《introduction to plant physiology P560》求取 ⇩

Chapter 1 · Cells, Tissues, and Organs:The Architecture of Plants1

1.1The Plant Cell2

1.2Building Blocks: Lipids, Proteins,and Carbohydrates2

1.2.1 Lipids Are a Class of Molecules That Includes Fats,Oils, Sterols, and Pigments4

1.2.2 Proteins Play a Central Role in the Biochemistry of Cells and Are Responsible for Virtually All the Properties of Life as We Know it6

1.2.3 Carbohydrates Are the Most Abundant Class of Biological Molecules8

1.3Biological Membranes11

1.3.1 The Membrane Lipid Forms a Bilayer, a Highly Fluid but Very Stable Structure11

1.3.2 Membranes Contain Significant Amounts of Protein12

1.4Cellular Organelles13

1.4.1 Most Mature Plant Cells Contain a Large, Central Vacuole13

1.4.2 The Nucleus Is the Information Center of the Cell13

1.4.3 The Endoplasmic Reticulum and Golgi Apparatus Are Centers of Membrane Biosynthesis and Secretory Activities14

1.4.4 The Mitochondrion Is the Principal Site of Cellular Respiration15

1.4.5 Plastids Are a Family of Organelles with a Variety of Functions15

1.4.6 Microbodies Are Metabolically Very Active16

1.5 Cytoskeleton16

1.6The Extracellular Matrix17

1.6.1 The Primary Cell Wall Is a Flexible Network of Cellulose Microfibrils and Cross-Linking Glycans17

1.6.2 The Cellulose-Glycan Lattice is Embedded in a Matrix of Pectin and Protein19

1.6.3 Cellulose Microfibrils Are Assembled at the Plasma Membrane as They Are Extruded into the Cell Wall20

1.6.4 The Secondary Cell Wall Is Deposited on the Inside of the Primary Wall in Maturing Cells21

1.6.5 Plasmadesmata Are Cytoplasmic Channels Extend Through the Wall to Connect the Protoplasts of Adjacent Cells21

1.7Tissues and Organs22

1.7.1 Tissues Are Groups of Cells That Form an Organized, Functional Unit22

1.7.2 Meristems Are Regions of Perpetually Dividing Cells22

1.7.3 Parenchyma Is the Most Abundant Living Tissue in Plants24

1.7.4 Supporting Tissues Are Distributed Throughout the Primary and Secondary Plant Bodies24

1.7.5 Vascular Tissues Are the Principal Conducting Tissues for Water and Nutrients25

1.7.6 Epidermis Is a Superficial Tissue That Forms a Continuous Layer over the Surface of the Primary Plant Body25

1.8Plant Organs26

1.8.1 Roots Anchor the Plant and Absorb Water and Minerals from the Soil26

1.8.2 Stems Elevate the Photosynthetic Organs, the Leaves, Toward the Sun26

1.8.3 Leaves Are the Principal Photosynethic Organs27


Chapter Review28

Further Reading28

Part 1 ·Plants and Energy29

Chapter 2 · Bioenergetics and ATP Synthesis31

2.1Bioenergetics and Energy Transformations in Living Organisms31

2.1.1 The Sun Is a Primary Source of Energy31

2.1.2 What Is Bioenergetics?32

2.1.3 The First Law of Thermodynamics Refers to Energy Conservation32

2.1.4 The Second Law of Thermodynamics Refers to Entropy and Disorder33

2.1.5 The Ability to Do Work is Dependent on the Availability of Free Energy33

2.1.6 Free Energy Is Related to Chemical Equilibria34

2.2Energy Transformations and Coupled Reactions35

2.2.1 Free Energy of ATP Is Associated with Coupled Phosphate Transfer Reactions35

2.2.2 Free Energy Changes Are Associated with Coupled Oxidation-Reduction Reactions36

2.3Energy Transduction and the Chemiosmotic Synthesis of ATP39

2.3.1 Chloroplasts and Mitochondria Exhibit Specific Compartments39

2.3.2 Chloroplasts and Mitochondria Synthesize ATP by Chemiosmosis41


Chapter Review43

Further Reading43

Chapter 3 · The Dual Role of Sunlight:Energy and Information45

3.1The Physical Nature of Light45

3.1.1 Light Is Electromagnetic Energy Which Exists in Two Forms45

3.1.2 Light Can Be Characterized as a Wave Phenomenon46

3.1.3 Light Can Be Characterized as a Stream of Discrete Particles46

3.1.4 Light Energy Can Interact with Matter47

3.1.5 How Does One Illustrate the Efficiency of Light Absorption and Its Physiological Effects49

3.1.6 Accurate Measurement of Light Is Important in Photobiology50

3.2 The Natural Radiation Environment51

3.3Photoreceptors Absorb Light for Use in a Physiological Process52

3.1.1 Chlorophylls Are Primarily Responsible for Harvesting Light Energy for Photosynthesis52

3.3.2 Phycobilins Serve as Accessory Light-Harvesting Pigments in the Red Algae and Cyanobacteria or as a Critical Regulatory System in Green Plants54

