Allelopathy Development of crop plants genetically engineered to be allelopathic to weeds Phototoxicity UV-A ( 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

(B) cyanogenic glycosides In black mustard seed and horseradish roots (3) Nitrogen-containing compounds R is CH 2 =CH-CH 2 - sinigrin Broken down to give off poisons

(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 Cyclization p. 335R Low level JA mutant: are easily killed by insect Exogeneous: restore resistance (true) Endogenous level Octadecanoid pathway 12C 18 C

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 (200 aa) (18 aa) LRR receptor: a leucine-rich repeat protein with kinase activity dual function: the receptor of systemin and brassinolide Conjugated form proteinase inhibitors biosynthesis

Plant cell physiology (2000) 41: Prosystemin orthologues in the other Solanaceous species C-terminal requirement, prosystemin still exist activity dual function receptor

Herbivore-induced volatiles Include terpenes, alkaloids, and phenolics  Specific for each insect herbivore species general- vs. nicotine-tolerant caterpillars (p )  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 Host: R genes encode Protein receptors (Chitinases, glucanases) ROS: formed by the reduction of molecular oxygen superoxide anion, hydrogen peroxide, hydroxyl radical Arg

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 H 2 O 2 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 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: