Plant Physiology, Fourth Edition

Lincoln Taiz and Eduardo Zeiger

2006
705 pages, 586 illustrations
casebound

About This Title

Plant Physiology, Fourth Edition continues to set the standard for textbooks in the field, making plant physiology accessible to virtually every student. Authors Lincoln Taiz and Eduardo Zeiger have again collaborated with a stellar group of contributing plant biologists to produce a current and authoritative volume that incorporates all the latest findings. Changes for the new edition include:

A new chapter (Chapter 24) on Brassinosteroids
A completely rewritten Chapter 16 (Growth and Development)
Updates on recent developments in the light reactions and the biochemistry of photosynthesis, respiration, ion transport, and water relations
In the hormone chapters, new information about signaling pathways and regulatory mechanisms
Coverage of major breakthroughs on the control of flowering, including the latest findings on the identity of the long-sought-after photoperiodic floral stimulus, “florigen.”

As with the Third Edition, material typically considered prerequisite for plant physiology courses, as well as advanced material, is posted at the companion website. New material has been added here as well, including new Web topics and Web essays.

About the Authors

Lincoln Taiz is Professor of Biology in the Department of Molecular, Cellular, & Developmental Biology at the University of California, Santa Cruz. He earned a B.A. at the University of Utah, Salt Lake City and a Ph.D. (Botany) at the University of California, Berkeley. Dr. Taiz has served in an editorial capacity for the journals Plant Physiology, Plant Physiology and Biochemistry, New Phytologist, and Botanica Acta. His research interests have included cell walls and cell expansion, the structure and function of vacuolar H⁺-ATPases, plant metal tolerance, auxin transport, stomatal regulation, and the history of botany.

Eduardo Zeiger is Professor of Biology in the Department of Ecology and Environmental Biology at the University of California, Los Angeles. He earned his B.S. from the University of Buenos Aires and his Ph.D. (Genetics) from the University of California, Davis. In addition to Plant Physiology, Dr. Zeiger is the author of Stomatal Function (Stanford University Press). His research focuses on stomatal function and blue-light responses in plants.

Chapter Contributors
Richard Amasino • Sarah M. Assmann • Robert E. Blankenship • Arnold J. Bloom • Ray A. Bressan • John Browse • Thomas Brutnell • Robert Buchanan • Joanne Chory • Daniel Cosgrove • Susan Dunford • Jim Ehleringer • Jurgen Engelberth • Ruth Finkelstein • Paul M. Hasegawa • Michele Holbrook • Joseph Kieber • Robert D. Locy • Ian Max Møller • Angus Murphy • Allan G. Rasmusson • Sigal Savaldi-Goldstein • Valerie M. Sponsel • Bruce Veit • Ricardo A. Wolosiuk

Reviews and Commentary

“With contributions from 25 distinguished professors and plant researchers from prestigious universities, research institutes, and biotechnology companies, Taiz and Zeiger have brought together a collection of fundamental discussions in basic plant physiology, which should be treasured by educators who will find it most suitable for teaching undergraduate plant physiology.”
—Tzvi Tzfira, The Quarterly Review of Biology

1. Plant Cells

Plant Life: Unifying Principles
Overview of Plant Structure

Plant cells are surrounded by rigid cell walls
New cells are produced by dividing tissues called meristems
Three major tissue systems make up the plant body

The Plant Cell

Biological membranes are phospholipid bilayers that contain proteins
The nucleus contains most of the genetic material of the cell
Protein synthesis involves transcription and translation
The endoplasmic reticulum is a network of internal membranes
Secretion of proteins from cells begins with the rough ER
Golgi stacks produce and distribute secretory products
Proteins and polysaccharides destined for secretion are processed in the Golgi apparatus
Two models for intra-Golgi transport have been proposed
Specific coat proteins facilitate vesicle budding
Vacuoles play multiple roles in plant cells
Mitochondria and chloroplasts are sites of energy conversion
Mitochondria and chloroplasts are semiautonomous organelles
Different plastid types are interconvertible
Microbodies play specialized metabolic roles in leaves and seeds
Oleosomes are lipid-storing organelles

The Cytoskeleton

Plant cells contain microtubules, microfilaments, and intermediate filaments
Microtubules and microfilaments can assemble and disassemble
Microtubules function in mitosis and cytokinesis
Motor proteins mediate cytoplasmic streaming and organelle movements

Cell Cycle Regulation

Each phase of the cell cycle has a specific set of biochemical and cellular activities
The cell cycle is regulated by cyclin-dependent kinases

Plasmodesmata

There are two types of plasmodesmata: primary and secondary
Plasmodesmata have a complex internal structure
Macromolecular traffic through plasmodesmata is important for developmental signaling

Summary
Web Material
Chapter References

2. Energy and Enzymes (available only at the website)

3. Water and Plant Cells

Water in Plant Life
The Structure and Properties of Water

The polarity of water molecules gives rise to hydrogen bonds
The polarity of water makes it an excellent solvent
The thermal properties of water result from hydrogen bonding
The cohesive and adhesive properties of water are due to hydrogen bonding
Water has a high tensile strength