3.3.3 Carotenoids Account for the Autumn Colors55

3.3.4 Cryptochrome Is a Photoreceptor Sensitive to Blue and UV-A Light57

3.3.5 UV-B Radiation May Act as a Developmental Signal57

3.3.6 Flavonoids Provide the Myriad of Flower Colors and Act as a Natural Sunscreen58

3.3.7 Betacyanins and Beets60


Chapter Review61

Further Reading61

Chapter 4 · Energy Conservation in Photosynthesis: Harvesting Sunlight63

4.1Leaves Are Photosynthetic Machines Which Maximize the Absorption of Light64

4.2 Photosynthesis Is an Oxidation-Reduction Process66

4.3Photosynthetic Electron Transport68

4.3.1 Photosystems Are Major Components of the Photosynthetic Electron Transport Chain68

4.3.2 Photosystem Ⅱ Oxidizes Water to Produce Oxygen71

4.3.3 The Cytochrome Complex and Photosystem ⅠOxidize Plastoquinol72

4.4 Photophosphorylation Is the Light-Dependent Synthesis of ATP73

4.5 Lateral Heterogeneity Is the Unequal Distribution of Thylakoid Complexes75

4.6 Light-Harvesting Complexes Are Superantenna Complexes that Regulate Energy Distribution76

4.7Photoinhibition of Photosynthesis: Photoprotection versus Photodamage78

4.7.1 Carotenoids Serve a Dual Function: Light Harvesting and Photoprotection78

4.7.2 Oxygen May Protect against Photoinhibition by Acting as an Alternative Electron Acceptor80

4.7.3 The D1 Repair Cycle Overcomes Photodamage to PSII82

4.8 Inhibitors of Photosynthetic Electron Transport Are Effective Herbicides83


Chapter Review86

Fur ther Reading87

Box 4.1 · Historical Perspective—The Discovery of Photosynthesis66

Box 4.2 · The Case for Two Photosystems84

Chapter 5 · Energy Conservation in Photosynthesis: CO2 Assimilation89

5.1Stomatal Complex Controls Leaf Gas Exchange and Water Loss90

5.2 CO2 Enters the Leaf by Diffusion92

5.3 How Do Stomata Open and Close?94

5.4Stomatal Movements Are Also Controlled By External Environmental Factors96

5.4.1 Light and Carbon Dioxide Regulate Stomatal Opening96

5.4.2 Water Status and Temperature Influence Stomatal Opening98

5.4.3 Stomatal Movements Follow Endogenous Rhythms98

5.5The Photosynthetic Carbon Reduction (PCR) Cycle98

5.5.1 The PCR Cycle Reduces CO2 to Produce a 3-Carbon Sugar98

5.5.2 The Carboxylation Reaction Fixes the CO299

5.5.3 ATP and NADPH Are Consumed in the PCR Cycle102

5.5.4 What Are the Energetics of the PCR Cycle?102

5.6The PCR Cycle Is Highly Regulated102

5.6.1 The Regeneration of RuBP Is Autocatalytic102

5.6.2 Rubisco Activity Is Regulated Indirectly by Light103

5.6.3 Other PCR Enzymes Are also Regulated by Light104

5.7Chloroplasts of C3 Plants also Exhibit Competing Carbon Oxidation Processes104

5.7.1 Rubisco Catalyzes the Fixation of Both CO2 and O2105

5.7.2 Why Photorespiration?106

5.7.3 In Addition to PCR, Chloroplasts Exhibit an Oxidative Pentose Phosphate Cycle (OPPC)108

5.8 The C4 Syndrome: Another Biochemical Mechanism to Assimilate CO2108

5.9 The C4 Syndrome Is Usually Associated with Kranz Leaf Anatomy112

5.10The C4 Syndrome Has Ecological Significance112

5.10 .1 The C4 Syndrome Is Differentially Sensitive to Temperature113

5.10 .2 The C4 Syndrome Is Associated with Water Stress113

5.11Crassulacean Acid Metabolism (CAM): An Adaptation to Life in the Desert115

5.11 .1 Is CAM a Variation of the C4 Syndrome?115

5.11 .2 CAM Plants Are Particularly Suited to Dry Habitats115

5.12 C4 and CAM Photosynthesis Require Precise Regulation and Temporal Integration117


Chapter Review122

Further Reading122

Box 5.1 · Enzymes118

Chapter 6 · Allocation, Translocation, and Partitioning of Photoassimilates123

6.1Starch and Sucrose Are Biosynthesized in Two Different Compartments124

6.1.1 Starch Is Biosynthesized in the Stroma124

6.1.2 Sucrose Is Biosynthesized in the Cytosol125

6.2 Starch and Sucrose Biosynthesis Are Competitive Processes126

6.3Photoassimilates Are Translocated over Long Distances128

6.3.1 What Is the Composition of the Photoassimilate Translocated by the Phloem?129

6.4Sieve Elements Are the Principal Cellular Constituents of the Phloem131

6.4.1 Phloem Exudate Contains a Significant Amount of Protein132

6.5 Direction of Translocation Is Determined by Source-Sink Relationships133

6.6 Phloem Translocation Occurs by Mass Transfer133

6.7Phloem Loading and Unloading Regulate Translocation and Partitioning136

6.7.1 Phloem Loading Can Occur Symplastically or Apoplastically136

6.7.2 Phloem Unloading May Occur Symplastically or Apoplastically138

6.8Photoassimilate Is Distributed Between Different Metabolic Pathways and Plant Organs139

6.8.1 Photoassimilates May Be Allocated to a Variety of Metabolic Functions in the Source or the Sink140

6.8.2 Distribution of Photoassimilates Between Competing Sinks Is Determined By Sink Strength141

6.9 Xenobiotic Agrochemicals Are Translocated in the Phloem143


Chapter Review144

Further Reading144

Chapter 7 · Cellular Respiration: Unlocking the Energy Stored in Photoassimilates145

