1- First line of defense: Plant perimeter protection

2- Second line of defense: Chemical warfare - Terpenes

Classes of plant defensesClasses of plant defenses

PHYSICAL DEFENCESPHYSICAL DEFENCES

•Spines, thornsSpines, thorns

•Cutins, waxes, suberinsCutins, waxes, suberins

SECONDARY DEFENCESSECONDARY DEFENCES

• TerpenesTerpenes

Physical Defenses

Stem spines Colletia paradoxa Leaf spines- Opuntia invicta

Shoot spines- Dovyalis caffra Otherwise known as kei appleDrought tolerant

Why did spines often evolve in areas that are dry or in other ways “stressful”?

Other roles - competition, camouflage?

Hydrophobic: having water-repelling properties

These compounds are non-polarFatty acids are one type of

hydrophobic compound

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

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.

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

•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.