Water Transport Processes

Diffusion is the movement of molecules by random thermal agitation
Diffusion is rapid over short distances but extremely slow over long distances
Pressure-driven bulk flow drives long-distance water transport
Osmosis is driven by a water potential gradient
The chemical potential of water represents the free-energy status of water
Three major factors contribute to cell water potential
Water enters the cell along a water potential gradient
Water can also leave the cell in response to a water potential gradient
Small changes in plant cell volume cause large changes in turgor pressure
Water transport rates depend on driving force and hydraulic conductivity
Aquaporins facilitate the movement of water across cell membranes
The water potential concept helps us evaluate the water status of a plant
The components of water potential vary with growth conditions and location within the plant

Summary
Web Material
Chapter References

4. Water Balance of Plants

Water in the Soil

A negative hydrostatic pressure in soil water lowers soil water potential
Water moves through the soil by bulk flow

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”

Water Transport through the Xylem

The xylem consists of two types of tracheary elements
Water movement through the xylem requires less pressure 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 challenges
Plants minimize the consequences of xylem cavitation

Water Movement from the Leaf to the Atmosphere

The driving force for water loss is the difference in water vapor concentration
Water loss is also regulated by the pathway resistances
Stomatal control couples leaf transpiration to leaf photosynthesis
The cell walls of guard cells have specialized features
An increase in guard cell turgor pressure opens the stomata
The transpiration ratio measures the relationship between water loss and carbon gain

Overview: The Soil–Plant–Atmosphere Continuum
Summary
Web Material
Chapter References

5. Mineral Nutrition

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

Treating Nutritional Deficiencies

Crop yields can be improved by addition of fertilizers
Some mineral nutrients can be absorbed by leaves

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 minerals in the soil limit plant growth
Plants develop extensive root systems
Root systems differ in form but are based on common structures
Different areas of the root absorb different mineral ions
Mycorrhizal fungi facilitate nutrient uptake by roots
Nutrients move from the mycorrhizal fungi to the root cells

Summary
Web Material
Chapter References

6. Solute Transport

Passive and Active Transport
Transport of Ions across a Membrane Barrier

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

Membrane Transport Processes

Channel transporters 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

Membrane Transport Proteins

The genes for many transporters have been identified
Transporters exist for diverse nitrogen-containing compounds
Cation transporters are diverse
Some anion transporters have been identified
Metals are transported by ZIP proteins
Aquaporins may have novel functions
The plasma membrane H⁺-ATPase has several functional domains
The tonoplast H⁺-ATPase drives solute accumulation into vacuoles
H⁺-pyrophosphatases also pump protons at the tonoplast

Ion Transport in Roots

Solutes move through both apoplast and symplast
Ions cross both symplasm and apoplasm
Xylem parenchyma cells participate in xylem loading

Summary
Web Material
Chapter References

7. Photosynthesis: The Light Reactions

Photosynthesis in Higher Plants
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

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

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
Anoxygenic photosynthetic bacteria have a single reaction center

Organization of Light-Absorbing Antenna Systems

The antenna funnels energy to the reaction center
Many antenna complexes have a common structural motif

Mechanisms of Electron Transport

Electrons from chlorophyll travel through the carriers of 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 photosystem II reaction center is a multisubunit pigment–protein complex
Water is oxidized to oxygen by photosystem II
Pheophytin and two quinones accept electrons from photosystem II
Electron flow through the cytochrome b₆f complex also transports protons
Plastoquinone and plastocyanin carry electrons between photosystems II and I
The photosystem I reaction center reduces NADP⁺
Cyclic electron flow generates ATP but no NADPH
Some herbicides block photosynthetic electron flow

Proton Transport and ATP Synthesis in the Chloroplast
Repair and Regulation of the Photosynthetic Machinery

Carotenoids serve as photoprotective agents
Some xanthophylls also participate in energy dissipation
The photosystem II reaction center is easily damaged
Photosystem I is protected from active oxygen species
Thylakoid stacking permits energy partitioning between the photosystems

Genetics, Assembly, and Evolution of Photosynthetic Systems

Chloroplast, cyanobacterial, and nuclear genomes have been sequenced
Chloroplast genes exhibit non-Mendelian patterns of inheritance
Many chloroplast proteins are imported from the cytoplasm
The biosynthesis and breakdown of chlorophyll are complex pathways
Complex photosynthetic organisms have evolved from simpler forms

Summary
Web Material
Chapter References

8. Photosynthesis: Carbon Reactions

The Calvin Cycle

The Calvin cycle has three stages: carboxylation, reduction, and regeneration
The carboxylation of ribulose-1,5-bisphosphate is catalyzed by the enzyme rubisco
Operation of the Calvin cycle requires the regeneration of ribulose-1,5-bisphosphate
The Calvin cycle regenerates its own biochemical components
The Calvin cycle uses energy very efficiently

Regulation of the Calvin Cycle

Light regulates the Calvin cycle
The activity of rubisco increases in the light
The ferredoxin–thioredoxin system regulates the Calvin cycle
Light-dependent ion movements regulate Calvin cycle enzymes

