1. Plant Defences

2. Plant Defences 1- First line of defense: Plant perimeter protection
2- Second line of defense: Chemical warfare
- Terpenes
General introduction to plant defense and attraction

3. Classes of plant defenses
PHYSICAL DEFENCES
Spines, thorns
Cutins, waxes, suberins
SECONDARY DEFENCES
Terpenes

4. Physical Defenses

5. Stem spines Colletia paradoxa Leaf spines- Opuntia invicta
Shoot spines- Dovyalis caffra
Otherwise known as kei apple
Drought tolerant

6. A closer look…

7. Why did spines often evolve in areas that are dry or in other ways “stressful”?
Other roles - competition, camouflage?

8. Waxes, Cutins, and Suberins

9. Cutin, Waxes, Suberins Hydrophobic: having water-repelling properties
These compounds are non-polar
Fatty acids are one type of hydrophobic compound

10. Cutin composed of long fatty acid chains
a major component of plant cuticle

11. PP13020.jpg

12. Cutin Plants’ cuticles often vary with the climate in which they live.
Cactus cuticle
Cactus cuticle

13. 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.

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

15. 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

16. Suberin can form transport barriers between the soil and the roots

17. 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

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

19. 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.

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

21. Non-volatile terpenes - limonene apparently distasteful to herbivores
PP1306a.jpg
Non-volatile terpenes - limonene
apparently distasteful to herbivores

22. PP1306b.jpg
Volatile terpenes such as menthol broadcast a smell that warns herbivores that the plant is toxic to them before herbivore feeding commences.

23. 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.

24. 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.