 8Enhancement of Storage Quality and Shelf Life 9pH Regulation 9Compatible Osmolyte 10Biotic and Abiotic Stress 10Temperature Stress 11Low Temperature 11High Temperature 11Drought 12Heavy Metals 12Ros 12Salt 13Conclusion 14What People Will Learn by Reading This Chapter 14How This Chapter Helps People Due to its Collective Content 15References 152 GABA Biosynthesis Pathways and its Signaling in Plants 19Nader Adamipour, Farzad Nazari, and Jaime A. Teixeira da SilvaGABA Production and Degradation Pathway 19Is GABA Only a Metabolite? 21Role of GABA in Signaling between Eukaryotes and Bacteria 22The Role of GABA Signaling in Regulating Pollen Tube Growth 23The Role of GABA Signaling in Regulating Stomatal Aperture 23Role of the GABA Shunt in Plants 24The Effect of GABA on Plant Growth 24The Effect of GABA on the Regulation of C:N Metabolism 25The Role of GABA in Improving Shelf Life and the Storage Quality of Products 26Role of GABA in Cytosolic pH Homeostasis 28The Impact of GABA on ROS 28Crosstalk of GABA with Other Signaling Molecules 29Abscisic Acid 29Ethylene 29Auxins 30Cytokinins 30Gibberellins 31Interaction of GABA, PAs, NO, and H 2 O 2 31GABA and Proline Interaction 32Conclusion and Future Prospects 32References 333 GABA and Its Crosstalk with Other Metabolites in Relation to Abiotic Stress Responses in Plants 43Akhilesh Kumar Pandey and Nishtha SrivastavaIntroduction 43Enzymes in GABA Metabolic Pathways 44Role of GABA Under Stressful Conditions in Plants 45GABA and Salt Stress 46GABA and Drought Stress 46GABA and Chilling Stress 48Crosstalk of GABA with Other Metabolites and Chemicals 48GABA with H 2 O 2 49GABA with Nitric Oxide (NO) 50GABA with Calcium 50Interplay of GABA with Plant Hormones 51GABA with Auxin 51GABA with Abscisic Acid 51GABA with Ethylene 52Mechanisms of Action of GABA in Plants Under Stress 52Conclusions and Future Perspectives 54References 544 GABA as a Signaling Molecule in Plants 65Navya Sreepathi, Deepthi Puttegowda, Nagma Firdose, Bhavya Somaplara Gangadharappa, V B Chandana Kumari, and Ramith RamuAbbreviations 65Introduction 66GABA in Plants as a Stress Response 67GABA as a Drought-Induced Stress Response in Plants 68GABA as a Stress Response in Plants Induced by Salinity 70GABA as a Temperature-Induced Stress Response in Plants 73GABA’s Role in Mediating Oxidative Stress-Induced Responses in Plants 74GABA’s Role in Mediating Pathogen and Herbivore Attack Stress-Induced Responses in Plants 76GABA Signaling in attKLM Operon (Bacteria) 76GABA Signaling Against Viruses, Fungi, and Insect Attack 77GABA Signaling in Plant Growth and Development 78GABA Signaling in Seed Germination 79GABA in ABA (Abscisic Acid) Signaling Pathway 80GABA Signaling for Auxin Biosynthesis for Plant Growth Under Fe Deficiency 81GABA in Root and Shoot Development 81GABA Influence in Pollen Tube Elongation 83GABA in Flowering, Fruit Development, and Ripening 83GABA-Mediated Regulation of Stomatal Aperture in Plants 85GABA Regulation in Stomatal Closure 85GABA Signaling for GORK Channels Under Hypoxia 86GABA in Ion-Exchange Regulation 86GABA’s Interplay with Diverse Signaling Pathways in Plants 88Conclusion and Future Prospectives 89References 905 GABA and Drought Stress 97Petronia Carillo and Andrea CarraIntroduction 97GABA Shunt in Plants 99GABA Accumulates in Plants Under Drought Stress 99GABA Accumulation Increases Drought Tolerance 100GABA Signaling and the Regulation of Stomatal Opening 102Conclusion 105References 1056 The Role of GABA on Programmed Cell Death and Senescence in Plants 111Fazilet Özlem Albayrak, Filiz Vardar, and Nihal