Transcript (3) Nitrogen-containing compounds

Allelopathy
Development of crop plants genetically
engineered to be allelopathic to weeds
Phototoxicity
UV-A (320-400 nm)
(3) Nitrogen-containing compounds
(A) alkaloids, a heterocyclic ring. A ring that contains both
nitrogen and carbon atoms.
(B) cyanogenic glycosides, (C) nonprotein amino acids
2007.6
(3) Nitrogen-containing compounds
(B) cyanogenic glycosides
Broken down to give off poisons
R is CH2=CH-CH2- sinigrin
In black mustard seed and horseradish roots
(3) Nitrogen-containing compounds
(C) Nonprotein amino acids
Induced plant defense against insect herbivores
two categories:
Constitutive defense responses:
always present; species-specific;
may exist as stored compounds (conjugated form) or precursors
of active compounds that can easily be activated upon damage
most of the second metabolites
Induced defense responses
are initiated only after actual damage occurs
must be activated quickly to be effective
Insect herbivores: aphids, whiteflies, mites, thrips, caterpillars,
grasshoppers, beetles…
Plants can recognize specific compounds of insect saliva
elicitors:
certain insect-derived compounds
can serve as enhancers of wound response and trigger signaling
pathways systemically
e.g., fatty acid-amino acid conjugates,
volicitin: to induce volatile secondary
metabolites in corn
Polygalacturonic acid
Jasmonic acid is a plant hormones
activates many defense responses
elicitors
Octadecanoid pathway
18C
Cyclization
12C
p. 335R
Low level JA mutant: are easily killed by insect
Exogeneous: restore resistance
(true) Endogenous level
JA induces
anticancer alkaloids
proteins, such as
lectins: bind to the epithelial cells lining the digestive tract and
interfere with nutrient absorption
-amylase inhibitors:
proteinase inhibitors:
Some insect herbivores have become adapted to plant proteinase
inhibitors by production of digestive proteinase resistant to
inhibition.
P.336 L
Herbivore damage induces systemic defenses
proteinase
inhibitors
biosynthesis
Conjugated
form
LRR receptor:
(18 aa)
a leucine-rich repeat protein
with kinase activity
(200 aa)
dual function: the receptor of
systemin and brassinolide
Prosystemin orthologues in the other Solanaceous species
dual function
receptor
C-terminal requirement,
prosystemin still exist activity
Plant cell physiology (2000) 41: 825-830
Herbivore-induced volatiles
Include terpenes, alkaloids, and phenolics
 Specific for each insect herbivore species
general- vs. nicotine-tolerant caterpillars (p. 337-338)
 green-leaf volatiles, a mixture of 6-carbon aldehydes, alcohols,
and esters which are derived from lipid
 functions: are manifold
to attract natural enemies of the attacking herbivore  predators or
parasites
act as signals for neighboring plants to initiate expression of
defense-related genes, even induction of phytoalexins and other
antimicrobial compounds
reciprocal evolutionary change between plant and insect, a type of
co-evolution  plant-insect interactions have led to a standoff in
which can develop and survive under suboptimal conditions
Plant defense against pathogens
— resist to diseases caused by the fungi, bacteria, viruses, and nematodes
— some antimicrobial compounds are synthesized before pathogen attack
e.g., saponins, a group of triterpenes, disrupt fungal membranes
— hypersensitive response (HR):
a type of programmed cell death
cells surrounding the infection site die rapidly
the rapid accumulation of reactive oxygen species (ROS) and
nitric oxide (NO)
— systemic acquired resistance (SAR):
a special type of plant immunity
p. 735 The increased resistance throughout a plant to a range of
pathogens following the infection of a pathogen at one site
Pathogen:
avirulence (avr) genes encode specific elicitors
Arg
Host:
R genes encode
Protein receptors
(Chitinases,
glucanases)
ROS:
formed by the reduction of molecular oxygen
superoxide anion, hydrogen peroxide, hydroxyl
radical
Pathogen:
avirulence (avr) genes encode specific elicitors, include proteins, peptides,
sterols, and polysaccharide fragments arising from pathogen cell wall or
outmembrane, or a secretion process
Host:
R genes product activate the various modes of antipathogen defense,
some encode protein receptors, a nucleotide-binding site (ATP or GTP),
a protein kinase domain
NADPH-dependent oxidase:
located at the plasma membrane, produce superoxide anion
inhibitor: diphenylene iodonium (applied concentration ?)
Phytoalexins:
a chemicals with strong antimicrobial activity that accumulate around the
site of infection, e.g., isoflavonoids, sesquiterpenes (p. 340)
Systemic acquired resistance (SAR):
Green-leaf volatiles
H2O2
not a long-distance
signal
DIR1 gene (p. 341)
Defective in Induced
Resistance 1,
Encodes a lipid
transfer protein,
expressed in phloem
Block the SAR
response
Spray SA, reduced virus infection in Phalaenopsis
The most studied of the signaling pathways about
localized and systemic defense mechanisms are regulated
by salicylic acid , jasmonic acid, and ethylene or their
derivatives. These pathways have been associated with
resistance to different types of pathogens, with the SAdependent pathway mainly providing resistance to
biotrophic pathogens while the JA and ET pathways
provide resistance predominantly to necrotrophic
pathogens.
Plant Physiology (2007) 143: 400-409