Plant Metabolism PDF
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PLANT METABOLISM PLANT METABOLISM H. D. Kumar Professor of Botany Banaras Hindu University Varanasi and H. N. Singh Reader in Botany Banaras Hindu University Varanasi M @Affiliated East-West Press Private Limited 1976 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. First published in India 1976 by Affiliated East-West Press Private Limited First published in Great Britain 1979 by THE MACMILLAN PRESS LTD London and Basingstoke Associated companies in Delhi Dublin Hong Kong Johannesburg Lagos Melbourne New York Singapore and Tokyo British Library Cataloguing in Publication Data Kumar, Har Darshan Plant metabolism. 1. Plants - Metabolism I. Title II. Singh, Hriday Narain S81.1'33 QK881 ISBN 978-0-333-25638-1 ISBN 978-1-349-04283-8 (eBook) DOI 10.1007/978-1-349-04283-8 This book is sold subject to the standard conditions of the Net Book Agreement. The paperback edition of this book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, resold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. Contents Preface ix 1 Structure and Function of Plant Cells 1 Introduction, 1; General Structure, 3; Cell Wall, 4; Protoplast, 5; Isolation of Protoplasts, 12; Structure-Function Correlations, 13; Multiple Forms of Biological Macromolecules, 14; References, 15 2 Bioenergetics 17 Introduction, 17; Flow of Energy and Matter in the Biological World, 17; Principles of Thermodynamics, 20; Free Energy and Equilibria, 23; Phosphorylation, 25; References, 32 n J&ey~ Introduction, 33; Apoenzymes and Coenzymes, 33; Enzyme Structure, 38; Factors Affecting Enzyme Activity, 41; Mechanism of Catalysis, 45; Enzymic Control of Metabolism, 47; Classifica- tion and Nomenclafure, 49; Isoenzymes, 50; References, 51 4 Photosynthetic Apparatus 52 The Chloroplast, 52 Introduction, 52; Organization, 53; Ultrastructure ofThylakoids, 54; Development, 57; Origin, Phylogeny, and Genetics, 58; Ultra structure and Micromorphology, 60; Nucleic Acid Biochemistry, 62; Genetical Homology and Hybridization, 63; Comments, 66 Photosynthetic Pigments, 68 Introduction, 68; Chlorophylls, 68; Phycobiliproteins, 71; Carate ooids, 74; Factors Affecting Pigmentation, 76; Functions, 78; References, 81 5 Photosynthesis: Light Reactions 85 Introduction, 85; Photophysical Phase, 86; Photochemical Phase, 88; Photosynthetic Unit, 90; Light Reactions, 92; Sequence of Photosynthetic Electron Transport Chain, 96; Photophosphoryla tion,l01; Energetic Efficiency of Photosynthesis,106; Comparison of Higher Plant and Bacterial Photosynthesis, 107; References, 112 6 Genetics of Photosynthesis in Algae 113 Introduction, 113; Methodology and Techniques, 114; Studies of vi Contents Photosynthesis in Algal Mutants, 11 5; References, 117 7 Photosynthesis: Carbon Fixation 119 Introduction, 119; Benson-Calvin (C3) Cycle, 1 20; C4 Pathway, 125; Comparison between Space and Time Functions in C4 Plants and CAM Plants, 129; Glycollate Pathway, 131; Carbamyl Phosphate Pathway, 133; Generality of Photosynthetic Carbon Cycles, 133; Regulation of Photosynthesis, 134; Photosynthesis in vitro, 135; War burg Effect, 135; References, 136 8 Respiration 138 Introduction, 138; Respiratory Quotient, 1 38; Mitochondria, 139; Origin of Pyruvate, 142; Acetyl CoA Formation, 148; Origin of Oxaloacetate, 150; Operation of TCA Cycle, 150; Oxidative Phosphorylation, 154: TCA Cycle as a Metabolic Pool, 156; Glyoxylate Cycle, 158; Dicarboxylic Acid Cycle, 159; Regulation of Carbon Path in Respiration, 159; Controls of Glycolysis, TCA Cycle, and Glyoxylate Cycle, 160; References, 161 9 Photorespiration and Glycollate Metabolism 163 Introduction, 163; Comparison between Photorespiration and Dark Respiration, 163; Evidences, 164; Site, 165; Measure ment, 165; Biochemical Mechanism, 165; Anatomical Differences between Photorespiring and Nonphotorespiring Plants, 169; Ecological and Physiological Consequences of the Presence or Absence of Photorespiration in Plants, 172; References, 173 10 Nitrogen and Sulphur Metabolism 175 Introduction, 175; Nitrogen Cycle, 176; Biological Nitrogen Fixation, 179; Nitrate Reduction, 183; Mechanism of Reduction, 184; Sulphur Metabolism, 185; Sulphate Uptake, 186; Sulphate Reduction, 186; Sulphotransferase Reactions. 