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Ascorbic acid (AsA), vitamin C, is one of the most abundant water-soluble antioxidant in plants and animals. In plants AsA serves as a major redox buffer and regulates various physiological processes controlling growth, development, and stress tolerance. Recent studies on AsA homeostasis have broadened our understanding of these physiological events. At the mechanistic level, AsA has been shown to participate in numerous metabolic and cell signaling processes, and the dynamic relationship between AsA and reactive oxygen species (ROS) has been well documented. Being a major component of the ascorbate-glutathione (AsA-GSH) cycle, AsA helps to modulate oxidative stress in plants by controlling ROS detoxification alone and in co-operation with glutathione. In contrast to the single pathway responsible for AsA biosynthesis in animals, plants utilize multiple pathways to synthesize AsA, perhaps reflecting the importance of this molecule to plant health. Any fluctuations, increases or decreases, in cellular AsA levels can have profound effects on plant growth and development, as AsA is associated with the regulation of the cell cycle, redox signaling, enzyme function and defense gene expression. Although there has been significant progress made investigating the multiple roles AsA plays in stress tolerance, many aspects of AsA-mediated physiological responses require additional research if AsA metabolism is to be manipulated to enhance stress-tolerance. This book summarizes the roles of AsA that are directly or indirectly involved in the metabolic processes and physiological functions of plants. Key topics include AsA biosynthesis and metabolism, compartmentation and transport, AsA-mediated ROS detoxification, as well as AsA signaling functions in plant growth, development and responses to environmental stresses. The main objective of this volume is therefore to supply comprehensive and up-to-date information for students, scholars and scientists interested in or currently engaged in AsA research.

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Ascorbic acid (AsA), vitamin C, is one of the most abundant water-soluble antioxidant in plants and animals. In plants AsA serves as a major redox buffer and regulates various physiological processes controlling growth, development, and stress tolerance. Recent studies on AsA homeostasis have broadened our understanding of these physiological events. At the mechanistic level, AsA has been shown to participate in numerous metabolic and cell signaling processes, and the dynamic relationship between AsA and reactive oxygen species (ROS) has been well documented. Being a major component of the ascorbate-glutathione (AsA-GSH) cycle, AsA helps to modulate oxidative stress in plants by controlling ROS detoxification alone and in co-operation with glutathione. In contrast to the single pathway responsible for AsA biosynthesis in animals, plants utilize multiple pathways to synthesize AsA, perhaps reflecting the importance of this molecule to plant health. Any fluctuations, increases or decreases, in cellular AsA levels can have profound effects on plant growth and development, as AsA is associated with the regulation of the cell cycle, redox signaling, enzyme function and defense gene expression. Although there has been significant progress made investigating the multiple roles AsA plays in stress tolerance, many aspects of AsA-mediated physiological responses require additional research if AsA metabolism is to be manipulated to enhance stress-tolerance. This book summarizes the roles of AsA that are directly or indirectly involved in the metabolic processes and physiological functions of plants. Key topics include AsA biosynthesis and metabolism, compartmentation and transport, AsA-mediated ROS detoxification, as well as AsA signaling functions in plant growth, development and responses to environmental stresses. The main objective of this volume is therefore to supply comprehensive and up-to-date information for students, scholars and scientists interested in or currently engaged in AsA research.

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Intro -- Preface -- Contents -- About the Editors -- Chemistry and Metabolism of Ascorbic Acid in Plants -- 1 Introduction -- 2 Chemical Properties and Redox Reaction of Ascorbic Acid -- 3 Metabolism of Ascorbic Acid -- 3.1 Biosynthetic Pathways of Ascorbic Acid -- 3.2 d-Mannose/l-Galactose Pathway -- 3.3 d-Galacturonate Pathway -- 3.4 Euglenid Pathway -- 3.5 d-Glucuronate Pathway -- 3.6 Degradation of Ascorbic Acid -- 4 Conclusions -- References -- The Role of Ascorbate in Plant Growth and Development -- 1 Introduction -- 2 Cell Cycle and Cell Elongation -- 3 Embryogenesis -- 4 Seed Germination -- 5 Root and Shoot Development -- 6 Flowering -- 7 Conclusions -- References -- Ascorbate as a Key Player in Plant Abiotic Stress Response and Tolerance -- 1 Introduction -- 2 H2O2 Scavenging and Ascorbate Recycling Under Abiotic Stress -- 2.1 Monodehydroascorbate Radical: Generation and Decay -- 2.2 Extracellular ROS Scavenging by Ascorbate in Abiotic Stress -- 3 Non-enzymatic Antioxidative and Pro-oxidative Activities of Ascorbate -- 4 Signalling Role of Ascorbate Under Abiotic Stress -- 4.1 Subcellular Distribution of Ascorbate Under Abiotic Stress -- 5 Photoprotective Role of Ascorbate to High Light -- 5.1 Ascorbate in Cross-Tolerance to High Light and UV-B Radiation -- 5.2 Ascorbate and Anthocyanins Biosynthesis -- 6 Ascorbate and Phytohormones in Cross-Tolerance -- 7 Role of Ascorbate in Response to Drought -- 8 Role of Ascorbate Under Metal Excess -- 9 Ascorbate as a Major Player in Growth-Defence Trade-Offs -- 10 Conclusions and Future Perspectives -- References -- Ascorbate Peroxidases: Crucial Roles of Antioxidant Enzymes in Plant Stress Responses -- 1 Introduction -- 2 Distribution of APX Isoforms in Plant Cells -- 3 Expression and Regulation -- 3.1 Transcriptional Regulation -- 3.2 Post-transcriptional Regulation -- 3.3 Post-transcriptional Regulation -- 4 Role as Antioxidant Enzymes -- 4.1 Chloroplastic APXs -- 4.2 Cytosolic APXs -- 4.3 Peroxisomal and Mitochondrial APXs -- 5 Role as Redox Signaling Regulators -- 6 Conclusion and Future Perspectives -- References -- Molecular and Functional Characterization of Monodehydro- ascorbate and Dehydroascorbate Reductases -- 1 Introduction -- 2 Monodehydroascorbate Reductase (MDHAR) -- 2.1 Molecular Properties -- 2.2 Isoforms and Their Localization -- 2.3 Enzymatic Properties -- 2.4 Structure -- 3 Dehydroascorbate Reductase (DHAR) -- 3.1 Molecular Properties -- 3.2 Isoforms and Localization -- 3.3 Enzymatic Properties -- 3.4 Structure -- References -- Regulation of Ascorbic Acid Biosynthesis in Plants -- 1 Introduction -- 2 Ascorbic Acid Accumulation in Plants -- 3 Internal Factors to Regulate Ascorbic Acid Biosynthesis -- 4 Environmental Factors to Regulate Ascorbic Acid Biosynthesis -- 5 Conclusion and Future Perspectives -- References -- Ascorbate-Glutathione Cycle and Abiotic Stress Tolerance in Plants -- 1 Introduction -- 2 AsA and GSH Functions -- 2.1 As Antioxidants -- 2.2 Other Functions of .