Outline

Control of Growth and Responses in Plants

Chapter 27

2Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants

OutlineOutline

Plant ResponsesPlant ResponsesTropismsTropismsNastic MovementsNastic Movements

Plant HormonesPlant HormonesAuxins Auxins GibberellinsGibberellinsCytokininsCytokininsAbscisic AcidAbscisic AcidEthyleneEthylene

PhotoperiodismPhotoperiodism


Plant ResponsesPlant Responses

TropismsTropisms

Plant growth toward or away from a Plant growth toward or away from a unidirectional stimulus is called a unidirectional stimulus is called a tropismtropism

Positive is towards stimulusPositive is towards stimulus

Negative is away from stimulusNegative is away from stimulus

Phototropism - LightPhototropism - Light

Gravitropism - GravityGravitropism - Gravity

Thigmotropism - TouchThigmotropism - Touch

4Phototropism


PhototropismPhototropism

Positive phototropism:Positive phototropism:

Occurs because cells on the shady side Occurs because cells on the shady side of the stem elongateof the stem elongate

A pigment related to riboflavin A pigment related to riboflavin thought to act as a photoreceptor thought to act as a photoreceptor when phototropism occurswhen phototropism occurs

Auxin migrates to shady side of stemAuxin migrates to shady side of stem

Shady sides elongate faster than bright Shady sides elongate faster than bright sideside


GravitropismGravitropism

When a plant is placed on its side, the When a plant is placed on its side, the stem grows upward, opposite of the stem grows upward, opposite of the pull of gravity pull of gravity

Stems with root caps grow downwardStems with root caps grow downward

Root cells contain statolithsRoot cells contain statoliths

Auxin is responsible for:Auxin is responsible for:

Positive gravitropism of roots, andPositive gravitropism of roots, and

Negative gravitropism of shootsNegative gravitropism of shoots

7Gravitropism


ThigmotropismThigmotropism

Unusual growth due to contact with Unusual growth due to contact with solid objects is called thigmotropismsolid objects is called thigmotropism

Coiling of tendrilsCoiling of tendrils

Thigmomorphogenesis occurs when Thigmomorphogenesis occurs when the entire plant responds to the the entire plant responds to the presence of environmental stimulipresence of environmental stimuli

WindWind

RainRain

9Coiling Response


Nastic MovementsNastic MovementsNastic movements:Nastic movements:

Do not involve growth andDo not involve growth and

Are not dependent on the stimulus directionAre not dependent on the stimulus direction

Seismonastic movements result from:Seismonastic movements result from: TouchTouch

Shaking, orShaking, or

Thermal stimulationThermal stimulation

Sleep movements:Sleep movements: Occur daily in response to light and dark Occur daily in response to light and dark changeschanges

Prayer PlantPrayer Plant

11Seismonastic Movement

12Sleep Movement


Circadian RhythmsCircadian Rhythms

A circadian rhythms:A circadian rhythms:

Biological rhythms with a 24-hour Biological rhythms with a 24-hour cyclecycle

Tend to be persistentTend to be persistent

Rhythm is maintained in the absence of Rhythm is maintained in the absence of environmental stimuli environmental stimuli

Caused by a biological clockCaused by a biological clock


Plant HormonesPlant Hormones

Almost all communication on a plant is Almost all communication on a plant is done by hormonesdone by hormones

Synthesized in one part of the plantSynthesized in one part of the plant

Travels within phloem in response to Travels within phloem in response to the appropriate stimulusthe appropriate stimulus


AuxinsAuxins

Auxin is produced in shoot and apical Auxin is produced in shoot and apical meristem and is found in young meristem and is found in young leaves and in flowers and fruitsleaves and in flowers and fruits

Apically produced auxin prevents the Apically produced auxin prevents the growth of axillary budsgrowth of axillary buds

Apical dominanceApical dominance

Weak solution of auxin applied to Weak solution of auxin applied to woody cutting causes rapid growth of woody cutting causes rapid growth of adventitious rootsadventitious roots

Promotes fruit growthPromotes fruit growth

16Apical Dominance

17Demonstrating Phototropism


How Auxins WorkHow Auxins Work

Auxins bind to plasma membrane Auxins bind to plasma membrane receptorsreceptors

Activated proton pumps HActivated proton pumps H++ out of cell out of cell

Cell wall loosensCell wall loosens

Turgor pressure increases due to the Turgor pressure increases due to the entry of waterentry of water

Cell enlargesCell enlarges

19Auxin Mode of Action


GibberellinsGibberellins

Gibberellins:Gibberellins:

Growth promoting hormonesGrowth promoting hormones

Bring about elongation of the resulting Bring about elongation of the resulting cellscells

Gibberellic acidGibberellic acid

Stem elongationStem elongation

Breaking of dormancyBreaking of dormancy

21Effect of Gibberellins

22Gibberellic Acid:Structure and Mode of

Action


CytokininsCytokinins

CytokininsCytokinins

A class of plant hormones that A class of plant hormones that promote cell divisionpromote cell division

Derivatives of adenineDerivatives of adenine

Prevent senescencePrevent senescence

Initiate growthInitiate growth

24Interaction of Hormones


Abscisic AcidAbscisic Acid

Abscisic acid (ABA):Abscisic acid (ABA):

Initiates and maintains seed and bud Initiates and maintains seed and bud dormancy, anddormancy, and

Brings about closure of stomataBrings about closure of stomata

Produced by:Produced by:

Any “green tissue” with chloroplastsAny “green tissue” with chloroplasts

Monocot endosperm, andMonocot endosperm, and

RootsRoots

26Abscisic Acid:Control of Stoma

Opening


EthyleneEthylene

Ethylene is involved in abscissionEthylene is involved in abscission

Once abscission has begun:Once abscission has begun:

Ethylene stimulates certain enzymesEthylene stimulates certain enzymes

Cause leaf, fruit, or flower to dropCause leaf, fruit, or flower to drop

Also ripens fruit by increasing activity Also ripens fruit by increasing activity of enzymes that soften fruitof enzymes that soften fruit

28Functions of Ethylene



Photoperiodism:Photoperiodism:

Any physiological response prompted Any physiological response prompted by changes in day or night lengthby changes in day or night length

Short-day plants Short-day plants

Long-day plants Long-day plants

Day-neutral plants Day-neutral plants

Some plants may require a specific Some plants may require a specific sequence of day lengths in order to sequence of day lengths in order to flower flower

30Photoperiodism and Flowering


PhytochromePhytochrome

Phytochrome is a blue-green leaf Phytochrome is a blue-green leaf pigment that alternately exists in pigment that alternately exists in two formstwo forms

Phytochrome red (PPhytochrome red (Prr))

Phytochrome far-red (PPhytochrome far-red (Pfrfr))

Conversion of forms allows a plant to Conversion of forms allows a plant to detect photoperiod changesdetect photoperiod changes

Also promotes seed germination and Also promotes seed germination and inhibits stem elongationinhibits stem elongation

32Phytochrome Conversion Cycle

33Phytochrome Control of Growth Pattern


ReviewReview

Plant ResponsesPlant ResponsesTropismsTropismsNastic MovementsNastic Movements

Plant HormonesPlant HormonesAuxins Auxins GibberellinsGibberellinsCytokininsCytokininsAbscisic AcidAbscisic AcidEthyleneEthylene


Control of Growth and Responses in Plants

Ending Slide Chapter 27

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