Flowering Plant Reproduction

1
Flowering Plant Reproduction

• Chapter 38

2
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Meiosis occurs in sporangia of sporophytes
Sporophyte
Meiosis
Megasporangium
Gametophytes
Megaspore
Fertilization
Fig. 30.10
3
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Pollen
Spores divide by mitosis and develop into mature
gametophytes
Sporophyte
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo sac
Fertilization
Fig. 30.10
4
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Pollen
Specialized gametophyte cells divide by mitosis
to form gametes
Sporophyte
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo sac
Egg
2 sperm
Fertilization
Fig. 30.10
5
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Pollen
Gametes fuse during fertilization to produce a
zygote
Sporophyte
Seedling
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo
Embryo sac
Egg
Zygote
2 sperm
Endosperm
Fertilization
Fig. 30.10
6
A sporophytes male reproductive
structures Stamen Anther Filament
Figs. 30.7 38.2
7
A sporophytes male reproductive
structures Each anther contains multiple pollen
sacs (microsporangia)
Fig. 38.4
8
A sporophytes male reproductive
structures Each pollen sac contains mutiple
diploid microsporocytes (microspore mother cells)
Fig. 38.4
9
A sporophytes male reproductive
structures Each microsporocyte divides by
meiosis to produce 4 haploid microspores
Fig. 38.4
10
A sporophytes male reproductive
structures Each microspore divides once by
mitosis to form an immature male gametophyte
(pollen grain)
Fig. 38.4
A single tube cell encloses a single generative
cell
11
A sporophytes male reproductive
structures The pollen grain matures into an
adult male gametophyte when its generative cell
divides by mitosis to produce two sperm
Fig. 38.4
The adult male gameto-phyte is a fully mature,
indepen-dent plant with only 3 cells
12
A sporophytes female reproductive
structures Carpel Stigma Style Ovary
Ovule Receptacle
Figs. 30.7 38.2
13
A sporophytes female reproductive
structures Each ovule contains a
megasporangium
Fig. 38.4
Each megasporangium contains a megasporocyte
(megaspore mother cell)
14
A sporophytes female reproductive
structures A megasporocyte divides by meiosis
to form 4 cells
Fig. 38.4
Only 1 of the 4 cells survives the megaspore
15
A sporophytes female reproductive
structures The megaspores nucleus divides 3
times giving 1?2?4?8 nuclei
Fig. 38.4
Membranes then partition the 8-nucleate immature
gametophyte cell into 7 smaller cells (one with 2
nuclei)
16
A sporophytes female reproductive
structures The 7 cells 1 egg 1 cell with
2 polar nuclei 5 other cells
Fig. 38.4
The 7 cells comprise the mature, completely
dependent female gametophyte (embryo sac)
17
Double fertilization of angiosperms (and
independently derived in a few gymnosperms)
A pollen grain disperses to a stigma (pollination)
The tube cell grows into a pollen tube
Fig. 38.6
18
Double fertilization of angiosperms (and
independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to
the embryo sac
Fig. 38.6
19
Double fertilization of angiosperms (and
independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to
the embryo sac
Fig. 38.6
20
Double fertilization of angiosperms (and
independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to
the embryo sac
Fig. 38.6
21
Double fertilization of angiosperms (and
independently derived in a few gymnosperms)
1 sperm fuses with the egg (fertilization)
1 sperm fuses with the polar nuclei to form the
first cell of the endosperm (triploid)
Fig. 38.6
22
In chapter 30 we saw some mechanisms used by
plants to avoid self-fertilization bisexual
flowers also use
Structural barriers to pollination, e.g., pin
vs. thrum flowers
Fig. 38.5
23
Other mechanisms used by bisexual flowers to
avoid self-fertilization
Genetic self-incompatibility, gauged by S-genes
24
Other mechanisms used by bisexual flowers to
avoid self-fertilization
Genetic self-incompatibility, gauged by S-genes
25
Other mechanisms used by bisexual flowers to
avoid self-fertilization
Genetic self-incompatibility, gauged by S-genes
26
Development of the seed and fruit
The first mitotic division of the zygote is
asymmetric
This asymmetry provides the first environmental
difference experienced by the differentiating
cells and establishes the root-shoot axis
Ovary
Receptacle
Fig. 38.7
27
Development of the seed and fruit
The sporophyte embryo develops from the zygote
The endosperm develops from the triploid
endosperm nucleus
Ovary
Receptacle
Fig. 38.7
28
Development of the seed and fruit
The ovule integuments become the seed coat
Tissues of the ovary (and sometimes the
receptacle) become the fruit
Ovary
Receptacle
Fig. 38.7
29
Development of the seed and fruit
The ovule integuments become the seed coat