189; Sulphur Selenium Interrelations, 189; Amino Acids, 190; Metabolism and Function of Individual Amino Acids, 198; References, 202 11 Nucleic Acid Metabolism 204 Introduction, 204; Kinds, 208; Structure, 209; DNA Synthesis, 212; RNA Synthesis, 219; References, 223 12 Protein Metabolism 224 Introduction, 224; Protein-Synthesizing Machinery, 226; Model of Protein Synthesis, 236; Co~trol of Protein Synthesis, 239; P-Proteins, 243; References, 244 Contents vii 13 Lipid Metabolism 246 Introduction, 246; Fatty Acids and Their Synthesis, 247; Glycerol Synthesis, 250; Fat Synthesis, 251; Fatty Acid Catabolism, 251; Conversion of Fats into Sugars, 252; Other Plant Lipids, 252; Lipid Transfers and Turnover in vitro, 254; References, 254 14 Secondary Plant Products 256 Introduction, 256; Terpenoids, 259; Phenols, 263; Flavonoids, 266; Alkaloids, 268; Nonprotein Amino Acids, 271; References, 274 Suggestions/or Further Reading 275 Author Index 279 Subject Index 284 Preface Research in plant metabolism during the last few decades has revealed diverse aspects of interlocking metabolic cycles. Living 'ells which. with their subcellular organelles, are the ultimate units of function, are now best understood as molecular machines dispensing energy in a highly ordered and controlled manner for various biochemical and biophysical reactions involved in anabolic and catabolic processes. It should be noted that inside the living cell these reactions do not occur in isolation, but rather are inter connected in complex pools and cycles. However, in a book, they have to be arbitrarily classified and described under discrete chapter headings, such as photosynthesis and respiration, erroneously making the processes appear independent of each other. Further, some overlap in the distribu tion of topics under different chapters being inherent in the very nature of the subject cannot be entirely avoided. Since most metabolic processes are highly complicated and interconnected, they may best be studied through the application of computer-based system analyses, but this has not so far been done to any appreciable extent. Our aim has been to provide a simple and straightforward account of otherwise complex metabolic events. We therefore suggest that, after having grasped the essence of a process, a beginning student consult some original papers and the more advanced recent publications listed at the end of this book. Two of the most important new contributions to plant physiology in the last decade are: ( 1) the detection of a major new pathway of photosynthe tic C02 assimilation, and (2) the discovery of the process ofphotorespiration in some green plants. We find that these metabolic activities, and their interrelations with the anatomical, morphological, economic, and ecological characteristics of the plants, have not received the coverage they deserve in the available books on plant physiology. These exciting discoveries have a strong bearing on plant productivity and photosynthetic efficiency. Many succulent plants exhibit a pronounced variation in their cell sap pH which rises during the night and falls during the day. Recent findings have disclosed a remarkable similarity between the carbon fixation reac tions of CAM plants and those of plants with the C4 dicarboxylic acid pathway. However, a major difference between the two is that reactions that are spatially separated in C4 plants (as between the chloroplasts of bundle-sheath cells and those of mesophyll cells) are temporally (night and day) isolated in CAM plants (see Chapter 7). We have included some other topics of current interest which we feel reflect the new emerging trends of research in this fascinating discipline of x Preface biology. These are the dynamic nature of cell membranes; the isolation of plant cell protoplasts; the multiplicity of form of several biological macro molecules and compounds, such as chlorophylls and enzymes; the endo symbiotic theory of plastid origin and its economic potential; photosynthesis in vitro; and lipid transfers in vitro. Also we have briefly covered sulphur compounds and sulphur-selenium interreiations because of their importance in metabolism. And, instead of highlighting the effects of various factors on different metabolic phenomena, we