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Chapter 38
Angiosperm Reproduction
Angiosperms have 3 unique Features:
1.
2.
3.
Flowers
Fruits
Double
Fertilization
(by 2 sperm)
REPRODUCTIVE VARIATIONS

Pollination: transfer pollen from anther to
stigma
Some plants are self-pollinated
 Cross-pollinated plants:
◦ Self-incompatibility: plant rejects own pollen or
closely related plant
◦ Maximize genetic variation

Stigma
Stigma
Anther
with
pollen
Pin flower
Thrum flower
“Pin” and “thrum” flower types reduce self-fertilization
The development of a plant embryo
Fruit
Egg cell  plant embryo
 Ovules inside ovary  seeds
 Ripe ovary  fruit
 Fruit protects enclosed seed(s)
 Aids in dispersal by water, wind, or animals

Types of Fruit
Seeds
Mature seed  dormancy (resting)
◦ Low metabolic rate
◦ Growth & development suspended
◦ Resumes growth when environmental
conditions suitable for germination
Germination
Seed take up water (imbibition)  trigger
metabolic changes to begin growth

◦

Root develops  shoot emerges  leaves expand
& turn green (photosynthesis)
Very hazardous for plants due to vulnerability
 Predators, parasites, wind
Plant Reproduction
Sexual
Asexual
(Vegetative Reproduction)
Flower  Seeds
Runners, bulbs, grafts, cuttings
vegetative (grass), fragmentation,
test-tube cloning
Genetic diversity
Clones
More complex & hazardous for
seedlings
Simpler (no pollinator needed)
Advantage in unstable
environments
Suited for stable environments
Asexual
reproduction in
aspen trees
Test-tube cloning
of carrots
Humans Modify Crops
Artificial selection of plants for breeding
 Plant Biotechnology:
◦ Genetically modified organisms
 “Golden Rice”: engineered to produce betacarotene (Vit. A)
 Bt corn: transgenic – expresses Bt (bacteria)
gene  produces protein toxic to insects
◦ Biofuels – reduce CO2 emissions
 Biodiesel: vegetable oils
 Bioethanol: convert cellulose into ethanol

Chapter 39
Plant Responses to Internal and External Signals
Experiments with Light and the coleoptile
Conclusion: Tip of coleoptile senses light  some signal
was sent from tip to elongating region of coleoptile
Excised tip placed
on agar block
Cells on darker side
elongate faster than
cells on brighter side
AUXIN = chemical
messenger that
stimulates cell
elongation
Growth-promoting
chemical diffuses
into agar block
Control
(agar block
lacking
chemical)
has no
effect
Control
Agar block
with chemical
stimulates growth
Offset blocks
cause curvature
Hormones: chemical messengers that coordinate
different parts of a multicellular organism
Important plant hormones:
1. Auxin – stimulate cell elongation  phototropism &
gravitropism (high concentrations = herbicide)
2. Cytokinins – cell division (cytokinesis) &
differentiation
3. Gibberellins – stem elongation, leaf growth,
germination, flowering, fruit development
4. Abscisic Acid – slows growth; closes stomata during
H2O stress; promote dormancy
5. Ethylene – promote fruit ripening (positive feedback!);
involved in apoptosis (shed leaves, death of annuals)
The effects of gibberellin on stem elongation
and fruit growth
Ethylene Gas: Fruit Ripening
Canister of ethylene gas to ripen
bananas in shipping container
Untreated tomatoes vs. Ethylene
treatment
Plant Movement
1.
Tropisms: growth responses  SLOW
 Phototropism – light (auxin)
 Gravitropism – gravity (auxin)
 Thigmotropism – touch
2.
Turgor movement: allow plant to make
relatively rapid & reversible responses
 Venus fly trap, mimosa leaves, “sleep”
movement
Positive gravitropism in roots: the statolith
hypothesis.
Thigmotropism: rapid turgor movements by
Mimosa plant  action potentials
Plant Responses to Light
Plants can detect direction, intensity, &
wavelenth of light
 Phytochromes: light receptors, absorbs mostly
red light

◦ Regulate seed germination, shade avoidance
Biological Clocks
Circadian rhythm: biological clocks
 Persist w/o environmental cues
 Frequency = 24 hours
Phytochrome system + Biological clock =
plant can determine time of year based on
amount of light/darkness
Photoperiodism: physiological response
to the relative length of night & day (i.e.
flowering)
Short-day plants: flower when nights are
long (mums, poinsettia)
 Long-day plant: flower when nights are
short (spinach, iris, veggies)
 Day-neutral plant: unaffected by
photoperiod (tomatoes, rice, dandelions)

Night length is a critical factor!
How does
interrupting the
dark period with
a brief exposure
to light affect
flowering?
Plant responses to stress
1.
Drought (H2O deficit):
 close stoma
 release abscisic acid to keep stoma closed
 Inhibit growth
 roll leaves  reduce SA & transpiration
 deeper roots
2.
Flooding (O2 deprivation):
 release ethylene  root cell death  air tubes
formed to provide O2 to submerged roots
3.
Excess Salt:
 cell membrane – impede salt uptake
 produce solutes to ↓ψ - retain H2O
4.
Heat:
 evap. cooling via transpiration
 heat shock proteins – prevent denaturation
5.
Cold:
 alter lipid composition of membrane (↑unsat.
fatty acids, ↑fluidity)
 increase cytoplasmic solutes
 antifreeze proteins
6.
Herbivores:
 physical (thorns)
 chemicals (garlic, mint)
 recruit predatory animals (parasitoid wasps)
7.
Pathogens:
 1st line of defense = epidermis
 2nd line = pathogen recognition, host-specific