7.1Cellular Respiration Consists of a Series of Pathways by Which Photoassimilates Are Oxidized146

7.2Sucrose and Starch Are Broken Down into Glucose147

7.2.1 α-Amylase Produces Maltose and Limit Dextrins148

7.2.2 β-Amylase Produces Maltose148

7.2.3 Limit Dextrinase Is a Debranching Enzyme148

7.2.4 α-Glucosidase Hydrolyzes Maltose148

7.2.5 Starch Phosphorylase Catalyzes the Phosphorolytic Degradation of Starch149

7.3Glycolysis Converts Sugars to Pyruvic Acid150

7.3.1 Hexoses Must Be Phosphorylated to Enter Glycolysis150

7.3.2 Triose Phosphates Are Oxidized to Pyruvate151

7.4 The Oxidative Pentose Phosphate Pathway Is an Alternative Route for Glucose Metabolism151

7.5 The Fate of Pyruvate Depends on the Availability of Molecular Oxygen152

7.6Oxidative Respiration Is Carried Out by the Mitochondrion153

7.6.1 In the Presence of Molecular Oxygen, Pyruvate Is Completely Oxidized to CO2 and Water by the Citric Acid Cycle153

7.6.2 Electrons Removed from Substrate in the Citric Acid Cycle Are Passed to Molecular Oxygen Through the Mitochondrial Electron Transport Chain154

7.7 Energy Is Conserved in the Form of ATP in Accordance with Chemiosmosis156

7.8Plants Contain Several Alternative Electron Pathways157

7.8.1 Plant Mitochrondria Contain External Dehydrogenases157

7.8.2 Plants Have a Rotenone-Insensitive NADH Dehydrogenase158

7.8.3 Plants Exhibit Cyanide-Resistant Respiration158

7.9 Many Seeds Store Carbon as Oils Which Are Converted to Sugar159

7.10 Respiration Provides Carbon Skeletons for Biosynthesis161

7.11 Respiration Rate Varies with Development and Metabolic State162

7.12Respiration Rate Responds to Environmental Conditions163

7.12 .1 Light163

7.12 .2 Temperature164

7.12 .3 Oxygen Availability164


Chapter Review165

Further Reading165

Chapter 8 · Nitrogen Assimilation167

8.1The Nitrogen Cycle: A Complex Pattern of Exchange167

8.1.1 Ammonification, Nitrification, and Denitrification Are Essential Processes in the Nitrogen Cycle168

8.1.2 Nitrogen Fixation Reduces N2 to Ammonia168

8.2Biological Nitrogen Fixation Is Exclusively Prokaryotic169

8.2.1 Some Nitrogen-Fixing Bacteria Are Free-Living Organisms169

8.2.2 Symbiotic Nitrogen Fixation Involves Specific Associations Between Bacteria and Plants169

8.3Legumes Exhibit Symbiotic Nitrogen Fixation170

8.3.1 Rhizobia Infect the Host Roots Which Induces Nodule Development170

8.4The Biochemistry of Nitrogen Fixation174

8.4.1 Nitrogen Fixation Is Catalyzed by the Enzyme Dinitrogenase174

8.4.2 Nitrogen Fixation Is Energetically Costly175

8.4.3 Dinitrogenase Is Sensitive to Oxygen175

8.4.4 Dinitrogenase Results in the Production of Hydrogen Gas176

8.5The Genetics of Nitrogen Fixation177

8.5.1 nif Genes Code for Nitrogenase177

8.5.2 nod Genes and nif Genes Regulate Nodulation177

8.5.3 What Is the Source of Heme for Leghemoglobin?177

8.6NH3 Produced by Nitrogen Fixation is Converted to Organic Nitrogen178

8.6.1 Ammonium Is Assimilated by GS/GOGAT178

8.6.2 Fixed Nitrogen Is Exported As Asparagine and Ureides179

8.7 Plants Generally Take up Nitrogen in the Form of Nitrate181

8.8 Nitrogen Cycling: Simultaneous Importand Export182

8.9 Agricultural and Ecosystem Productivity Is Dependent on Nitrogen Supply183


Chapter Review185

Further Reading185

Box 8.1 · Lectins—Proteins with a Sweet Tooth172

Chapter 9 · Carbon Assimilation and Productivity187

9.1Productivity Refers to an Increase in Biomass187

9.2 Carbon Economy Is Dependent on the Balance Between Photosynthesis and Respiration188

9.3Productivity Is Influenced by a Variety of Genetic and Environmental Factors189

