Hypersensitive Response

• Pathogen produced elicitor binds to host elicitor binding site
• Recognition and activation of defense responses
• Defense response triggered to kill infected host cell
• kill pathogen before further spread
• kill pathogen via buildup of toxic compounds in infected cell

• Death occurs quickly killing cell - necrosis
• cal be localized or large areas
• Not orderly or organized
• DNA cut a various lengths

Hypersensitive Response

Programmed Cell Death

• Concept developed in animal systems
• Each cell has intrinsic genetic program for ordered cell death
• Cell suicide pathway encoded by genome of dying cell
• Self-execution and dismantling

Programmed Cell Death - Functions

• Control development and morphogenesis of multicellular organisms
• Remove unwanted or displaced cells, without exposing cell contents to trigger response
• Defense mechanism against pathogens, cancer and environmental insults
• Development is a balance between cell division and cell elimination
• Disease can result from malfunctions of this pathway - mistakes in regulations

Apoptosis - a specific type of Programmed Cell Death

• Characterized in animal systems
• Term coined in 1972 by Kerr
• Events are ordered and organized
• Not chaotic
• Occurs in animal and plant cells
• Has a distinct set of morphological features
• Shrinkage and vesiculation of cytoplasm
• Condensation and shrinkage of nucleus
• Condensation of chromatin
• Endonuclease cleavage of chromatin in to 300 and 50 bp fragments
• Cleavage at DNA linker sites between nucleosomes, resulting in DNA fragments multimers of 180 bp
• Results in DNA laddering

Programmed Cell Death - Functions

• Devacuolization
• Proteolysis
• Restriction cleavage of DNA into 180 bp multimers
• Cell Death

Crown Rust of Oats

Avena sativa :: Helminthosporium victoriae

Toxin = Victorin
• Binds specifically to a 100 kD-protein in mitochondria of oats with a vb (Victorin Binding) gene.
• Binding inhibits glycine decarboxylase (GDC) enzyme.
• GDC is responsible for catalysis of glycine synthesized in illuminated leaves during photorespiration.
• Inhibition of GDC catalysis of glycine to ammonia and CO2 leads to reduction in photosynthesis.
• Chitinases (enzymes that catalyze chitin to glucosamine)
• Induced in parallel with Phytoalexin production
• PR proteins (28 and 40kD proteins) induced specifically by victorin.
• Chitin and Chitosan cleaved by Chitinases
•       Elicitors of avenalumins (oat phytoalexins)
•             Hypersensitive-collapsed cells

This page is authored and maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

jpartridge1@unl.edu Home Page Specific References Home Page