flowering plant reproduction and development lecture slides

7/29/2019 Flowering Plant Reproduction and Development Lecture Slides

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Flowering Plant

Reproduction and

DevelopmentDr. Art ConwayCopley 127 and Honors House Office


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r-type

maximizes rate of production of offspring

(called r in population equation) minimizes parental investment in each

offspring

K-type

attempts to stabilize population at or below

carrying capacity (K in population equation)so the reproductive rate is uaually low

heavy parental investment in each

offspring

Reproductive Strategies


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Reproductive Strategies


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Methods of Reproduction Asexual reproduction

Offspring are typically genetically identical

to the parent Dispersal of offspring is usually minimal

(except in parthenogenesis or asexual

seed production) Sexual reproduction

Involves meiosis and fertilization, sooffspring are genetically variable

Seeds allow extensive dispersal and may

remain viable for extended periods underunfavorable conditions


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Angiosperm Flower Structure


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Flowers

containthe sex

organs offlowering

plants


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Flowers

containthe sex

organs offlowering

plants


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maturesporophyte

malegametophyte

femalegametophyte

DIPLOID

HAPLOIDfertilization

meiosis(withinanther)

meiosis(withinovary)

seed

gametes(sperm) microspores

megaspores

gametes

(eggs)

(mitosis)

(mitosis)

Sporophyte - a vegatative

body that grows, by mitoticcell divisions, from a plant

zygote that produces

spore-bearing structures.

Gametophyte - haploid

gamete-producing body

that forms during plant life


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Reproductive Structures of Flowering Plants

Components of Flowers(fertile parts) :

Male parts, called stamens,

are located inside thecorolla

- often the stamen

consists ofa slenderstalk(filament) cappedwith an anther.

- the anthers areinternally divided intopollen sacs in whichpollen grains develop

(male gametophytes).

filament anther

receptacle

sepal (all sepalscombined are the

flowers calyx)

petal (all petals

combined are theflowers corolla)

STAMEN(male reproductive part)


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A New Generation Begins

From Microspores to PollenGrains

In anthers, each diploid mother

cell divides by meiosis to form 4haploid microspores.

Each haploid microspore willdevelop an elaborate wall and will

divide by mitosis becoming a

pollen grainOne cell in each pollen grain will

produce the sperm; the other will

form thepollen tube.

pollen sacAnther

(cutaway view)

filament

one of the microspore mothercells inside a pollen sac

Meiosis

pollen tube

sperm nuclei

mature malegametophyte

stigma

style

Diploid Stage

Haploid Stage


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Pollen Sets Me Sneezing - Focus on Environment

Allergic rhinitis - hypersensitivity to a normally harmless substance;

while blood cells respond by mounting an immune response againstsome of the proteins that project from the surface of pollen grainwalls.runny nose, reddened and itchy eyelids, congestion, sneezing


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filament anther

receptacle

SEPAL (all sepals

combined are theflowers calyx)

OVULE(forms within ovary)

PETAL (all petals combinedare the flowers corolla)

STAMEN(male reproductive part)

CARPEL(female reproductive part)

stigma ovarystyle


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seed coat

embryo (2n)

endosperm (3n)

seedling (2n)

Double Fertilization Meiosis

ovary (cutaway view)

ovarywall stalk

an ovule

cell

integument

embryo sac

inside ovule

integuments

pollen tube

Endosperm

mother cell(n + n)

egg (n)

Diploid Stage

Haploid Stage

seed

The pollen tube grows through the ovarys

tissues, then penetrates the ovule & releases its

2 sperm. One sperm fertilizes the egg. The

other will fertilize the endosperm mother cell.

Cytoplasmic division results in a seven-celled embryo sac

(the mature female gametophyte). Six of those cells have a

single nucleus, but one cell has two nuclei (2n).


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Pollen Transfer in Flowering Plants

Most flowering plants rely on an outside force to transferpollen from the male parent to the female parent.

A pollinatoris any agent that transfers pollen from male tofemale reproductive parts of flowers of the same plant

species.

Pollinators include:Wind

Water

Insects (moth, butterfly, fly, bees, beetles)

Bats

Birds and other animals


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OK, then

why dolarge,

colorfulflowers

exist?

Anthers

Stigmas

Petals

No

Petals??????

Wind-

pollinated

Flowers

Sugar Maple

Wild Rose


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OK, then

why dolarge,

colorful

flowers

exist?Butterfly on Henbit

Bee on Aster

Bribery

i.e. Pay insects

and otherpollinators with

nectar so they visit

flowers andtransfer pollen


17/76How we see it How bees see it

Ultraviolet Light

Coevolution

The Hummingbirds long

narrow bill coevolved with

long, narrow floral tubes.


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A New Generation Begins

From Microspores to PollenGrains

In anthers, each diploid mother

cell divides by meiosis to form 4haploid microspores.

