Download Plant Defense - Henriksen Science

Plant Defenses
1- First line of defense: Plant
perimeter protection
2- Second line of defense:
Chemical warfare
3- Mutalistic Relationships
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
Physical Defenses
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 spinesDovyalis caffra
Otherwise known
as kei apple
Drought tolerant
Leaf spinesOpuntia
invicta
A closer look…
• Why did spines often evolve in
areas that are dry or in other
ways “stressful”?
“Secondary” Metabolites- a
term that has stuck
They do not play a role in
photosynthesis, growth, or
respiration. HOWEVER…
Sec Plant secondary metabolites
•protect primary
metabolism
by deterring
ondary
Compounds
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.
Constitutive vs. Induced
Defenses
Constitutive defense always present
Induced defense - synthesized
in response to challenge
Non-volatile
Volatile
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.
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
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