The C₂ Oxidative Photosynthetic Carbon Cycle

Photosynthetic CO₂ fixation and photorespiratory oxygenation are competing reactions
Photorespiration depends on the photosynthetic electron transport system
The biological function of photorespiration is under investigation

CO₂-Concentrating Mechanisms
I. CO₂ and HCO₃- Pumps
II. The C₄ Carbon Cycle

Malate and aspartate are carboxylation products of the C₄ cycle
Two different types of cells participate in the C₄ cycle
The C₄ cycle concentrates CO₂ in the chloroplasts of bundle sheath cells
The C₄ cycle also concentrates CO₂ in single cells
The C₄ cycle has higher energy demand than the Calvin cycle
Light regulates the activity of key C₄ enzymes
In hot, dry climates, the C₄ cycle reduces photorespiration and water loss

III. Crassulacean Acid Metabolism (CAM)

The stomata of CAM plants open at night and close during the day
Some CAM plants change the pattern of CO₂ uptake in response to environmental conditions

Sucrose and Starch

Chloroplast starch is synthesized during the day and degraded at night
Starch is synthesized in the chloroplast
Starch degradation requires phosphorylation of amylopectin
Triose phosphates synthesized in the chloroplast build up the pool of hexose phosphates in the cytosol
Fructose-6-phosphate can be converted to fructose-1,6-bisphosphate by two different enzymes
Fructose-2,6-phosphate is an important regulatory compound
The hexose phosphate pool is regulated by fructose-2,6-bisphosphate
Sucrose is continuously synthesized in the cytosol

Summary
Web Material
Chapter References

9. Photosynthesis: Physiological and Ecological Considerations

Light, Leaves, and Photosynthesis
Units in the Measurement of Light

Leaf anatomy maximizes light absorption
Plants compete for sunlight
Leaf angle and leaf movement can control light absorption
Plants acclimate and adapt to sun and shade

Photosynthetic Responses to Light by the Intact Leaf

Light-response curves reveal photosynthetic properties
Leaves must dissipate excess light energy
Absorption of too much light can lead to photoinhibition

Photosynthetic Responses to Temperature

Leaves must dissipate vast quantities of heat
Photosynthesis is temperature sensitive

Photosynthetic Responses to Carbon Dioxide

Atmospheric CO₂ concentration keeps rising
CO₂ diffusion to the chloroplast is essential to photosynthesis
Patterns of light absorption generate gradients of CO₂ fixation
CO₂ imposes limitations on photosynthesis

Crassulacean Acid Metabolism

Carbon isotope ratio variations reveal different photosynthetic pathways
How do we measure the carbon isotopes of plants?
Why are there carbon isotope ratio variations in plants?

Summary
Web Material
Chapter References

10. Translocation in the Phloem

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

Patterns of Translocation: Source to Sink

Source-to-sink pathways follow anatomic and developmental patterns

Materials Translocated in the Phloem

Phloem sap can be collected and analyzed
Sugars are translocated in nonreducing form

Rates of Movement
The Pressure-Flow Model for Phloem Transport

A pressure gradient drives translocation in the pressure-flow model
The predictions of mass flow have been confirmed
Sieve plate pores are open channels
There is no bidirectional transport in single sieve elements
The energy requirement for transport through the phloem pathway is small
Pressure gradients are sufficient to drive a mass flow of phloem sap
Significant questions about the pressure-flow model still exist

Phloem Loading

Phloem loading can occur from the apoplast or symplast
Sucrose uptake in the apoplastic pathway requires metabolic energy
Phloem loading in the apoplastic pathway involves a sucrose–H⁺ symporter
Phloem loading is symplastic in plants with intermediary cells
The polymer-trapping model explains symplastic loading
The type of phloem loading is correlated with several factors

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

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

The Transport of Signaling Molecules

Turgor pressure and chemical signals coordinate source and sink activities
Signal molecules in phloem regulate growth and development

Summary
Web Material
References

11. Respiration and Lipid Metabolism

Overview of Plant Respiration
Glycolysis: A Cytosolic and Plastidic Process

Glycolysis converts carbohydrates into pyruvate, producing NADH and ATP
Plants have alternative glycolytic reactions
In the absence of O₂, fermentation regenerates the NAD⁺ needed for glycolysis
Fermentation does not liberate all the energy available in each sugar molecule
Plant glycolysis is controlled by its products
The pentose phosphate pathway produces NADPH and biosynthetic intermediates

The Citric Acid Cycle: A Mitochondrial Matrix Process

Mitochondria are semiautonomous organelles
Pyruvate enters the mitochondrion and is oxidized via the citric acid cycle
The citric acid cycle of plants has unique features

Mitochondrial Electron Transport and ATP Synthesis

The electron transport chain catalyzes a flow of electrons from NADH to O₂
Some electron transport enzymes are unique to plant mitochondria
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
Several subunits of respiratory complexes are encoded by the mitochondrial genome
Plants have several mechanisms that lower the ATP yield
Mitochondrial respiration is controlled by key metabolites
Respiration is tightly coupled to other pathways

Respiration in Intact Plants and Tissues

Plants respire roughly half of the daily photosynthetic yield
Respiration operates during photosynthesis
Different tissues and organs respire at different rates
Mitochondrial function is crucial during pollen development
Environmental factors alter respiration rates

