Flashcards in Biotic and Abiotic Interactions Deck (33):
interactions between living things
interactions between organism and non-living factors
the pathogen is entirely dependent on the host for nutrition
kills host tissue as grows through them
Steps of pathogen (disease)
Locate the host
Penetration and entry
Suppression or avoidance of host defences
Dispersal from host
What do pathogens produce that causes part or all of the disease syndrome?
Types of defences by host plant:
inducible and constitutive
Resistance gene (plant) interacts with product of avirulence gene (pathogen).
Resistance gene (plant) interacts with product of avirulence gene (pathogen). Elicitor activates defence response by plant receptor.
Responses to pathogen recognition
(through NADPH-dependent oxidases)
What do hydrogen peroxide and hydroxyl radicals do in plant defence?
Initiate hypersensitive response
What is the hypersensitive response?
Cells kill themselves at the site of infection to prevent further spread.
When does the hypersensitive response work?
What is systemic acquired resistance?
plant survives infection at one site the plant develops increased resistance at subsequent attack at sites throughout the plant
What is the use of methyl salicylate in plant defence?
Important signalling molecule for systematic acquired resistance.
Thought to be important in local signalling of pathogen attack to other plants (transpiration from leaves).
How is methyl salicylate transported around plant?
mostly likely through the vascular system
What are pathogen-related proteins (plant)?
hydrolytic enzymes that destroy pathogens macromolecules
Example of constitutive defence
For insect herbivory (deters feeding):
Terpenes – stored in resin canals or glandular hairs on plant surface
Example of inducible defence
Triggered by substance in insect saliva, Jasmonic acid
-> Protease inhibitors (block protein digestion)
-> amylase (block starch digestion)
-> signals to local area (other plants)
What are alkaloids?
constitutive defence molecule produced and stored by plants. Has a dramatic effect on vertebrate animals.
What are phenolic compounds?
stored compounds that deter insect feeding or have anti-fungal effects
E.g. benzoic acid
What are cyanogenic glycosides?
Present in the vacuole and enzymes required to release cyanide in the cytosol.
E.g. apple seeds
What are phytoalexins
produced by de novo synthesis in response to stress, particularly pathogen attack
E.g. rishitin (potatoes)
Two categories for response to abiotic stress
Physiological or metabolic response of individuals in response to changing environmental factors
Constant or recurrent environmental challenges exert selective pressure driving evolution of traits that increase fitness under stress. Occurs over generations and across populations.
Physio-chemical variables in the environment
Water (lack and excess)
Oxygen (and reactive derivatives)
Response(s) to water deficit and osmotic stress
Vacuolar accumulation of salts
Cytoplasm and organelles accumulated compatible solutes(sol. @ high conc. and non-toxic)
Stomatal closure (abscisic acid)
Response(s) to flooding (excess water)
Generate ATP in glycolysis
Regenerate NAD+ through production of ethanol
Aerenchyma in roots to help O2 diffusion controlled by ethylene production
Suberin and lignin deposits at the hypodermis help stop O2 leaking out of the root
Response(s) to cold stress
Accumulation of compatible solutes (osmoprotectants) allows cellular water to ‘super cool’ without freezing down to -40ºC.
Response(s) to chilling sensitivity
more unsaturated fatty acids the membrane contains the lower the temperature at which the liquid to gel transition of cell membrane occurs.
Response(s) to excess light
Light receive by violaxanthin then given to chlorophyll
When too much light, violaxanthin can be converted into zeaxanthin (reversible).