Biotechnological Approaches to Enhance Plant Secondary Metabolites

Recent Trends and Future Prospects

Mohd. Shahnawaz

• Publisher: CRC Press
• Year: 2021
• Print ISBN:
  9780367473365
• eBook ISBN:
  9781000174960
• Topic: Biological Sciences
• Subtopic: Biotechnology in Medicine
• Index: Biological Sciences

Thousands of secondary metabolites are produced by plants to withstand unfavourable environmental conditions and are important molecules for nutraceutical, agro, cosmetic and pharmaceutical industries, etc. Harvesting of plants for the extraction of these important metabolites can threaten the plant germplasm, and various medicinally important plants are at the verge of extinction. Based on need, various methods and strategies were developed and followed by researchers from time to time to save the plant germplasm and produce important secondary metabolites efficiently to meet their growing demands.

Biotechnological Approaches to Enhance Plant Secondary Metabolites: Recent Trends and Future Prospects provides a comprehensive introduction and review of state-of-the-art biotechnological tools in this field of research at global level. The methodologies are highlighted by real data examples in both in vitro and in vivo level studies.

The book:

• Highlights and provides overviews of the synthesis, classification, biological function and medicinal applications of the recent advancements for the enhanced production of novel secondary metabolites in plants

• Provides an overview of the role of induced mutation, salinity stress and brassinosteroids impact to increase the secondary metabolic contents in plants and suggests an increase in enzymatic activity in plants could be due to various point mutations, which in turn could play a role at transcriptome levels

• Discusses the significant role of endophytes to enhance the contents of plant secondary metabolites

• Alternatively, suggests the urgent need to set up the standard operating procedures using hydroponics system of cultivation for significant enhancement of secondary metabolite contents

• Enlists various in vitro techniques to enhance plant secondary metabolites contents using plant tissue culture approaches

• Provides a systematic overview of state-of-the-art biotechnological tools CRISPER Cas9 and RNAi to enhance the plant secondary metabolite contents

• Recommends CRISPER Cas9 technology over RNAi, ZFNs and TALENs because of its relatively simple and high precision method with an easily programmable tool

This serves as a reference book for the researchers working in the field of plant secondary metabolites and pharmaceutical industries at global level.

1Plant Secondary Metabolites—The Key Drivers of Plant's Defence MechanismsA General Introduction

D. Sruthi and C. Jayabaskaran

DOI: 10.1201/9781003034957-1

CONTENTS

1. 1.1Introduction
2. 1.2Classification of Secondary Metabolites
   1. 1.2.1Terpenes (Terpenoids)
      1. 1.2.1.1Synthesis of Terpenes
      2. 1.2.1.2Classification of Terpenes
      3. 1.2.1.3Extraction and Identification of Terpenes
      4. 1.2.1.4Role and Application of Terpenes
      5. 1.2.1.5Essential Oil
   2. 1.2.2Alkaloids
      1. 1.2.2.1Synthesis of Alkaloids
      2. 1.2.2.2Classification of Alkaloids
      3. 1.2.2.3Extraction and Identification of Alkaloids
      4. 1.2.2.4Role and Application of Alkaloids
   3. 1.2.3Phenolics
      1. 1.2.3.1Synthesis of Phenolics
      2. 1.2.3.2Classification of Phenolics
      3. 1.2.3.3Extraction and Identification of Phenolics
      4. 1.2.3.4Role and Application of Phenolics
3. 1.3Current Biotechnological Approaches for the Enhancement of Secondary Metabolite Contents in Plants
4. 1.4Conclusion
5. Acknowledgements
6. References

1.1INTRODUCTION

Plants are rich in bioactive phytoconstituents with enormous ethnopharmacological potential and these high-value phytochemicals are broadly categorized into two classes (primary and secondary metabolites) based on their function (Hussein and El-Anssary 2019). The primary metabolites are distributed widely in all plants and carry out metabolic functions which are crucial for normal physiological growth and energy requirements of the plants and are normally evident (Hussain et al. 2012; Wink 2016). In contrast, plants synthesize myriads of organic compounds; most of them do not involve directly in plant growth and development. These phytochemicals, normally known as secondary metabolites, are distributed differentially in restricted taxonomic groups of the plant kingdom (Tiwari and Rana 2015). Briefly, secondary metabolites are normally not essential for plant growth and its development, but they are essential for surviving in the ecosystem through chemical defence (Iriti and Faoro 2009). Plant secondary metabolites are the chemical constitutes primarily responsible for the chemical defences to regulate the relationship between the plant and their ecosystem and further take part in protecting plants from abiotic and biotic stress conditions (Mazid et al. 2011). Secondary metabolites are not essentially synthesized under all circumstances but produced undoubtedly for really appreciated reasons, few of such include, toxic materials to protect the plant from predators, as volatile attractants or as an agent to impart colour and thereby warn or attract other species and thus, it is evident that all of them play some crucial function for the safety of their producer (Adeyemi and Mohammed 2014). Plant defence metabolites arise from the isoprenoid, the alkaloid and the phenylpropanoid pathways which form three major secondary metabolite classes viz., terpenes, alkaloids and phenolics, respectively (Iriti and Faoro 2009). Generally, precursors for secondary metabolite synthesis are products of the primary metabolism (Iriti and Faoro 2004). Besides their role in plant protection, secondary metabolites are well studied for various pharmacological and medicinal potentials and many drugs of natural origin against human ailments have been discovered from different plants (Velu et al. 2018).