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
Fatty acid biosynthesis consists of cycles of two-carbon addition
Glycerolipids are synthesized in the plastids and the ER
Lipid composition influences membrane function
Membrane lipids are precursors of important signaling compounds
Storage lipids are converted into carbohydrates in germinating seeds

Summary
Web Material
Chapter References

12. Assimilation of Mineral Nutrients

Nitrogen in the Environment

Nitrogen passes through several forms in a biogeochemical cycle
Unassimilated ammonium or nitrate may be dangerous

Nitrate Assimilation

Many factors regulate nitrate reductase
Nitrite reductase converts nitrite to ammonium
Both roots and shoots assimilate nitrate

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

Amino Acid Biosynthesis
Biological Nitrogen Fixation

Free-living and symbiotic bacteria fix nitrogen
Nitrogen fixation requires 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 several phytohormones
The nitrogenase enzyme complex fixes N₂
Amides and ureides are the transported forms of nitrogen

Sulfur Assimilation

Sulfate is the absorbed form of sulfur in plants
Sulfate assimilation requires the reduction of sulfate to cysteine
Sulfate assimilation occurs mostly in leaves
Methionine is synthesized from cysteine

Phosphate Assimilation
Cation Assimilation

Cations form noncovalent bonds with carbon compounds
Roots modify the rhizosphere to acquire iron
Iron forms complexes with carbon and phosphate

Oxygen Assimilation
The Energetics of Nutrient Assimilation
Summary
Web Material
Chapter References

13. Secondary Metabolites and Plant Defense

Cutin, Waxes, and Suberin

Cutin, waxes, and suberin are made up of hydrophobic compounds
Cutin, waxes, and suberin help reduce transpiration and pathogen invasion

Secondary Metabolites

Secondary metabolites defend plants against herbivores and pathogens
Secondary metabolites are divided into three major groups

Terpenes

Terpenes are formed by the fusion of five-carbon isoprene units
There are two pathways for terpene biosynthesis
Isopentenyl diphosphate and its isomer combine to form larger terpenes
Some terpenes have roles in growth and development
Terpenes defend against herbivores in many plants

Phenolic Compounds

Phenylalanine is an intermediate in the biosynthesis of most plant phenolics
Some simple phenolics are activated by ultraviolet light
The release of phenolics into the soil may limit the growth of other plants
Lignin is a highly complex phenolic macromolecule
There are four major groups of flavonoids
Anthocyanins are colored flavonoids that attract animals
Flavonoids may protect against damage by ultraviolet light
Isoflavonoids have antimicrobial activity
Tannins deter feeding by herbivores

Nitrogen-Containing Compounds

Alkaloids have dramatic physiological effects on animals
Cyanogenic glycosides release the poison hydrogen cyanide
Glucosinolates release volatile toxins
Nonprotein amino acids defend against herbivores

Induced Plant Defenses against Insect Herbivores

Plants can recognize specific components of insect saliva
Jasmonic acid is a plant hormone that activates many defense responses
Some plant proteins inhibit herbivore digestion
Herbivore damage induces systemic defenses
Herbivore-induced volatiles have complex ecological functions

Plant Defense against Pathogens

Some antimicrobial compounds are synthesized before pathogen attack
Infection induces additional antipathogen defenses
Some plants recognize specific substances released from pathogens
Exposure to elicitors induces a signal transduction cascade
A single encounter with a pathogen may increase resistance to future attacks

Summary
Web Material
Chapter References

14. Gene Expression and Signal Transduction (available only at the website)

15. Cell Walls: Structure, Biogenesis, and Expansion

The Structure and Synthesis of Plant Cell Walls

Plant cell walls have varied architecture
The primary cell wall is composed of cellulose microfibrils embedded in a polysaccharide matrix
Cellulose microfibrils are synthesized at the plasma membrane
Matrix polymers are synthesized in the Golgi and secreted via vesicles
Hemicelluloses are matrix polysaccharides that bind to cellulose
Pectins are gel-forming components of the matrix
Structural proteins become cross-linked in the wall
New primary walls are assembled during cytokinesis
Secondary walls form in some cells after expansion ceases

Patterns of Cell Expansion

Microfibril orientation influences growth directionality of cells with diffuse growth
Cortical microtubules influence the orientation of newly deposited microfibrils

The Rate of Cell Elongation

Stress relaxation of the cell wall drives water uptake and cell elongation
The rate of cell expansion is governed by two growth equations
Acid-induced growth is mediated by expansins
Glucanases and other hydrolytic enzymes may modify the matrix
Many structural changes accompany the cessation of wall expansion

Wall Degradation and Plant Defense

Enzymes mediate wall hydrolysis and degradation
Oxidative bursts accompany pathogen attack
Wall fragments can act as signaling molecules

Summary
Web Material
Chapter References

16. Growth and Development

Overview of Plant Growth and Development

Sporophytic development can be divided into three major stages
Development can be analyzed at the molecular level

