Transcript 07 - Plant Reproduction (ch.38)

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.
Life Cycle
VI. Gametophyte Production
VII. Fertilization
VIII. Germination
IX. Preparation for next lecture
2
Angiosperm Overview
Stamen
Anther
Stigma
Carpel
Style
A flower is a
specialized
shoot with up
to 4 rings of
modified
leaves
(sporophylls)
Filament
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
ABC Model
8
Based on the ABC model for flower development,
if ‘A’ class genes are missing, what develops?
A.
B.
C.
D.
sepal, sepal, stamen, carpel
petal, petal, stamen, carpel
stamen, petal, petal, stamen
carpel, stamen, stamen, carpel
Looking at the images below, which class
of genes is deficient in the mutant?
1.
2.
3.
4.
5.
Class A
Class B
Class C
Classes A & B
Classes B & C
Male
structure
Pollen = male gametophyte
Ovule(s) = female gametophyte
Female
structure
11
Angiosperm Pollination
• 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!
12
Abiotic Pollination by Wind
Hazel staminate flowers
(stamens only)
Hazel carpellate flower
(carpels only)
13
Pollination by Bees
Common dandelion under
normal light
Common dandelion under
ultraviolet light
14
Pollination by Moths and Butterflies
Anther
Stigma
Moth on yucca flower
15
Pollination by Flies
Fly egg
Blowfly on carrion flower
16
Pollination by Birds
Hummingbird drinking nectar of poro flower
17
Pollination by Bats
Long-nosed bat feeding on cactus flower at night
18
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
19
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
20
Angiosperm Gametophytes
• 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
21
Angiosperm Gametophytes
22
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
23
The megaspore mother cell gives rise to:
1.
2.
3.
4.
5.
pollen
petals
egg cells
seeds
ovaries
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
25
Double Fertilization
One sperm fuses with the egg – diploid (zygote)
One sperm fuses with the two polar nuclei – triploid (endosperm)
26
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
27
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
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
29
Dispersal by Water
Coconut
30
Dispersal by Wind
Winged seed
of Asian
climbing gourd
Dandelion “parachute”
Winged fruit of maple
Tumbleweed
31
Dispersal by Animals
Barbed fruit
Seeds carried to
ant nest
Seeds in feces
Seeds buried in caches
32
The Mature Seed
Seed coat
Epicotyl
Hypocotyl
• The embryo and its
food supply enclosed
by a hard, protective
seed coat
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
Seed coat
Endosperm
• The seed enters a
state of dormancy
• In dicots, the embryo
has two cotyledons
(seed leaves)
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
• A monocot embryo
has one cotyledon
Scutellum
(cotyledon)
Pericarp fused
with seed coat
Coleoptile
Endosperm
Epicotyl
Hypocotyl
Coleorhiza
Radicle
33
(c) Maize, a monocot
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
34
Seed Germination (bean)
(a) Common garden bean
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
35
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.