Plant Defences Against Pathogens Flashcards
What is a form of Passive defence?
Defences present before infection, role to prevent entry and spread of the pathogen. Includes physical barriers and chemicals.
List the Physical defences
Cellulose cell wall - physical barrier, contains chemical defences that can be activated when a pathogen is detected.
Lignin thickening of cell walls - water proof and ingestible
Waxy cuticles - prevent water from collecting on the cell surfaces. Pathogens collect in water (they need to survive in) not having much water is a defence.
Bark - chemical defences that work against pathogenic organisms
Stomatal closure- possible points of entry for pathogens. Stomatal aperture is controlled by the guard cells will close the stomata in that part of the plant
Callose - large polysaccharide deposited in sieve tubed at the end of a growing season. It is deposited around the sieve plates and blocks flow of sieve tubes. Prevents pathogen spreading around the plant
Tylose formation - balloon like swelling or projection that fills xylem vessel. When tylose is fully formed, it plugs the vessel cannot carry water. Prevents spread of pathogens through the heartwood. Tylose contains chemicals which are toxic to pathogens.
What are chemical defences?
Plant tissues contain a variety of chemicals that have anti-pathogenic properties. These include terpenoids, phenols, alkaloids and hydrolytic enzymes.
Some of these chemicals, such as terpenes in tyloses and tannins in bark are present before infection. However, due to chemicals they require a lot of energy,
Many chemicals aren’t produced until the plant detects an infections.
What are active defences?
When a pathogen attack, specific chemicals in their cell wall can be detected by the plant cell. These chemicals included specific proteins and glycolipids. The plant respond by fortifying the defences already present. Includes increasing physical defences and producing more chemicals. Active defences include;
- cell walls become thicker and stronger
- deposition of callose between plant cell wall and cell membrane near the invading pathogen. Callose deposits are polysaccharides polymers that impede cellular penetration at the site of infection. It strengthens the cell wall and blocks plasmodesmata.
- oxidative bursts that produce highly reactive oxygen molecules capable of damaging the cells of invading organisms
- an increase in production chemicals
What is necrosis?
Deliberate cell suicide. A few cells are sacrificed to save the rest of the plant. By killing cells surrounding the infection, the plant can limit the pathogens access to water and nutrients and can therefore stop is spreading further around the plant. It is done by intracellular enzymes that are activated by injury. These enzymes destroy damaged cells and produce brown spots on leaves snd dieback
