MOLECULAR ACTIVITIES OF PLANT CELLS

Transcription

1 MOLECULAR ACTIVITIES OF PLANT CELLS An introduction to plant biochemistry JOHN W. ANDERSON BAgrSc, PhD Reader, Botany Department, School of Biological Sciences, La Trobe University, Bundoora, Victoria, Australia JOHN BEARDALL BSc, PhD Department of Ecology and Evolutionary Biology, Monash University, Clayton, Victoria, Australia OXFORD BLACKWELL SCIENTIFIC PUBLICATIONS LONDON EDINBURGH BOSTON MELBOURNE PARIS BERLIN VIENNA

2 Contents Preface, xi Nomenclature and Abbreviations, xiii PART 1: GENERAL BIOCHEMISTRY, 1 1 Plant growth and biochemistry the connection, Plant growth involves the synthesis of biological matter, Synthesis of biological matter requires an energy source, Characteristics of autotrophs and heterotrophs, Photosynthesis definitions, Major activities of producer and consumer cells, Molecular traffic between producer and consumer cells, Plant growth and carbon dioxide assimilation rates, 7 Further reading, 8 2 Molecules of plant cells, Classes of compounds in plant matter, Organic molecules of plants occur in specific isomeric forms, Carbohydrates are quantitatively the most important compounds in plants, Lipids are biological molecules with little affinity for water, Proteins are constructed from 20 amino acids, Nucleotides and nucleic acids, Some phenylpropanoid compounds are important constituents of plant cell walls, Secondary compounds are not essential for plant function, 34 Further reading, 35 3 Structural organization of plant cells, Cellular organization is essential for cellular activity, Membrane structure, Ribosomes, Nucleus, Chloroplasts, Mitochondria, Microbodies, Other membrane-limited organelles, Cytoplasm its inclusions and cytosol, Plant cell walls, The cell cycle involves non-sexual production of two daughter cells, Preparation of subcellular fractions from plants, 46 Further reading, 49 4 Cellular energetics, The free energy change of a chemical reaction is related to its equilibrium constant, Cells have mechanisms for coupling endergonic reactions to exergonic reactions, Hydrolysis of a few key compounds provides important intermediary energy sources in cells, A few redox pairs are important intermediary electron acceptors and donors in cells, The free energy change of a redox reaction is related to the electrode potentials of the two redox pairs, Differences in electrical potential and ion concentration across a membrane cause free energy differences between the ions across the membrane, Proton electrochemical gradients across membranes are important energy sources in cells, A mole of pigment can absorb a mole of photons, the energy of which varies with the wavelength, 59 Further reading, 60

3 VI 5 Enzymes and post-translational enzyme regulation, Enzymes are protein molecules which catalyse specific biological reactions, Some enzymes require the presence of cofactors for activity, Kinetics of reactions catalysed by non-regulatory enzymes, Inhibition of enzyme-catalysed reactions, Some enzymes have a regulatory role in metabolism, 79 Further reading, 82 6 Membranes and metabolite transport, Membranes exhibit variation in their composition and cellular function, Membranes are responsible for transport of materials into and out of cells and organelles, Movement of many materials across plant membranes involves carrier proteins, 'Patch clamping' is a powerful tool for studying membrane transport of ions, 95 Further reading, 96 PART 2: ENERGY-GENERATING MECHANISMS OF PLANTS, 97 7 Aerobic oxidation of sugars to carbon dioxide, Respiratory rates vary between different tissues and stages of development, Storage products are mobilized before they are respired, Glycolysis involves the anaerobic oxidation of hexoses to pyruvate, Reactions of glycolysis occur both in the cytosol and in plastids, Flow of metabolites through the glycolytic sequence is regulated, The tricarboxylic acid cycle oxidizes pyruvate to carbon dioxide, NADH and FADH 2 are oxidized by oxygen via the mitochondrial electron transport chain, The free energy of oxidation of NADH by oxygen is conserved by ADP phosphorylation, Analysis of input and output associated with respiration, Glycolysis and the TCA cycle contribute both ATP and carbon skeletons for biosynthetic pathways, 125 Further reading, Secondary oxidative mechanisms in plants, Oxidative pentose phosphate pathway, Oxidation of lipids is important in germinating oil-bearing seeds, The glyoxylate pathway provides a mechanism for linking j3-oxidation to carbohydrate synthesis, 137 Further reading, Light reactions of green plants, Properties of solar radiation in relation to plant growth, Plants absorb light by specific pigments contained in thylakoids, Light is absorbed by chlorophyll and the energy is transferred to specialized chlorophyll molecules the reaction centres, Light is required for production of ATP and reducing equivalents, Two light reactions are involved, The photosynthetic unit, Properties of the photosystems and their antenna complexes, Transport of electrons from water to N ADP, Functional organization of thylakoid membranes, Transverse heterogeneity of electron transport components results in a trans-thylakoid proton gradient, The trans-thylakoid proton gradient is coupled to ADP phosphorylation, The CFt-CFo ATP synthetase, How many protons are transported for each ATP formed? Analysis of inputs and outputs and efficiency of non-cyclic electron transport, Monitoring the photosystems in vivo by fluorescence and fluorescence quenching, Regulation of energy distribution between PSII and PSI, Cyclic photophosphorylation, Light-dependent reduction of oxygen: the Mehler reaction and pseudocyclic photophosphorylation, 163 Further reading, 163

