plant hormones

5/25/2018 Plant Hormones

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Plant Hormones & Tropisms


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Plant hormones

Hormone was first used to describesubstances in animals

a substance produced in a gland that

circulates in the blood and has an effect faraway from the site of production

In plants used to mean a compound

that acts at low concentrations to affectgrowth and development.

Affect division, elongation anddifferentiation


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Primary growth

Apical meristem

Leaf primordia

Forming axillary bud

Ground meristem

protoderm

procambium


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Secondary growth

xylem

Phloem withbands of fibers

Vascular cambium

Ray parenchyma

cork


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Plant Responses to EnvironmentTropisms vs Taxisms +/-

Thigmotropism Physical Contact. Chemotropism Chemicals

Thermotropism Temperature

Traumotropism

Wounding Electrotropism Electricity

Skototropism Dark

Aerotropism Oxygen

Gravitropism Gravity Phototropism light

Plants in Motion

Tropisms
http://www.carnivorousplantnursery.com/media/vfttrappingt003.movhttp://214bio.com/SWF/auxin_geotropism.gifhttp://214bio.com/SWF/auxin_phototropism.swfhttp://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.htmlhttp://214bio.com/SWF/auxin_phototropism.swfhttp://214bio.com/SWF/auxin_geotropism.gifhttp://www.carnivorousplantnursery.com/media/vfttrappingt003.mov


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Tropic responses

Directional movements inresponse to a directional stimulus


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Thigmotropism


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Thigmotropic Response & Turgormovementin Mimosa pudica
http://www.gifbin.com/985126


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Phototropism

Photoperiodism, or the

response to change in lengthof the night, that results inflowering in long-day andshort-day plants
http://bcs.whfreeman.com/thelifewire/content/chp39/3902002.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp39/3902002.html


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Geotropism/Gravitropism


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Plant hormones Five plant hormones known by the mid 1960s,

new compounds called plant growth regulators Signal molecules produced at specific locations.

Occur in low concentrations.

Cause altered processes in target cells at otherlocations.

The five hormonesAuxins

Cytokinins

Gibberellins

Ethylene (ethene)

Abscisic acid

Other plant growthregulators

Brassinosteroids

Salicylic acid

Jasmonic acid

Systemin


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Summary of Functions of Major Plant Hormones

Hormone Function Location

Auxins(IAA)*

stem elongation

apical dominanceroot formation

produced in shootapical meristem

Cytokininscell divisiondifferentiation

produced in roots

Gibberellins(GA)*

stem & internodeelongationseed germination

produced in apical portionof root & shoot

Ethylene* abscission fruit ripening

produced in leaves, stems

& young fruits

Abscisic Acidsuppression of bud growthstomatal openingleaf senescence

mature leaves, fruits &root caps

*most horticultural/ agricultural applications
http://library.thinkquest.org/C006669/data/Biol/phormone_1.html


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AuxinAuxins primarily stimulate cellelongation

Auxins also have many secondaryactions: root initiation, vasculardifferentiation, tropic responses,

apical dominance and thedevelopment of auxiliary buds,flowers and fruits.

Auxins are synthesized in the stem

and root apices and transportedthrough the plant axis.

Auxins are often most effective ineliciting their effects when combined

with cytokinins.
http://library.thinkquest.org/C006669/data/Biol/phormone_1.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://library.thinkquest.org/C006669/data/Biol/phormone_1.html


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Auxin associated with phototropism - early experiments

demonstrate tip as receptor.


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Additional responses to auxin

Inhibits abscission - loss of leaves

flower initiation

sex determination

fruit development

Auxin Flavors: Indoleacetic Acid (IAA)

Phenylacetic Acid (PAA) 4-chloroindoleacetic Acid (4-chloroIAA)

Indolebutyric Acid (IBA)


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Loosening of cell wall


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Auxin promotes rooting


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Promotes Apical dominance


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Auxin as a weed killer

Many synthetic auxins are usedas selective weed killers andherbicides. 2, 4 - D (2, 4 -dichloro phenoxy acetic acid) isused to destroy broad leaved

weeds. It does not affectmature monocotyledonousplants. Causes a plant to growitself to death

More readily absorbed bybroad-leaved plants

Most often the weed of Weedand Feed lawn fertilizers


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Parthenocarpy

Auxin induces parthenocarpy, the formation ofseedless fruits without the act of fertilization.