Embryogenesis: The Origins of Polarity

The pattern of embryogenesis differs in dicots and monocots
The axial polarity of the plant is established by the embryo
Position-dependent signaling guides embryogenesis
Auxin may function as a morphogen during embryogenesis
Genes control apical–basal patterning
Embryogenesis genes have diverse biochemical functions
MONOPTEROS activity is inhibited by a repressor protein
Gene expression patterns correlate with auxin
GNOM gene determines the distribution of efflux proteins
Radial patterning establishes fundamental tissue layers
Two genes regulate protoderm differentiation
Cytokinin stimulates cell divisions for vascular elements
Two genes control the differentiation of cortical and endodermal tissues through intercellular communication
Intercellular communication is central to plant development

Shoot Apical Meristem

The shoot apical meristem forms at a position where auxin is low
Forming an embryonic SAM requires many genes
Shoot apical meristems vary in size and shape
The shoot apical meristem contains distinct zones and layers
Groups of relatively stable initial cells have been identified
SAM function may require intercellular protein movement
Protein turnover may spatially restrict gene activity
Stem cell population is maintained by a transcriptional feedback loop

Root Apical Meristem

High auxin levels stimulate the formation of the root apical meristem
The root tip has four developmental zones
Specific root initials produce different root tissues
Root apical meristems contain several types of initials

Vegetative Organogenesis

Periclinal cell divisions initiate leaf primordia
Local auxin concentrations in the SAM control leaf initiation
Three developmental axes describe the leaf’s planar form
Spatially regulated gene expression controls leaf pattern
MicroRNAs regulate the sidedness of the leaf
Branch roots and shoots have different origins

Senescence and Programmed Cell Death

Plants exhibit various types of senescence
Senescence involves ordered cellular and biochemical changes
Programmed cell death is a specialized type of senescence

Summary
Web Material
Chapter References

17. Phytochrome and Light Control of Plant Development

The Photochemical and Biochemical Properties of Phytochrome

Phytochrome can interconvert between Pr and Pfr forms
Pfr is the physiologically active form of phytochrome

Characteristics of Phytochrome-Induced Responses

Phytochrome responses vary in lag time and escape time
Phytochrome responses can be distinguished by the amount of light required
Very low–fluence responses are nonphotoreversible
Low-fluence responses are photoreversible
High-irradiance responses are proportional to the irradiance and the duration

Structure and Function of Phytochrome Proteins

Phytochrome has several important functional domains
Phytochrome is a light-regulated protein kinase
Pfr is partitioned between the cytosol and nucleus
Phytochromes are encoded by a multigene family

Genetic Analysis of Phytochrome Function

Phytochrome A mediates responses to continuous far-red light
Phytochrome B mediates responses to continuous red or white light
Roles for phytochromes C, D, and E are emerging
Phy gene family interactions are complex
PHY gene functions have diversified during evolution

Phytochrome Signaling Pathways

Phytochrome regulates membrane potentials and ion fluxes
Phytochrome regulates gene expression
Phytochrome interacting factors (PIFs) act early in phy signaling
Phytochrome associates with protein kinases and phosphatases
Phytochrome-induced gene expression involves protein degradation

Circadian Rhythms

The circadian oscillator involves a transcriptional negative feedback loop

Ecological Functions

Phytochrome regulates the sleep movements of leaves
Phytochrome enables plant adaptation to light quality changes
Decreasing the R:FR ratio causes elongation in sun plants
Small seeds typically require a high R:FR ratio for germination
Phytochrome interactions are important early in germination
Reducing shade avoidance responses can improve crop yields
Phytochrome responses show ecotypic variation
Phytochrome action can be modulated

Summary
Web Material
Chapter References

18. Blue-Light Responses: Stomatal Movements and Morphogenesis

The Photophysiology of Blue-Light Responses

Blue light stimulates asymmetric growth and bending
How do plants sense the direction of the light signal?
Blue light rapidly inhibits stem elongation
Blue light regulates gene expression
Blue light stimulates stomatal opening
Blue light activates a proton pump at the guard cell plasma membrane
Blue-light responses have characteristic kinetics and lag times
Blue light regulates osmotic relations of guard cells
Sucrose is an osmotically active solute in guard cells

Blue-Light Photoreceptors

Cryptochromes are involved in the inhibition of stem elongation
Phototropins mediate blue light–dependent phototropism and chloroplast movements
The carotenoid zeaxanthin mediates blue-light photoreception in guard cells
Green light reverses blue light–stimulated opening
The xanthophyll cycle confers plasticity to the stomatal responses to light

Summary
Web Material
Chapter References

19. Auxin: The Growth Hormone

The Emergence of the Auxin Concept
Identification, Biosynthesis, and Metabolism of Auxin

The principal auxin in higher plants is indole-3-acetic acid
IAA is synthesized in meristems and young dividing tissues
Multiple pathways exist for the biosynthesis of IAA
IAA can also be synthesized from indole-3-glycerol phosphate
Seeds and storage organs contain large amounts of covalently bound auxin
IAA is degraded by multiple pathways
IAA partitions between the cytosol and the chloroplasts

