SEEDS Physiology of Development and Germination J. Derek Bewley Plant Physiology Research Group Department of Biology University of Calgary Calgary, Alberta, Canada and Michael Black Department of Biology Queen Elizabeth College University of London London, England Plenum Press New York and London
Chapter 1 Seeds: Germination, Structure, and Composition 1.1. Introduction 1 1.2. Seed Germination Some General Features 1 1.3. Measurement of Germination. 2 1.4. Seed Structure 5 1.4.1. Embryo 6 1.4.2. Nonembryonic Storage Tissues 8 1.4.3. Seed Coat Testa 9 1.5. Seed Storage Reserves 10 1.5.1. Carbohydrates 12 1.5.2. Fats and Oils (Lipids) 15 1.5.3. Proteins 17 1.5.4. Phytin 24 1.5.5. Other Constituents '. > 25 Chapter 2 Seed Development and Maturation 2.1. Embryogeny and Storage Tissue Formation 29 2.2. Source of Assimilates for Grain and Seed Filling 33 2.2.1. Cereals 33 2.2.2. Legumes 35 2.2.3. Translocation of Assimilates into the Developing Seed 38
viii Contents 2.3. Deposition of Reserves within Storage Tissues 40 2.3.1. Starch Synthesis 40 2.3.2. Deposition of Polymeric Carbohydrates Other than Starch 43 2.3.3. Fat (Oil) Synthesis 45 2.3.4. Storage Protein Synthesis 52 2.3.4.1. Cereals 52 2.3.4.2. Dicots 56 2.3.5. Phytin Deposition 67 2.3.6. Deposition of Several Reserves Correlative Patterns 68 2.4. Maturation Drying The Effects of Water Loss on Developmental Events 70 2.5. Hormones in the Developing Seed 74 2.5.1. Composition and Location 75 2.5.1.1. Auxins 75 2.5.1.2. Gibberellins 76 2.5.1.3. Cytokinins 78 2.5.1.4. ABA 78 2.5.2. Possible Roles of Seed Hormones 79 2.5.2.1. Seed Growth and Development 79 2.5.2.2. Fruit Growth and Development 82 2.5.2.3. Hormones for Germination and Growth 82 2.5.2.4. Other Effects of the Seed Hormones 83 Chapter 3 Storage, Imbibition, and Germination 3.1. The Longevity of Seeds ;; 89 3.2. Viability of Seeds in Storage 92 3.2.1. The Relationship between Temperature and Moisture during Storage 92 3.2.2. Other Factors That Affect Seed Viability during Storage.. 95 3.2.2.1. Cultivar and Harvest Variability 96 3.2.2.2. Pre- and Postharvest Conditions : 96 3.2.2.3. Oxygen Pressure during Storage 97 3.2.2.4. Fluctuating Storage Conditions 97 3.2.3. Microflora and Seed Deterioration 98 3.2.4. Seed Storage Facilities 99 3.2.5. Recalcitrant Seeds 100
ix 3.3. The Biochemical Basis of Deterioration of Orthodox Seeds 101 3.3.1. Respiration and ATP Synthesis 102 3.3.2. Protein and Ribonucleic Acid Synthesis 104 3.3.3. Damage to Chromosomes and DNA 107 3.3.4. Aging and the Deterioration of Membranes 110 3.4. Metabolism of the Dry Seed 114 3.5. Imbibition 115 3.5.1. Uptake of Water from the Soil 115 3.5.2. Kinetics of Water Uptake by Seeds 118 3.5.3. Soaking Injury, Solute Leakage, and Imbibitional Chilling Damage 120 3.6. The Completion of Germination: Radicle Elongation and Its Control 124 3.7. Seedling Development 128 Chapter 4 Cellular Events during Germination and Seedling Growth 4.1. Respiration Oxygen Consumption 135 4.1.1. Pathways, Intermediates, and Products 135 4.1.2. Respiration during Imbibition and Germination 136 4.1.2.1. Phase I 137 4.1.2.2. Phase II 137 4.1.2.3. Phase III 137 4.1.2.4. Phase IV 137 4.2. Mitochondrial Development and Oxidative Phosphorylation 139 4.2.1. Site of ATP Production during Early Imbibition 139 4.2.2. The Route of Electrons between Substrate and Molecular Oxygen \... 140 4.2.3. Mitochondrial Development in Imbibed Seeds 143 4.2.4. ATP Synthesis and Adenylate Energy Charge during Germination 149 4.2.5. The Synthesis and Utilization of Reducing Power: Pyridine Nucleotides.151 4.3. Respiration under Anaerobic Conditions 153 4.4. Protein and Ribonucleic Acid Synthesis 156 4.4.1. The Mechanism and Measurement of Protein Synthesis.157 4.4.2. Protein Synthesis during Germination and Its Dependence on Messenger RNA Synthesis 158
