Transcript The Seed Plants

29
Chapter 29 - Sadava
The Evolution of
Seed Plants
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
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
Surviving seed plants fall into two
groups:
– Gymnosperms: conifers and cycads
– Angiosperms: flowering plants
Gametophyte generation is reduced even
further than it is in ferns
– Haploid gametophyte develops partly or
entirely attached to sporophyte
Vascular,
Nonvascular seedless – Ferns
– Mosses
Vascular, seed plants
Seed plants are heterosporous
– Produce two types of spores
• One becomes female gametophyte, one
becomes male gametophyte
• Seed plants form separate
megasporangia (female) and
microsporangia (male)
http://bio1151.nicerweb.com/doc/c
lass/bio1151/Locked/media/ch30/
30_03OvuleToSeedA.jpg
The Seed Plants - Megasporangium
• Megasporangium
• Contains the
megagametophyte
• develops into an egg
that is eventually
fertilized  next
generation
(sporophyte)
• Surrounded by
integument made up of
sporophyte structures
• Megasporangium and
integument together
form ovule
• Will become seed
after fertilization
http://herbarium.usu.edu/teaching/4420/seed.GIF
Seed Plants - Microsporangium
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
Pollination
– When pollen grain
lands near a female
gametophyte
– Pollen tubes are
produced 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
After Pollination
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
Pumpkin seeds
http://nosheteria.com/uploaded_images/PumpkinSeeds.jpg
Seed
Seed contain tissues from three
generations
• Seed coat (from integument)
and megasporangium develop
from ovule tissues of diploid
sporophyte parent
• 2n outside
• Within megasporangium is
haploid female gametophyte
tissue, contains nutrients for
next generation
• 1n
• Third generation, the embryo, is
the new diploid sporophyte is
contained in the center of seed
package.
• 2n inside – new generation
Seeds
• 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.
Besides seeds,
secondary growth
also contributes to
success of seed
plants
– Wood: proliferated
xylem, gives support
and allows plants to
grow above their
competitors for
sunlight
http://cache.eb.com/eb/image?id=72251&rendTypeId=35
http://mayhem-chaos.net/photoblog/images/pine_tree_med.jpg
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
Gymnosperms
– Gymnosperm
• “naked-seeded”
• ovules and seeds are not protected by ovary
or fruit tissue
Pinus longaeva, Bristlecone
pine, cone and needles
http://www.conifers.org/pi/pin/lambertiana5.jpg
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
Gymnosperms
Four major groups of living gymnosperms:
• Cycads: Cycadophyta
http://www.biologyreference.com/images/biol_02_img0213.jpg
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
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
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
Gymnosperms
Four major groups of living gymnosperms:
• Gnetophytes: Gnetophyta
Ephedra viridis (Mormon tea or
joint fir) with cones; Arizona
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
Gymnosperms
Four major groups of living gymnosperms:
• Conifers: Coniferophyta— the cone
bearers
http://www.nasa.gov/centers/goddard/images/content/156030main_Conifers_JPG.jpg
• All living gymnosperms
except gnetophytes
have only tracheids for
water conduction and
support
Tracheids and
fiber tracheids
• Gymnosperms were
dominant during
Mesozoic
• Tallest gymnosperms are
California coastal
redwoods
• over 100 m
• Angiosperms have vessel
elements and fibers
alongside of tracheids http://www.uri.edu/cels/bio/plant_anatomy/images/47.gif
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-poiancient-bristlecone-pine-forest-af.jpg
Gymnosperms
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
– Microstrobilus (male, pollen-bearing cone)
• “Cone-like” structure
• Scales are modified leaves; not woody
• Microsporangia produces microspores  pollen grains
(microgametophyte)
Gymnosperms
Pine life cycle:
– Wind carries pollen grains from microstrobilus
to megastrobilus
The Gymnosperms: Naked Seeds
• Pollen grains enter ovule through a small
opening in the integument at tip of the
ovule called the micropyle
• 2 sperm enter
• 1 fertilizes
• 1 degenerates
Pollen grains. Note the swollen bladders
which helps them float in air currents.
www.botany.hawaii.edu/faculty/webb/BOT201/Conifers
Gymnosperms
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
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.
• Not true fruits
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
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
Extreme of evolutionary trends in vascular
plants:
– Sporophyte generation becomes larger,
gametophyte become smaller
– Female gametophyte even more reduced —
usually only seven cells
Angiosperms
• 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
Phalaenopsis Orchid
http://www.gallerym.com/images/work/big/schatz_howard_Botanica-%20Orchid%20Phala%20001_L.jpg
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
(embryo)
http://www.lclark.edu/~seavey/images%20/carpel.jpg
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 selfpollination
– Angiosperms also produce
flowers and fruits
– Fiber cells: important in supporting plant
body (associated with xylem)
http://student.nu.ac.th/u46410387/fiber.jpeg
Angiosperms
Flowers
– Stamens bear
microsporangia
• Male
• consist of filament
and anther
Angiosperms
Flowers
– Carpels bear
megasporangia
• Female
• One or more
carpels form the
pistil — stigma,
style, ovary and
ovule
In this example, the
pistil is a single carpel
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
Angiosperms – Perfect and Imperfect Flowers
Types of flowers:
– Perfect flowers
• have both mega- and
microsporangia
– Imperfect flowers
• either mega or
microsporangia, but
not both
http://leon.ifas.ufl.edu/images
– 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
• Have to have imperfect flowers
• 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
Mimulus aurantiacus, bush monkeyflower
http://www.dkimages.com/discover/previews/931/50375608.JPG
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
Figure 29.14 The Life Cycle of an Angiosperm
Angiosperms - Fruit
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
Angiosperms - Fruit
Types of fruits:
– Simple fruits develop from one carpel
• Plums, cherries
– Aggregate fruits develop from several carpels on
same flower
• raspberries
– Multiple fruits form from a cluster of flowers
• pineapples
– Accessory fruits develop from parts other than
carpels
• Apples, pears, strawberries
http://www.youtube.com/watch?v=bwCpQflmQG4
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
cotyledons
www.botany.hawaii.edu/faculty/webb/Bot201/Angiosperm/MagnoliophytaLab99
Embryophytes
Vascular Plants
Euphyllophytes (“True Leaves”)
Seed Plants
Angiosperms
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
Monocots and Eudicots Are Not the Only Surviving Angiosperms
Water lilies
Amborella
trichopoda
Black pepper
Star anise
Dutchmean’s
pipe
Avocado
Magnoliid clade
Monocots
Lilies
Wheat
Date palm
Eudicots
Prickly pear
cactus
Catclaw Brier
Dogwood
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
– 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://3.bp.blogspot.com/_vhhw-dmXBE/SEKkOrSMjVI/AAAAAAAAAtw/E3uz7yigtU/s400/biopact_cassava_biofuels.jpg
Cassava root is
an important
food in Africa
http://scienceafrica.com/cms/wp-content/uploads/2010/06/cassava-ethanol.jpg
– 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
Many medicines come from
seed plants
– Medicines are found by
screening large numbers
of plants, or screening
large numbers of
chemical compounds
http://www.mountainvalleycenter.com/store/images/cherheal.JPG