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From the phytopathogenic fungus, Colletotrichum nicotianae, three phytotoxic substances have been isolated and named colletotrichin, colletotrichins B and C (1, 2 and 3). The struc tures of these compounds have been elucidated from the physical and chemical evidence. When applied on the tobacco leaves, colletotrichins induced the symptom similar to that of the tobacco anthracnose caused by C. nicotianae. The compounds were also toxic to the lettuce and rice seedlings. with C. nicotianae. 1 was identified to acetyl colletotriehin3> isolated from C. capsi by J. F. Grove through the comparison of physico chemical data of 1 with those of authentic sample kindly gifted by Dr. Grove. Because of the complexity and intimate relations in their structures, the structure determination of those compounds was made by the X-ray crystallographic analysis on the crystal of I along with the correlations of their structures. Just after accomplishment of the X-ray analysis, we noticed that J. MacMillan briefly reported the X-ray analysis on the acetyl derivative (4) of acetylcolletotrichin and changed the name of I to colletotrichin." Then the compounds of 2 and 3 were named as colletotrichins B and C, respectively. We have reported the structure elucidation of 1 and 2 preliminarily.' ' This paper deals with the details of isolation, structures and biological

The effect of colletotrichin, purified from Colletotricbum tabacum, on a diverse array of physiological processes was determined. Colletotrichin caused rapid loss of membrane integrity, as measured by cellular electrolyte leakage, in leaf discs of tobacco, cucumber, and four nightshade (Solanum) species floated on a 0.3 mM solution of the phy to toxin. The first ultrastructural damage observable was plasmolysis and disruption of the plasmalemma. Loss of membrane integrity occurred at similar rates in light or darkness and was dependent upon the presence of atmospheric oxygen. Membrane destruction was associated with an increase in malondialdehyde formation, an indicator of membrane lipid peroxidation. However, several free radical‐quenching compounds did not reduce the effect of colletotrichin on cellular leakage. No direct effect of colletotrichin was found on photosynthesis, respiration, ATPase activity, or membrane‐generated proton gradients. Calcium uptake and transport by plant roots were inhibited by the compound; however, the effect was relatively slow and was probably a secondary effect. Colletotrichin acted synergistically with atrazine, additively with paraquat, and antagonistically with acifluorfen. Acifluorfen activity requires oxidation of plastidsynthesized protoporphyrinogen to protoporphyrin IX at the plasmalemma. This process was inhibited by colletotrichin. These data indicate that colletotrichin causes oxidative plasmalemma destruction by an unknown mechanism. Zusammenfassung Colletotrichin verursacht eine rasche Beschädigung der Membran in Pflanzenzellen Ermittelt wurde der Einfluß von CoEetotrichin, gereinigt aus Colletotrichum tabacum, auf eine Reihe von physiologischen Prozessen. Blattscheiben von Tabak, Gurken und vier Nachtschattengewächsen (Solanum spp.), die auf einer 0,3 mM‐Lösung des Phytotoxins schwammen, zeigten eine rasche Beschädigung der Membran, festgestellt durch zellularen Elektrolytenverlust, als Folge der Colletotrichin‐Behandlung. Eine Plasmolyse und der Zerfall des Plasmalemmas wurde als erste ultrastrukturelle Beobachtung ermittelt. Ein Verlust der Membranintegrität ereignete sich mit einer ähnlichen Geschwindigkeit im Licht wie in Dunkelheit, und zwar in Abhängigkeit vom Vorhandensein von atmospharischem Sauerstoff. Die Membranzerstorung war mit einer Erhöhung der Malondialdehydproduktion verbunden, ein Zeichen der Membranlipidperoxidation. Einige, Freie Radikale löschende Substanzen konnten jedoch den CoUetotrichin‐Einfluß auf den zellularen Verlust nicht reduzieren. Ein direkter Einfluß des Colletotrichins auf die Photosynthese, die Atmung, die ATPase‐ Aktivitat oder auf membranerzeugte Protongradienten wurde nicht festgestellt. Die Kalziumaufnahme und dessen Transport durch Pflanzenwurzeln wurde durch die Verbindung gehemmt, dies erfolgte relativ langsam und konnte daher als sekundäre Wirkung der Substanz betrachtet werden. Colletotrichin wirkte synergistisch mit Atrazin, ergänzend mit Paraquat, und antagonistisch mit Acifluorfen. Acifluorfen‐Aktivität benö...