9.3.1 Fluence Rate189

9.3.2 Available CO2190

9.3.3 Temperature192

9.3.4 Soil Water Potential193

9.3.5 Nutrient Supply, Pathology, and Pollutants193

9.3.6 Leaf Factors194

9.4 Primary Productivity on a Global Scale196


Chapter Review197

Further Reading198

Part 2 · Plants, Water, and Minerals200

Chapter 10 · Plant Cells and Water201

10.1Water Has Unique Physical and Chemical Properties202

10.2The Thermal Properties of Water Are Biologically Important203

10.2.1 Water Exhibits a Unique Thermal Capacity203

10.2.2 Water Exhibits a High Heat of Fusion and Heat of Vaporization203

10.3 Water Is the Universal Solvent204

10.4 Polarity of Water Molecules Results in Cohesion and Adhesion205

10.5Water Movement May Be Governed by Diffusion or by Bulk Flow205

10.5.1 Bulk Flow Is Driven by Hydrostatic Pressure205

10.5.2 Fick's First Law Describes the Process of Diffusion206

10.6Osmosis Is the Diffusion of Water Across a Selectively Permeable Membrane207

10.6.1 Osmosis in Plant Cells Is Indirectly Energy Dependent207

10.6.2 The Chemical Potential of Water Has an Osmotic as Well as Pressure Component209

10.7 Hydrostatic Pressure and Osmotic Pressure Are Two Components of Water Potential210

10.8 Water Potential Is the Sum of Its Component Potentials211

10.9 Dynamic Flux of H2O Is Associated with Changes in Water Potential212

10.10 How Elastic Are Cell Walls?213


Chapter Review217

Further Reading217

Box 10.1 · Osmosensors214

Chapter 11 · Whole Plant Water Relations219

11.1Transpiration Is Driven by Differences in Vapor Pressure220

11.2 Transpiration Can Be Measured by Weight Loss and Gas Exchange221

11.3 The Driving Force of Transpiration Is Differences in Vapor Pressure221

11.4The Rate of Transpiration Is Influenced by Environmental Factors222

11.4.1 What Are the Effects of Humidity?223

11.4.2 What Is the Effect of Temperature?224

11.4.3 What Is the Effect of Wind?224

11.5 Water Conduction Occurs via Tracheary Elements225

11.6The Ascent of Xylem Sap Is Explained by Combining Transpiration with Cohesive Forces of Water228

11.6.1 Root Pressure Is Related to Root Structure229

11.6.2 Water Rise by Capillarity Is Due to Adhesion and Surface Tension231

11.6.3 The Cohesion Theory Best Explains the Ascent of Xylem Sap231

11.7Water Loss Due to Transpiration Must Be Replenished235

11.7.1 Soil Is a Complex Medium235

11.8 Roots Absorb and Transport Water237

11.9 The Permeability of Roots to Water Varies237

11.10 Radial Movement of Water Through the Root Involves Two Possible Pathways238


Chapter Review240

Further Reading240

Box 11.1 · Why Transpiration?226

Box 11.2 · Forces Involved in Capillary Rise232

Chapter 12 · Plants and Inorganic Nutrients241

12.1Methods and Nutrient Solutions242

12.1.1 Interest in Plant Nutrition Is Rooted in the Study of Agriculture and Crop Productivity242

12.1.2 The Use of Hydroponic Culture Helped to Define the Mineral Requirements of Plants242

12.1.3 Modern Techniques Overcome Inherent Disadvantages of Simple Solution Culture243

12.2The Essential Nutrient Elements245

12.2.1 Seventeen Elements Are Deemed to Be Essential for Plant Growth and Development245

12.2.2 The Essential Nutrients Are Generally Classed as either Macronutrients or Micron Nutrients245

12.2.3 Determining Essentiality of Micronutrients Presents Special Problems245

12.3Beneficial Elements246

12.3.1 Sodium Is an Essential Micronutrient for C4 Plants247

12.3.2 Silicon May Be Beneficial for a Variety of Species247

12.3.3 Cobalt Is Required by Nitrogen-Fixing Bacteria247

12.3.4 Some Plants Tolerate High Concentrations of Selenium247

12.4Nutrient Functions and Deficiency Symptoms247

12.4.1 A Plant's Requirement for a Particular Element Is Defined in Terms of Critical Concentration248

12.4.2 Nitrogen Is a Constituent of Many Critical Macromolecules249

12.4.3 Phosphorous Is Part of the Nucleic Acid Backbone and Has a Central Function in Intermediary Metabolism249

12.4.4 Potassium Activates Enzymes and Functions in Osmoregulation250

12.4.5 Sulfur Is an Important Constituent of Proteins,Coenzymes, and Vitamins250

12.4.6 Calcium Is Important in Cell Division, Cell Adhesion, and as a Secondary Messenger251

12.4.7 Magnesium Is a Constituent of the Chlorophyll Molecule and Is an Important Regulator of Enzyme Reaction251

12.4.8 Iron Is Required for Chlorophyll Synthesis and Electron Transfer Reactions251

12.4.9 Boron Appears to Have a Role in Cell Division and Elongation and Contributes to the Structural Integrity of the Cell Wall253