Each haploid microspore willdevelop an elaborate wall and will

divide by mitosis becoming a

pollen grainOne cell in each pollen grain will

produce the sperm; the other will

form thepollen tube.

pollen sacAnther

(cutaway view)

filament

one of the microspore mothercells inside a pollen sac

Meiosis

pollen tube

sperm nuclei

mature malegametophyte

stigma

style

Diploid Stage

Haploid Stage


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seed coat

embryo (2n)

endosperm (3n)

seedling (2n)

Double Fertilization Meiosis

ovary (cutaway view)

ovarywall stalk

an ovule

cell

integument

embryo sacinside ovule

integuments

pollen tube

Endosperm

mother cell(n + n)

egg (n)

Diploid Stage

Haploid Stage

seed

The pollen tube grows through the ovarys

tissues, then penetrates the ovule & releases its

2 sperm. One sperm fertilizes the egg. The

other will fertilize the endosperm mother cell.

Cytoplasmic division results in a seven-celled embryo sac

(the mature female gametophyte). Six of those cells have a

single nucleus, but one cell has two nuclei (2n).

S i


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From Zygote to Seeds and Fruits

Formation of the Embryo Sporophyte

Zygote undergoes repeated division to

form an embryo sporophyte.

Embryo sporophyte develops as part ofan ovule and is accompanied by

formation of a fruit. (Fruit = mature ovary)

Cotyldons (seed leaves) develop for the

purpose of utilizing the endosperm

during germination.

Cotyledons form as part of the

embryo, embryo absorb nutrients

from the endosperm and stores theminside the cotyledons.

EMBRYOSPOROPHYTE

endosperm

cotyledon


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Nutrients in Female Parent

Ovary

Ovule Wall

Endosperm

Cotyledon(s)

Body of Embryo


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mature embryowithin ovule

A fruit

(mature ovary)

cut open to

show seeds

(matureovules).

EMBRYOSPOROPHYTE

endosperm

cotyledon


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Seed and Fruit Formation

From Zygote to embryo, the plant

supplies nutrition until the time

when the connection b/w the ovule

and ovary wall is broken.

Mature ovules integuments

thicken into a seed coat.

The embryo, food reserves and

coat are a self-contained package

the seed!

Seed is a mature ovule.

A fruit is a mature ovary with

seeds (ovules) inside

Seeds in ovary

wall ofovary

ovule


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Fleshy Fruits have three divisions :

The pericarp of a fruit consists

- Endocarp (around the seed)

- Mesocarp (fleshy portion)

- Exocarp (skin)

From Zygote to Seeds and Fruits

Multiple Fruits combined from


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fleshy fruit (fromovary tissues) seed

one of many individual fruits

Simple (Fleshy Fruit) - from one

ovary of one flower

Multiple Fruits - combined from

ovaries of many flowers.


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Fig. 31.8c, p. 537

remnants of

sepals, petals

ovary tissue

seed

enlarged

receptacle

Fruit formation on an apple (Malus) tree.

Accessory Fruit - most tissues of the flesh

are not derived from ovary; mainly from thereceptacle.


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ovary

receptacle

Aggregate Fruit - many ovaries of one flower, all attached to the

same receptacles, many Seeds(also, an accessory fruit , flesh derived from receptacle)


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Numerous fruits perched on thesurface of the mature receptacle

fruit wall

Strawberry (Fragaria) flower

cotyledons

fruit wall


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seed (in carpel)

wing

Winged seed of maple (Acer)


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seed wing

Dispersal of Fruits and Seeds

Seeds have co-evolved with particular

dispersing agents - currents of air or

water, or animals passing by.

Human are perhaps the grand

dispersing agents by virtue of the long

distances to which they carry seeds, by

design or accident.


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Questions?


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Basic Patterns ofAsexual Reproduction

Budding or bud activation

Fission or fragmentation

Parthenogenesis oragamospermy

Asexual Reproduction in Flowering Plants


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Asexual Reproduction in Flowering PlantsAsexual reproduction by bud activation (budding) can occur

in a variety of modified stem structures. Like all asexualprocesses, the cells involved are produced by mitosis,therefore the offspring are identical to (clones of) the parent.

Runners (ex. Strawberry) new plants arise at nodes alongaboveground horizontal stems.

