Weapons Of War Flashcards
What are the two components of plant defence?
Spatial
Temporal
What is a spatial defence?
„The defence of a medieval castle - outer and inner walls surrounded by a moat“
What is the temporal defence?
The production of defences following the attack as well as during plant development
What is the first point of contact between a plant and its attacker?
The cuticle
How does the cuticle help attackers?
Differnces in cuticular waxes can be used by specialist insects
The waxes are also important cues for the development of various fungi on the leaf surface
What is the cell wall capable of?
Providing structure for the cell as well as protection against outside stresses
What is the cell wall composed of?
Cellulose
A long chain of linked sugars (gives wood its strength)
What does the glucose in the cell wall form?
Dietary fiber
How are the bundled cellulose fibers called?
Microfibrils
What are microfibrils cross - linked with?
Hemicelluloses - this provides great strength to the structure
What are the fibers of the cell walls embedded in?
Pectins
What are secondary cell walls frequently impregnated with?
With lignin
A polymer composed of phenolic compounds, which provides great rigidity to the cell wall
Lignified cell walls are highly impermeable to pathogens
How can pathogens breach these cell wall?
By using a cocktail of enzymes capable of breaking down the individual components
What are enzymes to breach the cell wall
Cellulases
Hemicellulases
Pectinases
What does xylanase degrade?
The linear backbone of xylan - the major hemicellulose in cell walls
What do Polygalacturonase enzymes degrade?
The pectic backbone of the cell wall, which is comprised of homogalacturonan
How is the homogalacturonan protected by in newly formed pectin?
By the addition of methyl (CH3) groups (They are methyl esterified)
How do pathogens overcome the methyl groups of the homogalacturonan?
By methylesterase which removes the methyl groups - now the pathogen can break down the homogalacturonan
Why do plants increase their own pectin methylesterases?
The plant is stimulating the release of cell wall fragments with this (DAMPS) that therefore activate defences
Why are pectin methylerases important to the ability of some pathogens to infect their hosts?
Pectin methylerases can be inhibited by specific proteins that are used to regulate the cell wall
When overexpressing these inhibitor genes in a plant the pathogens ability to infect the plants is greatly reduced
How does the plant protect itself from these enzymes?
By producig proteins that are capable of inhibiting the component enzymes
What are examples for enzyme inhibitors?
Xylanase inhibitors
PGIPs (polygalacturonase inhibitor proteins)
Where are PGIPs located?
In the cell wall - it can limit fungal invasion
How does a fungal polygalacturonase work?
1.They attack the pectin in the cell wall
2. By doing this, cell wall fragments get released - the polygalacturonases reduces these fragments to a size that doesnt trigger defences
How does the plants PGIPs cope with the fungal polygalacturonases?
How do plants degrade the fungal cell walls?
By producing chitinases ans glucanases, that attack these components in the fungal cell walls.
Plants dont contain chitin, so it is thought that these chitinases are for fungal protection only
How can fungi overcome these chitinases?
The tomato leaf mold produces a protein which binds to its own cell wall, that protects the fungus against the tomatos chitinases
This protein binds any fragments of chitin liberated by plant chitinase
One fungus produces the enzyme called fungalysin which cleaves and inactivates the defensive chitinases produced by its plant hosts
What are wheat antimicrobial peptides
Molecules in plants (not just in wheat!!) that inhibit hyphal growth
What are papillae?
Structures that repair the plant immediately after assault
Also known as cell wall appositions
What additional constituents does papillae contain?
Phenolics
Lignin
Hydrogen peroxide
Peroxidase (enzyme)
What does the lignin do in pappilae?
Adds great structural strength
What does the peroxidase do in pappilae?
It can use hydrogen peroxide to cross-link phenolic compunds and proteins -> reinforces pappilae
In which defence stage does pappilae occur
In the early stages of defence response
It slows down pathogen ingress, allowing time for additional defence to be deployed
Where is papillae found?
At sites of successful pathogen penetration
At sites of successful plant defence
How can cell wall degrading enzymes, produced by fungi, enter the cell wall
By so called nanopores
How does a plant stop the fungi from entering via nanopores?
