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Transcript of The Evolution of Seed...
The Evolution of
Seed Plants
29
29 The Evolution of Seed Plants
• 29.1 How Did Seed Plants Become
Today’s Dominant Vegetation?
• 29.2 What Are the Major Groups of
Gymnosperms?
• 29.3 What Features Contributed to the
Success of the Angiosperms?
• 29.4 How Do Plants Support Our
World?
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Late in Devonian, some
plants developed
secondary growth
Thickened woody
stems of xylem
The first species with
secondary growth were
progymnosperms
seedless vascular
plants, now extinct
http://www.futura-sciences.com/uploads/tx_oxcsfutura/comprendre/d/images/600/fig_1213.jpg
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Earliest seed plants from Devonian
These seed ferns were also woody
Clades of seed ferns are known only
as fossils
Two of the clades are basal to
surviving seed plants
http://www.palaeos.com/Plants/Lists/Glossary/Images/SeedFern.jpg
Figure 29.1 The Fossil Record of Seed Plants and Some of Their
Extinct Seedless Relatives
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Surviving seed plants fall into two groups:
Gymnosperms: conifers and cycads
Angiosperms: flowering plants
Figure 29.2 The Major Groups of Living Seed Plants
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Gametophyte generation is reduced even
further than it is in ferns
Haploid gametophyte develops partly or
entirely attached to sporophyte
Nonvascular
– Mosses
Vascular,
seedless – Ferns
Vascular, seed plants
Figure 29.3 The Relationship between Sporophyte and
Gametophyte (Part 1)
Figure 29.3 The Relationship between Sporophyte and
Gametophyte (Part 2)
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Only earliest gymnosperms had swimming
sperm
Without swimming sperm, seed plants
were independent of water for sexual
reproduction
Major advantage for terrestrial lifestyle
http://www1.fccj.cc.fl.us/dbyres/pollen400_small1.jpg
Pine pollen germinating
to produce a pollen tube
that will carry the male
gamete to the egg.
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Seed plants are heterosporous
Produce two types of spores
One becomes female gametophyte, one
becomes male gametophyte
Seed plants form separate megasporangia
and microsporangia
http://bio1151.nicerweb.com/doc/c
lass/bio1151/Locked/media/ch30/
30_03OvuleToSeedA.jpg
The Seed Plants
Megaspores develop into female
(mega-)gametophytes
Retained within megasporangia
and dependent on sporophyte
Only one of the meiotic products
in megasporangium survives
Surviving haploid nucleus
produces a multicellular female
(mega-)gametophyte
Retained within megasporangium,
megagametophyte matures into
egg and is eventually fertilized
next generation (sporophyte)
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/Seed%20Plants
Seed Plant Reproduction
Sporophyte
MeiosisFertilization
Seed
MegasporesMicrospores
Megagametophyte
Microgametophyte(pollen grain)
Sperm Eggs
ZygoteDiploid (2n)
Haploid (1n)
(inside megasporangium)
MegasporangiaMicrosporangia
Contained in
parent sporophyte
The Seed Plants
Retained within
megasporangium, the
megagametophyte
develops into an egg
that is eventually
fertilized next
generation
(sporophyte)
http://herbarium.usu.edu/teaching/4420/seed.GIF
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Megasporangium is surrounded by integument made of sporophytic (2n) structures
Megasporangium and the integument together form the ovule, which develops into a seed
http://herbarium.usu.edu/teaching/4420/seed.GIF
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
In microsporangium, microspores divide mitotically to produce the male gametophyte, or pollen grain
Walls of pollen grains contain sporopollenin, the most resistant biological compound known protects pollen grain from chemicals and dehydration
Figure 29.4 Pollen Grains
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Pollination
When pollen grain lands near a female gametophyte
Pollen tubesproduced that digests way through sporophyte tissue to megagametophyte
Sperm are released from the tube, and fertilization results in a diploid zygote.
http://pix.botany.org/Setabot/abot-90-5_700.jpg
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Resulting diploid zygote
divides to produce an
embryonic sporophyte
Growth is then
suspended
Embryo enters a
dormant stage, with
the end product being
a multicellular seed
http://nosheteria.com/uploaded_images/PumpkinSeeds.jpg
Pumpkin seeds
Seed Plant Reproduction
Sporophyte
MeiosisFertilization
Seed
MegasporesMicrospores
Megagametophyte
Microgametophyte(pollen grain)
Sperm Eggs
ZygoteDiploid (2n)
Haploid (1n)
(inside megasporangium)
MegasporangiaMicrosporangia
The Seed Plants
Seed contain tissues from three generations
Seed coat (from integument) and megasporangiumdevelop from ovule tissues of diploid sporophyte parent
Within megasporangium is haploid female gametophytetissue (contains nutrients) of next generation
Third generation, the embryo,is the new diploid sporophyteis contained in the center of seed package.
