Plant defences against Pathogens

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  • Plant defences against Pathogens
    • Physical
      • High levels of callose are made
        • Deposited in the plasmodesmata between infected cells, sealing them off from healthy ones
        • Synthesised and deposited between cells walls and membrane soon after an initial attack
        • Large amounts continue to be deposited and lignin is added , this makes the meechanical barrier even stronger.
        • Callose papillae acts as barriers stopping pathogens from entering cells
        • Blocks seive plates in the phloem, sealing off infected area, stopping it spreading
        • Scientists still aren't sure of the functions  of callose in the defence mechanism
    • Chemical
      • Often powerful chemicals are produced which repel or kill invading insects or pathogens.
      • insect repellants- pine resin and citronella
      • Insecticides- caffeine and pyrethrins
      • Antibacterial compounds (inc. antibiotics)- phenols, defensins. lysosomes
      • Antifungal compounds- phenols, antifungal gossypol, saponins chitinases
      • Anti-oomycetes- glucananses and P.infestans
      • General toxins- cyanide
    • Recognising attacks
      • Receptors on cells respond to pathogenic molecules
      • Signalling molecules are released. They appear to switch on genes in the nuclleus of the cell.
      • A cellular response is triggered, this informs unaffected cells.
      • Unaffected cells thicken their walls and trigger defence system.


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