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A Novel Enolic -Ketoaldehyde Phytotoxin Produced by Stemphylium botryosum f. sp. lycopersici ¹

PARTIAL CHEMICAL AND BIOLOGICAL CHARACTERIZATION

Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel, Department of Chemistry, Tel Aviv University, Israel, Division of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

A new phytotoxin, stemphyloxin I, C₂₁H₃₂O₅, was isolated from cultures of the pathogenic fungus Stemphylium botryosum f. sp. lycopersici. The toxin is a tricyclic compound possessing a most unusual -ketoaldehyde group. Injection of stemphyloxin I into a tomato leaflet caused unlimited necrotic spots and a loss of turgor, which at higher toxin concentration wilted the whole compound leaf. Visible symptoms could be observed at a toxin concentration as low as 2.7 micromolar. Stemphyloxin I is a nonspecific toxin. It exhibits a differential toxicity towards various plants, tomato and eggplant being the most sensitive. Incorporation of [¹⁴C]amino acids into proteins of exponentially growing tomato cell suspension was completely suppressed in the presence of 1 micromolar toxin. The toxin showed no significant difference in its inhibitory activity against green and white tomato cell cultures. The methoxy derivative of stemphyloxin I, in which the -ketoaldehyde group is exclusively modified, showed a reduction of approximately 50 times in its inhibitory activity as compared to the toxin. The diacetate derivative conferred the same activity as stemphyloxin I.

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