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Lecture 7 Outline (Ch. 38 – although some material is Ch. 30 in our text, pp 625-628)

I. Flower Structures

II. Flower Development

IV. Pollination

V. Life Cycle

VI. Gametophyte Production

VII. Fertilization

VIII. Germination

IX. Preparation for next lecture

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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)

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Angiosperm Overview

• Environmental signalseg. Day length, temperature

• Internal signalseg. 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

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ABC Model

1. Class A genes alone – Sepals2. Class A and B genes together – Petals 3. Class B and C genes together – Stamens4. Class C genes alone – Carpels

Mutant flower – some floral organs missing

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ABC Model

Based on the ABC model for flower development, if ‘A’ class genes are missing, what develops?

A. sepal, sepal, stamen, carpel

B. petal, petal, stamen, carpel

C. stamen, petal, petal, stamen

D. carpel, stamen, stamen, carpel

Looking at the images below, which class of genes is deficient in the mutant?

1. Class A

2. Class B

3. Class C

4. Classes A & B

5. Classes B & C

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Male structure

Female structure

Pollen = male gametophyteOvule(s) = female gametophyte

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• brings female and male gametophytes together

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

Angiosperm Pollination

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

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!

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Abiotic Pollination by Wind

Hazel staminate flowers(stamens only)

Hazel carpellate flower(carpels only)

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Pollination by Bees

Common dandelion undernormal light

Common dandelion underultraviolet light

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Pollination by Moths and Butterflies

Moth on yucca flower

Anther

Stigma

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Pollination by Flies

Blowfly on carrion flower

Fly egg

17Hummingbird drinking nectar of poro flower

Pollination by Birds

18Long-nosed bat feeding on cactus flower at night

Pollination by Bats

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Anther

Pollen tube

Germinated pollen grain (n)(male gametophyte)

Ovary

Ovule

Embryo sac (n)(female gametophyte)

Egg (n)

Sperm (n)

Zygote(2n)

Seed

SeedEmbryo (2n)(sporophyte)

Simple fruit

Germinatingseed

Mature sporophyteplant (2n)

(b) Simplified angiosperm life cycle

Key

Haploid (n)

Diploid (2n)

FERTILIZATION

Angiosperm Lifecycle

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• 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

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• Female gametophytes:

In a megasporangium in an ovule in the ovary of the carpel

meiosis megaspore mother cells gives rise to megaspores

mitosis mature gametophyte

• Cells: 7 cells and 8 nuclei (3 antipodal; 1 endosperm mother cell with 2 nuclei, 1 egg and 2 synergids)

All in embryo sac

Ovule is now the female gametophyte plus integuments

Angiosperm Gametophytes

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Angiosperm Gametophytes

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Angiosperm Gametophytes

• Male gametophytes:

In a microsporangium in an anther of the stamen

meiosis microspore mother cells give rise to 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

The megaspore mother cell gives rise to:

1. pollen

2. petals

3. egg cells

4. seeds

5. ovaries

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• 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

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Double Fertilization

One sperm fuses with the egg – diploid (zygote)

One sperm fuses with the two polar nuclei – triploid (endosperm)

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• 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

Double fertilization refers to:

1. Two sperm fuse with the egg cell

2. Two sperm fuse with the polar nuclei

3. One sperm fuses with the egg, one with the polar nuclei

4. One sperm fuses with the endosperm, one with the tube cell

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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

30Coconut

Dispersal by Water

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Tumbleweed

Dispersal by Wind

Winged fruit of maple

Dandelion “parachute”Winged seedof Asianclimbing gourd

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Dispersal by Animals

Seeds carried toant nest

Seeds buried in caches

Seeds in fecesBarbed fruit

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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

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 fusedwith seed coat

Endosperm

Epicotyl

Hypocotyl

Coleoptile

RadicleColeorhiza

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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

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(a) Common garden bean

Seed coat

Radicle

Hypocotyl

Cotyledon

Cotyledon

Hypocotyl

Epicotyl

Foliage leaves

Cotyledon

Hypocotyl

Seed Germination (bean)

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.