Transcript PLANT DIVERSITY II: THE EVOLUTION OF SEED PLANTS

PLANT DIVERSITY II: THE
EVOLUTION OF SEED PLANTS
CHAPTER 30
Dates for plant group origins:
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•
•
Mosses 500-475
Ferns 420
Gymnosperms 360
Angiosperms 140
Overview of Seed Plant
Evolution
• Reduction of the gametophyte
– Male gametophyte becomes pollen grains
– Female develops inside the ovule
• Gymnosperms
– use seeds to disperse offspring
– Use pollen for fertilization eliminating the
need for water for fertilization
• Angiosperms
– Dispersed seeds inside fruits
– evolved flowers to attract pollinators
Origins
• Angiosperms and Gymnosperms
evolved from the progymnosperms
– Origins of seeds at about 360 MYA
– More suited to a drier climate forming
on land at the time
• Angiosperms with flowers & fruits
form much later around 140 MYA
• gymnosperms
are in four
divisions
• angiosperms are
all in one division
• both are
monophyletic
groups
Gametophyte reduction
Gametophyte/sporophyte
Sporophyte
(2n)
Sporophyte
(2n)
Gametophyte
(n)
(a) Sporophyte dependent
on gametophyte
(mosses and other
bryophytes).
Gametophyte
(n)
(b) Large sporophyte and
small, independent
gametophyte (ferns
and other seedless
vascular plants).
Microscopic female
gametophytes (n) in
ovulate cones
(dependent)
Microscopic male
gametophytes (n)
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
in pollen cones
(dependent)
Sporophyte (2n)
(independent)
(c) Reduced gametophyte dependent on sporophyte
(seed plants: gymnosperms and angiosperms).
Microscopic female
gametophytes (n)
inside these parts
of flowers
(dependent)
Sporophyte (2n),
the flowering plant
(independent)
Retention of gametophyte
• Evolution has not eliminated gametophyte
• Gametophyte may provide a mechanism
for “screening” new alleles
• All sporophyte embryos are dependent, at
least to some extent, on tissues of the
female gametophyte.
Heterosporous
• Makes two different types of
sporangia.
• Megasporangia give rise to ovules,
which are retained in the sporophyte
• Microsporangia give rise to pollen
Unnumbered figure page 586
Homosporous spore production
Sporangium
in sporophyll
Single
type of spore
Typically a
bisexual
gametophyte
Eggs
Sperm
Heterosporous spore production
Megasporangium
in megasporophyll
Microsporangium
in microsporophyll
Megaspore
Female
gametophyte
Eggs
Microspore
Male
gametophyte
Sperm
What about Mosses???
• An ovule consists of: integuments (2n), megaspore (n), and
megasporangium.
Figure 30.3 From ovule to seed
Female
gametophyte (n)
Integument
Seed coat
(derived from
integument)
Egg nucleus (n)
Spore wall
Food supply
(female
gametophyte
tissue) (n)
Megasporangium
(2n)
Male gametophyte
(within germinating
pollen grain) (n)
Discharged
sperm nucleus (n)
Megaspore (n)
Micropyle
(a) Unfertilized ovule. In this sectional
view through the ovule of a pine
(a gymnosperm), a fleshy
megasporangium is surrounded by
a protective layer of tissue called
an integument. (Angiosperms
have two integuments.)
(b) Fertilized ovule. A megaspore
develops into a multicellular
female gametophyte. The
micropyle, the only opening
through the integument, allows
entry of a pollen grain. The
pollen grain contains a male
gametophyte, which develops
a pollen tube that discharges
sperm.
Pollen grain (n)
Embryo (2n)
(new sporophyte)
(c) Gymnosperm seed. Fertilization
initiates the transformation of
the ovule into a seed, which
consists of a sporophyte embryo,
a food supply, and a protective
seed coat derived from the
integument.
What’s new in Gymnosperms?
• Pollen
• Seeds
• Greatly reduced gametophyte
The Pine Life cycle Fig. 30.9
• The resistant seed coat is derived from the
integuments of the ovule.
