mills ap bio 2003/2013 chapter 26 control of plant growth responses in flowering plants read ch 26...

Mills AP Bio 2003/2013

Chapter 26Control of Plant Growth Responses in Flowering

Plants

Read Ch 26 in TextbookRead pg 210-214 in Cliffs AP Book


• Topics– 26.1 Plant Hormones– 26.2 Plant Responses

Chapter 26Control of Plant Growth Responses in Flowering

PlantsOverview

• Mechanism of action – hormones– Receptor– Transduction pathway– Cellular response


Chapter 26 Control of Plant Growth Responses26.1 Plant Hormones

Second Messenger Animation



• Groups of Plant Hormones– Auxins– Gibberellins– Cytokinins– Inhibitory hormones

– Hormones work together to cause various effects



• Auxins– Most common auxin is

indoleacetic acid(IAA)– Prevent growth of axillary

buds supports apical dominance

– Promotes adventitious root growth (roots from stem)

– Promotes root branching– Auxins produced by seeds

promote growth of fruit. If auxins high in fruits and low in stems and leaves, fruit won’t fall off.

– Promote phototropism and gravitropism



• How Auxins work–Auxin binds to receptors on cell membrane

–Activates ATP driven proton (H+) pump

–Pumps H ions into space between cell membrane and cell wall.

–H ions (acid) weaken cell wall.

–Gradient set up that pulls solutes then water into cell causing it to swell

–Pushes on cell wall

–Cell elongates


• Gibberellins– About 70 different

gibberellins, GA3 the most common

– Promote stem elongation especially in dwarf plants

– Can break dormancy in seeds and buds

– Sources: young leaves, roots, embryos, seeds, fruits



• How Gibberellins work– Gibberellin binds to a

receptor on the cell membrane

– Activates a second messenger inside the cell – Ca++

– Ca++ combines with a protein called calmodulin

– This complex activates the gene that codes for amylase

– Amylase acts on starch to release sugars



• Cytokinins(remember cytokinesis?)– Derivatives of adenine

• Zeatin • Kinetin

– Promote cell division and differentiation– Prevent senescence (aging process)

• In senescence, large molecules in the plant are broken down

• Can lead to leaf loss etc• Cytokinins inhibit leaf death and can promote leaf growth

– Varying ratios of cytokinins and auxins can effect how plant differentiates

In tissue culture:

Auxin and cytokonins in usual amounts – tobacco strip develops into undifferentiated callous.

If ratio of auxin to cytokinins is appropriate, the callous produces shoots.

A different ratio promotes vegetative shoots and leaves.

A different ratio promotes floral shoots.



• Inhibitory Hormones– Abscisic acid (stress hormone)

• Promotes bud and seed dormancy• Closes stomates(when water

supply low) by causing K+ to leave guard cells

• Inhibits gibberellins (which break dormancy)

• Produced by any “green tissue” with chloroplasts, by endosperm and by roots.

• Abscission=dropping of leaves, fruit and flowers from plants

– Originally thought that abscisic acid caused this – now believe it is ethylene

– Ethylene• Induces leaf, flower and fruit

abscission (falling off)• Promotes fruit ripening-increases

activity of enzymes that soften fruit (ex. cellulase)

• Gas released from fruit (wound?)



Functions of Plant Hormones

Hormone Function – all of these hormones work together

Auxins Stimulate growthInvolved in stem and root cell elongation in phototropism and gravitropism

Gibberellins Stimulate growth especially stems, especially in dwarf plants.Can break seed and bud dormancy

Cytokines Stimulate growth by causing cell division

Abscisic Acid Inhibit growthCauses stomates to closeMaintains seed and bud dormancy

Ethylene Inhibit growthCauses fruit to ripen and fall



• 38.1 Plant responses– Tropisms– Nastic movements

• Tropisms– Plant growth toward (positive) or away (negative) from a

stimulus– Receptiontransductionresponse– Common tropisms

• Phototropism• Gravitropism• Thigmotropism

Chapter 26 Control of Plant Growth Responses26.2 Plant Responses



• Phototropism– Cells on dark side of plant

grow faster, so plant bends toward the light – positive phototropism

– Pigment related to riboflavin acts as a receptor which somehow causes the release of the hormone auxin, which migrates to the shady side, causing increased growth.

