1. Plant Growth and Responses

2. Plant Growth Types of Flowering Plants:
Annuals – 1 year life cycle
Biennials – 2 years
Perennials – continuous life cycle for many years
Meristem: perpetually embryonic tissues
Cells divide for plant growth
Apical meristem: growth at tips of roots & buds of shoots; cause primary growth (increase length)
Lateral meristem: growth thickens shoots and roots; secondary growth

3. Secondary Growth = increase diameter
Involves lateral meristems
Vascular cambium:: (wood)
Cork cambium: bark

4. Unusual nutritional adaptations:
Epiphyte: grow on another plant, absorb H2O from rain through leaves

5. Parasitic Plants: not photosynthetic; absorb sugar and minerals from living hosts

6. Carnivorous Plants: photosynthetic, but obtain some nitrogen and minerals by digesting small animals

7. Angiosperm ( Flowering Plants) Reproduction

8. Angiosperms have 3 unique Features:
Flowers
Double Fertilization (by 2 sperm)
Fruits

9. REPRODUCTIVE VARIATIONS
Flower
REPRODUCTIVE VARIATIONS

10. Pollination: transfer pollen from anther to stigma
Be sure to review plant-animal interactions. Flower color reflects the type of animal that pollinates. Day time pollinators are attracted to colorful flowers where flowers that are white tend to be pollinated by night time pollinators.

11. “Pin” and “thrum” flower types reduce self-fertilization
Some plants are self-pollinated
Cross-pollinated plants:
Self-incompatibility: plant rejects own pollen or closely related plant
Maximize genetic variation
Stigma
Pin flower
Anther
with
pollen
Thrum flower
“Pin” and “thrum” flower types reduce self-fertilization
Remind students the more related offspring are, the more possibility of genetic errors.

12. Double Fertilization 1 sperm produces the seed
1 sperm produces the endosperm (fruit)
The endosperm nourishes the seed by providing sugar or starch

13. 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
Again dispersal of seeds is related to the method of dispersal. Wind dispersal moved light seeds (dandelions). Water dispersal tends to move well protected seeds. Seeds with barbs will stick to animal fur and move with the animal

16. Seeds Mature seed  dormancy (resting) Low metabolic rate
Growth & development suspended
Resumes growth when environmental conditions suitable for germination
Stress that pollination, fertilization and germination are three separate processes in plant development.

17. 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

18. (Vegetative Reproduction)
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

19. Humans Modify Crops Artificial selection of plants for breeding
Plant Biotechnology:
Genetically modified organisms
“Golden Rice”: engineered to produce beta-carotene (Vitamin 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

20. Plant Responses

21. Hormones: chemical messengers that coordinate different parts of a multi-cellular organism
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)

22. Excised tip placed
on agar block
Growth-promoting
chemical diffuses
into agar block
Agar block
with chemical
stimulates growth
Offset blocks
cause curvature
Control
(agar block
lacking
chemical)
has no
effect
AUXIN = chemical messenger that stimulates cell elongation Cells on darker side elongate faster than cells on brighter side

23. The effects of gibberellin on stem elongation and fruit growth

24. Ethylene Gas: Fruit Ripening
Canister of ethylene gas to ripen bananas in shipping container
Untreated tomatoes vs. Ethylene treatment

25. Experiments with Light and the coleoptile
Conclusion: Tip of coleoptile senses light  some signal was sent from tip to elongating region of coleoptile

26. 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

27. Positive gravitropism in roots: the statolith hypothesis.

28. Thigmotropism: rapid turgor movements by Mimosa plant  action potentials

29. Plant Responses to Light
Plants can detect direction, intensity, & wavelenth of light
Phytochromes: light receptors, absorbs mostly red light
Regulate seed germination, shade avoidance

31. 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

32. Night length is a critical factor!
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!

33. How does interrupting the dark period with a brief exposure to light affect flowering? (often see this on exam)

35. Flooding (O2 deprivation):
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

36. Excess Salt: Heat: Cold: cell membrane – impede salt uptake
produce solutes to ↓ψ - 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

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