Accumulation of caffeoyl-D-quinic acids and catechins in plums affected by the fungus Taphrina pruni

Abstract

Plums (Prunus domestica) affected by the fungus Taphrina pruni and healthy ones were harvested in intervals of about four days. Photometric comparison of their methanolic extracts proved that infected fruits contained ten times more compounds with phenolic hydroxyl groups. Further structure elucidation and quantification of these phenolic differences by gas chromatography and gas chromatography / mass spectrometry revealed that the content of caffeoyl-D-quinic acid isomers and (+)-catechin had changed: The amount of chlorogenic acid and its isomers was increased in infected fruits about 15 times compared to nonaffected ones. Contrary, (+)-catechin content was decreased. Additional photometric assays demonstrated that (+)-catechin reduction is accompanied by a corresponding increase of proanthocyanidins in infected fruits. All the compounds identified in infected plums in increased concentrations had a common structural feature: they were o-diphenols. After oxidation to corresponding o-quinones they are able to add to substances with active hydrogen atoms, e.g. fungal enzymes. Consequently, the accumulation of a high concentration of o-diphenols may be a defence response directed towards fungal enzymes.