Growth Responses and Regulation of Growth Chapter 11.

Growth Responses and Growth Responses and Regulation of GrowthRegulation of Growth

Chapter 11Chapter 11

LEARNING OBJECTIVESLEARNING OBJECTIVES• 1 Discuss genetic and environmental factors that affect 1 Discuss genetic and environmental factors that affect

plant growth and development . plant growth and development . • 2 Describe phototropism, gravitropism, and 2 Describe phototropism, gravitropism, and

thigmotropism . thigmotropism . • 3 List several ways in which each of the following hor-3 List several ways in which each of the following hor-

mones affects plant growth and development: auxin, gib-mones affects plant growth and development: auxin, gib-berellin, cytokinin, ethylene, abscisic acid. berellin, cytokinin, ethylene, abscisic acid.

• 4 Relate which hormone or hormones is/ are involved in 4 Relate which hormone or hormones is/ are involved in each of the following biological processes: leaf each of the following biological processes: leaf abscission, seed germination, apical dominance. abscission, seed germination, apical dominance.

• 5 Explain how varying amounts of light and darkness 5 Explain how varying amounts of light and darkness induce flowering, and describe the role of phytochrome. induce flowering, and describe the role of phytochrome.

• 6 Explain how temperature affects flower induction in 6 Explain how temperature affects flower induction in certain plants. certain plants.

• 7 Define circadian rhythm, and give an example. 7 Define circadian rhythm, and give an example. • 8 Give an example of a turgor movement, and distinguish 8 Give an example of a turgor movement, and distinguish

between turgor movements and tropisms.between turgor movements and tropisms.

LEARNING OBJECTIVE 1LEARNING OBJECTIVE 1

• Discuss Discuss geneticgenetic and and environmental environmental factorsfactors that affect plant growth and that affect plant growth and development development

Internal Genetic FactorsInternal Genetic Factors

• The location of a cell in the young plant The location of a cell in the young plant body affects gene expression during body affects gene expression during development development

• Causes some genes in that cell to be Causes some genes in that cell to be turned off and others to be turned on turned off and others to be turned on

External Environmental FactorsExternal Environmental Factors

• Factors in the physical environment Factors in the physical environment determine gene expression, affect plant determine gene expression, affect plant growth and development growth and development • changing day lengthchanging day length• variation in precipitationvariation in precipitation• temperature temperature

Spring FlowersSpring Flowers


• Describe Describe phototropism, gravitropism,phototropism, gravitropism, and and thigmotropismthigmotropism

TropismsTropisms

• Are directional growth responsesAre directional growth responses

• Are permanent Are permanent

KEY TERMSKEY TERMS

• PHOTOTROPISM PHOTOTROPISM • Directional growth of a plant caused by lightDirectional growth of a plant caused by light

• GRAVITROPISM GRAVITROPISM • Plant growth in response to direction of gravityPlant growth in response to direction of gravity

• THIGMOTROPISMTHIGMOTROPISM • Growth in response to contact with a solid objectGrowth in response to contact with a solid object

PhototropismPhototropism

GravitropismGravitropism

Fig. 11-3a, p. 223

On day 3, turned onits side

One hour later

Fig. 11-3a, p. 223

Fig. 11-3b, p. 223

Darwins’ ExperimentsDarwins’ Experiments

Fig. 11-4a, p. 224

Fig. 11-4b, p. 224

Light rays

(a) (b) (c) (d)

Fig. 11-4b, p. 224

Auxin in ColeoptilesAuxin in Coleoptiles

Agar block

Coleoptile tip

(a) (b) (c)

Fig. 11-5, p. 225


• List several ways in which each of the List several ways in which each of the following hormones affects plant following hormones affects plant growth and development: growth and development: auxin, auxin, gibberellin, cytokinin, ethylene, gibberellin, cytokinin, ethylene, abscisic acidabscisic acid

KEY TERMSKEY TERMS

• HORMONE HORMONE • An organic chemical messenger that An organic chemical messenger that

regulates growth and development in plants regulates growth and development in plants and other multicellular organismsand other multicellular organisms

Communication MoleculesCommunication Molecules

• Five major classes of plant Five major classes of plant hormoneshormones• auxin, gibberellin, cytokinin, ethylene, auxin, gibberellin, cytokinin, ethylene,

abscisic acidabscisic acid

• A variety of signaling molecules A variety of signaling molecules

KEY TERMSKEY TERMS

• AUXIN AUXIN • Plant hormone involved in growth and Plant hormone involved in growth and

development, including stem elongation, development, including stem elongation, apical dominance, and root formation on apical dominance, and root formation on cuttingscuttings