Rhizomes (ex. Bermuda grass) new plants arise at nodes of

underground horizontal stems.Corms (ex. Gladioulus) new plants arise from axillary buds onshort, thick, vertical underground stems

Tubers (ex. Potato) new shoots arise from axillary buds ontubers, which are the enlarged tips of slender undergroundrhizomes

Bulbs (ex. Onion, lily) new bulbs arise from axillary buds onshort underground stems

Asexual Reproduction of Flowering Plants


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Asexual Reproduction of Flowering Plants

Parthenogenesis results in embryo development from an

unfertilized egg

Vegetative Propagation (cuttings) can result in new plants

produced from leaves or stems that form roots. This can occurnaturally (fragmentation) or artificially (cuttings)

Tissue Culture propagation can result in whole plants producedfrom a group of cells. (ex. Orchid, lily, wheat, rice, corn)


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How to make a plant

Create a body axis with a

shoot apex at one end and aroot apex at the other end

Activate the apices to formthe adult plant parts


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How to make a plantShoot Apex

Shoot Apex

Stem

Leaves

Lateral Buds

Root ApexRoot Apex

Root

Lateral Roots

M i ti i i


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Meristems

Meristems are localizedregions of dividing cells.

Two kinds of meristems:

(1) Apical Meristems at

the tips of roots and stems

is responsible forPrimaryGrowth. Descendants of

these cells will develop into

the specialized tissues ofthe elongating root and

stem.

activity at meristems

new cells elongate &start to differentiate

into primary tissues

new cells elongate &

start to differentiate

into primary tissues

activity at meristems

M i t


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Meristems

(2) Lateral Meristem tissues are responsible for the

increase in diameter of older roots and stems.

Vascular cambium and cork cambium are the 2kinds of lateral meristems. These are responsible for

Secondary Growth which adds to the diameter of

woody parts of trees.

vascular cambrium

cork cambrium

secondary

phloem

secondary

xylem

thickening


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Lateral or Branch Root Formation


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Angiosperm Body Structure


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Taproot system ofa California poppy

Fibrous root systemof a grass plant

Immature leaf

S i St f P i G th


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ground meristem

primary pholem

primary

xylempith

cortex procambrium

Shoot Apical MeristemZone for primary growth

Immature leaf

shoot apical

meristem

Lateral bud

forming

Successive Stages of Primary Growth:

Protoderm

epidermis

Apical meristem gives

rise to protoderm, ground

meristem, and

procambium

which matureinto epidermis,

ground tissue

and vascular

tissue


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terminal budprimary xylem

primary phloem

VASCULAR CAMBIUM

secondary xylem

secondary phloem

lateral bud

Twig from a walnut tree (Juglans) inwinter, after its leaves dropped

lateral shoot(aka branch)


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lateral shoot

(aka branch)

Patterns of Early Growth and Development


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Patterns of Early Growth and Development

Seed Germination

Germination is the resumption of growth after a time of arrested

embryonic development (dormancy)

Environmental factors influence germination:

- spring rains provide the waternecessary to swell and rupture the

seed coat.

- Once the seed coat splits, Oxygen moves in and allows the embryo

to switch to aerobic metabolism

-Increased temperature & # ofdaylight hours are also influential

-many seeds will only germinate after they have been exposed to cold

temperatures

Repeated Cell division produce a seedling with a primary root.

(The root meristem is the first to be activated)

Plant Growth and Development


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Plant Growth and Development

Growth vs Development

Growth is defined as an increase in the #, size and volume of

cells

Development is the emergence of specialized,

morphologically different body parts.

- cells divide in certain planes and enlarge in certain

directions, resulting in plant parts with specific shapes and

functions- different cell types express different genes, resulting in

different structural and functional phenotypes


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prop roots that formon corn seedlings and

that afford additionalsupport for the rapidlygrowing stem

seedcoat

primary root

coleoptile

primaryroot

branchroot

first foliageleaf

first internodeof stem

adventitiousroot

branch root

primaryroot


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first foliage leaf

coleoptile


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seed coat

primaryroot

cotyledons (two)

hypocotyl

primary leaf

witheredcotyledon

one foliage leaf (thistype is divided intothree leaflets)

primary leaf

point at whichcotyledons

were attached

branchroots

primaryroot

root nodules


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nucleus

primary wall

centralvacuole

Meristems of root and shoot apices

provide new cells for growth.

Each small new cell doubles in size,

then divides.

One daughter cell remains meristematic;

the other differentiates into a specialized

cell.


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Hormonal Effects on Plant Growth and


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Development

Plant Hormones selectively regulate gene expression,

resulting in altered cellular differentiation and growth.At least 5 different classes of hormones have been

shown to have major developmental effects in

flowering plants.

Gibberellins

AuxinsCytokinins

Ethylene

Abscisic acid

Gibberellins-


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Promote Stem

Elongation

Contribute to flowering

Help end dormancy of

seeds and buds

Grapes stems lengthen,

which improved air

circulation around grapes

and gave them more room

to grow. Bigger Grapes!

