Plant Secondary Metabolites and Abiotic Stress E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
This book provides a comprehensive overview of cutting-edge biotechnological approaches for enhancing plant secondary metabolites to address abiotic stress, offering valuable insights into the future of utilizing plants for medicinal and industrial purposes.
Various books on plant secondary metabolites are available, however, no book has an overview of the recent trends and future prospects of all the methods available to enhance the contents of the plant secondary metabolites. Plant Secondary Metabolites and Abiotic Stress aims to give an overview of all the available strategies to ameliorate abiotic stress in plants by modulating secondary metabolites using biotechnological approaches including plant tissue cultures, synthetic metabolic pathway engineering, targeted gene silencing, and editing using RNAi and CRISPR CAS9 technologies.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Dedication Page
Foreword
Preface
Acknowledgments
About the Book
1 Biochemical Responses of Plants to Individual and Combined Abiotic Stresses
1.1 Introduction
1.2 Biochemical Responses to Individual Abiotic Stresses
1.3 Biochemical Responses to Combined Abiotic Stresses
1.4 Conclusion
References
2 Unraveling the Dynamics of Antioxidant Defense in Plants Under Drought Conditions
2.1 Introduction
2.2 Oxidative Stress in Plants Under Drought Condition
2.3 Antioxidant Defense System of Plants
2.4 Enzymatic Antioxidants and Their Response Against High ROS Under Drought Stress
2.5 ROS-Scavenging Non-Enzymatic Antioxidants and Their Response Under Drought Stress
2.6 Interplay of ROS With Reactive Carbonyl, Nitrogen, and Sulfur in Plant Cells: A Crosstalk Saga
2.7 Conclusion
References
3 Plant Metabolism and Abiotic Stress in Crops
3.1 Introduction
3.2 Concepts and Types of Abiotic Stress in Crop Plants
3.3 Plant Metabolism
3.4 Conclusion
References
4 Targeting Compatible Solutes for Abiotic Stress Tolerance in Plants
4.1 Introduction
4.2 Stress Caused by Abiotic Factors
4.3 Present Compatible Solutes for Stress Tolerance in Plants
4.4 Genetic Engineering Perspective for Compatible Solutes Mediated Abiotic Stress Resistance in Plants
4.5 Importance of Ethylene in the Controlling of Osmolytes Under Abiotic Stress
4.6 Importance of Salicylic Acid in Controlling of Osmolytes Under Abiotic Stress
4.7 Importance of Cytokinin in the Controlling of Osmolytes Under Abiotic Stress
4.8 Importance of Abscisic Acid in the Controlling of Osmolytes in an Abiotic Environment
4.9 Conclusion
Author Contributions
Conflict of Interest
References
5 Oxalate Crystals and Abiotic Stress Tolerance in Plants
5.1 Introduction
5.2 Formation of Crystals of Calcium Oxalate
5.3 Forms of Oxalate Crystals in Plants
5.4 Role of Oxalate Crystals to Cope with Abiotic Stresses
5.5 Conclusion
Acknowledgments
Competing Interests
References
6 Role of Signaling Molecules in Enhancing Abiotic Stress Tolerance in Plants
6.1 Introduction
6.2 Signaling Molecules
6.3 ROS Signaling
6.4 ABA in Stress Tolerance
6.5 Mitogen-Activated Protein Kinase (MAPK)
6.6 Cross-Talk Between Plants MAPK During Abiotic Stress Signal Transduction
6.7 CRISPR-Cas9 in Stress Tolerance
6.8 Conclusion
References
7 Impact of Abiotic Stress Signals on Secondary Metabolites in Plants
7.1 Introduction
7.2 Abiotic Stresses in Plants
7.3 Conclusion
7.4 Future Prospective
References
8 Role of Reactive Oxygen Species (ROS) in Plant Responses to Abiotic Stress
8.1 Introduction
8.2 Role of ROS in Plant Growth and Development
8.3 Involvement of ROS in Plants’ Stress Response
8.4 ROS Regulation in Plants
8.5 Genes and Proteins Involved in ROS Regulation in Plants
8.6 Conclusion
References
9 Reactive Oxygen, Nitrogen, and Sulfur Species Under Abiotic Stress in Plants
9.1 Introduction
9.2 Abiotic Stress in Plants: Molecular Perspective
9.3 Role of Oxygen in Abiotic Stress
9.4 Role of Sulfur in Abiotic Stress
9.5 Role of Nitrogen in Abiotic Stress
9.6 Cross-Talk Between Oxygen, Sulfur, and Nitrogen During Abiotic Stress
9.7 Conclusion and Future Prospective
References
10 Regulation of Plant Hormones Under Abiotic Stress Conditions in Plants
10.1 Introduction
10.2 ABA’s Function in Plant Defense Mechanisms
10.3 Hormonal Cross-Talk in Plant Defense
10.4 Plant Morphology and Anatomy
10.5 Photosynthesis
10.6 Hormonal Balance
10.7 Plants Under Abiotic Stress Benefit from Phytohormones Mediated by PGPR
10.8 Changes in Phytohormone Activity Caused by PGPR Under Drought
10.9 Future Prospects
10.10 Conclusion
Acknowledgments
References
11 Altering Secondary Metabolite Profiles in Barley for Crop Enhancement: Role of Novel ACT Domain Proteins
11.1 Introduction
11.2 Methods
11.3 Results
11.4 Discussion
11.5 Conclusion and Future Research Directions
References
12 Metabolites and Their Regulation During Salinity Stress in Plants
12.1 Introduction
12.2 Salt Stress Affects Plant Growth
12.3 Chloride Ion Toxicity
12.4 Na
+
Toxicity
12.5 Salinity Stress–Induced Oxidative Stress
12.6 Plant Responses Through Signaling and Metabolite Production
12.7 Metabolites and Their Regulation
12.8 Sugars and Sugar Alcohols
12.9 Secondary Metabolites
12.10 Nitrogen-Containing Metabolites
12.11 Other Metabolites
12.12 Metabolic Responses of Halophytes and Glycophytes During Salinity
12.13 How Plants Adapt to Salt Stress? A Comparative Approach
12.14 Conclusions and Future Perspectives
Acknowledgments
References
13 Phenolic Compounds in Plants
13.1 Introduction
13.2 Phenolic Acids
13.3 Flavonoids
13.4 Stilbenoids
13.5 Lignans
13.6 Conclusions and Further Research
References
14 Modulation of Metabolic Pathways Under Abiotic Stress in Plants
14.1 Introduction
14.2 Agriculture’s Vulnerability to Abiotic Stressors
