The response to reactive electrophile species (RES) is now considered as part of the plant response to pathogen and insect attacks. Thanks to a previously established high-performance liquid chromatography tandem mass spectrometry methodology, we have investigated the production of oxylipin RES adducts to glutathione (GSH) during the hypersensitive response (HR) of plants. We have observed that RES conjugation to GSH in tobacco (Nicotiana tabacum) leaves is facile and nonspecific. In cryptogein-elicited tobacco leaves, we show that the oxylipin RES adducts to GSH are produced in correlation with GSH consumption, increase in glutathione S-transferase activity, and the appearance of the cell death symptoms. In this model, the adducts arise mainly from the downstream 13 lipoxygenase (LOX) metabolism, although the induced 9 LOX pathway leads massively to the accumulation of upstream metabolites. The main adducts were obtained from 2-hexenal and 12-oxophytodienoic acid. They accumulate transiently as 1-hexanol-3-GSH, a reduced adduct, and 12-oxo-phytodienoic acid-GSH, respectively. RES conjugation does not initiate cell death but explains part of the GSH depletion that accompanies HR cell death. The nature of these GSH conjugates shows the key role played by the 13 LOX pathway in RES signaling in the tobacco HR.

The basidiomycete Marasmius quercophilus is commonly found during autumn on the decaying litter of the evergreen oak (Quercus ilex L.), a plant characteristic of Mediterranean forest. This white-rot fungus colonizes the leaf surface with rhizomorphs, causing a total bleaching of the leaf. In synthetic liquid media, this white-rot fungus has strong laccase activity. From a three-step chromatographic procedure, we purified a major isoform to homogeneity. The gene encodes a monomeric glycoprotein of approximately 63 kDa, with a 3.6 isoelectric point, that contains 12% carbohydrate. Spectroscopic analysis of the purified enzyme (UV/visible and electron paramagnetic resonance, atomic absorption) confirmed that it belongs to the "blue copper oxidase" family. With syringaldazine as the substrate, the enzyme's pH optimum was 4.5, the optimal temperature was 75°C, and the K m was 7.1 M. The structural gene, lac1, was cloned and sequenced. This gene encodes a 517-aminoacid protein 99% identical to a laccase produced by PM1, an unidentified basidiomycete previously isolated from wastewater from a paper factory in Spain. This similarity may be explained by the ecological distribution of the evergreen oak in Mediterranean forest.Litter mineralization is an important component of biogeochemical cycles in terrestrial environments. Lignin is the most difficult litter polymer to degrade, and the only organisms known to completely mineralize lignin are white-rot fungi (6,17). In the last two decades, several such organisms have been studied. At present, three main enzymes (i.e., manganese and lignin peroxidases and laccases) (15, 30) are implicated in the biodegradation of lignin. In addition to fundamental studies on lignin mineralization, these enzymes also have potential uses in industrial processes such as the bleaching of paper pulp (1) or the remediation of xenobiotics in effluents (3). There is no clear relationship between the distribution of ligninolytic enzymes and lignin degradation, since white-rot fungi with only one, with a combination of two, or with all three enzymes are known and can degrade lignin (15,27,34).The role of laccases in lignin degradation has only recently become well established (38). Laccases (p-diphenol oxidase, EC 1.10.3.2) are polyphenol oxidases that catalyze the reduction of oxygen to water with a concomitant oxidation of phenolic compounds. They are typically glycoproteins containing 2 to 4 atoms of copper per molecule and are found in plants and fungi (25,33,35).The evergreen oak (Quercus ilex) forms a characteristic forest climax common in the Western Mediterranean area (22,28). The leaf of Q. ilex, highly lignous and covered by a thick and waxy upper cuticle, is typical of sclerous plants exposed to dryness, particularly during the summer. The white-rot fungus Marasmius quercophilus colonizes dead leaves of Quercus ilex (32). Under favorable temperature and humidity conditions, i.e., in autumn and sometimes in May and June, this fungus becomes predominant among litter fungi and produces ma...

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