Plants for week of 2-23-09

8/14/2019 Plants for week of 2-23-09

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Plant HormonesPlant Hormones

Controls of growth, developmentControls of growth, development

and movementand movement


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Processes in growthProcesses i

n growth

lCell division.Cell division.

lCell enlargment.Cell enlargment.

lCell differentiation.Cell differentiation.


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Seed GerminationSeed Germination

lScarification

kmechanical

kchemical

kheat

lMobilization of reserves


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Movement in PlantsMovement in Plants

lTurgor movements (changes in turgor

pressure in selected cells)

lGrowth movements (elongation of selected

cells in response to stimulus)

kphototropism

kgeotropism

kthigmotropism


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Tropic responsesTro

pic responses

Directional movements in response to

a directional stimulus


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Turgor movementTurgor movement

Mimosa pudicaMimosa pudica L. (sensitive plant)L. (sensitive plant)


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PhototropismPhototropism


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GeotropismGeotropism


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ThigmotropismThigmotropism


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Plant growth substancesPlant growth substances

Artificially synthesized substances

which produce hormone like

responses


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HormonesHormones

lSignal molecules produced at specific

locations.

lOccur in low concentrations.

lCause altered processes in target cells at

other locations.


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General plant hormonesGeneral plant hormones

lAuxins

lGibberellins

lCytokinins

lAbscisic acid

lEthylene


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AuxinAuxin

lDiscovered as substance associated with

phototropic response.

lOccurs in very low concentrations.

kIsolated from human urine, (40mg 33 gals-1)

kIn coleoptiles (1g 20,000 tons-1)

lDifferential response depending on dose.


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Auxin associated with phototropism - early experimentsAuxin associated with phototropism - early experiments

demonstrate tip as receptor.demonstrate tip as receptor.


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Loosening of cell wallLoosening of cell wall


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Additional responses to auxinAdditional responses to auxin

labscission - loss of leaves/Prevents leaf abscission

lflower initiation

lsex determination

lfruit development

lApical dominance

lEnhances fruit growth Auxin from the developing seeds results in fruit growth


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Auxin promotes rooting

Fig. 28-6


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Gibberellins

A large family of compounds with a

few biologically active members

Found as the toxin produced by some

fungi that caused rice to grow too tall

Now known to be essential for stem

elongation

Dwarf plant varieties often lack

gibberellins

Fig. 28-15


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Discovered in association with FoolishDiscovered in association with Foolish

disease of rice (disease of rice (Gibberella fujikuroi)Gibberella fujikuroi)

infecteduninfected


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Effects of GibberellinsEffects of Gibberellins

lGeneral cell elongation.

lBreaking of dormancy.

lPromotion of flowering.

lTransport is non-polar, bidirectional

producing general responses.


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Gibberellins

Gibberellins are involved in bolting of

rosette plants

Gibberellins are used to improve grapes

Gibberellins are involved in seed

germination

gibberellins will induce genes to make enzymes

that break down starch


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Fig. 28-19


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Function of cytokininsFunction ofcytokinins

lPromotes cell division.

lMorphogenesis.

lLateral bud development.

lDelay of senescence.

l

Stomatal opening.lRapid transport in xylem stream.


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Functions of abscisic acidFunctions of abscisic acid

lGeneral growth inhibitor.

lCauses stomatal closure.

lReadily translocated.

lProduced in response to stress.


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Functions of ethyleneFunctions of ethylene

lGaseous in form.

lRapid diffusion.

lAffects adjacent

individuals.

lFruit ripening.

lSenescence and abscission.

lInterference with auxin

transport.lInitiation of stem

elongation and bud

development.

The smallest hormone

A gas

Important in seed

germination, fruitripening, epinasty,

abscision of leaves

Sex expression in

cucurbits


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Abscisic AcidInvolved with leaf and fruit abscission (fall),

onset of dormancy in seeds and onset of

dormancy (rest period) in perennial flowers

and shrubs

ABA is effective in inducing closure of

stomata in leaves, indicating a role in the

stress physiology in plants. (ex: increases inABA following water, heat and high salinity

stress to the plant)

Fi 28 21


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How Do Hormones Work?

Ion channels acid growth of auxin

stomatal closure by ABA

Receptors on the cell surface integral membrane proteins that bind hormones

can trigger messenger cascades (ethylene receptor)

Gene expression especially ABA responsive element

senescence-stimulated production of cytokinin

Fig. 28-21

Fig. 28-24


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Inhibitors Abscisic Acid (ABA)

Widespread in plant body moves readily

through plant

ABA appears to be synthesized (made) by

the leaves.

