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2. Life Cycle of Flowering Plants
Compare Fig Pg. 824
SYNGAMY
zygote
Sporophyte
Gametophyte
sporangium
sporocyte
spores
gametangia
gametes
germination
mitosis
differentiation 1N 2N
MEIOSIS
The flowering plant is a multicellular diploid sporophyte.
The sporophyte encloses the multicellular haploid gametophyte.
The life history is thus diplohaplontic.
The gametes are oogamous but the sperm lack flagellae.
Gender expression has moved from gametophyte to sporophyte.

3. Flower Organization-building a flower from the bottom up!
Compare Fig. 41.4a Pg. 826
Flower Organization-building a flower from the bottom up!
A flower is a short shoot (stem with leaves)
The stem is the receptacle with very short internodes
The leaves appear in four whorls
stigma
carpel
gynoecium
flower
perfect
style
locule
ovary
anther
superior
stamen
ovule
pollen
filament
androecium
flower hypogynous
petal
corolla
receptacle
sepal
complete
perianth
calyx
pedicel

4. Microsporogenesis: Prophase I of Meiosis

5. Microsporogenesis: Late Prophase I of Meiosis
Synapsis: homologs join
Recombination: crossing over

6. Microsporogenesis: Metaphase I of Meiosis

7. Microsporogenesis: Anaphase I of Meiosis
Centromeres do not breakdown
Homologs are separated: not sister chromatids

8. Microsporogenesis: Telophase I of Meiosis
Already haploid but
sister chromatids still joined

9. Microsporogenesis: Metaphase II and Anaphase II of Meiosis

10. Microsporogenesis: Telophase II of Meiosis

11. Microsporogenesis: Meiosis complete (but prophase of mitosis)

12. Microsporogenesis: Completed, Separated Microspores (note prophase)

13. Pollen Grain: Mitosis Makes Endosporic Microgametophyte
Pollen Wall: Microspore Wall (allergenic?)
Tube Cell
Nucleus
Cytoplasm
Generative Cell
Nucleus
Cytoplasm
The tube cell digests a path from the stigma to the egg.
The generative cell follows the path to the egg, and divides to make two sperm cells. Both participate in syngamy.
Pollination: vector-assisted movement of the pollen grain from the anther to the stigma.
Compare Fig Pg. 829

14. The tube cell germinates through the pollen wall.
Pollen Tube Growth
The tube cell germinates through the pollen wall.
The cell grows chemotropically toward the egg.
The pollen tube must find the ovule’s micropyle.
The generative cell slides along this tube.
It divides by mitosis to form two sperm cells.

15. Life Cycle of Flowering Plants
sperm
cells
SYNGAMY
zygote
Sporophyte
Gametophyte
sporangium
sporocyte
spores
gametangia
gametes
germination
mitosis
differentiation 1N 2N
MEIOSIS
pollen
grain
tube cell
generative cell
anther
microspore
The large plant is a sporophyte.
Its flower produces the sporangia; on the male side, the anther of the stamen
The anther contains sporocytes that divide by meiosis to make spores
The spore cell divides to make an endosporic microgametophyte… a pollen grain
The tube cell digests a path to the egg
The generative cell divides into two sperm cells that participate in syngamy

16. Compare Fig. 41.4a Pg. 826
Flower Organization
Now we focus on what is happening on the female side…
We will examine what is going on inside the ovule of the carpel.
stigma
carpel
gynoecium
androecium
filament
anther
stamen
flower
perfect
flower hypogynous
pollen
style
locule
ovary
superior
ovule
petal
corolla
calyx
sepal
pedicel
receptacle
complete
perianth

17. Alstroemeria: What is different two weeks later?
Bisexual
…but functionally unisexual
…by being trans-sexual
protandrous:
first-male
protogynous:
first-female
(antonym)

18. Megasporogenesis: taking place inside the ovule inside the ovary.
megasporocyte
4 megaspores
meiosis I
meiosis II
3 disintegrate
functional
megaspore
mitotic divisions without cytokinesis
megagametophyte
3 antipodals
central cell
egg
cytokinesis
2 synergids
Compare Fig Pg. 828 and Fig Pg. 832

19. Life Cycle of Flowering Plants
central cell
egg
SYNGAMY
zygote
Sporophyte
Gametophyte
sporangium
sporocyte
spores
gametangia
gametes
germination
mitosis
differentiation 1N 2N
MEIOSIS
embryo sac
ovule
antipodals
synergids
megasporocyte
The large plant is a sporophyte.
Its flower produces the sporangia; on the female side, the ovule of the carpel
The ovule contains a megasporocyte that divides by meiosis to make four megaspores
Three megaspores disintegrate.
The remaining megaspore cell divides by mitosis to make 8 nuclei.
Cytokinesis divides the 8 nuclei into seven cells of the megagametophyte (embryo sac)
The egg cell and the central cell are gametes that fuse with two sperm cells in syngamy
The ovule, with zygotic embryo and triploid endosperm, becomes a seed.

20. karyogamy! In Flowering Plants, syngamy is a double event: syngamy#2:
Compare Fig Pg. 832
In Flowering Plants, syngamy is a double event:
syngamy#2:
2 x 1N polar nuclei + 1N sperm
= 3N primary endosperm cell
sperm
nuclei
no miracle-grow, no compost!
1N egg + 1N sperm = 2N zygote
syngamy#1:
synergids
disintegrating
In this slide, plasmogamy has already occurred…but what part of syngamy has not occurred yet?
karyogamy!