2n
1n
2n
2n
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Seeds are well-protected resting stages.
May remain viable for many years,
germinating when conditions are favorable.
Seed coat protects from drying out as well
as predators.
Many seeds have adaptations for dispersal.
http://winemaking.jackkeller.net/sandburr.jpg
Common sand burr
(Cenchrus echinatus)
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
Seeds are one of the main reasons for success of
seed plants — dominant life forms in terrestrial
environments
www.utexas.edu/research/ica/metaponto/meta81www.anselm.edu/homepage/jpitocch/genbios
Dandelion
Secondary growth also
contributes to their success
Wood: proliferated xylem,
gives support and allows
plants to grow above their
competitors for sunlight
In the course of seed plant
evolution, many lost the
woody growth habit; but have
other advantages.
http://cache.eb.com/eb/image?id=72251&rendTypeId=35 http://mayhem-chaos.net/photoblog/images/pine_tree_med.jpg
29.1 How Did Seed Plants Become Today’s Dominant
Vegetation?
29.2 What Are the Major Groups of Gymnosperms?
Extant gymnosperms are probably a clade
Gymnosperm
―naked-seeded‖
ovules and seeds are not protected
by ovary or fruit tissue
http://www.conifers.org/pi/pin/lambertiana5.jpg
Pinus longaeva, Bristlecone
pine, cone and needles
Figure 29.2 The Major Groups of Living Seed Plants
Four major groups of living gymnosperms:
• Cycads: Cycadophyta—140 species
http://www.biologyreference.com/images/biol_02_img0213.jpg
29.2 What Are the Major Groups of Gymnosperms?
Four major groups of living gymnosperms:
• Ginkgos: Ginkgophyta—one living
species, Ginkgo biloba
Branch of male Ginkgo biloba with
clusters of pollen-producing
microsporophylls
Branch of female Ginkgo biloba
with leaves and ovules
29.2 What Are the Major Groups of Gymnosperms?
Four major groups of living gymnosperms:
• Gnetophytes: Gnetophyta—90 species in 3 genera
Ephedra viridis (Mormon tea or
joint fir) with cones; Arizona
29.2 What Are the Major Groups of Gymnosperms?
Four major groups of living gymnosperms:
• Conifers: Coniferophyta—600 species,
the cone bearers
http://www.nasa.gov/centers/goddard/images/content/156030main_Conifers_JPG.jpg
29.2 What Are the Major Groups of Gymnosperms?
Figure 29.6 Diversity among the Gymnosperms
All living gymnosperms except gnetophytes have only tracheids for water conduction and support
Gymnosperms were dominant during Mesozoic
Tallest gymnosperms are California coastal redwoods — over 100 m
Angiosperms have vessel elements and fibers alongside of tracheids
Tracheids and
fiber tracheids
http://www.uri.edu/cels/bio/plant_anatomy/images/47.gif
29.2 What Are the Major Groups of Gymnosperms?
29.2 What Are the Major Groups of Gymnosperms?
Gymnosperms were dominant
during the Mesozoic, until
about 65 Mya.
Today, conifers still dominate
many forests, especially at
high latitudes and altitudes.
The oldest living organism on
Earth is a bristlecone pine
that germinated about 4,800
years ago.
http://media.rd.com/rd/images/rdc/family-travel/poi/CA-poi-
ancient-bristlecone-pine-forest-af.jpg
Male and female cones contain the
reproductive structures of conifers.
Megastrobilus (female, seed-bearing Cone)
Modified stem, bearing a tight cluster of woody
scales (reduced branches)
Produces seeds
29.2 What Are the Major Groups of Gymnosperms?
Microstrobilus (male, pollen-bearing cone)
―Cone-like‖ structure
Scales are modified leaves; not woody
Microsporangia produces microspores
pollen grains (microgametophyte)
29.2 What Are the Major Groups of Gymnosperms?
Pine life cycle:
Wind carries pollen grains from microstrobilus to
megastrobilus
29.2 What Are the Major Groups of Gymnosperms?
The ovule consists of the integument, the
megasporangium inside it, and the tissue
attaching it to the maternal sporophyte
www.umanitoba.ca/Biology/lab8/images
Micropylar
end
29.2 What Are the Major Groups of Gymnosperms?
The Gymnosperms: Naked Seeds
Pollen grains enter ovule through a small opening in the integument at tip of the ovule called the micropyle
www.botany.hawaii.edu/faculty/webb/BOT201/Conifers
Pollen grains. Note the
swollen bladders
which helps them float
in air currents.
