Chapter 11 - growth and development

Question 1

5 hormone types FIX

Answer 1

• 5 major types of plant hormones:
  o Auxin
  o Gibberellins
  o Abscissic acid
  o Cytokinins
  o Ethylene
• Auxin:
  o “to increase”
  o Made in apical meristems, buds, and young leaves
  o Depends on concentration and location
  o Growing, flowering, and fruiting
  o Effects:
   Bending the stem towards light
   Downward root growth
   Promotion of apical dominance
   Induces flower formation
• Gibberellins
  o Involved in the same process as auxins
  o Synthesized in root tips and leaves
  o Causes dicots and some monocots to grow faster
  o Effects:
   Regulate cell division and elongation
   Dramatically increases stem growth
   Speed germination of seeds
   Delay of aging in fruits and leaves
• Abscissic acid
  o Forms from carotenoid pigments
  o Common in fleshy fruits
  o Effects:
   Inhibits effects of other hormones
   Inhibits premature seed germination
   Induces bud dormancy
   Helps leaves respond to water loss
   Inhibits K ions to close the stomata
• Cytokinins
  o Synthesized in roots
  o Works WITH auxin
  o Effects:
   Cell growth and differentiation
   Affects apical dominance
   Delays leaf sessenence
• Ethylene
  o Exists ONLY as a gas
  o Derived from amino acid methionine
  o Made by fruits, flowers, leaves, and roots
  o Increases when a plant is stressed or dying
  o Stops when no O2 is around
  o Effects:
   Fruit ripening
   Abscission of leaves, fruits, and flowers

Question 2

Factors and hormone effects FIX

Answer 2

• Plants are affected by 4 factors:
  o Gene factors
  o Environmental conditions – temp, PH, humidity, salinity, wind
  o Resource availability – light, water, nutrients
  o Hormones
• Hormone effects:
  o Stimulate or inhibit activity
  o Can have multiple effects
  o Can inhibit other hormones

Question 3

Hormone interactions FIX

Answer 3

• Hormone interactions
  o Apical dominance
   One main stem is more dominant than other stems
   Terminal bud control auxiliary buds
   Ensures resources spent on vertical growth
   Auxins released by terminal bud
   Suppresses lateral buds to promote elongation
   Found mostly in conical shaped trees
  o Senescene
   Describes death of plant
   Promoted by absc acid and ethylene
   Delayed by auxin, gibberellins, and cytokinin

Question 4

Movement FIX

Answer 4

• Plant movement
  o Bend, twist, and elongate
  o Autonomic movement
   Response to stimulus within the plant
  o Induced movement
   External stimulus
   Include tropic and nastic movements
• Autonomic:
  o Nutation (common)
   Spiral movement of growing tip
  o Nodding
   Slow, swinging motion of emerging stem
  o Twining
   Starts with object contact
   Basically coiling
  o Contraction movement
   Movement of bulbs further into soil
• Induced
  o Tropisms
   Positive movement: towards stimulus
   Negative movement: away from stimulus
   Three steps/phases:
• Initial perception
• Transduction
• Asymmetric growth
   Phototropism
• Growth towards or away from light
• Roots: negative
• Everything else: positive
• Auxin migrates away from the light (roots), which elongates them
   Gravitropism
• Gravity
• Roots: POSITIVE
• Everything else: negative
• Amyloplasts help the plant detect gravity
   Hydrotropism
• Water
• Roots are positive
   Chemotropism
• Chemicals (like salt)
• Roots are positive or negative depending on if its nutrients or not
  o Nastic movements:
   Response direction unrelated to stimulus location
   Reversible and repeatable movements
   Seismonastic
• Touch or vibration
• Ex: Venus flytrap
   Photonastic
• Light
• flowers that open or close dinurally
• Ex: dandelion?? (morning glory fs)
   Thermonastic
• Temp change
• Close in frigid temps
   Nyctinastic
• “sleeping movement”
• Dinural change in light and temp

Question 5

Photoperiodism FIX

Answer 5

• Photoperiodism
  o Seasonal activity timed to day length
  o Uses pigments called phytochromes
  o Strategies:
   Short day plants
   Long day plants
   Day neutral plants