12.4.10 Copper Is a Necessary Cofactor for Oxidative Enzymes254

12.4.11 Zinc Is an Activator of Numerous Enzymes254

12.4.12 Manganese Is an Enzyme Cofactor as Well as Part of the Oxygen-Evolving Complex in the Chloroplast254

12.4.13 Molybdenum Is a Key Component of Nitrogen Metabolism254

12.4.14 Chlorine Has a Role in Photosynthetic Oxygen Evolution and Balances Charge Across Cellular Membranes255

12.4.15 The Role of Nickel Is Not Clear255

12.5 Toxicity of Micronutrients256


Chapter Review256

Further Reading257

Chapter 13 · Roots, Soils, and Nutrient Uptake259

13.1The Soil as a Nutrient Reservoir260

13.1.1 Colloids Are a Significant Component of Most Soils260

13.1.2 Colloids Present a Large, Negatively Charged Surface Area260

13.1.3 Soil Colloids Reversibly Adsorb Cations from the Soil Solution261

13.1.4 The Anion Exchange Capacity of Soil Colloids Is Relatively Low 26113.2 Nutrient Uptake262

13.2.1 Nutrient Uptake by Plants Requires Transport of the Nutrient across Root Cell Membranes262

13.2.2 Simple Diffusion Is a Purely Physical Process262

13.2.3 The Movement of Most Solutes across Membranes Requires the Participation of Specific Transport Proteins263

13.2.4 Active Transport Requires the Expenditure of Metabolic Energy263

13.3 Selective Accumulation of Ions by Roots266

13.4Electrochemical Gradients and Ion Movement266

13.4.1 Ions Move in Response to Electrochemical Gradients266

13.4.2 The Nernst Equation Helps to Predict Whether an Ion Is Exchanged Actively or Passively267

13.5Active Transport and Electrogenic Pumps269

13.5.1 Active Transport Is Driven by ATPase-Proton Pumps269

13.5.2 The ATPase-Proton Pumps of Plasma Membranes and Vacuolar Membranes Are Different270

13.5.3 K+ Exchange Is Mediated by Two Classes of Transport Proteins271

13.6Ion Uptake by Roots272

13.6.1 A First Step in Mineral Uptake by Roots Is Diffusion into the Apparent Free Space272

13.6.2 Apparent Free Space Is Equivalent to the Apoplast of the Root Epidermal and Cortical Cells273

13.7The Radial Path of Ion Movement Through Roots274

13.7.1 Ions Entering the Stele Must First Be Transported from the Apparent Free Space into the Symplast274

13.7.2 Ions Are Actively Secreted into the Xylem Apoplast274

13.7.3 Emerging Secondary Roots May Contribute to the Uptake of Some Solutes275

13.8Root-Microbe Interactions276

13.8.1 Bacteria Other Than Nitrogen Fixers Contribute to Nutrient Uptake by Roots276

13.8.2 Mycorrhizae Are Fungi that Increase the Volume of the Nutrient Depletion Zone Around Roots276


Chapter Review279

Further Reading280

Box 13.1 · Electrophysiology—Exploring Ion Channels264

Part 3 · Plant Development281

Chapter 14 · Patterns in Plant Development283

14.1Growth, Differentiation, and Development283

14.1.1 Development Is the Sum of Growth and Differentiation283

14.1.2 Growth Is an Irreversible Increase in Size284

14.1.3 Differentiation Refers to Qualitative Changes That Normally Accompany Growth284

14.2Control of Development285

14.2.1 The Orderly Development of a Plant Requires a Programmed Sequence of Gene Expression285

14.2.2 Hormones Coordinate Cell-Cell Interactions287

14.2.3 A Continuous Stream of Environmental Signals Provide Information That Plants Use to Modify Their Development287

14.3Signal Perception and Transduction287

14.3.1 Signals Are Perceived by Protein Receptors288

14.3.2 Signal Transduction Includes a Diverse Array of Second Messengers and Biochemical Mechanisms288

14.3.3 There Is Extensive Cross-Talk among Signal Pathways291

14.4Cell Walls and Cell Growth291

14.4.1 Cell Growth Is Driven by Water Uptake and Limited by the Strength and Rigidity of the Cell Wall291

14.4.2 Extension of the Cell Wall Requires Wall-Loosening Events That Enable Load-Bearing Elements in the Wall to Yield to Turgor Pressure292

14.4.3 Wall Loosening and Cell Expansion Are Stimulated by Low pH and Expansins293

14.5A Survey of Plant Development294

14.5.1 Seed Structure and Development294

14.5.2 Seed Germination295

14.5.3 Shoot Development295

14.5.4 Root Development299

14.5.5 Flower Evocation and Development301

14.5.6 Flower and Fruit Development301

14.5.7 Senescence and Programmed Cell Death Are the Final Stages of Development302

14.6Kinetic Analysis of Growth303

14.6.1 Growth of Microorganisms in Culture Exhibit Exponential Growth303

14.6.2 Growth of Multicellular Organisms Is Determined by the Activity of the Meristem306


Chapter Review306

Further Reading306

Box 14.1 · Development in a Mutant Weed286

Box 14.2 · Ubiquitin and Proteosomes—Cleaning Up Unwanted Proteins304

Chapter 15 · The Plant Hormones:Biochemistry and Metabolism309

15.1Do Plants Have Hormones?309

15.1.1 There Are Subtle Differences Between Animal and Plant Hormones310

15.1.2 The List of Plant Hormones Is Growing312

15.1.3 The Amount of Hormone in a Tissue Is Governed by Several Factors312


15.2.1 The Principal Auxin in Plants Is Indole-3-Acetic Acid (IAA)314

15.2.2 IAA Is Synthesized from the Amino Acid L-Tryptophan316

15.2.3 Some Plants Do Not Require Tryptophan for IAA Biosynthesis316

15.2.4 IAA May Be Stored As Inactive Conjugates318

15.2.5 There Are Two Principal Mechanisms for Deactivation of IAA318


15.3.1 There Are Three Principal Sites for Gibberellin Biosynthesis320

15.3.2 Gibberellins Are Terpenes, Sharing a Core Pathway with Several Other Hormones and a Wide Range of Secondary Products322

15.3.3 Gibberellins Are Synthesized from Geranylgeranyl Pyrophosphate (GGPP)323

15.3.4 Growth Retardants Block the Synthesis of Gibberellins324

15.3.5 Gibberellins Are Deactivated by 2β-Hydroxylation324

15.3.6 Gibberellin Transport Is Poorly Understood325


15.4.1 Cytokinins Are Synthesized Primarily in the Root325

15.4.2 Cytokinin Biosynthesis Begins with the Condensation of an Isopentenyl Group with the Amino Group of Adenosine Monophosphate326