Auxin Transport

Polar transport requires energy and is gravity independent
A chemiosmotic model has been proposed to explain polar transport
P-glycoproteins are also auxin transport proteins
Inhibitors of auxin transport block auxin influx and efflux
Auxin is also transported nonpolarly in the phloem
Auxin transport is regulated by multiple mechanisms
Polar auxin transport is required for development

Actions of Auxin: Cell Elongation

Auxins promote growth in stems and coleoptiles, while inhibiting growth in roots
The outer tissues of dicot stems are the targets of auxin action
The minimum lag time for auxin-induced growth is ten minutes
Auxin rapidly increases the extensibility of the cell wall
Auxin-induced proton extrusion increases cell extension
Auxin-induced proton extrusion may involve both activation and synthesis

Actions of Auxin: Phototropism and Gravitropism

Phototropism is mediated by the lateral redistribution of auxin
Gravitropism involves lateral redistribution of auxin
Dense plastids serve as gravity sensors
Gravity sensing may involve pH and calcium as second messengers
Auxin is redistributed laterally in the root cap

Developmental Effects of Auxin

Auxin regulates apical dominance
Auxin transport regulates floral bud development and phyllotaxy
Auxin promotes the formation of lateral and adventitious roots
Auxin induces vascular differentiation
Auxin delays the onset of leaf abscission
Auxin promotes fruit development
Synthetic auxins have a variety of commercial uses

Auxin Signal Transduction Pathways

A subunit of ubiquitin E3 ligase is an auxin receptor
Auxin-induced genes are negatively regulated by AUX/IAA proteins
Auxin binding to SCF^TIR1 stimulates AUX/IAA destruction
Auxin-induced genes fall into two classes: early and late
Rapid auxin responses may involve a different receptor protein

Summary
Web Material
Chapter References

20. Gibberellins: Regulators of Plant Height and Seed Germination

Gibberellins: Their Discovery and Chemical Structure

Gibberellins were discovered by studying a disease of rice
Gibberellic acid was first purified from Gibberella culture filtrates
All gibberellins are based on an ent-gibberellane skeleton

Effects of Gibberellins on Growth and Development

Gibberellins can stimulate stem growth
Gibberellins regulate the transition from juvenile to adult phases
Gibberellins influence floral initiation and sex determination
Gibberellins promote pollen development and tube growth
Gibberellins promote fruit set and parthenocarpy
Gibberellins promote seed development and germination
Commercial uses of gibberellins and GA biosynthesis inhibitors

Biosynthesis and Catabolism of Gibberellins

Gibberellins are synthesized via the terpenoid pathway
Some enzymes in the GA pathway are highly regulated
Gibberellin regulates its own metabolism
GA biosynthesis occurs at multiple cellular sites
Environmental conditions can influence GA biosynthesis
GA₁ and GA₄ have intrinsic bioactivity for stem growth
Plant height can be genetically engineered
Dwarf mutants often have other defects in addition to dwarfism

Gibberellin Signaling: Significance of Response Mutants

Mutations of negative regulators of GA may produce slender or dwarf phenotypes
Negative regulators with DELLA domains have agricultural importance
Gibberellins signal the degradation of transcriptional repressors
F-box proteins target DELLA domain proteins for degradation
A possible GA receptor has been identified in rice

Gibberellin Responses: The Cereal Aleurone Layer

GA is synthesized in the embryo
Aleurone cells may have two types of GA receptors
GA signaling requires several second messengers
Gibberellins enhance the transcription of α-amylase mRNA
GA-MYB is a positive regulator of α-amylase transcription
DELLA domain proteins are rapidly degraded

Gibberellin Responses: Flowering in Long-Day Plants

There are multiple independent pathways to flowering
The long day and gibberellin pathways interact
GA-MYB regulates flowering and male fertility
MicroRNAs regulate MYBs after transcription

Gibberellin Responses: Stem Growth

The shoot apical meristem interior lacks bioactive GA
Gibberellins stimulate cell elongation and cell division
GAs regulate the transcription of cell cycle kinases
Auxin promotes GA biosynthesis and signaling

Summary
Web Material
Chapter References

21. Cytokinins: Regulators of Cell Division

Cell Division and Plant Development

Differentiated plant cells can resume division
Diffusible factors may control cell division
Plant tissues and organs can be cultured

The Discovery, Identification, and Properties of Cytokinins

Kinetin was discovered as a breakdown product of DNA
Zeatin was the first natural cytokinin discovered
Some synthetic compounds can mimic or antagonize cytokinin action
Cytokinins occur in both free and bound forms
The hormonally active cytokinin is the free base
Some plant pathogenic bacteria, fungi, insects, and nematodes secrete free cytokinins

Biosynthesis, Metabolism, and Transport of Cytokinins

Crown gall cells have acquired a gene for cytokinin synthesis
IPT catalyzes the first step in cytokinin biosynthesis
Cytokinins from the root are transported to the shoot via the xylem
A signal from the shoot regulates the transport of zeatin ribosides from the root
Cytokinins are rapidly metabolized by plant tissues

