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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?
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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
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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
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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
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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
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17Hummingbird drinking nectar of poro flower
Pollination by Birds
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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
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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
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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
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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)
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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.