plant defence responses to pathogens — HSC biology, live

Plant Defence Responses to Pathogens

Plants have no antibodies, no white blood cells and no way to run, yet most plants resist most pathogens. Every cell carries its own receptors, and when a resistant broad-leaved paperbark (Melaleuca quinquenervia) detects myrtle rust (Austropuccinia psidii) it kills the cells around each entry point, so the fungus, which can only feed on living tissue, starves inside a ring of dead cells. Salicylic acid then primes the rest of the plant. A susceptible paperbark fails at the recognition step, and the same spores become yellow pustules within about a fortnight. This is the real knowscape from knowhere, not a picture of one. Drag it. Watch what actually changes.

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Plant defence works like walling off a spill.

A plant can't run, can't make antibodies, can't call in a cell to eat the invader — so it defends with what it can't move: barriers it built before the attack, and chemistry it triggers the instant a cell is breached. Every plant defence is either the wall or the alarm.

The whole room is intact before any spill appears.

You seal the affected corner, giving up that small patch.

The mess is contained; the rest stays safe.

what examiners catch — Students describe antibodies, phagocytes or memory cells in a plant answer, or call the hypersensitive response whole-plant immunity.

five things, not forty.

Pre-formed barriers come first: the waxy cuticle, thick cell walls and stomatal closure stop many spores before any active response is needed.

Pattern recognition receptors detect fungal chitin and trigger wall thickening, callose papillae and antimicrobial compounds at the entry point.

The hypersensitive response is programmed cell death confined to the infection site: dead cells starve a biotrophic fungus that only feeds on living tissue.

Systemic acquired resistance uses salicylic acid signalling to prime distant tissue; it sharpens later responses but is not sterilising immunity.

Resistant Melaleuca quinquenervia shows small necrotic flecks where myrtle rust (Austropuccinia psidii) enters; susceptible trees grow yellow spore pustules within about a fortnight.

nothing here is a standalone fact.

knowhere maps every concept to what it rests on and what rests on it — 3 underneath this one, 1 built on top. Each one says why, in a sentence, not as an arrow on a diagram.

this conceptplant defence responses to pathogensA young paperbark leaf in cross-section over fourteen days after myrtle rust spores land: one spore dries on the cuticle, one is walled off by a papilla, and in the resistant genotype the rest are ringed by dead cells and their hyphae fade while surrounding tissue is primed; in the susceptible genotype the hyphae spread between cells and erupt as yellow spore pustules.

sits under itpathogens: types and adaptationsbecause Students need to know a fungal biotroph feeds on living cells before cell death makes sense as a defence.

sits under itfirst-line barriers to infectionbecause The cuticle and cell wall parallel the skin and mucous membranes already met in animals.

sits under itapoptosis and programmed cell deathbecause The hypersensitive response is programmed cell death used as a weapon.

built on ithow animal hosts fight backbecause the plant playbook is the comparison case the syllabus sets up

they don't read it. they run it.

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Plant defence works like walling off a spill.

five things, not forty.

nothing here is a standalone fact.

2 more, same treatment.

they don't read it. they run it.