Gören-SağlamIntroduction 111GABA Pathways 112The Roles of GABA under Stress Conditions 113GABA as a Signal Molecule 115GABA-Mediated Avoidance from PCD 116The Role of GABA on Leaf Senescence 118Conclusions 121References 1217 GABA and Nodulation in Plants 129Shubhra Khare, Ajey Singh, Km Niharika, Nimisha Amist, Zeba Azim, Rangoli Krishna, Nishtha Srivastava, and Narsingh Bahadur SinghIntroduction 129Nodulation in Leguminous Plants 130Functioning of γ-Aminobutyric Acid in Plants 132Functioning of GABA in Nodulation 134Conclusions and Future Prospects 136References 1378 GABA and Wounding Stress in Plants 143Neeraj Kumar Dubey, Vijay Bahadur Yadav, Kunwar Deelip Singh, Satyendra Kumar Yadav, Ran Vijay Singh, Amarjeet Singh, and Jogeswar PanigrahiIntroduction 143GABA: An Important Molecule for Plant 144GABA and Abiotic Stress 145Biotic Stress and Wound-Mediated GABA Fluctuation 146Transgenic Plants Expressing GABA and Effect on Herbivorous Performance 147References 1489 GABA in Plant Stress Response and Tolerance Mechanisms 155Şerife Palabıyık, İrem Çetinkaya, Tülay Öztürk, and Melike BorIntroduction 155Abiotic Stress and GABA 158Salt Stress and GABA 159Drought and GABA 161High Temperature and GABA 162Cold Stress and GABA 163Heavy Metal Stress and GABA 164Biotic Stress and GABA 165Conclusion and Future Prospects 166References 16610 GABA Priming Induced Modulations in the Redox Homeostasis of Plants under Osmotic Stress 173Kakkuzhiyulla Parambath Raj Aswathi, Kolothodi Chandran Jisha, Mathew Veena, Akhila Sen, Nair Gopalakrishnan Sarath, and Jos Thomas PuthurIntroduction 173Role of GABA in Plants 174GABA Priming and Oxidative Stress Mitigation 174Morphological Response 176Physiological Response: With Special Emphasis on ROS and Antioxidant Machinery 176Molecular Response 180Stress Signaling Cross-Talk 181Conclusion and Future Prospects 182Acknowledgments 182References 18211 Gamma-Aminobutyric acid-Mediated Heavy Metal Stress Tolerance in Plants 189Srijita Ghosh and Aryadeep RoychoudhuryIntroduction 189Health Benefits of GABA 191Biosynthesis of GABA 191GABA Transport in Plants 192Role of GABA in Abiotic Stress Tolerance 194GABA and Drought Stress 194GABA and Polyamines in Drought Stress 197GABA and Salt Stress 198GABA and Heat Stress 199GABA and Cold Stress 200GABA and Heavy Metal Stress 200Conclusion 202Acknowledgments 202References 20312 GABA and Heat Stress 211Zeba Azim, Shubhra Khare, Narsingh Bahadur Singh, Km Niharika, Ajey Singh, Ravi Kumar Yadav, and Nimisha AmistIntroduction 211GABA-Biosynthesis and Transport/Pathways in Plant 213GABA Morphological and Physiological Functions within Plants 213GABA and Abiotic Stress 214GABA and Heat Stress 215Conclusion 217References 21813 GABA and Oxidative Stress and the Regulation of Antioxidants 225Somayeh Rastegar and Pegah Sayyad-AminIntroduction 225Types and Characteristics of ROS 226ROS Generation in Plants under Normal and Stress Conditions 227The Importance of ROS Compartmentation for Plant Stress Adaptation 228Antioxidant Defense System in Plants 229Nonenzymatic Antioxidants 229Enzymatic Antioxidants 231Relationships of GABA Shunt and ROS during Stress Conditions 233The Response of GABA under Abiotic Stress Conditions 235Synthesis of Ascorbic Acid (AsA) 235Synthesis of Phenolic Compounds 236Conclusion 237References 23814 GABA in Relation to Cold and Chilling Stress 243Somayeh Rastegar and Emad Hamdy KhedrIntroduction 243Plant Strategies to Overcome Cold Stress 245γ-Aminobutyric Acid (GABA) 247GABA Biosynthesis in Plants 247Response Strategies of GABA in Cold Stress Tolerance 248Mitigating