Plant Defense Against Pathogens Flashcards
What is callose?
A large polysaccharide deposit that blocks old phloem sieve tubes.
What are the two types of passive defences?
Physical and chemical defences.
What are the physical defences of plants?
Cellulose cell wall Lignin thickening of cell walls Waxy cuticles Bark Stomatal closure Callose Tylose formation
How does the cellulose cell wall defend the plant?
It acts as a physical barrier but most plant cell walls contain a variety of chemical defences that can be activated when a pathogen is detected.
How does bark defend a plant?
Most bark contains a variety of chemical defences that work against pathogenic organisms.
How does tylose formation defend a plant?
A tylose is a balloon-like swelling or projection that fills the xylem vessel. When a tylose is fully formed, it plugs the vessel and the vessel can no longer carry water. Blocking the xylem vessels prevents spread of pathogen through the heart wood.
Give examples of active defences.
Cell walls become thickened and strengthened with additional cellulose.
Deposition of callose between the plant cell wall and cell membrane near the invading pathogen.
Oxidative bursts that produce highly reactive oxygen molecules capable of damaging the cells of invading organisms.
An increase in production of chemicals.
What do typenoids do?
A range of essential oils that have antibacterial and antifungal properties. They may also create scent, for examples, the menthols and menthones produced by mint plants.
What do phenols do?
These also have antifungal and antibiotic properties. Tannins found in bark inhibit attack by insects. These compounds bind to salivary proteins and digestive enzymes deactivating the enzymes. Insects that ingest tannins do not grow and will eventually die.
What do alkaloids do?
Give a bitter taste to inhibit herbivores feeding. Some alkaloids inhibit protein synthesis.
What do defensive proteins (defensins) do?
These are small cysteine-rich proteins that have broad anti-microbial activity. Appear to affect molecules in the plasma membrane, possibly inhibiting the action of ion transport channels.
Where are hydrolytic enzymes found in plants?
These are found in the spaces between cells.
What do chitinases do?
Break down the chitin found in fungal cell walls.
What do glucanases do?
Hydrolyse the glycosidic bonds in glucans.
What do lysozomes do?
Capable of degrading bacterial cell walls.
