plant defences against pathogens Flashcards
1
Q
what are passive defences ?
A
- defences present before infection
2
Q
what is the role of a passive defence ?
A
- to prevent entry and spread of a pathogen
3
Q
what do passive defences include ?
A
- both physical barrier and chemicals
4
Q
what does physical barrier decrease the chance of ?
A
- a pathogen entering the cell
5
Q
what are examples of passive physical barriers ?
A
bark , waxy cuticle , cellulose cell wall , lignin thickening of cell walls
6
Q
how does bark act as a passive physical barrier ?
A
- contains tannins (chemical barrier) which inhibits digestion in insects
7
Q
how does the waxy cuticle act as a physical barrier ?
A
- stops water collecting on the leaf
–> absence of water makes conditions less favourable for pathogens
8
Q
how does a cellulose cell wall act as a physical barrier ?
A
- makes it harder for pathogens to get inside a cell +
- chemical defences can be activated when a pathogen is activated
9
Q
how does lignin thickening cell walls act as a physical barrier ?
A
- waterproof and almost completely indigestible
10
Q
define callose
A
- a large polysaccharide deposit that blocks old phloem sieve tubes
11
Q
what happens when a plant is stressed ?
A
- callose is deposited between plant cell walls + plasma membranes near the invading pathogen
12
Q
what does callose deposition make harder ?
A
- for pathogens to enter cells
13
Q
what does callose strengthen and block ?
A
- the cell walls + plasmodesmata
14
Q
what does callose prevent ?
A
-pathogens being transported around the plant
15
Q
define tyloses
A
- balloon - like structures produced by the xylem
16
Q
what is role of tyloses ?
A
- to block old zylem vessels causing it to become non-functional
- also contains terpenes which are toxic
17
Q
what does tyloses prevent ?
A
- pathogens being transported around the plant
18
Q
how can pathogens invade externally ?
A
through wounds and an open stomata
19
Q
what can some pathogens do within the cell walls ?
A
- can puncture the plant tissue by growing through cell walls
20
Q
what do some pathogens use ?
A
- enzymes to dissolve their way in the plant cell
21
Q
what happens when pathogens enter the stomata ?
A
- guard cells close when pathogens are detected in that part of the plant
22
Q
how do plant cells use chemical defences against pathogens ?
A
- they make anti-microbial substances
23
Q
define chemical defences
A
- plants produce antimicrobial chemicals
24
Q
what is the role of antimicrobial ?
A
- chemicals kill pathogens or inhibit their growth
25
describe necrosis in 3 words
deliberate cell suicide
26
what do healthy cells around an infection do ?
commit suicide
27
what happens when the host cell dies ?
- stops the infection spreading through the plant
28
how does cell suicide occur ?
- intracellular enzymes are activated by injury
--> destroy damaged cells + produce brown spots on leaves or die back
29
what is does a canker ?
- causes the death of the cambium tissue in the bark
30
what is a canker ?
- a sunken necrotic lesion in the woody tissue
--> such as main stem or branch
31
make a table of the differences between active and passive defences
PASSIVE DEFENCE
- present before infection
-prevents entry + spread of a pathogen
- includes physical defences + chemicals
ACTIVE DEFENCE
- produced in response to infection
- physical defences are increased
- defensive chemicals are produced
32
what a the 5 chemicals are produced as a result of an active defence ?
- terpenoids , phenols , alkaloids , defensive proteins , hydrolytic enzymes
33
what is the action that terpenoids take ?
- have strong smells that can deter insects
- some may also have anti-bacterial and antifungal properties , helping a plant fight infections
e.g. methanol --> found in mint plants --> repels insects
pyrethrins --> from chrysanthemums --> used in insecticides
34
what is the action phenols take ?
- help protect plants from being eaten by herbivores and from infections caused by bacteria and fungi
- making the plant taste bad or toxic to animals
- some phenols attack enzymes in insect pests --> stopping from growing properly
e.g. - tannins found in tea and unripe fruits
--> make leaves taste bitter , so herbivores don't want to eat them
35
what is the action alkloids take ?
- bitter-tasting , toxic chemicals that stop herbivores from eating the plant
- can also affect the nervous system of insects and animals --> making them feel sick or even poisoning them
- reduces plant damage and protect the plant from being eaten
e.g. caffeine - stops insects from feeding on the plant
nicotine - poisonous to insects , acting as a natural pesticide
36
what is the action do defensive proteins take ?
- some attack the digestive system of insects and pests , making it harder for them to eat the plant
- stop bacteria and fungi from growing --> preventing infections
- help the plant stay healthy and survive attacks from predators and diseases
e.g. enzyme inhibitors - stop insects from properly digesting food , so they stop eating the plant
defensins - small proteins --> kill bacteria and fungi --> by damaging their cell membranes
37
what is the action that hydrolytic enzymes take ?
- enzymes break down the cell walls of bacteria and fungi --> destroying them before they can harm the plant
- usually found in plant cell walls and spaces between cells --> ready to fight off infections
e.g. chitinases - break own chitin --> which is found in fungal cell walls
glucanases - break down glucans --> another part of fungal cell walls
lysozymes - attack bacterial cell walls , breaking them apar
