Plant responses to herbivory Flashcards
what is herbivory?
the process by which animals eat plants
Why do plants need responses to herbivory?
cannot escape herbivores
What physical defences protect plants?
thrones
barbs
spikes
spiny leaves
fibrous and inedible tissue
hairy leaves
stings
What chemical defences do plants have?
tannins
alkaloids
terpenoids
What are tannins?
part of group of compounds called phenols
can make up to 50% of the dry weight of leaves
bitter taste
toxic to insects- bind to digestive enzymes in saliva and inactivate them
What are alkaloids?
group of bitter tasting nitrogenous compounds
some act as drugs, affect metabolism of animals, sometimes poisoning them
include- caffeine, nicotine, morphine, cocaine
caffeine- toxic to fungi and insects, caffeine produced by coffee bush spreads through soil and prevents germination of other seedlings- protects against herbivores and plant rivals
nicotine- toxin produced in the roots of tobacco plants, transported to leaves, stored in vacuoles, released when leaf eaten
What are terpenoids?
group of compounds produced by plants, often form essential oils, also act as toxins to insects and fungi that might attack the plant
pyrethrin- acts as insect neurotoxin, interfering with NS
some act as insect repellents
citronella, produced by lemon grass, repels insects
What are pheromones?
chemical made by an organism, affecting the social behaviour of other members of the sae species
Why do plants not rely a lot on pheromones?
they don’t behave socially
How do plants rely on phenols to defend themselves?
maple tree attacked by insects, releases pheromone absorbed by leaves of other branches, leaves produce chemicals like callose to help protect them, leaves on nearby trees also prepare for attack in response to this phenol
evidence plants communicate through root systems, warning others when they under water stress.,
What are volatile organic compounds?
VOC’s
chemicals produced by plants, usually only when chemicals in insects saliva are detected
act like pheromones- between themselves and other organisms, like insects
diffuse through air in and around plant
may also cause other plants to produce the VOC before its even attacked
Give examples of defence mechanisms by VOC’s
cabbages attacked by caterpillars or butterfly, , produce chemical signal attracting the parasitic wasp, lays its eggs in caterpillars, which are then eaten alive, also deters any female butterfly from laying their eggs
apple trees attacked by spider mites, VOCs attract predatory mice
some wheat seedlings produce VOCs when they have been attacked by aphids, repel other aphids from the plant
Why do some plants move in response to touching?
frightens off larger herbivores
dislodges insects
How do plants responsive to touch operate?- eg. venus fly trap
leaf falls in a few seconds, recovers in minutes as a result of potassium ion movement into specific cells, followed by osmotic water movement