Animation: PhototropismAnimation: Phototropism

CLICKTO PLAY

Auxin and PhototropismAuxin and Phototropism

Light rays

Illuminatedside ofcoleoptile

Shaded sideof coleoptile

Aux

in

Fig. 11-6, p. 226

Auxin and Auxin and Root DevelopmentRoot Development

Animation: Auxin’s EffectsAnimation: Auxin’s Effects

CLICKTO PLAY

KEY TERMSKEY TERMS

• GIBBERELLINGIBBERELLIN • Plant hormone involved in growth and Plant hormone involved in growth and

development, including stem elongation, development, including stem elongation, flowering, and seed germinationflowering, and seed germination

Effects of GibberelinEffects of Gibberelin

KEY TERMSKEY TERMS

• CYTOKININCYTOKININ • Plant hormone involved in growth and Plant hormone involved in growth and

development, including cell division and delay development, including cell division and delay of senescenceof senescence

Hormones and Tissue CultureHormones and Tissue Culture

(a) Initialexplant

b) Callus (c) Roots d) Shoots

Cell divisionwithout differentiation

Cell divisionwith differentiation

Fig. 11-10, p. 229

Cytokinin and Cytokinin and SenescenceSenescence

KEY TERMSKEY TERMS

• ETHYLENE ETHYLENE • A gaseous plant hormone involved in growth A gaseous plant hormone involved in growth

and development, including leaf abscission and development, including leaf abscission and fruit ripeningand fruit ripening

Ethylene and Fruit RipeningEthylene and Fruit Ripening

KEY TERMSKEY TERMS

• ABSCISIC ACIDABSCISIC ACID • A plant hormone involved in growth and A plant hormone involved in growth and

development, including dormancy and development, including dormancy and responses to stressresponses to stress

Other Signaling MoleculesOther Signaling Molecules

Day-neutral plant graftedto long-day plant

Both plants flower

Long-dayinductionGraft

Fig. 11-14, p. 232

Plant cell responses to infection by fungi, bacteria, or viruses. As aresult of an initial infection and a subsequent signal-transduction pathway, plants produce a variety of antimicrobial molecules

Signal TransductionSignal Transduction

Ubiquitin isattached to proteinsthat inhibit certaingenes.

Inhibited genesare turned on.

Nuclear envelope

DNA (contains genes)

Nucleus

Cell wallPlasma membrane

Proteins aredestroyed.

Cytoplasm

ProteinAuxin bindsto receptor.

Auxin

Ubiquitin

Receptor

2

4

31

Fig. 11-15, p. 233

Cytoplasm

Plasma membrane Cell wall

Nuclear envelope

Nucleus

Stepped Art

Proteins are targeted for destruction.

3

Previously repressed genes are activated and expressed.

Transcription

DNA

4Ubiquitin

2 Ubiquitin is tagged to proteins that inhibit certain genes.

Protein

Auxin

1 Auxin binds to TIR1 receptor.

Receptor

Fig. 11-15, p. 233


• Relate which hormone or hormones Relate which hormone or hormones is/are involved in each of the following is/are involved in each of the following biological processes: biological processes: leaf abscissionleaf abscission, , seed germinationseed germination, , apical dominanceapical dominance

Leaf AbscissionLeaf Abscission

• Ethylene and auxin Ethylene and auxin • As a leaf ages, auxin level in the leaf As a leaf ages, auxin level in the leaf

decreases, and ethylene level increases decreases, and ethylene level increases

Seed GerminationSeed Germination

• Gibberellins involved in seed germinationGibberellins involved in seed germination• in certain plants (cereals, grasses) in certain plants (cereals, grasses) • substitutes for low-temperature or light substitutes for low-temperature or light

requirements in some seeds (lettuce, oats, requirements in some seeds (lettuce, oats, tobacco)tobacco)

• Ethylene and abscisic acidEthylene and abscisic acid• Ethylene promotes seed germination; abscisic Ethylene promotes seed germination; abscisic

acid inhibits seed germination acid inhibits seed germination

Abscisic Acid and GerminationAbscisic Acid and Germination

Apical Dominance 1Apical Dominance 1

• Inhibition of axillary bud growth by the Inhibition of axillary bud growth by the apical meristemapical meristem

• Auxin Auxin • Produced in shoot apical meristemProduced in shoot apical meristem• Inhibits axillary buds near apical meristem Inhibits axillary buds near apical meristem

from developing into actively growing shoots from developing into actively growing shoots

Apical Dominance 2Apical Dominance 2

• Cytokinins and ethylene Cytokinins and ethylene • Cytokinins promote growth of axillary buds; Cytokinins promote growth of axillary buds;

ethylene inhibits axillary bud developmentethylene inhibits axillary bud development

Auxin and Auxin and Axillary Bud DevelopmentAxillary Bud Development


• Explain how varying amounts of light Explain how varying amounts of light and darkness induce flowering and darkness induce flowering

• Describe the role of Describe the role of phytochromephytochrome

KEY TERMSKEY TERMS

• PHOTOPERIODISMPHOTOPERIODISM • Physiological response (such as flowering) of Physiological response (such as flowering) of

plants to variations in length of daylight and plants to variations in length of daylight and darknessdarkness

