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Genus Rheum (Polygonaceae) Genus Rheum (Polygonaceae) A Global Perspective Shahzad A. Pandith Mohd Ishfaq Khan First edition published 2022 by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 and by CRC Press 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN © 2022 Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, LLC Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publica- tion and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. 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ISBN: 9780367355760 (hbk) ISBN: 9780429340390 (ebk) ISBN: 9781032058429 (pbk) DOI: 10.1201/9780429340390 Typeset in Times by Deanta Global Publishing Services, Chennai, India Contents Preface.................................................................................................................vii Authors .................................................................................................................ix Chapter 1 Introduction .....................................................................................1 1.1 Introduction ..........................................................................1 References .......................................................................................4 Chapter 2 Botany and Ecology ........................................................................7 2.1 Occurrence and Distribution ................................................7 2.2 Taxonomy and Classification ................................................7 2.3 Morphology ........................................................................14 2.4 Synonyms and Vernacular Names ......................................25 2.5 Pollen Studies .....................................................................25 2.6 Ecology ...............................................................................33 References .....................................................................................34 Chapter 3 Traditional Uses .............................................................................39 3.1 Rhubarb as a Food Plant .....................................................42 References .....................................................................................44 Chapter 4 Phytochemistry ..............................................................................47 4.1 Phenolics .............................................................................48 4.2 Anthraquinones ..................................................................61 4.3 Stilbenoids ..........................................................................62 4.4 Other Constituents ..............................................................65 4.4.1 Anthraglycosides ...................................................70 4.4.2 Dianthrones ...........................................................71 References .....................................................................................71 Chapter 5 Pharmacology ................................................................................75 5.1 Antimicrobial Activity .......................................................75 5.2 Anticancer Activity ............................................................77 5.3 Antidiabetic Activity ..........................................................80 5.4 Anti-Inflammatory Activity ...............................................83 5.5 Antioxidative Activity ........................................................84 5.6 Immunoenhancing Activity ................................................87 5.7 Nephroprotective Activity ..................................................87 v vi Contents 5.8 Hepatoprotective Activity ...................................................90 5.9 Miscellaneous Activities ....................................................92 References .....................................................................................94 Chapter 6 Molecular Aspects .......................................................................107 6.1 Cytogenetics .....................................................................107 6.2 Genetics .............................................................................110 6.2.1 Rhubarb in the Wild .............................................111 6.2.2 Rhubarb Cultivars ................................................114 6.3 Biotechnological Interventions ..........................................119 References ...................................................................................126 Chapter 7 Conservation ................................................................................135 7.1 Threat Status .....................................................................135 7.2 In vitro Propagation Studies as a Conservation Measure ......................................................136 References ...................................................................................138 Chapter 8 Conclusions and Future Prospects................................................141 References ...................................................................................146 Preface Plants, sessile but promising organisms, have been well-known for benefiting human existence in the form of a variety of natural products for ages. Among this vast reservoir of natural economic wealth, rhubarb (Polygonaceae) is one of the important medicinal herbs with an intricate historical background and an immense value for the associated societies for centuries. Rhubarb, a significant object of botanical, commercial, and horticultural interest, is presently repre- sented by about 60 extant species occurring across Asian and European countries with a major distribution found in the mountainous regions of the Qinghai- Tibetan Plateau in China. This perennial species is documented for use in various traditional medical systems from varied cultures across different regions as one of the most sought-after crude drugs due to its mildness, efficacy, and lack of unwanted side effects. Indeed, in therapeutic history, there has probably been no medicine which has provided better relief to more people than the rhizome/root powder made from medicinal rhubarb (Rheum officinale). Moreover, there has been remarkable interest from researchers around the world in some of the highly medicinal herbs from this genus which, although not limited to, include R. aus- trale, R. tanguticum, R. palmatum, and R. officinale, among others. Pertinently, the remedying properties of Rheum are attributed to a group of diverse biologi- cally active secondary chemical constituents, predominantly anthraquinones, and stilbenoids to a lesser extent, as well as the dietary flavonoids known for their puta- tive health benefits. But unfortunately, human greed has prevailed and rendered some of the important species from this Polygonaceous herb threatened in the natural stands, causing the need for their conservation. Further, with the advance- ment of the state-of-the-art scientific techniques, current and related research is mainly focused on various promising metabolic pathways from medicinal plants like Rheum to decipher the biosynthesis of their key bioactive chemical constituents, which may help in modulating the specific pathways in alternate (microbial) hosts while preserving the natural wild stock. This book is literally the biography of the rhubarb plant and presents a global perspective of this important medicinal herb while covering almost every aspect, ranging from its history to the application of contemporary biotechnological interventions. It provides updated information on nearly all aspects of the plant covering varied forms of related literature since the 18th century, and include: • The historical background detailing its earlier trade and commerce; • Global distribution giving an idea of the source of its origin and dissemination; • Botany for classical taxonomic aspects; • Ecology to understand the ecological and evolutionary implications; • Ethnobotany, phytochemistry and pharmacology vis-à-vis therapeutic potential; vii viii Preface • Genetic diversity with regard to the polymorphism and ploidy status gained across varied geographies; • Biotechnological invasions to assess the success level we have achieved so far in accepting and utilizing rhubarb as a suitable drug reservoir; and • In vitro propagation studies as a conservation and exploitation (at indus- trial scale) measure. We are hopeful that it will prove to be of great help to the researchers working on rhubarb. Shahzad A. Pandith Mohd Ishfaq Khan Authors Shahzad A. Pandith received his MSc in botany from the University of Kashmir, Srinagar, India, in 2009, and PhD in plant molecular biology from CSIR Indian Institute of Integrative Medicine, Jammu, India, in 2017. He has since served in the Department of Botany, University of Kashmir as DST-INSPIRE Faculty (position equivalent to IITian assistant professor). In this capacity, he supervises a DST-sponsored project on one of the important medicinal herbs from the north- western Himalayas, Rheum. In general, Pandith seeks to use various “omics” approaches to elucidate and understand the basic biology of plants, important pathways operating in them and their modulation, rate-limiting pathway genes, and the regulatory factors controlling their constitutive/inducible expression vis- à-vis ecological/environmental factors and/or stress conditions. He has published about 15 research papers in highly reputed peer-reviewed international journals with an average impact of around three per paper. In addition, he is an active reviewer of many reputed journals from well-known publishing houses like Springer, Elsevier, and Brill, etc. Shahzad has many national-level exams and awards to his credit, which include the Joint CSIR-UGC JRF and ICAR-ASRB NET exams, and the highly prestigious DST-INSA INSPIRE Faculty award. Mohd Ishfaq Khan holds a BSc degree from the University of Kashmir, Srinagar, India, and received his MSc degree in botany from the same institu- tion in 2015. Since 2017, he is actively engaged in a DST-sponsored project at the University of Kashmir. His active areas of research include DNA barcoding, genetics, taxonomy, and eco-physiology which he uses to understand and resolve the genetic/taxonomic complexity in high-value medicinal herbs from the north- western Himalayas. He has some good research articles to his credit. In addition, he has qualified in many competitive exams at state and national level including the Graduate Aptitude Test in Engineering (GATE)-2019 in the subject of life sciences. Khan also holds a bachelor’s degree in education and has been a good teacher-cum-motivator for students at higher secondary level. ix