• A seed may remain dormant for years
• The gymnosperms the seed is released
from the cone
• Angiosperms retain
seeds inside fruit
Pollen (Staminate) Cone:
• Produced yearly
• Short lived- die after
releasing pollen
Pollen
• are the male gametophytes
• No longer need film of water to fertilize
Ovulate cone
• very small and fleshy when young
• Forms the “Pine Cone” with seeds
– often matures over 2-3 years
Ovule
• Forms inside female (ovulate) cone
• Zygote develops into embryo, inside
nutritive female gametophyte tissue.
• Embryo goes dormant, integuments
harden and ovule now becomes a
seed
PHYLUM CYCADOPHYTA
PHYLUM GINKGOPHYTA
Cycas revoluta
PHYLUM GNETOPHYTA
Gnetum
Welwitschia
Ovulate cones
Ephedra
PHYLUM CONIFEROPHYTA
Douglas fir
Common juniper
Wollemia pine
Pacific yew
Bristlecone pine
Sequoia
A progymnosperm
What’s new in angiosperms?
•
•
•
•
Fruits
(3n) endosperm in seeds
Flowers
Fibers and Vessels
Angiosperms
•
•
•
•
•
•
•
•
•
•
Cones modified into flowers
Pollen delivered to flower by pollinator
Ovules enclosed inside an ovary
Double fertilization
Ripened ovary (with seeds inside) is the
fruit
Fruits disperse seeds
Coevolved with pollinators and disperses
Have complex xylem with fibers and
vessels.
Not more independent from water.
About 160 MYA
The flower
• Sepals
• Petals
• Stamens (male)
– Anther - pollen
– Filament
• Carpel (female)
–
–
–
–
Stigma
Style
Ovary
Ovule-eggs
• Petals attract animal pollinators
– Many flowers also have nectaries to
reward
• Stamens consists of:
– the filament– the anther
• Carpels produce female
gametophytes.
– stigma.
– style
– ovary
– ovule
Fig 38.12 Fruit development
Key
Haploid (n)
Diploid (2n)
Anther
Microsporangium
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n)
Male gametophyte
(in pollen grain)
Ovary
MEIOSIS
Megasporangium
(n)
Surviving
megaspore
(n)
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Synergids
Egg (n)
Pollen
tube
Sperm
(n)
Generative cell
Tube cell
The life cycle of an angiosperm
Key
Haploid (n)
Diploid (2n)
Anther
Microsporangium
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n)
Generative cell
Tube cell
Male gametophyte
(in pollen grain)
Ovary
Pollen
grains
MEIOSIS
Stigma
Megasporangium
(n)
Pollen
tube
Sperm
Surviving
megaspore
(n)
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Synergids
Egg (n)
Egg
nucleus (n)
Pollen
tube
Sperm
(n)
Discharged
sperm nuclei (n)
Pollen
tube
Style
The life cycle of an angiosperm
Key
Haploid (n)
Diploid (2n)
Anther
Microsporangium
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n)
Generative cell
Tube cell
Male gametophyte
(in pollen grain)
Ovary
Stigma
Megasporangium
(n)
Embryo (2n)
Endosperm
(food
supply) (3n)
Pollen
tube
Sperm
Surviving
megaspore
(n)
Seed
Seed coat (2n)
Female gametophyte
(embryo sac)
Nucleus of
developing
endosperm
(3n)
Pollen
grains
MEIOSIS
Germinating
seed
Antipodal cells
Polar nuclei
Synergids
Egg (n)
Zygote (2n)
Egg
nucleus (n)
Pollen
tube
Sperm
(n)
FERTILIZATION
Discharged
sperm nuclei (n)
Pollen
tube
Style
Figure 30.11 A primitive
flowering plant?
Carpel
Stamen
5 cm
(a) Archaefructus sinensis, a 125-million-yearold fossil.
(b) Artist’s reconstruction of
Archaefructus sinensis
Gametophyte formation Fig 38.4
Gametophyte growth
Pollen Tube growth
Double fertilization Fig 38.9
• Two sperm nuclei enter the ovule.
