Fundamentals of Plant Physiology

Cover
Brief Contents
Table of Contents
Preface
1 Plant and Cell Architecture
1-1 Plant Life Processes: Unifying Principles 1-1
1-2 Plant Classification and Life Cycles
Box 1.1 Evolutionary Relationships among Plants
Plant life cycles alternate between diploid and haploid generations
1-3 Overview of Plant Structure
Plant cells are surrounded by rigid cell walls
Primary and secondary cell walls differ in their components
The cellulose microfibrils and matrix polymers are synthesized via different mechanisms
Plasmodesmata allow the free movement of molecules between cells
New cells originate in dividing tissues called meristems
Box 1.2 The Secondary Plant Body
1-4 Plant Cell Types
Dermal tissue covers the surfaces of plants
Ground tissue forms the bodies of plants
Vascular tissue fom1s transport networks between different parts of the plant
1-5 Plant Cell Organelles
Biological membranes are bilayers that contain proteins
1-6 The Nucleus
Gene expression involves both transcription and translation
Posttranslational regulation determines the life span of proteins
1-7 The Endomembrane System
The endoplasmic reticulum is a network of internal membranes
Vacuoles have diverse functions in plant cells
Oil bodies are lipid-storing organelles
Microbodies play specialized metabolic roles in leaves and seeds
1-8 Independently Dividing Semiautonomous Organelles
Proplastids mature into specialized plastids in different plant tissues
Chloroplast and mitochondrial division are independent of nuclear division
1-9 The Plant Cytoskeleton
The plant cytoskeleton consists of microtubules and microfilaments
Actin, tubulin, and their polymers are in constant flux in the living cell
Microtubule protofilaments first assemble into flat sheets before curling into cylinders
Cytoskeletal motor proteins mediate cytoplasmic streaming and directed organelle movement
1-10 Cell Cycle Regulation
Each phase of the cell cycle has a specific set of biochemical and cellular activities
The cell cycle is regulated by cyclins and cyclin- dependent kinases
Mitosis and cytokinesis involve both microtubules and the endomembrane system
Summary
2 Water and Plant Cells
2-1 Water in Plant Life
2-2 The Structure and Properties of Water
Water is a polar molecule that forms hydrogen bonds
Water is an excellent solvent
Water has distinctive thermal properties relative to its size
Water molecules are highly cohesive
Water has a high tensile strength
2-3 Diffusion and Osmosis
Diffusion is the net movenent of molecules by random thermal agitation
Diffusion is most effective over short distances
Osmosis describes the net movement of water across a selectively permeable barrier
2-4 Water Potential
The chemical potential of water represents the free-energy status of water
Three major factors contribute to cell water potential
Water potentials can be ,measured
2-5 Water Potential of Plant Cells
Water enters the cell along a water potential gradient
Water can also leave the cell in response to a water potential gradient
Water potential and its components vary with growth conditions and location within the plant
2-6 Cell Wall and Membrane Properties
Small changes in plant cell volume cause large changes in turgor pressure
The rate at which cells gain or lose water is influenced by plasma membrane hydraulic conductivity
Aquaporins facilitate the movement of water across plasma membranes
2-7 Plant Water Status
Physiological processes are affected by plant water status
Solute accumulation helps cells maintain turgor and volume
Summary
3 Water Balance of Plants
3-1 Water in the Soil
A negative hydrostatic pressure in soil water lowers soil water potential
Water moves through the soil by bulk flow
3-2 Water Absorption by Roots
Water moves in the root via the apoplast, symplast, and transmembrane pathways
Solute accumulation in the xylem can generate "root pressure"
3-3 Water Transport through the Xylem
The xylem consists of two types of transport cells
Water moves through the xylem, by pressure-driven bulk flow
Water movement through the xylem requires a smaller pressure gradient than movement through living cells
What pressure difference is needed to lift water 100 meters to a treetop?