14.3 Adaptations of Plants Under Abiotic Stress
14.4 Chemical Signaling in Plants Under Abiotic Stress
14.5 Gene Modification in the Acetic Acid Pathway
14.6 Tolerability to Abiotic Stress Caused by Salicylic Acid
14.7 Modifying the Metabolism of Thiamine
14.8 Abiotic Oxidative Stress Tolerance is Modulated by Hydrogen Peroxide Priming: Implications From ROS Scavenging and Detoxification
14.9 Stress and Innate Immunity in the Synthesis of Secondary Metabolites in Plants
14.10 Conclusion
References
15 Specific Secondary Metabolites of Medicinal Plants and Their Role in Stress Adaptation
Abbreviations
15.1 Introduction
15.2 Use of Selected Plants as Potential Immunostimulants
15.3 Plants and Plant-Derived Compounds With Immunomodulatory Potential
15.4 Plant Secondary Metabolite: Description and Their Health Effects
15.5 Plant Secondary Metabolites: Adaptative Potential
15.6 Conclusion
References
16 Effect of Abiotic Stress on Terpene Biosynthesis in Plants
16.1 Introduction
16.2 Terpenes: An Introduction and Classification
16.3 Biosynthesis of Terpenes
16.4 Functions and Mechanisms of Terpenes During Abiotic Stress
16.5 Conclusion
References
17 Exogenous Application of Plant Metabolites to Enhance Abiotic Stress Tolerance in Plants
17.1 Introduction
17.2 Plant’s Responses to Abiotic Stress
17.3 Exogenous Application of Plant Metabolites
17.4 Glutathione (GSH)
17.5 Melatonin (MEL)
17.6 Ascorbic Acid (AsA)
17.7 Nitric Oxide (NO)
17.8 Auxin
17.9 24-Eppibrassinolide (EBL)
17.10 Proline
17.11 Market Development and Cost Analysis of Plant Metabolites
17.12 Future Prospects
17.13 Conclusion
Acknowledgments
References
18 Genetic Engineering of Secondary Metabolic Pathways in Crops for Improving Abiotic Stress
18.1 Introduction
18.2 Role of Secondary Metabolites in Plants
18.3 Abiotic Stress and Secondary Metabolites
18.4 Genetic Engineering for Secondary Metabolite Production
18.5 Genome Editing Techniques for Generating Abiotic Stress–Tolerant Crops by Targeting SM Biosynthesis
18.6 Conclusion
References
19 Nanoelicitors Mediated Abiotic Stresses in Plant Defense Response Mechanisms: Current Review and Future Perspectives
19.1 Introduction
19.2 Major Classes of Secondary Metabolites
19.3 Nanomaterial as Elicitor
19.4 The Use of NPs to Protect Plants From Abiotic Stress
19.5 Nanoparticle Uptake, Translocation, and Internalization Pathways in Plants
19.6 How Nanoelicitors Respond to Abiotic Stressors?
19.7 The Way That NPs Signal Under Abiotic Stress Circumstances
19.8 Conclusion and Future Perspectives
References
20 Light Signaling and Plant Secondary Metabolites
20.1 Introduction
20.2 Photoregulation of PSMs
20.3 Role of Plant Secondary Metabolites in Regulating High Light Stress
20.4 Enhancing the PSM Production by Modulating the Light Environment
20.5 Conclusion
Acknowledgments
References
About the Editors
Index
Also of Interest
End User License Agreement
List of Tables
Chapter 2
Table 2.1 List of major enzymatic and non-enzymatic antioxidants in plants alo...
Chapter 4
Table 4.1 A brief list of a few compatible solute pathway genes that have been...
Chapter 7
Table 7.1 Effect of drought stress on plant secondary metabolites.
Table 7.2 Effect of salinity stress on plant secondary metabolites.
Table 7.3 Effect of UV-B stress on plant secondary metabolites.
Table 7.4 Effect of heavy metals stress on plant secondary metabolites.
Chapter 8
Table 8.1 Major genes involved in plants abiotic stress response through ROS r...
Chapter 9
Table 9.1 Sulfate transporters in plants, their role, and cellular localizatio...
Table 9.2 List of reactive species and responsive antioxidant explored for eng...
Chapter 10
Table 10.1 Phytohormones working mechanism in abiotic stress condition.
Table 10.2 Biological role of JA, SA, and ET in plant resistance response [jas...
Table 10.3 Abiotic stress–mediated responses.
Table 10.4 Exemplary studies showing how plants react to jasmonic acid (JA) in...
Chapter 11
Table 11.1 Summary information on the physiological and biochemical properties...
Table 11.2 Predicted molecular weight (Da), isoelectric point (pI), and protei...
Table 11.3 Amino acid similarities among
Hordeum vulgare
ACR-like protein.
Chapter 12
Table 12.1 Transgenic glycophytic plants harboring genes encoding enzymes invo...
Table 12.2 Different types of metabolites produced by halophytic plants during...
Chapter 15
Table 15.1 Plant-derived compounds with immunomodulatory potential from roots ...
Table 15.2 Plant-derived compounds with immunomodulatory potential from aerial...
Table 15.3 Plant-derived compounds with immunomodulatory potential from reprod...
Table 15.4 Plant-derived compounds with immunomodulatory potential from vegeta...
Chapter 16
Table 16.1 Various classes of terpenes.
Table 16.2 Role of terpene derivatives in membrane stabilization.
Chapter 17
Table 17.1 Impact of exogenous metabolite application: A quantitative analysis...
Table 17.2 Exogenously applied melatonin in plants: a quantitative analysis on...
Chapter 18
Table 18.1 Plant secondary metabolites and their functions.
Table 18.2 Different SMs produced in plants under various abiotic stresses.
Chapter 19
Table 19.1 Plant reactions to different nanoparticles when nanoelicited.
Chapter 20
Table 20.1 Effect of UV, fluorescent, and LED light sources on the production ...
List of Illustrations
Chapter 1
Figure 1.1 Different abiotic stress conditions leading to plant stress toleran...
Figure 1.2 Plant biochemical response to combined abiotic stress.
Chapter 2
Figure 2.1 Schematic representation of a plant showing the radical and non-rad...
Figure 2.2 Schematic representation of a plant exposed to the drought induced ...
Chapter 3
Figure 3.1 As part of the primary carbon metabolism process, the four biosynth...
