Transcript 14.4 The Life Cycle of Flowering Plants

14.4 The Life Cycle of Flowering
Plants
Biology 1001
November 28, 2005
Photoperiod and the Control of Flowering
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The events of the life cycle, such as flowering, seed
germination and leaf growth, need to be appropriately timed
with respect to season
The environmental stimulus that plants use to detect the time
of year is photoperiod, or the relative lengths of night and day
A physiological response to photoperiod, such as flowering, is
called photoperiodism
The Effect of Photoperiod on Flowering
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On the basis of photoperiod requirement for
flowering there are three types of plants
“Long-day” plants flower early in the season,
in the spring or early summer, when the days
are long
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“Short-day” plants flower late in the season,
in late summer, fall or early winter, when the
days are short
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“Long-day” plants are really short night plants
Examples include radishes and irises
“Short-day” plants are really long night plants
Examples include poinsettias, chrysanthemums,
and strawberries
“Day-neutral” plants flower at a certain stage
of maturity regardless of photoperiod
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Examples include tomatoes and dandelions
How does interrupting the dark period with a
brief exposure to light affect flowering?
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“Short-day” plants require a
period of darkness greater
than a critical period
“Long-day” plants require a
period of darkness less than
the critical period
A flash of light given in the
night to a short-day plant
inhibits flowering
A flash of light given in the
night to a long-day plant
promotes flowering
Figure 39.22!
Phytochrome is the pigment that intercepts light
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A unique characteristic of
the pigment phytochrome
is its reversibility in
response to red and far-red
light
Red light is the most
effective at interrupting
night
Because this effect is
reversible by a flash of farred light it is though that
the pigment involved in
photoperiod is phytochrome
Figure 39.23!
Figure 39.24! – Is there a flowering hormone?
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It is leaves that detect
photoperiod and transmit a
signal to flower to buds
The flowering signal is a
hormone or combination of
hormones, as yet unidentified,
called florigen
A bud’s meristem changes
from a vegetative state to a
flowering state – involves
expression of a set of organ
identity genes
Flowering
photoperiod
Non-flowering
photoperiod
Fruits Develop From Ovaries, Figure 38.9!
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A fruit is a mature ovary that protects the seed and aids in
its dispersal
The fruit begins to develop after pollination
The wall of the ovary becomes the pericarp, the thickened
wall of the fruit
Fertilization clip
Fruit development clip
FRUITS
~ Some variation in fruit structure ~
~ Some variation in fruit dispersal ~
SEEDS
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Seeds are mature ovules that contain the multicellular plant
embryo, the endosperm and a protective coat
SEED DORMANCY & GERMINATION
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As a seed matures, it dehydrates and
enters dormancy
Breaking dormancy requires an
environmental stimulus such as fire,
abrasion, rainfall, digestion
Dormancy increases the chances that
germination occurs under ideal
conditions
Germination begins with the
imbibition of water which causes the
seed coat to rupture and triggers the
embryo tor resume growth
Enzymes digest the storage material in
the endosperm
The embryonic root is the first organ
to emerge, the the shoot breaks the soil
surface
Figure 38.10!!
Figure 30.10!,!! - The life cycle of an
angiosperm
Figure 38.2!,!! – An Overview of
Angiosperm Reproduction