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2 Lecture 7 Outline (Ch. 38 – although some material is Ch. 30 in our text, pp ) I.Flower Structures II.Flower Development IV.Pollination V.Gametophyte Production VI.Fertilization VII.Germination VIII.Preparation for next lecture

3 Angiosperm Overview Stamen Anther Filament Stigma Carpel Style Ovary Receptacle Sepal Petal (a) Structure of an idealized flower – not all flowers have all parts! A flower is a specialized shoot with up to 4 rings of modified leaves (sporophylls)

4 Angiosperm Overview Environmental signals eg. Day length, temperature Internal signals eg. hormones Floral meristem identity genes Vegetative growth (indeterminate) Growth of flower (determinate) When and how are flowers produced?

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 Cues lead to activation of floral organ identity genes –These define the four concentric whorls Sepal, petal, stamen, and carpel

ABC Model 3 classes of floral organ identity genes Specify 4 organ types Classes A and C mutually inhibitory When any one class is missing, aberrant floral organs occur in predictable positions 6

7 ABC Model 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 Mutant flower – some floral organs missing

8 Fertilization brings female and male gametophytes together Fertilization (syngamy) is preceded by pollination, the placing of pollen on the stigma of the carpel Angiosperm Pollination One of my favorite pollinator systems: Think about how the mode of pollination compares with the number of pollen grains distributed, and how this compares with attracting specific pollinators! Pollen = male gametophyte Ovule(s) = female gametophyte

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

10 Pollination by Bees Common dandelion under normal light Common dandelion under ultraviolet light

11 Pollination by Moths and Butterflies Moth on yucca flower Anther Stigma

12 Pollination by Flies Blowfly on carrion flower Fly egg

13 Hummingbird drinking nectar of poro flower Pollination by Birds

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

15 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

100  m MEIOSIS MITOSIS Key to labels Haploid (n) Diploid (2n) (LM) Embryo sac Ovule Megasporangium Megasporocyte Integuments Micropyle Surviving megaspore Antipodal cells (3) Polar nuclei (2) Egg (1) Synergids (2) Ovule Integuments Female gametophyte (embryo sac) 16 In megasporangium in an ovule in the ovary of the carpel meiosis  megaspores develop mitosis  mature gametophyte Cells: 7 cells, 8 nuclei All in embryo sac Ovule is now the female gametophyte plus integuments Angiosperm Gametophytes Female gametophytes:

17 Angiosperm Gametophytes Microsporangium (pollen sac) Microsporocyte Microspores (4) Each of 4 microspores Generative cell (will form 2 sperm) (LM) 75  m 20  m MEIOSIS MITOSIS Male gametophyte (in pollen grain) Nucleus of tube cell Ragweed pollen grain (colorized SEM) Key to labels Haploid (n) Diploid (2n) Male gametophytes: In microsporangium in an anther of the stamen meiosis  produces 4 microspores Each microspore becomes a pollen grain mitosis  mature gametophyte Cells: 2 cells - generative cell (will form 2 sperm) inside the tube cell All in pollen grain

18 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

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

20 Ovule becomes a seed - embryo and supply of nutrients embryo has apical meristems and one or two cotyledons Mitosis of triploid endosperm gives rise to nutrient-rich mass Angiosperm Seed Formation Ovule Endosperm nucleus Integuments Zygote Cotyledons Plant embryo Seed coat Endosperm

21 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 Epicotyl Hypocotyl Cotyledons Radicle Seed coat (a) Common garden bean, a eudicot with thick cotyledons (c) Maize, a monocot Scutellum (cotyledon) Endosperm Epicotyl Hypocotyl Radicle

22 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

23 Coconut Dispersal by Water

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

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

26 Seed coat Radicle Hypocotyl Cotyledon Hypocotyl Epicotyl Foliage leaves Cotyledon Seed Germination (bean) Germination: seeds imbibe water – expands rupturing its coat, triggers metabolic changes causing embryo to resume growth Radicle (root) first to emerge Next, the embryonic shoot breaks through the soil surface

Things To Do After Lecture 7… Reading and Preparation: 1.Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. 2.Ch. 38 Self-Quiz: # 1-4 (correct answers in back of book) 3.Read chapter 38, focus on material covered in lecture (terms, concepts, and figures!) 4.Skim next lecture. “HOMEWORK” (NOT COLLECTED – but things to think about for studying): 1.Compare and contrast methods of pollination and methods of seed dispersal used by angiosperms. 2.Explain the difference between pollination and fertilization. 3.Diagram the parts of an idealized flower with labels. 4.Describe the ABC model of flower development.