• One fertilizes the egg
– becomes a zygote
– develops into the embryo
• The second sperm nucleus fuses with
the (2n) polar nuclei.
– Forms a triploid (3n) nucleus, the
endosperm
– Divides by mitosis and takes over remains
of ovule forming a large multinucleate cell
mass.
– Endosperm forms before embryo develops
– Is nutritive tissue for embryo (at least
initially)
• All in one division
• Several early groups
Angiosperm
• We’ll look at two classes Diversity
– Monocots
– Eudicots
• The enclosure of seed within the ovary (the
carpel), probably evolved from a seedbearing leaf that became rolled into a tube.
Origin of the ovary (Goethe)
Fruit – Fig. 30.15
• A fruit is a mature ovary.
• As seeds develop from ovules after
fertilization, the wall of the ovary
thickens to form the fruit.
• Fruits protect dormant seeds and aid
in their dispersal.
This flower has an
ovary consisting
of a single carpel
with multiple
ovules /seeds.
• Both gymnosperms and angiosperms have
tracheids
• Angiosperms have two additional xylem cell
types:
– Fibers
– Vessels
Fig. 30.12
Pollination
Angiosperm seed formation
Angiosperm Diversity
BASAL ANGIOSPERMS
Amborella trichopoda
Star anise (Illicium
floridanum)
Water lily (Nymphaea
“Rene Gerard”)
MAGNOLIIDS
Southern magnolia (Magnolia
grandiflora)
Eudicots
Monocots
Magnoliids
Star anise
and relatives
Water lilies
Amborella
HYPOTHETICAL TREE OF FLOWERING PLANTS
MONOCOTS
EUDICOTS
Monocot
Characteristics
Orchid
(Lemboglossum
rossii)
Eudicot
Characteristics
Embryos
One cotyledon
Two cotyledons
Leaf
venation
Veins usually
parallel
Pygmy date palm
(Phoenix roebelenii)
Lily (Lilium
“Enchantment”)
California
poppy
(Eschscholzia
californica)
Pyrenean oak
(Quercus
pyrenaica)
Veins usually
netlike
Stems
Vascular tissue
usually arranged
in ring
Vascular tissue
scattered
Root
Barley (Hordeum vulgare),
a grass
Root system
Usually fibrous
(no main root)
Dog rose (Rosa canina), a wild rose
Taproot (main root)
usually present
Pollen
Pollen grain with
one opening
Pea (Lathyrus nervosus,
Lord Anson’s blue pea),
a legume
Pollen grain with
three openings
Flowers
Anther
Filament
Stigma Floral organs
usually in
Ovary multiples of three
Floral organs usually
in multiples of
four or five
Zucchini (Cucurbita
Pepo), female
(left) and male flowers
Figure 30.13 Flower-pollinator
relationships
(a) A flower pollinated by honeybees.
(b) A flower pollinated by hummingbirds.
This honeybee is harvesting pollen
The long, thin beak and tongue of this
and Nectar (a sugary solution secreted
rufous hummingbird enable the animal
by flower glands) from a Scottish
to probe flowers that secrete nectar
broom flower. The flower has a tripping
deep within floral tubes. Before the
Mechanism that arches the stamens
hummer leaves, anthers will dust its
over the bee and dusts it with pollen,
beak and head feathers with pollen.
some of which will rub off onto the
Many flowers that are pollinated by
stigma of the next flower the bee visits.
birds are red or pink, colors to which
bird eyes are especially sensitive.
(c) A flower pollinated by nocturnal animals.
Some angiosperms, such as this cactus,
depend mainly on nocturnal pollinators,
including bats. Common adaptations
of such plants include large, light-colored,
highly fragrant flowers that nighttime
pollinators can locate.
Medicines Derived from Seed
Plants
Unnumbered figure page 607
Green algae
Mosses
Fems
Gymnosperms
Angiosperms
10.
9.
8.
7.