29.2 What Are the Major Groups of Gymnosperms?
Two sperm travel through pollen tube
One fertilizes egg
One degenerates
29.2 What Are the Major Groups of Gymnosperms?
Animation 29.1 Life Cycle of a Conifer
Figure 29.8 The Life Cycle of a Pine Tree
Most conifer ovules
are born on the
upper surfaces of
the cone scales
Stone pine cone with pine
nuts - note two nuts (seeds)
that develop from the ovule
under each cone scale
29.2 What Are the Major Groups of Gymnosperms?
29.2 What Are the Major Groups of Gymnosperms?
Some pine cone scales (e.g., longleaf and
slash pines) can only be opened by fire
to release the seeds
helps insure new growth after fires.
Some conifers have soft, fleshy, fruit-like tissue
around seeds (e.g., juniper and yew ―berries‖)
Animals may eat these and then disperse
the seeds in their feces.
www.bevlaw.com/imageshttp://botit.botany.wisc.edu/courses/img/bo
t/402/Reference_Images/Taxus_cuspidata
Juniper “berries”
used in gin
Yew “berries”
29.2 What Are the Major Groups of Gymnosperms?
29.3 What Features Contributed to the Success
of the Angiosperms?
Angiosperms:
―enclosed seed‖
Oldest fossils are Jurassic, 150 my old
Explosive species radiation angiosperms became dominant during Tertiary in only 60 million years
Over 250,000 species exist today
http://gpc.edu/~pgore/myphotos/fossils/angiosperm-leaf.jpg
29.3 What Features Contributed to the Success
of the Angiosperms?
Extreme of evolutionary trends in vascular plants:
Sporophyte generation becomes larger,
gametophyte become smaller
Female gametophyte even more reduced —
usually only seven cells
Synapomorphies (shared, derived traits) in angiosperms:
Double fertilization
Triploid endosperm – nutritive tissue in seeds
Ovules and seeds enclosed in a carpel
Flowers
Fruits
Xylem with vessel elements and fibers
Phloem with companion cells
http://www.gallerym.com/images/work/big/schatz_howard_Botanica-%20Orchid%20Phala%20001_L.jpg
Phalaenopsis Orchid
29.3 What Features Contributed to the Success
of the Angiosperms?
Double fertilization:
Microgametophyte has two male gametes
One nucleus combines with egg
Second nucleus combines with two haploid nuclei of female gametophyte to form triploid nucleus endosperm (3n)
Endosperm nourishes developing sporophyte
http://www.lclark.edu/~seavey/images%20/carpel.jpg
29.3 What Features Contributed to the Success
of the Angiosperms?
Angiosperm (―enclosed seed‖)
Ovules and seeds are enclosed in a modified leaf called a carpel
Carpels provide protection
May interact with pollen to prevent self-pollination
Angiosperms also produce flowers and fruits
29.3 What Features Contributed to the Success
of the Angiosperms?
Xylem contains vessel elements
specialized for water transport
Figure 7. Longitudinal section of the stem showing
primary and secondary xylem.
Figure 8. Detail of Fig. 7 showing vessel element
with oblique perforation plate (pp) and scalariform
pitting (sp) pattern.
Figure 9. Detail of Fig. 7 showing helically thickened
walls (ht) of the smaller vessel elements, probably of
metaxylem and xylem parenchyma (pa).
http://lifesciences.asu.edu/plb306/t3.JPG
29.3 What Features Contributed to the Success
of the Angiosperms?
Fiber cells: important in supporting plant
body
http://student.nu.ac.th/u46410387/fiber.jpeg
29.3 What Features Contributed to the Success
of the Angiosperms?
Phloem contains
companion cells
Woody angiosperms
show secondary
growth, producing
secondary xylem and
phloem and growing
in diameter
http://www.botany.hawaii.edu/faculty/webb/Bot201/CellTissOrgan/201LabTypVascPlantTheme.htm
29.3 What Features Contributed to the Success
of the Angiosperms?
Flowers
Stamens bear
microsporangia
consist of filament
and anther
29.3 What Features Contributed to the Success
of the Angiosperms?
Flowers
Carpels bear
megasporangia
One or more
carpels form the
pistil — stigma,
style, ovary and
ovule
In this example, the
pistil is a single carpel
29.3 What Features Contributed to the Success
of the Angiosperms?
