Transcript Sexual reproduction haploid gametogenesis in flowers

Plant Growth & Development
3 stages
1. Embryogenesis
Fertilization to seed
2. Vegetative growth
Juvenile stage
Germination to adult
"phase change" marks transition
3. Reproductive development
Make flowers, can
reproduce sexually
Basic pattern of
floral development
A, B, C genes
= transcription factors
http://en.wikipedia.org/wiki/File:Flower_poster_2.jpg
The ABC model: model for
floral organ identity determination

Arabidopsis
Homeotic transformations
– formation of a normal
plant/animal body
structure in place of
another at an abnormal
Antirrhinum
site
– e.g., sepals forming in
the 2nd whorl

http://biology.kenyon.edu/courses/biol114/Chap13/Chapter_12C.ht
ml
ABC model: E. Coen and E.
Meyerowitz 1991
The ABC model: model for
floral organ identity determination
Sepal formation:
needs class A genes
http://www.its.caltech.edu/~plantlab/html/research.html
Petal:
A+B
Stamen:
B+C
Carpel:
C
– Mutual inhibition of
class A and class C
function
Sexual reproduction
1. haploid gametogenesis in flowers: reproductive organs
• Female part = pistil (gynoecium)
• Stigma
• Style
• Ovary
• Ovules
• Male part :
anthers
• Make pollen
Sexual reproduction
1. making haploid gametes in flowers
• Pollen = male, 2-3 cells
• Made in anther locules
Archesporial cell
Primary
sporogenous
cells
Primary
parietal
cells
Pollen mother 2o parietal cells
cells
Endothecium
meiosis
Tapetum
Microspores
Middle cell layer
(Wilson & Yang, 2004, Reproduction)
Sexual reproduction
1. making haploid gametes in flowers
• Pollen = male, contains 2-3 cells
• Made in anthers
• Microspores divide to form vegetative cell and germ cell
• Germ cell divides to form 2 sperm cells, but often not
until it germinates
• Pollen grains dehydrate and are coated
• Are released, reach stigma, then germinate
Sexual reproduction
1. making haploid gametes in flowers
• Pollen = male, contains 2-3 cells
• Egg = female, made in ovaries
Sexual reproduction
Megaspore mother cell → meiosis → 4 haploid megaspores
• 3 die
• Functional megaspore divides 3 x w/o cytokinesis
• Cellularization forms egg, binucleate central cell, 2
synergids & 3 antipodals
http://www.biologie.uni-hamburg.de/bonline/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/OvuleForm700.jpg
Sexual reproduction
Pollen lands on stigma &
germinates if good signals
• Forms pollen tube that grows
through style to ovule
• Germ cell divides to form sperm
nuclei
Pollen tube reaches micropyle
& releases sperm nuclei into ovule
Sexual reproduction
Pollen tube reaches micropyle
& releases sperm nuclei into ovule
Double fertilization occurs!
One sperm fuses with egg
to form zygote
Other fuses with central cell to
form 3n endosperm
Embryogenesis
One sperm fuses with egg to form zygote
Other fuses with central cell to form 3n endosperm
Development starts immediately!
Embryogenesis
Development starts immediately! Controlled by genes,
auxin & cytokinins
Apical cell after first division becomes embryo, basal cell
becomes suspensor
Embryogenesis
Development starts immediately! Controlled by genes,
auxin & cytokinins
Apical cell after first division becomes embryo, basal cell
becomes suspensor
Key events
1. Establishing polarity: starts @ 1st division
Embryogenesis
1. Establishing polarity: starts @ 1st division
2. Establishing radial patterning: periclinal divisions form
layers that become dermal, ground & vascular tissue
Embryogenesis
1. Establishing polarity: starts @ 1st division
2. Establishing radial patterning: periclinal divisions form
layers that become dermal, ground & vascular tissue
3. Forming the root and shoot meristems
1.
2.
3.
4.
Embryogenesis
Establishing polarity: starts @ 1st division
Establishing radial patterning: periclinal divisions form
layers that become dermal, ground & vascular tissue
Forming the root and shoot meristems
Forming cotyledons & roots
Embryogenesis
1. Establishing polarity: starts @ 1st division
2. Establishing radial patterning: periclinal divisions form
layers that become dermal, ground & vascular tissue
3. Forming the root and shoot meristems
4. Forming cotyledons & roots
Body plan is formed during embryogenesis: seedling that
germinates is a juvenile plant with root and apical
meristems
Embryogenesis
End result is seed with embryo packaged inside protective
coat
Embryogenesis
End result is seed with embryo packaged inside protective
coat
Endosperm feeds developing embryo (3n grows faster)
Embryogenesis
End result is seed with embryo packaged inside protective
coat
Endosperm feeds developing embryo (3n grows faster)
In many dicots endosperm is absorbed as seed develops
Embryogenesis
End result is seed with embryo packaged inside protective
coat
Endosperm feeds developing embryo (3n grows faster)
In many dicots endosperm is absorbed as seed develops
In many monocots
endosperm is seedling food
Embryogenesis
Body plan is formed during embryogenesis: seedling that
germinates is a juvenile plant with root and apical
meristems, roots & shoots
Embryogenesis
Body plan is formed during embryogenesis: seedling that
germinates is a juvenile plant with root and apical
meristems, roots & shoots
Later stages of seed development load nutrients and form
protective coat
Embryogenesis
Later stages of seed development load nutrients and form
protective coat
Final stages involve desiccation (to 5% moisture content)
& dormancy
Embryogenesis
Later stages of seed development involve loading nutrients
and forming protective coat
Final stages involve desiccation (to 5% moisture content)
& dormancy -> Abscisic acid plays important role
Embryogenesis
Later stages of seed development load nutrients and form
protective coat
Final stages involve desiccation (to 5% moisture content)
& dormancy -> Abscisic acid plays important role
Coordinated with fruit ripening: fruit’s job is to protect &