The cohesion-tension theory explains water transport in the xylem
Xylem transport of water in trees faces physical changes
Plants minimize the consequences of xylem cavitation
3-4 Water Movement from the Leaf to the Atmosphere
Leaves have a large hydraulic resistance
The driving force for transpiration is the difference in water vapor concentration
Water loss is also regulated by the pathway resistances
The boundary layer contributes to diffusion resistance
Stomata resistance is another major component of diffusional resistance
The cell walls of guard cells have specialized features
An increase in guard cell turgor pressure opens the stomata
3-5 Coupling Leaf Transpiration and Photosynthesis: Light-dependent Stomatal Opening
Stomatal opening is regulated by light
Stomatal opening is specifically regulated by blue light
3-6 Water-use efficiency
3-7 Overview: The Soil- Plant- Atmosphere Continuum
Summary
4 Mineral Nutrition
4-1 Essential Nutrients, Deficiencies, and Plant Disorders
Special techniques are used in nutritional studies
Nutrient solutions can sustain rapid plant growth
Mineral deficiencies disrupt plant metabolism and function
Analysis of plant tissues reveals mineral deficiencies
4-2 Treating Nutritional Deficiencies
Crop yields can be improved by the addition of fertilizers
Some mineral nutrients can be absorbed by leaves
4-3 Soil, Roots, and Microbes
Negatively charged soil particles affect the adsorption of mineral nutrients
Soil pH affects nutrient availability, soil microbes, and root growth
Excess mineral ions in the soil limit plant growth
Some plants develop extensive root systems
Root systems differ in form but are based on conmmon structures
Different areas of the root absorb different mineral ions
Nutrient availability influences root growth
Mycorrhizal symbioses facilitate nutrient uptake by roots
Nutrients move between mycorrhizal fungi and root cells
Summary
5 Assimilation of Inorganic Nutrients
5-1 Nitrogen in the Environment
Nitrogen passes through several forms in a biogeochemical cycle
Unassimilated ammonium or nitrate may be dangerous
5-2 Nitrate Assimilation
Many factors regulate nitrate reductase
Nitrite reductase converts nitrite to ammonium
Both roots and shoots assimilate nitrate
5-3 Ammonium Assimilation
Converting ammonium to amino acids requires two enzymes
Ammonium can be assimilated via an alternative pathway
Transamination reactions transfer nitrogen
Asparagine and glutamine link carbon and nitrogen metabolism
5-4 Amino Acid Biosynthesis
5-5 Biological Nitrogen Fixation
Free-living and symbiotic bacteria fix nitrogen
Nitrogen fixation requires microanaerobic or anaerobic conditions
Symbiotic nitrogen fixation occurs in specialized structures
Establishing symbiosis requires an exchange of signals
Nod factors produced by bacteria act as signals for symbiosis
Nodule formation involves phytohormones
The nitrogenase enzyme complex fixes N2
Amides and ureides are the transported forms of nitrogen
5-6 Sulfur Assimilation
Sulfate is the form of sulfur transported into plants
Sulfate assimilation occurs mostly in leaves
Methionine is synthesized from cysteine
5-7 Phosphate Assimilation
5-8 Iron Assimilation
Roots modify the rhizosphere to acquire iron
Iron cations form complexes with carbon and phosphate
5-9 The Energetics of Nutrient Assimilation
Summary
6 Solute Transport
6-1 Passive and Active Transport
6-2 Transport of Ions across Membrane Barriers
Different diffusion rates for cations and anions produce diffusion potentials
How does membrane potential relate to ion distribution?
The Nernst equation distinguishes between active and passive transport
Proton transport is a major determinant of the membrane potential
6-3 Membrane Transport Processes
Channels enhance diffusion across membranes
Carriers bind and transport specific substances
Primary active transport requires energy
Secondary active transport uses stored energy
Kinetic analyses can elucidate transport mechanisms
6-4 Membrane Transport Proteins
The genes for many transporters have been identified
Transporters exist for diverse nitrogen-containing compounds
Cation transporters are diverse
Anion transporters have been identified
Transporters for metal and metalloid ions transport essential micronutrients
Aquaporins have diverse functions
Plasma membrane tt+ -ATPases are highly regulated P-type ATPases
The tonoplast H+ -ATPase drives solute accumulation in vacuoles
H+ -pyrophosphatases a !so pump protons at the tonoplast
6-5 Ion Transport in Stomatal Opening
Light stimulates ATPase activity and creates a stronger electrochemical gradient across the guard cell plasma membrane
Hyperpolarization of the guard cell plasma membrane leads to uptake of ions and water
6-6 Ion Transport in Roots
Solutes n1ove through both apoplast and symplast
Ions cross both symplast and apoplast
Xylem parenchyma cells participate in xylem loading
Summary
7 Photosynthesis: The Light Reactions
7-1 Photosynthesis in Higher Plants
7-2 General Concepts
Light has characteristics of both a particle and a wave
When molecules absorb or emit light, they change their electronic state
Photosynthetic pigments absorb the light that powers photosynthesis
7-3 Key Experiments in Understanding Photosynthesis
Action spectra relate light absorption to photosynthetic activity
Photosynthesis takes place in complexes containing light-harvesting antennas and photochemical reaction centers
The chemical reaction of photosynthesis is driven by light
Light drives the reduction of NADP+ and the formation of ATP
Oxygen-evolving organisms have two photosystems that operate in series
7-4 Organization of the Photosynthetic Apparatus
The chloroplast is the site of photosynthesis
Thylakoids contain integral membrane proteins
Photosystems I and II are spatially separated in the thylakoid membrane
7-5 Organization of Light-Absorbing Antenna Systems
Antenna systems contain chlorophyll and are membrane-associated
The antenna funnels energy to the reaction center
Many antenna pigment-protein complexes have a common structural motif
7-6 Mechanisms of Electron Transport
Electrons from chlorophyll travel through the carriers organized in the Z scheme
Energy is captured when an excited chlorophyll reduces an electron acceptor molecule
The reaction center chlorophylls of the two photosystems absorb at different wavelengths
The PSII reaction center is a multi-subunit pigment-protein complex
Water is oxidized to oxygen by PSII
Pheophytin and two qui nones accept electrons from PSII
Electron flow through the cytochrome b6f complex also transports protons
Plastoquinone and plastocyanin carry electrons between photosystem II and photosystem I
The PSI reaction center reduces NADp+
Cyclic electron flow generates ATP but no NADPH
Some herbicides block photosynthetic electron flow
7-7 Proton Transport and ATP Synthesis in the Chloroplast
Summary
8 Photosynthesis: The Carbon Reactions
8-1 The Calvin- Benson Cycle
The Calvin-Benson cycle has three phases: carboxylation, reduction, and regeneration
The fixation of CO2 via carboxylation of ribulose 1,5-bisphosphate and the reduction of the product 3-phosphoglycerate yield triose phosphates
The regeneration of ribulose 1,5-bisphosphate ensures the continuous assimilation of CO2
An induction period precedes the steady state of photosynthetic CO2 assimilation
Many mechanis.ms regulate the Calvin-Benson cycle
Rubisco activase regulates the catalytic activity of Rubisco
Light regulates the Calvin-Benson cycle via the ferredoxin-thioredoxin system
Light-dependent ion movements modulate enzymes of the Calvin-Benson cycle
8-2 Photorespiration: The C2 Oxidative Photosynthetic Carbon Cycle
The oxygenation of ribulose 1,5-bisphosphate sets in motion the C2 oxidative photosynthetic carbon cycle
Photorespiration is linked to the photosynthetic electron transport chain
8-3 Inorganic Carbon-Concentrating Mechanisms
8-4 Inorganic Carbon-Concentrating Mechanisms: The C4 Carbon Cycle
