2n

1
3 Life Cycles Fig 13.6
gametophyte
mitosis
mitosis
spores
gametes
n
meiosis
syngamy
2n
zygote
sporophyte
mitosis
kelps, plants Fig 28.16
2
trends in evol of plant life cycle

• adaptation to dry environment
• reduction in size of gametophyte
• loss of antheridium, archegonium
• increase in size of sporophyte
• gametophyte retained on sporophyte

3
preview major events in plant evolution
Fig 29.7
4
Fig 29.4
what are plants?
5
share derived characters of plants charophycean
green algae

• way of making cellulose walls
• enzyme glycolate oxidase (recovery when rubisco
  grabs O2 instead of CO2)
• cell division mechanism
• sperm ultrastructure
• DNA sequences, genomic architecture

6
shared derived characters of plants are life
cycle features (alt of gen)

• 1) gametophytes producing gametes in
  multicellular gametangia
• 2) multicellular diploid embryo (young
  sporophyte) retained on parent plant
• embryo protected, nourished
• plants called embryophytes (Fig 29.4)
• 3) spores in multicellular sporangia
• sporopollenin (very resistant) in spore walls

7
origin of plant life cycle?

• Coleochaete
• retains egg and zygote
• protects and nourishes
• charophyceans have haploid life cycle (only
  zygote is diploid)

8
3 Life Cycles Fig 13.6
gametophyte
mitosis
mitosis
spores
gametes
n
meiosis
syngamy
2n
zygote
sporophyte
mitosis
kelps, plants Fig 28.16
9
hypothesis plant life cycle arose from delay in
meiosis

• zygote undergoes mitosis first
• multicellular sporophyte
• many cells undergo meiosis
• advantage on land (less water for
  fertilization)

10
life on land plenty of light, CO2 but
dessication, UV light
11
preadaptations to life on land

• 1) resistance to desiccation
• resistant compounds incl. sporopollenin (Col
  eochaete zygotes, plant spores pollen)
• 2) protection from UV light
• surface layer

12
strategies for life on land

• 1) H2O same as environment poikilohydry
• stay in wet places OR dry rehydrate
• 2) maintain internal H2O homeohydry (type of
  homeostasis)
• cuticle, stomata, lignified H20 cond. cells

13
physiology and anatomy of bryophytes

• poikilohydry
• small, attach via rhizoids
• some have water conducting cells
• but not lignified
• stomata only on sporophytes of hornworts
  mosses
• cuticle on some sporophytes, and parts of
  gametophytes (leaves, pores)

14
diversity of bryophytes

• not a clade but a grade
• 1) liverworts (leafy OR thalloid)
• 2) hornworts (horn-like sporophyte)
• 3) mosses (most obvious diverse)

15
thalloid liverwortspots are pores for gas
exchange
gemma cupsasexual reproduction
gemma cup with gemmae a single gemma
liverwort sperm release, when sprayed with
water http//www.youtube.com/watch?vALGDLzWcvnU
16
http//www.palaeos.com/Plants/Bryophyta/Bryophyta.
html
Physcomitrella patens genome moss model organism
http//moss.nibb.ac.jp/what.html
17
bryophyte life cycle

• gametophyte is prominent
• sperm require water
• sporophyte smaller, dependent
• spores dispersed by wind

18
diversification of spore dispersal in
bryophytes height facilitates dispersal gametophy
te or sporophyte may be tall
19
bryophyte ecology

• diverse habitats, especially mosses
• 1) Andreaea (habitat like early Earth)
• thick walls resist UV, store C
• 2) Sphagnum (peat moss) stores CO2
• assoc. methanotrophs CH4--gtCO2
• gardening, dead cells hold water

20
82 of Andreaea dry biomass survives acetolysis!
21
Sphagnum leaves with thin cells for PS and thick
dead cells
22
evidence of early plants

• molecular data plants est. 700 my old
• fossil evidence at least 475 mya
• Mystery where is fossil record?
• Answer microfossils
• spores
• sheets of cells (from sporangia)
• lower epidermis with rhizoids