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Ch 13: Secondary metabolism and plant defense 1- First line of defense: Plant perimeter protection 2- Second line of defense: Chemical warfare 3- Three major groups of secondary compounds - Terpenes - Phenolics - N-containing compounds. Agricultural pests – economic damage
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1- First line of defense: Plant perimeter protection
2- Second line of defense: Chemical warfare
3- Three major groups of secondary compounds
- N-containing compounds
– economic damage
- cost of prevention and eradication
Cotton boll weevil
phenolic glycosides peroxidases
bound phenolics polyphenol oxidase
condensed tannins hydrolysable tannins
TerpenesN-containing monoterpenes Alkaloids
diterpene acids Mustard oils
Leaf spines- Opuntia invicta
Shoot spines- Dovyalis caffra
Otherwise known as kei apple
must pass through plasma membrane to get to stele
Constitutive defense - always present
Induced defense - synthesized in response to challenge
(terpenes also called “isoprenoids”)
Monoterpenes have two C5 units (10C)
Sesquiterpenes have three C5 units (15C)
Diterpenes have four C5 units (20C)
Triterpenes 30 C
Polyterpenes ([C5]n), n>8
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.
1. cardenolides (glycosides) - acutely toxic
influence Na+/K+ ATPase of heart muscle
medicinal application - digitalis (from foxglove), used to
treat heart disease. Can slow and strengthen heart beat
2. Saponins (soaplike) - steroid, triterpenes glycosides
have lipid and water soluble parts of molecule
toxicity related to sterol binding, membrane
Molecular Evolutionary Implications
Trapp & Croteau, 2001
Some 30,000 known terpenes.
Common evolutionary origins
may predate angiosperms. Extensive gene duplication events may drive the diversity.
Prior to divergence of gymnosperms and angiosperms, during the carboniferous, the duplication of an ancestral terpene synthase gene…occurred. Once copy of the duplicated ancestral gene remained highly conserved in structure and function, and this gene may have contemporary descendants in the terpene synthases involved in giberellins biosynthesis. The second ancestral gene copy diverged in structure and function, by adaptive evolutionary processes, to yield a large superfamily of terpene synthases involved in secondary metabolic pathways.
limonene - monoterpenoid (C10) dietary anticarcinogen
Artemisnin - sesquiterpenoid (C15) antimalarial
Taxol - diterpenoid anticancer drug from Pacific yew (Taxus brevifolia)
Taxol was isolated from bark of Pacific Yew in 1970s. Taxol interferes with cell division by binding to the protein tubulin, a key factor in mitosis. Taxol and related compounds now widely used in treating breast and ovarian cancer.