Malate and aspartate are the primary carboxylation products of the C4 cycle
The C4 cycle assimilates CO2 by the concerted action of two different types of cells
Bundle sheath cells and mesophyll cells exhibit anatomica I and biochemical differences
The C4 cycle also concentrates CO2 in single cells
Light regulates the activity of key C4 enzymes
Photosynthetic assimilation of CO2 in C4 plants den1ands more transport processes than in C3 plants
In hot, dry climates, the C4 cycle reduces photorespiration
8-5 Inorganic Carbon-Concentrating Mechanisms: Crassulacean Acid Metabolism (CAM)
Different mechanisms regulate C4 PEPCase and CAM PEPCase
CAM is a versatile mechanism, sensitive to environmental stimuli
8-6 Accumulation and Partitioning of Photosynthates-Starch and Sucrose
Summary
9 Photosynthesis: Physiological and Ecological Considerations
9-1 The Effect of leaf Properties on Photosynthesis
Leaf anatomy and canopy structure maximize light absorption
Leaf angle and leaf movement can control light absorption
Leaves acclimate to sun and shade environments
9-2 Effects of light on Photosynthesis in the Intact leaf
Light-response curves reveal photosynthetic properties
Leaves must dissipate excess light energy
Absorption of too much light can lead to photoinhibition
9-3 Effects of Temperature on Photosynthesis in the Intact leaf
Leaves must dissipate vast quantities of heat
There is an optimal temperature for photosynthesis
Photosynthesis is sensitive to both high and low temperatures
Photosynthetic efficiency is temperature-sensitive
9-4 Effects of Carbon Dioxide on Photosynthesis in the Intact leaf
Atmospheric CO2 concentration keeps rising
CO2 diffusion to the chloroplast is essential to photosynthesis
CO2 imposes limitations on photosynthesis
How will photosynthesis and respiration change in the future under elevated CO2 conditions?
Summary
10 Translocation in the Phloem
10-1 Patterns of Translocation: Source to Sink
10-2 Pathways of Translocation
Sugar is translocated in phloem sieve elements
Mature sieve elements are living cells specialized for translocation
Large pores in cell walls are the prominent feature of sieve elements
Damaged sieve elements are sealed off
Companion cells aid the highly specialized sieve elements
10-3 Materials Translocated in the Phloem
Phloem sap can be collected and analyzed
Sugars are translocated in a nonreducing form
Other solutes are translocated in the phloem
10-4 Rates of Movement
10-5 The Pressure-Flow Model, a Passive Mechanism for Phloem Transport
An osmotically generated pressure gradient drives translocation in the pressure-flow model
Some predictions of pressure flow have been confirmed, while others require further experimentation
There is no bidirectional I transport in single sieve elements, and solutes and water move at the same velocity
The energy requirement for transport through the phloem pathway is small in herbaceous plants
Sieve plate pores appear to be open channels
Pressure gradients in the sieve elements may be modest; pressures in herbaceous plants and trees appear to be similar
10-6 Phloem Loading
Phloem loading can occur via the apoplast or symplast
Abundant data support the existence of apoplastic loading in some species
Sucrose uptake in the apoplastic pathway requires metabolic energy
Phloem loading in the apoplastic pathway involves a sucrose-H+ symporter
Phloen, loading is symplastic in some species
The polymer-trapping model explains symplastic loading in plants with intermediary-type companion cells
Phloem loading is passive in several tree species
10-7 Phloem Unloading and Sink-to-Source Transition
Phloem unloading and short-distance transport can occur via symplastic or apoplastic pathways
Transport into sink tissues requires metabolic energy
The transition of a leaf from sink to source is gradual
10-8 Photosynthate Distribution: Allocation and Partitioning
Allocation includes storage, utilization, and transport
Various sinks partition transport sugars
Source leaves regulate allocation
Sink tissues compete for avaiLable translocated photosynthate
Sink strength depends on sink size and activity
The source adjusts over the long term to changes in the source-to-sink ratio
10-9 Transport of Signaling Molecules
Turgor pressure and chemical signals coordinate source and sink activities
There is no bidirectional transport in single sieve elements, and solutes and water move at the same velocity
