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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.

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slide1

Allelopathy

Development of crop plants genetically engineered to be allelopathic to weeds

Phototoxicity

UV-A (320-400 nm)

slide2

(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

slide3

(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

slide4

(3) Nitrogen-containing compounds

(C) Nonprotein amino acids

slide5

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…

slide6

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

slide7

Jasmonic acid is a plant hormones

activates many defense responses

Octadecanoid pathway

elicitors

18C

12C

Cyclization

p. 335R

Low level JA mutant: are easily killed by insect

Exogeneous: restore resistance

(true) Endogenous level

slide8

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

slide9

Herbivore damage induces systemic defenses

proteinase inhibitors biosynthesis

Conjugated

form

LRR receptor:

a leucine-rich repeat protein

with kinase activity

dual function: the receptor of

systemin and brassinolide

(18 aa)

(200 aa)

slide10

dual function receptor

Prosystemin orthologues in the other Solanaceous species

C-terminal requirement,

prosystemin still exist activity

Plant cell physiology (2000) 41: 825-830

slide11

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 undersuboptimal conditions

slide12

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

slide13

Pathogen:

avirulence (avr) genes encode specific elicitors

Arg

(Chitinases, glucanases)

Host:

R genes encode

Protein receptors

ROS:

formed by the reduction of molecular oxygen

superoxide anion, hydrogen peroxide, hydroxyl

radical

slide14

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)

slide15

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

slide16

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 SA-dependent 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