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Control of abscission by auxinFormation of an abscission

layer at the base of petioleor pedicel results inshedding of leaves, flowersor fruits. But auxins inhibitabscission, as they preventthe formation of abscissionlayer.

Auxin Spray Prevents

Premature Fruit Abscissionand Increase in Yield.

a) Auxin Sprayed; b) Auxinnot Sprayed


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The infamous side of auxin

Active ingredient in Agent Orange

Chemicals with auxin activity sprayed(together with kerosene) on forests in

Viet Nam to cause leaf drop (and fire) The chemical process used to make the

auxins also made dioxin, an extremely

toxic compound


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CytokininsCytokinins are able to stimulate cell

division and induce shoot budformation in tissue culture.

They usually act as antagonists toauxins.

Morphogenesis.Lateral bud development.Delay of senescence.

Stomatal opening.Rapid transport in xylem stream.


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Function of cytokinins

Promotes cell division.

Morphogenesis.

Lateral bud development.

Delay of senescence.

Stomatal opening.

Rapid transport in xylem stream.


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Other cytokinin facts

Cytokinins delay andeven reversesenescence

Release buds fromapical dominance Cytokinins

Auxin

I t ti f


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Interaction ofcytokinin andauxin in

tobacco callustissue

High cytokinin to auxin ratio causes differentiation of shoots.A low ratio of cytokinin to auxin causes root formation.Intermediate cytokinin to auxin ratio causes formation of roots aswell as shoots.Intermediate cytokinin to low auxin causes growth of largeamount of callus.


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Gibberellin

Gibberellins are an extensivechemical family with >80compounds in plants

The main effect of gibberellins

in plants is to cause stemelongation and flowering.

Also prominently involved in

mobilization of endospermreserves during early embryogrowth and seed germination.

Gibberellin Signal Transduction
http://academic.kellogg.edu/herbrandsonc/bio111/animations/0071.swfhttp://academic.kellogg.edu/herbrandsonc/bio111/animations/0071.swfhttp://academic.kellogg.edu/herbrandsonc/bio111/animations/0071.swf


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Gibberellins

Now known to beessential for stemelongation

Dwarf plant varieties oftenlack gibberellins

Gibberellins are involvedin seed germination

gibberellins will inducegenes to make enzymesthat break down starch

Promotion of flowering.

Seed Ge mination ca sed b


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Seed Germination caused byMobilization of reserves

Scarification

mechanical

chemical

heat

Gibberellins are involved in bolting


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Gibberellins are involved in boltingof rosette plants

Gibberellin induces stemelongation in rosette plants.Cabbage is a rosette plant withprofuse leaf growth and retarded

internodal length. Just prior toflowering, internodes elongateenormously. This is called bolting.Bolting needs either long days orcold nights. When a cabbage headis kept under warm nights, itretains its rosette habit. Boltingcan be induced artificially by theapplication of gibberellins under

normal conditions.

Di d i i ti ith F li h


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Discovered in association with Foolishdisease of rice (Gibberella fujikuroi)

infecteduninfected

Found as the toxin produced by some fungi that caused rice to grow too

tall

Gibberellins are used to improve


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Gibberellins are used to improvegrapes

EK2 E 1: Timing and coordination of specific


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EK2.E.1: Timing and coordination of specificevents are necessary for the normal

development of an organism, and theseevents are regulated by a variety of

mechanisms.

b. Induction of transcription factors duringdevelopment results in sequential gene

expression.