4.4.3. Ribosomal and Transfer RNA Synthesis 164 4.4.4. Enzymes and Precursors of RNA Synthesis 165 4.4.5. Protein and RNA Synthesis in Storage Tissues 166 4.5. DNA Synthesis and Cell Division 168 Chapter 5 Dormancy and the Control of Germination 5.1. Introduction 175 5.2. Internal Controls 175 5.2.1. Dormancy Its Biological Role 175 5.2.2. Categories of Dormancy 177 5.2.3. Mechanism of Dormancy 178 5.2.4. Embryo Dormancy The Inherent Constraints 179 5.2.5. Coat-Imposed Dormancy The Constraints 180 5.2.5.1. Interference with Water Uptake 181 5.2.5.2. Mechanical Restraint 182 5.2.5.3. Interference with Gas Exchange 184 5.2.5.4. Prevention of Exit of Inhibitors 187 5.2.5.5. Supply of Inhibitors to the Embryo 189 5.2.6. Coat-Imposed Dormancy A Summary 189 5.3. Embryonic Inadequacy The Causes 189 5.3.1. Metabolism of Dormant Seeds 190 5.3.2. Membranes and Dormancy 191 5.4. Development of Dormancy 193 5.4.1. When Does Primary Dormancy Occur? 193 5.4.2. Genetic Control of Dormancy 193 5.4.3. Correlative Effects in Dormancy ; 194 5.4.4. Dormancy Induction by Inhibitors 195 5.4.5. The Environment in Dormancy Inception. 197 5.4.6. Development of Hard Coats 200 5.4.7. Secondary Dormancy 200 5.5. The External Controls 201 5.5.1. The Release from Dormancy. 201 5.5.1.1. Afterripening 201 5.5.1.2. Low Temperatures (Chilling) 202 5.5.1.3. Other Effects of Temperatures on Dormancy... 206 5.5.1.4. Light 207 5.5.1.4a. Action Spectra and Phytochrome... 207 5.5.1.4b. Photoequilibria 212
xi 5.5.1.4c. Where Is Phytochrome Located?... 212 5.5.1.4d. Photoconversions of Phytochrome... 213 5.5.1.4e. Phytochrome The Sensor 214 5.5.1.5. Seeds with Impermeable Coats 215 5.5.1.6. Breaking of Dormancy by Chemicals 215 5.5.1.7. The Mechanism of Dormancy Release 217 5.5.1.8. Hormones in Dormancy Breakage 218 5.5.1.9. Dormancy Breakage and Metabolism 220 5.5.1.10. Dormancy Breakage and Cell Enlargement... 223 5.5.2. Environmental Control of Germination 225 5.5.2.1. Effects of Light 225 5.5.2.2. Inhibition by Short Periods of Far-Red Light... 227 5.5.2.3. Effects of Temperature 229 5.5.2.4. Water Stress 231 5.5.2.5. Oxygen and Carbon Dioxide 233 Chapter 6 Some Ecophysiological Aspects of Germination 6.1. Introduction 237 6.2. Seed Burial 237 6.2.1. The Seed Bank 237 6.2.2. Light and Seed Burial 238 6.3. Germination under Leaf Shade 241 6.4. Temperature 243 6.5. Water 246 6.6. Interactions 246 6.7. Secondary Dormancy 247 6.8. Germination, Plant Distribution, and Plant Origin 248 Chapter 7 Mobilization of Stored Seed Reserves 7.1. Stored Carbohydrate Catabolism 253 7.1.1. Pathways of Starch Catabolism. 253 7.1.2. Synthesis of Sucrose 255 7.2. Mobilization of Stored Carbohydrate Reserves in Cereals 256 7.2.1. The Embryo Reserves 256 7.2.2. The Endosperm Reserves 256 7.2.3. The Fate of the Products of Starch Hydrolysis 263
xii Contents 7.3. Mobilization of Stored Carbohydrate Reserves in Legumes 264 7.3.1. Nonendospermic Legumes 264 7.3.2. Endospermic Legumes 266 7.3.3. Mannan-Containing Seeds Other than Legumes 269 7.4. Stored Lipid Catabolism 271 7.4.1. General Catabolism 271 7.4.2. Mobilization of Fats from Oil Bodies 273 7.4.3. The Fate of Glycerol and Fatty Acids 276 7.4.4. Role of the Glyoxysome, Mitochondrion, and Cytosol in Gluconeogenesis 278 7.4.5. Glyoxysome Biosynthesis and Degradation 279 7.4.6. Utilization of the Products of Fat Catabolism 284 7.5. Stored Protein Catabolism 284 7.5.1. General Catabolism 284 7.5.2. Protein Mobilization in Cereals 285 7.5.3. Protein Mobilization in Dicots 287 7.5.4. Utilization of the Liberated Amino Acids 293 7.5.5. Proteinase Inhibitors 297 7.6. Stored Phosphate Catabolism 298 7.6.1. General Catabolism 298 7.6.2. Phosphate Catabolism in Seeds 298 7.6.3. Mobilization of Nucleic Acids from the Storage Regions. 300 Chapter 8 Control of the Mobilization of Stored Reserves 8.1. Control of Reserve Mobilization in Cereals 305 8.1.1. Gibberellin and the Induction of a-amylase Synthesis in Barley 305 8.1.2. Regulation of a-amylase Production within the Intact Grain 310 8.1.3. Regulation of Other Hydrolases in the Barley Aleurone Layer 314 8.1.4. Gibberellin Induction of Hydrolytic Enzymes in Other Cereals 317 8.2. Control Processes in Other Seeds 317 8.2.1. When Are the Mobilizing Enzymes Produced? 318 8.2.2. Regulation of Mobilization 319
xiii 8.2.3. Mode of Regulation by the Axis 322 8.2.3.1. Hormonal Control by the Axis 322 8.2.3.2. The Axis as a Sink 325 Chapter 9 Seeds and Germination: Some Agricultural and Industrial Aspects 9.1. Introduction, 329 9.2. Malting 329 9.3. Preharvest Sprouting 334 9.3.1. Conditions under Which Preharvest Sprouting Occurs... 334 9.3.2. The Physiology of Preharvest Sprouting in Wheat 337 9.4. Genetic Conservation Seed Gene Banks 340 9.5. Enhancement of Seed Germination by Osmotic Stress and Dehydration Treatments 343 9.5.1. Osmotic Stress 343 9.5.2. Dehydration-Rehydration 345 Index 349