Plant defense against Pathogens

• Physical barriers; Waxy cuticle on leaves, Bark on trees, Cellulose cell walls, Lignified cell walls and Callus formation (like scars)
• Chemical defences - chemicals toxic to pathogens often called secondary metabolites (not needed for normal plant processes such as photosynthesis) - help plant be resit infection
• Terpenoids - toxins which deter plant feeding insects (insect repellants) and mammals, e.g. peppermint, lemon, basil and sage essential oils as well as antibacterial essential oils e.g. menthols and tea tree oil
• Phenols - antibiotics and antifungal e.g. tannins which inactivate enzymes and kill attacking insects
• Alkaloids - N containing compounds synthesised from 4 different amino acids e.g. caffeine, cocaine, morphine, atropine, which give the plant a bitter taste to insects and inhibits their enzyme (toxic)
• Cyanogenic glycosides - protect against mammals, insects and molluscs e.g. amygdalin
• Hydrolytic enzymes - found in spaces between cells e.g. chitinases which breaks down chitin in fungal cells walls and glucanase and lysozymes which damage bacteria cell walls
• Resins - viscous secretions produced by plants during wound healing, act as sealants, protecting plants from pathogens, herbivore attacks, and water loss (some resins, like myrrh and frankincense, have antiseptic properties)