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4.1.3 Plant Defences (Passive Defenses (Physical (cellulose cell wall with…
4.1.3 Plant Defences
Passive Defenses
Physical
cellulose cell wall with lignin thickening; physical barrier, waterproof, indigestible
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callose; a large polysaccharide deposit in ends of sieve tubes to block phloem in case pathogen is in there
tylose formation; balloon like swelling in xylem so water cannot be transported; pathogen cannot travel; disease can't be spread around the plant
Chemical
many chemicals are not produced before an infection is detected due to large amount of energy needed to produce
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Active Defenses
Physical
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callose is deposited between plant cell wall and plasma membrane near pathogen; strengthens cell wall; blocks plasmodesmata
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Chemical
Defensins
small cystine rich proteins that have broad antimicrobial properties; act on plasma membrane of pathogens
Alkaloids
nitrogen containing compounds; give bitter taste to stop herbivores feeding; act on metabolic reactions like protein synthesis or enzyme action; e.g. caffeine, nicotine , cocaine, morphine
Phenols
antibacterial and antifungal properties; e.g. tannins found in bark bind to insects salivary proteins and eventually insect cannot grow and dies
Hydrolytic enzymes
found in spaces between cells; e.g. chitinases (break down chitin in fungal cell walls), glycanases (hydrolyse glycosidic bonds in glucans), lysozomes (degrade bacterial cell walls)
Terpenoids
essential oils that have antibacterial and antifungal properties; may produce scent e.g. menthol produced by mint plant
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