Transcript Chapter 13 Secondary metabolites and plant defense *

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
*cutin: on most aboveground parts
ester-linkage
or epoxide
*waxes: associate with both cutin
and suberin
aldehyde, ketones, esters and free fatty acids
*suberin: on underground parts,
woody stem, and healed wounds
in the Casparian strip
to reduce transpiration and pathogen invasion
the mechanism of wax formation (？), natural wax
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)
Three groups:
(1) terpenes: isoprene unit
 essential oil
 + ester: pyrethroids
insecticides
 essential oil, ABA
 brassinosterol, saponin, limonoids,
cardenolides (p. 322)
 GA
 carotenoids
[C5]n n  8, dolichols
Saponins
Functions: growth, development, defense, perfumes, medicals,….
C10 monoterpene
Glandular hair on a young
leaf of spring sunflower
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
Plant phenolics are biosynthesized in several different ways
(2) Phenols:
Glyphosphate (Roundup)
Not in animals
Tannins: unripe fruits, wine,…
Flavonoids (C6-C3-C6)
(salicylic acid)
p. 325
(allelopathy)
(phototoxicity)
C6-C3
Functions: protection (pathogen, UV-light), color, antimicrobial activity,
mechanical strengthen,…