Lecture 8 Outline (Ch. 42)

2. Lecture 8 Outline (Ch. 42) • I. Flower Structures • II. Life Cycle • Gametophyte Production • Flower Development • Pollination • Fertilization • Germination

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

4. Angiosperm Overview • In alternation of generations in angiosperms, the dominant stage is the diploid  sporophyte • Spores develop inside the flower into tiny, haploid gametophytes: • the malepollen grainand thefemaleembryo sac

5. 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

6. 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

7. Model for Flowering • Flowering leads to an adult meristem becoming a floral meristem • Activate or repress the inhibition of floral meristem identity genes • 2 key genes: LFY and AP1 • Turn on floral organ identity genes • Define the four concentric whorls • Sepal, petal, stamen, and carpel

8. Model for Flowering

9. 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

10. ABC Model

11. ABC Model

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

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. Angiosperm Fertilization

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. Angiosperm Seed Formation

24. 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

25. Dispersal by Water Coconut

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

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

28. The Mature Seed • The embryo and its food supply are enclosed by a hard, protective seed coat • The seed enters a state of dormancy • In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves) • A monocot embryo has one cotyledon

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 Angiosperm Seeds

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 various methods for asexual propagation of angiosperms • Cuttings can be taken from many kinds of plants • They are asexually reproduced from plant fragments • 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. Lecture 8 Summary • Parts of a flower (Ch. 42) • Gamete Formation (Ch. 42) • 3. Flowering and flower development (Ch. 42) • ABC Model • 4. Pollination (Ch. 42) • Modes • Events • Fertilization (Ch. 42) • - Steps: what happens to pollen and in ovules • 6. Fruit/Seed (Ch. 42) • Development • Germination