In thale cress, callose (Papillae) seals these pores and form a waxy layer on the surface of the cell wall, preventing entry of the enzymes
What does the plants vascular system consist of?
The xylem and phloem
What does the xylem do?
Transport water and mineral nutrients from the root to the shoot
What does the phloem do?
Moving sugars formed in leaves to all other parts of the plant
What does the phloem consist of?
Sieve elements and companion cells
Plasmodesmata connects these cells
What happens when sieve elements mature?
The plasmodesmata in the cell wall widens to form sieve plates
They stack on top of each other and form long vessels capable of conducting sugars and other materials
How does the plant ward of insects that drink out of the phloem?
Callose is deposited on the sieve plates at the point of stylet insertion
Where is lignin found?
It is a major component in secondary cell walls
What is lignins task in the secondary cell wall?
It cross links cellulose microfibrils
This provides a rigid and impermeable structure
What does the presence of lignin imply in plants
That they can grow strong an tall, can form stems and branches capable of bearing flowers and fruits
What is lignin?
A complex polymer - formed of subunits called monolignols
Where are lignin monolignols synthesized?
In the cell and then transported to the cell wall where they are polymerized to form lignin
How is lignin used by the plant for defence?
Lignins get deposited at the site of attack
It provides a structural barrier against attack
Its presence limits degradation of polysaccharides by cell wall degrading enzymes
Can reduce the diffusion of toxins from the pathogen to the plant and of nutrients from the cell towards the pathogen
What does imply that plants can monitor the integrity of their cell wall and respond accordingly?
Plants can compromise in their ability to produce cellulose activated lignin synthesis
How do herbivores adapt to lignin rich plants?
They prefer plants with low lignin content
How is cork formed?
From a layer of cells in the cortex of stems -> Cork camibium
When cells in the cork camibium divide, they grow parenchyma cells facing inward and cork cells outwards
Cork cells get invested with waxy, waterproof suberin
When they reach maturity, they die
What are Cork cambium and the cells deriving from it called?
The periderm
What role does cork play in plant defence?
just beyond the site of pathogen attack, some plants produce multiple layers of cork cells
-> this halts the progress of the pathogen and blocks water and nutrient flow, which starves it
How do plants expel the invader?
The ornamental cherry for example:
They dissolve the middle lamella (Glue that holds cells together) - the circle of invaded cells dies off
What are pits?
Unlignified areas of the xylems vessel walls that allow waterflow between adjacent xylem vessels
What is a tylose?
When an invader enters the xylem, these can be produced by the plant
Parenchyma cells surrounding the invaded xylem vessel let their protoplast reach out into the lumen of the vessel - this can block the flow of water and the spread of the pathogen
What is chlorogenic acid in plant defence?
It has antimicrocial properties
When it is Oxidized in the plant it is able to inactivate enzymes, including those used by pathogens as they attempt to gain acess to plants
How can chlorogenic acid protect the plant against fungal attacks?
By inhibiting fungal cutinase and polygalacturonase
What are the two types of rtrichomes do exist?
Nonglandular
Glandular
What does the nonglandular trichome do?
It acts as a physical barrier to the insects movement on the plants surface
What do glandular trichomes do?
They release various forms of chemical repellents
How much percent of vascular plants produce glandular trichomes?
30%
How do glandular trichomes get activated?
They have a touch sensitive mechanism that opens a secretory cell when touched
What cells does a trichome comprise?
A basal cell in the epidermal cell layer
One or more stalk cells
Secretory cells at the apex
How do fibre cells help in plant defence=
Even tho they are made to provide the plant with mechanical strenght, it can also prevent herbivores from eating the plant
What are fiber cells?
Sclerenchyma tissue
Heavily lignified cells
Which mineral is commonly taken up by grasses and ferns to make them stronger?
Silica - plants take it up as silicic acid and deposit it primarily in solid bodies called phytoliths in vacuoles and epidermal cell walls
Also in trichomes and spines
What are phytoliths?
For example: peach pits
Which is the most common mineral accumilating in plant tissues?
Calcium - usually present as calcium oxalate
How are star shaped calcium crystals called?
Raphides
What function does calcium oxalate have?
Anti herbivore defence
Where is calcium found in cornifers?
In the secondary phloem where it get distributed for defence against bark beetles