15.4.3 Cytokinins May Be Reversibly or Irreversibly Deactivated by Conjugation and Irreversibly Deactivated by Oxidation329

15.5. Abscisic Acid329

15.5.1 Abscisic Acid Is Synthesized Primarily in Mature Leaves330

15.5.2 Abscisic Acid Is Synthesized from the Cleavage Product of a 40-Carbon Carotenoid Precursor330

15.5.3 Abscisic Acid Is Degraded by Oxidation to PhaseicAcid332


15.6.1 Ethylene Is Synthesized from the Amino Acid Methionine332

15.6.2 Ethylene and Polyamine Biosynthesis Share a Common Precursor334

15.6.3 Excess Ethylene Is Subject to Oxidation334


15.7.1 Brassinosteroids Are Polyhydroxylated Sterols Derived from the Triterpene Squalene335

15.7.2 Several Routes for Deactivation of Brassinosteroids Have Been Identified335


15.8.1 The Pathway for Polyamine Biosynthesis Is the Same in Plants, Microorganisms, and Mammals337

Summm y338

Chapter Review338


Box 15.1 · Historical Perspectives—Discovering Plant Hormones311

Chapter 16 · The Plant Hormones: Control of Development341

16.1Cell Division, Enlargement, and Differentiation341

16.1.1 Cytokinins Are a Significant Factor in Regulating Cell Division341

16.1.2 Cytokinins Regulate Progression Through the Cell Cycle342

16.1.3 Auxins Stimulate Cell Enlargement in Excised Tissues344

16.1.4 The Acid-Growth Hypothesis Explains Auxin Control of Cell Enlargement344

16.1.5 Maintenance of Auxin-Induced Growth Requires Gene Activation347

16.1.6 Many Aspects of Plant Development Are Linked to the Polar Transport of Auxin349

16.1.7 Auxins and Cytokinins Regulate Vascular Differentiation351

16.2Seed Development and Germination352

16.2.1 The Level and Activities of Various Hormones Change Dramatically During Seed Development352

16.2.2 Gibberellins Stimulate Mobilization of Nutrient Reserves During Germination of Cereal Grains353

16.3Shoot and Root Development356

16.3.1 Gibberellins Stimulate Hyperelongation of Intact Stems, Especially in Dwarf and Rosette Plants356

16.3.2 Inhibition of Gibberellin Biosynthesis Has Commercial Applications357

16.3.3 Hormone Mutants Indicate a Role for Brassinosteroids and Ethylene in Stem Growth358

16.3.4 The Ratio of Auxin to Cytokinin Controls the Growth of Axillary Buds358

16.3.5 Root Elongation and Development Is Particularly Sensitive to Auxin and Ethylene359

16.4Senescence and Abscission360

16.4.1 Cytokinins and Ethylene Are Antagonistic in the Regulation of Nutrient Mobilization and Senescence360

16.4.2 Auxin Regulates Leaf Abscission362

16.5Flower and Fruit Development362

16.5.1 Gibberellins Promote Precocious Flowering in Some Species363

16.5.2 Auxin and Gibberellin Influence the Sex of Flowers363

16.5.3 Hormones Influence Fruit Set and Development364


16.6.1 The Study of Ethylene Presents a Unique Set of Problems364

16.6.2 Ethylene Affects Many Aspects of Vegetative Development364


Chapter Review366

Further Reading366

Box 16.1 · The Cell Cycle and Control of Cell Division343

Box 16.2 · Commercial Applications of Hormones348

Chapter 17 · Photomorphogenesis:Responding to Light367


17.2Phytochrome: Responses to Red and Far-Red Light368

17.2.1 Photoreversibility Is the Hallmark of Phytochrome Action370

17.2.2 Phytochromes Are Phycobilin Pigments371

17.2.3 Conversion of Pr to Pfr in Etiolated Seedlings Leads to a Loss of Both Pfr and Total Phytochrome372

17.3Phytochrome Responses Can Be Grouped According to Their Fluence Requirements374

