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1- First line of defense: Plant perimeter protection
2- Second line of defense: Chemical warfare - Terpenes
Classes of plant defensesClasses of plant defenses
PHYSICAL DEFENCESPHYSICAL DEFENCES
•Spines, thornsSpines, thorns
•Cutins, waxes, suberinsCutins, waxes, suberins
SECONDARY DEFENCESSECONDARY DEFENCES
• TerpenesTerpenes
Stem spines Colletia paradoxa Leaf spines- Opuntia invicta
Shoot spines- Dovyalis caffra Otherwise known as kei appleDrought tolerant
Why did spines often evolve in areas that are dry or in other ways “stressful”?
Other roles - competition, camouflage?
Hydrophobic: having water-repelling properties
These compounds are non-polarFatty acids are one type of
hydrophobic compound
complex mixtures of long-chain lipids that are extremely hydrophobic.
are synthesized by epidermal cells.exuded through pores in the
epidermal cell wall by an unknown mechanism.
often within roots. can protect against pathogens and other
damage. older parts of roots more suberized endodermis has suberin side walls, water must pass through plasma membrane to
get to stele
•protect primary metabolism by deterring herbivores, reduce tissue loss.
•also attract pollinators and seed-dispersing animals.
•formed from the byproducts or intermediates of primary metabolism
Secondary Defences
Secondary defence may be in place prior to an organism invading a plant, or as a result of the invading organism
•constituents of essential oils
•function as herbivore deterrents
•can be produced in response to herbivore feeding, and to attract predatory insects and parasites of the feeding herbivore.
Terpene functions
1.Growth and development
2. As defensive compounds•Toxins•feeding deterrents to insects and mammals
Volatile terpenes such as menthol broadcast a smell that warns herbivores that the plant is toxic to them before herbivore feeding commences.
Phytoecdysones are plant steroids (within the terpene class) that have the same basic structure as insect molting hormones and thus interfere with molting. These compounds sometimes cause death of the insect herbivore.