VIEW ARTICLE

Physiology and Biochemistry

Cercosporin, a Photosensitizing Toxin from Cercospora species. Margaret E. Daub, Research associate, Department of Crop and Soil Sciences, Michigan State University, East Lansing 48824; Phytopathology 72:370-374. Accepted for publication 15 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-370.

Cercosporin, a nonspecific toxin produced by members of the genus Cercospora, is structurally related to the photosensitizing compound hypericin. Cercosporin was isolated from cultures of Cercospora beticola and Cercospora nicotianae and tested for toxic effects on suspension-cultured cells of tobacco. Cercosporin was toxic to tobacco cells only when they were incubated in the light. The action spectrum of the killing response agreed with the absorption spectrum of cercosporin. Dabco and bixin, two compounds that quench singlet oxygen, delayed killing of cells by cercosporin. Cercosporin is thus acting as a photosensitizing agent in host plants. The possible role of photosensitizing compounds in plant diseases is discussed.