Plasmodesmata function in phloem signaling
Summary
11 Respiration and Lipid Metabolism
11-1 Overview of Plant Respiration
11-2 Glycolysis
Glycolysis metabolizes carbohydrates from several sources
The energy-conserving phase of glycolysis extracts usable energy
Plants have alternative glycolytic reactions
In the absence of oxygen, fermentation regenerates the NAD+ needed for glycolytic ATP production
11-3 The Oxidative Pentose Phosphate Pathway
The oxidative pentose phosphate pathway produces NADPH and biosynthetic intermediates
The oxidative pentose phosphate pathway is redox-regulated
11-4 The Tricarboxylic Acid Cycle
Mitochondria are semiautonomous organelles
Pyruvate enters the mitochondrion and is oxidized via the TCA cycle
The TCA cycle of plants has unique features
11-5 Mitochondrial Electron Transport and ATP Synthesis
The electron transport chain catalyzes a flow of electrons from NADH to O2
The electron transport chain has supplen,entary branches
ATP synthesis in the mitochondrion is coupled to electron transport
Transporters exchange substrates and products
Aerobic respiration yields about 60 molecules of ATP per molecule of sucrose
Plants have several mechanisms that lower the ATP yield
Short-term control of mitochondrial respiration occurs at different levels
Respiration is tightly coupled to other pathways
11-6 Respiration in Intact Plants and Tissues
Plants respire roughly half of the daily photosynthetic yield
Respiratory processes operate during photosynthesis
Different tissues and organs respire at different rates
Environmental factors alter respiration rates
11-7 Lipid Metabolism
Fats and oils store large amounts of energy
Triacylglycerols are stored in oil bodies
Polar glycerolipids are the main structural lipids in membranes
Membrane lipids are precursors of important signaling compounds
Storage lipids are converted into carbohydrates in germinating seeds, releasing stored energy
Summary
12 Signals and Signal Transduction
12-1 Temporal and Spatial Aspects of Signaling
12-2 Signal Perception and Amplification
Signals must be amplified intracellularly to regulate their target molecules
Ca2+ is the most ubiquitous second messenger in plants and other eukaryotes
Changes in the cytosolic or cell wall pH can serve as second messengers for hormonal and stress responses
Reactive oxygen species act as second messengers mediating both environmental and developmental signals
12-3 Hormones and Plant Development
Auxin was discovered in early studies of coleoptile bending during phototropism
Gibberellins promote stem growth and were discovered in relation to the "foolish seedling disease" of rice
Cytokinins were discovered as cell division-promoting factors in tissue culture experiments
Ethylene is a gaseous hormone that promotes fruit ripening and other developmental processes
Abscisic acid regulates seed maturation and stomatal closure in response to water stress
Brassinosteroids regulate floral sex determination, photomorphogenesis, and germination
Salicylic acid and jasmonates function in defense responses
Strigolactones suppress branching and promote rhizosphere interactions
12-4 Phytohormone Metabolism and Homeostasis
Indole-3-pyruvate is the primary intermediate in auxin biosynthesis
Gibberellins are synthesized by oxidation of the diterpene ent-kaurene
Cytokinins are adenine derivatives with isoprene side chains
Ethylene is synthesized from methionine via the intermediate ACC
Abscisic acid is synthesized from a carotenoid intermediate
Brassinosteroids are derived from the sterol campesterol
Strigolactones are synthesized from ￎﾲ-carotene
12-5 Signal Transmission and Cell-Cell Communication
12-6 Hormonal Signaling Pathways
The cytokinin and ethylene signal transduction pathways are derived from the bacterial two-component regulatory system
Receptor-like kinases mediate brassinosteroid signaling
The core ABA signaling components include phosphatases and kinases
Plant hormone signaling pathways generally employ negative regulation
Protein degradation via ubiquitination plays a prominent role in hormone signaling
Plants have mechanisms for switching off or attenuating signaling responses
The cellular response output to a signal is often tissue-specific
Cross-regulation allows signal transduction pathways to be integrated
Summary
13 Signals from Sunlight
13-1 Plant Photoreceptors
Photoresponses are driven by light quality or spectral properties of the energy absorbed
