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

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

4 In alternation of generations in angiosperms, the dominant stage is the diploid  sporophyte Spores develop inside the flower into tiny, haploid gametophytes: –the male pollen grain and the female embryo sac Angiosperm Overview

5 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 Angiosperm Lifecycle

6 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 Angiosperm Gametophytes

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 7

8 Model for Flowering

ABC Model 3 classes of floral organ identity genes specify 4 organ types 1.Class A genes alone – Sepals 2.Class A and B genes together – Petals 3.Class B and C genes together – Stamens 4.Class C genes alone – Carpels When any one class is missing, aberrant floral organs occur in predictable positions 9

10 ABC Model

11 ABC Model

12 Male structure Female structure

13 brings female and male gametophytes together Fertilization (syngamy) is preceded by pollination, the placing of pollen on the stigma of the carpel Angiosperm Pollination

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 Moth on yucca flower Anther Stigma

17 Pollination by Flies Blowfly on carrion flower Fly egg

18 Hummingbird drinking nectar of poro flower Pollination by Birds

19 Long-nosed bat feeding on cactus flower at night Pollination by Bats

20 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 Angiosperm Pollination  Fertilization

21 Angiosperm Fertilization

22 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 Angiosperm Seed Formation

23 Angiosperm Seed Formation

24 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

25 Coconut Dispersal by Water

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

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

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 Epicotyl Hypocotyl Cotyledons Radicle Seed coat Endosperm (a) Common garden bean, a eudicot with thick cotyledons Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons (c) Maize, a monocot Scutellum (cotyledon) Pericarp fused with seed coat Endosperm Epicotyl Hypocotyl Coleoptile Radicle Coleorhiza Angiosperm Seeds

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 (a) Common garden bean Seed coat Radicle Hypocotyl Cotyledon Hypocotyl Epicotyl Foliage leaves Cotyledon Hypocotyl Seed Germination (bean)

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 Part of plantFunctionLater becomes…Examples: OvaryContains eggs (ovules) Flesh of fruitApples, strawberries, coconut meat Pollen Ovule Integuments Cotyledons Endosperm

Lecture 8 Summary 1.Parts of a flower (Ch. 42) 2.Gamete Formation (Ch. 42) 3.Flowering and flower development (Ch. 42) -ABC Model 4.Pollination (Ch. 42) -Modes -Events 5.Fertilization (Ch. 42) - Steps: what happens to pollen and in ovules 6. Fruit/Seed (Ch. 42) -Development -Germination