Figure 3.2 Shikimic acid pathway.
Figure 3.3 MVA and MEP biosynthetic pathways for terpenoid compounds.
Chapter 4
Figure 4.1 Common abiotic stresses that affect plant growth.
Figure 4.2 Compatible solutes mediated abiotic stress resistance in plants.
Chapter 5
Figure 5.1 Different types of abiotic stress.
Figure 5.2 Mechanism of oxalate crystal mediated abiotic stress tolerance in p...
Chapter 6
Figure 6.1 Localization and processes for the generation of ROS in plant cells...
Chapter 7
Figure 7.1 Plant responds to different abiotic stresses by accumulation of var...
Chapter 8
Figure 8.1 Various abiotic stress conditions, leading to ROS production.
Figure 8.2 Damaging effect of ROS on plant growth and development.
Figure 8.3 Role of ROS in plant responses to abiotic stress: I. Synthesis and ...
Chapter 9
Figure 9.1 The interaction of reactive oxygen species (ROS) created in various...
Chapter 10
Figure 10.1 An indication of the mechanisms behind phytohormone-mediated stres...
Figure 10.2 An explanation of the signaling networks for plant hormones and ho...
Figure 10.3 General defense arrangements and underlying regulatory networks ar...
Figure 10.4 Integration of signal from abiotic stressors and adaptation in pla...
Chapter 11
Figure 11.1 Mapping the genomic landscape: Chromosomal locations and gene stru...
Figure 11.2 Unveiling evolutionary relationships: (a) Phylogenetic tree of bar...
Figure 11.3 Schematic diagram of barley (
Hordeum vulgare
ssp.
vulgare
) ACR-lik...
Figure 11.4 Comparative transcriptome analysis reveals differentially expresse...
Chapter 12
Figure 12.1 Overview of salt stress responses in glycophytic and halophytic pl...
Chapter 13
Figure 13.1 The basic division of the phenolic compounds.
Figure 13.2 The structures of the major phenolic acids.
Figure 13.3 The basic division of the flavonoids.
Figure 13.4 The structures of the flavanones naringenin and hesperetin.
Figure 13.5 The structures of the flavones luteolin and apigenin.
Figure 13.6 The structures of the isoflavones daidzein and genistein.
Figure 13.7 The structures of the flavan-3-ols catechin and epicatechin.
Figure 13.8 The structures of the quercetin, kaempferol, and myricetin.
Figure 13.9 The structures of the major anthocyanidins.
Figure 13.10 The structure of the stilbenoid resveratrol.
Figure 13.11 The basic lignan chemical structure.
Chapter 14
Figure 14.1 A typical plant stress response pathway. Initiating a major and co...
Figure 14.2 The calcium signaling network’s components. Calmodulin, a signific...
Figure 14.3 The signaling molecule NO. Arginine is used to create NO (a). An e...
Figure 14.4 The production of acetic acid by plants. The enzyme PDC1 converts ...
Figure 14.5 Scheme for the production of TDP and thiamine in plants the routes...
Figure 14.6 Diagram showing the production of H
2
O
2
at various intra- and extra...
Figure 14.7 The diverse stresses and biotic disturbances that plants encounter...
Chapter 15
Figure 15.1 Scheme of primary and secondary metabolism with an accent on origi...
Chapter 16
Figure 16.1 Molecular structure of isoprene.
Figure 16.2 Formation of a monoterpene molecule from two isoprene units.
Figure 16.3 Structures of selected iridoid molecules.
Figure 16.4 Structures of selected monoterpene molecules.
Figure 16.5 Formation of a sesquiterpene (C15) molecule from three isoprene un...
Figure 16.6 Selected sesquiterpenoid molecules.
Figure 16.7 Formation of a diterpene molecule from four isoprene units.
Figure 16.8 Molecular structure of paclitaxel.
Figure 16.9 Formation of a triterpene molecule from squalene (six isoprene uni...
Figure 16.10 The mevalonic acid pathway.
Figure 16.11 The MEP pathway.
Figure 16.12 Generation of various types of terpenoids from DMAPP.
Figure 16.13 The biosynthetic pipeline to sterols and triterpenes. Sterols and...
Chapter 17
Figure 17.1 Plants exhibit various defense mechanisms and possess a regulatory...
Figure 17.2 An illustration of the general molecular processes involved in a p...
Chapter 18
Figure 18.1 Agrobacterium-mediated genetic engineering of plant for secondary ...
Chapter 19
Figure 19.1 Different methods of absorbing, ingesting, and translocating nanop...
Figure 19.2 Diagrammatic representation of a potential process for the inducti...
Guide
Cover Page
Table of Contents
Series Page
Title Page
Copyright Page
Dedication Page
Foreword
Preface
Acknowledgments
About the Book
Begin Reading
About the Editors
Index
Also of Interest
WILEY END USER LICENSE AGREEMENT
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Plant Secondary Metabolites and Abiotic Stress
Edited by
Ganesh C. Nikalje
Mohd. Shahnawaz
Jyoti Parihar
Hilal Ahmad Qazi
Vishal N. Patil
and
Daochen Zhu
This edition first published 2024 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2024 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 978-1-394-18580-1
Front cover images supplied by Pixabay.comCover design by Russell Richardson
Dedication
Each editor wishes to dedicate this book to their respective parents, spouses, and kids.
Foreword
In an ever-changing world, plants are constantly subjected to a multitude of environmental challenges, ranging from drought and salinity to extreme temperatures and chemical imbalances. These abiotic stresses pose significant threats to global agricultural productivity, prompting an urgent need for innovative solutions to enhance plant resilience. This edited volume, Plant Secondary Metabolites and Abiotic Stress, stands at the forefront of this critical endeavor, offering a comprehensive exploration of the intricate interplay between plants and their environment.
The chapters within this volume provide an in-depth examination of the biochemical responses of plants to individual and combined abiotic stresses, shedding light on the remarkable adaptability that nature has bestowed upon these organisms. From the unraveling of antioxidant defense mechanisms to the modulation of metabolic pathways, each chapter unravels a distinct facet of how plants navigate through adversity.
Through the collective wisdom of esteemed experts in the field, this book delves into the intricate dance between plant metabolism and abiotic stresses in crops, offering crucial insights into how we can fortify our agricultural systems against future challenges. The chapters on targeting compatible solutes and oxalate crystals underscore the potential of harnessing nature’s own arsenal to bolster stress tolerance in plants.