Plant responses to light can be distinguished by the amount of light required
13-2 Phytochromes
Phytochrome is the primary photoreceptor for red and far-red light
Phytochrome can interconvert between Pr and Pfr forms
13-3 Phytochrome Responses
Phytochrome responses vary in lag time and escape time
Phytochrome responses fall into three n1ain categories based on the amount of light required
Phytochrome A mediates responses to continuous far-red light
Phytochrome regulates gene expression
13-4 Blue-Light Responses and Photoreceptors
Blue-light responses have characteristic kinetics and lag times
13-5 Cryptochromes
Blue-light irradiation of the cryptochrome FAD chromophore causes a conformational change
The nucleus is a primary site of cryptochrome action
Cryptochrome interacts with phytochrome
13-6 Phototropins
Phototropism requires changes in auxin mobilization
Phototropins regulate chloroplast movements
Stomatal opening is regulated by blue light, which activates the plasma membrane H+-ATPase
13-7 The Coaction of Phytochrome, Cryptochrome, and Phototropins
13-8 Responses to Ultraviolet Radiation
Summary
14 Embryogenesis
14-1 Overview of Embryogenesis
14-2 Comparative Embryology of Eudicots and Monocots
Morphological similarities and differences between eudicot and monocot embryos dictate their respective patterns of development
Apical-basal polarity is maintained in the embryo during organogenesis
Embryo development requires regulated communication between cells
Auxin signaling is essential for embryo development
Polar auxin transport is mediated by localized auxin efflux carriers
Auxin synthesis and polar transport regulate embryonic development
Radial patterning guides formation of tissue layers
The protoderm differentiates into the epidermis
The central vascular cylinder is elaborated by cytokinin-regulated progressive cell divisions
14-3 Formation and Maintenance of Apical Meristems
Auxin and cytokinin contribute to the formation and maintenance of the RAM
SAM formation is also influenced by factors involved in auxin movement and responses
Cell proliferation in the SAM is regulated by cytokinin and gibberellin
Summary
15 Seed Dormancy, Germination, and Seedling Establishment
15-1 Seed Structure
Seed anaton,y varies widely among different plant groups
15-2 Seed Dormancy
There are two basic types of seed dormancy mechanisms: exogenous and endogenous
Non-dormant seeds can exhibit vivipary and precocious germination
The ABA:GA ratio is the primary determinant of seed dormancy
15-3 Release from Dormancy
Light is an important signal that breaks dormancy in small seeds
Some seeds require either chilling or after-ripening to break dormancy
Seed dormancy can be broken by various chemical compounds
15-4 Seed Germination
Germination and postgermination can be divided into three phases corresponding to the phases of water uptake
15-5 Mobilization of Stored Reserves
The cereal aleurone layer is a specialized digestive tissue surrounding the starchy endosperm
15-6 Seedling Establishment
The development of emerging seedlings is strongly influenced by light
Gibberellins and brassinosteroids both suppress photomorphogenesis in darkness
Hook opening is regulated by phytochrome, auxin, and ethylene
Vascular differentiation begins during seedling emergence
Growing roots have distinct zones
Ethylene and other hormones regulate root hair development
Lateral roots arise internally from the pericycle
15-7 Cell Expansion: Mechanisms and Hormonal Controls
The rigid primary cell wall must be loosened for cell expansion to occur
Microfibril orientation influences growth directionality of cells with diffuse growth
Acid-induced growth and cell wall yielding are mediated by expansins
Auxin promotes growth in stems and coleoptiles, while inhibiting growth in roots
The outer tissues of eudicot stems are the targets of auxin action
The o'linimum lag tin1e for auxin-induced elongation is 10 minutes
Auxin-induced proton extrusion loosens the cell wall
Ethylene affects microtubule orientation and induces lateral cell expansion
15-8 Tropisms: Growth in Response to Directional Stimuli
Auxin transport is polar and gravity-independent
The Cholodny-Went hypothesis is supported by auxin movements and auxin responses during gravitropic growth
Gravity perception is triggered by the sedimentation of amyloplasts