The Biological Roles of Cytokinins

Cytokinins regulate cell division in shoots and roots
Cytokinins regulate specific components of the cell cycle
The auxin:cytokinin ratio regulates morphogenesis in cultured tissues
Cytokinins modify apical dominance and promote lateral bud growth
Cytokinins induce bud formation in a moss
Cytokinin overproduction has been implicated in genetic tumors
Cytokinins delay leaf senescence
Cytokinins promote movement of nutrients
Cytokinins promote chloroplast development
Cytokinins promote cell expansion in leaves and cotyledons
Cytokinin-regulated processes are revealed in plants that overproduce cytokinins

Cellular and Molecular Modes of Cytokinin Action

A cytokinin receptor related to bacterial two-component receptors has been identified
Cytokinins increase expression of the type-A response regulator genes via activation of the type-B ARRs
Histidine phosphotransferases are also involved in cytokinin signaling

Summary
Web Material
Chapter References

22. Ethylene: The Gaseous Hormone

Structure, Biosynthesis, and Measurement of Ethylene

The properties of ethylene are deceptively simple
Bacteria, fungi, and plant organs produce ethylene
Regulated biosynthesis determines the physiological activity of ethylene
Environmental stresses and auxins promote ethylene biosynthesis
Ethylene biosynthesis and action can be blocked by inhibitors

Developmental and Physiological Effects of Ethylene

Ethylene promotes the ripening of some fruits
Leaf epinasty results when ACC from the root is transported to the shoot
Ethylene induces lateral cell expansion
The hooks of dark-grown seedlings are maintained by ethylene production
Ethylene breaks seed and bud dormancy in some species
Ethylene promotes the elongation growth of submerged aquatic species
Ethylene induces the formation of roots and root hairs
Ethylene induces flowering in the pineapple family
Ethylene enhances the rate of leaf senescence
Some defense responses are mediated by ethylene
Ethylene regulates changes in the abscission layer that cause abscission
Ethylene has important commercial uses

Ethylene Signal Transduction Pathways

Ethylene receptors are related to bacterial two-component system histidine kinases
High-affinity binding of ethylene to its receptor requires a copper cofactor
Unbound ethylene receptors are negative regulators of the response pathway
A serine/threonine protein kinase is also involved in ethylene signaling
EIN2 encodes a transmembrane protein
Ethylene regulates gene expression
Genetic epistasis reveals the order of the ethylene signaling components

Summary
Web Material
Chapter References

23. Abscisic Acid: A Seed Maturation and Stress Signal

Occurrence, Chemical Structure, and Measurement of ABA

The chemical structure of ABA determines its physiological activity
ABA is assayed by biological, physical, and chemical methods

Biosynthesis, Metabolism, and Transport of ABA

ABA is synthesized from a carotenoid intermediate
ABA concentrations in tissues are highly variable
ABA can be inactivated by oxidation or conjugation
ABA is translocated in vascular tissue

Developmental and Physiological Effects of ABA

ABA regulates seed maturation
ABA inhibits precocious germination and vivipary
ABA promotes seed storage reserve accumulation and desiccation tolerance
The seed coat or the embryo can cause dormancy
Environmental factors control the release from seed dormancy
Seed dormancy is controlled by the ratio of ABA to GA
ABA inhibits GA-induced enzyme production
ABA closes stomata in response to water stress
ABA promotes root growth and inhibits shoot growth at low water potentials
ABA promotes leaf senescence independently of ethylene
ABA accumulates in dormant buds

ABA Signal Transduction Pathways

ABA regulates ion channels and the PM-ATPase in guard cells
ABA may be perceived by both cell surface and intracellular receptors
ABA signaling involves both calcium-dependent and calcium-independent pathways
ABA-induced lipid metabolism generates second messengers
ABA signaling involves protein kinases and phosphatases
ABA regulates gene expression
Other negative regulators also influence the ABA response

Summary
Web Material
Chapter References

24. Brassinosteroids

Brassinosteroid Structure, Occurrence, and Genetic Analysis

BR-deficient mutants are impaired in photomorphogenesis

Biosynthesis, Metabolism, and Transport of Brassinosteroids

Brassinolide is synthesized from campesterol
Catabolism and negative feedback contribute to BR homeostasis
Brassinosteroids act locally near their sites of synthesis

Brassinosteroids: Effects on Growth and Development

BRs promote both cell expansion and cell division in shoots
BRs both promote and inhibit root growth
BRs promote xylem differentiation during vascular development
BRs are required for the growth of pollen tubes
BRs promote seed germination

The Brassinosteroid Signaling Pathway

BR-insensitive mutants identified the BR cell surface receptor
Phosphorylation activates the BRI1 receptor
BIN2 is a repressor of BR-induced gene expression
BES1 and BZR1 regulate different subsets of genes
Prospective Uses of Brassinosteroids in Agriculture

Summary
Chapter References

25. The Control of Flowering

Floral Meristems and Floral Organ Development

The shoot apical meristems in Arabidopsis change with development
The four different types of floral organs are initiated as separate whorls
Three types of genes regulate floral development
Meristem identity genes regulate meristem function
Homeotic mutations led to the identification of floral organ identity genes
Three types of homeotic genes control floral organ identity
The ABC model explains the determination of floral organ identity