The role of signaling molecules emerges as a central theme, with a dedicated chapter illustrating their pivotal contribution to enhancing abiotic stress tolerance. From there, the focus shifts toward the profound impact of abiotic stress signals on secondary metabolites, illuminating a nexus that holds great promise for advancing our understanding of plant resilience.
Reactive oxygen species (ROS) have long stood as double-edged swords in plant physiology, and their complex role in abiotic stress responses is masterfully dissected in two chapters that explore the intricacies of oxygen, nitrogen, and sulfur species. The regulation of plant hormones under abiotic stress follows suit, unveiling the nuanced orchestration of signaling networks that underpin plant survival strategies.
In a testament to the power of biotechnological innovation, this volume unveils pioneering research on genetic engineering of secondary metabolite pathways. By harnessing the potential of novel ACT domain proteins, we glimpse a future where crop enhancement is not only achievable but also sustainable and transformative.
From specific secondary metabolites in medicinal plants to the delicate balance of terpene biosynthesis, this collection provides a diverse array of insights that resonate across disciplines. The application of exogenous plant metabolites emerges as a potent tool in enhancing stress tolerance, demonstrating the potential for holistic approaches to agricultural resilience.
The book concludes with a visionary exploration of nanoelicitors, offering a glimpse into the future of plant defense mechanisms. By harnessing cutting-edge technologies at the nanoscale, we embark on a path toward unprecedented strides in abiotic stress management.
As we navigate the uncharted territories of an increasingly unpredictable climate, the knowledge distilled within this volume serves as a beacon of hope and a call to action. Plant Secondary Metabolites and Abiotic Stress stands as a testament to the power of interdisciplinary collaboration and the boundless potential of scientific inquiry. May its insights inspire and equip a new generation of scholars and practitioners dedicated to securing the future of our agricultural landscapes.
(Dr. Charles Oluwaseun Adetunji)
Professor,
Applied Microbiology, Biotechnology and Nanotechnology Laboratory,
Department of Microbiology, Edo State University Uzairue,
Iyamho, Nigeria
Preface
We are dependent on plants for food, furniture, constructions, and fuel since pre-historic times. Plants in all forms have tendered their services to mankind. Human have selected plants based on the value and potential for domestication. Among the various factors, affecting the plant growth and crop yield, abiotic stresses are regarded as most common factor. Abiotic stresses, such as extreme temperatures, drought, flood, salinity, and heavy metals, severely restrict crop productivity and quality and result in yield reductions of more than 60%. Plant synthesizes various secondary metabolites to resist in the changing environment and to cross talk with other biological entities. So, in the present book, an attempt was made to understand impact of abiotic stress on the secondary metabolites of the plant under varied habitat. We have selected 20 excellent chapters contributed by the experts across the globe.
The opening chapter (Chapter 1) of the book provides an insightful overview of the biochemical responses exhibited by plants in response to both individual and combined abiotic stresses. Chapter 2 delves into unraveling the dynamics of antioxidant defense mechanisms in plants experiencing drought conditions. In Chapter 3, a comprehensive exploration of plant metabolism and its relationship with abiotic stresses in crops is presented. Moving forward, Chapter 4 meticulously describes the targeting of compatible solutes as a strategy for enhancing abiotic stress tolerance in plants. Chapter 5 reports on oxalate crystals and their role in conferring abiotic stress tolerance to plants. Chapter 6 sheds light on the pivotal role played by signaling molecules in augmenting abiotic stress tolerance in plants. Chapter 7 pools together the various impacts of abiotic stress signals on secondary metabolites in plants. Chapter 8 provides insights into the role of reactive oxygen species (ROS) in mediating plant responses to abiotic stress. Chapter 9 specifically highlights the involvement of reactive species, including oxygen, nitrogen, and sulfur, under abiotic stress conditions in plants. In Chapter 10, the regulation of plant hormones in response to abiotic stress is thoroughly examined. Chapter 11 details the alteration of secondary metabolite profiles in wheat for crop enhancement, focusing on the role of novel ACT domain proteins. Chapter 12 addresses the modulation of metabolites and their regulation during salinity stress in plants. Chapter 13 explores the role of phenolic compounds under combined abiotic stress in plants. Chapter 14 reports on the intricate modulation of metabolic pathways under various abiotic stresses. Chapter 15 delves into the specific secondary metabolites found in medicinal plants and their significant role in stress adaptation. Chapter 16 explores the effects of abiotic stress on terpene biosynthesis in plants. Chapter 17 discusses the application of exogenous plant metabolites to enhance abiotic stress tolerance. Chapter 18 provides insights into genetic engineering approaches for manipulating secondary metabolite pathways in crops to improve abiotic stress resilience. Chapter 19 focuses on nanoelicitors and their mediated effects on abiotic stress responses in plant defense mechanisms, offering a current review and future perspectives. Finally, Chapter 20 provides an overview of the impact of plant photoreceptors and transcription factors on plant growth and development, influencing secondary metabolite synthesis and shaping defense strategies for stress tolerance.
We sincerely hope that this reference book proves to be a valuable resource for learning and appreciating the diverse facets covered within its chapters. We eagerly welcome suggestions and constructive criticism from students, teachers, and researchers to further enhance the quality and relevance of this comprehensive work.
Acknowledgments
We are deeply grateful to all the individuals and institutions that have played a significant role in the realization of this edited book. Their unwavering support, expertise, and dedication have made this project possible.
First and foremost, we would like to express our gratitude to the esteemed authors who have contributed their insightful chapters to this book. Your expertise and willingness to share your knowledge have enriched the content and scope of this work.
We extend our heartfelt appreciation to our colleagues and fellow researchers who provided invaluable feedback during the development of this book. Your suggestions and critiques have helped shape it into its final form.
We are indebted to Scrivener Publishing–John Wiley and Sons, Beverly, MA, for believing in the importance of this book project, providing necessary resources, and guiding us through the publication process with professionalism and commitment.
We would also like to thank the reviewers who meticulously evaluated the chapters, offering constructive feedback that contributed to the overall quality of the book.
A special note of appreciation goes to our family and friends for their unwavering support and understanding during the countless hours dedicated to this endeavor.
Lastly, we want to acknowledge the broader academic and research community for fostering an environment where collaboration and the sharing of ideas are valued and encouraged.
Thank you all for your contributions, encouragement, and support. This book would not have been possible without each and every one of you.