Secondary metabolites provide major pharmacologically active high-value natural products used to treat various diseases since ancient times and it ranges from migraine up to cancer (Hussein and El-Anssary 2019; Jain et al. 2019). Vinca alkaloids (vinblastine and vincristine), taxanes [e.g. paclitaxel (Taxol) and docetaxel (Taxotere)] and combretastatin are some of the secondary metabolites used to treat cancer (Hartwell 1984; Kingston 2012; Pinney et al. 2012; Roussi et al. 2012). Further, secondary metabolite drugs have been obtained from plants with anti-diabetic (e.g. galegine alkaloid from Galega officinalis,), anti-inflammatory (e.g. curcumin and resveratrol) and anti-viral (e.g. betulinic acid and calanolides) efficacies (Min et al. 1999; Dharmaratne et al. 2002; Furst and Zudorf 2014; Rios et al. 2015). So there is a huge demand for medicinal plants to isolate pharmaceutically active molecules (Dar et al. 2017a). These secondary metabolites are produced in low quantity in plants; hence, a large amount of plant material is used to extract the drug molecules (Dar et al. 2017b). To meet the demand of pharmaceutical companies, huge medicinal plants are being exploited at a mass level. This practice leads to threat the germplasm and various plants were extinct from the natural environment (Maxted et al. 2020). Hence, it was needed to enhance the contents of such pharmaceutically active plant secondary metabolites to reduce the exploitation of the medicinal plants from the natural environment (Jimenez-Garcia et al. 2013). With this regard, various biotechnological strategies were used by different workers across the globe (Guerriero et al. 2018). So, in this chapter, an effort was made to overview the plant secondary metabolites, to discuss different classes of plant secondary metabolites, to discuss the biosynthetic pathways that took part in the production of plant secondary metabolites and to highlight various approaches adopted to enhance the secondary metabolite contents in plants.

1.2CLASSIFICATION OF SECONDARY METABOLITES

Secondary metabolites are classified primarily as terpenoids, alkaloids and phenolics depending on their chemical structure (Shamina and Sarma 2001).

1.2.1TERPENES (TERPENOIDS)

Terpenes are ubiquitous in plants and are the largest class of secondary metabolites with more than 22000 compounds (Freeman and Beattie 2008). The high concentration of compounds in turpentine oil has given the alternate name ‘terpenoid’ to these compounds. All terpenes are said to be the derivative of branched, basic, five-carbon unit isoprene (C₅H₈) (Bramley 1997; Goodwin and Mercer 2003). Isoprene is a volatile gas emitted by leaves during photosynthesis and that might prevent the damage of plant cell membranes due to high temperature or light (Freeman and Beattie 2008). Terpenes are the essential metabolite for photosynthesis and also for regulating the plant metabolic processes (Bramley 1997; Goodwin and Mercer 2003). Even though most of the terpenes are...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• Acknowledgements
• Editor
• Contributors
• Chapter 1 Plant Secondary Metabolites—The Key Drivers of Plant's Defence Mechanisms: A General Introduction
• Chapter 2 Generation of Plant Mutant Lines Using Gamma Radiation with Enhanced Secondary Metabolite Contents
• Chapter 3 Salinity Stress and Plant Secondary Metabolite Enhancement: An Overview
• Chapter 4 Enhancement of Plant Secondary Metabolites Using Fungal Endophytes
• Chapter 5 Hydroponic Cultivation Approaches to Enhance the Contents of the Secondary Metabolites in Plants
• Chapter 6 Tissue Culture Approaches to Enhance Plant Secondary Metabolites Production
• Chapter 7 Hairy Roots and Plant Secondary Metabolites Production: An Update
• Chapter 8 Brassinosteroids: The Phytohormones with Potential to Enhance the Secondary Metabolite Production in Plants
• Chapter 9 CRISPR-Cas9 Approaches to Enhance Contents of Plant Secondary Metabolites
• Chapter 10 RNA Interference for Improvement of Secondary Metabolite Production in Plants
• Index