Lecture 14: Plant Response to Stimuli

Question 1

What are some stimuli that plants can detect (9)?

Answer 1

• light
• gravity
• pressure
• humidity
• seasonal changes
• time of day
• wounds
• herbivore attacks
• signals from other plants or symbionts

Question 2

Explain how an external stimulus on a sensory cell travels to the target cell (information processing)

Answer 2

• see google doc

Question 3

define: phototropism

Answer 3

• the orientation of a plant or other organism in response to light

Question 4

• explain phototropism using some key words:
• coleoptile
• bending
• blue light
• elongate/elongation
• phototropin
• auxin

Answer 4

• see google doc

Question 5

define: auxin

- what releases auxin

Answer 5

• plant hormone produced in the stem tip that promotes cell elongation and causes phototropism
• apical buds release auxin down the stem to the leaves and roots
• auxins inhibit growth of lateral buds to maintain apical dominance

Question 6

amyloplasts

• location
• function

Answer 6

• location: root cap
• contains starch; involved in gravity sensing (gravitropism) and helping plant roots grow in a downward direction; activate pressure receptors that change auxin distribution; see google doc

Question 7

gravitropism

Answer 7

a coordinated process of differential growth by a plant or fungus in response to gravity pulling on it

Question 8

list the notable plant hormones (4)

Answer 8

• auxin
• ethylene
• gibberellin
• abscisic acid (ABA)

Question 9

ethylene

- function

Answer 9

• hormone
• leaf abscission (natural detachment of dead leaves, ripe fruit, etc)
• fruit ripening
• flower fading

Question 10

gibberellin and abscisic acid ABA

Answer 10

• involved in seed dormancy and germination

- ABA: controls closing of stomata

Question 11

explain the control of the opening/closing of stomata

Answer 11

• see google doc

Question 12

List 5 physical defence mechanisms plants have

Answer 12

• waxy cuticle
• stomata closing
• thorns
• spines
• trichomes

Question 13

List 4 chemical defence mechanisms plants have; why are these known as inducible defence mechanisms?

Answer 13

• insect repellants
• insecticides
• tannins
• bitter tasting or neuro-disruptive compounds
• often produced only when needed

Question 14

What is a plant’s response to a pathogen attack(6)? What is this known as?

Answer 14

when a pathogen enters through stomata or wounds the following will occur within hours of infection:
- receptor proteins bind to pathogen derived molecules
- stomata close
- toxins produced
- cell walls of adjacent cells strengthened
- suicide of infected cells
- alarm hormone is produced that travels through plant (leads to SAR: systemic acquired resistance)
- SAR signal induces the
expression of pathogenesis-related genes
* hypersensitve response

Question 15

What is a plant’s response to a herbivore attack?

Answer 15

- When insects attack, cells	
release a peptide hormone	
(oligopeptide,	18 residues)	
- Systemin binds receptor on	
adjacent	cells	
- Activated receptor produces	 jasmonic	acid	
- Jasmonic acid activates	
transcription of proteinase