In this chapter the hypersensitive response is defined, described and analyzed. HR is described at the levels of physiology (e.g. changes in membrane potentials, ion channels etc.), biochemistry (e.g. protein phosphorylation in signal transduction, lipoxygenase and reactive oxygen intermediates in membrane damage), and genetics (e.g. studies with various classes of mutants).

The Hypersensitive Response

▪ Abstract Elicitors are molecules that stimulate any of a number of defense responses in plants. Research over the past decade has focused on the mechanisms by which plant cells perceive and transduce these biological signals to activate defense responses. Of particular interest has been the identification of specific elicitor-binding proteins that might function as physiological receptors in the signal transduction cascade. The existence of specific high-affinity binding sites has been demonstrated for oligosaccharide, glycopeptide, and peptide elicitors, and candidate elicitor-binding proteins have been identified for several of them. The properties of these binding sites/proteins are consistent with those expected of physiologically important receptors, although experimental verification of the role of these binding proteins as receptors has not yet been obtained. The purification and characterization of specific elicitor-binding proteins is essential for a detailed understanding of the molecular basi...

Microbial elicitors and their receptors in plants

The role of the oxidative burst, transient production of activated oxygen species such as H(2)O(2) and superoxide (O(2) (-)) in elicitation of phytoalexins and the hypersensitive reaction (HR) was investigated in white clover (Trifolium repens L.) and tobacco (Nicotiana tabacum L.). H(2)O(2) and O(2) (-) production was measured as chemiluminescence (CL) mediated by luminol, which was added to suspension-cultured white clover just before measurement in an out-of-coincidence mode scintillation counter. Maximum CL occurred between 10 and 20 min after addition of 0.4 x 10(8) colony-forming units/mL of incompatible Pseudomonas corrugata or 158 mum HgCl(2). Autoclaved P. corrugata produced a slightly higher response. Elicitation of cells with 25 mum HgCl(2) did not produce CL. Preincubation of plant cells in superoxide dismutase, which converts O(2) (-) to H(2)O(2), for 2 min before addition of bacteria did not significantly increase maximum CL levels (P >/= 0.05). Preincubation of plant cells with catalase for 2 min before addition of bacteria prevented the increase in CL, confirming that H(2)O(2) is the substrate for the luminol reaction. Addition of live bacteria or HgCl(2) (25 and 158 mum) to white clover increased levels of the phytoalexin medicarpin during a 24-h period, but addition of autoclaved bacteria did not elicit formation of medicarpin. Preincubation of plant cells with catalase, which quenched the bacteria-induced oxidative burst, did not decrease phytoalexin accumulation. Live bacteria infiltrated into Havana 44 tobacco leaf panels induced development of the HR, but autoclaved bacteria did not. Incubation of live bacteria with superoxide dismutase and catalase before infiltration into tobacco leaves did not interfere with development of the HR. Tobacco leaf panels infiltrated with up to 158 mum HgCl(2) did not develop an HR. These results suggest that an oxidative burst consisting of H(2)O(2) and O(2) (-) does occur during these two plant defense responses, but it may not be a necessary element of the signaling system for HR and phytoalexin formation.

/pdf/involvement-of-the-oxidative-burst-in-phytoalexin-3obttc1z8g.pdf

Involvement of the oxidative burst in phytoalexin accumulation and the hypersensitive reaction.

SUMMARY
Pseudomonas corrugata is the causal agent of tomato pith necrosis yet it is also used in the biological control of plant pathogenic bacteria and fungi. Potentially it could be used in other fields, such as the production of commercial biomolecules with a wide range of application and including bioremediation. This review reports the multiple characteristics of the bacterium, highlights its known molecular features and speculates on the possible underlying mechanisms of action.

Taxonomy:  Bacteria; Proteobacteria; γ subdivision; order Pseudomonadales; family Pseudomonadaceae; genus Pseudomonas.

Microbiological properties:  Gram-negative, oxidase-positive, non-spore forming rods; non-fluorescent on King's B medium; produces wrinkled and rarely smooth colonies on yeast peptone glucose agar or nutrient dextrose agar; yellow to brown diffusible pigments are frequently produced.

Disease symptoms:  The typical symptom on tomato is necrosis and/or hollowing of the pith of the stem; the syndrome determines loss of turgidity of the plant, hydropic/necrotic areas and long conspicuous adventitious roots on the stem.

Biological control agent:In vitro assessed against plant pathogenic fungi and bacteria, as well as the phytotoxin indicator microorganims Rhodotorula pilimanae and Bacillus megaterium; in vivo used against pre- and post-harvest plant pathogens.

Pseudomonas corrugata: plant pathogen and/or biological resource

Abstract From the culture medium of the phytopathogenic bacterium Pseudomonas corrugata, a lipopeptide siderophore was isolated that comprises interesting structural elements such as cyclic condensation products of the two amino groups of 2,4-diamino butyric acid with the carboxyl group of a second amino acid, and the rarely encountered L-threo-β-hydroxy histidine.

Corrugatin, a Lipopeptide Siderophore from Pseudomonas corrugata

Metabolites and viable cells of Pseudomonas corrugata from liquid culture medium elicited biosynthesis of the phytoalexin medicarpin in ladino white clover (Trifolium repens) leaflets and callus. The biologically active elicitor components were soluble in 80% ethanol. They were partially purified by removing components greater than 3,500 Da by dialysis and fractionating by preparative reversed-phase high-performance liquid chromatogrpahy (HPLC). None of the four fractions separated by HPLC elicited appreciable quantities of medicarpin in callus, but fraction 1 combined with fraction 4 elicited high concentrations of medicarpin (...)

Metabolites from Pseudomonas corrugata elicit phytoalexin biosynthesis in white clover.

Three elicitor-active fractions were isolated from culture fluids of the rough isolate of Pseudomonas corrugata, a tomato pathogen that elicits the hypersensitive reaction (HR) in tobacco. Lyophilized, filtered culture fluids were extracted with methanol-ethyl acetate (80:20, vol/vol) to produce a water-soluble crude extract (CE). CE was partitioned with ethyl acetate to produce water-soluble aqueous (AQ) and organic (EA) fractions containing purified elicitor. P corrugata and the three fractions were tested for their ability to elicit HR in tobacco leaves, pith necrosis in tomato, and K + /H + exchange in tobacco tissue culture. Only P corrugata elicited pith necrosis in tomato; both bacteria and the fractions elicited HR in tobacco leaves; and bacteria and EA elicited K + /H + exchange in tobacco cells. The primary component in EA, HR2, did not cause a spreading lesion in tobacco and was therefore not a toxin. HR2 was found to be 95% pure by analytical high-performance liquid chromatography, to contain a fluorescent chromophore, and to be a peptide. HR2 contains glutamic acid, tyrosine, aspartic acid, glycine, alanine and/or arginine, isoleucine and/or leucine, and methionine and/or valine (approximate molar ratio 10:3:1:1:1:1:1). Since P corrugata is a useful biocontrol agent, these elicitors may have potential use in biocontrol.

D. L. Gustine

Papers

Metabolites from Pseudomonas corrugata elicit phytoalexin biosynthesis in white clover.

Evidence for a new class of peptide elicitor of the hypersensitive reaction from the tomato pathogen Pseudomonas corrugata

Metabolites ofPseudomonas corrugataThat Elicit Plant Defense Reactions