Plant Defences Flashcards
What are passive defences?
some chemicals are present in plant structures already, and are therefore passive (eg. tannins in bark)
What are active defences?
-when plants actively defend themselves by detecting pathogens with molecules in their walls (pattern recognition receptors)
-then fortifying defences by producing attacking pathogens
Name 5 passive plant defences
-cellulose cell wall
-lignin thickening of cell walls
-waxy cuticles
-bark
-stomatal closure
How does cellulose cell wall act as a defence?
surround plant cells and act as a physical barrier against pathogens that have passed the waxy cuticle
How does lignin thickening of cell walls act as a defence?
-provides a basic barrier and reduces infiltration of fungal enzymes and toxins into plant cell walls
How does waxy cuticles act as a defence?
-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
How does bark act as a defence?
-layers of dead cells around plant stems
-stops passage of pathogens and protects against infection
How does stomatal closure act as a defence?
-response to drought condition
-‘pathogen associated molecular patterns’ detect bacteria and fungi and trigger stomatal closure to prevent penetration through these pores
What is callose?
a polysaccharide that is deposited in sieve tubes at the end of the growing season
What is callose made out of?
beta glucose with 1-3 glycosidic linkages
How does callose help defend the plant from infection?
-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
What is tylose?
a swelling/projection that fills xylem vessels
How does tylose act as a defence?
-plugs xylem vessel and stops water from passing through
-contains chemicals, such as terpenes, that are toxic to pathogens
What are 6 chemical defences of plants?
-terpenoids
-tannins
-alkaloids
-pheromones
-hydrolytic enzymes
-defensins
What are terpenoids?
oils that have antibacterial and antifungal properties
What are tannins?
-have antibacterial and antifungal properties
-reduce insect attacks by binding to salivary proteins and digestive enzymes
What are alkaloids?
-N containing compounds (caffeine, nicotine, cocaine, morphine)
-give a bitter taste
-inhibit enzyme action and protein synthesis
How could alkaloids inhibit protein synthesis?
block ribosomal protein by binding to receptor
What are pheromones?
chemicals which affects social behaviour of other organisms
What are hydrolytic enzymes? Examples
-found in spaces between cells eg. chitinases, glucanases, lysozymes
What is the effect of chitinases?
weaken cell walls of pests and pathogens
What is the effect of glucanases?
destroy cell walls of some fungi and split off its fragments
What is the effect of lysozymes?
-antimicrobial activity
-immune-modulatory effects against infection and inflammation
What are defensins?
cysteine rich proteins that inhibit the action of ion transport channels
