plant - insect herbivore interactions Flashcards
Tell me about plant responses to insect herbivory
constitutive response: always happening
induced response: in response to something
induced split into:
- Pattern triggered response
- effector triggered response
These don’t kill insects directly, just enhances chemical barriers and defence capacity
Tell me about structural defences
structural defences are a direct response
They are a physical barrier for herbivores, preventing feeding
- surface wax, thick cell walls, lignification, trichomes
trichomes - produce secondary metabolites that can be poisonous
Tell me about the production of toxic chemicals
Production of toxic chemicals is a direct response.
secondary metabolites, including phytometabolites (constitutive) and phytoalexins (effector triggered) composed of phenols, polyphenols and flavonoids, prevent digestion after undergoing oxidation
enzymes:
Lectins = bind to carbs producing damage
protease inhibitors = bind to digestive enzymes and inhibit activity
peroxidases = anit-oxidant
polyphenol oxidases = produce reactive compounds inducing ROS
tell me about herbivore induced plant volatiles
herbivore induced plant volatiles are an indirect response.
they are a VOCs that attract herbivore predators
Tell me about killer fungi
Entomopathogenic fungi are fungi that predate insects
such as cordyceps (Ascomycota).
fungus cause ant workers to leave nest and search for suitable microclimate, where they climb and bite onto vegetation. the bite remains due to major atrophy of mandibles (from fungi colonisation). after death, fungi grows stroma from base of ants head and spreads ascospores from high ground
Specific fungi must be present on insect surface, and penetration can be direct or via appressorium. once cuticle is penetrated, mycelium grows or single celled hyphal bodies form
Secondary metabolites accelerate insect death
Tell me about killer bacteria
Insect pathogenic bacteria, such as some Bacillus
It produces endospores and if conditions are favourable, endospores germinate into vegetative cell, producing more. If not, endospore toxins accumulate into crystals.
ingested crystals are cleaved and become toxic in alkaline insect digestion
