Angiosperm Reproduction

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Chapter 38

• Angiosperm Reproduction

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Angiosperms have 3 unique Features

1. Flowers
2. Fruits
3. Double Fertilization (by 2 sperm)

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REPRODUCTIVE VARIATIONS
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• Pollination transfer pollen from anther to stigma

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• Some plants are self-pollinated
• Cross-pollinated plants
• Self-incompatibility plant rejects own pollen or
  closely related plant
• Maximize genetic variation

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The development of a plant embryo
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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

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Seeds

• Mature seed ? dormancy (resting)
• Low metabolic rate
• Growth development suspended
• Resumes growth when environmental conditions
  suitable for germination

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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

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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
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Asexual reproduction in aspen trees
Test-tube cloning of carrots
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Humans Modify Crops

• Artificial selection of plants for breeding
• Plant Biotechnology
• Genetically modified organisms
• Golden Rice engineered to produce
  beta-carotene (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

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Chapter 39

• Plant Responses to Internal and External Signals

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Experiments with Light and the coleoptile
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Cells on darker side elongate faster than cells
on brighter sideAUXIN chemical messenger that
stimulates cell elongation
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• Important plant hormones
• Auxin stimulate cell elongation ? phototropism
  gravitropism (high concentrations herbicide)
• Cytokinins cell division (cytokinesis)
  differentiation
• Gibberellins stem elongation, leaf growth,
  germination, flowering, fruit development
• Abscisic Acid slows growth closes stomata
  during H2O stress promote dormancy
• Ethylene promote fruit ripening (positive
  feedback!) involved in apoptosis (shed leaves,
  death of annuals)

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The effects of gibberellin on stem elongation and
fruit growth
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Ethylene Gas Fruit Ripening
Canister of ethylene gas to ripen bananas in
shipping container
Untreated tomatoes vs. Ethylene treatment
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Plant Movement

• Tropisms growth responses ? SLOW
• Phototropism light (auxin)
• Gravitropism gravity (auxin)
• Thigmotropism touch
• Turgor movement allow plant to make relatively
  rapid reversible responses
• Venus fly trap, mimosa leaves, sleep movement

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Positive gravitropism in roots the statolith
hypothesis.
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Thigmotropism rapid turgor movements by Mimosa
plant ? action potentials
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Plant Responses to Light

• Plants can detect direction, intensity,
  wavelenth of light
• Phytochromes light receptors, absorbs mostly red
  light
• Regulate seed germination, shade avoidance

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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

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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)

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How does interrupting the dark period with a
brief exposure to light affect flowering?
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Plant responses to stress
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• Drought (H2O deficit)
• close stoma
• release abscisic acid to keep stoma closed
• Inhibit growth
• roll leaves ? reduce SA transpiration
• deeper roots
• Flooding (O2 deprivation)
• release ethylene ? root cell death ? air tubes
  formed to provide O2 to submerged roots

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• Excess Salt
• cell membrane impede salt uptake
• produce solutes to ?? - retain H2O
• Heat
• evap. cooling via transpiration
• heat shock proteins prevent denaturation
• Cold
• alter lipid composition of membrane (?unsat.
  fatty acids, ?fluidity)
• increase cytoplasmic solutes
• antifreeze proteins

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• Herbivores
• physical (thorns)
• chemicals (garlic, mint)
• recruit predatory animals (parasitoid wasps)
• Pathogens
• 1st line of defense epidermis
• 2nd line pathogen recognition, host-specific