17.3.1 The Most Studied Low Fluence Responses (LFRs) Are De-etiolation and Seed Germination374

17.3.2 Very Low Fluence Responses Are Not Photoreversible376

17.3.3 High Irradiance Reactions Require Prolonged Exposure to Relatively High Fluence Rates377

17.4Phytochrome under Natural Conditions377

17.4.1 PhA May Function to Detect the Presence of Light378

17.4.2 Phytochrome Detects Canopy Shading and End-of-Day Signals378

17.5Responses to Blue and UV-A Light381

17.5.1 Cryptochrome Is a Flavoprotein381

17.5.2 Phototropin Is a Blue Light-Dependent Kinase382

17.5.3 A Hybrid Blue-Light Photoreceptor Has Been Isolated from a Fern382

17.6 De-etiolation in Arabidopsis. A Case Study in Photoreceptor Interactions383

17.7Photoreceptor Signal Transduction384

17.7.1 Phytochromes Have Kinase Activity384

17.7.2 Pfr Regulates Gene Expression384

17.7.3 Phytochrome May Migrate from the Cytoplasm to the Nucleus386

17.8 Some Plant Responses Are Regulated by UV-B Light387


Chapter Review388

Further Reading388

Box 17.1 · Historical Perspectives: The Discovery of Phytochrome369

Chapter 18 · Plant Movements—Orientation in Space391


18.1.1 Phototropism Is a Response to a Light Gradient across an Organ392

18.1.2 Phototropism in Coleoptiles Is Mediated by a Flavoprotein393

18.1.3 Fluence Response Curves Illustrate the Complexity of Phototropic Responses394

18.1.4 The Phototropic Response Is Attributed to a Lateral Redistribution of Diffusible Auxin395


18.2.1 Gravitropism Is More Than Simply Up and Down398

18.2.2 The Gravitational Stimulus Is the Product of Intensity and Time399

18.2.3 In Roots, Gravity Is Perceived in the Root Cap401

18.2.4 The Sedimentation of Starch-Filled Amyloplasts Is an Initial Gravity-Sensing Event402

18.2.5 Gravitropism, Like Phototropism, Is an Auxin-Dependent Differential Growth Response403

18.2.6 The Gravitropic Signal Transduction Chain May Involve Stretch-Activated Ion Channels, pH Changes in the Root Cap, and Redistribution of Calcium Ions405

18.2.7 Gravitropism in Grass Stems Occurs in the False Pulvinus407

18.2.8 Plants Follow Different Rules in the Microgravity Environment of Space408

18.3Nastic Movements408

18.3.1 Nyctinastic Movements Are Rhythmic Movements Involving Reversible Turgor Changes408

18.3.2 Nvctinastic Movements Are Due to Ion Fluxes and Resulting Osmotic Responses in Specialized Motor Cells409

18.3.3 Seismonasty Is a Response to Mechanical Stimulation412


Chapter Review414

Further Reading414

Box 18.1 · Methods in the Study of Gravitropism400

Chapter 19 · Measuring Time: The Control of Development by Photoperiod and Endogenous Clocks415


19.1.1 Photoperiodic Responses May Be Characterized By a Variety of Response Types416

19.1.2 Critical Daylength Defines Short-Day and Long-Day Responses417

19.1.3 Plants Actually Measure the Length of the Dark Period419

19.1.4 The Photoperiodic Signal Is Perceived by the Leaves420

19.1.5 Phytochrome Is the Principal Photoreceptor for Photoperiodism421

19.1.6 Photoperiodism Normally Requires a Period of High Fluence Light Before or After the Dark Period422

19.1.7 Three Different Hypotheses Have Been Proposed to Account for the Floral Stimulus422

19.1.8 Photoperiodic Behavior Is Often Modified by Temperature423

19.2The Biological Clock426

19.2.1 Clock-Driven Rhythms Persist under Constant Conditions426

19.2.2 The Circadian Clock Is Temperature-Compensated428

19.2.3 Light Resets the Biological Clock on a Daily Basis428

19.2.4 The Circadian Clock Is a Significant Component in Photoperiodic Time Measurement429

19.2.5 Several Clock-Associated Genes Have Been Identified431

19.2.6 The Circadian Clock in Insects, Animals, and Cyanobacteria Is a Negative Feedback Loop432

19.3Floral Induction433

19.3.1 Flower Initiation and Development Involves the Sequential Action of Three Sets of Genes433

19.3.2 Flowering Time Genes Influence the Duration of Vegetative Growth434

19.3.3 Floral Identity Genes and Organ Identity Genes Overlap in Time and Function435

19.4 Photoperiodism in Nature436


Chapter Review438

Further Reading439

Box 19.1 · Historical Perspectives: The Discovery of Photoperiodism416

Box 19.2 · Historical Perspectives: The Biological Clock424

Chapter 20 · Temperature: Plant Development and Distribution441

20.1Temperature in the Plant Environment441

20.2Temperature and Flowering Response443

20.2.1 Vernalization Occurs Most Commonly in Winter Annuals and Biennials443

20.2.2 The Effective Temperature for Vernalization Is Variable444

20.2.3 The Vernalization Treatment Is Perceived by the Shoot Apex445

20.2.4 The Vernalized State Is Transmissible445

20.2.5 Gibberellin and Vernalization Operate Through Independent Genetic Pathways446

20.3Bud Dormancy446

20.3.1 Bud Dormancy Is Induced Primarily by Photoperiod447

20.3.2 Temperature Is a Significant Factor in Breaking Bud Dormancy447

20.4Seed Dormancy and Germination448

20.4.1 Numerous Factors Influence Seed Dormancy and Germination448

20.4.2 Temperature Has a Significant Impact on Seed Dormancy449

20.5 Responses to Change in Temperature450

20.6Influence of Temperature on Growth and Plant Distribution451

20.6.1 Coasts and Deserts: A Case Study452

20.6.2 Temperature Influences the Distribution of C3 and C4 Grasses on Mountain Slopes454


Chapter Review455

Further Reading455

Part 4 · Stress and Secondary Metabolism457

Chapter 21 · Plant Environmental Stress Physiology459

21.1What Is Plant Stress?459

21.2 Plants Respond to Stress in Several DifferentWays460

21.3Abiotic Stress461

21.3.1 Water Stress Is a Persistent Threat to Plant Survival461

21.3.2 Water Stress Leads to Membrane Damage462

21.3.3 Photosynthesis Is Particularly Sensitive to Water Stress462

21.3.4 Stomata Respond to Water Deficit463

21.3.5 Osmotic Adjustment Is a Response to Water Stress465

21.3.6 Water Deficit Affects Shoot and Root Growth466

21.3.7 Water Stress May Induce a Decrease in Leaf Area467

21.4Temperature Stress467

21.4.1 Many Plants Are Chilling Sensitive468

21.4.2 North Temperate Overwintering Plants Survive Freezing Stress468

21.4.3 Cold Acclimation Increases Resistance to Freezing Stress470

21.4.4 Cold Acclimation and Freezing Tolerance in Herbaceous Species Is a Complex Interaction Between Light and Low Temperature471