disperse seed
Seed germination
Coordinated with fruit ripening: fruit’s job is to protect &
disperse seed
Seeds remain dormant until sense appropriate conditions:
some date palms germinated after 2000 years!
Seed germination
Seeds remain dormant until sense appropriate conditions:
some date palms germinated after 2000 years!
• Water
Seed germination
Seeds remain dormant until sense appropriate conditions:
some Lotus germinated after 2000 years!
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
Seed germination
Seeds remain dormant until sense appropriate conditions:
some Lotus germinated after 2000 years!
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• May degrade hydrophobic seed coat
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• May degrade hydrophobic seed coat
• May disperse inhibitor (eg Abscisic acid)
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• May degrade hydrophobic seed coat
• May disperse inhibitor (eg Abscisic acid)
• Many require light
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• May degrade hydrophobic seed coat
• May disperse inhibitor (eg Abscisic acid)
• Many require light: says that they will soon be able to
photosynthesize
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• May degrade hydrophobic seed coat
• May disperse inhibitor (eg Abscisic acid)
• Many require light: says that they will soon be able to
photosynthesize: often small seeds with few reserves
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• Many require light: says that they will soon be able to
photosynthesize: often small seeds with few reserves
• Some need acid treatment or scarification
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature: some seeds require vernalization =
prolonged cold spell
• Many require light: says that they will soon be able to
photosynthesize: often small seeds with few reserves
• Some need acid treatment or scarification
• Passage through bird gut
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Water
• Temperature
• Many require light
• Some need acid treatment or scarification
• Passage through bird gut
• Some need fire
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Some need acid treatment or scarification
• Passage through bird gut
• Some need fire
• Hormones can also trigger (or stop) germination
Seed germination
Seeds remain dormant until sense appropriate conditions:
• Hormones can also trigger (or stop) germination
Germination is a two step process
• Imbibition is purely physical: seed swells as it absorbs
water until testa pops. Even dead seeds do it.
Seed germination
Germination is a two step process
• Imbibition is purely physical: seed swells as it absorbs
water until testa pops. Even dead seeds do it.
• Next embryo must start metabolism and cell elongation
Seed germination
Germination is a two step process
• Imbibition is purely physical: seed swells as it absorbs
water until testa pops. Even dead seeds do it.
• Next embryo must start metabolism and cell elongation
• This part is sensitive to the environment, esp T & pO2
Seed germination
Germination is a two step process
• Imbibition is purely physical: seed swells as it absorbs
water until testa pops. Even dead seeds do it.
• Next embryo must start metabolism and cell elongation
• This part is sensitive to the environment, esp T & pO2
• Once radicle has emerged, vegetative growth begins
Vegetative growth
Once radicle has emerged, vegetative growth begins
• Juvenile plants in light undergo photomorphogenesis
• Initially live off reserves, but start
making photosynthetic leaves
Vegetative growth
Once radicle has emerged, vegetative growth begins
• Juvenile plants in light undergo photomorphogenesis
• Initially live off reserves, but start
making photosynthetic leaves
• Roots grow down seeking
water & nutrients
reproductive phase
Eventually switch to reproductive phase & start flowering
• Are now adults!
reproductive phase
Eventually switch to reproductive phase & start flowering
• Are now adults!
• Time needed varies from days to years
reproductive phase
Eventually switch to reproductive phase & start flowering
• Are now adults!
• Time needed varies from days to years.
• Shoot apical meristem now starts making new organ:
flowers, with many new structures & cell types
Date
JAN 14
16
18
21
23
25
28
30
FEB 1
4
6
8
11
13
15
18
Plan B schedule- Spring 2013
TOPIC
General Introduction
plant structure I
plant structure II
plants and water I
plants and water II
mineral nutrition I
mineral nutrition II
solute transport I
solute transport II
Photosynthetic light reactions I
Photosynthetic light reactions II
Calvin cycle
C4 and CAM
Environmental effects
Phloem transport I
Exam 1
20
22
25
27
MAR 1
4
6
8
11
13
15
18
20
22
25
27
29
APR 1
Phloem transport II
Respiration I
Respiration II
Respiration III
Lipid synthesis
Spring Recess
Spring Recess
Spring Recess
Biofuels
Nutrient assimilation I
Nutrient assimilation II
Cell wall synthesis and growth I
Cell wall synthesis and growth II
Growth and development I
Growth and development II
Light regulation of growth I
Easter
Easter
APR 3
5
8
10
12
15
17
19
22
24
26
29
May 1
???
Light regulation of growth II
Growth regulators I
Growth regulators II
Growth regulators III
Growth regulators IV
Exam 2
Elective
Elective
Elective
Elective
Elective
Elective
Elective
Last Class!
Final examination
Lab Schedule
Date
Jan
Feb
Mar
Apr
TOPIC
18
General introduction, plant structure
25
Water potential and transpiration
1
Mineral nutrition
8
Light reactions of photosynthesis
15
CO2 assimilation, C3 vs C4 and CAM
22
Environmental effects on CO2 assimilation
1
Respiration
8
Spring Recess
15
Induction of nitrate reductase
22
Growth and development I
29
Easter
5
Independent project
12
Independent project
19
Independent project
26
Independent project