PhotoperiodismPhotoperiodism

• Some plants are Some plants are short-day plantsshort-day plants, , some some are are long-day plants, long-day plants, others areothers are intermediate-day plantsintermediate-day plants • Plant measures length of dark period Plant measures length of dark period

• In In day-neutral plantsday-neutral plants, , photoperiod does photoperiod does not affect flowering not affect flowering

Short-Day PlantsShort-Day Plants

Photoperiodic ResponsesPhotoperiodic Responses

Black-eyed Susan (long-day/short-night plant)

Chrysanthemum (short-day/ long-night plant)

(a) Short daysand long nights

(b) Long daysand short nights

(c) Short daysand long nights(interrupted witha brief period oflight)

(d) Long days(interrupted witha brief period ofdark) and shortnights

Day Night

1

2

Fig. 11-17, p. 234

KEY TERMSKEY TERMS

• PHYTOCHROMEPHYTOCHROME • A blue-green proteinaceous pigment involved A blue-green proteinaceous pigment involved

in many plant responses to light, independent in many plant responses to light, independent of photosynthesisof photosynthesis

PhytochromePhytochrome

• There are about five different phytochrome There are about five different phytochrome proteins proteins

• Each exists in two forms and readily Each exists in two forms and readily converts from one form to the other after converts from one form to the other after absorption of light of specific wavelengths absorption of light of specific wavelengths

Phytochrome FormsPhytochrome Forms

• PrPr s strongly absorbs red light with a trongly absorbs red light with a relatively short wavelength (660 nm)relatively short wavelength (660 nm)• Changes to the second form Changes to the second form (Pfr)(Pfr)

• PfrPfr absorbs red light with a relatively long absorbs red light with a relatively long wavelength (730 nm)wavelength (730 nm)• The active form, triggers or inhibits responses The active form, triggers or inhibits responses

such as floweringsuch as flowering

Phytochrome ConversionPhytochrome Conversion

Physiologicalresponse(such as

flowering)

Far-red light(730 nm)

Short-livedintermediate forms Pfr

Active form

Red light (660 nm)

Pr

Inactiveform

Short-livedintermediate forms

Fig. 11-18, p. 235

Animation: Phytochrome Animation: Phytochrome ConversionsConversions

CLICKTO PLAY


• Explain how temperature affects flower Explain how temperature affects flower induction in certain plantsinduction in certain plants

Temperature RequirementsTemperature Requirements

• Certain plants have temperature Certain plants have temperature requirements that must be met in order for requirements that must be met in order for them to flowerthem to flower

KEY TERMSKEY TERMS

• VERNALIZATIONVERNALIZATION • The low-temperature requirement for The low-temperature requirement for

flowering in some plant speciesflowering in some plant species

Temperature RequirementsTemperature Requirements


• Define Define circadian rhythmcircadian rhythm

• Give an exampleGive an example

KEY TERMSKEY TERMS

• CIRCADIAN RHYTHMCIRCADIAN RHYTHM • A biological activity with an internal rhythm A biological activity with an internal rhythm

that approximates the 24-hour daythat approximates the 24-hour day

Circadian RhythmsCircadian Rhythms

• Reset by the rising and setting of the sun Reset by the rising and setting of the sun

• Circadian rhythms in plants affect Circadian rhythms in plants affect • gene expression gene expression • rate of photosynthesisrate of photosynthesis• opening and closing of stomataopening and closing of stomata

Sleep MovementsSleep Movements


• Give an example of a turgor movement, Give an example of a turgor movement, and distinguish between and distinguish between turgor turgor movementsmovements and and tropismstropisms

KEY TERMSKEY TERMS

• TURGOR MOVEMENTTURGOR MOVEMENT • Temporary plant movement that results from Temporary plant movement that results from

changes in internal water pressure in a plant changes in internal water pressure in a plant partpart

• Examples:Examples: Leaves of the sensitive plant and Leaves of the sensitive plant and Venus flytrap Venus flytrap

Sensitive PlantSensitive Plant

Fig. 11-21a, p. 237

Fig. 11-21b, p. 237

Fig. 11-21c, p. 237

(c) How the folding and drooping occurs. Pulvini occur in three areas: thebase of each leaflet, the base of each cluster of leaflets, and the base of eachleaf. Only changes in the pulvini at the bases of leaflets are shown. (Top right)A section through two leaflets, showing their pulvini when the leaf is undisturbed.(Bottom right) A section through the two leaflets, showing how a lossof turgor produces the folding of the leaves.

Leafletopen Leaflet

Pulvinus

Vasculartissue

Decrease ofturgor inparenchymacells

Parenchymacells retainingturgor

Cross-sectional views

Leafletfolded

Fig. 11-21c, p. 237

Turgor and TropismsTurgor and Tropisms

• Turgor movementsTurgor movements are temporary plant are temporary plant movementsmovements

• TropismsTropisms are permanent growth are permanent growth responses responses

Growth Responses and Regulation of Growth Chapter 11.

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