ROS Generation and Improving Antioxidant Systems During Cold Stress in Plants 248GABA Improves Nonenzyme Antioxidant System 250Regulating Phenol Metabolism 250Regulating Ascorbic Acid Metabolism 251Promoting Polyamine Synthesis 252Protecting Chloroplast Integrity 253Maintaining Higher ATP Content and Energy Charge 254Future Perspectives, Challenges, and Conclusion 256Future Perspectives 256Challenges 256Conclusion 256References 25715 Role of GABA Under Bacterial Stress in Plants 263Kuldeep Lahry, Akhilesh Kumar Pandey, and Sudhir SinghIntroduction 263GABA and Biotic Stress in Plants 266GABA and Bacterial Stress Response in Plants 267Molecular Basis of GABA Accumulation in Response to Bacterial Pathogens 269Glu-dependent Accumulation of GABA 269Glu-independent Accumulation of GABA 270The Involvement of GABA in the Interaction of Microbes with Plants 270Ralstonia solanacearum 270Pseudomonas syringae pv. tabaci 271Conclusions and Future Perspectives 272References 27316 GABA-Mediated Salt Stress Tolerance Through Physiological and Molecular Mechanisms 287Riya Johnson, Joy Mulakkal Joel, Koravantakamparambil Sulaiman Anjitha, Louis Noble, Parammal Faseela, and Jos Thomas PuthurIntroduction 287Concept of Salt Stress to Plants 288Salt Stress and Related Metabolic Changes 289GABA and Salinity Stress Tolerance 290GABA Improves Photosynthesis and Chlorophyll Fluorescence Parameters Under Salt Stress 291GABA Alleviates Oxidative Injury Induced by Salt Stress via Accumulation of the Osmolytes in Plants 295Molecular Changes Associated with GABA-Induced Salinity Stress Tolerance 298Conclusion 299Acknowledgments 299References 29917 GABA and Nutrient Deficiency 305Km Niharika, Shubhra Khare, Ajey Singh, Zeba Azim, Nimisha Amist, and Narsingh Bahadur SinghIntroduction 305An Overview of GABA 306Role of GABA in Plant Development 306Role of GABA in Different Stress Tolerance 307Different Mineral Nutrients and Their Role in Plant Development 308Different Nutrient Deficiencies in Plants 310Role of GABA in Nutrient Deficiency 311Concluding Remarks 315References 31518 GABA and Plant-Derived Therapeutics 321Lakshmi Jayaram, Deepthi Puttegowda, V. H. Pushpa, Shashank M. Patil, and Ramith RamuList of Abbreviations 321Introduction 322The Mechanism of GABA in Action: Neurotransmission and Its Effect on Neurons 322Plants with Reported GABAergic Activity: A Novel Source of Therapeutics 325Passiflora incarnata (Passion Flower) 327Piper methysticum (Kava) 328Withania somnifera (Ashwagandha, Indian Ginseng, Winter Cherry) 328Valeriana officinalis, (Valeriana) 329Scutellaria lateriflora, (Scullcap, Blue Skullcap) 330Melissa officinalis, (Lemon Balm) 330Ginkgo biloba, (Maiden Hair) 330Humulus lupulus, (Hops) 331Matricaria recutita, (True Chamomile) 331Centella asiatica, (Gotu Kola) 332Conclusion and Future Perspective 332References 333Index 343

Dr. Samiksha Singh, Assistant Professor in the Department of Botany, S.N. Sen B.V. Post Graduate College, Chhatrapati Shahu Ji Maharaj University, Kanpur, India. The Stanford University, USA, has named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2022 and 2023. Dr. Durgesh Kumar Tripathi, Associate Professor and Joint Coordinator (Research and Development) at Amity Institute of Organic Agriculture, Amity University Uttar Pradesh, Noida, India. Dr. Tripathi has worked extensively on heavy metals and toxic nanoparticles detoxification and has elaborated tolerance mechanisms in plants like rice, wheat, maize, tomato and brassica which could help in improving crop productivity benefitting for the society. Dr. Vijay Pratap Singh, Assistant Professor (Level 12) in the Department of Botany, C.M.P. Degree College, University of Allahabad, India. Clarivate Analytics has named Dr. Singh among the top 1% of the world’s most highly cited researchers for 2021–2023. Moreover, the Stanford University has also named Dr. Singh amongst the top 2% of the world’s most highly cited researchers for 2019–2023.

