Transcript video slide - Des Moines Area Community College, Iowa

Chapter 29
Plant Diversity I
How Plants
Colonized Land
Land Ho! The Greening of Earth
•
•
•
•
For the first 3 billion years of Earth’s history, the land was lifeless
Cyanobacteria existed on land about 1.2 billion years ago
~500 million years ago plants, fungi and animals joined them
DiversificationOver 290,00 species of plants inhabit Earth today
Plant Evolution
• Land plants evolved from green algae
• Charophyceans (a type of green algae) are the
closest relatives of land plants
Accumulation of adaptations to
the terrestrial environment
allowed the first land plants to
live permanently above the
waterline
(a) Chara,
a pond
organism
10 mm
40 µm
(b) Coleochaete orbicularis
Defining the Plant Kingdom
• Systematists
– Are currently debating the boundaries of the
plant kingdom
Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes Charophyceans Embryophytes
Ancestral alga
Derived Traits of Plants
• Five key traits appear in nearly all land
plants but are absent in the charophyceans
– Apical meristems
– Alternation of generations
– Walled spores produced in sporangia
– Multicellular gametangia (gametes produced here)
– Multicellular dependent embryos
Apical meristems and alternation of
generations
APICAL
MERISTEMS
Localized
regions of cell
division at tips
of roots and
shoots
Apical
meristem
of shoot
Developing
leaves
.
Apical meristem
of root
Shoot
100 µm
Root
100 µm
Haploid multicellular
organism (gametophyte)
Mitosis
Mitosis
n
n
n
ALTERNATION OF GENERATIONS
Spores
n
n
Gametes
Generations
Gametophyte (haploid)
Sporophyte (diploid)
MEIOSIS
FERTILIZATION
2n
2n
Zygote
Mitosis
Diploid multicellular
organism (sporophyte)
Alternation of generations: a generalized scheme
Walled spores; multicellular gametangia;
and multicellular, dependent embryos
WALLED SPORES PRODUCED IN SPORANGIA
Spores
Sporangium
Sporophyte and sporangium
of Sphagnum (a moss)
Longitudinal section of
Sphagnum sporangium
Sporophyte
Gametophyte
MULTICELLULAR GAMETANGIA
(where gametes are produced)
Female gametophyte
Archegonium
with egg
Antheridium
with sperm
Archegonia and antheridia
of Marchantia (a liverwort)
Female gametangia
(archegonia)
Male gametangia
(antheridia)
Male
gametophyte
MULTICELLULAR, DEPENDENT EMBRYOS
Land plants are also known as
EMBRYOPHYTES
Embryo retained within
tissues of female parent.
The parental tissues
provide the developing
embryo with nutrients.
Embryo
Maternal tissue
Embryo and placental
transfer cell of Marchantia
Wall ingrowths
Placental transfer cell
Fossilized spores and tissues
– Have been extracted from 475-million-yearold rocks
Fossilized spores.
Unlike the spores of
most living plants,
which are single
grains, these spores
found in Oman are
in groups of four
(left; one hidden)
and two (right).
Fossilized
sporophyte tissue.
The spores were
embedded in tissue
that appears to be
from plants.
Diversity of Modern Plants
Land plants can be
informally grouped based on
the presence or absence of
vascular tissue
An overview of land plant evolution
Land plants
Vascular plants
Angiosperms
Origin of seed plants
(about 360 mya)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Seed plants
Gymnosperms
Pterophyte
(ferns, horsetails, whisk fern)
Seedless vascular plants
Lycophytes
(club mosses, spike mosses, quillworts)
Mosses
Hornworts
Liverworts
Charophyceans
Bryophytes
(nonvascular plants)
Bryophytes
• The life cycles of mosses and other
bryophytes are dominated by the
gametophyte stage
• Bryophytes are represented today by three
phyla of small herbaceous (nonwoody)
plants
– Liverworts, phylum Hepatophyta
– Hornworts, phylum Anthocerophyta
– Mosses, phylum Bryophyta
Bryophytes…the video clip
Plant Classifications: Bryophytes." Online . Encyclopædia Britannica Online. 14 Jan. 2008 <http://www.britannica.com/eb/art-68471>.
