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Plant defences against disease 4.1.1 - Coggle Diagram
Plant defences against disease 4.1.1
passive defences
already present before pathogen arrives
prevent entry & spread of the pathogen
include physical barriers & chemicals
physical defences
cellulose cell wall
is a physical barrier & will also contain many defensive chemicals
lignin thickening
is almost indigestible
lignin is waterproof, tough & part of cells walls
waxy cuticle
stops water entering leaves & carrying pathogens
bark
a physical structure protecting he plant & also contains defensive chemicals
defensive chemical only produced when under attack rather than all the time cause its very energy taxing
stomatal closure
stomata are always present & the guard cells will cause them to close when pathogens are detected
Callose
a large polysaccharide that is deposited in the sieve tubes at the end of the growing season
can help prevent pathogens spreading in the phloem - slows down transport
chemical defences
plants have a variety of chemicals that have anti-pathogenic properties
includes; terpenoids, phenols, alkaloids & hydrolytic enzymes
some chemicals are always present but this requires energy to make so many are only made when a plant detects a pathogen
Tannins
always present in bark
have a bitter taste
Terpenes
always present in tylose formations
active defences
plants will detect the chemicals of pathogens (e.g. proteins & glycolipids)
they will respond by fortifying defences already present & producing defensive chemicals
cell walls
thickened & strengthen with additional cellulose
deposition of callose
deposited between plant wall & cell membrane near invading pathogen
plasmodesmata will ne blocked
chemical defences
Terpenoids
have string orders e.g. methanol & mint in some plants
essential oils - kill bacteria & fungi
Phenols
tannins are a derivative of phenols & found in bark, they inhibit insects by bonding to their digestive enzymes starving them to death
kill bacteria & fungi
Alkaloids
they're nitrogenous (contain nitrogen compounds)
e.g. caffeine, nicotine, cocaine, morphine, solanine
bitter taste to inhibit herbivores - less herbivory will mean less damage & fewer pathogens entering - inhibit or activate various enzymes to interfere with metabolism of herbivore
affect nervous system
some alkaloids inhibit protein synthesis
Defensins
they're defensive proteins
rich in cysteine
antibacterial properties
inhibits ion channels in plasma membrane of pathogens
Hydrolytic enzymes
found in the spaces between cells
includes chitinases which break down the chitin in fungal cell walls
includes lysosomes which break down bacterial cell walls
includes glucanases - break down glyosidic bonds in glucans ( sugars found in cell walls of bacterial & fungi)
other active defences
Necrosis
deliberate cell destruction
a few cells are sacrificed to save the rest of the plant
the cells surrounding infection are killed - intracellular enzymes are activated in which the plants cells destroy themselves stopping the pathogen from gaining nutrients & water & therefore stops it spreading
Canker
a sunken necrotic lesion in woody tissue - causes death of cambium tissue (under bark)
