Transcript Control of Flowering

9.3 – Reproduction in
Angiospermophytes
Flowers
Flowers – reproductive structures of
angiospermophytes
 Flowers evolved from modified leaves and stems
Non-Reproductive Floral Structures:
 Sepals – “leaves,” at base of flower – enclose
the flower before it opens
 Petals – brightly colored structures that aid in
attracting birds and insects
 Both sepals and petals are not directly involved
in reproduction
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9.3.1
Floral Structure
9.3.1
Reproductive Structures
Reproductive Floral Structures:
 Stamen – male reproductive structure
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Anther – sac where pollen in produced
Filament – stalk that supports anther
Carpel (Pistil) – female reproductive
structure
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Stigma – sticky area on top of carpel that
receives pollen
Style – tube that connects stigma to ovary
Ovary – base of carpel that contains ovule
and egg sac
9.3.1
Floral Structure
9.3.1
Control of Flowering
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Photoperiodism – plant response to light
involving relative lengths of day and night.
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Very important factor in flowering – why?
9.3.6
Control of Flowering
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Long-day plants – bloom when days are
longest and nights are shortest (mid-summer)
Short-day plants – bloom in spring, late
summer, and autumn when days are shorter and
nights are longer
Day-neutral plants – day-length not important
for flowering
Day length is not as critical as night length in
regulation of flowering.
9.3.6
Control of Flowering
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Control by light is due to a pigment in
plants called phytochrome.
Phytochrome – blue-green pigment that
controls various growth responses
(including flowering) in plants
Two forms of phytochrome:
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Pr – inactive form
Pfr – active form
9.3.6
Control of Flowering
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Phytochrome is converted from inactive to active
forms due to different light wavelengths:
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In red light (660 nm) inactive Pr is rapidly converted to
active Pfr.
Active Pfr can absorb far-red light (730 nm)
In daylight, Pfr is rapidly converted to back to Pr
In darkness, Pfr is very slowly converted back to Pr
The slow conversion of Pfr to Pr helps plants time the
night length.
9.3.6
Control of Flowering
9.3.6
Control of Flowering
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In long-day plants, the remaining Pfr at the
end of the night stimulates flowering
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Pfr remains due to slow conversion at night
In short-day plants, the remaining Pfr at the
end of the night inhibits flowering
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Short-day plants only flower when enough Pfr
has been converted to Pr. (this only occurs
during long nights)
9.3.6
Control of Flowering
9.3.6
Pollination
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Process of moving pollen grains from the
anther to the sticky stigma on the carpel
Plants have evolved numerous
adaptations for pollination
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Wind pollinated plants produce large amounts
of pollen = allergies! Why do they do this?
Different colors and shapes of flowers allow
plants to attract different pollinators
9.3.2
Pollination
What we see…
What insects see…
Pollination
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Most plants have evolved adaptations to
limit self-pollination – why is this
important?
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Stamens and carpels may mature at different
times
Floral structure makes self pollination difficult
Flowers are self-incompatible – biochemical
mechanisms block prevents pollination
Fertilization
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Process of fusing sperm and egg to produce
new embryo
After pollination – the pollen grain produces a
tube that extends down the style toward the
ovary
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Growth of the tube is directed by a chemical attractant
(usually calcium produced by the ovary)
Sperm within the pollen grain fertilize the egg
and produce the plant embryo
Pollination does not always lead to fertilization
9.3.2
Seed Structure
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Seed coat (testa) – hard shell that
encases and protects embryo
Radicle (hypocotyl) – embryonic root
Plumule (epicotyl) – embryonic shoot
Cotyledons – seed leaves
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Dicots have two seed leaves
Monocots have one seed leaf
9.3.3
Seed Structure
9.3.3
Seed Dormancy
Evolutionary adaptation that germination
(sprouting) will take place when conditions are
favorable
For example:
 Desert plants will only germinate after significant
rainfall
 Many forest species require heat from fire to
germinate – how is this an advantage?
 In areas with harsh winters – seed require a long
“chilling,” period before germinating – why?
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9.3.4
Germination
Begins with imbibition – the absorption of
water
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Causes seed coat to rupture and triggers metabolic
changes within embryo
The embryo begins producing a plant growth
hormone – gibberellins
Gibberellins stimulate the production of
amylase in the seed
Amylase begins digesting food stores of the
endosperm (starch) into maltose
9.3.5
Germination
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Maltose is transferred to the growing regions of
the embryo – the embryonic root (radicle) and
shoot (plumule)
Maltose is converted to glucose – where it
used in aerobic respiration for energy or it is
used to make cellulose and other materials
needed for growth
Once the seedling breaks ground,
photosynthesis can begin and the endosperm
food stores are not needed
9.3.5
Germination
Factors Affecting Germination
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Water – must be available for imbibition
Oxygen – required for aerobic respiration
during germination
Temperature – enzyme action (amylase)
can be affected by fluctuations in
temperature
9.3.4