Bryophyte Gametophytes
• In all three bryophyte phyla
– Gametophytes are larger and longer-living
than sporophytes
Moss Life Cycle…The Movie
The life cycle of a moss
Raindrop
1 Spores develop into
threadlike protonemata.
Key
Male
gametophyte
Haploid (n)
Diploid (2n)
Sperm
“Bud”
2 The haploid
protonemata
produce “buds”
that grow into
gametophytes.
Protonemata
4 A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg.
Antheridia
3 Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively.
“Bud”
Egg
Spores
Gametophore
Female
Archegonia
spores develop in the sporangium gametophyte
of the sporophyte. When the
Rhizoid
sporangium lid pops off, the
peristome “teeth” regulate
6 The sporophyte grows a
gradual release of the spores. long stalk, or seta, that emerges
Seta
from the archegonium.
8 Meiosis occurs and haploid
Peristome
Sporangium
MEIOSIS
Mature
Mature
sporophytes
sporophytes
Capsule
(sporangium)
FERTILIZATION
(within archegonium)
Calyptra
Zygote
Embryo
Foot
Archegonium
Young
sporophyte
Capsule with
peristome
Female
gametophytes
7 Attached by its foot, the
sporophyte remains nutritionally
dependent on the gametophyte.
5 The diploid zygote
develops into a
sporophyte embryo within
the archegonium.
Bryophyte gametophytes
• Bryophyte gametophytes
– Produce flagellated sperm in antheridia
– Produce ova in archegonia
– Generally form ground-hugging carpets and are
at most only a few cells thick
• Some mosses
– Have conducting tissues in the center of their
“stems” and may grow vertically
Bryophyte Sporophytes
• Bryophyte sporophytes
– Grow out of archegonia
– Are the smallest and simplest of all extant plant groups
– Consist of a foot, a seta (an elongated stalk), and a
sporangium
• Hornwort and moss sporophytes
– Have stomata (like vascular plants) (an opening for gas exchange)
Bryophyte diversity
Gametophore of
female gametophyte
LIVERWORTS (PHYLUM HEPATOPHYTA)
Plagiochila
deltoidea,
a “leafy”
liverwort
Foot
Seta
Marchantia sporophyte (LM)
HORNWORTS (PHYLUM ANTHOCEROPHYTA)
An Anthoceros
hornwort species
Sporophyte
Sporangium
500 µm
Marchantia polymorpha,
a “thalloid” liverwort
MOSSES (PHYLUM BRYOPHYTA)
Polytrichum commune,
hairy-cap moss
Sporophyte
Gametophyte
Gametophyte
Ecological and Economic Importance of
Mosses
• Sphagnum, or “peat moss”
–
–
Forms extensive deposits of partially decayed organic material known
as peat
Peatlands play an important role as carbon reservoirs an help stabilize
atmospheric carbon dioxide levels.
(a) Peat being harvested from a peat bog
(b) Closeup of Sphagnum. Note the “leafy” gametophytes
and their offspring, the sporophytes.
Gametophyte
(c) Sphagnum “leaf” (LM). The combination of living photosynthetic
cells and dead water-storing cells gives the moss its spongy quality.
(d) “Tolland Man,” a bog mummy dating from 405–100 B.C.
The acidic, oxygen-poor conditions produced by
Sphagnum can preserve human or other animal bodies
for thousands of years.
Sporangium at
tip of sporophyte
Living
photo- Dead watersynthetic storing cells
100 µm
cells
Origin and Diversity of Vascular Plants
• Ferns and other seedless vascular plants
formed the first forests
• Bryophytes and bryophyte-like plants
– Were the prevalent vegetation during the first
100 million years of plant evolution
• Vascular plants
– Began to evolve during the Carboniferous
period
– Fossils of the forerunners of vascular plants
date back about 420 million years
Seedless Vascular Plants
• These early tiny plants
– Had branching sporophytes that weren’t dependent
on gametopyhtes for growth, but lacked other derived
traits of vascular plants
Dichotomous (Y-shaped)
branching made possible
multiple sporangia. This
evolutionary development
allowed for greater spore
production.
