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Transcript
CHAPTER 30
LECTURE
SLIDES
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Overview of Green Plants
Chapter 30
Defining Plants
• All green algae and the land plants shared
a common ancestor a little over 1 BYA
– Kingdom Viridiplantae
– Not all photoautotrophs are plants
• Red and brown algae excluded
• A single species of freshwater green algae
gave rise to the entire terrestrial plant
lineage
3
• The green algae split into two major
clades
– Chlorophytes – Never made it to land
– Charophytes – Did – sister to all land plants
• Land plants…
– Have multicellular haploid and diploid stages
– Trend toward more diploid embryo protection
– Trend toward smaller haploid stage
4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Green plants
Streptophyta
Land plants
Bryophytes
Tracheophytes
Euphyllophytes
Red Algae
Green algae
Green algae
Chlorophytes
Charophytes
Seed plants
Liverworts
Mosses
Hornworts
Lycophytes
Ferns + Allies
Gymnosperms
Angiosperms
Ancestral alga
5
• Adaptations to terrestrial life
– Protection from desiccation
• Waxy cuticle and stomata
– Moving water using tracheids
• Tracheophytes have tracheids
– Xylem and phloem to conduct water and food
– Dealing with UV radiation caused mutations
• Shift to a dominant diploid generation
– Haplodiplontic life cycle
• Mulitcellular haploid and diploid life stages
• Humans are diplontic
6
Haplodiplontic Life Cycle
• Multicellular diploid stage – sporophyte
– Produces haploid spores by meiosis
– Diploid spore mother cells (sporocytes) undergo
meiosis in sporangia
• Produce 4 haploid spores
• First cells of gametophyte generation
• Multicellular haploid stage – gametophyte
– Spores divide by mitosis
– Produces gametes by mitosis
– Gametes fuse to form diploid zygote
• First cell of next sporophyte generation
7
8
• All land plants are haplodiplontic
• Relative sizes of generations vary
• Moss
– Large gametophyte
– Small, dependent sporophyte
• Angiosperm
– Small, dependent gametophyte
– Large sporophyte
9
Green algae
Liverworts
Charophytes
– Chlorophytes – Gave rise to
aquatic algae
– Streptophytes – Gave rise
to land plants
• Modern chlorophytes closely
resemble land plants
Chlorophytes
• Green algae have two
distinct lineages
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
– Chloroplasts are biochemically
similar to those of the plants
10
Chlorophytes
• Early green algae probably resembled
Chlamydomonas reinhardtiii
– Individuals are microscopic
– 2 anterior flagella
– Most individuals are haploid
• Always unicellular
11
• Volvox
– Colonial chlorophyte
– Hollow sphere of a
single layer of 500–
60,000 cells
– Individual cells each
have 2 flagella
12
• Ulva
– Multicellular
chlorophyte
– Haplodiplontic life cycle
• Gametophyte and
sporophyte have
identical appearance
• No ancestral
chlorophytes gave rise
to land plants
© Dr. Diane S. Littler
13
Charophytes
• Also green algae
• Distinguished from
chlorophytes by close
phylogenetic
relationship to land
plants
• Both charophyte clades
form green mats around
the edges of freshwater
ponds and marshes
• One species must have
successfully inched its
way onto land through
adaptations to drying
14
• Charophytes have haplontic life cycles
– Evolution of diplontic embryo and haplodiplontic life
cycle occurred after move to land
• 2 candidate Charophyta clades
– Charales
– Coleochaetales
15
Bryophytes
• Closest living descendants of the first land
plants
• Called nontracheophytes because they
lack tracheids
– Do have other conducting cells
• Mycorrhizal associations important in
enhancing water uptake
– Symbiotic relationship between fungi and
plants
16
• Simple, but highly adapted to diverse terrestrial
environments
• 24,700 species in 3 clades
– Liverworts
– Mosses
– Hornworts
• Gametophyte – conspicuous and photosynthetic
– Sporophytes – small and dependent
• Require water for sexual reproduction
17
Liverworts (phylum Hepaticophyta)
• Have flattened
gametophytes with
liverlike lobes
– 80% look like mosses
• Form gametangia in
umbrella-shaped
structures
• Also undergo asexual
reproduction
18
Mosses (phylum Bryophyta)
• Gametophytes consist of small, leaflike
structures around a stemlike axis
– Not true leaves – no vascular tissue
• Anchored to substrate by rhizoids
• Multicellular gametangia form at the tips of