21.4.5 High Temperature Stress Is a Major Factor in Plant Productivity472

21.5 Salt Stress, Water Deficits and Ion Toxicity474

21.6Pollution Represents a Relatively New Abiotic Stress476

21.6.1 Heavy Metals476

21.6.2 Air Pollution477

21.7Insects and Disease Represent Potential Biotic Stresses479

21.7.1 Hypersensitive Reaction Is a Sensing/Signalling Mechanism Initiated by a Biotic Stress479

21.7.2 How Do Plants Recognize Potential Pathogens and Initiate Defense Responses?479

21.7.3 Systemic Acquired Resistance Represents a Plant Immune Response480

21.7.4 Jasmonates Mediate Insect and Disease Resistance481


Chapter Review491

Further Reading491

Box 21.1 · Monitoring Plant Stress by Chlorophyll Fluorescence482

Box 21.2 · Ecophysiology, Plant Biomes, and Weather484

Chapter 22 · Secondary Plant Metabolites493

22.1Primary and Secondary Metabolites493


22.2.1 The Terpenoids Are a Chemically and Functionally Diverse Group of Molecules That Share a Common Biosynthetic Pathway494

22.2.2 Many Terpenoids Are Active against Insect Herbivory495

22.2.3 Steroids and Sterols Are Tetracyclic Triterpenoids497

22.2.4 Polyterpenes Include the Carotenoid Pigments and Natural Rubber497


22.3.1 Saponins Are Terpene Glycosides with Detergent Properties499

22.3.2 Cardian Glycosides Are Highly Toxic, Modified Steroid Glycosides500

22.3.3 Cyanogenic Glycosides Are a Natural Source of Hydrogen Cyanide501

22.3.4 Glucosinolates Are Sulfur-Containing Precursors to Mustard Oils502


22.4.1 Shikimic Acid Is a Key Intermediate in the Synthesis of Aromatic Amino Acids and Phenylpropenoids503

22.4.2 The Simplest Phenolic Molecules Are Essentially Deaminated Versions of the Corresponding Amino Acids503

22.4.3 Coumarins and Coumarin Derivatives Function as Anticoagulants506

22.4.4 Lignin Is a Major Structural Component of Secondary Cell Walls507

22.4.5 Flavonoids and Stilbenes Have Parallel Biosynthetic Pathways508

22.4.6 Tannins Denature Proteins and Provide an Astringent Taste to Foods508


22.5.1 Alkaloids Are a Large Family of Chemically Unrelated Molecules510

22.5.2 Alkaloids Are Noted Primarily for Their Pharmacological Properties and Medical Applications510

22.5.3 Like Many Other Secondary Metabolites,Alkaloids Serve as Preformed Chemical Defense Molecules512


Chapter Review513

Further Reading513

Part 5 · Biotechnology515

Chapter 23 · Biotechnology: Engineering Plants for the Future517

23.1Modern Biotechnology Is Synonymous with Recombinant DNA Technology518

23.1.1 DNA Recombination Allows the Movement of Selected Genes Between Organisms518

23.1.2 The Most Widely Used Vector for Introducing Foreign Genes into Plants is the Ti Plasmid of the Crown-Gall Bacterium Agrobacterium Tumefaciens519

23.1.3 Electroporation and Biolistics Are Methods for Direct Delivery of DNA into Plant Cells522

23.1.4 Genetic Engineering Is a New Chapter in the Long Histoy of Plant Breeding522

23.2Tissue and Cell Culture and Protoplast Fusion523

23.2.1 The Culture of Plant Cells and Tissues Has Been Exploited Since the 1930s523

23.2.2 Protoplasts Are Naked Plant Cells That Can Be Fused to Make Somatic Hybrids523

23.2.3 Tissue Culture Has Made Possible Large-Scale Cloning of Plants524

23.3Plant Protection524

23.3.1 Herbicide-Resistant Crops Encourage More Efficient Use of Herbicides525

23.3.2 Herbicide Resistance Can Be Achieved by Overexpression of Tolerant Enzymes525

23.3.3 Herbicide Resistance in Weeds Is a Potentially Undesirable Side-Effect of Herbicide Use526

23.3.4 Several Strategies Are Available for Protection against Insects and Disease527

23.4Metabolic Engineering: Improving Yield and Nutrition528

23.4.1 One Target of Biotechnology Is Improved Carbon Gain and Nitrogen Metabolism528

23.4.2 Boosting Vitamin Content Is One Way to Improve the Nutritional Quality of Foods529

23.4.3 Oilseed Crops May Be Engineered to Produce Healthier Edible Oils529

23.5Molecular Farming Uses Plants as Living Factories530

23.5.1 Transgenic Plants May Provide a Low-Cost Delivery System for Vaccines531

23.5.2 Plants Can Be Engineered to Produce Biodegradable Plastics531

23.6 Plants Have Potential as an Alternative Source of Renewable Fuels532

23.7 Plants Remain Useful as a Source of Secondary Products533


Chapter Review534

Further Reading534

Box 23.1 · Engineering Plants with Their Own Genes519

Appendix Ⅰ · Standard Amino Acids and Their Structures535

Appendix Ⅱ · Measuring Water Potential and Its Components539


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