Also increased survival in the
face of herbivory. If some
sporangia were eaten others
might survive.
Life Cycles with Dominant
Sporophytes
• In contrast with bryophytes
– Sporophytes of seedless vascular plants are
the larger generation, as in the familiar leafy
fern
– The gametophytes are tiny plants that grow
on or below the soil surface
Tracheophytes-Pterophyta (ferns)
…the video clip
fern." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 13 Jan. 2008 <http://www.britannica.com/eb/article-9110635>.
Fern Life Cycle…The Movie
The life cycle of a fern
1 Sporangia release spores.
Most fern species produce a single
type of spore that gives rise to a
bisexual gametophyte.
Key
2 The fern spore
develops into a small,
photosynthetic gametophyte.
3 Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes.
Haploid (n)
Diploid (2n)
Antheridium
Spore
MEIOSIS
Young
gametophyte
Sporangium
Archegonium
Mature
sporophyte
New
sporophyte
Sperm
Egg
Zygote
Sporangium
FERTILIZATION
Sorus
6 On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia.
Gametophyte
Fiddlehead
5 A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte.
4 Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia.
Transport in Xylem and Phloem
• Vascular plants have two types of vascular tissue
– Xylem and phloem
• Xylem
– Conducts most of the water and minerals
– Includes dead cells called tracheids. Their cell walls remain to
provide the internal ‘pipe system’.
– Cell walls are strengthened by the polymer lignin. This allows
vascular plants to grow to greater heights than bryophytes
• Phloem
– Distributes sugars, amino acids, and other organic products
– Consists of living cells
Evolution of Roots
• Roots
– Are organs that anchor vascular plants
– Enable vascular plants to absorb water and
nutrients from the soil
– May have evolved from subterranean stems
Evolution of Leaves
• Leaves
– Are organs that increase the surface area of vascular
plants, thereby capturing more solar energy for
photosynthesis
• Leaves are categorized by two types
– Microphylls, leaves with a single vein
– Megaphylls, leaves with a highly branched vascular
system
Evolution of Leaves
• According to one model of evolution
– Microphylls evolved first, as outgrowths of
stems
Vascular tissue
(a) Microphylls may have originated as small stem
outgrowths supported by single, unbranched strands
of vascular tissue.
(b) Megaphylls, which have branched vascular
systems, may have evolved by the fusion of
branched stems.
Sporophylls and Spore Variations
• Sporophylls
– Are modified leaves with
sporangia (may look like a
“photosynthetic leaf” may not)
• Most seedless vascular
plants
– Are homosporous,
producing one type of
spore that develops into a
bisexual gametophyte
– All seed plants and some
seedless vascular plants
are heterosporous, having
two types of spores that
give rise to male and
female gametophytes
Classification of Seedless
Vascular Plants
• Seedless vascular plants form two phyla
– Lycophyta, including club mosses, spike
mosses, and quillworts. Are small herbaceous
plants
– Pterophyta, including ferns, horsetails, and
whisk ferns and their relatives. Ferns are the
most diverse seedless vascular plants
Groups of seedless vascular plants
LYCOPHYTES (PHYLUM LYCOPHYTA)
Selaginella apoda,
a spike moss
Isoetes
gunnii,
a quillwort
Strobili
(clusters of
sporophylls)
Diphasiastrum tristachyum, a club moss
Psilotum
nudum,
a whisk
fern
PTEROPHYTES (PHYLUM PTEROPHYTA)
Equisetum
arvense,
field
horsetail
Vegetative stem
Athyrium
filix-femina,
lady fern
Strobilus on
fertile stem
WHISK FERNS AND RELATIVES
HORSETAILS
FERNS
Significance of Seedless Vascular Plants
• The ancestors of modern lycophytes, horsetails, and ferns grew to
great heights during the Carboniferous, forming the first forests
The growth of these early forests may have helped produce the major
global cooling that characterized the end of the Carboniferous period.
They decayed and eventually became coal