Plant defences

Transmission of pathogens in plants

• direct transmission

  • contact with any part of a diseased plant

• vectors

  • wind

  • water

  • animals

  • humans

• soil contamination

  • spores remain in soil

Reducing chances of disease transmission

• Use plants that are not susceptible to a specific disease

• Do not plant too close together

• Provide minerals

• Ensure environmental conditions are good

  • not damp and warm

  • reduce climate change

3 factors for disease

• Following strict hygiene practices - removes pathogen

• rotate crops - removes favourable environment

• leave room between plants - removes favourable environment

• clear fields at harvesting - removes all

• control insect vectors - removes pathogen and favourable environment

• using disease resistant plants - removes susceptible host

Plant defences

• similar to humans

  • barriers

    • bark

    • waxy cuticle

    • cellulose cell walls

    • stomata closing

• different to humans

  • do not repair damaged tissue

  • seal off and replace using meristem tissue

Physical defences

• molecules or chemicals from a pathogen are detected by receptors in the plant cell

• signalling molecules are produced which switch on genes in the nucleus

• transcription and translation of these genes results in a range of defensive responses

• defensive chemicals are used to:

  • warm other cells

  • attack pathogen directly

• Callose and lignin produced

  • strengthens cell walls from further attack from pathogenic enzymes (eg)

  • callose seals sieve plates and plasmodesmata so infected part of plant sealed off and pathogen cannot spread

    • (callose is made of glucose molecules joined by BETA 1,3 and BETA 1,6 linkages)

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Chemical defences

• plants produce chemicals to:

  • repel disease vectors

  • kill pathogens

• We also make use of these chemicals:

  • eg insecticides, antifungals, antimicrobials

  • herbs and spices

  • caffeine