4 vn PART 3: ASSIMILATORY MECHANISMS IN PLANTS, C 3 carbon reduction cycle and associated processes, Most autotrophic organisms possess an active C 3 carbon reduction cycle, Experimental approaches to define the pathway of carbon dioxide assimilation, Incorporation of carbon dioxide into triose phosphates involves a series of chloroplast enzymes, Carbon dioxide in chloroplasts is in equilibrium with a pool of bicarbonate, Ribulose-1,5-P 2 is regenerated from triose-p, Energy inputs from ATP and NADPH satisfy the energy requirements for production of carbohydrate from carbon dioxide, The chloroplast envelope is impermeable to many intermediates of the C 3 -CR cycle, Triose phosphates are exported to the cytosol by the phosphate translocator, Sucrose is synthesized via UDP-glucose in the cytosol, Sucrose is exported from photosynthetic cells and loaded into the phloem, Starch is synthesized in chloroplasts via ADP-glucose, Starch is metabolized to sucrose when demand for carbon in the cytosol exceeds the rate of carbon dioxide assimilation, Activities of the C 3 -CR cycle and starch and sucrose synthesis are regulated, Aspects of carbon metabolism can be monitored by chlorophyll fluorescence, 182 Further reading, Photorespiration, Light enhances carbon dioxide evolution by C 3 plants, Photorespired carbon dioxide is derived from recently assimilated carbon dioxide and is strongly influenced by oxygen and carbon dioxide concentrations, Ribulose-1,5-P 2 oxygenase activity accounts for several features of photorespiration, Glycollate-2-P is returned to the C 3 -CR cycle via the C 2 photorespiratory cycle, Enzymes of the C 2 -PR cycle and their subcellular location, The C 2 -PR cycle is associated with metabolite transport between organelles and with nitrogen cycling, The C 2 -PR cycle requires a large input of energy, Why is photorespiration light-dependent?, What does photorespiration achieve?, Some plants have strategies for suppressing photorespiration, Some algae possess alternative routes of photorespiratory glycollate metabolism, 194 Further reading, C 4 mechanisms of carbon dioxide assimilation, Carbon dioxide assimilation characteristics of some plants do not reflect the properties of ribulose-l,5-p 2 carboxylase, C 4 plants and CAM plants assimilate carbon dioxide into oxaloacetate and other C 4 dicarboxylates, C 4 plants have distinctive biochemical, physiological and anatomical characteristics, The pathway of carbon dioxide assimilation in C 4 plants can be determined by the order in which metabolites are labelled with [ 14 C]carbon dioxide, Establishing the functions of mesophyll and bundle sheath cells, Leaves of C 4 plants have a quantitatively distinctive complement of enzymes, Mechanisms for decarboxylating C 4 dicarboxylates in bundle sheath cells vary between species, Enzymes of the C 3 -CR cycle occur in bundle sheath cells but some are also found in mesophyll cells, C 4 plants expend more energy in assimilating carbon dioxide than do C 3 plants, Carbon dioxide assimilation in C 4 plants involves extensive intracellular and intercellular transport of metabolites, The C 4 mechanism of carbon dioxide assimilation explains many of the physiological properties of C 4 plants, CAM plants assimilate carbon dioxide into malate at night and reassimilate carbon dioxide into carbohydrate in the light, CAM affords an explanation for many physiological and ecological features of CAM plants, 207