3. Temperature and the availability of waterdetermine seed germination in most plants.
http://www4.schoolnet.lk/edusoft/agriculture/grade-12_13/flash/english/AG-11-03.swfhttp://www4.schoolnet.lk/edusoft/agriculture/grade-12_13/flash/english/AG-11-03.swf


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Abscisic acid (ABA)

Incorrectly named, not related to abscission,slows plant growth

Important in drought stress and other stresses Causes stomatal closure

Prevents premature germination of seeds

(enhances dormancy) Changes gene expression patterns
http://www.freshvent.com.au/page_6.html


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Ethylene

The smallest hormoneA gas

Important in seed

germination, fruitripening, epinasty,abscision of leaves

Sex expression incucurbits
http://www.freshvent.com.au/page_6.htmlhttp://www.freshvent.com.au/page_6.html


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Functions of ethylene Gaseous in form.

Rapid diffusion.

Affects adjacent individuals.

Fruit ripening.

Senescence and abscission. Interference with auxin transport.

Inhibition of stem elongation

Positive feedback mechanisms amplify responses inorganisms. Amplification occurs when the stimulus isfurther activated which, initiates an additionalresponse that produces system change.

EK2 C 2 O i d t h i


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EK2.C.2: Organisms respond to changes intheir external environments.

a. Organisms respond to changes in theirenvironment through behavioral and

physiological mechanisms. Photoperiodism and phototropism in plants

EK 2 E 2 Ti i d di i f


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EK 2.E.2: Timing and coordination ofphysiological events are regulated by

multiple mechanisms.

a. In plants, physiological events involve

interactions between environmental stimuli andinternal molecular signals.

1. Phototropism, or the response to the presence oflight

2. Photoperiodism, or the response to change inlength of the night, that results in flowering in long-day and short-day plants

EK 2 E 2 Ti i d di ti f


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EK 2.E.2: Timing and coordination ofphysiological events are regulated by

multiple mechanisms.b. Responses to information and communicationof information are vital to natural selection.

1. In phototropism in plants, changes in the lightsource lead to differential growth, resulting inmaximum exposure of leaves to light forphotosynthesis.

2. In photoperiodism in plants, changes in the lengthof night regulate flowering and preparation for winter.

Mammalian Circadian Rhythms

Resources


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ResourcesPlant Hormones Info

Plant Hormones, Nutrition & Transport

Tropism Animation

Auxin in Cell Walls

Plant Responses to Environmental Challenges: Signaling betweenPlants and Pathogens

Growth/HormonesPlants in MotionAuxin AnimationTranspirationLesson

How Hormones Protect Seed Development in Peas Virtual labHerbicide Mechanisms & Animations
http://www.plant-hormones.info/Index.htmhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTHORM.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802003.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp40/40020.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp40/40020.htmlhttp://academic.kellogg.cc.mi.us/herbrandsonc/bio111/growthhormones.htmhttp://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.htmlhttp://www.kscience.co.uk/animations/auxin.swfhttp://www.sciencemag.org/sciext/vis2005/show/transpiration.swfhttp://www.mhhe.com/biosci/genbio/tlw3/virtual_labs/lab18/home.htmlhttp://plantandsoil.unl.edu/croptechnology2005/pagesincludes/printModule.jsp?informationModuleId=998688536http://plantandsoil.unl.edu/croptechnology2005/pagesincludes/printModule.jsp?informationModuleId=998688536http://www.mhhe.com/biosci/genbio/tlw3/virtual_labs/lab18/home.htmlhttp://www.sciencemag.org/sciext/vis2005/show/transpiration.swfhttp://www.kscience.co.uk/animations/auxin.swfhttp://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.htmlhttp://academic.kellogg.cc.mi.us/herbrandsonc/bio111/growthhormones.htmhttp://bcs.whfreeman.com/thelifewire/content/chp40/40020.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp40/40020.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802003.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp38/3802001.htmlhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTHORM.htmlhttp://www.plant-hormones.info/Index.htm

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