Gravity sensing may involve pH and calcium ions (Ca T) as second messengers
Phototropins are the tight receptors involved in phototropism
Phototropism is mediated by the lateral redistribution of auxin
Shoot phototropism occurs in a series of steps
Summary
16 Vegetative Growth and Senescence
16-1 The Shoot Apical Meristem
The shoot apical meristem has distinct zones and layers
16-2 Leaf Structure and Phyllotaxy
Auxin-dependent patterning of the shoot apex begins during embryogenesis
16-3 Differentiation of Epidermal Cell Types
A specialized epidermal lineage produces guard cells
16-4 Venation Patterns in Leaves
The primary leaf vein is initiated in the leaf primordium
Auxin canalization initiates development of the leaf trace
16-5 Shoot Branching and Architecture
Auxin, cytokinins, and strigolactones regulate axillary bud outgrowth
The initial signal for axillary bud growth may be an increase in sucrose availability to the bud
16-6 Shade Avoidance
Reducing shade avoidance responses can improve crop yields
16-7 Root System Architecture
Plants can modify their root system architecture to optimize water and nutrient uptake
Monocots and eudicots differ in their root system architecture
Root system architecture changes in response to phosphorus deficiencies
16-8 Plant Senescence
During leaf senescence, nutrients are remobilized from the source leaf to vegetative or reproductive sinks
The developmental age of a leaf may differ from its chronological age
Leaf senescence may be sequential, seasonal, or stress-induced
The earliest cellular changes during leaf senescence occur in the chloroplast
Reactive oxygen species serve as internal signaling agents in leaf senescence
Plant hormones interact in the regulation of leaf senescence
16-9 Leaf Abscission
The timing of leaf abscission is regulated by the interaction of ethylene and auxin
16-10 Whole Plant Senescence
Angiosperm life cycles may be annual, biennial, or perennial
Nutrient or hormonal redistribution may trigger senescence in monocarpic plants
Summary
17 Flowering and Fruit Development
17-1 Floral Evocation: Integrating Environmental Cues
17-2 The Shoot Apex and Phase Changes
Plant development has three phases
Juvenile tissues are produced first and are located at the base of the shoot
Phase changes can be influenced by nutrients, gibberellins, and epigenetic regulation
17-3 Photoperiodism: Monitoring Day Length
Plants can be classified according to their photoperiodic responses
Photoperiodism is one of many plant processes controlled by a circadian rhythm
Circadian rhythms exhibit characteristic features
Circadian rhythms adjust to different day-night cycles
The leaf is the site of perception of the photoperiodic signal
Plants monitor day length by measuring the length of the night
Night breaks can cancel the effect of the dark period
Photoperiodic timekeeping during the night depends on a circadian clock
A coincidence model links oscillating light sensitivity and photoperiodism
Phytochrome is the primary photoreceptor in photoperiodism
17-4 Vernalization: Promoting Flowering with Cold
17-5 Long-distance Signaling Involved in Flowering
Gibberellins and ethylene can induce flowering
17-6 Floral Meristems and Floral Organ Development
The SAM in Arabidopsis changes with development
The four different types of floral organs are initiated as separate whorls
Two major categories of genes regulate floral development
The ABC model partially explains the determination of floral organ identity
17-7 Pollen Development
17-8 Female Gametophyte Development in the Ovule
Functional megaspores undergo a series of free nuclear mitotic divisions followed by cellularization
17-9 Pollination and Double Fertilization in Flowering Plants
Two sperm cells are delivered to the female gametophyte by the pollen tube
Pollination begins with adhesion and hydration of a pollen grain on a compatible flower
Pollen tubes grow by tip growth
Double fertilization results in the formation of the zygote and the primary endosperm cell
17-10 Fruit Development and Ripening
Arabidopsis and tomato are model systems for the study of fruit development
Fleshy fruits undergo ripening
Ripening involves changes in the color of fruit
Fruit softening involves the coordinated action of many cell wall-degrading enzymes
Taste and flavor reflect changes in acids, sugars, and aroma compounds
The causal link between ethylene and ripening was demonstrated in transgenic and mutant tomatoes
