Chapter 13 Secondary metabolites and plant defense

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Chapter 13 Secondary metabolites and plant
defense Sedentary A wide variety of
attackers The mechanisms of self-protection
against herbivores and pathogenic
microbes 1. Surface protection reduce H2O
loss and help block the entry of pathogene
cutin, waxes, and suberin 2.
Secondary metabolites no direct function in
growth and development, also named
secondary products, natural products,
depend on plant species, functionless
end products of metabolism or metabolic wastes
? important medicinal drugs, poisons,
flavors, and industrial materials,
even have ecological functions 3. The
signaling processes during host-pathogen
interaction
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cutin on most aboveground parts
ester-linkage waxes associate with both
cutin and suberin suberin on
underground parts, woody stem, and healed
wounds in the Casparian strip
or epoxide
aldehyde, ketones, esters and free fatty acids
to reduce transpiration and pathogen
invasion
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the mechanism of wax formation (?), natural wax
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• Secondary metabolites
• the results of heritable mutations, natural
  selection, and
• evolution change
• Ecological functions in plants
• against being eaten by herbivores and infected
  by microbial pathogens
• as attractants for pollinators and
  seed-dispersing animals
• as agents of plant-plant competition
  (allelopathy, p.324) and
• plant-microbe symbioses
• From leaves, roots, and decaying litter,
  plants release a variety of primary and
• secondary metabolites into environment.
  Investigation of the effects of these
• compounds on neighboring plants.
• Many important crop plants have been
  artificially selected
• ? low levels of secondary metabolites
• (more susceptible to insects and diseases)

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Three groups
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1. terpenes isoprene unit

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? essential oil ? ester pyrethroids insecticide
s
? essential oil, ABA
? brassinosterol, saponin, limonoids,
cardenolides (p. 322)
? GA
? carotenoids
Saponins
C5n n ? 8, dolichols
Functions growth, development, defense,
perfumes, medicals,.
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C10
monoterpene
Glandular hair on a young leaf of spring
sunflower
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C30 triterpene
Powerful feeding deterrents to insects
From the neem tree (Azadirachta indica) 50 ppb
for some insects
From the common fern (Polypodium vulgare) Against
plant-parasitic nematodes
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Plant phenolics are biosynthesized in several
different ways
(2) Phenols
Glyphosphate (Roundup)
Not in animals
Tannins unripe fruits, wine,
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Flavonoids (C6-C3-C6)
(salicylic acid) p. 325
(allelopathy)
(phototoxicity)
C6-C3
Functions protection (pathogen, UV-light),
color, antimicrobial activity,
mechanical strengthen,
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