Plant Defences

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Plant Defences
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Plant Defences
1- First line of defense Plant perimeter
protection 2- Second line of defense Chemical
warfare - Terpenes
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• Classes of plant defenses
• PHYSICAL DEFENCES
• Spines, thorns
• Cutins, waxes, suberins
• SECONDARY DEFENCES
• Terpenes

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Physical Defenses
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Stem spines Colletia paradoxa
Leaf spines- Opuntia invicta
Shoot spines- Dovyalis caffra Otherwise known as
kei apple Drought tolerant
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A closer look
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• Why did spines often evolve in areas that are dry
  or in other ways stressful?
• Other roles - competition, camouflage?

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Waxes, Cutins, and Suberins
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Cutin, Waxes, Suberins

• Hydrophobic having water-repelling properties
• These compounds are non-polar
• Fatty acids are one type of hydrophobic compound

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Cutin

• composed of long fatty acid chains
• a major component of plant cuticle

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Cutin

• Plants cuticles often vary with the climate in
  which they live.

Cactus cuticle
Cactus cuticle
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Waxes

• 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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Suberin

• Also formed from fatty acids but has a different
  structure from cutin.
• A cell wall constituent.

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Suberin

• 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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Suberin can form transport barriers between the
soil and the roots
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Secondary Compounds

• 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

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Secondary Defences
Secondary defence may be in place prior to an
organism invading a plant, or as a result of the
invading organism
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Terpenes

• 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.

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• Terpene functions
• Growth and development
• 2. As defensive compounds
• Toxins
• feeding deterrents to insects and mammals

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Non-volatile terpenes - limonene apparently
distasteful to herbivores
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Volatile terpenes such as menthol broadcast a
smell that warns herbivores that the plant is
toxic to them before herbivore feeding commences.
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• 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.

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• 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.