• Contributors xiiiPreface xix1 Discovery and Background of GABA in Plants 1Gubbi Vani Ishika, Deepthi Puttegowda, Ranjith Raj, Manjunath Dammalli, and Ramith RamuAbbreviations 1Introduction 1History 2Background 3The GABA Metabolic Pathway in Plants 4Structure and Conformation of GABA 6Roles and Functions of GABA 7Plant Development 8Carbon and Nitrogen Metabolic Balance 8Enhancement of Storage Quality and Shelf Life 9pH Regulation 9Compatible Osmolyte 10Biotic and Abiotic Stress 10Temperature Stress 11Low Temperature 11High Temperature 11Drought 12Heavy Metals 12Ros 12Salt 13Conclusion 14What People Will Learn by Reading This Chapter 14How This Chapter Helps People Due to its Collective Content 15References 152 GABA Biosynthesis Pathways and its Signaling in Plants 19Nader Adamipour, Farzad Nazari, and Jaime A. Teixeira da SilvaGABA Production and Degradation Pathway 19Is GABA Only a Metabolite? 21Role of GABA in Signaling between Eukaryotes and Bacteria 22The Role of GABA Signaling in Regulating Pollen Tube Growth 23The Role of GABA Signaling in Regulating Stomatal Aperture 23Role of the GABA Shunt in Plants 24The Effect of GABA on Plant Growth 24The Effect of GABA on the Regulation of C:N Metabolism 25The Role of GABA in Improving Shelf Life and the Storage Quality of Products 26Role of GABA in Cytosolic pH Homeostasis 28The Impact of GABA on ROS 28Crosstalk of GABA with Other Signaling Molecules 29Abscisic Acid 29Ethylene 29Auxins 30Cytokinins 30Gibberellins 31Interaction of GABA, PAs, NO, and H 2 O 2 31GABA and Proline Interaction 32Conclusion and Future Prospects 32References 333 GABA and Its Crosstalk with Other Metabolites in Relation to Abiotic Stress Responses in Plants 43Akhilesh Kumar Pandey and Nishtha SrivastavaIntroduction 43Enzymes in GABA Metabolic Pathways 44Role of GABA Under Stressful Conditions in Plants 45GABA and Salt Stress 46GABA and Drought Stress 46GABA and Chilling Stress 48Crosstalk of GABA with Other Metabolites and Chemicals 48GABA with H 2 O 2 49GABA with Nitric Oxide (NO) 50GABA with Calcium 50Interplay of GABA with Plant Hormones 51GABA with Auxin 51GABA with Abscisic Acid 51GABA with Ethylene 52Mechanisms of Action of GABA in Plants Under Stress 52Conclusions and Future Perspectives 54References 544 GABA as a Signaling Molecule in Plants 65Navya Sreepathi, Deepthi Puttegowda, Nagma Firdose, Bhavya Somaplara Gangadharappa, V B Chandana Kumari, and Ramith RamuAbbreviations 65Introduction 66GABA in Plants as a Stress Response 67GABA as a Drought-Induced Stress Response in Plants 68GABA as a Stress Response in Plants Induced by Salinity 70GABA as a Temperature-Induced Stress Response in Plants 73GABA’s Role in Mediating Oxidative Stress-Induced Responses in Plants 74GABA’s Role in Mediating Pathogen and Herbivore Attack Stress-Induced Responses in Plants 76GABA Signaling in attKLM Operon (Bacteria) 76GABA Signaling Against Viruses, Fungi, and Insect Attack 77GABA Signaling in Plant Growth and Development 78GABA Signaling in Seed Germination 79GABA in ABA (Abscisic Acid) Signaling Pathway 80GABA Signaling for Auxin Biosynthesis for Plant Growth Under Fe Deficiency 81GABA in Root and Shoot Development 81GABA Influence in Pollen Tube Elongation 