– Auxin is produced in the shoot tips

– Roots are either insensitive to light or show negative phototropism

Phototropism short clip:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\phototrop1.2[1].mov



• Gravitropism– Roots show positive

gravitropism• If root cap removed, root

doesn’t respond to gravity• Statoliths in cap

– Stems show negative gravitropism

– Auxin moves to lower side of stem or root in response to gravity (may be newer theories)

• Auxin inhibits growth of root cells on lower side root grows down

• Stimulates growth of stem cells on lower side stem grows up

Gravitropism(negative) in stems movie. Time lapse/actual time 1 hour:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\gravitropism.mov

Section of pea root, showing statoliths settled at bottom of cells


• Thigmotropism– Unequal growth

due to contact with a solid object

– Cells opposite the side being touched elongate

– Hormones auxin and ethylene may be involved.

Thigmotropism movie – Pictures taken at 10 min intervals– morning glory vine grows:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Thigmotropism vine winding.mov




• Nastic Movements– Independent of direction of

stimulus– Types

• Seismonastic movements– Respond to touch, shaking

or thermal» Ex: Mimosa – sleeping

grass, Venus flytrap• Sleep movements

– Occur daily in response to light and dark changes

» Ex: Prayer plant – folds up at night

– Rhythmic sleep behavior = Circadian rhythms

– Circadian rhythms can persist even without the stimulus d/t biological clocks

Mimosa plant after being touched

..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\nastic sensitive_plant_open[2].avi


• Greenhouse-grown plants were placed in continuous light. The diurnal opening/closing of the leaflets (nyctinasty) is clearly observed.– Nastic movement over time movie

– Also (nyctnasty in silk plant) http://employees.csbsju.edu/ssaupe/images/Movies/silk_tree.avi

– From http://employees.csbsju.edu/ssaupe/biol327/Lab/movie/movies.ht

m




• Nastic Movements-how they work– Stimulus causes K ions

to move out of a specialized area of cells (pulvinus) at base of leaf.

– Water follows by osmosis decreased turgor pressure.

– Stimulus on one leaf can cause other leaves to close, so must have some system of communication.

Venus Flytrap movies:..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\venus flytrap movie.mov

..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Venus Fly Trap.wmv

..\..\Biology\Biology Clipart Movies Animations Sounds\Biology movies\Venus flytrap eating a spider.wmv

Three sensitive trigger hairs on each leaflet

Trigger Hairs


• Photoperiodism– Physiological

responses brought about by changes in the length of day or night.

• Three plant groups– Short-day plants

• Flower when the day length is shorter than a critical length.

– Long-day plants• Flower when the day length is

longer than a critical length.– Day-neutral plants

• Flowering not dependent on day length.

– Plant flowering actually depends on a critical length of darkness.

– Short days correspond with long nights.Kolonchoe –

short day plant




If light at least critical length or shorter flowers

More accurate:

If dark at least critical length or longer (regardless of length of light) and continuous flowers

flash of light during dark will inhibit flowering

If light at least critical length or longer flowers

More accurate:

If dark at least critical length or shorter (regardless of length of light) flowers

If critical darkness longer than critical length, but interrupted by a flash of light, flowering will occur.


• Phytochromes– Theory: pigment molecules that detect photoperiods,

and directs flowering of plants– Blue green leaf pigments that exist in two forms:

• Pr – phytochrome red (inactive form) – absorbs red light 660mm wavelength – gets converted to Pfr

• Pfr – phytochrome far red (active form) – absorbs red light 730nm – gets converted to Pr

– Sunlight has more red than far red wavelengths, shade and sunset have more far red wavelengths

• So in sunlight, Pr absorbs red light and gets converted to Pfr, which is the active form and induces flowering etc.

– Phytochrome conversion may be the first step in reception transduction reaction pathway?


Phytochrome Animation



• Phytochromes – other functions– Pr Pfr (in sunlight)

• Promotes seed germination, leaf expansion, stem branching, and inhibits stem elongation

– Presence of Pfr tells some seeds that conditions are right for germination

• Some seeds need dark to germinate, some do better with some light

– In presense of more far red (shade), Pfr increases, leading to shade avoidance strategies – stem elongation, flowering to produce seeds



The End

mills ap bio 2003/2013 chapter 26 control of plant growth responses in flowering plants read ch 26...

Documents

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plant responses chapter

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cliffs ap book slide

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