5 Vlll Phylogenetic distribution of C 4 and CAM plants and its implications for herbicide design, 207 Further reading, Assimilation of inorganic nitrogen into amino acids, Plants use inorganic nitrogen for synthesis of protein amino acids, Plants reduce nitrate to ammonia, Ammonia is incorporated via glutamine into glutamate by the C 5 - ammonia assimilation cycle, Ammonia produced by photorespiration is reassimilated via the C 5 - ammonia assimilation cycle, Light is an important energy source for the assimilation of inorganic nitrogen in leaves, Aminotransferases catalyse transfer of the amino group of amino acids to oxo acids to form other amino acids, Synthesis of some other amino acids, Some organisms use gaseous nitrogen as a nitrogen source by the process of nitrogen fixation, Some plants contain toxic non-protein amino acids, 229 Further reading, Other light-coupled assimilatory and reductive mechanisms, Light supports various processes in chloroplasts and protoplasts, Assimilation of inorganic sulphur, Q fragments have various origins, Reducing equivalents and phosphorylation potential are exported from illuminated chloroplasts by shuttle mechanisms, Illuminated chloroplasts reduce oxidized glutathione, Illuminated chloroplasts synthesize fatty acids, protein and other metabolites, Rates of processes associated with chloroplasts, 241 Further reading, 241 PART 4: SYNTHESIS OF NEW CELLS AND CELL STRUCTURES, Synthesis of nitrogenous compounds from amino acids, Synthesis of pyrimidines and pyrimidine nucleotides, Synthesis and metabolism of purines and purine nucleotides, Synthesis of chlorophyll, 252 Further reading, Synthesis of lipids, Fatty acids are synthesized from acetyl-coa, Waxes are derived from palmitate and stearate, Phosphatidate is an important intermediate in the synthesis of acyl lipids other than waxes, Biosynthesis of prenyllipids, Membranes have a capacity for self-assembly, 274 Further reading, Synthesis of plant cell walls, Plant cell walls are important biologically and economically, Molecular composition of plant cell walls, Plant cells vary in the composition of their walls, The orientation of cellulose microfibrils is normal to the direction of cell growth, Model for the organization of the primary cell wall, Structural studies indicate that microtubules and Golgi bodies are involved in cell wall synthesis, Monosaccharides are incorporated into cell wall polysaccharides as their nucleoside diphosphate derivatives, Cellulose microfibrils are thought to be formed by enzyme assemblies associated with the plasma membrane, Matrix polysaccharides are synthesized in Golgi bodies and the endoplasmic reticulum, Extensin synthesis involves post-translational oxidation of proline and attachment of sugars, Lignin is synthesized from phenylalanine, 288 Further reading, 290

6 IX 18 The plant genome and its replication, Organization of the plant genome, Replication of the plant genome, 296 Further reading, Processes involved in protein synthesis, The information required to build proteins is contained in a genetic code, Transcription of DNA to RNA, Translation of mrna into protein occurs in the cytoplasm, Many proteins are modified after mrna translation, Protein synthesis in mitochondria and chloroplasts, 313 Further reading, Regulation of gene expression, Control of gene expression can occur at several points, Regulation of some genes occurs at transcription, Control of gene expression also occurs post-transcriptionally or at translation, Gene expression is regulated in response to a range of environmental and developmental signals, Recombinant DNA technology is a powerful tool for investigating gene organization and function, Genetic engineering: manipulation of the genetic information of plant cells, 333 Further reading, Biogenesis of organelles, Mitochondria and chloroplasts are not formed de novo, Chloroplasts develop from proplastids, Perception of the light stimulus in chloroplast development involves a number of receptors, Biosynthesis of organelles involves interaction between organelles and the nucleus, Regulation of the interaction between nuclear and organelle genomes, 349 Further reading, 352 Further reading, 353 Index, 357