12.4 PLANT DEFENCES AGAINST PATHOGENS Flashcards
1
Q
how do plants recognise an attack?
A
- plants are not passive - they respond rapidly to pathogen attacks
- receptors in the cells respond to molecules from the pathogens, or to chemicals produced when the cell wall is attacked
- stimulates release of signalling molecules that appear to switch on genes in the nucleus
- this triggers cellular responses, which include producing defensive chemicals , sending alarm signals to unaffected cells to trigger their defences, and physically strengthening the cell walls
2
Q
what is produced in a plants physical defences?
A
- polysaccharide called callose, contains β-1, 3 linkages and β-1, 6 linkages between the glucose monomers
3
Q
what do scientists suggest are the roles played by callose in the defence mechanisms of a plant?
A
- within minutes of an initial attack, callose is synthesised and deposited between the cell walls and the cell membrane in cells next to infected cells (acts as a barrier, preventing pathogens entering other plant cells)
- large amounts continue to be deposited in cell walls after the initial infection, lignin is added making the mechanical barrier thicker and stronger
- callose blocks sieve plates in the phloem, sealing off infected part and preventing pathogen spread
- callose is deposited in plasmodium between infected cells and neighbours, sealing them off from healthy cells
4
Q
what are examples of plants chemical defences?
A
- insect repellents
- insecticides
- antibacterial compounds incl. antibiotics
- antifungal compounds
- anti-oomycetes
- general toxins
5
Q
what are examples of insect repellants?
A
- pine resin
- citronella from lemon grass
6
Q
what are insecticides?
A
- e.g. pyrethrins
- these are made by chrysanthemums and act as insect neurotoxins
- e.g. caffeine
- this is toxic to insects and fungi
7
Q
what are antibacterial compounds (incl. antibiotics)?
A
- e.g. phenols
- these are antiseptics made in many different plants
- e.g. antibacterial gossypol
- produced by cotton
- e.g. defensins
- plant proteins that disrupt bacterial and fungal cell membranes
- e.g. lysosomes
- organelles containing enzymes that break down bacterial cell walls
8
Q
what are antifungal compounds?
A
- e.g. phenols
- antifungals made in many different plants
- e.g. antifungal gossypol
- produced by cotton
- e.g. caffeine
- toxic to fungi and insects
- e.g. saponins
- chemicals in many plant cell membranes that interfere with fungal cell membranes
- e.g. chitinases
- enzymes that break down chitin in fungal cell walls
9
Q
what are anti-oomycetes?
A
- e.g. glucanases
- enzymes made by some plants that break down glucans
- e.g. polymers
- found in cell walls of oomycetes
10
Q
what are general toxins?
A
- some plants make chemicals that can be broken down to form cyanide compounds when the plant is attacked
- cyanide is toxic to most living things
