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Transcript
1
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.
Gametophyte Production
VI. Fertilization
VII. Germination
VIII. Preparation for next lecture
2
Angiosperm Overview
Stamen
Anther
Stigma
Carpel
Style
Filament
A flower is a
specialized
shoot with up
to 4 rings of
modified leaves
(sporophylls)
Ovary
Sepal
Petal
Receptacle
(a) Structure of an idealized flower – not all flowers have all parts!
3
Angiosperm Overview
Growth of flower
(determinate)
• Environmental signals
eg. Day length, temperature
• Internal signals
eg. hormones
When and how are
flowers produced?
Floral
meristem
identity
genes
Vegetative growth
(indeterminate)
4
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
ABC Model
1.
2.
3.
4.
Class A genes alone – Sepals
Class A and B genes together – Petals
Class B and C genes together – Stamens
Class C genes alone – Carpels
Mutant flower – some floral
organs missing
7
Angiosperm Pollination
Pollen = male gametophyte
Ovule(s) = female gametophyte
• Fertilization brings female and male gametophytes together
• Fertilization (syngamy) is preceded by pollination, the
placing of pollen on the stigma of the carpel
One of my favorite pollinator systems:
http://www.youtube.com/watch?v=-h8I3cqpgnA
Think about how the mode of pollination compares
with the number of pollen grains distributed, and how
this compares with attracting specific pollinators!
8
Abiotic Pollination by Wind
Hazel staminate flowers
(stamens only)
Hazel carpellate flower
(carpels only)
9
Pollination by Bees
Common dandelion under
normal light
Common dandelion under
ultraviolet light
10
Pollination by Moths and Butterflies
Anther
Stigma
Moth on yucca flower
11
Pollination by Flies
Fly egg
Blowfly on carrion flower
12
Pollination by Birds
Hummingbird drinking nectar of poro flower
13
Pollination by Bats
Long-nosed bat feeding on cactus flower at night
14
Angiosperm Lifecycle
Germinated pollen grain (n)
(male gametophyte)
Anther
Ovary
Pollen tube
Ovule
Embryo sac (n)
(female gametophyte)
FERTILIZATION
Egg (n)
Sperm (n)
Key
Zygote
(2n)
Mature sporophyte
plant (2n)
Haploid (n)
Diploid (2n)
Germinating
seed
Seed
Seed
Embryo (2n)
(sporophyte)
(b) Simplified angiosperm life cycle
Simple fruit
15
Angiosperm Gametophytes
Female gametophytes:
100 m
Haploid (n)
Diploid (2n)
Megasporangium
Megasporocyte
Integuments
Micropyle
Surviving
megaspore
Antipodal cells (3)
Polar nuclei (2)
Egg (1)
Synergids (2)
Female gametophyte
(embryo sac)
In megasporangium
in an ovule in the
Ovule
ovary of the carpel
MEIOSIS
meiosis 
megaspores develop
mitosis  mature
gametophyte
MITOSIS
Ovule
Cells: 7 cells, 8 nuclei
All in embryo sac
Ovule is now the
Integuments
female gametophyte
plus integuments
Key to labels
Embryo sac
(LM)
16
Angiosperm Gametophytes
Male gametophytes:
Microsporangium
(pollen sac)
Microsporocyte
MEIOSIS
Microspores (4)
Each of 4
microspores
MITOSIS
Male
gametophyte
(in pollen grain)
Generative cell
(will form 2 sperm)
Nucleus of tube cell
20 m
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
Key to labels
75 m
(LM)
Ragweed pollen grain
(colorized SEM)
Haploid (n)
Diploid (2n)
17
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 a diploid zygote and a triploid (3n) endosperm
18
Double Fertilization
One sperm fuses with the egg – diploid (zygote)
One sperm fuses with the two polar nuclei – triploid (endosperm)
19
Angiosperm Seed Formation
• 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
Ovule
Endosperm
nucleus
Integuments
Zygote
Cotyledons
Plant
embryo
Zygote
Seed
coat
Endosperm
20
The Mature Seed
• The embryo and its
food supply enclosed
by a hard, protective
seed coat
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
• The seed enters a
state of dormancy
(a) Common garden bean, a eudicot with thick cotyledons
• In dicots, the embryo
has two cotyledons
(seed leaves)
Scutellum
(cotyledon)
Endosperm
Epicotyl
Hypocotyl
• A monocot embryo
has one cotyledon
Radicle
(c) Maize, a monocot
21
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
22
Dispersal by Water
Coconut
23
Dispersal by Wind
Winged seed
of Asian
climbing gourd
Dandelion “parachute”
Winged fruit of maple
Tumbleweed
24
Dispersal by Animals
Barbed fruit
Seeds carried to
ant nest
Seeds in feces
Seeds buried in caches
25
Seed Germination (bean)
Germination: seeds imbibe water – expands rupturing its coat,
triggers metabolic changes causing embryo to resume growth
Radicle (root) first to emerge Foliage leaves
Next, the embryonic shoot Cotyledon
breaks through the soil
Epicotyl
surface
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Radicle
Seed coat
26
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.