Download S i Section 4

3/1/2011
Overview of the seed plants
First seed plants or spermatophytes
evolved from earlier seedless vascular
plants similar to modern lycophytes
p
y p y
and
pteridophytes
„ Following the early diversification of
gymnosperms, one ancestral gymnosperm
lineage gave rise to the angiosperms, the
flowering plants
„
Section 4
S i Professor Donald McFarlane
Lecture 11 Higher Plants:
Domination of the Land
2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Seed plants (spermatophytes)
Critical innovations
Angiosperms
A
Gnetophytes
Conifers
allows seed plants to disperse male
gametophytes
… Ovules
O l allows
ll
seed
d plants
l t tto di
disperse male
l
gametophytes
… Seeds allow plants to reproduce in diverse habitats
… Wood strengthens plants, allowing them to grow tall
and produce many branches, leaves, and seeds
KEY
Gymnosperms
Cycads
… Pollen
Pteridophytes
Shared by all seed plants
Lycophytes
„
Seedless vascular plants
Ginkgo
Major critical innovations
Flowers; fruits; endosperm;
vessels common
Wood; ovules, seeds, pollen
Euphylls having broad leaves with branched veins
Supportive vascular tissue; dominant branched sporophyte generation
3
4
1
3/1/2011
Gymnosperms
„
„
„
„
Wood
Produce seeds that are exposed rather than
enclosed in fruits
“Naked seeds”
Most modern forms are woody shrubs or trees
Seeds and wood are adaptations that allow
gymnosperms to cope with global climate
changes and to live in relatively cold and dry
habitats
„
Tissue composed of numerous empty waterconducting cells strengthened by lignin
… Allows
woody tissue to transport water upward for
greatt distances
di t
… Also provides structural support
„
Vascular cambium
… Produces
thick layer of wood and thin layer of inner
bark
… Inner bark used for transporting watery solutions of
organic compounds
5
„
Progymnosperms
6
Phylum Cycadophyta
… First
wood
… Vascular tissue in a
ring (eustele)
… Produces vascular
cambium and wood
… Reproduced by
means of spores,
not seeds
… Wood came before
seeds
300 cycad species today
„ Primarily tropical and subtropical
„ Many species rare
„ Habitats threatened by human activities
„ Nonwoody stems may emerge like tree
trunks or be underground
„ Leaves palm-like
„
7
8
2
3/1/2011
„
Produce corraloid roots
… Roots
are above ground and resemble corals
cyanobacteria for nitrogen fixation
… Harbor
Produce toxins to deter herbivorous
animals
„ Distinctive reproduction
„
… Conelike
structures bearing ovules and seeds
or pollen
… Cones emit odors that attract beetles
… Beetles carry pollen to ovules
9
10
Phylum Ginkgophyta
Ginkgo biloba single remaining species
„ Nearly extinct in the wild
„ Widely planted along city streets (only
males)
„ Individual trees produce either ovules and
seeds or pollen
„ Flagellate sperm
„
11
12
3
3/1/2011
Phylum Coniferophyta
Named for seed cones
„ 500 species in 50 genera
„ Particularly common in mountain and high
highlatitude forests
„
„
Ginkgos are long-lived- individuals can live
for more than a thousand years and grow
to 30 m in height
13
14
„
Simple pollen cones
… Leaflike
structures bearing microsporangia
producing pollen
„
More complex ovule-bearing cones
… Composed
of short branch system that bears
ovules
„
15
Mature pollen released to the wind
16
4
3/1/2011
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cone
scale
Megaspore
Scale
Ovule
cone
Mature
sporophyte
(2n)
Egg (n)
Ovule
Integument
Megasporangium
Meiosis
Female gametophyte (n)
Mitosis
Megasporangium (2n)
Seed
coat
Microspores
Archegonium (n)
Pollen grain (n)
Pollen
cone
Section
of cone
Microsporangium
KEY
Haploid
Diploid
S dli
Seedling
Seed coats may develop wings for wind
dispersal
„ Others produce seeds or cones with
bright-colored, have fleshy coatings to
attract birds for dispersal
„
Scale
Ovule
Seed
Sperm
Male gametophyte (n)
Embryo (2n)
Mitosis
17
„
18
„
Wood contains tracheids for water transport
… Pits
on side and end walls through which water moves
… Valve-like torus to prevent spread of air bubbles
„
Cold climate
adaptations
… Conical
shape
and flexible
branches
… Scale-like or
needle-shaped
needle
shaped
leaves
… Thick waxy
cuticle
Resin ducts – resin helps prevent attack by
pathogens and herbivores
„
19
Fertilization
Most conifers
are evergreens
20
5
3/1/2011
Modern angiosperms
„
„
„
„
Flowers
Defining features are
flowers and fruits
“Enclosed seeds”
Presence of seeds
within fruits
Seed endosperm
another defining
feature
„
„
„
Complex reproductive structures
Specialized for efficient production of
pollen and seeds
4 types of organs
1.