Sincerely,Editors
About the Book
Plant synthesizes various secondary metabolites beside its primary metabolites to resist the changing environment and to cross talk with other biological entities. These secondary metabolites have also found to have various activities against numerous human diseases. So, to harvest these medicinal principals from the medicinal plants, people have exploited the plant germplasm from the natural habitat at an alarming rate. Most of the medicinal plants are now considered as the endangered. As per the reports, the contents of these naturally occurring medicinal components were found low in most of the plants. So, it was needed to enhance the contents of such key principle components of the plants. Various people around the globe tried to enhance the contents of the secondary metabolites in the plants using different methods and were reported significant enhancement of the targeted secondary metabolites in the tested plants. The most common abiotic stress employed to enhance the contents of the plant secondary metabolites are (1) salinity stress, (2) mutagenic stress, (3) hypoxia stress, (4) drought stress, (5) cold stress, etc.
In the literature, various books on plant secondary metabolites are available; however, no book has overviewed the recent trends and future prospective of all the methods available to enhance the contents of the plant secondary metabolites. Hence, in the present intended edited book, we aimed to overview all the available strategies employed to ameliorate these abiotic stresses in the plants by modulating secondary metabolites using biotechnological approaches, viz., plant tissue culture, synthetic metabolic pathway engineering, targeted gene silencing, and editing using RNAi and CRISPR/Cas9 technologies.
These edited books highlighted the different aspects of the biotic and abiotic stress to enhance the stress tolerance potential of the plants. Another book have discussed genetic basis, metabolic insights, and plant signaling under both abiotic and biotic stresses to adapt the plants with improved responses to environmental stresses. Most of the books highlighted the different mechanism followed by the plant to alleviate the salinity stress and development of salt tolerant plants. Some authors also enlisted approaches to improve biotic and abiotic stress tolerance in plants and documented the role of major signaling molecules in different stresses and their use in crop improvement.
However, a book targeting plants ameliorating stress tolerance posed by all the abiotic stress factors (temperature, salinity, pH, drought, and mutagenic forces) is in the literature. So, in the present intended edited volume, an attempt was made to overview the current developments in regulation of plant secondary metabolites under varied abiotic stress forces with case studies from different parts of the world.
The primary audience of this work would be the people working in plant stress physiology and plant secondary metabolites. The secondary audience will be UG and PG students for their studies and dissertations.
The book covers all aspects of plant environment interaction with abiotic stress,
viz
., drought, temperature, salinity, photoperiod, and gamma radiations.
The chapters cover the latest evidence-based approaches to understand the insights of plant secondary metabolites response to the abiotic stress at both
in vitro
and
in vivo
levels.
It is easy to follow mechanism of stress tolerance and modulation of plant secondary metabolites in the book.
Each chapter will be supplemented with ample illustrations and figures at both
in vitro
and
in vivo
levels.
The intended book will have a special section that covers the controversies in genetic engineering to produce the transgenic lines to alleviate the level of abiotic stress.
The book will illustrate the biotechnological approaches, such as RNAi and CRISPR/Cas9 to enhance stress tolerance in the plants to overcome the abiotic stress.
1Biochemical Responses of Plants to Individual and Combined Abiotic Stresses
Kanchan Sharma1, Kritika Jalota1, Chiti Agarwal2, Puja Pal1 and Suruchi Jindal1*
1Division of Molecular Biology and Genetic Engineering, School of Bioengineering and Biosciences, Lovely Professional University, Phagwara, Punjab, India
2Washington State University, Pullman, Washington, USA
Abstract
The natural environmental conditions constantly subject the plants to different kinds of abiotic stress conditions, and multiple abiotic stress conditions at once are also common. Understanding the plant’s biochemical reactions to individual as well as combined abiotic stresses is essential to know the plant adaptation processes and develop strategies to increase stress tolerance. The main molecular pathways and biochemical processes in response to individual and combined abiotic stress situations were examined. Plants activate numerous biochemical defense mechanisms when specific stress conditions occur including high temperature, cold, drought, flood, salt stress, and heavy-metal contamination, which includes metal chelation procedures, compatible solute synthesis, the buildup of heat-shock proteins, and antioxidant defense mechanisms activation, among others. Plants, when subjected to combined abiotic stressors, can have distinctive responses dissimilar from those seen in single stress conditions. The stress factors that interact with one another can have positive or negative outcomes on physiology and metabolism of the plants. Furthermore, regulation of hormones and signaling pathways has an important part in the modulation of physiological responses to abiotic stressors through coordinated biochemical reactions.
Keywords: Abiotic stress, metabolites, signaling pathways, biochemical response
1.1 Introduction
Abiotic stress has been the subject of major recent advancements in flora. However, the majority of investigations depict the reaction of plants to environmental changes and have concentrated on a particular stress condition that is delivered to plants under laboratory conditions. In the natural environment, plants face a constant array of abiotic stresses, which can significantly impede their growth, development, and productivity. These stresses can manifest individually or in combination, posing significant challenges to plant survival and performance. The impact of these conditions on plant metabolism may exhibit unique characteristics that differ from the effects induced by individual stress conditions. Therefore, their response to abiotic challenges under the field settings can vary significantly from these responses observed in controlled laboratory conditions [1–3]. To fully understand the underlying processes of stress tolerance and to create methods to increase plant tolerance against changing environments, it is essential to know plant’s biochemical reactions against individual and combined abiotic stressors (Figure 1.1).
Figure 1.1 Different abiotic stress conditions leading to plant stress tolerance and adaptation.
1.2 Biochemical Responses to Individual Abiotic Stresses
1.2.1 Heat Stress
A primary abiotic stressor that adversely affects the growth, development, and agricultural productivity of plants is high temperature. Investigation of the plant’s biochemical responses to high-temperature stress becomes important in creating techniques to improve crop heat tolerance when global temperatures rise because of climatic changes. Protein denaturation and oxidative damage occur from stress due to high temperature, which disturbs cellular homeostasis. Different biochemical defense systems are triggered in response by plants. Heat-shock protein (HSP) buildup is one of these. These aid with protein folding and prevent aggregation and molecular chaperones [4]. To counteract ROS accumulation (reactive oxygen species) and mitigate oxidative stress, plants enhance their antioxidant defense mechanisms [5]. The primary impact of high-temperature stress is protein denaturation, which disrupts cellular homeostasis and impairs normal metabolic functions. The plants trigger particular metabolic reactions to combat protein denaturation. Under high-temperature stress circumstances, for protein folding and refolding, HSPs and molecular chaperones are essential. The physiological, biochemical, and molecular factors underlying a plant’s capacity to withstand heat stress were investigated, which emphasized the significance of HSPs in preserving protein integrity and avoiding aggregation under heat stress, especially small HSPs (sHSPs) and HSP70. As molecular chaperones, these proteins help denatured proteins fold correctly and stop them from irreversibly aggregating. Plant’s main metabolic reactions to heat stress are the synthesis and accumulation of these chaperones [4, 6].
