module 4 - 12.4 plant defences against pathogens Flashcards
how have plants evolved to defend themselves against pathogens that cause communicable diseases?
- waxy cuticle of plant leaves
- bark on trees
- cellulose cell walls of plant cells
why don’t plants heal diseased tissues?
- they seal it off and sacrifice it
- they are continually growing at the meristems they can replace damaged parts
why are plants not passive?
they respond rapidly to pathogen attacks
how do plants respond rapidly to a pathogen attack?
- receptors in cells respond to molecules from pathogens, or to chemicals produced when cell wall is attacked
- stimulates release of signalling molecules that ‘switch on’ genes in nucleus
after the genes have been switched on in the nucleus, what does this trigger?
cellular response -
- produces defensive chemicals
- sends alarm signals to unaffected cells to trigger defences & strengthen walls
what are the physcial defences of a plant?
they produce a polysaccharide called callose, which contain beta minus 1,3 and beta minus 1,6 linkages
what happens within minutes of the attack? (to do with callose)
- callose is synthesised & deposited between the cell walls & membrane in cells next to infected cell
- acts as barriers, prevents pathogens entering plant cells around infection
what happens after the intial infection to do with callose?
- large amount of callose continue to be deposited, lignin added making mechanical barrier thicker and stronger
- callose blocks sieve plates in the phloem, sealing off infected part & preventing spread
- callose is deposited in plasmodesmata between infected cells & neighbours, sealing off from healthy cells & stop spread
what are the chemical defences of a plant?
- insect repellents
- insecticides
- antibacterial compounds like antibiotics
- antifungal compounds
- anti-oomycetes
- general toxins
how are inseciticides a chemical barrier?
toxic to insects and fungi
how are antibacterial compounds a chemical barrier?
- defensins - plant proteins that disrupt bacterial and fungal cell membranes
- lysosomes - organelles containing enzymes that break down bacterial cell walls
how are antifungal compounds a chemical barrier?
- toxic to fungi and insects
- chemicals in many plant cell membranes interfere with fungal call membranes
- enzymes break down the chitin in fungal cell walls
how are anti-oomycetes a chemical barrier?
glucanases - enzymes that break down glucans (polymers found in cell walls of oomycetes)
how are general toxins a chemical defence?
some plants make chemicals that can be broken down to form cyanide compounds when the plant is attacked - toxic
