1.2 Plant defence toolbox

Question 1

Systemic resistance

Answer 1

• Effective throughout the plant, including tissues that have not been attacked
• Requires signal transmission and may take some time to be effective
• Involves phytohormone signalling, mostly SA, JA and Et

Question 2

Types of systemic resistance responses

Answer 2

• Systemic Acquired Resistance (induced and effective in vegetative tissue)
• Induced Systemic Resistance (induced in roots, effective in green tissue)
• Wound responses (induced by insect or nematode feeding damage)

Question 3

Main points on plant defence mechanisms

Answer 3

• preformed and induced
• defense compounds either targeting multiple types of attackers or specific to one type of attacker
• local cell death following hypersensitive response
• oxidative burst involving Reactive Oxygen Species
• local vs. systemic responses

Question 4

Types of preformed defence

Answer 4

Physical barriers: cuticle, cell walls

Phytoanticipins: antimicrobial metabolites

Volatile insect deterrants

Question 5

Basic pathway for plant defense

Answer 5

1) PROBLEM (attacker nearby)
2) RECOGNITION SIGNAL PROCESSING and TRANSMISSION
3) GENE ACTIVATION, ENZYME ACTIVITY
4) Synthesis of “DEFENSE PRODUCTS” (effectively COUNTERACTING INVASION or REPRODUCTION OF ATTACKER)

Question 6

Two basic types of plant defense mechanisms

Answer 6

• Pre-formed physical and chemical barriers

- Induced defense mechanisms

Question 7

Common themes in many defense mechanisms

Answer 7

Local cell death

Oxidative burst

Question 8

Local cell death

Answer 8

• Results from a hypersensitive response (HR)
• Cause by recognition of an attacker
• Mediated by interaction of resistance (R) protein and effector molecule

Question 9

Types of induced defence

Answer 9

Protease inhibitor: anti-feedant to insects

Phytoalexins: antimicrobial metabolites

Cell wall reinforcement: callose + lignin deposition

PR-proteins: chitinase, glucanase, protease, lysozyme dsRNA formation, RNA interference

Question 10

Oxidative burst

Answer 10

• The accumulation of reactive oxygen species (ROS)

- These serve as signalling molecules as well as causing cell death

Question 11

Effect of hypersensitive response (HR)

Answer 11

• Activates downstream defense

- Leads to oxidative burst

Question 12

Types of induced resistance

Answer 12

• Local

- Systemic

Question 13

Cell wall reinforcement by papilla formation

Answer 13

The plant produces a papilla beneath the cell wall to prevent invasion by fungus or oomycete

Question 14

Local resistance

Answer 14

Only effective in restricted areas (mostly around site of attacker invasion)

Question 15

Types of ROS

Answer 15

Superoxide anion - toxic and reactive

Hydrogen peroxide - highly soluble and mobile through membranes, possible signal molecule

OH radical - highly reactive, destroys lipds/proteins/DNA