Download Plant Defense - Unit3and4Biology

1- First line of defense: Plant perimeter
protection
2- Second line of defense: Chemical warfare
- Terpenes
Classes of plant defenses
PHYSICAL DEFENCES
•Spines, thorns
•Cutins, waxes, suberins
SECONDARY DEFENCES
• Terpenes
Physical Defenses
Stem spines Colletia paradoxa
Leaf spines- Opuntia invicta
Shoot spines- Dovyalis caffra
Otherwise known as kei apple
Drought tolerant
 Why
did spines often evolve
in areas that are dry or in
other ways “stressful”?
 Other roles - competition,
camouflage?
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Hydrophobic: having water-repelling
properties
These compounds are non-polar
Fatty acids are one type of
hydrophobic compound

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composed of long fatty acid chains
a major component of plant cuticle
Plants’ cuticles
often vary with
the climate in
which they live.
Cactus cuticle
Cactus
cuticle

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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.
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Also formed from fatty acids but has a
different structure from cutin.
A cell wall constituent.
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

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•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
Non-volatile terpenes - limonene
apparently distasteful to herbivores
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.
Terpenes such as
pyrethrum (from
chrysanthemums) and
azadirachtin (from the
Asian and African Neem
tree) can be used as
“natural” insecticides in
agricultural practices or
in horticulture.