Plant Defences

Question 1

What are passive defences?

Answer 1

some chemicals are present in plant structures already, and are therefore passive (eg. tannins in bark)

Question 2

What are active defences?

Answer 2

-when plants actively defend themselves by detecting pathogens with molecules in their walls (pattern recognition receptors)
-then fortifying defences by producing attacking pathogens

Question 3

Name 5 passive plant defences

Answer 3

-cellulose cell wall
-lignin thickening of cell walls
-waxy cuticles
-bark
-stomatal closure

Question 4

How does cellulose cell wall act as a defence?

Answer 4

surround plant cells and act as a physical barrier against pathogens that have passed the waxy cuticle

Question 5

How does lignin thickening of cell walls act as a defence?

Answer 5

-provides a basic barrier and reduces infiltration of fungal enzymes and toxins into plant cell walls

Question 6

How does waxy cuticles act as a defence?

Answer 6

-on most plant leaves and stems and provides a physical barrier against pathogens
-also stops water collecting on leaf, which prevents entry of pathogens that are transferred in water

Question 7

How does bark act as a defence?

Answer 7

-layers of dead cells around plant stems
-stops passage of pathogens and protects against infection

Question 8

How does stomatal closure act as a defence?

Answer 8

-response to drought condition
-‘pathogen associated molecular patterns’ detect bacteria and fungi and trigger stomatal closure to prevent penetration through these pores

Question 9

What is callose?

Answer 9

a polysaccharide that is deposited in sieve tubes at the end of the growing season

Question 10

What is callose made out of?

Answer 10

beta glucose with 1-3 glycosidic linkages

Question 11

How does callose help defend the plant from infection?

Answer 11

-deposited around sieve plates during times of stress, making it harder for pathogens to enter
-deposition of plasmodesmata may limit spread of viruses between cells

Question 12

What is tylose?

Answer 12

a swelling/projection that fills xylem vessels

Question 13

How does tylose act as a defence?

Answer 13

-plugs xylem vessel and stops water from passing through
-contains chemicals, such as terpenes, that are toxic to pathogens

Question 14

What are 6 chemical defences of plants?

Answer 14

-terpenoids
-tannins
-alkaloids
-pheromones
-hydrolytic enzymes
-defensins

Question 15

What are terpenoids?

Answer 15

oils that have antibacterial and antifungal properties

Question 16

What are tannins?

Answer 16

-have antibacterial and antifungal properties
-reduce insect attacks by binding to salivary proteins and digestive enzymes

Question 17

What are alkaloids?

Answer 17

-N containing compounds (caffeine, nicotine, cocaine, morphine)
-give a bitter taste
-inhibit enzyme action and protein synthesis

Question 18

How could alkaloids inhibit protein synthesis?

Answer 18

block ribosomal protein by binding to receptor

Question 19

What are pheromones?

Answer 19

chemicals which affects social behaviour of other organisms

Question 20

What are hydrolytic enzymes? Examples

Answer 20

-found in spaces between cells eg. chitinases, glucanases, lysozymes

Question 21

What is the effect of chitinases?

Answer 21

weaken cell walls of pests and pathogens

Question 22

What is the effect of glucanases?

Answer 22

destroy cell walls of some fungi and split off its fragments

Question 23

What is the effect of lysozymes?

Answer 23

-antimicrobial activity
-immune-modulatory effects against infection and inflammation

Question 24

What are defensins?

Answer 24

cysteine rich proteins that inhibit the action of ion transport channels

Question 25

How might defensins affect the microorganism?

Answer 25

-disallow ions to enter cell, becomes inefficient and malnourished
-prevents pathogen entry

Question 26

What bond is numerous in defensins?

Answer 26

disulfide

Question 27

What do necrosis work as a defence?

Answer 27

kill cells in order to prevent spread of infection further
-cell killing carried out by intracellular enzymes which are activated when cells are injured

Question 28

How is a canker a defence?

Answer 28

-produced by the death of a cambium (which provides unspecialised cells)
-creates a sunken lesion in the stem