plant responses to herbivory Flashcards
(15 cards)
What physical defences have plants evolved to deter herbivores?
- thorns, barbs, spikes, spiny leaves, fibrous/inedible tissue, stings
How do tannins deter herbivores?
- a type of phenol
- Can make up to 50% of the dry weight of leaves.
- Very bitter.
- Toxic to insects: bind to digestive enzymes produced in the saliva and inactivate them.
found in tea and red wine
How do alkaloids deter herbivores?
- Bitter tasting, nitrogenous.
- Act as drugs by affecting the metabolism of animals that take them.
- Can poison
- examples: caffeine, nicotine, morphine, cocaine
- caffeine is toxic to fungi and insects, can also inhibit germination of other seeds when released in soil
- nicotine: transported to leaves from roots of tobacco plant, stored in vacuoles and released when eaten.
How do terpenoids deter herbivores?
- such as pyrethrin (chrysanthemums) which acts as an insect neurotoxin.
- Can act as insect repellents e.g citronella.
What is a pheromone?
- a chemical made by an organism which affects the social behaviour of other members of the same species.
Examples of plant pheromones
- if a maple tree is attacked by insects it releases a pheromone which is absorbed by leaves on other branches (and other trees). promotes callose synthesis and deposition.
- Some evidence to suggest that plants can tell a neighbour when they’re under water stress.
What group of compounds do plants use more frequently than pheromones?
VOCs
How are VOCs different to pheromones?
- they can be used to affect the behaviour of other species such as insects .
How are VOCs transported?
- diffuse through the air in and around the plant.
What triggers plants to synthesise VOCs?
- They detect specific chemicals in insect saliva. This may elicit gene switching.
How do cabbages respond to attack by cabbage white butterfly caterpillars?
- produce a chemical signal which attracts parasitic wasp Cotesia glomerata.
- This lays eggs its eggs in the caterpillars which are then eaten alive, protecting the plant.
- Deters other female cabbage butterflies from laying their eggs.
How do cabbages respond to attack by mealy cabbage greenfly?
- sends out a singal to attract a parasitic wasp which only attacks greenfly.
What happens when apple trees are attacked by spider mites?
produce VOCs which attract predatory mites that come and destroy the apple tree pests.
How can VOCs act as pheromones?
- VOC release can stimulate neighbouring plants to produce VOCs before they are actually attacked.
What causes the plant response where leaves fold in response to touch?
- Potassium ion movement and osmotic water movement.
- Frightens larger herbivores and dislodges insects.