Interacts with other hormones in the plant,counteracting the growth promoting the

effects of auxins & gibberellins.


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Action and Interaction ofAction and Interaction of

HormonesHormones

lConstitutive enzymes - always present but

level of hormone can affect level.

lAdaptive enzymes - formed or activated as

a result of the presence of a hormone.


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Can you explain the use ofhormones in each diagram.

Click to reveal the answer.

Applications of plant hormones


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Fresh fruits are shippedaround the world.

Plant hormones are used

to slow the ripening ofthe fruit, so they are just

ripe as they reach the

supermarket.



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When a gardener takes cuttingsfrom a plant, the base of each

cutting is first dipped into a

rooting compound to stimulate

the growth of roots.

Many rooting compounds

contain auxin.





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Auxins can be sprayed onto

flowers so that the fruits

develop without pollination or

fertilisation.

These fruits are seedless.





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Weeds have broader leaves

than the grass on a lawn. The

weeds will take up more auxinthan the grass when the lawn is

sprayed.



Auxins can be used as herbicides.

The weeds will grow too quickly and die.


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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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True or false?

Gardeners prune to create bushier plants.

This is because pruning causes plants to create...

1. more auxin and this enables side shoots to grow

2. less auxin and this enables side shoots to grow

3. more auxin and this inhibits side shoots from growing

4. less auxin and this inhibits side shoots from growing

Which of the followingstatements is true?



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True or false?

Gardeners prune to create bushier plants.

This is because pruning causes plants to create...

1. more auxin and this enables side shoots to grow

2. less auxin and this enables side shoots to grow

3. more auxin and this inhibits side shoots from growing

4. less auxin and this inhibits side shoots from growing




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True or false?

Young roots always grow downwards.

This is because roots are...

1. positively phototropic

2. negatively hydrotropic

3. positively geotropic




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True or false?

Young roots always grow downwards.

This is because roots are...

1. positively phototropic

2. negatively hydrotropic

3. positively geotropic




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PhotoperiodismPhotoperiodism


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Definitions

Photoperiod

Photoperiodism

is the physiologicalreaction of

organisms to the

length of day or

night

http://hoopermuseum.earthsci.carleton.ca/vegetation/photoperiodism.gif


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Flowering Plants

Several flowering plants use the pigment

phytocrome to sense seasonal changes in

day length. Phytocrome responds to red and far red

light.

Plants use this as an indication to flower. Flowering plants can be classified as long

day plants, short day plants or day neutral

plants.


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Liatrus spp.

Cactus spp.


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Rosaceae Buds

Poppy

Cannnabis

Peyote


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Long Day Plants

http://www.williegreensorga

nicfarm.com/recipes/images/spinach.jpg

Spinach

http://www.worldcommunitycookbook.org/season/guide/photos/lettuce.jpg

LettuceSugar beets

http://www.biologie.uni-hamburg.de/b-

online/schaugarten/varaltissima/Bvaraltissima1.jpg


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Short Day Plants

http://www.tobacco.yaia.com/tobaccoindex.jpg

Tobacco

http://www.hlasek.com/foto/chrysanthemum_coronarium_4686.jpg

Chrysanthemum

Sunn Hemp


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Day Neutral Plants

http://www.ipm.msu.edu/CAT03_veg/images/5-

28Cucumber.jpg

http://www.oznet.ksu.edu/fieldday/kids/p

ictures/kidsfield600/cg_corn.jpg

Corn

Cucumber


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Garner and Allard

First individuals to discover

that plants are affected by the

amount of light they receivein a day.

Worked with tobacco,

soybean, cosmos, ragweed,spinach, radish, and lettuce.

Phytochrome
http://huntbot.andrew.cmu.edu/HIBD/Home/SiteImages/SiteImages-052.html


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Phytochrome

Major class of pigments.

Function in the photoperiodic response of plants. Phytochromes exist in two interconvertible forms

PR because it absorbs red (R; 660 nm) light

PFR because it absorbs far red (FR; 730 nm) light

These are the relationships: Absorption of red light by PR converts it into PFR

Absorption of far red light by PFR converts it into PR.

In the dark, PFR spontaneously converts back to PR.

The amount of PFR is what triggers the response.


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Plants for week of 2-23-09

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