have preferred to discuss the regu lation and control of such processes as photosynthesis and respiration. We wish to acknowledge the valuable help we received in the prepara tion of this text. We are grateful to Professor W. M. Laetsch (Berkeley, California) for his critical reviewing of the manuscript and his many useful suggestions for its improvement. We are greatly obliged to him as well as Professor C. C. Black and Dr W. T. Hall for supplying the electron micro graphs and reprints of their latest papers and for their interest in this venture. We thank our friends and colleagues, notably Dr A. R. Gopal Ayengar, Professors Mahatim Singh, B. M. Johri, and H. Y. Mohan Ram for encouraging, criticizing, and discussing our efforts from time to time. We are also indebted to Professor G. E. Fogg, Sc.D., F.R.S., and Professor W. D. P. Stewart for their constant help in various ways. Finally, we thank Dr A. K. Kashyap and Mr Subhash Bhardwaj for their pains in preparing some of the illustrations. We request our readers to send us their criticisms of this volume and their suggestions for its improvement. Although the book has resulted from the joint effort of the two authors, the first drafts of Chapters 1, 6, 7, 9, and 13, and "The Chloroplast" in Chapter 4 were prepared by H. D. Kumar and those of the remaining chapters by H. N. Singh. Chapters 6 and 9 and "The Chloroplast" in Chapter 4 are based on lectures delivered by H. D. Kumar at various Indian universities under the University Grants Commission (UGC) Scheme of National Lectureships (1972-73). Professor Kumar is indebted to the UGC for their permission to incorporate these lectures (now modified and updated) in this text. H. D. Kumar Varanasi H. N. Singh September 1975 1 : Structure and Function of Plant Cells INTRODUCTION Current biological usage generally recognizes the division of living organisms into two main categ<'ries, viz., noncellular and cellular. The former includes viruses which do not have a cellular construction, i.e., the viruses contain either DNA or RNA (not both) and have only a very limited number of enzymes. In contrast, a cell constitutes the basic structural and functional unit of all organisms (protists, plants, and animals), has both DNA and RNA, and also a wide variety of enzymes. Cellular organisms are further divided into procaryotes (bacteria and blue-green algae) and eucaryotes (higher plants, animals, fungi, algae, proto zoa, and nonvascular as well as vascular cryptogams). Procaryotes lack discrete, well-organized nuclei, chloroplasts, and mitochondria, and have chemically distinctive cell walls, largely composed of mucopolysaccharides containing amino sugars and muramic acid whereas eucaryotes have several kinds of discrete subcellular organelles, including mitochondria, endo plasmic reticulum, microbodies, Golgi bodies (dictyosomes), lysosomes, ribosomes, and, in green tissues of plants, also chromatophores or plastids. Some organelles, e.g., nucleus, mitochondria, and chloroplasts, are bounded by double membranes, others, e.g., microbodies, Golgi bodies, and lyso somes, are bounded by single membranes, and yet others, e.g., ribosomes, are membrane-free structures. When present, the cell wall of eucaryotes does not contain amino sugars and muramic acid. Further, the procaryotic cell is monogenomic whereas the eucaryotic cell is polygenomic. This means that the procaryote has a single genome in its nucleoplasm. (It also has extragenomic elements called plasmids which enhance its survival value.) In the eucaryotic cell, at least two (three in plant cells) different genomes, essential for the primary life processes, occur, one in the nucleus and the other in the mitochondria (the third in the chloroplast), the bio logical expression of the cell being a function of coordinated interaction between the different genomes. Plant cells differ from animal cells in many ways, the most important difference being that plant cells have a conspicuous cellulosic wall which is distinct from, and located external to, the cell membrane whereas animal cells have no cell walls but only cell membranes. Another noteworthy distinction is that most mature plant cells have large vacuoles whereas
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