Plant cells frequently produce ROS during high heat conditions. ROS includes superoxide radicals (O2–), hydrogen peroxide (H2O2), and hydroxyl radicals (OH). These can harm cellular constituents like lipids, proteins, and DNA through oxidative stress. Plants activate their antioxidant defensive mechanisms to combat ROS buildup and oxidative stress. The activation of antioxidant enzymes occurs as a biological response to high-temperature stress, including SOD (superoxide dismutase), CAT (catalase), and POX (peroxidases). These enzymes are essential for neutralizing ROS and preserving cellular redox balance. Superoxide radicals are changed into H2O2 by SOD, which is then detoxified by the enzymes CAT and POX. Additionally, plants are shielded from oxidative damage by the production and buildup of non-enzymatic antioxidants like ascorbate (vitamin C), glutathione (GSH), and tocopherols (vitamin E) [4, 7]. Under high-temperature stress, for combatting deleterious effects of heat, they undergo metabolic modifications[8]. These modifications entail changes to metabolic pathways, particularly those involved in osmolyte accumulation, energy metabolism, and the creation of secondary metabolites. To sustain cellular hydration and osmotic equilibrium while under the stress of high temperatures, plants acquire suitable solutes or osmolytes, like proline, glycine betaine, and carbohydrates. During heat stress, particularly proline is crucial for stabilizing proteins, preserving membrane integrity, and turgor pressure of cells. Furthermore, the ability of plants to use energy can be impacted by severe temperature stress. When cells are under stress, it frequently results in increased respiration rates and an increase in the need for ATP. To meet the energy requirements of heat-stressed cells, plants may boost glycolysis, respiration, and photosynthetic rates [4, 9].
Phytohormones are also essential for controlling the physiological reactions to stress caused by high temperatures. The hormone ABA (abscisic acid) is associated with plant stress reactions, especially high-temperature stress. For the reduction of the effects of high-temperature plant water status, ABA buildup under heat stress circumstances regulates stomatal closure, limiting water loss through transpiration [4, 10]. Additionally, ABA regulates the antioxidant enzyme and protein production genes in stress response, which helps plants adapt to high temperatures in general. Other hormones involved in the reaction to extreme temperature stress include ethylene and Jasmonic acid (JA). Under stressful circumstances, ethylene is known to control several physiological and biochemical mechanisms. These include aging, ripening of fruits, and defensive responses [8]. High-temperature stress activates both stress-related genes and generates ethylene. HSFs are genetic expression–controlling transcription factors that mediate heat genes that activate during stress to orchestrate high-temperature stress response [11]. Heat-shock domain, a conserved DNA-binding domain, is what distinguishes HSFs from other proteins (HSD). HSFs can attach to particular DNA sequences termed heat-shock elements (HSEs). These are located at the promoter regions of target genes because of the HSD. HSFs interact with chaperones to remain in an inactive monomeric state under typical circumstances. HSFs, however, experience conformational variations undergoing heat stress, which results in trimerization and activation [6]. Numerous high-temperature stress-responsive genes are upregulated when HSFs bind to HSEs in the target gene’s promoter. These genes produce heat stress proteins, also known as HSPs. HSPs play a role as molecular chaperones in high-temperature stress situations to aid protein folding, inhibit protein aggregation, and support protein stability [12].
Excessive heat stress causes osmotic equilibrium disruption within cells, which causes the cells to become dehydrated and get damaged. Plants accumulate osmoprotectants and suitable solutes including proline, glycine betaine, and carbohydrates to prevent these effects. These substances prevent damage to cellular structures, stabilize proteins, scavenge ROS, and preserve cellular osmotic potential. Under heat stress, proline in particular accumulates quickly and functions as a suitable solute to prevent the denaturation of proteins and membranes [13]. The fluidity and stability of cellular membranes can also be negatively impacted by heat stress, which can result in membrane lipid peroxidation and malfunction. In order to improve membrane stability and integrity in response to heat stress, plants modify their lipid metabolism. Specific lipids, including phospholipids, galactolipids, and sterols, are produced during heat stress and aid in maintaining membrane fluidity and stability. In order to maintain the best fluidity and stability under heat stress, the fatty acid content of membranes must be altered by lipid desaturation enzymes such as omega-3 fatty acid desaturase [14].
1.2.2 Cold Stress
When plants experience cold stress, particular genes involved in cold tolerance begin to express. C-repeat binding factors (CBFs), a transcription factor attaches dehydration-responsive element/C-repeat (DRE/CRT) cis-acting element found in the promoters of target genes, control the cold responding genes [15]. The gene expression leads to the production of antifreeze proteins, dehydrins, and cold-shock proteins (CSPs), which guard cellular structures and membranes against harm caused by low temperatures. It also causes osmoprotectants and compatible solutes to build up inside plant cells. These substances support cellular osmotic balance, stabilize proteins, and shield cellular structures from damage by the cold. In response to cold stress, solutes such as sugars (such as sucrose), proline, and polyamines (such as putrescine and spermidine) might accumulate [16]. Plants can avoid dehydration, preserve cellular hydration, and shield macromolecules from denaturation brought on by the cold by accumulating these solutes. Another reaction to cold stress is that plants may develop ROS accumulation leading to oxidative damage to parts of cells. Plants activate antioxidant defense mechanisms like that of heat stress. This is done to scavenge ROS and preserve redox equilibrium. Antioxidant enzymes including SOD, CAT, POD, and ascorbate peroxidase (APX) are essential for detoxifying ROS and preventing oxidative damage to the parts of cells [17]. Under cold stress circumstances, non-enzymatic antioxidants like ascorbate and glutathione also assist in scavenging ROS.
