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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
3Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
5Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
6Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
8Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
10Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
13Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
14Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
15Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
18Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
20Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
23Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
25Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
27Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
29Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
PhotoperiodismPhotoperiodism
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
31Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
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
34Control of GroControl of Growth and Respowth and Responses in Plantsnses in Plants
ReviewReview
Plant ResponsesPlant ResponsesTropismsTropismsNastic MovementsNastic Movements
Plant HormonesPlant HormonesAuxins Auxins GibberellinsGibberellinsCytokininsCytokininsAbscisic AcidAbscisic AcidEthyleneEthylene
PhotoperiodismPhotoperiodism
Control of Growth and Responses in Plants
Ending Slide Chapter 27