gametophytes
– Archegonia – Female gametangia
– Antheridia – Male gametangia
• Flagellated sperm must swim in water
19
20
Hornworts (phylum Anthocerotophyta)
•
•
•
•
Origin is puzzling – no fossils until Cretaceous
Sporophyte is photosynthetic
Sporophyte embedded in gametophyte tissue
Cells have a single large chloroplast
21
Tracheophyte Plants
• Cooksonia, the first vascular
land plant
– Appeared about 420 MYA
– Phylum Rhyniophyta
• Only a few centimeters tall
– No roots or leaves
22
Vascular tissues
• Xylem
– Conducts water and dissolved minerals upward from
the roots
• Phloem
– Conducts sucrose and hormones throughout the plant
• Enable enhanced height and size in the
tracheophytes
• Develops in sporophyte but not gametophyte
• Cuticle and stomata also found in land plants
23
Tracheophytes
• Vascular plants include seven extant phyla
grouped in three clades
1. Lycophytes (club mosses)
2. Pterophytes (ferns, whisk ferns, and horsetails)
3. Seed plants
• Gametophyte has been reduced in size relative
to the sporophyte during the evolution of
tracheophytes
• Similar reduction in multicellular gametangia has
occurred as well
24
• Stems
– Early fossils reveal stems but no roots or leaves
– Lack of roots limited early tracheophytes
• Roots
– Provide transport and support
– Lycophytes diverged before true roots appeared
• Leaves
– Increase surface area for photosynthesis
– Evolved twice
• Euphylls (true leaves) found in ferns and seed plants
• Lycophylls found in seed plants
25
• 400 million years between appearance of
vascular tissue and true leaves
• Seeds
– Highly resistant
– Contain food supply for young plant
– Lycophytes and pterophytes do not have seeds
26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chlorophytes
Charophytes
Liverworts
Mosses
Hornworts
Lycophytes
Ferns + Allies
Gymnosperms
Angiosperms
Flowers
Fruits
Seeds
Euphylls
Stems, roots, leaves
Dominant sporophyte
Vascular tissue
Stomata
Multicellular embryo
Antheridia and archegonia
Cuticle
Plasmodesmata
Chlorophyll a and b
Ancestral alga
• Fruits in the flowering plants (angiosperms) add
a layer of protection to seeds and attract animals
that assist in seed dispersal, expanding the
potential range of the species
27
Seed Plants
Ferns and Allies
Lycophytes
Lycophytes
Hornworts
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Worldwide distribution – abundant in
tropics
• Lack seeds
• Superficially resemble true mosses
• Sporophyte dominant
28
Pterophytes
• Phylogenetic
relationships among
ferns and their relatives
is still being sorted out
• Common ancestor gave
rise to 2 clades
• All form antheridia and
archegonia
• All require free water for
flagellated sperm
29
Whisk ferns
• Found in tropics
• Sporophyte consists of
evenly forking green stems
without true leaves or roots
• Some gametophytes
develop elements of
vascular tissue
– Only one known to do so
30
Horsetails
• 15 living species
• Constitute a single genus,
Equisetum
• Sporophyte consists of ribbed,
jointed photosynthetic stems
that arise from branching
rhizomes with roots at nodes
• Silica deposits in cells –
scouring rush
31
Ferns
• Most abundant group of
seedless vascular plants
– About 11,000 species
• Coal formed from forests
300 MYA
• Conspicuous sporophyte
and much smaller
gametophyte are both
photosynthetic
32
• Fern life cycle
differs from
that of a moss
• Much greater
development,
independence
, and
dominance of
the fern’s
sporophyte
• Gametophyte
lacks vascular
tissue
33
• Fern morphology
– Sporophytes have rhizomes
– Fronds (leaves) develop at the tip of the rhizome as
tightly rolled-up coils (“fiddleheads”)
34
Fern reproduction
• Produce distinctive sporangia in clusters
called sori on the back of the fronds
• Diploid spore mother cells in sporangia
produce haploid spores by meiosis
• Spores germinate into gametophyte
– Rhizoids but not true roots – no vascular
tissue
• Flagellated sperm
35
The Evolution of Seed Plants
• Seed plants first appeared 305–465 MYA
• Success attributed to evolution of seed
– Protects and provides food for embryo
– Allows the “clock to be stopped” to survive
harsh periods before germinating
– Later development of fruits enhanced
dispersal
36
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stored food
Integument
(seed coat)
Embryo
b: © Biology Media/Photo Researchers, Inc.
