Plant Defenses

1- First line of defense: Plant perimeter protection

2- Second line of defense: Chemical warfare

3- Mutalistic Relationships

Classes of plant defensesClasses of plant defensesPHYSICAL DEFENSESPHYSICAL DEFENSES

Spines, thorns, hairsSpines, thorns, hairs

Cutins, waxesCutins, waxes, , suberinssuberins

SECONDARY METABOLITESSECONDARY METABOLITES

Bad taste - limolene in lemonsBad taste - limolene in lemons

Scent to warn - mintScent to warn - mint

Poison – kills insectsPoison – kills insects

Prevent germination of other plants – allelopathic like pine Prevent germination of other plants – allelopathic like pine needlesneedles

Attract predators of herbivores – wasp and caterpillerAttract predators of herbivores – wasp and caterpiller

Hypersensitive response – plants kill infected cells offHypersensitive response – plants kill infected cells off

Mutualistic Relationships – ant and acaciaMutualistic Relationships – ant and acacia

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

Stem spines Colletia paradoxa

Leaf spines- Opuntia invicta

Shoot spines- Dovyalis caffra Otherwise known as kei appleDrought tolerant

Flower bud of a Capsicum pubescens with many trichomes.

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)

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

ondary Compounds•protect primary metabolism by deterring herbivores, reduce tissue loss, prevent competition.

•Bad tasteBad taste

•Scent to warnScent to warn

•Poison Poison

•Prevent germination of other plantsPrevent germination of other plants

•Attract predators of herbivoresAttract predators of herbivores

•Programmed death of plant cellsProgrammed death of plant cells

•also attract pollinators and seed-dispersing animals.

Constitutive defense - always present

Constitutive vs. Induced Defenses

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.

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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