8/28/2011
Transition to Land &
Life Cycles
y
What does it mean to be a plant?
Lecture 1
Background
•
•
•
•
•
Descendants of charophytan green algae
Photosynthesis
Modular growth (mitosis & apices)
Sexual Reproduction in Eukaryotes
Three basic life cycles
Plants from Algae
1
8/28/2011
Chlorophytes never made it Charophytes did
to land
Volvox
-Colonial chlorophyte
-Hollow sphere of
a single
i l llayer off
500-60,000 cells
-A few cells are
specialized for
reproduction
2
8/28/2011
Charophytes
Charales (300 species)
-Macroscopic
-Plant-like plasmodesmata
-Sister
S
clade to land plants
Choleocaetales (30 species)
-Microscopic
-Plant-like mitosis
-Next closest plant relatives
Charophytes (Cont.)
Bryophytes
Bryophytes are the closest living
descendants of the first land plants.
-Called nontracheophytes because they
lack tracheids (specialized transport cells)
Simple, but highly adapted to diverse
terrestrial environments.
3
8/28/2011
Photosynthesis
• Complete and balanced equation:
3CO2 + 6H2O
Light
C3H6O3 + 3O2 + 3H2O
Occurs in two stages:
Light & Dark Reactions
4
8/28/2011
Primary Photosynthetic Pigments
• Pigments absorb light
• Chlorophyll makes leaves green, absorbs
light in the visible spectrum.
• Reflects
R fl t green lilight
ht
– Therefore appears green
Primary Pigments
• Chlorophyll a
– All photosynthetic eukaryotes & cyanobacteria
• Chlorophyll b
– Plants,
Plants green algae
algae, & euglenoid algae
– Accessory pigment (not directly involved in
photosynthetic energy transduction)
– Broadens the range of light for photosynthesis
• Chlorophyll c
– Takes place of chlorophyll b in some algae
5
8/28/2011
Chlorophyll a
CHO
Chlorophyll b
Two other pigments
• Carotenoids (anti-oxidants protecting
chlorophyll)
– Red, orange, or yellow lipid-soluble pigments
• Found in chloroplasts & cyanobacteria
• Hydrophobic
• Two groups
– Carotenes & Xanthophylls
• Carotenoids break down giving rise to….?
6
8/28/2011
http://rawsilkandsaffron.files.wordpress.com/2010/10/fall_colors.jpg
• Phycobilins
– Found in cyanobacteria & chloroplasts of red
algae
– Water soluble
7
8/28/2011
Modular Growth
• Indeterminate growth
– Grow through entire life
– Add new body parts
– Repeated addition of
same basic units
• Above ground
– Bud-stem-leaf units
• Below ground
– New lateral roots
Primary Growth
• Plants increase in length by primary growth.
• Meristems
– Group of young, undifferentiated cells
– Give rise to new cells
• Apical
A i l meristem
i t
– Increase in length
• Shoot apical meristem
• Root apical meristem
• Cell division results in two cell populations
– Remain undifferentiated meristematic cells
– Rapidly dividing new growth descendent cells
8
8/28/2011
Eukaryotic Reproduction
Life Cycles 2
Sexual Reproduction
• Alternation between meiosis & fertilization
• Meiosis = Reduction from 2n – n.
• Fertilization = n + n = 2n
Meiosis
9
8/28/2011
Steps in meiosis
• Prophase I: Chromosomes come together, pairs
coil, become shorter.
• Metaphase I: Move to metaphase plate.
• Anaphase I: Paired chromosomes move to
opposite
pp
p
poles.
• Metaphase II: Chromosomes lined up at the
equatorial plane.
• Anaphase II: Centromeres separate, move toward
opposite poles of spindles.
• Telophase II: Completed migration. Four new
haploid nuclei are formed.
• Meiosis differs from Mitosis in 3 ways.
1. Two nuclear divisions in meiosis. In both
DNA only replicated once.
2 Nuclei produced in meiosis is haploid (1/2
2.
the number of chromosome).
3. Meiosis results in different gene
combinations.
10
8/28/2011
Inheritance
• Allele
– Alternative form of a gene.
– Occupy same site on homologous
chromosomes (locus)
(locus).
Gregor Mendel
11
8/28/2011
12
8/28/2011
Plant Life Cycles
Lecture III
Life Cycles
• Three types
1. Gametic meiosis
2. Zygotic meiosis
3 Sporic meiosis
3.
Gametic life cycle
• Animal kingdom (some protists & algae)
– The gamete is the only haploid cell produced.
2n
multicelled
meiosis
1n
gamete
fertilization
2n
zygote
mitosis
2n
multicelled
13
8/28/2011
Zygotic life cycle
• Fungi Kingdom
– The zygote is the only diploid cell produced
1n
multicelled
mitosis
1n
gamete
fertilization
2n
zygote
meiosis
1n
spore
mitosis
1n
14
8/28/2011
Allomyces arbusculus
Rhizopus stolonifer, Zygomycete
Ascomycetes
15
8/28/2011
Basidiomycota
Sporic life cycle
• Plant Kingdom
– Alternation of generations (plants, many
algae)
• Gametophyte = haploid
haploid, gamete-producing
gamete producing
generation.
• Sporophyte = diploid, spore-producing
generation.
2n
sporophyte
meiosis
1n
spore
fertilization
mitosis
1n
1n
2n
gamete
gametophyte
zygote
mitosis
mitosis
16
8/28/2011
Bryophytes
Pterophytes
Gymnosperms
17
8/28/2011
Angiosperms
18