Plant Defense

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Plant Defenses 1- First line of defense Plant
perimeter protection 2- Second line of defense
Chemical warfare 3- Mutalistic Relationships
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Classes of plant defenses PHYSICAL
DEFENSES Spines, thorns, hairs Cutins, waxes,
suberins SECONDARY METABOLITES Bad taste -
limolene in lemons Scent to warn - mint Poison
kills insects Prevent germination of other plants
allelopathic like pine needles Attract
predators of herbivores wasp and
caterpiller Hypersensitive response plants kill
infected cells off Mutualistic Relationships
ant and acacia
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Physical Defenses
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Dermal Tissue System

• The first-line defense of all plants
• Epidermal cells throughout the plant secrete a
  variety of lipid material that protects plant
  surfaces from water loss and attack
• -Wax, cutin, and suberin
• Example the leaves of holly plants, for
  instance, are very smooth and slippery making
  feeding difficult
• Example Cherry tree sap can trap insects

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• A plant's leaves and stem may be covered with
  sharp spines or trichomes (hairs)
• Slow down herbivores while feeding
• Add irritation (hairs stuck in mouth)

Flower bud of a Capsicum pubescens with many
trichomes.
Stem spines Colletia paradoxa
Shoot spines- Dovyalis caffra Otherwise known as
kei apple Drought tolerant
Leaf spines- Opuntia invicta
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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?

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Secondary Metabolites- a term that has
stuckThey do not play a role in photosynthesis,
growth, or respiration. HOWEVER
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Sec Plant secondary metabolites ondary Compounds

• protect primary metabolism by deterring
  herbivores, reduce tissue loss, prevent
  competition.
• Bad taste
• Scent to warn
• Poison
• Prevent germination of other plants
• Attract predators of herbivores
• Programmed death of plant cells
• also attract pollinators and seed-dispersing
  animals.

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Constitutive vs. Induced Defenses
Constitutive defense - always present
Induced defense - synthesized in response to
challenge
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Non-volatile
Volatile
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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.

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Toxin Defenses

• Allelopathic plants secrete chemicals to block
  seed germination or inhibit growth of nearby
  plants

-This strategy minimizes competition for
resources -Very little vegetation grows under
a black walnut tree
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Animals that Protect Plants

• Parasitoid wasps, caterpillars and leaves
• -As caterpillar chews away, a wound response in
  the plant leads to release of a volatile compound
• -Female parasitoid wasp is attracted
• -Lays fertilized eggs in caterpillar
• -Eggs hatch and larvae kill
  caterpillar

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Animals that Protect Plants
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Specific Defense Responses
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Animals that Protect Plants

• Complex coevolution of plants and animals has
  resulted in mutualistic associations
• -Relationships that benefit both
• Acacia trees and ants
• -Small armies of ants protect Acacia trees from
  harmful herbivores
• -Plant provides ants with food and shelter

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Animals that Protect Plants