Pseudomonas fluorescens WCR 417r induces systemic resistance in radish roots challenged by Fusarium oxysporum f. sp. raphani and, incidentally, in carnation stems challenged by Fusarium oxysporum f. sp. dianthi. The induced systemic resistance is not associated with accumulation of pathogenesis-related proteins (PRs) or, at least in case of radish, with increased peroxidase activity. We tested whether the induced systemic resistance might be associated with changes in the host cell wall composition. Cell wall degradation, using pyrolysis mass spectrometry, was demonstrated on fungal infection in carnation and probably in radish as well. Lignin was found to be demethoxylated, oxidized and depolymerized. In carnation both syringyl and guaiacyl lignin were broken down. In radish root probably mainly syringyl lignin was degraded. Cellulose and hemicellulose were degraded in carnation and possibly in radish. Bacterization with P. fluorescens WCS 417r prior to fungal infection reduced such cell wall degradation, consistent with its resistance inducing action. In the case of the radish roots it seems very improbable that this reduction is a necessary component of the induced fungal resistance. For carnation it remains to be investigated.

The cardenolide extracts from latex and aerial parts ofAsclepias fruticosa and ofDanaus plexippus reared onA. fruticosa orA. curassavica were purified by adsorption chromatography on silica gel. HPLC analysis on a C18 reverse-phase column with an acetonitrile-water gradient as mobile phase, separated 28 compounds with a UV spectrum typical forcardenolides. Afroside and gomphoside (major components), as well as calotropagenin, calotoxin, calotropin, calactin, uscharidin, uscharin, and voruscharin, occurred as single peaks in the profiles of latex and aerial plant parts ofA. fruticosa. Calactin and calotropin were the major cardenolides inDanaus plexippus reared onA. fruticosa orA. curassavica. Quantitative data obtained with digitoxin as internal standard showed that 1.3-1.5% of the leaf cardenolides were sequestered byDanaus plexippus in which levels of 70-80μg cardenolide per butterfly were measured. The calotropin from the leaves was almost completely sequestered, and 10-13% of the calactin was stored by the butterfly, assuming that no conversion occurred in larval tissues.

No abstract