Plant defences against pathogens 4.1.3 Flashcards
1
Q
What are 5 physical defences against pathogens in plants?
A
- Cellulose cell wall - lignin=waterproof and indigestible
- Waxy cuticle - prevents water from collecting on the surface (limits the growth of pathogens)
- Guard cells - can close the stomata
- Callose - large polysaccharide in sieve tubes which blocks the flow, at the end of growing season, so that pathogens can’t spread.
- Tylose - a balloon like swelling which plugs the xylem and prevents the spread of pathogens
2
Q
When is callose produced?
A
When a pathogen is detected, plant cells rapidly produce high levels of callose
3
Q
What is the structure of callose
A
It is made up of beta glucose, in a polysaccharide
4
Q
What is the role of callose in plant defence?
A
- Callose is deposited between cell walls and cell membranes next to infected cells (barrier to limit spread)
- Lignin is added to the callose to strengthen the barrier
- Callose also blocks the sieve cells of the phloem, preventing spread
- Callose is also deposited in the plasmodesmata of connecting cells
5
Q
Name 2 chemical defences in plants
A
- Terpenoids - antibacterial and anti fungal properties (why mint has this scent)
- Alkaloids - N containing compounds with a bitter taste like caffeine/morphine. This stops herbivores feeding on them
6
Q
How is the spread of disease by insect vectors prevented?
A
- Insect repellents
- Insecticides
7
Q
How are pathogens dealt with in plants?
A
Through antibacterial compounds containing antibiotics
E.g.
- Phenols
- Defensins
8
Q
How are fungi dealt with in plants?
A
Antifungal compounds such as:
- Gossypol
- Caffeine
9
Q
How do enzymes and toxins contribute to chemical defence in plants?
A
- Cyanide - toxin in most organisms
- Chitinases - break down fungal cell walls
