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Regenerating Protoplasts from Cercospora and Neurospora Differ in Their Response to Cercosporin. K. D. Gwinn, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Box 7616, Raleigh 27695-7616, Present address: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville 37901-1071; M. E. Daub, Assistant professor, Department of Plant Pathology, North Carolina State University, Box 7616, Raleigh 27695-7616. Phytopathology 78:414-418. Accepted for publication 2 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-414.

Cercospora species accumulate high quantities of the photosensitizing toxin, cercosporin, with no apparent harm. Growth of Neurospora crassa, however, is reduced in the presence of the toxin. Freshly isolated protoplasts from both C. nicotianae and N. crassa were killed by 10 μM cercosporin, but at 1 μM (a concentration lethal to plant cells), 50% of the fungal protoplasts remained viable. After an 8-hr incubation, all protoplasts of C. nicotianae were resistant to 1 μM cercosporin, and 35% were resistant to 10 μM cercosporin. Sensitivity of regenerating protoplasts of N. crassa did not differ significantly from that of freshly isolated protoplasts. Protoplasts of both species regenerated cell walls and started to divide during the time when differential resistance to cercosporin was expressed, but regeneration began earlier with protoplasts of N. crassa. Protoplasts of N. crassa became osmotically stable sooner than did protoplasts of Cercospora. Also, by 2 hr, some cells in the preparation of protoplasts of N. crassa had begun to divide, whereas no cell division was seen in preparations of C. nicotianae until 68 hr. The correlation between cell wall regeneration and acquisition of resistance to cercosporin suggests that cell wall components play an important role in resistance to cercosporin of regenerating C. nicotianae protoplasts.

Additional keywords: nonspecific toxin.