2. Lecture 8 Outline (Ch. 38) I. Flower Structures II. Life Cycle
Gametophyte Production
Flower Development
Pollination
Fertilization
Germination
Preparation for next lecture

3. Angiosperm Overview Anther Stigma Carpel Stamen Style Filament Ovary
Receptacle
Sepal
Petal
(a) Structure of an idealized flower

4. Angiosperm Lifecycle Germinated pollen grain (n) Anther
Pollen tube
Germinated pollen grain (n)
(male gametophyte)
Ovary
Ovule
Embryo sac (n)
(female gametophyte)
Egg (n)
Sperm (n)
Zygote
(2n)
Seed
Embryo (2n)
(sporophyte)
Simple fruit
Germinating
seed
Mature sporophyte
plant (2n)
(b) Simplified angiosperm life cycle
Key
Haploid (n)
Diploid (2n)
FERTILIZATION
Figure 38.2 An overview of angiosperm reproduction

5. Angiosperm Gametophytes
Develop in anthers, ovaries
Pollen: from microspores inside the anther
Within an ovule, a haploid megaspore divides by mitosis - forms the embryo sac, the female gametophyte

6. The megaspores give rise to:
pollen
petals
egg cells
seeds
ovaries

7. Model for Flowering (actually, end of ch. 35 in this text)
Flowering: adult meristem becoming a floral meristem
Activate or repress floral meristem identity genes
2 key genes: LFY and AP1
Turn on floral organ identity genes
These define the four concentric whorls
Sepal, petal, stamen, and carpel

8. ABC Model
3 classes of floral organ identity genes specify 4 organ types
Class A genes alone – Sepals
Class A and B genes together – Petals
Class B and C genes together – Stamens
Class C genes alone – Carpels
When any one class is missing, aberrant floral organs occur in predictable positions

9. ABC Model

10. ABC Model

11. Based on the ABC model for flower development, if ‘A’ class genes are missing, what develops?
sepal, sepal, stamen, carpel
petal, petal, stamen, carpel
stamen, petal, petal, stamen
carpel, stamen, stamen, carpel

12. Male structure
Female structure

13. Angiosperm Pollination
brings female and male gametophytes together
Fertilization (syngamy) is preceded by pollination, the placing of pollen on the stigma of the carpel
One of my favorite pollinator systems:

14. Abiotic Pollination by Wind
Figure 38.4 Flower pollination
Hazel staminate flowers
(stamens only)
Hazel carpellate flower
(carpels only)

15. Common dandelion under normal light
Pollination by Bees
Common dandelion under
normal light
Figure 38.4 Flower pollination
Common dandelion under
ultraviolet light

16. Anther Stigma Moth on yucca flower
Pollination by Moths and Butterflies
Anther
Figure 38.4 Flower pollination
Stigma
Moth on yucca flower

17. Blowfly on carrion flower
Pollination by Flies
Figure 38.4 Flower pollination
Fly egg
Blowfly on carrion flower

18. Hummingbird drinking nectar of poro flower
Pollination by Birds
Figure 38.4 Flower pollination
Hummingbird drinking nectar of poro flower

19. Long-nosed bat feeding on cactus flower at night
Pollination by Bats
Figure 38.4 Flower pollination
Long-nosed bat feeding on cactus flower at night

20. Angiosperm Pollination  Fertilization
The pollen grain produces a pollen tube that extends down the style toward the embryo sac
Two sperm are released and effect a double fertilization, resulting in a diploid zygote and a triploid (3n) endosperm

21. Double Fertilization One sperm fuses with the egg – diploid (zygote)
One sperm fuses with the two polar nuclei – triploid (endosperm)

22. Angiosperm Seed Formation
develops into a seed containing a sporophyte embryo and a supply of nutrients
The zygote gives rise to an embryo with apical meristems and one or two cotyledons
Mitosis of the triploid (3n) endosperm gives rise to a multicellular, nutrient-rich mass that feeds the developing embryo and later (in some plants) the young seedling

23. Double fertilization refers to:
Two sperm fuse with the egg cell
Two sperm fuse with the polar nuclei
One sperm fuses with the egg, one with the polar nuclei
One sperm fuses with the endosperm, one with the tube cell

24. Angiosperm Seed Formation

25. The Ovary ... develops into a fruit adapted for seed dispersal
a fruit is a mature ovary that protects the enclosed seeds and aids in their dispersal via wind, water, or animals

26. Dispersal by Water
Figure Fruit and seed dispersal
Coconut

27. Dandelion “parachute”
Dispersal by Wind
Winged seed
of Asian
climbing gourd
Dandelion “parachute”
Figure Fruit and seed dispersal
Winged fruit of maple
Tumbleweed

28. Dispersal by Animals Seeds carried to ant nest Seeds buried in caches
Seeds in feces
Barbed fruit
Figure Fruit and seed dispersal

29. The Mature Seed
Epicotyl
Hypocotyl
Cotyledons
Radicle
Seed coat
Endosperm
(a) Common garden bean, a eudicot with thick cotyledons
(b) Castor bean, a eudicot with thin cotyledons
(c) Maize, a monocot
Scutellum
(cotyledon)
Pericarp fused
with seed coat
Coleoptile
Coleorhiza
The embryo and its food supply enclosed by a hard, protective seed coat
The seed enters a state of dormancy
In dicots, the embryo has two cotyledons (seed leaves)
A monocot embryo has one cotyledon

30. Evolutionary Adaptations ...
the process of germination increases the probability that seedlings will survive
Germination begins when seeds imbibe water
this expands the seed, rupturing its coat, and triggers metabolic changes that cause the embryo to resume growth
The embryonic root, or radicle, is the first structure to emerge from the germinating seed
Next, the embryonic shoot breaks through the soil surface

31. Seed Germination (bean)
(a) Common garden bean
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Figure 38.9a Two common types of seed germination
Hypocotyl
Radicle
Seed coat

32. Vegetative Reproduction & Agriculture
Humans have devised methods for asexual propagation
Cuttings can be taken from many kinds of plants
Grafting is a modification of vegetative reproduction from cuttings
A twig or bud from one plant can be grafted onto a plant of a closely related species or a different variety of the same species
A twig or bud from one plant [scion(s)] can be grafted onto a plant of a closely related species or a different variety of the same species [stock]

33. Self-Check Part of plant Function Later becomes… Examples: Ovary
Contains eggs (ovules)
Flesh of fruit
Apples, strawberries, coconut meat
Pollen
Ovule
Integuments
Cotyledons
Endosperm

34. Things To Do After Lecture 7…
Reading and Preparation:
Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms.
Ch. 38 Self-Quiz: # 1-4 (correct answers in back of book)
Read chapter 38, focus on material covered in lecture (terms, concepts, and figures!)
Skim next lecture.
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
Compare and contrast methods of pollination and methods of seed dispersal used by angiosperms.
Explain the difference between pollination and fertilization.
Diagram the parts of an idealized flower with labels.
Describe the ABC model of flower development.