Flowers often have other specialized leaves that often play a role in attracting pollinators
Petals – inner whorl (collectively, the corolla)
Sepals – outer whorl (collectively, the calyx)
Calyx protects immature flower in bud before it opens
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.5 Pollination in an Angiosperm (Part 1)
Figure 29.5 Pollination in an Angiosperm (Part 2)
Types of flowers:
Perfect flowers
have both mega-
and microsporangia
http://leon.ifas.ufl.edu/images
Easter lily
29.3 What Features Contributed to the Success
of the Angiosperms?
Imperfect flowers
either mega or microsporangia, but not both
Begonia carpellate
(female) flower
Begonia stamenate (male) flower
www.botany.hawaii.edu/faculty/webb/BOT410/
29.3 What Features Contributed to the Success
of the Angiosperms?
Monoecious: ―one-housed‖
male and female flowers occur on the same plant or in perfect flowers
Dioecious: ―two-housed‖
male and female flowers on different plants
separate sexes
www.botany.hawaii.edu/faculty/webb/BOT410/Angiosperm
Dioecious squash
female and male
flowers
http://www.sidthomas.net/images/maize400.JPG
29.3 What Features Contributed to the Success
of the Angiosperms?
If petals and sepals are indistinguishable, they are called tepals
Inflorescence: grouping of flowers
different families have characteristic types
Magnolia flower with tepals
www.life.uiuc.edu/plantbio/digitalflowers/picts/Asclepiadaceae
Asclepias curassavica
from tropical America
http://encyclopedia.laborlawtalk.com/wiki/images
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.10 Inflorescences
Flowers of basal clades have many tepals, carpels, and stamens
Evolutionary trend toward
reduction in numbers of floral organs,
changes in symmetry, and…
fusion of parts
Basal group – magnolias
Higher group – orchids
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.11 Flower Form and Evolution
Carpels and stamens
may have evolved
from modified leaves
Carpels became
progressively more
fused and buried in
the receptacle tissue,
forming the ovary
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.12 Carpels and Stamens Evolved from Leaflike
Structures (Part 1)
Figure 29.12 Carpels and Stamens Evolved from Leaflike
Structures (Part 2)
Many flowers have long styles and filaments Natural selection favored length because it increases
likelihood of pollination — either making them more accessible to insects, or to catch the wind
Photo 29.27 Monocot flower
(daylily Hemorcallis sp.)
showing flower parts of
perianth in threes
29.3 What Features Contributed to the Success
of the Angiosperms?
Perfect flowers:
favors self-pollination, but
usually disadvantageous
many mechanisms have
evolved to circumvent this
problem
bush monkeyflower is
constructed so that two
different hummingbirds must
participate in pollination
http://www.dkimages.com/discover/previews/931/50375608.JPG
Mimulus aurantiacus,
bush monkeyflower
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.13 An Unusual Solution to Selfing
Figure 29.14 Stigma Behavior in Mimulus Flowers (Part 1)
Figure 29.14 Stigma Behavior in Mimulus Flowers (Part 2)
Most angiosperms are animal-pollinated by insects, birds, and bats Many flowers entice
pollinators with nectar and pollen
Plants and their pollinators have coevolved
Some relationships are very specific—e.g., one species of moth pollinates one species of yucca plant.
http://bobklips.com/BOBS_WEBSITE/ILF-
YUCCFILAlaying.jpg
29.3 What Features Contributed to the Success
of the Angiosperms?
Other pollinators are much
less specific, but even these
have some specialization
Bird-pollinated flowers are
often red and odorless.
Many insect-pollinated
flowers have characteristic
odors, and bee-pollinated
flowers may have
conspicuous markings, or
nectar guides, that may be
visible only to bees with UV
lightFlowers under sunlight and
UV, showing nectar guides
29.3 What Features Contributed to the Success
of the Angiosperms?
Angiosperm life cycle:
Zygote develops into an embryo
consists of embryonic axis (will become stem and root), and 1 or 2 cotyledons —seed leaves
Cotyledons absorb and digest endosperm, some become photosynthetic
www.botany.hawaii.edu/faculty/webb/Bot201/Angiosperm/MagnoliophytaLab99
Shepherd's Purse
(Capsella) Embryo, a dicot
cotyledons
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.14 The Life Cycle of an Angiosperm
Animation 29.2 Life Cycle of an Angiosperm
Ovary and seeds develop into fruits
Fruit protects seed and aids in dispersal,
(e.g., can become attached to or eaten
by animals)
http://www.hickerphoto.com/data/media/152/kiwi-fruit_3629.jpg
29.3 What Features Contributed to the Success
of the Angiosperms?
Types of fruits:
Simple fruits develop from one carpel
Aggregate fruits develop from several
carpels
Simple fruits – cherries
Aggregate fruits –
raspberries
29.3 What Features Contributed to the Success
of the Angiosperms?