Floral Evocation: Internal and External Cues
The Shoot Apex and Phase Changes

Shoot apical meristems have three developmental phases
Juvenile tissues are produced first and are located at the base of the shoot
Phase changes can be influenced by nutrients, gibberellins, and other chemical signals
Competence and determination are two stages in floral evocation

Circadian Rhythms: The Clock Within

Circadian rhythms exhibit characteristic features
Phase shifting adjusts circadian rhythms to different day–night cycles
Phytochromes and cryptochromes entrain the clock

Photoperiodism: Monitoring Day Length

Plants can be classified according to their photoperiodic responses
The leaf is the site of perception of the photoperiodic signal
The floral stimulus is transported in the phloem
Plants monitor day length by measuring the length of the night
Night breaks can cancel the effect of the dark period

The Circadian Clock and Photoperiodic Timekeeping

The coincidence model is based on oscillating light sensitivity
The coincidence of CONSTANS expression and light promotes flowering in LDPs
The coincidence of Heading-date 1 expression and light inhibits flowering in SDPs
Phytochrome is the primary photoreceptor in photoperiodism
A blue-light photoreceptor regulates flowering in some LDPs

Vernalization: Promoting Flowering with Cold

Vernalization results in competence to flower at the shoot apical meristem
Vernalization involves epigenetic changes in gene expression

Biochemical Signaling Involved in Flowering

Grafting studies have provided evidence for a transmissible floral stimulus
Indirect induction implies that the floral stimulus is self-propagating
Evidence for antiflorigen has been found in some LDPs
Florigen may be a macromolecule
FLOWERING LOCUS T is a candidate for the photoperiodic floral stimulus
Gibberellins and ethylene can induce flowering in some plants
The transition to flowering involves multiple factors and pathways

Summary
Web Material

26. Stress Physiology

Water Deficit and Drought Tolerance

Drought resistance strategies can vary
Decreased leaf area is an early response to water deficit
Water deficit stimulates leaf abscission
Water deficit enhances root extension
Abscisic acid signals stomatal closure during water deficit
Water deficit limits photosynthesis
Osmotic adjustment of cells helps maintain water balance
Water deficit increases resistance to water flow
Water deficit increases leaf wax deposition
Water deficit alters energy dissipation from leaves
CAM plants are adapted to water stress
Osmotic stress changes gene expression
ABA-dependent and ABA-independent signaling pathways regulate stress tolerance

Heat Stress and Heat Shock

High leaf temperature and minimal evaporative cooling lead to heat stress
At high temperatures, photosynthesis is inhibited before respiration
Plants adapted to cool temperatures acclimate poorly to high temperatures
Temperature affects membrane stability
Several adaptations protect leaves against excessive heating
At higher temperatures, plants produce protective proteins
A transcription factor mediates HSP accumulation
HSPs mediate tolerance to high temperatures
Several signaling pathways mediate thermotolerance responses

Chilling and Freezing

Membrane properties change in response to chilling injury
Ice crystal formation and protoplast dehydration kill cells
Limitation of ice formation contributes to freezing tolerance
Some woody plants can acclimate to very low temperatures
Some bacteria living on leaf surfaces increase frost damage
Acclimation to freezing involves ABA and protein synthesis
Numerous genes are induced during cold acclimation
A transcription factor regulates cold-induced gene expression

Salinity Stress

Salt accumulation in irrigated soils impairs plant function
Plant show great diversity for salt tolerance
Salt stress causes multiple injury effects
Plants use multiple strategies to reduce salt stress
Ion exclusion and compartmentation reduce salinity stress
Plant adaptations to toxic trace elements

Oxygen Deficiency

Anaerobic microorganisms are active in water-saturated soils
Roots are damaged in anoxic environments
Damaged O₂-deficient roots injure shoots
Submerged organs can acquire O2 through specialized structures
Most plant tissues cannot tolerate anaerobic conditions
Synthesis of anaerobic stress proteins leads to acclimation to O₂ deficit

Summary
Web Material
Chapter References

Media & Supplements

Companion Website

The Plant Physiology Companion Website (www.plantphys.net) supplements the coverage provided in the textbook with additional and more advanced material on selected topics of interest and current research. The site is available free of charge, and includes the following resources:

Web Topics: Additional coverage of selected topics across all chapters
Web Essays: Articles on cutting-edge research, written by the researchers themselves
Study Questions: A set of short answer-style questions for each chapter
Suggested Readings: Chapter-specific recommended readings for further study or research

References to specific Web Topics and Essays are included throughout the printed text, as well as at the end of each chapter. Also included on the website are two textbook chapters that are provided online only: Chapter 2: Energy and Enzymes, and Chapter 14: Gene Expression and Signal Transduction. These chapters are provided as PDF files, and may either be read online or printed out.

Instructor’s Resource CD

Available to qualified adopters of Plant Physiology, the Instructor’s Resource CD includes all the full-color illustrations, tables, and photographs from the textbook, in JPEG format, reformatted and relabeled for optimal readability. Also included are ready-to-use PowerPoint^® presentations of all illustrations and tables.

Pricing and Options

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Plant Physiology, Fourth Edition	0-87893-856-7	$117.95	Purchase	Request Exam Copy
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