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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
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Ultraviolet Light
Coevolution
The Hummingbirds long
narrow bill coevolved with
long, narrow floral tubes.
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Angiosperm Flower Structure
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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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Angiosperm Flower Structure
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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?