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Lecture 8 Outline (Ch. 42). I. Flower Structures II. Life Cycle Gametophyte Production Flower Development Pollination Fertilization Germination. Stigma. Anther. Carpel. Stamen. Style. Filament. Ovary. Sepal. Petal. Receptacle. (a) Structure of an idealized flower.

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Lecture 8 Outline (Ch. 42)

  • I. Flower Structures

  • II. Life Cycle

  • Gametophyte Production

  • Flower Development

  • Pollination

  • Fertilization

  • Germination


Stigma

Anther

Carpel

Stamen

Style

Filament

Ovary

Sepal

Petal

Receptacle

(a) Structure of an idealized flower

Angiosperm Overview


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


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


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


Model for flowering
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



Abc model
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




Malestructure

Femalestructure


Angiosperm Pollination

  • brings female and male gametophytes together

  • Fertilization (syngamy) is preceded by pollination, the placing of pollen on the stigma of the carpel


Abiotic Pollination by Wind

Hazel staminate flowers

(stamens only)

Hazel carpellate flower

(carpels only)


Pollination by Bees

Common dandelion under

normal light

Common dandelion under

ultraviolet light


Pollination by Moths and Butterflies

Anther

Stigma

Moth on yucca flower


Pollination by Flies

Fly egg

Blowfly on carrion flower


Pollination by Birds

Hummingbird drinking nectar of poro flower


Pollination by Bats

Long-nosed bat feeding on cactus flower at night


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



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



The ovary
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



Dispersal by Wind

Winged seed

of Asian

climbing gourd

Dandelion “parachute”

Winged fruit of maple

Tumbleweed


Dispersal by Animals

Barbed fruit

Seeds in feces

Seeds carried to

ant nest

Seeds buried in caches


The mature seed
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


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


Evolutionary adaptations
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


Seed Germination (bean)

(a) Common garden bean

Foliage leaves

Cotyledon

Epicotyl

Hypocotyl

Cotyledon

Cotyledon

Hypocotyl

Hypocotyl

Radicle

Seed coat


Vegetative reproduction agriculture
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



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


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