Lecture 8 Outline (Ch. 38)

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

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

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

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. Malestructure Femalestructure

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: http://www.youtube.com/watch?v=-h8I3cqpgnA

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

15. Pollination by Bees Common dandelion under normal light Common dandelion under ultraviolet light

16. Pollination by Moths and Butterflies Anther Stigma Moth on yucca flower

17. Pollination by Flies Fly egg Blowfly on carrion flower

18. Pollination by Birds Hummingbird drinking nectar of poro flower

19. Pollination by Bats 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 adiploidzygote and atriploid (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 withapical 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 forseed dispersal • a fruit is amature ovary that protects the enclosed seeds and aids in their dispersal via wind, water, or animals

26. Dispersal by Water Coconut

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

28. Dispersal by Animals Barbed fruit Seeds in feces Seeds carried to ant nest Seeds buried in caches

29. Seed coat Epicotyl Hypocotyl Radicle Cotyledons (a) Common garden bean, a eudicot with thick cotyledons Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons Pericarp fused with seed coat Scutellum (cotyledon) Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle (c) Maize, a monocot The Mature Seed • 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 thatseedlings 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 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

33. Self-Check

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.