plant defences physical passive and active Flashcards
what is a passive defence
prevent entry of pathogens into the plant before infection can occur
what is a active defence
after infection, these mechanisms either kill or prevent the further spread of the pathogen throughout the plant
what can passive and active defences be either:
physical or chemical
what is the function and structure of callose (physical passive defence)
-large polysaccharide found in the end of sieve tubes blocking flow in the phloem, plasmodesmata between cells and around cell membrane
-to prevent pathogen from spreading around the plant
why is callose a passive defence
-it is always deposited at the end of growing season, not only deposited when pathogen infects
what is the function of bark (physical passive defence)
-contains chemical defences, tough to chew through
what is the function and structure of the lignin in the cell wall (physical passive defence)
-a phenolic compound
-gives the cell walls strength, indigestible and difficult for pathogens to penetrate
what’s a phenolic compound
-a ring with one or more OH groups attached to it
what is the function of the waxy cuticle
it keeps pathogens out, waterproofs and prevents water containing pathogens from collecting on a cells surface
what is the function of the stomatal closure (physical passive defence)
controlled by guard cells
-when pathogens are detected they’re closed to prevent entry
what is the function of tylose (physical passive defence)
-swelling projection that fills the xylem vessel
-plugs the xylem vessel
-prevents spread of pathogens
-contains toxic chemicals
what is the function of the cellulose cell wall (physical passive defence)
-physical barrier
-contains chemical defences which can be activated by the presence of pathogens
what are the physical passive defences in plants
-callose
-bark
-tylose
-lignin in the cell wall
-waxy cuticle
-stomatal closure
-cellulose cell wall
examples of anti-pathogenic chemicals (passive chemical defence)
-tannins in bark
-terpenes in tyloses
-phenols, alkaloids and hydrolytic chemicals
why are chemicals not produced until plant detects an infection
-production of chemicals require lots of energy
why are anti-pathogenic chemicals a passive defence
they’re present in the plant before an infection occurs
what are the active physical defences in plants
-callose
-oxidative bursts
-necrosis
-cellulose
-canker
how does callose prevent the spread of pathogens
-deposits between cell wall and cell membrane
-impedes cellular penetration at the site of infection
how do oxidative bursts prevent the spread of pathogens
-produce highly reactive oxygen molecules capable of damaging the cells of invading organisms
how does necrosis prevent the spread of pathogens
-deliberate cell suicide brought about by intracellular enzymes that are activated by injury
-few cells sacrificed to save rest of plant
-by killing cells, plant limits pathogens access to water and nutrients to stop it spreading further
how does cellulose prevent the spread of pathogens
-cell walls become thickened and strengthened with additional cellulose
-chemicals in cell wall only get activated when pathogen invades
what’s a canker
-sunken necrotic lesion (area of abnormal tissue) in the woody tissue such as the main stem/branch
how is a canker an active defence
Plant can surround lesion with healthy tissue internally to stop spreading
Plant can help kill off that tissue as it causes death of cambium tissue
