Download 6. Reproduction of plants File - E

Reproduction and Flowering in
Plants
LO´s
• Know main parts of a flower
• Know how flowering is induced and controlled
• Know the seed structure and how the process
of germination works
Flowering in plants
• What is the environmental cue that
synchronizes flowering in plants?
• What are the advantages of synchronization of
flowering?
• Which substance causes a plant to produce a
flowering hormone that causes a plant to
produce flowers?
Control of flowering
• Photoperiodic activities are controlled
through the action of a pigment called
phytochrome.
• Phytochrome acts as a signal for some
biological clocks in plants and exists in two
forms, Pr (inactive) and Pfr (active).
• It is important in the flowering response in
plants but is also involved in other light
initiated responses, such as germination and
shoot growth.
Phytochrome
• Pfr interacts with genes that maintain the
plant´s biological clock (e.g. by producing a
flowering hormone)
• Pfr promotes flowering in long day plants and
inhibits flowering in short day plants.
• How does the plant measure day length?
Development of the Flower
•
In order to flower, a plant must
pass through several stages of
development with several
changes in gene expression
occurring at the shoot meristem.
– The plant must first pass from an
immature to a sexually mature
stage.
– The apical meristem must change
from a vegetative meristem to a
floral meristem,
– The organs of the flower must
grow and develop.
•
Apical meristem
Environmental cues perceived in
the leaves are transmitted to the
apical meristem by hormonal
messengers.
– The messengers activate the genes
LEAFY
and FLOWERING LOCUS T which
results
in flowering.
Dartmouth
Seeds
• A seed is an entire reproductive unit, housing the
embryonic plant in a state of dormancy.
• During the last stages of maturing, the seed dehydrates
until its water content is only 5-15% of its weight.
• The embryo stops growing and remains dormant until
the seed germinates.
• At germination, the seed takes up water and
the food store is mobilized to provide the
nutrients for plant growth
and development.
Energy source in the seed
• Monocots: Endosperm
• Dicots: Cotyledon