Plant hypersensitive response

Thordal-Christensen H, Zhang Z, Wei Y, Collinge DB (1997) Subcellular localization of H202 in plants. H202 accumulation in papillae and hypersensitive response during the barley-powdery mildew interaction. Plant J 11 1187-1194... 

The presence of catechols and more complex, oxidizable polyphenols in nature is widespread, and their functions are not limited to chemical defense. However, biological control of their oxidation is usually a feature of their function, as it is (1) in melanin synthesis,3 (2) in immunologically mediated delayed-type hypersensitivity responses,4 (3) in the hardening or curing of arthropod secretions (for example, as in the surface attachment adhesives of the barnacle and in tanning of the cuticle in insects),5 as well as (4) in defensive mechanisms in higher plants, particularly in the unleashing of immediate necrotrophic responses.6... 

The next figure (Figure 10) demonstrates that the intercellular mycelium in the treated tissue advanced to the mesophyll cells where it elicited a hypersensitive response within colonized, as well as in adjacent cells. The fungicide treatment induced in the susceptible wheat variety a reaction (hypersensitivity) which resembled that of a highly resistant host plant after rust attack, as described earlier for powdery mildew and barley. 

Newman, M.A., Daniels, M.J., Dow, J.M. The activity of lipid A and core components of bacterial lipopolysaccharides in the prevention of the hypersensitive response in pepper. Mol Plant-Microbe Interact 10 (1997) 926-928. 

Figure 10.5 Plant cell cultures have proven to be very useful for studying plant-pathogen interactions and isoprenoid metabolism. Tobacco cell cultures respond rapidly to the addition of fungal elicitors (0.5 pg cellulase/ml of culture) by browning (A) (analogous to a hypersensitive response) and the production of phytoalexins (B). Media was collected from elicited cell cultures at the indicated times, partitioned against an organic solvent, and concentrated aliquots run on a silica TLC plate. The plates were then sprayed with a suspension of Cladosporium cucumerinum spores and incubated in a humid environment for 5 days before viewing (B). The compound released from the elicitor-treated tobacco cells that inhibits spore germination is capsidiol, a sesquiterpene.

Another pathway is the fatty acid hydroperoxidase lyase (HPL) pathway. This pathway produces C6-aldehydes and C12-oxo acids. 2 C6-volatiles, including ( )-2-hexenal, (Z)-3-hexenal, hexanal, as well as their corresponding alcohols or esters, are produced from mechanically wounded plant tissue.197,203 C6-aldehydes are also formed during hypersensitive response to infection by bacterial pathogens, after insect feeding, and after exogenous application ofJA.204,205 As already shown in this chapter, some of C6-volatiles are known to be attractants of parasitoids and predators. 

Phytoalexins are an Important component of the plant disease defense reaction called the hypersensitive response. Successful pathogens have evolved methods for dealing with plant phytoalexins. Including suppressors of their production, detoxification of the phytoalexins and In some cases avoiding elaboration of substances, called elicitors, that would otherwise Initiate the defense reaction. Elicitors obtained from pathogens are of considerable utility for study of various aspects of plant biology because of their interaction with the products of plant disease resistance genes. Substantial information has been obtained on how elicitors are perceived by plant cells and how they function, but much remains to be done. Finally, elicitors may prove of value for the economic production of exotic plant secondary metabolites and as specific herbicides. 

Delledonne, M., Murgia, I., Ederle, D., Sbicego, P.F., Biondani, A., Polverari, A. and Lamb, C., 2002, Reactive oxygen intermediates modulate nitric oxide signaling in the plant hypersensitive disease-resistance response. Plant Physiol. Biochem. 40 605-610. 

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