Multiple fruits form from a cluster of flowers
Accessory fruits develop from parts other than carpels
Multiple fruits –
pineapple
Accessory fruits –
strawberries
http://www.botany.hawaii.edu/faculty/webb/BOT201/Angiosperm/Frui
ts/PineappleYoung240.jpg
Pineapple
flowers
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.15 Fruits Come in Many Forms and Flavors
Most angiosperms are in two major clades: Monocots
One cotyledon
Grasses, cattails, orchids, palms
Eudicots (dicots)
Two cotyledons
Majority of familiar flowering plants, most herbs, trees, shrubs
Other clades include star anise and relatives, water lilies, and magnoliids
29.3 What Features Contributed to the Success
of the Angiosperms?
Figure 29.17 Evolutionary Relationships among the Angiosperms
• Other clades include star anise and relatives, water lilies, and magnoliids
Figure 29.18 Monocots and Eudicots Are Not the Only Surviving
Angiosperms
Water lilies
Star anise
Avocado
Magnoliid clade
Black pepper Dutchmean’s
pipe
Amborella
trichopoda
Figure 29.19 Monocots
Date palm
Lilies
Wheat
Monocots
Figure 29.20 Eudicots
Prickly pear
cactus
Dogwood
Catclaw Brier
Eudicots
Basal clade of angiosperms is disputed
Two leading candidates used to be the
magnolia family
New molecular data indicates it is Amborella —
a clade consisting of only one species
http://www.biosurvey.ou.edu/okwild/images/Magnolia2.jpg
29.3 What Features Contributed to the Success
of the Angiosperms?
Magnolia
grandiflora
29.4 How Do Plants Support Our World?
Plants contribute to ecosystem services:
processes by which environment
maintains resources that benefit humans
Plants are primary producers:
photosynthesis traps energy and
carbon, making them available for their
own needs and for herbivores and
omnivores that consume them, and for
the whole food chain
29.4 How Do Plants Support Our World?
Plants produce O2 and remove CO2 from
the atmosphere
Contribute to soil formation and soil
fertility
Roots hold soil in place, preventing
erosion
Moderate local climate by increasing
humidity, providing shade, and blocking
wind.
Seed plants are our
primary food source
Twelve are most
important: rice,
coconut, wheat, corn,
potato, sweet potato,
cassava, sugarcane,
sugar beet, soybean,
common bean,
banana
http://scienceafrica.com/cms/wp-content/uploads/2010/06/cassava-ethanol.jpg
29.4 How Do Plants Support Our World?
http://3.bp.blogspot.com/_vhhw--
dmXBE/SEKkOrSMjVI/AAAAAAAAAtw/E-
3uz7yigtU/s400/biopact_cassava_biofuels.jpg
Cassava root is
an important
food in Africa
29.4 How Do Plants Support Our World?
Half the world’s
population gets most of
its food energy from
rice (Oryza sativa)
Rice been cultivated
for more than 8,000
years
http://www.equita.qc.ca/images/produits/gn_008.jpg
The coconut palm (Cocos nucifera) is
called the ―Tree of Life.‖
Every above-ground part is used.
http://www.uni-graz.at/~katzer/pictures/coco_12.jpghttp://www.pacsoa.org.au/palms/Cocos/nucifera.jpg
29.4 How Do Plants Support Our World?
Figure 29.20 The Tree of Life
Many medicines come from
seed plants
Medicines are found by
screening large numbers
of plants, or screening
large numbers of
chemical compounds
Ethnobotanists also
discover medicinal plants
by studying people and
their uses of plants all
over the worldhttp://www.mountainvalleycenter.com/store/images/cherheal.JPG
29.4 How Do Plants Support Our World?
29.4 How Do Plants Support Our World?
Extracts of Pacific yew bark (Taxus brevifolia)
showed antitumor activity in rodents
Taxol was isolated, tested, and approved for use
in treating several types of cancer.
http://www.freewebs.com/dicentra/Pacific%20Yew2.jpghttp://www.cas.vanderbilt.edu/bioimages/t/wta
br2-cofemale42577.jpg
29.4 How Do Plants Support Our World?
29.4 How Do Plants Support Our World?
Spanish priests in
Peru saw native
people used bark of
Cinchona trees to
treat fevers
The active ingredient,
quinine, was identified
in 1820, and was used
to treat malaria
Quinine is found in
tonic water
http://www.botanical.com/botanical/mgmh/c/calisa08-l.jpg
http://www.wellsj.com/library/images/uv/quinine.jpg