Lipid metabolism changes when plants are exposed to cold environments, improving the flexibility and stability of cellular membranes. To retain the best fluidity at low temperatures, plants increase the unsaturated FAs production like linolenic acid and alter the membrane lipid composition [10]. Under cold stress circumstances, these modifications in lipid metabolism aid in preventing membrane rigidification and maintaining membrane integrity. In the pathway for signal transduction reactions of plants to cold stimuli are included and calcium ions act as secondary messengers. Calcium ions from internal reserves and extracellular areas flood the cytosol. The primary signaling raises cytosolic calcium levels triggering subsequent reactions. Calcium sensors in plants become active when cytosolic calcium levels are increased. Among these are calcium-dependent protein kinases and Ca-dependent protein kinases (CDPKs) and CaM. CaM interacts with others and controls the activity of numerous downstream target proteins through the binding of calcium ions and conformational changes [18]. Specific target proteins are phosphorylated by CDPKs, which have both calcium-binding and kinase domains, in a calcium-dependent manner. These calcium sensors are essential for conveying calcium signals and controlling responses to cold stress [19]. Protein phosphorylation and dephosphorylation processes carried out by calcium-dependent kinases and phosphatases are frequently a part of calcium signaling against cold. Controlling the downstream target protein activities including transcription factors (TFs), enzymes, and ion channels, CDPKs phosphorylate them [10]. The dephosphorylation of target proteins by calcium-dependent protein phosphatases, such as protein phosphatase 2C (PP2C), provides a mechanism for the termination of the calcium signal and the fine-tuning of the responses [20].
Specific transcription factors implicated against low temperature can be activated by calcium signaling cascades. The TF:CBFs gets phosphorylated and activated by the CDPK3 [19]. CBFs also known as DREBs (dehydration-responsive element-binding factors), attach CRT/DRE in the promoter regions of in low temperature-responsive genes, causing them to be transcriptionally transcribed and subsequently express proteins involved in cold tolerance. Calcium signaling causes several cold-responsive genes involving plant acclimatization to cold become active. These genes include those that produce antifreeze, LEA (late embryogenesis abundant) proteins, CORs (cold-inducible proteins), and enzymes necessary for creation of osmoprotectants [21]. By activating TFs and other regulatory proteins, calcium signaling coordinates expression of these genes [21].
1.2.3 Drought Stress
During dehydrated conditions, plants make several metabolic adjustments to reduce water loss and preserve cellular hydration. As part of these reactions, suitable solutes like proline and sugars are synthesized and accumulated for osmotic adjustment [22, 23]. The severity as well as the period of occurrence of this stress is more as compared to other types of stresses, and, hence, the damage caused to crop plants is higher [24]. Agricultural drought refers to a continuous reduction in rainfall in combination with higher levels of evapotranspiration from crop plants. In other words, drought stresses a dearth in the sufficient soil moisture content that is required for correct plant growth and development. Due to changing environmental conditions, the problem of drought stress is becoming graver thereby, hampering the productivity of crops and putting food security at risk [25]. It is influenced by various factors like climate and agronomy [26]. However, resistance against the stress is present among almost all plant species but the degree of tolerance differs from one species to other or even differs within the same species of plants. Plant susceptibility to get attacked is dependent on stress severity, plant species type, stage of their growth, and other components reinforcing its effect. Strength to bear stresses caused by abiotic factors is highly complex due to considerable interactions between stress components, and phenomena occurring at different levels eventually affect plant growth and development [22, 26]. Furthermore, plant system undergoes different changes in morphology, physiology, and molecular levels to deal with such devastating situations. These changes occur due to various genes that encode proteins responsible for performing distinct functions. The capability of plants to resist harsh environments of water scarcity depends upon the growth and metabolic processes that are controlled through molecular regulations. This comprises their ability to sense stress, activating signaling pathways in response to water shortage through different genes expressing for encoding proteins and metabolites [27, 28]. The morphological responses of the plants include reduced leaf numbers per plant, reduced leaf area and length of stem, and a well-established root system. In addition to this, physiological responses undergone by the plant system include inactivation of the photosynthetic process, transpiration, osmotic adjustment, and stomatal closure. Accumulation of amino acids like proline, poly amine, enhanced nitrate reductase activity, carbohydrate storage, and liberation of oxidative radicals is a few biochemical responses that occur within plants under drought stress [29].
ROS also termed active oxygen species (AOS) are produced by the reduction of atmospheric oxygen. These oxidative radicals are considerably reactive in nature and can oxidize various types of cellular components like carbohydrates, lipids, DNA, or RNA. These compounds are produced by the plants when they are under stress-free circumstances during photosynthesis. However, the level of the reactive radicals is kept under control by different enzymatic and non-enzymatic antioxidants by functioning collectively. Under stressful situations of drought, ROS generation enhanced [30]. In response to dehydration, for reduction of the transpiration loss of water stomatal closure takes place. With the process of photosynthesis occurring continuously during daytime the increased gas exchange barrier facilitates intercellular removal of carbon dioxide. With the declining carbon dioxide concentration, the ribulose 1, 5-biphosphate oxygenation gets triggered; thereby, inside the peroxisomes, H2O2 concentration rises. Further, the lower carbon dioxide concentration lowers the nicotinamide adenine dinucleotide phosphate (NADPH) from getting oxidized in C3 cycle. Therefore, the production of O2− and H2O2 upsurge due to the insufficient NADH+ and over-reduction of oxygen being employed as an alternative oxygen acceptor [31]. Multiple damaging effects are produced by stress-induced ROS. These oxidative radicals are toxic to different macromolecules including sugars, proteins, lipids, and nucleic acids and can lead to cell death. The enhanced production of oxidative compounds against stressful conditions also stimulates and works as signaling molecules for other stress-induced pathways [32]. ABA is produced from carotenoids derived from isopentenyl diphosphate through a pathway of methylerythritol phosphate. Abscisic acid helps in plant growth and development and reconstructs the signaling pathways within the plant system to handle environmental stresses specifically drought. In addition to this, it is involved in other functions like the germination of seeds, closing and opening of stomata, biomolecule synthesis, and changes in root development patterns. Under the stressful conditions of water shortage, as a water conservatory act, ABA-mediated stomata closing occurs, therefore, preventing loss of water from leaves through transpiration. The ABA helps in managing the ROS by activating antioxidative enzymes like SOD, POD, CAT, APX, and growth regulators (GR) and thus reduces the harm caused due to oxidative radicals [33]. During drought synthesis, accumulation of ABA increases substantially as a result of gene-producing enzymes involved in ABA biosynthesis. In crop plants like tomato, cowpea, avocado, and maize, the 9-cis-epoxycarotenoid dioxygenase (NCED) genes were upregulated in times of water scarcity. Further, the transcription factors Histone acetyltransferase 1 (HAT1) and HAT3 belonging to class HD-ZIP are involved in regulating ABA synthesis. Three-step regulation process is involved in the signaling of ABA, which comprises receptors, protein kinase mediators, and targets [34]. The primary synthesis of ABA takes place in plastids, and xanthoxin is turned into abscisic acid within the cytoplasm of the cell. It begins with the synthesis of trans-violaxanthin from zeaxanthin, a process regulated by ZEP (Zeaxanthin epoxidase). During drought conditions, the expression of ZEP gets enhanced. Following this is the oxidative process in which the conversion of trans-violaxanthin to xanthoxin takes place. NCED (9-cis epoxy carotenoid dioxygenase) is employed for regulating this step genetic expression is considerably regulated in water-deficit situations. Next to this, ABA is produced from xanthoxin. Xanthoxin is transported to the cytosol of the cell through a series of oxidation steps with an intermediate product, i.e., abscisic aldehyde, and the catalyzation of SDR occurs (short-chain dehydrogenase/reductase) [35].
