Responses to pathogens

Plant Response to Pathogen: Physical

Physical barriers - Prevent the pathogen from entering

• Waxy cuticles made of lignin and cutin  prevent pathogens from entering plant

• Cell wall - prevent pathogens from entering cell

• Bark with lignin - highly impermeable

• Trichomes, thorns, spines and prickles - repels insects

• Vertically hanging leaves - prevents accumulation of water that allows pathogens to accumulate and reproduce

Plant Response to Pathogen: Recognition of non-self-antigens

• Each cell has microbe associated molecular patterns (MAMPs) - structure on the surface of plant cells that detects pathogens

• Allows them to trigger immune response without needing specialised immune cells

Plant Response to Pathogen: Immune responses

Basal resistance → occurs immediately after detecting a pathogen

• Releases chemical irritants and toxic compounds

• Tailor-made for a specific function like natural insect repellents

  • E.g. Stinging nettle releases histamines out of its trichomes to promote redness and itching

    • Makes antimicrobial and antifungal chemicals

    • They target the pathogen’s cell membrane or inhibit growth

• Plant fortifies itself to become impenetrable

  • Guard cell closes the stomata → prevent pathogens from entering and exiting to be transmitted to other plants

  • Callose deposition → a polysaccharide that fills the gap between cell walls of plants to limit disease spread

Gene for Gene Resistance - a relationship between the plant and the pathogen where, the plant must have a resistance gene that matches a pathogen’s avirulence gene to be immune

• Some mutations in the plants DNA allows it to have genes that make the plant resistant to specific pathogens

  • Gene allows plant to produce the right proteins to kill the pathogen

  • Plant cells have receptors that recognise the pathogen to trigger a specific defence response

  • ∴ Need genetic variety = the likelihood that one individual has this gene increases

• Some viruses have an avirulence gene against a specific plant  makes it not pathogenic against the plant

Hypersensitive response → occurs when basal resistance fails, or it lacks the resistant gene

• When apoptosis - programmed cell death occurs  it restricts the pathogen to the infected site by killing the cells around it, and saving the rest of the plant

System acquired resistance → Activated in a plant after exposed to a pathogen

• Through a series of chemical reaction, the system enables the plant to generate a faster attack after subsequent exposure to the pathogen (similar to memory cells in plants)

Eucalyptus Trees’ response to myrtle rust

Animal Responses to Pathogens