Auxins


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treatedwith auxin untreated

Auxins

Stimulate the lengthening of stems and

coleoptiles

Participate in growth responses to light

& gravity

Promote root development and growth

Indoleacetic Acid (IAA) is applied to

fruit trees to

Promote uniform flowering

Prevent premature fruit drop

Set the fruit and encouragesynchronous fruit development

Synthetic auxins (2,4-D) are used as

herbicides

Hormonal Effects on Plant Growth and Development


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Cytokinins - used commercially to prolong the life of stored vegetables &

cut flowers- stimulate cell division in root and shoot meristems, where they aremost abundant

Ethylene

-stimulates the ripening of fruit and is used commercially

Abscisic Acid (ABA) - growers often apply to nursery stock beforeshipping

- inhibits cell growth

- promotes seed and bud dormancy;

- helps prevent water loss by promoting stomata closure

Other less well known hormones trigger flowering and inhibit the growth of

lateral buds (apical dominance).


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Do notpost onInternet

Gravitropism + Phototropism


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Rays of sunlight strikeone side of a coleoptile.

The coleoptile bends after auxindiffuses down from its tip tocells on its shaded side.


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a Rays from sun strikeon side of a coleoptile.

b The coleoptile bends after auxin diffusesdown from tip to cells on its shaded side.

Auxin moves from the tip of a coleoptile into cells less

exposed to light and makes them elongate faster than cells

on the illuminated side.The differences in their growth rates brings about the

bending toward light.

Adjustments in the rate and direction of growth


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Thigmotropism is a shift in growth triggered by

physical contact with surrounding objects.Response is prevalent in climbing vines & in tendrilsthat support some plants.

Auxin and ethylene may have roles in this response.

Thigmotropism-Response to physical contact

Responses to Mechanical Stress


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Responses to Mechanical Stress

Responses to the mechanical stress of strong winds explain

why plants grown at higher mountain elevations are morestubby than their counterparts at lower elevations.

Human intervention such as shaking can inhibit plant growth.

Response to

Mechanical

Stress


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Flowering - A Case of Photoperiodism


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g p

Photoperiodism is any biological response to change in

relative length of daylight and darkness in a 24 hr cycle.(this re-setting of the biological clocks is necessary to make

seasonal adjustment).

The flowering process is keyed to changes in daylength

throughout the year.

- Short-day plants - flower in late summer or earlyautumn when daylength becomes shorter (ex.

Poinsettia)

- Long-day plants - flower in the spring as daylengthbecomes longer

- Day-neutral plants - flower when they are matureenough to do so.


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long day short night

short day long night

pulse of white light

pulse of red light

10 minutes of far-red light

follows pulse of red light

Biological Clocks and Their Effects


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g

Biological Clocks are internal time-measuring mechanisms that adjust todaily & seasonal patterns of growth, development & reproduction.

(1) Phytochrome, a blue-green pigment, is part of a switching mechanism

that promotes or inhibits growth in response to the wavelength of light.(2) Phytochrome can absorb both red & far-red wavelengths with differentresults.

- the pigment is converted to an active form (Pfr) at sunrise (when red

light dominates) and to an inactive form (Pr) (when far-red lightdominates) - this cycle induces various biological responses.

Pr Pfr response

red light

far-red light

Pfrreverts to Pr

in the dark.

(inactive) (active) Growth of plantpart is promoted

or inhibited.

Senescence


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The dropping of leaves, flowers, fruits and so on is called

abscission. (the abscission zone is composed of thin-walled parenchyma cells at the base of a petiole or other

plant part)

Senescence is the sum total of the processes leading tothe death of plant parts or the whole plant.

- the recurring cue for senescence is a decrease in

daylength that triggers a decrease in auxin production.

(other cues include drought, wounds and nutrient

deficiencies)

- cell in abscission zones produce ethylene which

causes cells to deposit suberin in their walls.

- simultaneously, enzymes digest cellulose and pectinin the middle lamella to weaken the abscission zone


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tissues of stem cells of abscission zone


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control(pods not

removed

experimentalplant (pods

removed)

Note: if you interrupt the diversion of nutrients into flower, seeds or fruits,

you can prevent senescence in a plant.

Example- remove each new flower or seed pod from a plant, its leaves and

stems will remain vigorous and green much longer.


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Entering Dormancy

Dormancy is when metabolic activities idle. Dormancy

occurs in Autumn when daylength shortens and growthstops in many trees and non-woody perennials; it will

not resume until spring.

Strong cues for dormancy include: Short Days, Cool

Nights and Dry, Nitrogen-deficient soil

Dormancy has great adaptive value in preventing plantgrowth on occasional warm autumn days only to be

killed by later frost.

Vernalization


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Vernalization is the stimulation of flowering only after

plants (either adults or seeds) have been exposed to

low temperatures (winter)

Deliberately exposing seeds to low temperature tostimulate flowering the next season is common

agricultural practice.

Breaking Dormancy

Dormancy is broken by milder temperatures, rains and

nutrients

It probably involves gibberellin and abscisic acid, and

frequentlyrequires exposure to specific periods of low

temperature.


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Questions?

flowering plant reproduction and development lecture slides

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