312 m
• Seed
– Embryo protected by integument
• An extra layer or 2 of sporophyte tissue
• Hardens into seed coat
– Megasporangium divides meiotically inside ovule to
produce haploid megaspore
– Megaspore produces egg that combines with sperm
to form zygote
– Also contain food supply for embryo
37
• Seed plants produce 2 kinds of
gametophytes
• Male gametophytes
– Pollen grains
– Dispersed by wind or a pollinator
– No need for water
• Female gametophytes
– Develop within an ovule
– Enclosed within diploid sporophyte tissue in
angiosperms
38
Angiosperms
• Plants with “naked seeds”
• There are four living groups
Gymnosperms
Gymnosperms
Ferns and Allies
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
– Coniferophytes
– Cycadophytes
– Gnetophytes
– Ginkgophytes
• All lack flowers and fruits of angiosperms
• All have ovule exposed on a scale
39
Conifers (phylum Coniferophyta)
• Most familiar gymnosperm phylum
• Pines, spruces, firs, cedars, and others
– Coastal redwood – Tallest living vascular plant
– Bristlecone pine – Oldest living tree
• Found in colder and sometimes drier
regions of the world
• Conifers are sources of important products
– Timber, paper, resin, and taxol (anti-cancer)
40
• Pines
– More than 100 species,
all in the Northern
hemisphere
– Produce tough
needlelike leaves in
clusters
– Leaves have thick
cuticle and recessed
stomata to retard water
loss
– Leaves have canals with
resin to deter insect and
fungal attacks
41
• Pine reproduction
• Male gametophytes (pollen grains)
– Develop from microspores in male cones by
meiosis
• Female pine cones form on the upper
branches of the same tree
– Female cones are larger, and have woody
scales
– Two ovules develop on each scale
– Each contains a megasporangium
• Each will become a female gametophyte
42
43
• Female cones usually take 2 or more seasons to
mature
• During the first spring, pollen grains drift down
between open scales
– Pollen grains drawn down into micropyle
– Scales close
• A year later, female gametophyte matures
– Pollen tube is digesting its way through
– Mature male gametophyte has 2 sperm
• 15 months after pollination, pollen tube reaches
archegonium and discharges contents
– One sperm unites with egg = zygote
– Other sperm degenerates
44
Cycads (phylum Cycadophyta)
• Slow-growing
gymnosperms of tropical
and subtropical regions
• Sporophytes resemble
palm trees
• Female cones can weigh
45 kg
• Have largest sperm cells
of all organisms!
45
Gnetophytes (phylum Gnetophyta)
• Contain three
(unusual) genera
– Welwitschia
– Ephedra
– Gnetum
46
Ginkgophytes (phylum Ginkgophyta)
• Only one living species
remains
– Ginkgo biloba
• Flagellated sperm
• Dioecious
– Male and female
reproductive structures
form on different trees
47
Angiosperms
• Flowering plants
• Ovules are enclosed in diploid tissue at
the time of pollination
• Carpel, a modified leaf that covers seeds,
develops into fruit
48
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ovules
(seeds)
Carpel
(fruit)
Ovules
Cross section
Modified leaf
with ovules
Folding of leaf
protects ovules
Fusion of
leaf margins
(bottom right): © Goodshoot/Alamy RF
49
• Angiosperm origins are a mystery
– Origins as early as 145–208 MYA
– Oldest known angiosperm in the fossil record
is Archaefructus
– Closest living relative to the original
angiosperm is Amborella
50
51
• Flower whorls
– Outermost whorl – sepals
– Second whorl – petals
– Third whorl – stamens (androecium)
• Pollen is the male gametophyte
• Each stamen has a pollen-bearing anther and a
filament (stalk)
– Innermost whorl – gynoecium
• Consists of one or more carpels
• House the female gametophyte
52
• Carpel has 3 major regions
– Ovary – swollen base containing ovules
• Later develops into a fruit
– Stigma – tip where pollen lands
– Style – neck or stalk
53
• Embryo sac = female gametophyte
– 8 nuclei in 7 cells
– 8 haploid daughter nuclei (2 groups of 4)
• 1 from each group of 4 migrates toward center
– Functions as polar nuclei – may fuse
• Egg
– 1 cell in group closest to micropyle
– Other 2 are synergids
• Antipodals
– 3 cells at other end – no function
54
55
• Pollen production occurs in the anthers
– It is similar but less complex than female
gametophyte formation
– Diploid microspore mother cells undergo
meiosis to produce four haploid microspores
– Binucleate microspores become pollen grains
56
• Pollination
– Mechanical transfer of pollen from anther to
stigma
– May or may not be followed by fertilization
– Pollen grains develop a pollen tube that is
guided to the embryo sac
– One of the two pollen grain cells lags behind
• This generative cell divides to produce two sperm
cells
• No flagella on sperm
57
• Double fertilization
– One sperm unites with egg to form the diploid
zygote
• New sporophyte
– Other sperm unites with the two polar nuclei
to form the triploid endosperm
• Provides nutrients to embryo
• Seed may remain dormant for many years
– Germinate when conditions are favorable
58