For the maintenance of turgor pressure plants accumulate a variety of different organic as well as inorganic compounds. In underwater shortage conditions, the process of osmotic adjustment happens because of the buildup of osmotic components including proline, alanine, glycine, glutamine, citrulline, and carbohydrates. The extent of adjustment in osmotic potential depends upon the stress faced by the crop plant [36]. At the cellular level, the accumulation, amount, and compartmentalization of different osmo protectants are considerably changed by different parameters like species of plants, degree of stress, and stage of plant growth and development. The osmoprotectant substances help in plant protection making it tolerant against unfavorable growth conditions by maintaining the membrane integrity, oxidative radicals detoxification, and preventing the denaturation of proteinaceous structures and other elements present within the cell. Furthermore, these osmolytes are involved in activating the genes that enable plant systems to cope with harsh environmental stresses. In addition to this, these compounds help in controlling stress signaling by regulating the folding of protein molecules [37]. Sucrose non-fermenting 1–related protein kinase 2 (SnRK2) is inhibited by PP2C and is then relieved by interactions with ABA receptors like the PYR/PYL/RCAR proteins and PP2C. In response to drought stress, phosphorylated downstream target proteins including ion channels and transcription factors are phosphorylated by activated SnRK2, influencing stomatal closure and gene expression (Park et al., 2009). Plants adapt the osmotic potential against drought stress to preserve cellular water balance. To keep cells hydrated and stop water loss, they build up suitable solutes. When there is a water shortage, these solutes function as osmoprotectants, protein stabilization, and cellular structures and assist in the maintenance of turgor pressure [16, 38]. Drought stress can induce several gene expressions that encode proteins included in tolerance against stress. These proteins include chaperones, antioxidants, and enzymes involved in the synthesis of compatible solutes. Several transcription factors, including AREB and drought-responsive element binding protein, control the expression of DREB [39, 40]. Several transcription factors, including AREB and drought-responsive element binding protein, control the expression of these genes (DREB). To deal with drought stress, plants also activate ABA-independent signaling pathways in addition to ABA-dependent pathways. These processes each involve different protein kinases, transcription factors, and hormones, like DREBs, mitogen-activated protein kinase (MAPKs), and JA, respectively. Interaction and regulation of gene expression by these signaling elements activate genes that responses to drought and are included in stress tolerance, water conservation, and osmotic adjustment [29].
1.2.4 Flood Stress
Under flood stress, ethylene hormone is produced in gas form and accumulated. Ethylene is essential for controlling how plants react to floods. Genes encoding flood tolerance-related enzymes, including ADH (alcohol dehydrogenase), PDC (pyruvate decarboxylase), and LDH (lactate dehydrogenase), are activated by ethylene [41, 42]. These enzymes are a part of anaerobic metabolism, which enables plants to adapt to low oxygen levels during flooding. Moreover, the oxygen shortage causes anaerobic conditions in the root zone. In order to produce energy, plants convert from aerobic to anaerobic respiration pathways under these circumstances. In flood-stressed plants, glycolysis and fermentation become significant metabolic processes [43]. For continuous glycolytic action under anaerobic conditions, NAD+ is renewed by ethanol fermentation and the formation of lactate, alanine, and other compounds. Due to these metabolic changes, plants can continue to produce energy even in the absence of oxygen [44]. Numerous genes that code for proteins involved in stress tolerance can be activated by flooding stress. These proteins include antioxidants, chaperones, and enzymes necessary for complementary solutes. Several transcription factors, including ABA-responsive element–binding protein (AREB) element–binding protein in response to water shortage, control the expression of these genes. Numerous genes that code for proteins involved in stress tolerance can be activated by flooding stress. These proteins include antioxidants, chaperones, and enzymes necessary for the synthesis of complementary solutes. Several transcription factors, including AREB and drought-responsive element binding protein (DREB), control the expression of these genes [45].
Plants create aerenchyma, a tissue with air gaps that allows gases to diffuse, in order to improve oxygen transfer to submerged tissues. Primary sites for aerenchyma development in plants under flood stress are the roots and stems [46]. Ethylene signaling manages Aerenchyma development and certain TFs’ activation, including Submergence 1A (SUB1A). Aerenchyma facilitates gas exchange between aerial regions and submerged tissues, which helps plants withstand oxygen shortage) [47]. Plants create aerenchyma, a tissue with air gaps that allows gases to diffuse, in order to improve oxygen transfer to submerged tissues. Primary sites for aerenchyma development in plants under flood stress are the roots and stems [46]. ROS scavenging, and antioxidative defense ROS can be produced inside plant cells because of flooding stress. Cellular components may become oxidatively damaged as a result of elevated ROS levels. Flood-stressed plants engage antioxidant defense mechanisms to combat this. SOD, CAT, POD, and GR are a few examples of enzymes that are crucial for neutralizing ROS and preserving redox equilibrium. Under flood stress circumstances, non-enzymatic antioxidants like ascorbate and glutathione also assist in scavenging ROS [48, 49].
1.2.5 Salinity Stress
Salinity stress is a significant environmental element that poses a harm to the productivity and growth of plants worldwide. When excessive salt concentrations build up in the soil, plants experience osmotic and ionic imbalances. Plants activate a wide range of biochemical pathways against salinity for the reduction of deleterious effects and preserve their survival. Osmotic potential is adjusted to protect against dehydration. They produce osmoprotectants like proline, glycine betaine, and carbohydrates, which stabilize enzymes, reduce protein denaturation, eliminate ROS, and maintain cell turgor [50]