83GABA in Flowering, Fruit Development, and Ripening 83GABA-Mediated Regulation of Stomatal Aperture in Plants 85GABA Regulation in Stomatal Closure 85GABA Signaling for GORK Channels Under Hypoxia 86GABA in Ion-Exchange Regulation 86GABA’s Interplay with Diverse Signaling Pathways in Plants 88Conclusion and Future Prospectives 89References 905 GABA and Drought Stress 97Petronia Carillo and Andrea CarraIntroduction 97GABA Shunt in Plants 99GABA Accumulates in Plants Under Drought Stress 99GABA Accumulation Increases Drought Tolerance 100GABA Signaling and the Regulation of Stomatal Opening 102Conclusion 105References 1056 The Role of GABA on Programmed Cell Death and Senescence in Plants 111Fazilet Özlem Albayrak, Filiz Vardar, and Nihal Gören-SağlamIntroduction 111GABA Pathways 112The Roles of GABA under Stress Conditions 113GABA as a Signal Molecule 115GABA-Mediated Avoidance from PCD 116The Role of GABA on Leaf Senescence 118Conclusions 121References 1217 GABA and Nodulation in Plants 129Shubhra Khare, Ajey Singh, Km Niharika, Nimisha Amist, Zeba Azim, Rangoli Krishna, Nishtha Srivastava, and Narsingh Bahadur SinghIntroduction 129Nodulation in Leguminous Plants 130Functioning of γ-Aminobutyric Acid in Plants 132Functioning of GABA in Nodulation 134Conclusions and Future Prospects 136References 1378 GABA and Wounding Stress in Plants 143Neeraj Kumar Dubey, Vijay Bahadur Yadav, Kunwar Deelip Singh, Satyendra Kumar Yadav, Ran Vijay Singh, Amarjeet Singh, and Jogeswar PanigrahiIntroduction 143GABA: An Important Molecule for Plant 144GABA and Abiotic Stress 145Biotic Stress and Wound-Mediated GABA Fluctuation 146Transgenic Plants Expressing GABA and Effect on Herbivorous Performance 147References 1489 GABA in Plant Stress Response and Tolerance Mechanisms 155Şerife Palabıyık, İrem Çetinkaya, Tülay Öztürk, and Melike BorIntroduction 155Abiotic Stress and GABA 158Salt Stress and GABA 159Drought and GABA 161High Temperature and GABA 162Cold Stress and GABA 163Heavy Metal Stress and GABA 164Biotic Stress and GABA 165Conclusion and Future Prospects 166References 16610 GABA Priming Induced Modulations in the Redox Homeostasis of Plants under Osmotic Stress 173Kakkuzhiyulla Parambath Raj Aswathi, Kolothodi Chandran Jisha, Mathew Veena, Akhila Sen, Nair Gopalakrishnan Sarath, and Jos Thomas PuthurIntroduction 173Role of GABA in Plants 174GABA Priming and Oxidative Stress Mitigation 174Morphological Response 176Physiological Response: With Special Emphasis on ROS and Antioxidant Machinery 176Molecular Response 180Stress Signaling Cross-Talk 181Conclusion and Future Prospects 182Acknowledgments 182References 18211 Gamma-Aminobutyric acid-Mediated Heavy Metal Stress Tolerance in Plants 189Srijita Ghosh and Aryadeep RoychoudhuryIntroduction 189Health Benefits of GABA 191Biosynthesis of GABA 191GABA Transport in Plants 192Role of GABA in Abiotic Stress Tolerance 194GABA and Drought Stress 194GABA and Polyamines in Drought Stress 197GABA and Salt Stress 198GABA and Heat Stress 199GABA and Cold Stress 200GABA and Heavy Metal Stress 200Conclusion 202Acknowledgments 202References 20312 GABA and Heat Stress 211Zeba Azim, Shubhra Khare, Narsingh Bahadur Singh, Km Niharika, Ajey Singh, Ravi Kumar Yadav, and Nimisha AmistIntroduction 211GABA-Biosynthesis and Transport/Pathways in Plant 213GABA Morphological and Physiological Functions within Plants 213GABA and Abiotic Stress 214GABA and Heat Stress 215Conclusion 217References 21813 GABA and Oxidative Stress and the Regulation of Antioxidants 225Somayeh Rastegar and Pegah Sayyad-AminIntroduction 225Types and