Tissues of the ovary (and sometimes the
receptacle) become the fruit
30
Development of the seed and fruit
There are many kinds of fruits
Carpels
Flower
Stigma
Stamen
Ovule
Carpel (fruitlet)
Each segment develops from the carpel of one
flower
Stigma
Seed
Stamen
Pea
Pineapple
Raspberry
Multiple fruit - many carpels of many flowers
Simple fruit - single carpel of one flower
Aggregate fruit - many separate carpels of one
flower
Fig. 38.9
31
Development of the seed and fruit
Fruits aid seed dispersal
The ovary wall becomes either a dry or fleshy
fruit
32
Development of the seed and fruit
Fruits aid seed dispersal
Many dry fruits are wind dispersed
33
Development of the seed and fruit
Fruits aid seed dispersal
Some dry fruits are animal dispersed
34
Development of the seed and fruit
Fruits aid seed dispersal
Many fleshy fruits are animal dispersed
35
Development of the seed and fruit
Fruits aid seed dispersal
Unless the dispersers become extinct!
36
Development of the seed and fruit
Fruits aid seed dispersal
Some fruits disperse seeds explosively (e.g.,
some mistletoes)
37
Development of the seed and fruit
Fruits aid seed dispersal
Some fruits make seeds buoyant, to aid dispersal
by water
38
Development of the seed and fruit
Eudicot embryos develop two cotyledons
Fig. 38.8
39
Development of the seed and fruit
Eudicot embryos develop two cotyledons
Monocot embryos develop a single cotyledon
Fig. 38.8
40
Development of the seed and fruit
Cotyledons may absorb endosperm throughout their
functional lives (e.g., castor bean)
Cotyledons may alternatively function as storage
organs that absorb the endosperm prior to a
seeds germination (e.g., common bean)
Fig. 38.8
41
Development of the seed and fruit
The radicle is the first structure out of the
seed coat
In some eudicots the hypocotyl (embryonic axis
below cotyledons) pushes up through the soil
Fig. 38.10
42
Development of the seed and fruit
The radicle is the first structure out of the
seed coat
In some eudicots the epicotyl (embryonic axis
above cotyledons) pushes up through the soil
Fig. 38.10
43
Development of the seed and fruit
In many monocots, the cotyledon remains in the
seed coat, and the coleoptile pushes up through
the soil
Fig. 38.10
44
Gymnosperms rely on wind to move pollen from male
to female cones
The ovule exudes sap to trap pollen
45
Around 150 m.y.a. some insects fed on both
protein-rich pollen of male cones and sugar-rich
secretions of female cones
This may have led evolutionarily to the origin of
Angiosperms and animal-mediated pollination
46
Angiosperms have formed many partnerships with
animals to move their pollen
47
Some of these partnerships are the best known
cases of co-evolution mutual evolutionary
influence
Figs and fig wasps
48
Some flowers provide nurseries for their
pollinators offspring
Figs and fig wasps
49
Some flowers provide food (e.g., nectar or
pollen) to their pollinators
Honey bee collecting pollen and nectar
50
Some flowers provide food (e.g., nectar or
pollen) to their pollinators
Kigelia africana sausage tree
51
Nectar is usually presented together with
attractive structures, e.g., showy petals and
fragrances
Night Blooming Cirrus
52
Petals sometimes exploit the sensory
capabilities of pollinators
Ultraviolet patterns
53
Some flowers trick their pollinators
Bucket Orchid
54
Some flowers trick their pollinators
Bee Orchid
55
Seed dormancy
Most seeds become dormant as they mature, i.e.,
they will not germinate without the appropriate
environmental stimuli
The stimuli are species-specific, and include
Drying, which avoids germination in the fruit
56
Seed dormancy
Most seeds become dormant as they mature, i.e.,
they will not germinate without the appropriate
environmental stimuli
The stimuli are species-specific, and include
Cold, which may prevent germination in the wrong
season
57
Seed dormancy
Most seeds become dormant as they mature, i.e.,
they will not germinate without the appropriate
environmental stimuli
The stimuli are species-specific, and include
Disruption of the seed coat, e.g., by acids or
soaking in water
58
Biotechnology
Humans have modified many food plants by
artificial selection on reproductive structures
(and other traits)
59
Biotechnology
Geneticists have successfully created transgenic
or genetically modified (GM) organisms through
genetic engineering
GM organisms have and express a foreign gene
Bt toxin gene
The Bt toxin gene from Bacillus thuringiensis has
been introduced into some varieties of cotton,
corn, etc.
60
Biotechnology
For a balanced, well-reasoned discussion of GM
crops, see the last sections of Chapt. 38 E.g.,
decisions about the risks and benefits of GM
crops should be based on sound scientific
information and testing rather than on reflexive
fear or blind optimism