Climacteric and non-climacteric fruits differ in their ethylene responses
Summary
18 Biotic Interactions
18-1 Beneficial Interactions between Plants and Microorganisms
Other types of rhizobacteria can increase nutrient availability, stimulate root branching, and protect against pathogens
18-2 Harmful Interactions of Pathogens and Herbivores with Plants
Mechanical barriers provide a first line of defense against insect pests and pathogens
Specialized plant metabolites can deter insect herbivores and pathogen infection
Plants store constitutive toxic compounds in specialized structures
Plants often store defensive chemicals as nontoxic water-soluble sugar conjugates in specialized vacuoles
18-3 Inducible Defense Responses to Insect Herbivores
Plants can recognize specific components of insect saliva
Phloem feeders activate defense signaling pathways similar to those activated by pathogen infections
Jasmonic acid activates defense responses against insect herbivores
Hormonal interactions contribute to plant-insect herbivore interactions
JA initiates the production of defense proteins that inhibit herbivore digestion
Herbivore damage induces systemic defenses
Long-distance electrical signaling occurs in response to insect herbivory
Herbivore-induced volatiles can repel herbivores and attract natural enemies
Herbivore-induced volatiles can serve as long-distance signals within and between plants
Insects have evolved mechanisms to defeat plant defenses
18-4 Plant Defenses against Pathogens
Microbial pathogens have evolved various strategies to invade host plants
Pathogens produce effector molecules that aid in the colonization of their plant host cells
Pathogen infection can give rise to molecular "danger signals" that are perceived by cell surface pattern recognition receptors (PRRs)
R proteins provide resistance to individual pathogens by recognizing strain-specific effectors
The hypersensitive response is a common defense against pathogens
A single encounter with a pathogen may increase resistance to future attacks
18-5 Plant Defenses against Other Organisms
Some plant parasitic nematodes form specific associations through the formation of distinct feeding structures
Plants compete with other plants by secreting allelopathic secondary metabolites into the soil
Some plants are biotrophic pathogens of other plants
Summary
19 Abiotic Stress
19-1 Defining Plant Stress
Physiological adjustment to a biotic stress involves trade-offs between vegetative and reproductive development
19-2 Acclimation versus Adaptation
19-3 Environmental Stressors
Water deficit decreases turgor pressure, increases ion toxicity, and inhibits photosynthesis
Salinity stress has both osmotic and cytotoxic effects
Temperature stress affects a broad spectrum of physiological processes
Flooding results in anaerobic stress to the root
Light stress can occur when shade-adapted or shade-acclimated plants are subjected to full sunlight
Heavy metal ions can both mimic essential mineral nutrients and generate ROS
Combinations of abiotic stresses can induce unique signaling and metabolic pathways
Sequential exposure to different a biotic stresses sometimes confers cross-protection
Plants use a variety of mechanisms to sense abiotic stress
19-4 Physiological Mechanisms That Protect Plants against Abiotic Stress
Plants can alter their morphology in response to abiotic stress
Metabolic shifts enable plants to cope with a variety of abiotic stresses
Heat shock proteins maintain protein integrity under stress conditions
Membrane lipid composition can adjust to changes in temperature and other abiotic stresses
Chloroplast genes respond to high-intensity light by sending stress signals to the nucleus
A self-propagating wave of ROS mediates systen1ic acquired acclimation
Abscisic acid and cytokinins are stress-response hormones that regulate drought responses
Plants adjust osmotically to drying soil by accumulating solutes
Epigenetic mechanisms and small RNAs provide additional protection against stress
Submerged organs develop aerenchyma tissue in response to hypoxia
Antioxidants and ROS-scavenging pathways protect cells from oxidative stress
Exclusion and internal tolerance mechanisms allow plants to cope with toxic metal and metalloid ions
Plants use cryoprotectant molecules and antifreeze proteins to prevent ice crystal formation
Summary
Glossary
Illustration Credits
Index