2.
3.
4.
21
Sepals
Petals
Stamens – produce pollen
Carpels – produce ovules
22
Flower organs supported by receptacle
„ Pedicel – tip of the flower stalk
„ Perinath – petals and sepals
„ Complete flowers – all 4 flower organs
„ Incomplete
p
flowers – lack one or more
organs
„ Perfect flowers – contain both stamens
and carpels
„ Imperfect flowers – lack either stamens or
carpels
„
23
24
6
3/1/2011
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pollen grains (n)
(immature male
gametophytes)
Single and compound carpels called pistil
„ Pistil anatomy
„
… Stigma
„
Meiosis
Microspores
Anther
Mitosis
Male gametophyte
– receives and recognizes pollen
Ovule
Stigma
Only appropriate pollen will be allowed to
germinate
Two sperm (n)
Megasporangium
… Style
… Ovary
Pollen tube
Integuments
Surviving
Megaspore precursor
megaspore (n)
in megasporangium
Gametophyte nuclei
Embryo (2n)
Egg (n)
Mitosis
First endosperm cell (3n)
Sporophyte (2n)
– encloses and protects ovules
Style
KEY
Female
gametophyte
Pollen tube delivers sperm to ovule
„ Ovaries develop into fruits
„
Double
fertilization
Seed
coat
Endosperm
Haploid
Diploid
Zygote (2n)
Pollen tube
25
26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Early flowers
Front
view
Microsporangia
Anther
Filament
Stamen
Anther
Early
stamen
„
„
„
First appeared 140 mya
Flowers were a critical innovation that led to
extensive angiosperm diversification
Stamen development
Filament
Cross
section
(a) Stamen evolution
Stigma
Front
view
… Early
flowers had broad leaf-shaped stamens
… Narrowed to form filaments and anthers (clusters or
microsporangia producing pollen)
„
Ovules
Early carpel
to protect ovules
Fused
seam
Style
Secretion
Ovules
Carpels also developed from leaf-like structures
… Folded
Leaf
Pistil
composed
of one
carpel
Compound
pistil with
multiple
carpels
Ovary
Cross
section
(b) Carpel evolution
27
28
7
3/1/2011
Eudicots
Monocots
Magnoliids
and relatives
Star anise
and relatives
Water lilies
Amborella
Extinct gymn
nosperm ancestor
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Monocots and eudicots are named for
differences in the number of embryonic
leaves called cotyledons
„ Monocots differ from eudicots in several
additional ways
„
29
30
Whole Genome Duplication Influenced
Flowering Plant Diversification
„
„
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
An estimated 40–70% of all plants are polyploid
2 majors types of polyploidy
… Autoploidy
– nondisjunction results in extra
chromosomes in gametes
… Alloploidy – hybridization between 2 species with
different chromosome counts followed by whole genome
duplication
„
Plants are also known to obtain mitochondrial
genes from other plant species by horizontal gene
transfer
(a) Zinnia flower and butterfly
„
(b) Hibiscus flower and hummingbird
(c) Saguaro cactus flower and bat
Floral tubes and coevolved pollinators
32
8
3/1/2011
Fruits
Develop from ovary walls
„ Aid the dispersal of enclosed seeds
„ Dispersal prevents competition and aids in
colonization
„ Fruits may be adapted to
„
… Attract
animals to eat them, wind dispersal,
attach to animal fur or float in water
33
34
Secondary metabolites
„
„
Synthesis of molecules that are not
essential for cell structure and growth
Three major classes in plants
1.
2.
3.
35
Terpenes and terpenoids
Phenolics (flavonoids and related
compounds)
Alkaloids
36
9
3/1/2011
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1.
Terpenes and terpenoids
…
2.
3.
…
Taxol, citronella, rubber, turpentine, rosin
and amber
…
Phenolics (flavonoids and related
compounds)
…
…
…
…
Alkaloids
…
Some flower and fruit colors
Flavors cinnamon, nutmeg, ginger, clove,
chilies, vanilla
Prevent UV damage
Some are antioxidants
Contain nitrogen
Potent effects on
animal nervous
system
Caffeine nicotine,
Caffeine,
nicotine
morphine,
ephedrine,
cocaine, and
codeine
Alkaloid
O
H3C
CH3
N
N
H
O
N
N
CH3
Caffeine
(c) Caffeine produced by Coffea
arabica is an example of an alkaloid.
37
38
39
10