Characteristics of ROS 226ROS Generation in Plants under Normal and Stress Conditions 227The Importance of ROS Compartmentation for Plant Stress Adaptation 228Antioxidant Defense System in Plants 229Nonenzymatic Antioxidants 229Enzymatic Antioxidants 231Relationships of GABA Shunt and ROS during Stress Conditions 233The Response of GABA under Abiotic Stress Conditions 235Synthesis of Ascorbic Acid (AsA) 235Synthesis of Phenolic Compounds 236Conclusion 237References 23814 GABA in Relation to Cold and Chilling Stress 243Somayeh Rastegar and Emad Hamdy KhedrIntroduction 243Plant Strategies to Overcome Cold Stress 245γ-Aminobutyric Acid (GABA) 247GABA Biosynthesis in Plants 247Response Strategies of GABA in Cold Stress Tolerance 248Mitigating ROS Generation and Improving Antioxidant Systems During Cold Stress in Plants 248GABA Improves Nonenzyme Antioxidant System 250Regulating Phenol Metabolism 250Regulating Ascorbic Acid Metabolism 251Promoting Polyamine Synthesis 252Protecting Chloroplast Integrity 253Maintaining Higher ATP Content and Energy Charge 254Future Perspectives, Challenges, and Conclusion 256Future Perspectives 256Challenges 256Conclusion 256References 25715 Role of GABA Under Bacterial Stress in Plants 263Kuldeep Lahry, Akhilesh Kumar Pandey, and Sudhir SinghIntroduction 263GABA and Biotic Stress in Plants 266GABA and Bacterial Stress Response in Plants 267Molecular Basis of GABA Accumulation in Response to Bacterial Pathogens 269Glu-dependent Accumulation of GABA 269Glu-independent Accumulation of GABA 270The Involvement of GABA in the Interaction of Microbes with Plants 270Ralstonia solanacearum 270Pseudomonas syringae pv. tabaci 271Conclusions and Future Perspectives 272References 27316 GABA-Mediated Salt Stress Tolerance Through Physiological and Molecular Mechanisms 287Riya Johnson, Joy Mulakkal Joel, Koravantakamparambil Sulaiman Anjitha, Louis Noble, Parammal Faseela, and Jos Thomas PuthurIntroduction 287Concept of Salt Stress to Plants 288Salt Stress and Related Metabolic Changes 289GABA and Salinity Stress Tolerance 290GABA Improves Photosynthesis and Chlorophyll Fluorescence Parameters Under Salt Stress 291GABA Alleviates Oxidative Injury Induced by Salt Stress via Accumulation of the Osmolytes in Plants 295Molecular Changes Associated with GABA-Induced Salinity Stress Tolerance 298Conclusion 299Acknowledgments 299References 29917 GABA and Nutrient Deficiency 305Km Niharika, Shubhra Khare, Ajey Singh, Zeba Azim, Nimisha Amist, and Narsingh Bahadur SinghIntroduction 305An Overview of GABA 306Role of GABA in Plant Development 306Role of GABA in Different Stress Tolerance 307Different Mineral Nutrients and Their Role in Plant Development 308Different Nutrient Deficiencies in Plants 310Role of GABA in Nutrient Deficiency 311Concluding Remarks 315References 31518 GABA and Plant-Derived Therapeutics 321Lakshmi Jayaram, Deepthi Puttegowda, V. H. Pushpa, Shashank M. Patil, and Ramith RamuList of Abbreviations 321Introduction 322The Mechanism of GABA in Action: Neurotransmission and Its Effect on Neurons 322Plants with Reported GABAergic Activity: A Novel Source of Therapeutics 325Passiflora incarnata (Passion Flower) 327Piper methysticum (Kava) 328Withania somnifera (Ashwagandha, Indian Ginseng, Winter Cherry) 328Valeriana officinalis, (Valeriana) 329Scutellaria lateriflora, (Scullcap, Blue Skullcap) 330Melissa officinalis, (Lemon Balm) 330Ginkgo biloba, (Maiden Hair) 330Humulus lupulus, (Hops) 331Matricaria recutita, (True Chamomile) 331Centella asiatica, (Gotu Kola) 332Conclusion and Future Perspective 332References 333Index 343